Dissertations / Theses on the topic 'Tip wear'

Atomic force microscope (AFM) probe-based mechanical nanomachining has been considered as a potential low-cost alternative method for the generation of nanoscale features on the surface of components and devices. Therefore, it is important to understand the factors that influence the tip wear of AFM probes in order to achieve reliable and accurate machining operations when implementing this process. Despite the fact that the basic applicability of AFM probe-based machining has been demonstrated for many years, studies focussing on the wear of the tips as a function of processing conditions are relatively scarce. In addition, the accuracy and practical suitability of in-situ techniques to monitor the condition of AFM probes is not adequately acknowledged. To address these issues, a series of experimental studies were conducted in this PhD research when implementing the AFM probe-based machining process on a single crystal copper workpiece at selected values of applied normal loads, machining distances and for different machining directions. First, the assessment of the wear of AFM silicon probes was carried out based on two dimensional (2D) tip profile data. This particular study also presented a simple method for improving the accuracy of the tip wear assessment procedure when conducted on 2D profiles. Next, AFM silicon probes with diamond-coated tips were used as cutting tools for a different range of applied normal loads and along various processing directions. For this particular study, the AFM probes wear assessment relied on two different three dimensional (3D) in-situ measurement techniques, namely the ultra-sharp tip scan approach and the reverse imaging method. Reliability and practical suitability aspects between these two in-situ techniques were also assessed and discussed. For each set of experiments, different qualitative and quantitative ii wear metrics were observed and analysed. Particularly, from the qualitative perspective, the evolution of the AFM tip apex profiles along selected machining distances and directions was considered. As for the quantitative measurement, tip radius and tip volume loss measurements were estimated. The most important findings reached in this study are given as follows. First, it was shown that the error associated with the traditional method of assessing the tip volume from 2D profiles could be 26% in comparison with the simple method proposed here. In addition, among the 3D in-situ AFM probe characterisation methods considered, the reverse imaging approach was judged to be the most reliable technique. This study also showed that tips in silicon were very prone to initial tip fracture during the AFM probe-based nanomachining process. This phenomenon could also take place, albeit to a lesser extent, when silicon tips coated with diamond were utilised. When the nanomachining process is not in control due to such tip fracture, it is difficult to extract firm conclusions about the influence of the processing parameters on the tip wear. Besides, this rules out the application of a design of experiments approach where the minimisation of the tip wear volume may be the objective. The study also showed that the AFM probe-based nanomachining process was more likely to be in control when using silicon tips coated with polycrystalline diamond with no nitrogen doping. In this case, a much reduced likelihood of tip fracture could be achieved accompanied with negligible tip wear. In addition, the associated results suggested that the evolution of the tip wear was not equal in all machining directions investigated, with the largest wear occurring in a direction parallel and away to the cantilever long axis. The reason for this should be due to the fact that this was also the direction where the process was most likely to be conducted in the ploughing-dominated regime. Finally, when the nanomachining process was realised in iii control, the wear volume was seen to increase with the increase in the normal load for all directions considered.

Master of Science
Department of Physics
Robert Szoszkiewicz
Nanoscale modifications of polymer surfaces by scratching them with sharp tips with curvature radii of tens of nanometers and at variable temperatures are expected to provide wealth of information characterizing wear response of these polymers. Such studies are important in the light of understanding the nanoscale behavior of matter for future applications in advanced polymer coatings. This thesis describes how Atomic Force Microscopy (AFM) and hot-tip AFM (HT-AFM) methods were used to characterize thermal and mechanical properties of a 30 nm thick film of poly(styrene-block-ethylene oxide), PS-b-PEO, and modify its lamellar surface patterns. Additionally, it is revealed how contact AFM and HT-AFM methods can efficiently characterize the wear response of two popular polymer surfaces, poly(methyl methacrylate), PMMA, and polystyrene, PS. The AFM and HT-AFM studies on PS-b-PEO copolymer were aimed at producing spatial alignment of respective PS and PEO parts. Instead, however, surface ripples were obtained. These measurements are explained using mode I crack propagation model and stick-and-slip behavior of an AFM tip. In addition, HT-AFM studies allowed extraction of several thermo-physical properties of a PS-b-PEO film at local volumes containing about 30 attograms of a polymer. These thermo-physical quantities are: PEO melting enthalpy of, 111 ± 88 J g[superscript]-1, PS-b-PEO local specific heat of 3.6 ± 2.7 J g[superscript]-1K[superscript]-1, and molecular free energy of Helmholtz of 10[superscript]-20 J nm[superscript]-2 for the PEO within PS-b-PEO. Utilizing a spiral scan pattern at constant angular speed and at various temperatures at the AFM tip-polymer interfaces, the wear response of PS and PMMA polymers was characterized. Cross-sections along the obtained spiral wear patterns provided plots of polymer corrugation as a function of scanning speed. From these studies it was found that the corrugation of the modified polymer surface decays exponentially with linear velocity of the scanning tip.

The automotive industry is reliant on resistance spot-welding just as the sandwich making industry is reliant on bread. An automobile contains an average of 5000 welds. The quality of these welds is inspected and governed by certain standards. In order to maintain these standards there are different approaches to quality control. There are many factors that are accountable to a successful weld. The main factors are the voltage across the electrodes, the pressure applied by the electrodes at the interface of the metal sheets, the current applied, the surface condition and the composition of the sheets. The main problem in determining whether a weld complies with the standard is that the most reliable test is a destructive test, which not only destroys a potentially good weld, but it stalls the entire production line in order to perform the test. This is a process where the weld is taken apart sometimes with a chisel. Once the weld is dismantled the quality can be analysed. During the course of this thesis the chisel test, and other comparable tests were carried out. The following thesis presents an overview of electrode current selection and its variance over the lifetime of the electrode tip. This also describes the proposed analysis system for the selection of welding parameters for the spot welding process, as the electrode tip wears. Data from the practical tests is analysed using SORPAS Software Package in order to compare between real life practical tests, and theoretical simulations preformed in SORPAS. Reducing sparks caused during each weld is another requirement to prevent bumps on the bodywork that may cause further complications at later stages, this project will greatly improve productivity in the production line, since damaged tips can be identified and changed during the manufacturing process. The results show that at a pressure of 4.0bar productivity of welds that conform with the necessary British standards was increased three fold. A new type of non-invasive plastic bond testing is also investigated. This bond testing research was driven by the industrial need for a novel real-time non-destructive method of measuring both the quantity and type of material. Microwave sensors which monitor the change in permittivity of PF glue were developed for this purpose and successfully tested. These sensors have also been used to differentiate between different plastics.

his Diploma thesis concentrates on problems related to cutting tools, their wear, durability, and cutting conditions. The work provides basic analysis of technology applied to two selected parts. Further, there is also analysis of cutting tools suppliers. The work gives brief characteristics of the basic types of wear and their origins. In the experimental section is a statistical evaluation of selected tools, calculation of optimal cutting conditions and durability, and finally selected tools wear evaluated. The technical and economical evaluation compares cutting conditions provided in theory with the real cutting conditions.

Tin alloy coatings have traditionally been used as corrosion resistant bamens due to their inert nature and comprehensive coverage, and have seldom been considered in physically demanding applications, such as wear resistant coatings owing to misconceptions associated with the soft nature of tin metal. The alloying of tin with copper has already been shown to significantly increase its mechanical properties, as demonstrated by the adoption of tin-copper alloys for use as bearing materials. Unfortunately, its cyanide plating technology makes tin-copper environmentally unsustainable, whilst the process requires constant regulation and monitoring, and there are disposal costs associated with the cyanide waste products. The tin-nickel alloy, however, can be produced with minimal supervision and its plating process uses less harmful precursors, making it an alternative consideration. The research documented in this thesis assesses this increase by quantifying the resistance of tin, tin-nickel and tin-copper coatings to removal from sliding wear. As tin is a soft material and behaves dissimilarly to conventional coatings in a sliding wear environment, traditional wear assessment techniques are not appropriate. A novel approach is therefore devised and implemented, and this involves the continually monitoring the effect of damage introduced to the surface of the tin and tin alloy coatings, from an abrading ceramic ball. Using an elemental detection tool, it is possible to analyse wear scars that exhibit progressively depleted coating material, by identifying the underlying substrate material as it becomes exposed. In this way, it is possible to quantify the improvements made to tin from alloying with nickel and copper. The large volume of data acquired from this research is presented in a matrix format to enable simultaneous depiction of multiple parameters, and to allow quick and easy interpretation. The tin-nickel coating is found to be comparable to tin-copper in terms of resistance to removal. Despite tin-copper being slightly superior over the range of test conditions used, tin-nickel as been shown to be an environmentally friendly and cost effective alternative coating alloy to tin-copper.

Progress in chemomechanical functionalization was made by investigating the binding of molecules and surface coverage on the silicon surface, demonstrating functionalization of silicon with gases by chemomechanical means, analyzing atomic force microscopy probe tip wear in atomic force microscopy (AFM) chemomechanical nanografting, combining chemomechanical functionalization and nanografting to pattern silicon with an atomic force microscope, and extending chemomechanical nanografting to silicon dioxide. Molecular mechanics of alkenes and alkynes bound to Si(001)-2x1 as a model of chemomechanically functionalized surfaces indicated that complete coverage is energetically favorable and becomes more favorable for longer chain species. Scribing a silicon surface in the presence of ethylene and acetylene demonstrated chemomechanical functionalization with gaseous reagents, which simplifies sample cleanup and adds a range of reagents to those possible for chemomechanical functionalization. Thermal desorption spectroscopy was performed on chemomechanically functionalized samples and demonstrated the similarity in binding of molecules to the scribed silicon surface and to the common Si(001)-2x1 and Si(111)-7x7 surfaces. The wearing of atomic force microscope probe tips during chemomechanical functionalization was investigated by correlating change over time and force with widths of created lines to illustrate the detrimental effect of tip wear on mechanically-driven nanopatterning methods. In order to have a starting surface more stable than hydrogen-terminated silicon, silicon reacted with 1-octene was used as a starting surface for AFM chemomechanical functionalization, producing chemomechanical nanografting. Chemomechanical nanografting was then demonstrated on silicon dioxide using silane molecules; the initial passivating layer reduced the tip friction on the surface to allow only partial nanografting of the silane molecules. These studies broadened the scope and understanding of chemomechanical functionalization and nanografting.

Ti and Ti-based alloys are used in many aerospace and automotive components due to their high strength-to-weight ratio and corrosion resistance. However, room and elevated temperature wear resistance remain an issue, thus requiring some form of secondary hard phase, e.g., refractory carbides and oxides, as well as solid lubrication to mitigate wear. In this study, Ti-TiC (14, 24 and 35 vol% TiC) composite coatings were deposited on mild steel substrates using cold spray with comparisons made to baseline cold-sprayed Ti. The dry sliding friction and wear behavior were studied from 25°C to 575°C and during thermal cycling in this temperature range. While the room temperature friction coefficient of all the coatings remained relatively constant at ~0.5, the wear rate continually decreased from ~1x10-3 to ~2x10-5 mm3/N-m with increasing the TiC loading. Raman spectroscopy measurements determined that the same TiO2 tribochemical phases (rutile and anatase) were present on the room temperature sliding wear surfaces, thus responsible for similar friction coefficients. With increasing sliding temperatures to 575°C, the Ti-35%TiC composite coating exhibited the best overall tribological behavior, i.e., the friction coefficient decreased to ~0.3 along with a negative wear rate of -6.6x10-5 mm3/N-m (material gain on the wear track was recorded due to oxidation and transfer from the counterface). These friction and wear reductions were determined to be due to the formation of stable, low interfacial shear strength oxide glaze layers on the wear surfaces, composed of TiO2, WO3, and CoWO4 (transfer from WC-Co counterface). In addition, self-adaptive friction behavior was observed during thermal cycling as a result of the microstructural and tribochemical differences in the tribolayers.

The aim of the study presented here was to investigate the potential for chemical wear of carbon-based refractory materials in a silicomanganese furnace tap-hole. In the study, three research questions were addressed: 1. Is chemical reaction between refractory and slag or refractory and metal a potential wear mechanism? 2. Is the choice in carbon-based refractory material important from a tap-hole refractory life perspective? 3. What are the implications for the life of the tap-hole in a SiMn furnace? To study the potential for chemical wear, thermodynamic calculations were conducted to determine the potential for the formation of SiC and SiMn at 1600°C through reduction of SiO2 and MnO and dissolution of C (and subsequent reaction with Si) in metal. The thermodynamic calculations were based on published [1] metal and slag composition and carbon. Cup test experiments based on synthetic slag and graphite proved SiC formation conclusively, but not SiMn formation. To study the effect of the choice in carbon-based refractory material, two types of refractory materials – carbon block and ramming paste – available commercially and industrial slag were sourced, prepared and characterised. Wettability studies proved the formation of SiC at 1588°C with slag being wetting towards refractory in an argon atmosphere and non-wetting in a CO-atmosphere. Under wetting conditions, the wetting angle of slag on carbon block was slightly higher (50°) at holding temperature compared to that of ramming paste (30°). Under non-wetting conditions the angles were 160° and 150° respectively. Cup test experiments based on industrial slag and carbon-based refractory material proved both SiC and SiMn formation at 1600°C conclusively and confirmed the wetting behaviour of slag towards refractory at larger scale. To study the implications for the life of the tap-hole in a SiMn furnace, the tap-hole of a 48 MVA SiMn furnace was excavated and profiled. The wear predicted by thermodynamic modelling was supported by mass flow calculations. It was concluded that chemical reaction between carbon-based refractory materials and slag and metal is one of the mechanisms responsible for wear in the tap-hole of a silicomanganese furnace.
Thesis (PhD)--University of Pretoria, 2014.
tm2015
Materials Science and Metallurgical Engineering
PhD
Unrestricted

Thesis (M.Sc.)--City University of Hong Kong, 2004.
At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Aug. 31, 2006) Includes bibliographical references.

Thesis (M.Sc.)--City University of Hong Kong, 2004.
At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

An experimental methodology for wear assessment of extracted polyethylene hip implants was designed in this diploma thesis. Methodology uses optical 3D scanner and optical profilometer for analysis of wear. Designed methodology for wear analysis was validated by gravimetric method. The results of validation were in good agreement with the increase of wear rate. Validation results show that the methodology is not suited for wear assessment of metal and ceramic implants which have small wear rates. On the other hand the methodology is more than useful for wear assessment of polyethylene implants. Designed methodology for wear assessment was applied on the set of thirteen extracted polyethylene hip implants. Results of the wear analysis were wear volumes and linear wear noted in the wear maps. Roughness of the surface was measured on explanted cups and results were noted in the roughness map. On articulating surface of the cups different areas were observed for measured roughness. Those areas were described as area with machining marks from manufacturing process, polished area from combination of abrasive and adhesive wear, polished area from micro-contact fatigue and area including plastic deformation.

The primary purpose of this study was to identify dimensions of weak tie relationships including characteristics (e.g., distinctive qualities, traits, or properties), functions (e.g., outcomes, purposes, or meanings derived from the interaction) and determinants of engagement to gain insight into the weak tie exchange process and develop frameworks that can be used to operationalize the concept. Data were collected through stories provided by participants during face-to-face interviews. Respondents recounted a situation when someone they did not know well and to whom they did not feel particularly close provided them with assistance. Over 70 stories were collected from 50 adults aged 65 and older who were active in their community. Stories collected were analyzed using an inductive approach that was supported by the concepts of interpersonal tie strength, loose connections, social exchange theory, and social support. Findings suggest that weak tie relationships occur in a variety of community settings and in response to a variety of daily challenges. The exchanges occur more frequently with acquaintances than strangers and the initiator of the exchange is generally the person offering support. The types of support offered are broad-based and include instrumental, emotional, and informational support. Weak tie exchanges range from one-time brief interactions to intermittent exchanges over extended periods, depending on the circumstances. Findings also suggest that weak ties have a specific task or purpose, encourage awareness about the value and purpose of social interactions, and influence participantsâ future social interactions. Six factors were identified as determinants of engagement in weak ties: situational factors, personal characteristics, judgments of responsibility, attitudes about helping behaviors, personal network type, and exchange history. The findings from this study provide a foundation for further conceptualization of weak ties and a framework on which to develop instruments to measure tie strength and the potential for engaging in weak tie exchanges.
Ph. D.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A indústria busca uma melhor otimização e performance de seus equipamentos, há muito notou-se a importância da contenção do desgaste para o aumento de vida útil dos componentes de máquinas. Em condições operacionais onde há o desgaste por abrasão, comumente faz-se o endurecimento da camada superficial ou a aplicação de uma liga mais nobre e de dureza mais elevada, visando conter este desgaste. A técnica também é chamada de revestimento. Entender melhor os parâmetros que influenciam nos resultados da aplicação destes revestimentos torna-se importante possibilitando menores perdas e uma maior economia, pois busca-se como alvo trabalhar com a melhor performance do revestimento. Objetivou-se neste trabalho o estudo das ligas a base de Cobalto que são aplicadas cada vez mais rotineiramente nas indústrias petroquímicas, onde os componentes e órgãos de máquinas estão expostos a condições severas de desgaste por abrasão e corrosão além da severidade dos trabalhos a altas temperaturas e pressão. Relacionando o desgaste, as ligas a base de Cobalto possuem uma posição destacada e a liga é conhecida comercialmente como “Stellite 6”. Em alguns trabalhos é chamada também de liga coringa por sua versatilidade e destaque em especial. Neste trabalho procurou-se variar as velocidades de resfriamento em cinco patamares, analisou-se a influência da diluição na micro-dureza e os efeitos da variação da velocidade de resfriamento no mecanismo de endurecimento. A aplicação do revestimento ocorreu em três camadas através do processo TIG. Verificamos ainda a interferência da diluição na dureza em cada camada de revestimento. A terceira e última camada foi a que apresentou maior dureza devido à menor diluição com o metal base principalmente no corpo de prova que possuía à menor velocidade de resfriamento devido ao tempo para a formação de precipitados e carbonetos na liga metálica.
The industry searchs a better optimization and performance of their equipment, long noted the importance of containment to increase the wear life of components of machines. In operating conditions where there is wear by abrasion, usually it is the hardening of the surface layer or the application of a more noble alloy and high hardness, wear it to contain. The technique also called hardfacing. Better understand the parameters that influence the results of applying these coatings becomes important because it enables lower losses and greater economy as it seeks to target work with the best performance of the coating. The objective of this research is complements the study of cobalt-based alloys that are applied more routinely in petrochemical industries, where the component units and machines are exposed to severe conditions of wear by abrasion and corrosion than the severity of the work at high temperatures and pressure. Relating the wear, the cobalt-based alloys have a prominent position and the league is known commercially as “Stellite 6”. Some work is also called the league wildcard for its versatility and highlight in particular. In this work we have tried to vary the speed of cooling in five steps, looked up the influence of dilution on micro hardness and the effects of variation in the rate of cooling in the hardening mechanism. The application of the coating occurred in three layers using the TIG process. We note also the interference of dilution in hardness in each layer of coating. The third and final layer was the one with higher hardness due to less dilution with the base metal mainly in the body of evidence that had the lowest rate of cooling due to the time for the formation of precipitates and carbides in the metal.

High chromium cast iron (HCCI) is considered as one of the most useful wear resistance materials and their usage are widely spread in industry. The wear resistance and mechanical properties of HCCI mainly depend on type, size, number, morphology of hard carbides and the matrix structure (γ or α). The Hypereutectic HCCI with large volume fractions of hard carbides is preferred to apply in wear applications. However, the coarser and larger primary M7C3 carbides will be precipitated during the solidification of the hypereutectic alloy and these will have a negative influence on the wear resistance. In this thesis, the Ti-added hypereutectic HCCI with a main composition of Fe-17mass%Cr-4mass%C is quantitatively studied based on the type, size distribution, composition and morphology of hard carbides and martensite units. A 11.2μm border size is suggested to classify the primary M7C3 carbides and eutectic M7C3 carbides. Thereafter, the change of the solidification structure and especially the refinement of carbides (M7C3 and TiC) size by changing the cooling rates and Ti addition is determined and discussed. Furthermore, the mechanical properties of hypereutectic HCCI related to the solidification structure are discussed. Mechanical properties of HCCI can normally be improved by a heat treatment process. The size distribution and the volume fraction of carbides (M7C3 and TiC) as well as the matrix structure (martensite) were examined by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Especially for the matrix structure, EBSD is a useful tool to classify the fcc (γ) and bcc (α) phases. In conclusion, low holding temperatures close to the eutectic temperature and long holding times are the best heat treatment strategies in order to improve wear resistance and hardness of Ti-alloyed hypereutectic HCCI.

QC 20121130

Today is the implantation of joint replacements, although a radical, but very functional restoration frequent way ill joint. The implants are placed high demands on their biocompatible and long-term function, which is directly related to wear of joint replacements in the human body. Therefore, analysis of the complex behavior of the implant in the human body is a fundamental problem of biomechanics of implants. This issue is dedicated, this dissertation thesis. Dissertation thesis deals with the solution design and development of experimental device for testing the TEP acetabula and wear identification using optical method. The proposed device allows the joint burden hole TEP physiological manner, but by working with the acetabulum burdened by Power resultant joint axis passes through the hole. The physiological loading of articular wells and evaluating the size of the loss of polyethylene is currently intensively addressed. The results of this study may in the near future, serving as information for assessing the conduct of wear prosthetic hip joint in vivo. The work is devoted to solving the problem of the size required to detect the loss of polyethylene for joint replacement arthroplasty: Design and development of experimental equipment for testing the acetabulum of the hip joint arthroplasty. Identify wear using optical methods. Design and development of experimental equipment was made in the system Inventor Professional 2010 at the level of 3D modeling. Great attention was paid to the design fit into the acetabulum TEP testing machines and gripping the acetabulum into an optical device. Management options were tested with combinations of experimental equipment engines. Suggestions were made and then tests for fixing the acetabulum into an optical device. Has the possibility of depth analysis and identification of wear joined with innovative solutions to evaluate the loss of polyethylene acetabulum arthroplasty. Identification of abrasion (loss of polyethylene) joint arthroplasty holes were carried out experimental measurements using an optical holographic interferometry. The comprehensive analysis of the results of experimental measurement of the loss of polyethylene shows that this method can identify both the size but also an area where there is even to small changes in the surface, which depend on the abrasion. One can also say that using this method we are able to affect the will or displacements that affect the size of the loss of polyethylene in joint arthroplasty hole. Despite the number of known and lessons learned arising from the results of solving the problem of design and development of experimental equipment for testing the acetabulum and hip arthroplasty wear identification using optical methods, this work is that the initial study to identify problematics wear of joint replacements. Complete resolution of this issue is beyond the scope of one doctoral thesis.

High chromium cast iron (HCCI) is considered as one of the most useful wear resistance materials and their usage are widely spread in industry. The mechanical properties of HCCI mainly depend on type, size, number, morphology of hard carbides and the matrix structure (γ or α). The hypereutectic HCCI with large volume fractions of hard carbides is preferred to apply in wear applications. However, the coarser and larger primary M7C3 carbides will be precipitated during the solidification of the hypereutectic alloy and these will have a negative influence on the wear resistance. In this thesis, the Ti-alloyed hypereutectic HCCI with a main composition of Fe-17mass%Cr-4mass%C is studied based on the experimental results and calculation results. The type, size distribution, composition and morphology of hard carbides and martensite units are discussed quantitatively. For a as-cast condition, a 11.2μm border size is suggested to classify the primary M7C3 carbides and eutectic M7C3 carbides. Thereafter, the change of the solidification structure and especially the refinement of carbides (M7C3 and TiC) size by changing the cooling rates and Ti addition is determined and discussed. Furthermore, the mechanical properties of hypereutectic HCCI related to the solidification structure are discussed. Mechanical properties of HCCI can normally be improved by a heat treatment process. The size distribution and the volume fraction of carbides (M7C3 and TiC) as well as the matrix structure (martensite) were examined by means of scanning electron microscopy (SEM), in-situ observation by using Confocal Laser Scanning Microscope (CLSM), Transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). Especially for the matrix structure and secondary M7C3 carbides, EBSD and CLSM are useful tools to classify the fcc (γ) and bcc (α) phases and to study the dynamic behavior of secondary M7C3 carbides. In conclusion, low holding temperatures close to the eutectic temperature and long holding times are the best heat treatment strategies in order to improve wear resistance and hardness of Ti-alloyed hypereutectic HCCI. Finally, the maximum carbides size is estimated by using statistics of extreme values (SEV) method in order to complete the size distribution results. Meanwhile, the characteristic of different carbides types will be summarized and classified based on the shape factor.

QC 20130913

Master’s thesis “Revovation of tools steels for cold forming“ characterizes wear resistant welds for tool steels. The thesis is dividend into two main chapters. The first chapter of the thesis is focused on the theory of wear for cold work steels. The theory is combined with an experimental chapter. The experimental part describes particular materials and technology for welding. The conclusion of the thesis is evaluated results of test for mentioned technology and welding conditions.

A tendência mundial de se buscar a sustentabilidade econômica tem causado uma crescente demanda por novas técnicas e novos materiais que gerem: aumento da produtividade, maior velocidade de operação, aumento da vida útil de ferramentas e matrizes, e que reduzam o custo ambiental atual. Nesta busca a modificação de superfícies metálicas é um campo promissor e o bombardeamento com íons de Xe+ tem sido utilizada para texturizar a superfície do substrato, seja para o aumento da aderência de revestimentos com grande dureza ou para melhorar a difusão de N. Neste estudo são relatados os resultados obtidos de ensaios de dureza, desgaste, DRX (fases e tensão residual) e microscopias MEV, AFM e MET, efetuadas em amostras de aço 100Cr6 (globulizada) modificadas superficialmente por meio de bombardeamento com íons de Xe+ e revestimento duplex. Para esse fim, foram preparadas amostras combinando: bombardeamento com íons de Xe+ com energia de 400 e 1000 eV; implantação de N por feixe de íons e plasma pulsado; e deposição do revestimento de TiN por sputtering com diferentes temperaturas em um sistema reativo com N2-IBSD. Uma análise desses resultados permitiu constatar que o bombardeamento de íons de Xe+ gera refinamento de grãos, texturização, e aumenta a densidade de defeitos na estrutura cristalina na superfície tratada em função da energia utilizada. O bombardeamento de Xe+ com energia de 1000 eV melhorou o aprisionamento de nitrogênio e a difusão a 380°C (via feixe de íons) o que levou a formação dos nitretos γ\'-Fe4N e ε-Fe2-3N. Enquanto que com energia de 400 eV levou a formação apenas do nitreto γ\'-Fe4N. As propriedades adquiridas na combinação dos pré-tratamentos de bombardeamento de Xe+ com energia de 400 eV, nitretação a plasma pulsado (520°C) e a deposição do filme de TiN (500°C/240 min) levaram ao melhor desempenho no ensaio de desgaste.
The global trend of seeking economic sustainability has caused a growing demand for new materials that generate: increased productivity, higher operating speed, increased service life of tools and dies, and to reduce the current environmental cost. In this search, the modification of metallic surfaces is a promising field and bombardment Xe+ ions has been used to texture the surface of the substrate, is to increase the tack coatings with high hardness or to improve the N diffusion. In this study are reported the results obtained from testing the hardness, wear, XRD (phase and residual stress) and microscopy SEM, AFM and TEM, made in 100Cr6 steel samples (globulized) surface modified by bombardment with Xe+ and duplex coating. To this end, samples were prepared by combining: bombardment Xe+ ions with energy of 400 and 1000 eV; N implantation by ion beam and pulsed plasma; and deposition of the TiN coating by sputtering at different temperatures in a N2 reaction system-IBSD. An analysis of these results helped to confirm that the bombardment of Xe+ ions produces grain refinement, texturing, and increases the defect density in the crystalline structure of the surface treated according to the energy used. Bombardment of Xe+ ions with energy 1000 eV improved nitrogen trapping and diffusion to 380°C (via ion beam) which led to the formation of γ\'-Fe4N and ε-Fe2-3N nitrides. Whereas with energy 400 eV led to the formation of only γ\'-nitride Fe4N. The properties acquired in the combination of the pre-treatments of Xe+ ions bombardment at 400 eV, pulsed plasma nitriding (520°C) and the deposition of TiN coating (500°C/240 min) leads to a superior performance in wear test.

This study investigates the tool wear of advanced PVD TiALN/TiN multilayer coated end mill inserts when dry and semi-dry machining 4340 low alloy medium carbon steel. A factorial design of experiment setup consisting of two levels of speed, three levels of feed, two levels of depth of cut, and two levels of cutting conditions (semi-dry and dry) was used for the study. The combination of cutting conditions that gave the best response for different components of cutting force, cutting power, surface roughness and tool life were determined using MANOVA & ANOVA analysis and Tukey comparison of means test using MINITAB statistical software package. From a study of the Energy Dispersive X ray (EDX) analysis and primary back scatter images obtained from the worn out crater surface of the insert, it was observed that diffusion wear prevailed under both dry and semi-dry machining conditions. A tool life model was developed using multiple regression analysis within the range of cutting conditions selected. A model for flank wear progression was also developed using mixed effects modeling technique using S Plus statistical software package. This technique takes into account between and within work piece variations during end milling and produces a very accurate model for tool wear progression. This is the first time application of the mixed effects modeling technique in metal cutting literature.

Abstract Title: Last Exit? A Study of Prison Sentenced Recidivists’ Subsequently Choice to Make Use of Criminals Return Into Society (KRIS) as a Resource in Order to Terminate the Criminal Lifestyle  Author: Jimmy Karlsson  A point of departure for this essay is my and my co-author’s bachelor thesis The Refuse to Walk More Yards Prison Corridor.   The purpose of the present essay is to illuminate in which conditions the organization KRIS (Criminals Return Into Society) develops from being directly or indirectly realizable to being a realized resource for recidivists who have served several prison sentences. The theoretical basis is Caroline Tovatt’s concepts potential, realizable and realized resources combined with Pierre Bourdieu’s capital metaphors and Mark S. Granovetter’s concept of strong and weak ties. To illustrate the process that led the interviewees (which I have interviewed from a life story perspective) to the realization of KRIS as a resource and ultimately the ending of the criminal lifestyle, I have used Helen Rose Fuchs Ebaughs stage theory of the role exit process.   The results indicate that recidivists’ choice to realize the resource KRIS has been occasioned by a specific composition of necessary components and a social capital. The necessary components are represented by negative life experiences which via a transformation in three stages have resulted in making KRIS available as a resource for the interviewees. The social capital in turn, which has to interact with the necessary components, is represented by weak and negative ties subsequently remodeled into positive ones. These ties have paved the way for the interviewees to access the organization. To finally fulfill the role exit process the interviewees have to possess or acquire an embodied cultural capital which allows them to differentiate and maintain all aspects linked to the previous and the current role, both to themselves and also to other individuals.

The industrial development of metal cutting processes in gear manufacturing aims at continuously increasing productivity, including increased tool reliability. Basically, the parameters that have an influence on the cutting processes should be known and possible to control. Gear manufacturing is highly important for the automotive industry. The prevalent manufacturing method is gear hobbing with hobs consisting of solid Powder Metallurgical High Speed Steel (PM HSS) with Physical Vapor Deposited (PVD) coatings. The hob teeth have to be reconditioned before wear reaches such levels that the gear quality becomes impaired. Such wear often results in a total breakdown of the tool. One crucial reason for this is that hobbing processes for the present often lack reliability; which makes it difficult for the gear manufacturers to predict the tool wear on the hob teeth and decide when the tool should be replaced in order to avoid severe damages. A consequence of catastrophic tool wear is that it leads to an instantaneously changed geometry of the cutting edge, which in turn implies that the machined gears do not comply with the stipulated properties on the machined gear products. A single tooth milling test (STMT) with tools of PM-HSS in a conventional milling machine has been developed in this research project, aiming at characterizing the effect of tool preparation on the type of wear mechanism. The experience and conclusions from these tests may probably be transferred to real PM-HSS hob tooling (HT). The advantages of such a test, compared to a real gear hob test, are primarily the cost reductions and time saving aspects with respect to both the design and the manufacturing of the cutting teeth The research presented in this thesis is based on experimental investigations and theoretical studies of significant parameters, i.e. the surface roughness and edge rounding, contributing to the robust and reliable design of a PM-HSS cutting tool. The research work has in addition to, the development of the milling test method, also comprised development of measuring methods and a simulation model based on the Finite Element Model (FEM).

QC 20121105

The National Center for Complementary and Integrated Health, National Institutes of Health, U.S. Department of Health and Human Services, has highlighted a need for research to better understand the usage of complementary and alternative medicine practices. The purpose of this study was to investigate the flow of complementary and alternative medicine information among yoga practitioners. The study consisted of 51 yoga practitioners from 7 yoga studio locations. This mixed-methods study used interviews, surveys, and field notes to collect data. Content and social network analyses provided supporting evidence for Rogers' diffusion of innovations theory and Granovetter's strength of weak ties theory. Key findings included a preference for face-to-face communications, students having both strong and weak relationship ties to directors and instructors, and yoga being the top recommended practice. The study suggested that yoga practitioners related to complementary and alternative medicine information through the lens of their friends and relatives, sought information from trusted sources, and used this information to determine which practices were right for them to pursue.

Background/Problematization: Many purchase decisions are made in-store and one wayof influencing the decision making process is through signs. Signs are said to drawattention to the product on which they are placed and result in increased sales. Sale signsare widely used to influence purchase decisions, but are there other types of signs that canimpact the purchase decision? Recommendations have also shown to affect consumer’spurchase decisions. However, most of the research within the subject have been done on thepower of social influences from friends and family, e.g. strong-tie relationships. Howrecommendations from experts (e.g. weak-tie relationships) can influence purchases is lessresearched, especially which type of recommendation sign have the most effect. Purpose: The purpose is to examine and map how different types of signs on shelvesrelated to staff recommendations for specific products affect their sales. Method: The scientific approach of the study is deductive and the corresponding researchmethod is a quantitative study with an experimental design and a descriptive focus. Anexperiment was executed in a supermarket on 28 products to test stimuli with differentlevels of information concerning staff recommendations with the use of signs. Result/Conclusion: The result showed only one stimuli to have significantly increasedsales. The stimuli consisted of adding a name of a specific staff member to therecommendation sign. The increase in sales might however have been caused by otherfactors than the applied sign as the outbreak of Covid-19 resulted in changed consumerbehavior at the time of the experiment. The results showed that no significant differences insales could be seen according to the number of alternatives each product had. This mighthowever be a result of the tampered data caused by the changed consumer behavior.

Cette étude met en évidence le rôle des lacunes d’azote et des défauts structuraux dans l’ingénierie de revêtements durs à stabilité de phase améliorée et dont les propriétés mécaniques sont compatibles avec des applications à haute température. Le nitrure de titane et d’aluminium (Ti,Al)N sous forme de revêtements est un matériau de choix pour la protection des outils de coupe pour métaux en raison de sa résistance supérieure à l’oxydation et à l’usure à haute température. La décomposition spinodale à haute température de la phase métastable cubique (Ti,Al)N en domaines cohérents de taille nanométrique de c-TiN et de c-AlN donne une dureté importante aux températures élevées. Un apport thermique encore plus élevé conduit à la transformation de c-AlN en w-AlN, ce qui nuit aux propriétés mécaniques du revêtement. Un moyen de retarder cette transformation est d'introduire des lacunes d'azote. Dans cette thèse, je montre que la combinaison d’une réduction de la teneur globale en azote du revêtement c-(Ti,Al)Ny(y <1) avec une faible tension de polarisation du substrat lors du dépôt par arc cathodique induit un retard encore plus prononcé de la transformation de la phase c-AlN en w-AlN. Dans de telles conditions, le durcissement par vieillissement est conservé jusqu'à 1100 ° C, ce qui correspond à la température la plus élevée signalée pour les films de (Ti,Al)N. Au cours des opérations de coupe, le mécanisme d'usure des films c-(Ti0.52Al0.48)Ny déposés par arc cathodique avec des teneurs en N de y = 0.92, 0.87 et 0.75 est influencé par l'interaction des lacunes d'azote, de la microstructure et des réactions chimiques avec le matériau de la pièce. Le revêtement y = 0.75 contient le plus grand nombre de macroparticules et présente, après usinage, une microstructure non homogène qui en abaisse la résistance à l'usure sur les flancs et les cratères. Le durcissement par vieillissement de l'échantillon y = 0.92 entraîne une résistance supérieure à l'usure sur le flanc, tandis que la structure dense de l'échantillon y = 0.87 empêche l'usure chimique qui se traduit par une excellente résistance à l'usure sur les cratères. Des films hétéroépitaxiés c-(Ti1-x, Alx)Ny (y = 0.92, 0.79 et 0.67) ont été déposés sur des substrats de MgO(001) et (111) en utilisant une technique de pulvérisation magnétron pour examiner en détail les défauts structuraux pendant la décomposition spinodale. À 900 °C, les films se décomposent pour former des domaines cohérents riches en c-AlN et c-TiN de forme allongée le long de la direction <001>. Les cartographies de déformation montrent que la plupart des contraintes se trouvent près de l'interface des domaines ségrégés et à l'intérieur des domaines c-TiN. Les dislocations s'agrègent favorablement dans c-TiN plutôt que dans c-AlN car ce dernier a une directionnalité plus forte des liaisons chimiques covalentes. À température élevée, la taille de domaine des films de c- (Ti, Al)Ny orientés (001) et (111) augmente avec la teneur en azote. Cela indique qu'il y a un retard dans le grossissement dû à la présence de plus de lacunes d’azote dans le film. [...]
This study highlights the role of nitrogen vacancies and defect structures in engineering hard coatings with enhanced phase stability and mechanical properties for high temperature applications. Titanium aluminum nitride (Ti,Al)N based materials in the form of thin coatings has remained as an outstanding choice for protection of metal cutting tools due to its superior oxidation resistance and high-temperature wear resistance. High-temperature spinodal decomposition of metastable (Ti,Al)N into coherent c-TiN and c-AlN nm-sized domains results in high hardness at elevated temperatures. Even higher thermal input leads to transformation of c-AlN to w-AlN, which is detrimental to the mechanical properties of the coating. One mean to delay this transformation is to introduce nitrogen vacancies. In this thesis, I show that by combining a reduction of the overall N-content of the c-(Ti,Al)Ny (y < 1) coating with a low substrate bias voltage during cathodic arc deposition an even more pronounced delay of the c-AlN to w-AlN phase transformation is achieved. Under such condition, age hardening is retained until 1100 °C, which is the highest temperature reported for (Ti,Al)N films. During cutting operations, the wear mechanism of the cathodic-arc-deposited c-(Ti0.52Al0.48)Ny with N-contents of y = 0.92, 0.87, and 0.75 films are influenced by the interplay of nitrogen vacancies, microstructure, and chemical reactions with the workpiece material. The y = 0.75 coating contains the highest number of macroparticles and has an inhomogeneous microstructure after machining, which lower its flank and crater wear resistance. Age hardening of the y = 0.92 sample causes its superior flank wear resistance while the dense structure of the y = 0.87 sample prevents chemical wear that results in excellent crater wear resistance. Heteroepitaxial c-(Ti1-x,Alx)Ny (y = 0.92, 0.79, and0.67) films were grown on MgO(001) and (111) substrates using magnetron putter deposition to examine the details of their defect structures during spinodal decomposition. At 900 °C, the films decompose to form coherent c-AlN- and c-TiN- rich domains with elongated shape along the elastically soft <001> direction. Deformation maps show that most strains occur near the interface of the segregated domains and inside the c-TiN domains. Dislocations favorably aggregate in c-TiN rather than c-AlN because the later has stronger directionality of covalent chemical bonds. At elevated temperature, the domain size of (001) and (111)- oriented c-(Ti,Al)Ny films increases with the nitrogen content. This indicates that there is a delay in coarsening due to the presence of more N vacancies in the film. The structural and functional properties (Ti1-x,Alx)Ny are also influenced by its Al content (x). TiN and (Ti1-x,Alx)Ny (y = 1, x = 0.63 and x = 0.77) thin films were grown on MgO(111) substrates using magnetron sputtering technique. Both TiN and Ti0.27Al0.63N films are single crystals with cubic structure. (Ti0.23,Al0.77)N film has epitaxial cubic structure only in the first few atomic layers then it transitions to an epitaxial wurtzite layer, with an orientation relationship of c-(Ti0.23,Al0.77)N(111)[1-10]ǀǀw-(Ti0.23,Al0.77)N(0001)[11-20]. The w-(Ti0.23,Al0.77)N shows phase separation of coherent nm-sized domains with varying chemical composition during growth. After annealing at high temperature, the domains in w-(Ti0.23,Al0.77)N have coarsened. The domains in w-(Ti0.23,Al0.77)N are smaller compared to the domains in c-(Ti0.27,Al0.63)N film that has undergone spinodal decomposition. The results that emerged from this thesis are of great importance in the cutting tool industry and also in the microelectronics industry, because the layers examined have properties that are well suited for diffusion barriers

No presente trabalho foi avaliado o efeito da microestrutura e da capacidade de suportar carregamento de camadas nitretadas produzidas em aços ferramenta AISI H13 e AISI D2 sobre a aderência e a resistência ao desgaste microabrasivo de revestimentos de TiN-PVD. Em cada um desses aços, foram produzidas camadas nitretadas de diferentes estruturas e espessuras, e foram determinadas experimentalmente as curvas potencial início de formação de camada branca, para a nitretação a 520oC. Para o aço ferramenta AISI H13, o emprego de tempos de pré-tratamento de nitretação mais prolongados ( aproximadamente 11 h) foi necessário para aprofundar a camada nitretada e, conseqüentemente, aumentar a capacidade de suportar carregamento dos revestimentos, evitando a formação de bordas que provocam o lascamento e a escamação das camadas de TiN. Observou-se que esse tipo de falha persiste se a zona de endurecimento for pouco profunda, uma vez que a transição de propriedades mecânicas da camada de TiN para o núcleo não nitretado continua abrupta e a capacidade de suportar carregamento da camada nitretada ainda é baixa. Por outro lado, curtos tempos de nitretação (aproximadamente 42 min.) foram suficientes para aumentar a aderência das camadas de TiN ao aço ferramenta D2, pois o núcleo não nitretado desse aço possui uma capacidade de suportar carregamento razoável. Observou-se que a resistência ao desgaste microabrasivo e a aderência dos revestimentos são prejudicadas com a presença de uma camada preta na interface camada de TiN/camada nitretada. Quando a superfície dos revestimentos é carregada, falhas do tipo “casca de ovo” facilmente ocorrem.
In this work, the influence of both the microstructure and the load-bearing capacity of nitrided layers, formed on top of AISI D2 and AISI H13 tool steels, on adhesion and wear resistance of PVD-TiN coatings was studied. The threshold nitriding potential curves for the above mentioned steels and the optimum conditions of the pre-treatments which increased the adhesion as well as the wear resistance of the PVD-TiN were determined experimentally. By using longer nitriding times (about 11 h) and lower nitrogen contents in the gas mixture (about N2-5%vol.), it was possible to minimize the pile-up degree of the TiN/H13 nitrided substrates and, consequently, the occurrence of coatings chipping. This flaw persists when the nitrided layer is thin, due to an abrupt transition of mechanical properties at the TiN coating / steel core interface. Shorter nitriding times (about 42 min.) and lower nitrogen contents (about N2-5%vol.), on the other hand, are sufficient to guarantee a better adhesion of TiN coatings on AISI D2 tool steel, as the core of such steel possesses relatively better load-bearing capacity than the AISI H13 tool steel. The presence of a black layer at the TiN/nitrided layer interface was observed in all coatings deposited over nitrided layers produced above the threshold nitriding potential curves. This layer affects adversely the wear resistance and the adhesion of the TiN coatings. When higher loads are applied on the coated surface, “egg shell” type flaws easily occur.

Dans les applications automobiles et dans d'autres domaines (énergie, aviation, etc), le nombre d'appareils électroniques a augmenté de façon significative au cours des dernières décennies. La sécurité des systèmes et des personnes repose sur la qualité de connecteurs électriques. Toutefois, soumis à des vibrations (moteur de la voiture, de l'environnement) des microdéplacements sont induits à l’interface. La problématique du contact électrique est principalement liée à l'altération de la conduction de faible courant (5mA) dans les interfaces soumises à des contraintes mécaniques de glissement répétitifs engendrant un phénomène bien connu de fretting par l’usure. La sollicitation de fretting usure apparait comme un processus de dégradation très pénalisant. Outre la détérioration des surfaces, ce processus conduit à une augmentation de la résistance électrique des contacts et à une possible perte du signal électrique. Ceci est particulièrement le cas pour les connecteurs bas niveau très sensibles aux fluctuations de la résistance électrique. Pour remédier à cela, les acteurs de la connectique développent de nouveaux dépôts pour limiter l’utilisation de dépôts nobles tels que l’or. Les objectifs de cette thèse sont d’établir une "table d’utilisation" des revêtements en fonction de sollicitations précises et de mettre en place une méthodologie dans le choix des dépôts en vue d’optimiser la durée de vie des connecteurs. L’étude aborde différents aspects tels que les influences des conditions de chargements mécaniques, des épaisseurs de dépôts, du type de dépôt (noble, non noble, dopé), de l’amplitude de débattement (micro-déplacement et grand déplacement) et la formalisation de l’endurance électrique (loi puissance et approche énergétique)
In automotive applications and in other areas (energy, aviation, etc.), the number of electronic devices has increased significantly in recent last decades. Systems and people securities are based on the quality of electrical connectors. However, submitted to vibrations (car engine, environment) micro-displacements are induced at the interface. The problem of electrical contact is mainly due to the impairment of low current conduction (5mA) in interfaces subjected to repetitive sliding displacement generating a well-known fretting wear phenomenon. Fretting wear solicitation appears as a process of very detrimental degradation. Besides surface deterioration, this process leads an increase of the electrical contact resistance and a possible loss of the electrical signal. This is particularly the case of the low level connectors which are very sensitive to electrical contact fluctuations. To remedy, connections actors develop new deposits to limit the use of noble ones such as gold. The objectives of this thesis are to establish a "table of use" coatings based on specific solicitations and define a methodology for the selection of deposits to optimize the lifetime connectors. The study covers different aspects such as the mechanical loading conditions influence, the thickness deposits influence, the type of deposit (noble, non-noble, doped), the displacement amplitude (microdisplacement and large displacement) and the electrical endurance formalization (energetic approach and power law)

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O aparelho endoscópico utilizado atualmente para estudo do trato gastro-intestinal (o video-endoscópio) é resultado de quase 200 anos de evolução tecnológica. Estes endoscópios não podem ser esterilizados pelos métodos clássicos. Por sua complexidade, o processo de limpeza e desinfecção de endoscópios não é somente uma preocupação da enfermagem, ela se tornou multidisciplinar, pois exige discussão sobre riscos físicos, biológicos e químicos, tanto para o paciente quanto para a equipe. A borracha da ponta flexível dos endoscópios é uma peça fundamental para a preservação da vedação do endoscópio e principalmente preservação do paciente. Esta borracha sofre desgaste tanto durante o exame como pelos processos de desinfecção do equipamento que acabam agredindo a superfície do material. O seu desgaste ou ruptura pode acarretar na queima do gerador de imagem. A troca da borracha da ponta é considerada uma manutenção parcial e deve sempre ser executada periodicamente. Baseado no exposto este trabalho teve como objetivo principal estudar e avaliar a degradação ocorrida em ponteiras flexíveis de endoscópios digestivos submetidos a procedimentos médicos. Como resultados pode-se verificar nas microscopia, tanto ótica como eletrônica, morfologia rugosa com presença de poros para a ponteira virgem, nas ponteiras utilizadas por diferentes períodos de tempo verificou-se intensificação destas rugosidades. Por DRX pode-se observar um perfil praticamente amorfo típico de elastômero, além de identificar a presença de compostos de carga no polímero. Por FTIR pode-se comprovar diferentes estruturas para as amostras estudadas, levando a crer que algumas possuem polidimetilsiloxana em excesso com relação ao fluorelastômero. Por EDS pode-se verificar a exteriorização de compostos presentes no interior do elastômero após o período de degradação. No ensaio de tração foi verificada diminuição das propriedades físicas do elastômero devido a degradação ocorrida. No ensaio de ângulo de molhabilidade verificou-se que mesmo após o processo de degradação todas as amostras ainda apresentavam-se hidrofóbicas. Em síntese, este trabalho observou a necessidade de se desenvolver um material específico para utilização como ponteiras de endoscópios, já que os existentes no mercado aparentemente não tem destino especifico para aplicações biológicas. Ou seja, mesmo em sua forma virgem o elastômero em questão já apresenta fatores que não tornam sua utilização em meio biológico tão viável.
The endoscopic device currently used to study the gastrointestinal tract (the videoendoscope) is the result of nearly 200 years of technological evolution. These endoscopes can not be sterilized by the classical methods. Due to its complexity, the process of cleaning and disinfection of endoscopes is not only a concern of nursing, she became multidisciplinary, since it requires discussion of physical, biological and chemical hazards, both for the patient and for the team. The flexible rubber tip of the endoscope is a key piece to preserve the seal of the endoscope and especially preservation of the patient. This rubber wears out both during the test as the disinfection of equipment that processes attacking the end surface of the material. Your wear or breakage may result in the image generator burns. The replacement of the rubber tip is considered a partial maintenance and must always be performed periodically. Based on the above this work aimed to study and evaluate the degradation occurred in flexible tips of digestive endoscopes undergoing medical procedures. The results can be seen in microscopy, both optical and electronic, rough morphology with the presence of pores to the virgin tip, the tips used for different periods of time there was intensification of these ridges. XRD can observe typical listing a substantially amorphous elastomer, and identify the presence of compounds in the polymer charge. FTIR can prove different structures for the studied samples, leading to the belief that some have polydimethylsiloxane in excess with respect to the fluoroelastomer. EDS can verify the externalization of compounds within the elastomer after the degradation period. In the tensile test was observed decrease in physical properties of the elastomer due to degradation occurred. On test wetting angle was found that even after the degradation process all the samples still had become hydrophobic. In summary, this study observed the need to develop a specific material for use as tips of endoscopes, since on the market apparently has no specific target for biological applications. That is, even in its virgin form the elastomer in question already has factors that do not make their use in biological environment as possible.

Os controladores de caudal, normalmente implementados em sistemas Supervisory control and data acquisition (SCADA), apresentam uma grande relevância no controlo automático de canais de adução. Para garantir que os controladores de caudal sejam fiáveis em todo o seu domínio de funcionamento (em situações de escoamento com ressalto livre ou submerso e de transição entre escoamentos com ressalto livre e ressalto submerso) foram comparados os resultados dos ensaios experimentais com diferentes métodos de cálculo da vazão em comportas e/ou sobre soleiras. O programa de ensaios foi realizado nos canais laboratorial e experimental da Universidade de Évora. Foram realizados ensaios em comportas planas verticais e em soleiras do tipo Waterways Experiment Station (WES) controladas ou não por comportas planas verticais. Em ambos os casos, foram contempladas as situações de escoamento com ressalto livre e submerso. Os resultados obtidos mostram que: a) para as comportas, o método Rajaratnam e Subramanya (1967a) conduz a bons resultados com um erro percentual médio absoluto MAPE < 1% para o escoamento com ressalto livre e MAPE < 4% para o submerso; a transição entre escoamentos foi identificada corretamente por este método; b) para as soleiras, obtiveram-se bons resultados para o escoamento com ressalto livre para o método USACE (1987), com MAPE < 2%, e para o submerso através do método Alves e Martins (2011), com MAPE < 5%; a transição entre escoamentos pode ser considerada adequada de acordo com a curva experimental de Grace (1963); c) para soleiras controladas por comporta, conseguiram-se bons resultados para o escoamento com ressalto livre recorrendo à equação dos orifícios de pequenas dimensões, com MAPE < 1, 5%, e para o submerso com a equação dos orifícios totalmente submersos com MAPE < 1, 6%; em ambos os casos foi necessária calibração do coeficiente de vazão; a transição entre escoamentos foi adequada pelo método de Grace (1963). Com base nos resultados obtidos, foi possível definir um algoritmo de vazão generalizado para comportas e/ou soleiras que permite a determinação da vazão para as situações de escoamento com ressalto livre e submerso incluindo a transição entre escoamentos; ABSTRACT: Flow controllers, usually implemented in Supervisory Control and Data Acquisition (SCADA) systems, are very important in the automatic control of irrigation canal systems. To ensure that flow controllers are reliable for the entire operating range (free or submerged flow and flow transitions) the experimental results were compared with different methods of flow measurement for gates and/or weirs. The test program was conducted in the laboratory flume and in the automatic canal of the University of ´Evora. Tests were carried in sluice gates and in broad-crested weirs controlled or not by sluice gate. In both cases free and submerged flow conditions were analyzed. The results show that: a) for the sluice gates, the method of Rajaratnam e Subramanya (1967a) leads to good results with a mean absolute percentage error (MAPE) < 1% for free flow and MAPE < 4% for submerged flow. The transition between flows is correctly identified by this method; b) for the uncontrolled weir, good results were obtained for free flow with the method USACE (1987) with MAPE < 2%, and for submerged flow by the method Alves e Martins (2011) with MAPE < 5%. The transition between flows can be accurately defined by the experimental curve of Grace (1963); c) for the controlled weir, good results were achieved for the free flow with the small orifice equation with MAPE < 1.5% and for submerged flow with the submerged orifice equation with MAPE < 1.6%; in both cases the calibration of the discharge coefficient is needed. The transition between flows can be accomplished through Grace (1963) method. Based on the obtained results, it was possible to define a generalized flow algorithm for gates and/or weirs that allows flow determination for free and submerged flow conditions including the transition between flows.

O objetivo central desta tese é estudar o percurso artístico e intelectual de Leon Hirszman a partir dos filmes Que país é este? (1976-77), ABC da greve (1979- 90) e Eles não usam black-tie (1981). Discutindo as relações entre cinema e História, a pesquisa se concentra nas práticas culturais, estéticas e ideológicas do realizador, procurando analisar as interpretações que ele mobilizou em torno do Brasil durante a vigência do regime militar. A despeito de Hirszman ter consolidado a sua trajetória como integrante do Cinema Novo, questão que percorre as páginas deste doutorado, propõe-se também uma aproximação entre a sua obra e o projeto dramatúrgico construído por autores oriundos do Teatro de Arena. Na década de 1970, face à crise que se instalou no campo cultural da esquerda, em especial o colapso da crença revolucionária anterior a 1964 e o refluxo da leitura do povo como vanguarda heroica para uma transformação do mundo, o cineasta se aproximaria do revisionismo artístico proposto, principalmente, por Gianfrancesco Guarnieri, Paulo Pontes e Vianinha. Mantendo em seus filmes uma abordagem politizada da classe popular, sem abdicar da figura do intelectual como mediador de denúncias contra a ditadura, o diretor se voltaria para uma produção em sintonia com o viés comunista de engajamento, em diálogo com a tradição do realismo crítico e disposta a elaborar narrativas e registros documentais em confronto ao autoritarismo dos militares. Nesse sentido, mesmo sem partilhar do ideário do novo sindicalismo surgido sobretudo entre os metalúrgicos da cidade paulista de São Bernardo do Campo, Hirszman deslocaria a figura do operário para o centro do processo criativo de ABC da greve e de Black-tie, representando-o em uma chave próxima à resistência articulada pelo Partido Comunista Brasileiro (PCB), na qual o trabalhador seria visto como parte de uma ampla frente organizada para superar a ditadura e atuar em prol da redemocratização. Uma obra realizada com o intuito de responder aos dilemas sociais de seu contexto histórico, a propor uma abordagem particular sobre a classe popular e a militância antiautoritária, a partir de leituras e experiências estéticas construídas em meio aos impasses que percorreram a esquerda política e cultural na segunda metade dos anos 1970.
The main goal of this thesis is to study Leon Hirszman\'s artistic and intellectual trajectory through the films Que país é este? (1976-77), ABC da greve (1979-90) and They don\'t wear black-tie (1981). Discussing the relation between film and History, the research concentrates itself on the cultural, aesthetic and ideological practices of the director, aiming to analyze his interpretations about Brazil during its military dictatorship. Despite Hirszman\'s consolidated career as a member of the Cinema Novo movement, issue that is described during this doctoral thesis, it also proposes an approach of his work with the dramaturgical project originated by authors from the Teatro de Arena. On the 1970\'s, in virtue of the crisis installed in the left wing\'s cultural sphere, specially the collapse of the revolutionary belief preceding 1964 and the retrocession of the interpretation placing the people as the heroic vanguard leading a structural transformation, the filmmaker would court the artistic revisionism proposed by Gianfrancesco Guarnieri, Paulo Pontes and Vianinha. Maintaining a politicized approach about the popular class on his films, without abdicating the image of the intellectual as a mediator of denounces against the dictatorship, the director would proceed to a production in tune with the communist\'s active participation project, establishing a dialogue with the tradition of critical realism, willing to elaborate narratives and documental registers confronting with the authoritarian way of the military. In this sense, even without sharing the ideology originated from the newly born trade unionism, especially among the steelworkers from São Bernardo do Campo\'s city, Hirszman shifted the figure of the worker, making it the core of the creative process of ABC da greve and Black-tie. In these movies, it was represented as a key-piece close to the resistance articulated by the Brazilian Communist Party (PCB), in which it was seen as part of a large front, organized to overcome the military regime and act in favor of the country\'s redemocratization. A work realized with the intention of responding to the social dilemmas of its time, proposing a singular approach about the popular class and the anti-authoritarian militancy, originating interpretations and aesthetic experiences constructed among conflicts that filled the left-wing politic and cultural manifestations on the second half of the seventies.

Cette thèse est divisée en six parties. La première partie est consacrée à l'étude de propriétés de Hadamard et à l'obtention de théorèmes de Liouville pour des solutions de viscosité d'équations aux dérivées partielles elliptiques complètement non-linéaires avec des termes de gradient,
This thesis is divided into six parts. The first part is devoted to prove Hadamard properties and Liouville type theorems for viscosity solutions of fully nonlinear elliptic partial differential equations with gradient term

碩士
國立虎尾科技大學
機械設計工程研究所
103
Abstract Tin-lead alloys with stable performance, embedded, low melting point, good fluidity, and corrosion resistance properties. Currently most often used in solder, bearings, aerospace and electronics industry, and if we can increase the bearing strength, it can reduce the overall dimensions of the bearing will be more cost and space. This experiment will carbon fiber soaking in 0.1mol/L of concentrated sodium hydroxide (NaOH) electrolytic liquid placed 3 minutes, in placed sulfuric acid nickel bath, by 8 volts and 10 amps plating 12-15 minutes, completed fiber surface processing, will carbon fiber into mold cavity, put mold temperature warming to 150 ℃, then will liquid solder heating to 300 ℃ pour mold, maintained in 150 ℃ and pressure range 30 to 50 MPa, immediately through piston in mold top Department put pressure on, in pressure maintained 10 minutes, While the mold is cooled to near room temperature. Test results found that after surface treatment of carbon fiber composite material and without surface treatment of carbon fiber composites, by contrast, after surface treatment has a high tensile strength and abrasion conditions, containing coated fiber composites are relatively good, but under sliding wear does not contain the coating of fiber composites are relatively good.

When loss of material due to sliding of two solids is promoted/prevented, in the presence of chemically reacting liquid or gas, tribochemical wear is said to occur. Tribochemical wear, in which corrosive media promotes material loss, is a serious concern in a variety of applications like machining, bio-implants, gas turbine engines etc. The most pervasive corrosive media encountered in applications are water and air. Air also contains water vapour along with oxygen, both of which adsorb and react with most materials, thus influencing their wear behaviour. The need for higher operating temperatures and compression ratios in gas turbine engines require development of high temperature wear resistant coatings to protect their soft metallic components. Ti based nitride coatings with Ti, Al, Si, Cr, Ta, Nb, V are known for wear resistance because of their high hardness which is second only to diamond and c-BN. High O affinity of these elements, induce the coatings to form passive oxide scale up to reasonably high temperatures and offer superior corrosion and oxidation resistance. However, sliding can remove the passivating layer, exposing the native surface to the environment which can lead to enhanced tribochemical wear. Oxidation resistance under static conditions does not guarantee low tribochemical wear; however, the tribochemical reactions causing the corrosion are of interest. Another concern is that sliding in unison with high temperatures can activate processes like enhanced diffusion, phase transformations in nitride coatings as well as in the substrate. Hence one of our objectives is to perform wear tests at high temperatures to understand the dominant mechanisms that affect wear in nitride coatings. Wear tests in the range of room temperature up to the oxidation limit of these coatings are designed.In this study TiN and high aluminium containing TiAlN coatings are chosen to study understand the wear behaviour as function of temperature up to 800°C [1]–[3]. In order to study wear of coatings, it is necessary to identify the best possible materials and methods. Though under the targeted application the coatings have to perform under fretting tests, pin on disk configuration is used which simplifies the analysis and gives deeper insight into the wear mechanism. Coated ball is used as the pin which is stationary unlike many earlier studies where the coating is applied on the rotating disk. The purpose of keeping the pin stationary is to minimize the counter-face wear and, instead, accelerate wear in these hard coatings. This method also enables easy and accurate measurement of wear depth and volume by using an optical microscope, while the conventional coated disk method requires profilometry and statistically sound measurements. To enable coating performance, substrate should not undergo much loss of strength before 800°C and hence aerospace grade IN718 alloy is chosen as the substrate which softens slowly beyond 650°C. Alumina is used as counter-face, since it has high hardness, excellent mechanical, chemical and thermal stability. In the current study, TiAlN coating is tested for wear in the range of room temperature to 800°C. Figure 1 represents the data obtained from the wear experiments. It is found that the wear is higher with large scatter at room temperature while it remains constant from 200- 750°C. Two important observations are made, firstly that the TiAlN is susceptible to some kind of a corrosive wear at room temperature which depended on the timing of the tests and secondly that the coating shows a surprisingly constant wear behaviour over the temperature range of 200-750°C. The scatter at room temperature is found to be linked with seasonal fluctuation of humidity which is verified by performing tests under controlled humidity conditions. Water vapour and oxygen are potential reacting gases present in air. Oxidation and oxidative wear is known to occur in many materials as temperatures increase which seem to be linked to thermal activation of oxidation. However lower wear at 200°C and above compared to room temperatures suggests something else to be happening .It is evident then that between room temperature and 200°C lies a transition of some kind in the tribochemical reaction which is responsible for the observed wear behaviour of TiAlN. A detailed study to understand this transition is then undertaken for the composition of TiN coatings so that benchmarking and comparison with TiAlN is possible. Also if the wear behaviour of TiN is found similar to TiAlN then it would indicate a general phenomenon which can be extended to Ti based nitrides. Figure 1 Wear rate as a variation of temperature for TiAlN coatings In contrast to low temperature wear behaviour of TiAlN, a constant wear in the range of 200-750°C is surprising because the primary suspect which is oxidation is thermally activated. The oxide scale though expected to be thin at low temperatures, has to increase in thickness with temperature due to increased diffusion and reaction rates. The oxide scale also undergoes a change in morphology and composition which indicate a lower oxidation resistance as temperature increases. A preliminary characterization of the wear scar on the ball shows that the oxide inside the worn region is thinner than the oxide outside at 750°C. The amount of O within the wear scar is similar to levels observed on as deposited surface while the surface outside the wear scar shows oxidation and discolouration. The results suggest that oxidation inside worn region at high temperatures might be slower than the expected parabolic oxidation occurring outside the wear region. It is speculated that a double layer oxide is formed with TiO2 towards the surface and Al2O3 towards the nitride which is responsible for the lower wear at high temperature. This is supported by the fact that larger amount of Ti is found in the wear debris as temperature inceases. Superficial surface cracks appear at higher loads at temperatures as low as 600°C but they affect wear only above 800°C due to substrate softening. This shows that the coatings are still limited by the substrate softening temperature and could be used at higher temperatures. Tribo-reaction in metals, nitrides and carbides can be brought about in the presence of O2 or water vapour. Tribochemical wear of SiN, SiC, TiN, TiAlN, alumina and most other ceramics at room temperature are found to depend on humidity[4]–[6]. But only tribo-oxidation due to O2 is found to operate at high temperatures[7], [8]. Notwithstanding, it is known that SiC and SiN are more resistant to attack from O2 above 800°C than from steam. Hence the role played by water vapour is found to be convoluted. Moreover, relative humidity is the frequently mentioned quantity with regard tribochemical wear at room temperatures. It should be noted that relative humidity is not a measure of chemical activity of water vapour. Rather the water vapour pressure which represents the chemical activity of water, is not given much importance in the earlier studies. In this study, the importance of humidity, water vapour pressure and temperature in influencing wear, is studied by performing controlled wear tests on TiN. To explore the effect of temperature and water vapour pressure, TiN is tested varying temperature range of 28 °C to 90°C and water vapour pressure in the range of 3-35 mm-of-Hg. Wear tests are conducted keeping temperature constant with varying water vapour pressure and vice versa. The results show that, wear increased with humidity/vapour pressure at a fixed temperature but wear dropped drastically with increase in temperature at constant vapour pressure up to a critical temperature beyond which wear remained constant. This is one of the major unexpected findings since temperature is expected to increase wear volume. Also the critical temperature is found to shift to higher temperatures as water vapour pressures increased. It was suspected that capillary condensation was playing a role in the wear which was later verified. The whole wear behaviour is shown to be correlated with the amount of capillary condensed water. The large radius of curvature of the asperities on the polished coating surface and the smooth surface formed on the counter-face due to debris compaction form conditions favourable for capillary condensation. Any two hydrophilic surfaces which come in contact can form capillary condensation to occur at the cusps formed around the contact. However a threshold pore size of about 1nm existed below which condensation did not influence wear. Another observation is that the water vapour did not affect wear significantly in the absence of condensation for TiN coatings. As temperatures increased condensation became unfavourable, but the high vapour pressure present showed no signs of wear enhancement. This is surprising and unexpected compared to earlier reports.[9], [10] On contrary tests in liquid water showed expected behaviour for tribochemical reaction i.e wear increased with temperature. The wear in liquid water is highest when compared studies in air at any given temperature. The X-ray electron emission spectroscopy (XPS) analysis is performed to understand the surface reactions. It appears that O2 forms a barrier oxide which protects the nitride from reacting with water vapour. However when condensation occurs or in water, the oxygen and water collude into forming softer hydroxide layer which is easily removed. Though chemically water and water vapour are same, they affect wear in TiN very differently. Summarising the synopsis, exploration into high temperature wear of TiAlN reveals that it can handle oxidative wear upto 750°C showing constant wear over the temperature range of 200-750°C. Reduction in residual stresses and substrate softening may be responsible for higher wear at higher loads since the cracking is observed at 5N is absent at 3N. The substrate is expected to soften above 650°C but this does not necessarily affect wear until the load is increased or the temperature is sufficiently high. However TiAlN and TiN coatings showed susceptibility to tribo-corrosion in water and high humidity at room temperature. At high humidity, condensation of water leads to increase in wear. The dependence of wear on humidity is found to be because of capillary condensation. The negligible dependence of wear on humidity in the absence of condensation is ascribed to formation of oxide layer due to reaction with O2 and coating. The oxide barrier formed due to atmospheric O2 protects the coating from reacting with the water vapour. The oxide barrier on TiN forms faster indicating O2 reaction to be faster than the reaction with water vapour. In the presence of capillary condensation or water, O2 is depleted from contacting surfaces thus hindering the formation of the barrier oxide, increasing wear. As temperature increases the condensation becomes unfavourable and barrier oxide dominates the wear mechanism upto high temperatures which is dominated by oxidative wear.

碩士
崑山科技大學
機械工程研究所
92
The function of the single layer film has been already unable to satisfy the demand in using. According to document report, with multilayer films or nano-multilayer films can improve the hardness and the toughness of superior properties to single layer film. The purpose of this paper, is given of the preparation by direct current magnetism sputtering of TiN/CrN multilayer films on SKD11, The microstructure and mechanical properties of multilayer films are discussed. In addition, annealing were also discussed during sputtering and the effects of the microstructure and mechanical properties, Substrate temperature of 250℃, showed a good adhesion strength for TiN/CrN multilayer films. Tribological properties of TiN/CrN multilayer films has been studied using pin-on-disc test procedures. Experimertal results indicate that the wear rate of TiN/CrN multilayer films has a low values after annealing at 500℃for 1 hr. The friction coefficient of 8-layer films was about 0.5, which is slightly higher than that of the 16-layer films about 0.29.The films with a total thicknes about 0.774μm and layer sequence TiN/CrN exhibits good wear resistance on reciprocating wear test.

博士
國立成功大學
材料科學及工程學系碩博士班
93
The Si3N4-based composites were manufactured by hot-pressing sintered at 1850℃ for 1h. The effects of TiN addition to Si3N4-based composites on its microstructure, mechanical properties, wear behaviors and electrical discharge machining were investigated. Residual stress analysis and failure simulation are performed based on finite element method (FEM) to explore the effects of the particle properties on the failure of particle-reinforced composite, using composite samples with various particle properties. The microstructure, strength, fracture toughness and electrical resistivity of Si3N4 containing two different sizes of TiN were investigated. The size and content of TiN particles were found having influence on the strength, toughness, hardness and electrical resistivity of Si3N4-based composites. The grain-boundary film and interface chemistry has been analysed by means of high resolution electron microscopy (HREM). The HREM observation exhibited a thin amorphous intergrangular films at both TiN- Si3N4 and Si3N4-Si3N4 grains boundary. In general, no obvious difference in composition between the grain-boundary film and the triple-grain junctions was detected. The results of the FEM simulation have been demonstrated using by the second phase particles reinforced the composites that displays an enhanced toughness but degraded strength, compared to the monolithic material. 　The friction and wear behavior of Si3N4-based composites against AISI-52100 steel were investigated in the ball -on- disc mode in a non-lubrication reciprocation motion. It has been found that under the conditions used all the ceramic components exhibited rather low friction and wear coefficients. The addition of TiN particles can increase the fracture toughness of Si3N4-based composites. The Si3N4-based composites exhibits a small friction and wear coefficient compared monolithic Si3N4. The contact load was varied from 100 to 300 N. For monolithic silicon nitride materials, high friction coefficients between 0.6 and 0.7 and wear coefficients between 1.63×10-8 and 1.389×10-6 ㎜3/N.m were measured. By adding titanium nitride, the friction coefficients was reduced to a value between 0.4 and 0.5 and wear coefficients between 1.09×10-8 and 0.32×10-6 ㎜3/N.m at room temperature. The fracture toughness of Si3N4-based composites played an important role for wear behavior. 　All materials and worn surfaces as well as wear debris were investigated by means of SEM, EDS, XRD, AFM and TEM before or after the tribological tests. The wear mechanisms of Si3N4-based composites are adhesive wear, tribo-chemical reaction induced wear, abrasive wear and three-bodies wear in non-lubrication sliding tests. Materials removal in the Si3N4-based composites occurs through a combination of micro-fracture and micro-groove deformation from micro-plowing along the sliding traces by the abrasive particles. The presence of twins and dislocation networks in Si3N4-TiN grains indicates that the wear of Si3N4-based composites is well accommodated plastic deformation. The TEM micrographs of wear track revealed plastic deformation through cracking along grain boundary propagation. This shows that the fracture toughness plays an important role in the fracture mechanism. 　The addition of TiN conductive phase is relatively uniformly distributed in silicon nitride matrix. The conductive grains are connected to each other an electric network. A low electrical resistivity of 1.25×10-3Ω.㎝ was obtained in 40vol% small TiN/Si3N4 composites. The Si3N4-based composites have high electrical conductive and can be used for electrical discharge machining (EDM). The EDM of the Si3N4-based composites was conducted using wire-EDM, sinker-EDM and micro-EDM cutting process. The model erosion mechanisms of EDM revealed melting and evaporation, the resolidified droplets almost are Ti element, as Si3N4 should be removed by evaporation. 　Machine ability was evaluated in terms of material removal rates, tool wear, and surface finish under different conditions. The removal rates of Si3N4-based composites were found to be dependent on working voltage, current, pulse duration and feed rate. High removal rate resulted in larger crater which features on the machined surface. Four point flexure testing was performed in accordance with the ASTM standard for the flexure testing of EDMed ceramics. Analysis of sixteen flexure tests indicated a Weibull modulus as high as 10.5 for fine EDM. The erosion rate is evaluated with copper and brass of tool electrode material by sinker-EDM test in Si3N4-based composites. The wear rates of brass are substantially greater than that of copper for all sinker-EDM tests. 　The results demonstrated the possibility of machining structural ceramics by the micro-EDM method through the incorporation of conductive toughening phases. This research has successful shown that EDM can be applied to Si3N4-based composites, if the electrical resistivity is below 10-1Ω.㎝. Electro-conductive ceramic miniaturized structures can be machined by wire-EDM. The vertical walls of Si3N4-base composite machined by wire-EDM, showing the pattern profile which has the minimum line width of 220μm and 217μm space width. Micropores of 800μm in depth and 50~70μm in diameter were successfully machined in Si3N4-based composites by the micro-EDM method.

Titanium carbide (TiC) and titanium carbonitride (Ti(C,N)) are both common components in hard, wear resistant ceramic-metal composites, or cermets. In this study the intermetallic nickel aluminide (Ni3Al) has been used as a binder for the production of TiC and Ti(C,N) based cermets. These cermets offer several improved characteristics relative to conventional WC-based ‘hardmetals’, such as lower mass and improved oxidation resistance, which are also combined with high fracture resistance, hardness and wear resistance. The cermets were produced using an in-situ, reaction sintering procedure to form the stoichiometric Ni3Al binder, with the binder contents varied from 20 to 40 vol%. However, for high N content Ti(C,N) cermets, the wettability of molten Ni3Al is relatively poor, which leads to materials with residual porosity. Therefore various amounts of Mo2C (1.25, 2.5, 5 and 10 vol%) were incorporated into the Ti(C0.3,N0.7)-Ni3Al cermets, with the aim of improving the densification behaviour. Mo2C was found to improve upon the wettability during sintering, thus enhancing the densification, especially at the lower binder contents. The tribological behaviour of TiC and Ti(C,N) cermets have been evaluated under reciprocating sliding conditions. The wear tests were conducted using a ball-on-flat sliding geometry, with a WC-Co sphere as the counter-face material, for loads from 20 to 60 N. The wear response was characterised using a combination of scanning electron microscopy, energy dispersive X-ray spectroscopy, and focused ion beam microscopy. Initially, two-body abrasive wear was observed to occur, which transitions to three-body abrasion through the generation of debris from the cermet and counter-face materials. Ultimately, this wear debris is incorporated into a thin tribolayer within the wear track, which indicates a further transition to an adhesive wear mechanism. It was found that Mo2C additions had a positive effect on both the hardness and indentation fracture resistance of the samples, but had a detrimental effect on the sliding wear response of the cermets. This behaviour was attributed to increased microstructural inhomogeneity with Mo2C additions.

博士
國立成功大學
材料科學及工程學系碩博士班
91
The use of hard ceramic coatings in industry is now well established, particularly in applications where wear resistance is an important consideration. TiN deposited either by CVD or low-temperature-plasma processes (PECVD or PVD) is commonly used as coating material. But in some cases, cracking and spalling of the TiN layer may accelerate the wear rate of tools under severe conditions. This could be due to an abrupt hardness difference existing between the TiN coating and the substrate. Besides, the adhesion of coating-substrate system is another important factor in tribological processes. In PECVD or PVD process, which works at lower substrate temperatures, little interaction takes place between the coating and the substrate, resulting in a poor adhesion. Therefore, researchers proposed the hybrid processes to overcome this problem. In other words, the hardness and/or adhesion of coating-substrate system can be enhanced by introducing an appropriate interlayer between them. 　　In this study, an attempt was made to further improve the mechanical properties of TiN/Ni-P hybrid coating by adding b-SiC particles into the Ni-P interlayer. A hybrid process that combines composite electroless plating and plasma-enhanced chemical vapor deposition was proposed to improve the mechanical properties of TiN coated tool steel. The hardness, adhesion, and sliding wear resistance of hybrid-coated SKD61 tools were investigated. 　　Experimental results show that SiC particles were successfully incorporated in the Ni-P alloy matrix by electroless composite plating method. The content of SiC in the composite coating increases with increasing SiC concentration in the plating bath, but decreases growth rate of the Ni-P-SiC composite coatings. The SiC particle addition did not change the structure of the Ni-P alloy matrix significantly when the annealing temperature was below 400oC. However, by raising the annealing temperature up to 450oC, the SiC particles decomposed and reacted with nickel to form g-Ni5Si2, b1-Ni3Si and graphite. The hardness and wear resistance of the composite coatings can be increased to a maximum at a temperature of 400oC, over which the coating experiences the formation of g-Ni5Si2, b1-Ni3Si and graphite and the mechanical strength is decreased. 　　The apparent hardness of the TiN/Ni-P-SiC hybrid coatings increases with increasing content of SiC particles in electroless Ni-P interlayer and affects the TiN hardness value. This could be due to an effect of SiC particles added on the coating growth of TiN and a high load carrying capability of Ni-P-SiC interlayer. In comparison with single TiN layer and TiN/Ni-P hybrid coating, a reduction in cracking and spalling for the TiN/Ni-P-SiC layer was observed during wear tests. Wear resistance is significantly improved due to the incorporation of SiC particles into electroless Ni-P interlayer, which increases hardness and adhesion of the coated TiN layer.

碩士
國立高雄應用科技大學
模具工程系碩士班
101
Die wear causes poor product quality, die life reduction and cost increase. It is a key factor influencing the forming processes. Therefore, understanding the characteristics of die wear can help die design and process planning, improve die life, and increase economical benefit. This study used a precision micro forging press to conduct micro combined forward and backward extrusion processes in order to investigate the characteristics of punch wear. The study considered two types of punch surfaces from different treatments. One was the high speed steel (SKH9) surface with polishing treatment. The other was the TiN coating surface of the punch with the same treatment as the previous one. The punches diameter were 0.9 mm in diameter and their shapes were spherical faces. The product rate were set as 50 pcs/min. In the experiments, the variations in surface texture, roughness and dimensions of the extruded products were carefully examined in both types of punch surfaces in order to understand the wear processes during the production runs. The observations of the wear were mainly divided into two stages. The first stage considered one examination per 100 pcs up to 1000 pcs. The rest runs up to 10000 pcs were examined every 1000 pcs. This study also used a finite element package DEFORM-2D and the Archard’s wear model to predict the punch wear. The predicted results were then used to identify severe wear locations which were selected for the observations. The experimental results show that the wear characteristic of the punch without coating is clearly different from the one with TiN coating, and the severe wear occurs in the first and second stages, respectively. Between the production runs from 6000 pcs to 8000 pcs, the surface texture of the punches have significant change. The wear on the TiN coated punch is mainly caused by fatigue wear. The wear on the punch without coating mostly results from abrasive wear. Moreover, the wear in both types of punches includes adhesive wear. After 6000 pcs, the thickness of the TiN coated layer on the punch gradually decreases and its surface texture becomes the same as the one of the punch without coating. The results show that the TiN coated layer clearly improves punch life.

碩士
崑山科技大學
機械工程研究所
96
Nowadays increase of the tools lifetime appears as an important objective and the conventional solutions, mainly based on TiN, become inadequate. In order to overcome and improve its mechanical and tribological performance, TiN/NbN multilayer coatings on die steel substrates have been explored of my study. The multilayer obtained are characterized in composition by means of X-ray diffraction (XRD) techniques, Microhardness and adhesion to the substrate were studied by atomic force microscopy (AFM) and scratch tests. The morphological analysis and coating structure are studied using scanning electron microscopy (SEM), and atomic force microscopy. The film thickness is measured by a stylus profiler (XP-2 stylus profiler). Wear tests were performed on Pin-on-disk configuration and dry sliding conditions, at 3N load by using hardened steel ball. The results of XRD pattern for different layers number. TiN/NbN multilayers caused the crystallization of the films, as represented by basically polycrystalline,TiN peak snch as (111),(200),(220), and NbN peak snch as(111),(200),(220),(311). TiN with highly (111) preferred orientation.On mechanical properties, Young，s modulus and hardness Values increase for different layers number.At 64 layers TiN/NbN multilayer films . 64 layers with the highest microhardness of 23.14Gpa. and Young，s modulus of 324Gpa.

碩士
國立中央大學
機械工程學系
104
Physical vapor deposition (PVD) super-hard in the industry for about 30 years of history of ceramic coated on the surface of the tool, the most representative of the titanium nitride coated as TiN, TiCN and TiAlN having a high hardness, low friction coefficient, corrosion resistance and other characteristics, it is widely used in the tool. In the present study, we used S50C, 420J2 two materials of commercially available cable tongs as a substrate, coated with TiN, TiCN, TiAlN, TiAlCrN / TiAlN bilayer, TiN / TiAlN / TiAlCN three-layer film coating was observed cross section morphology, elemental distribution, the surface properties of the surface roughness and friction coefficient, and a substrate measuring hardness, abrasion resistance, calculated sharpness index (BSI) to evaluate the coated substrate for different cutting ability. The results showed that the substrate hardness display S50C base temper softening phenomenon has to shadow tool durability. Sharpness aspect, BSI index after plating are better than the uncoated sample, wherein the sample S50C sample coated TiAlCrN / TiAlN bilayer membrane BSI index fell 27.93%, 420J2 is based on TiAlN coated samples decreased 30.71% best. Abrasion resistance portion TiN coating has the lowest coefficient of friction