Dissertations / Theses on the topic 'H13 tool steel'

Additive manufacturing brings versatility and new degree of freedom for part design and manufacturing possibilities. Binder jetting is powder bed printing technique that does not require direct energy transfer rather binding powder metal particles through mechanical entanglement by use of the organic binder. The polymer chains in the solution hardens when heated thus creating a green part. Green parts are sintered in high temperature to adhere metal powder particles together creating a solid body. Binder jetting still developing to its full potential in scalability and material portfolio. This thesis aims to contribute know how in process and material development of H13 tool steel in very fine particle size distributions from -16 µm to -10µm. Process parameters as well as sintering cycle developed specifically for H13 fine powders. With 52 samples printed, sintered in four different temperatures and analyzed material properties such as density and hardness to evaluate how particle size distributions affect printing process, densification and shrinkage in the sintering. Density of the green body has been evaluated through measurements of dimensions and weight, sintered density was analyzed by Archimedes method and light optical metallography. Trials for the processing and evaluation of the powders concluded that it is possible to use ultra-fine PSDs in binder jetting process with good results, this opens up opportunity for increased sustainability and profitability for powder manufacturing industry. Particle size distribution of -10 µm has outperformed the -16 µm in areas of relative density of the green body, sintered density and hardness. Although superior performance, the -10 µm requires higher ultrasonic intensity and lower spreading speed to achieve homogeneous powder bed. For the -16 µm powder it is worth noting that it is possible to bring up green density with further process development. Although materials presented high hardness in as printed state compared to that of PIM manufactured parts, achieved hardness is not satisfactory for the applications of the alloy and requires heat treatment corresponding to customer requirements.

High-accuracy miniaturized components are increasingly in demand for various industries such as aerospace, biomedical, electronics, environmental, communication and automotive, and this coupled with new developments of High Speed Machining (HSM) has led to the emergence of a strong and viable technology in High Speed Micro Machining. This technology is very important in bridging the macro-domain and the nano- and micro- domains for making functional miniaturized components. High speed Micro Machining is a specific technology where high spindle speeds, high performances cutting tools and high accuracy control systems are used. The understanding of this technology is still not well established and theories are still under development. A major implication of the High Speed Micro Machining process is the relatively high machining forces with respect to the cutting tool's size, which often cause low process reliability and high costs, due to frequent tool failures and short tool life. The aim of this investigation is to contribute towards a fundamental understanding of the effects of increased spindle speed in High Speed Micro Machining.

The use of High Speed Milling (HSM) for the production of moulds and dies is becoming more widespread. Critical aspects of the technology include cutting tools, machinability data, cutter path generation and technology. Much published information exists on cutting tools and related data (cutting speeds, feed rates, depths of cut, etc.), however, relatively little information has been published on the evaluation of cutter paths for this application. Most of the research work is mainly focused on cutter path generation techniques. Works with regard to cutter path evaluation on tool wear and tool life, surface integrity and relevant workpiece machinability characteristics are scant. Therefore, a detailed knowledge on the evaluation of cutter path strategies and orientations when high speed rough and finish milling is essential in order to improve productivity and surface quality respectively. The present work deals with some aspects related to the evaluation on the machinabiltiy of hardened AISI H13 hot work tool steel of 52 Rockwell Hardness C scale when high speed rough and finish milling using designated cutter path strategies and orientations. A literature review has been carried out to identify the various geometrical forms that are commonly utilised and common cutter path strategies presently employed in the mould and die industries. A review on the cutter path strategies and techniques is identified and classified according to the rough or finish milling stage. The selection and evaluation techniques notably feed rate, cutting tools and cutter path strategies and orientations are presented. Machinability criteria in terms of tool life and tool wear, cutting forces, tool wear and vibration signatures, cutting temperature and chip formation are reviewed. Last but not the least, surface integrity analysis on machined hardened steels are detailed and reviewed. The experimental work was divided into three phases. The first phase dealt with the investigation by employing high axial depths of cut (10 mm < Ai <20 mm) on three main cutter path strategies when rough milling hardened steels. In the second phase, the spotlight of the research was on finish milling an inclined workpiece surface using different cutter path orientations through machinability assessments in order to identify the optimum cutter path orientation. In the final phase, the effect of various cutter path orientations on workpiece surface integrity when finish milling hardened steels was investigated. The experimental results for Phase 1 revealed that in general where higher material removal rates, shorter machining time, longer tool life and higher volume of metal removed were of concern, raster cutter path strategy was the most favourable at all axial depths of cut employed. In Phase 2 when finish milling at an inclined workpiece angle of 75 0, tool life was highest when employing a downward cutter path orientation. On the other hand, upward cutter path orientation would be preferred where low workpiece surface roughness was concerned. In the final phase, surface integrity analysis revealed that upward cutter path orientation in particular the single direction raster vertical upward orientation was the most preferred in achieving optimum component life.

Orientador: Maria Clara Filippini Ierardi
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: A refusão superficial a laser é uma técnica muito promissora para a melhoria das propriedades mecânicas dos aços ferramentas através da homogeneização química e refino da estrutura. O tratamento a laser promove o aquecimento e resfriamento rápidos da camada superficial resultando em transformações microestruturais que promovem a melhoria do desempenho sem envolver o reprocessamento do material como um todo. Neste trabalho foram analisadas, além da microestrutura resultante do tratamento de refusão a laser, a resistência à corrosão e a resistência à flexão dos aços ferramenta para trabalho a quente AISI H13 e inoxidável martensítico AISI 420. Os resultados experimentais foram comparados com os mesmos aços sem tratamento. Observou-se que a microestrutura resultante do tratamento de refusão a laser é formada de martensita e austenita residual. A estrutura refinada e a presença de martensita resultaram em um aumento da dureza, apesar do grande volume de austenita residual. A dissolução de carbonetos e incorporação dos elementos de liga na matriz, como por exemplo o cromo, promoveu uma melhoria no comportamento em corrosão
Abstract: Laser surface melting is a very promising technique to improve the mechanical properties of tool steel by the chemical homogenization and refinement of the microstructure. Laser treatment promotes the rapid heating and cooling of the superficial layer resulting in microstructure transformations, which improve material performance without involving the reprocessing of the bulk material. In this work, besides the microstructure resulting from laser surface melting, corrosion resistance and deflection of hot-work tool steel AISI H13 and martensitic stainless steel AISI 420 were analyzed. The experimental results were compared to the same steels without treatment. The microstructure of the laser surface melting is formed by martensite and retained austenite. The refined structure and the presence of martensite increased hardness, despite the large volume of retained austenite. The carbides dissolution and incorporation of alloying elements into the matrix, for example chrome, improve the corrosion behavior
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

Tooling reliability is critical to welding success in friction stir welding, but tooling fatigue is not well understood because it occurs in conditions that are often unique to friction stir welding. A fatigue study was conducted on a commonly used tooling material, H13 tool steel, using constant stress loading at temperatures between 300°C and 600°C, and the results are presented. A model is proposed accounting for temperature and stress effects on fatigue life, utilizing a two-region Arrhenius temperature model. A transition in temperature effect on fatigue life is identified. Implications of the temperature effect for friction stir welding suggest that tooling fatigue life dramatically decreases above 500°C and accelerated testing should be conducted below 500°C.

Modern manufacturing processes are under a never ending evolvement. Lowered manufacturing costs, higher part quality, shorter lead times and lower environmental impact are some important drivers for this development. Aluminum die casting is an effective and attractive process when producing components for e.g. the automotive sector. Die casting process development, and hot work tool steel development for the die casting dies has led to the state of the art of die casting today. However, with the disruptive emergence of Additive Manufacturing (AM) of hot work steel alloys, new interesting features such as improved conformal cooling channels inside die casting molds can be produced. The new way to manufacture die casting dies, need basic investigating of the AM produced hot work tool steel properties, and their applicability in this demanding hot work segment. Die casting dies face several detrimental wear mechanisms during use in production, three of which has been isolated and used for testing three AM produced steel alloys and one conventional premium hot work tool steel. The wear mechanisms simulated are; thermal fatigue, static soldering and agitated soldering. The aim is to study the AM produced steels applicability in the die casting process. The tested materials are; Premium AISI H13 grade Uddeholm Orvar Supreme, AM 1.2709, AM UAB1 and AM H13. Based on current investigations the conclusion that can be made is that with right chemistry, and right AM processing, conventional material Uddeholm Orvar Supreme still is better than AM H13. This also complies with the literature study results, showing that conventional material still is better than AM material in general.
Våra moderna tillverkningsprocesser är under ständig utveckling. Drivande motiv är minskade tillverkningskostnader, högre tillverkningskvalitet, kortade ledtider samt minskad miljöpåfrestning. Pressgjutning av aluminium är en effektiv och attraktiv tillverkningsprocess ofta använd inom till exempel fordonsindustrin. Utvecklingen av pressgjutningsteknologin har gått hand i hand med utvecklingen av det varmarbets-verktygsstål som används i gjutformarna (pressgjutningsverktyget). Den utvecklingen har lett till dagens processnivå och branschstandard. Men med den revolutionerande additiva tillverkningsteknologins (AM) intåg, och möjlighet att producera komponenter av varmarbetsstål, kommer nya intressanta möjligheter att integrera komplex geometri så som yt-parallella kylkanaler i verktyget utan att tillverkningskostnaden blir för hög etc. Det nya sättet att producera pressgjutningsverktyg ger upphov till behovet av grundläggande materialundersökningar av sådant AM-material, samt hur tillförlitligt det är i pressgjutningsverktyg med pressgjutningens krävande materialegenskapsprofil. Pressgjutningsverktyg utsätts för många förslitningsmekanismer och för höga laster, tre av dessa mekanismer har isolerats för kontrollerade tester av ett konventionellt material och tre AM materials responser. Förslitningsmekanismerna som efterliknats är; termisk utmattning, statisk soldering och agiterad soldering. Målet med undersökningarna är att studera AM producerade materials lämplighet i pressgjutningsprocessen. De material som testats är konventionella premium varmarbetsstålet Uddeholm Orvar Supreme av typ AISI H13, AM 1.2709, AM UAB1 och AM H13. Undersökningarnas slutsats är att med rätt kemisk sammansättning, och med rätt AM printing parametrar, är konventionellt material fortfarande mer applicerbart i pressgjutning än AM producerat. Den slutsatsen faller väl I samklang med resultaten från mekanisk provning som återspeglas i litteraturstudien, som visade visar att konventionellt material är generellt bättre än AM material.

A falha devido à ocorrência de fadiga térmica de materiais utilizados como ferramentas para trabalho a quente é identificada durante serviço e ocorre devido ao acúmulo de dano localizado. O aço AISI H13 é comumente utilizado em ferramentas para a conformação a quente devido à sua boa tenacidade à fratura e resistência ao desgaste, e considerável resistência à perda de dureza a quente. Este trabalho teve como motivação estudar a relação entre a microestrutura do aço H13 e os carregamentos térmicos e mecânicos, que possam levar à falha de ferramentas para forjamento a quente. Para este estudo, fez-se uso de meios computacionais (simulação numérica) aliados aos conhecimentos de caracterização microestrutural e do comportamento mecânico dos materiais. Nesta abordagem, elabora-se uma malha na microestrutura do referido aço no software OOF2®, do NIST, e as análises são feitas a partir da aplicação do método dos elementos finitos com o emprego do software Abaqus®. Com isso, torna-se possível examinar o efeito de aspectos microestruturais, como a influência dos precipitados, na ocorrência de tensões e de deformações na microestrutura de forma a obter um mapeamento de regiões críticas ao dano e à falha na ferramenta de forjar a quente. Os estudos são baseados e comparados com trabalhos já publicados, e simulam carregamentos e variações de temperatura no material em questão de modo a verificar as condições que favorecem a nucleação de trincas por fadiga térmica. Como principais conclusões e contribuições obtidas da análise realizada, podem ser destacadas: (i-) as regiões críticas que vêm a propiciar a nucleação de trincas térmicas são os precipitados e as interfaces; (ii-) no campo de tensões, a propriedade das fases que exerce a maior influência é o módulo de elasticidade; (iii-) os diferentes coeficientes de expansão térmica das fases geram deformações térmicas mais elevadas e tensões compressivas nas interfaces; (iv-) as deformações térmicas nos precipitados são superiores às da matriz devido à influência no campo de tensões; (v-) em termos de tensões térmicas, o momento do ciclo térmico mais crítico para a matriz é o resfriamento; e (vi-) ao passo que, nos precipitados, a etapa mais crítica é o aquecimento.
Failure due to thermal fatigue can occur in hot working tool materials and its onset takes place in the regions where the highest stress and strain are reached. AISI H13 steel is often used as a hot working tool since it has good toughness and wear resistance, and also a sensible resistance to loss of hot hardness. This study was carried out by means of finite element method (FEM) combined with microstructural characterization and mechanical behavior of materials analysis. According to this approach, H13 steel microstructure, in which carbides could be observed, was meshed by means of OOF2® (NIST). Moreover, the ABAQUS® commercial FEM software was used to simulate thermal and mechanical loading applied in the tool throughout mechanical processing. The conducted analysis allowed to observe the effect of precipitates on stress-strain distribution at different temperatures and loads. Hence, critical regions, in which damage could be favored as well failure onset in the microstructure of the hot forging tool, are displayed. The investigation was based on and compared to literature results and it showed that it can be possible to design the microstructure of hot forging materials, in which an improvement in the thermal fatigue resistance could be improved. The main remarks and conclusions of this work are as follows: (i-) precipitates and interfaces are preferential regions to nucleation and growth of cracks, and they seem to work as stress concentrators; (ii-) modulus of elasticity of phases has the strongest influence in the stress fields of the microstructure; (iii-) the mismatch between thermal expansion coefficients of the phases leads to compressive stresses on interfaces and also the highest thermal strain; (iv-) thermal strains are higher on the precipitates than on the steel matrix; (v-) elastic-plastic properties of steel matrix influenced on thermal cycles. In addition, cooling is the most critical condition of thermal stresses by analyzing each thermal cycle in this phase; and (vi-) whereas the precipitates have elastic behavior, and the most critical step is the heating, in which the maximum temperature of the cycle is reached.

Orientador: Fernando Alvarez
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Este trabalho apresenta um estudo sobre os efeitos da incorporação de carbono e nitrogênio na formação de uma camada monofásica, compacta e homogênea, composta por carbonitretos do tipo e -Fe2-3(C,N), na superfície da liga metálica AISI H13. Também são apresentados estudos sobre os efeitos da incorporação desses elementos nas propriedades mecânicas, químicas e na microestrutura da superfície da liga metálica. A incorporação desses elementos na superfície do material foi feita utilizando-se o tratamento termoquímico de nitrocarburização por plasma pulsado em atmosferas contendo N2+ H2+ CH4 em diferentes proporções. Além da composição da atmosfera de tratamento, também foram variadas a temperatura e o tempo de tratamento. De maneira a complementar o estudo do comportamento da liga metálica frente ao tratamento termoquímico a plasma, também foram preparadas amostras com atmosferas oxidantes contendo CO2. A análise da composição química da superfície das amostras foi feita através de espectroscopia de fotoelétrons e mostra que a incorporação de nitrogênio sofre grande influência da quantidade de gás contendo carbono, presente no plasma. Porém a incorporação desses elementos não é diretamente proporcional à concentração do gás contendo esse elemento. Ao contrário do esperado, aumentando-se suficientemente a concentração desses elementos na atmosfera de tratamento, não acarreta em aumento na concentração dos mesmos no material. Por outro lado a análise através de difração de raios X revelou a formação de estruturas cristalinas consistentes com o diagrama de fases do sistema Fe-C-N. Para menores concentrações de compostos de carbono no plasma, a formação de nitretos e carbonitretos é predominante enquanto que maiores quantidades desse elemento levam ao surgimento da fase cementita e -Fe3 C, indesejável por possuir baixa resistência mecânica. As propriedades mecânicas da superfície foram estudadas através de medidas de nano e micro-dureza e seus resultados indicam que, como esperado, amostras com maior quantidade de nitrogênio incorporada possuim maior dureza da superfície. Esse comportamento é condizente com a microestrutura observada por microscopia eletrônica de varredura que mostra o entrelaçamento dos grãos da estrutura do aço e o preenchimento de seus contornos com carbonitretos de ferro que dificultam a movimentação dos planos cristalinos do cristal aumentando sua dureza. Foi verificado que as concentrações de carbono e de nitrogênio contido no material exercem grande influência sobre a reatividade da superfície das amostras frente a processos corrosivos em meios contendo íons cloreto. Esse comportamento foi verificado através de medidas de corrosão em solução aquosa de NaCl a 0,9 vol.%. Novamente os resultados apontam que maior concentração de nitrogênio é responsável por conferir a superfície maior proteção contra corrosão. Esses resultados são atribuídos a presença de uma mono-fase compacta formada pela fase e - Fe2-3 (C,N) na superfície das amostras. Resultados menos significativos foram obtidos quando a superfície continha uma mistura de fases contendo g -Fe4 N, e -Fe2-3 N, a -Fe e CrN
Abstract: This work presents a study on the effect of the incorporation of carbon and nitrogen on he formation of a singlephase homogeneous layer, composed by e -Fe2-3(C,N) carbonitrides, on the top surface of a AISI H13 tool steel. We also present studies on the effect of the incorporation of these elements (C and N) in the microstructure and in the mechanical and chemical properties of the surface of the metallic alloy. The incorporation of these elements in the surface of the material was made using the plasma nitrocarburizing termochemical treatment in atmospheres containing N2 + H2+CH4 in different ratios. Beyond the composition of the treatment atmosphere, the temperature and the time of treatment had been also varied. In way to complement the study of the behavior of the metallic alloy we had been also prepared samples with oxidating atmospheres containing CO2. The chemical composition analysis of the sample¿s surface was made through X-ray photo-electron spectroscopy and pointed that nitrogen incorporation suffers great influence from the amount of gas containing carbon, on the plasma atmosphere. However the incorporation of these elements is not directly proportional to the concentration of the gas containing this element. In con-trast, increasing enough the concentration of these elements in the treatment atmosphere, it does not cause increase in the concentration of the same element in the material¿s surface. On the other hand the X-ray diffraction analysis showed the formation of crystalline structures, consistent with the phase diagram of Fe-C-N system. For lesser carbon concentrations in the plasma, the formation of nitrides and carbides are predominant whereas bigger amounts of this element lead to the formarion of the cementite phase (q -Fe3 C , undesirable for possessing low resistance mechanics). The mechanical properties of the surface had been studied by means of nano and microhardness and its results indicate that, as expected, samples with bigger amount of incorporated nitrogen possesses bigger hardness in its surface. This behavior is in agreement with the observed microstructure observed by scanning electron microscopy that show the interlacement of the grains of the steel structure and the fulfilling of its boundaries with iron carbonitrides that make it difficult the movement of the crystalline plans of the lattice increasing its hardness. It was verified that the nitrogen and carbon concentrations in the material¿s surface, are of great influence on the reactivity of the surface regarding to corrosive processes in clorine solutions. This behavior was verified by measurements of corrosion in NaCl aqueous solution. Again the results pointed that bigger nitrogen concentration is responsible for protecting the surface against corrosion process. These results are attributed to the presence of a compact and homogeneous e -Fe2-3(C,N) surface layer on the surface of the samples. Less significant results had been gotten when the surface contained a mixture of phases containing g -F e4N, e -Fe2-3 N, a -Fe e CrN
Doutorado
Física da Matéria Condensada
Doutor em Ciências

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xxii, 185 p.; also includes graphics (some col.). Includes bibliographical references (p. 178-185).

Realizou-se neste trabalho uma investigação comparativa do comportamento dos aços ferramenta H13 e THYROTHERM 2999 EFS SUPRA, destinados à fabricação de matrizes para conformação a quente, quando submetidos à fadiga de baixo ciclo a altas temperaturas (FBCAT). A partir de suas curvas de revenimento, foram definidas três durezas de trabalho para cada material (durezas de 42, 52 e 58 HRC), correspondendo a três temperaturas de revenimento distintas e três condições de estudo, buscando-se a condição ótima apresentada por estes materiais para este tipo de aplicação, visando-se então analisar a influência da dureza inicial do material na vida do componente. Foi determinada também a temperatura de ensaio de fadiga isotérmica, em 400°C, correspondente à temperatura de utilização da matriz, ou seja, uma temperatura crítica típica que a matriz atinge durante a solicitação em trabalho. A seguir foram realizados para cada material os ensaios de tração a temperatura ambiente, e na seqüência, os ensaios de tração na temperatura de trabalho definida, que permitiram a determinação dos primeiros parâmetros monotônicos dos materiais, dentre eles uma previsão para os níveis de deformação a serem utilizados nos ensaios de fadiga (0.5,0.6,0.7,0.8,0.9,1.0 e 1.1%), e demais parâmetros como E, k, n, σe, σ’f, ε’f, b, c, que permitiram a elaboração de curvas ε−N, com um modelo estimativo já existente. Finalmente, foram então realizados os ensaios de fadiga isotérmica de baixo ciclo, à temperatura de 400°C, e os resultados foram utilizados para a elaboração das curvas ε−N, resultando então na proposta de um modelo de previsão de resistência à fadiga específico para os materiais pesquisados.
It was made in this work an investigative comparison of the behavior of the tool steels H13 and THYROTHERM 2999 EFS SUPRA, designed for die steels for hot forming, when exposed to high temperature low cycle fatigue (HTLCF). From their tempering curves three material working hardness were defined for each material (hardness of 42, 52 and 58 HRC), corresponding to three different tempering temperatures, and so three study cases for each material, searching for the best condition for this kind of application, and to assess the influence of the initial hardness on the part material life. The isothermal low cycle fatigue test temperature was either defined at 400°C, corresponding to the used temperature at the die steel, i.e., a critical typical temperature that the forging dies reach on hot working. After that, tensile tests were performed for both materials, at room temperature, and at the working temperature formerly defined, and these tests allowed the definition of the first monotonic parameters for these materials, among them predictions for strain levels (0.5, 0.6, 0.7, 0.8, 0.9, 1.0 and 1.1%), to be used on fatigue tests, and further parameters like E, k, n, σe, σ’f, ε’f, b, c, that allowed the elaboration of ε−N curves, based on a still existing prediction model. Finally, isothermal low cycle fatigue tests were performed, at 400°C, and the results were used for ε−N curves elaboration, resulting on a prediction model of the fatigue strength specified for the assessed materials.

The effect of process parameters on the creep-fatigue behavior of a hot-work tool steel for aluminum extrusion die was investigated through a technological test in which the specimen geometry resembled the mandrel of a hollow extrusion die. Tests were performed on a Gleeble thermomechanical simulator by heating the specimen using joule’s effect and by applying cyclic loading up to 6.30 h or till specimen failure. Displacements during the tests at 380, 490, 540 and 580°C and under the average stresses of 400, 600 and 800 MPa were determined. In the first set of test a dwell time of 3 min was introduced during each of the tests to understand the creep behavior. The results showed that the test could indeed physically simulate the cyclic loading on the hollow die during extrusion and reveal all the mechanisms of creep-fatigue interaction. In the second set a pure fatigue laod were induced and in the third set a static creep load were induced in the specimens. Furher type of tests, finite element and microstructural analysis were presented.

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.

碩士
國立中央大學
光機電工程研究所
105
Laser shock peening (LSP) is the use the high pressure, resulting from a momentum impulse generated by material vaporization at the target surface when rapidly heated by an ultrashort laser pulse, to impart long term, beneficial residual stresses in materials. To generate an instantaneously high pressure shock wave, the laser peak power should be very high, which is usually achieved by an ultrashort pulsed laser with pulse durations less than several nanoseconds. After the LSP processing, the surface is finer and roughness becomes smaller. The residual stress generated by LSP can reach 1 ~ 2 mm in depth that can effectively restrain the propagation of surface crack. In this study, the target is SKD 61 (AISI-H13) tool steel immersed in deionized water and the light source is from a pulsed Nd:YAG laser, with pulse duration of 5 ns and repetition rate of 10 HZ. The first part of this thesis discusses the improvements in the surface hardness and roughness of the target by LSP at various laser operation parameters. Surface hardness of the as-received SKD 61 was measured to be 200 HV. It can be apparently enhanced to 250 HV after the LSP processing using laser power of 200 mW and scan speed of 1 mm/s. It is noted, when the scan speed is 1 mm/s, as the laser power is enhanced from 200 to 450 mW, the hardness is enhanced monotonically with the laser power. It reaches a maximum of 300 HV at the power of 450 mW. But, there is no more recognizable increase if the power is larger than 450 mW, and this trend remains even the power is up to 700 mW. LSP treatment can also significantly reduce the surface roughness, the average roughness (Ra) showed an average decrease of 25% and the maximum roughness (Rmax) decreased by an average of 47%. The hardening mechanism of LSP is the impulse pressure from shock waves, generated by laser induced plasma. Thus, the magnitude of shock wave pressure is the key to the result of the surface modification. Therefore, the second part of this study aims to obtain the plasma pressure in the LSP process. This is accomplished by directly measuring the shock speeds based on the photo-acoustic effect, then convert them to the corresponding plasma pressures. Therefore, we can correlate the LSP treatment effect with the shock wave pressure. The results show that the speed of the shock wave is 3.99 km /s at a laser power of 450 mW, and the corresponding plasma pressure is 0.484 GPa.

碩士
國立臺北科技大學
材料科學與工程研究所
97
In order to effectively improve the aluminum melting loss of mold, this study uses the ways of different surface treatments to improve the aluminum thermal loss of the mold and increase the tool life. We Compare the moldings without treatment, with oxidizing treatment, nitriding treatment, and oxynitriding treatment. The experimental results show that the nitrided layer effectively delays the time of melt loss and is indeed able to protect AISI H13 steel. Due to the increased thickness of oxided layer, that result in the melting loss rate was 0% for oxynitriding at 580℃ for 3 hours, 600℃ for 2 hours and 600℃ for 3 hours after 4-hour aluminum melting test. The experimental results also show that the oxidized layer can enhance the surface corrosion resistance of tool steel. The passivation layer was rapidly formed on the surface of steel. Therefore, it exhibits the best corrosion resistance capability. In summary, oxynitride treatment has the best anti-aluminum melting and corrosion resistance capability, followed by oxidizing and nitriding treatments, and non-treatment sample shows the worst results.

碩士
國立臺北科技大學
材料科學與工程研究所
98
The experiment is used of different surface treatments and combinations, then to evaluate and improve the tool life of die casting materials. This research compares of erosion and wear resisatnce of A380 alloy via different surface treatment of untreated, oxynitriding, CrN coating, and CrN coated with oxynitriding specimens. The minimun melt loss was appeared in multiple surface treatments of CrN coated with oxynitriding after 3 hours eoosion test. It showed that only has 0.8% of weight lost, however the untreated specimen was 3.2%. The experimental results was obviously improved 75% of the weight loss, meanwhile the other surface treatment also has a lower erosion rate of A380 aluminum alloy. Increasing of the soaking time of melting aluminum alloy, the thinkness of Fe-Al-Si compounds was increased after erosion tests. The optical microstructure showed that the erosion mechanism of CrN coating specimens by A380 alloy which was beginning damage from the point of surface after 3 hours test. When the aluminium alloy is beggining to diffusion with iron elements, it will result in the Fe-Al-Si compound layer, which was quickly eroded by melting aluminum solution. All theses specimens of different surface treatment were showed the better wear- resistances after wear tests. Furhtermore the untreated specimen shows a very obviously trace of wear appear. However, there was very shallow of wear traces specimens of oxynitriding, CrN coating, and CrN coated with oxynitriding treatment. It shows the wear properties of AISI H13 tool steel can be enhanced by different surface treatment. In attition, the lowest frictional coefficient of H13 specimen was appeared in multiple surface treatments of CrN coated with oxynitriding. The average value of frictional coefficient is about 0.28.

碩士
國立臺北科技大學
材料科學與工程研究所
99
AISI H13 tool steels are almost exclusively used on extrusion and die-casting dies. They are characterized by high strength, ductility, good tempering resistance, and moderate cost. Thermal fatigue and erosion are the most important factors limiting tool life and resulting in the tool failure of hot work tool steels. A surface treatment is usually used to increase wear resistance as well as to improve corrosion resistance. The oxynitriding process uses air or steam at the end of the nitriding stage; used as an oxidizing medium, it is an integral part of the treatment. In addition, the TiAlN coating has high strength and thermally stable properties resulting from the cathodic arc PVD treatment; therefore, the oxynitriding/TiAlN duplex is used to treat AISI H13 tool steel in an attempt to increase tool life. In this study, the specimens were subjected to various surface treatments including oxynitriding, TiAlN coating, and oxynitriding/TiAlN duplex treatments. In order to investigate the molten loss for melting A390 aluminum alloy, wear resistance and corrosion resistance for different surface treatments were examined. XRD, SEM and OM microstructural inspections, erosion, wear and corrosion tests were performed. The experimental results indicated that a 0.03-0.04 mm oxynitride layer and a 3-4μm TiAlN thin film could be obtained after the oxynitride/TiAlN complex treatment. This duplex treatment had the highest surface hardness (Hv0.01 3463); thus, the wear behavior results showed both higher hardness and a lower wear volume (0.05 mm3). Moreover, the higher hardness and high thermally stable properties of the oxynitride/TiAlN duplex layer were found to have the most effective erosion resistance. The corrosion test results also showed the duplex layer to have the optimum corrosion currents of 9.64 × 10-5 and 4.42 × 10-6 A in 0.15 M HCl and 3.5 wt% NaCl solutions, respectively, signifying that the complex treatment resulted in the best corrosion resistance.

碩士
國立臺北科技大學
材料及資源工程系研究所
100
A surface treatment is usually used to improve tool life. DLC has many superior properties, such as high mechanical hardness, high wear resistance, a low friction coefficient and chemical inertness. The oxynitriding process uses air or steam at the end of the nitriding stage as an oxidizing medium, which is an integral part of the treatment. During the oxidation process, most steels can form several kinds of oxides (Fe2O3 and Fe3O4). Generally, the Fe3O4 layer of the oxidation treatment can effectively protect and improve the erosion and corrosion resistance of steels. Therefore, the oxynitriding/DLC duplex treatment was utilized for treating AISI H13 tool steel in an attempt to increase tool life. In this study, the diamond-like carbon films were prepared by DC-pulsed plasma CVD after the oxynitride treatment of AISI H13 tool steel. In order to investigate the DLC films properties, Raman spectroscopy analysis, wear test, adhesion and hardness tests were performed. The study of the parameters of DC-pulsed plasma CVD process included the pulsed voltage, pre-treatment of argon gas and the substrate temperature. The experimental results showed that a 0.05-0.06 mm oxynitride layer and 1-2 μm of DLC thin film could be obtained after the oxynitride/DLC duplex treatment. The duplex coating layers had the optimal properties when treated by a low pulse voltage (-1.5 kV), pre-treatment of argon gas for 15 min and the substrate kept at a 50°C condition. Meanwhile, the oxynitride/DLC duplex treatments possessed the highest surface hardness (Hv0.01 1457), lowest wear volume (2.25 × 10-3 mm3) and lower friction coefficient (0.06).

Dissertação de Mestrado em Engenharia de Materiais apresentada à Faculdade de Ciências e Tecnologia
A necessidade de implementação de medidas mais amigas do ambiente é essencial em processos industriais do séc. XXI. O aproveitamento dos resíduos de eléctrodos de grafite dos processos de electroerosão da industria de moldes foi um tema abordado neste trabalho. A utilização de grafite e de um dos seus produtos da exfoliação, o grafeno, em processos de fabrico aditivo, nomeadamente fusão selectiva por laser, foi o foco principal abordado. Aliar o reaproveitamento da grafite no processo de fusão selectiva por laser pode constituir uma nova oportunidade de negócio. Numa primeira instância grafite moída revestida com cobre por pulverização catódica, foi misturada com pó de aço ferramenta H13 para a produção de pastilhas em SLM. Os parâmetros utilizados foram optimizados em trabalhos anteriores para a produção de componentes deste tipo de aço. A segunda parte prendeu-se com a utilização de grafeno juntamente com pó de aço austenítico 316L, em que foi produzido um grupo de testes para optimização de parâmetros e, escolhidos os melhores valores, foram produzidas duas pastilhas. Por fim procedeu-se à caracterização das pastilhas com o intuito de perceber a presença de grafite revestida e grafeno e também análises de conductividade térmica para descortinar as propriedades térmicas das mesmas.
The need to implement environmentally friendly measures is essential in the industrial processes of the 20th century. The use of the graphite electrode residues from the EDM processes of the mold industry was an issue addressed in this work. The use of graphite and one of its exfoliation products, graphene, in additive manufacturing processes, namely Selective laser melting , was the main focus. Aligning the reuse of graphite in the process of Selective laser melting can be a new business opportunity. In a first instance ground graphite coated with copper by cathodic sputtering, it was mixed with H13 tool steel powder for the production of SLM parts. The parameters used were optimized in previous works for the production of components of this type of steel. The second part was with graphene mixed with austenitic steel powder 316L, in which a test group was produced for optimization of parameters and, with the best values chosen, two pellets were produced. Finally, we proceeded to the characterization of the pellets i n order to perceive the presence of coated graphite and graphene and also analysis of thermal conductivity to uncover the thermal properties of the same.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
O objectivo deste trabalho é estudar a viabilidade de uma ligação entre um material metálico e um cerâmico através da produção por Fusão Selectiva a Laser (SLM). Com o aumento constante das exigências industrias na produção de componentes de alta-performance, é, por muitas vezes, necessário recorrer ao desenvolvimento de componentes multimaterial para combinar as melhores propriedades que dois ou mais tipos diferentes de materiais podem oferecer. Graças a este novo processo de pulverometalurgia de produção 3-D é possível produzir rapidamente componentes de elevada complexidade e precisão fazendo incidir um laser de alta potência. Com recurso ao processo de Pulverização Catódica, é, ainda, possível formar um filme fino de revestimento sobre partículas de pó, com a finalidade de alterar as propriedades dos pós que são utilizados no processo de SLM. Foram realizados três estudos diferentes: no primeiro foi revestido pó de aço ferramenta H13 com o mesmo material de que é feito e foram produzidas amostras por SLM sobre o objectivo de estudar a influência do revestimento no processo; no segundo estudo foi revestido pó de carboneto de tungsténio (WC) com aço 316L com a finalidade de serem produzidas amostras sobre uma base em aço H13 e estudar a ligação que é criada entre os dois materiais; e finalmente, no terceiro estudo inverteu-se o processo, e foram utilizados os pós revestidos de aço H13, do primeiro estudo, para produzir amostras sobre uma base em WC-Co e comparar a ligação que foi criada. As análises feitas aos pós revestidos revelaram que a Pulverização Catódica é um processo eficaz para melhorar a escoabilidade e a reflectividade de pós e que permite a formação dum ligante metálico para os pós cerâmicos. As amostras que foram produzidas, demonstram que ainda há limitações no processo de SLM na produção de componentes cerâmicos, mas que é possível estabelecer uma ligação com um material metálico e que o uso da Pulverização Catódica contribui de forma positiva para o processo.
The main objective of this work is to study the viability of Selective Laser Melting (SLM) as a process for joining metallic and ceramic materials. With the increasing rate of industrial demand in the production of high-performance components, it is necessary to develop multimaterial components in order to combine the best properties that each material can offer. Thanks to this new powder metalurgy 3-D process, it is possible to quickly produce components with high precision and complexity, by using a high intensity laser. With the help of the Sputtering process, it is, also, possible to develop a thin film coating on the powder particles in order to change their properties when used in the SLM process.Three studies were carried out: in the first one, tool steel H13 powder was coated with the same material that is made and were produced samples in SLM in order to study the influence of the coating in the process; in the second study, tungsten carbide (WC) powders were coated with 316L steel and samples were produced over a H13 plate in order to study the typ of joining that is created; finally, in the third study, the process was inverted, and H13 steel powders from the first study were used to produce samples over a WC-Co plate and the results compared. The analysis that were carried out with coated powders revealed that the Sputtering process is effective in increasing the flowability and reflectivity of powders and that it is possible the formation of a steel binder in the ceramic powder. The samples that were produced prove that there are still limitation in the processing of ceramic components with SLM, however it is possible to establish a join with a metallic component and that the use of the Sputtering technique helps in the joining process.