Dissertations / Theses on the topic 'Laser Alloying'

A comprehensive, transient three-dimensional model of a single-pass laser surface alloying process has been developed and used to examine the heat, momentum and species transport phenomena. A numerical study is performed in a co-ordinate system moving with the laser at a constant scanning speed. In this model a fixed grid enthalpy-porosity approach is used, which predicts the evolutionary pool development. In this model two extreme cases of alloying element and base metal combinations are considered based on their relative melting points. One extreme case is for an alloying element with its melting point much lower than that of the base metal. In this case the alloying element melts almost instantaneously. Hence it is assumed that the alloying element introduced on the melt pool surface is in the molten state. Thus, while solving the species conservation equation a species flux condition is used on the entire melt pool surface. This case is analysed for aluminium alloying element on iron base metal. The final species distribution in the melt pool as well as in the solidified alloy is predicted. The other extreme case is studied for an alloying element with its melting point relatively higher than that of the base metal. In this case all the alloying element particles on the melt pool surface will not melt. Only those particles which fall in the region on the melt pool surface where the local temperature is higher than the melting point of the alloying element will melt. The particles which fall away from this region are advected into the melt pool, due to a strong Marangoni convection on the melt pool surface. If a particle is advected into the inner region in the melt pool (where the temperature is higher than its melting point), it starts melting and thus the molten species mass gets distributed. Hence, the species flux condition at the entire surface of the melt pool is not valid. The particles are tracked in the melt pool by assuming the alloying particles to be spherical in shape and moving without any relative velocity with the surrounding fluid. Simultaneously, the temperature field inside the spherical particle is solved by assuming its surface temperature to be the local temperature in the melt pool. The amount of particle mass that fuses as it passes through a particular control volume is noted. The same procedure is repeated for a large number of particles initiated at various locations on the pool surface, and a statistical distribution of the species mass source in the entire pool is obtained. This species mass source distribution is then used to solve the species conservation equation. Nickel alloying element on aluminium base metal is used to illustrate this case. The numerical results obtained from the two cases are compared with the available experimental results. A qualitative matching is found between the numerical and experimental results.

A comprehensive, transient three-dimensional model of a single-pass laser surface alloying process has been developed and used to examine the heat, momentum and species transport phenomena. A numerical study is performed in a co-ordinate system moving with the laser at a constant scanning speed. In this model a fixed grid enthalpy-porosity approach is used, which predicts the evolutionary pool development. In this model two extreme cases of alloying element and base metal combinations are considered based on their relative melting points. One extreme case is for an alloying element with its melting point much lower than that of the base metal. In this case the alloying element melts almost instantaneously. Hence it is assumed that the alloying element introduced on the melt pool surface is in the molten state. Thus, while solving the species conservation equation a species flux condition is used on the entire melt pool surface. This case is analysed for aluminium alloying element on iron base metal. The final species distribution in the melt pool as well as in the solidified alloy is predicted. The other extreme case is studied for an alloying element with its melting point relatively higher than that of the base metal. In this case all the alloying element particles on the melt pool surface will not melt. Only those particles which fall in the region on the melt pool surface where the local temperature is higher than the melting point of the alloying element will melt. The particles which fall away from this region are advected into the melt pool, due to a strong Marangoni convection on the melt pool surface. If a particle is advected into the inner region in the melt pool (where the temperature is higher than its melting point), it starts melting and thus the molten species mass gets distributed. Hence, the species flux condition at the entire surface of the melt pool is not valid. The particles are tracked in the melt pool by assuming the alloying particles to be spherical in shape and moving without any relative velocity with the surrounding fluid. Simultaneously, the temperature field inside the spherical particle is solved by assuming its surface temperature to be the local temperature in the melt pool. The amount of particle mass that fuses as it passes through a particular control volume is noted. The same procedure is repeated for a large number of particles initiated at various locations on the pool surface, and a statistical distribution of the species mass source in the entire pool is obtained. This species mass source distribution is then used to solve the species conservation equation. Nickel alloying element on aluminium base metal is used to illustrate this case. The numerical results obtained from the two cases are compared with the available experimental results. A qualitative matching is found between the numerical and experimental results.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2015
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Laser surface alloying (LSA) é uma poderosa técnica de modificação de camada limite de um componente, cada vez mais reconhecida, usada para aumentar a resistência ao desgaste e à corrosão em componentes de engenharia. Neste trabalho, a região próxima a superfície de uma ferramenta de estampagem automotiva (aço ASTM A681), foi tratada com um laser de fibra Nd: YAG contínuo de comprimento de onda de 1064 nm e com pó de adição WC-Cr-Co, na proporção de 86%, 6% e 8%. Este processo consiste basicamente em fundir uma camada próxima a superfície de um substrato, adicionando simultaneamente partículas de um material de adição na forma de um pó pré ligado, modificando a composição química e microestrutura, assim como tamanho de grão de forma localizada da ferramenta, alterando sua dureza e resistência ao desgaste. Para analisar a resistência ao desgaste para este processo, foram feitas mil estampagens em uma ferramenta tratada por LSA e em outra não tratada e seus resultados comparados entre si. A finalidade do processo LSA é a de aumentar o tempo de vida de uma ferramenta em uma aplicação industrial. As análises da ferramenta tratada apresentaram um resultado significativo quando comparada com uma ferramenta sem o tratamento. Obteve-se uma redução cerca de nove vezes na rugosidade superficial e uma maior resistência ao desgaste. Neste trabalho também foi analisada a influência do aumento da potência do laser no processo de laser surface alloying. Para isto cinco diferentes amostras foram tratadas e analisadas quanto a microdureza, composição química, identificação de fases e ensaios de resistência ao desgaste. Os resultados obtidos neste trabalho foram importantes para concluir que este é um processo muito complexo e deve ser rigorosamente controlado, pois diversos fatores alteraram a estrutura e resistência ao desgaste da camada próxima à superfície tratada.

Abstract : Laser Surface Alloying (LSA) is a powerful boundary limit of a component modification technique, increasingly recognized, used to increase the wear and the corrosion of engineering components resistance. In this thesis a near surface region of an automotive deep drawing tool (steel ASTM A681) was treated with a continuous fiber laser Nd: YAG with wavelength of 1064 nm and with WC-Cr-Co particles in ratio of 86%, 6% and 8%. This process consists basically in melting a substrate's layer near of surface adding simultaneously particles of a filler material in a pre-connected powder shape, altering the microstructure, as well as the grain size in localized form of the tool, altering the hardness and wear resistance. To perform a comparative analysis of this process one thousand deep drawings were made in a tool treated by LSA and in an untreated tool. The behavior's characteristics of these tools have been analyzed and their results compared with each other. The purpose of LSA process is to increase the lifetime of a tool in the industrial application. What could be observed after the analysis was the success of this process, because all the characteristics results showed significant improvement when compared with the untreated tool. As example cite a decrease of about nine times the roughness and significantly reducing of the treated tool wear. In this work the influence of the increase in laser power in the laser surface alloying process was analyzed. Five different samples were treated and analyzed, their hardness, chemical composition, phase identification and wear resistance were investigated. The results obtained of this work were important to conclude that LSA is a very complex process and must be strictly controlled, as there are several factors that can change the structure and wear resistance of the surface treated.

Aluminum (Al) and its alloys are widely used in various technological applications, mainly due to the excellent thermal conductivity, non-magnetic, ecofriendly, easy formability and good recyclability. However due to the inferior corrosion resistance its applications are hampered in various engineering sectors. Besides, the corrosion related failures such as leakage of gas from pipeline, catastrophic breakdown of bridges and fire accidents in processing plants further puts the human life in jeopardy. Within the United States over $ 400 billion dollars per year are spent over research to understand and prevent the corrosion related failures. Recently, the development of transition metal(TM) aluminides (AlxTMy, where, TM = Mo, W, Ta, Nb, Cr, Zr and V) has received the global attention mainly due to high strength at elevated temperatures, light-weight, excellent corrosion and wear resistance. In light of this, surface modification via laser surface alloying (LSA) is a promising engineering approach to mitigate the corrosion and wear problems. In the present study the attempts are made to study the Al-Mo, Al-W, Al-Nb, and Al-Ta systems as a potential corrosion resistant coatings on aluminum. The refractory metal (Mo, W, Nb, Ta) precursor deposit was spray coated separately on aluminum substrate and was subsequently surface alloyed using a continuous wave diode-pumped ytterbium laser at varying laser energy densities. Microstructural analysis was conducted using scanning electron microscopy and further X-ray diffractometry was carried out to evaluate the various phases evolved during laser surface alloying. Corrosion resistance of laser alloyed coatings were evaluated using open circuit potential, cyclic potentiodynamic polarization, electrochemical impedance spectroscopy measurements were performed in 0.6 M NaCl solution (pH:6.9±0.2, 23˚C). Open circuit potential measurements indicate the more stable (steady state) potential values over long periods after laser surface alloying. Cyclic polarization results indicated reduction in the corrosion current density, enhancement in the polarization resistance, and increase in coating/protective efficiency with increase in laser energy density compared to untreated aluminum. Electrochemical impedance spectroscopy measurements also indicated an increase in charge transfer resistance after laser surface alloying of refractory metals on aluminum. Additionally, first principle calculations of thermodynamic, electronic and elastic properties of intermetallics evolved during LSA were also thoroughly investigated to correlate the corrosion performance of intermetallic coatings with these properties. The present study indicates that novel Al-Mo, Al-W, Al-Nb, and Al-Ta intermetallics has a great potential for light weight structural applications with enhanced corrosion resistance.

The feasibility of in-situ alloying of AISI 410L martensitic stainless steel with nitrogen during Nd-YAG laser cladding was investigated with the aim of achieving a nitrogen content of at least 0.08 wt% and fully martensitic microstructures in the final clad deposit. Two in-situ nitrogen alloying techniques were studied. In the first set of experiments, the absorption of nitrogen from nitrogen-rich gas atmospheres was studied. Laser cladding with commercially available AISI 410L powder was performed using nitrogen-rich shielding and carrier gas. A marginal increase in deposit nitrogen content was observed, with the clad deposit displaying low hardness and mostly ferritic microstructures. Poor nitrogen absorption from nitrogen-containing atmospheres during Nd-YAG laser cladding is generally attributed to the short thermal cycle and to suppression of plasma formation above the weld pool. In the remaining experiments, Si3N4 powder was investigated as an alternative source for nitrogen during cladding. The addition of Si3N4 to the AISI 410L powder feed resulted in clad microstructures consisted of columnar -ferrite grains with martensite on the grain boundaries, higher hardness and an increase in deposit nitrogen content (to a maximum of 0.064 wt% nitrogen). Higher nitrogen contents in the clad deposit, however, significantly increased the volume percentage porosity in the clad layer. This prompted an investigation into the feasibility of raising the nitrogen solubility of the alloy through additions of manganese and nickel to the powder feed. Thermodynamic modelling revealed that the addition of manganese to AISI 410L powder increases the nitrogen solubility limit due to its negative interaction parameter with nitrogen. The addition of up to 3.5 wt% manganese to AISI 410L powder containing Si3N4 significantly increased the nitrogen solubility in the deposit. A martensitic microstructure with 0.12 wt% nitrogen and a peak hardness of 410 HV was achieved without any adverse increase in porosity in the clad layer. The clad nitrogen content easily exceeded the minimum requirement of 0.08 wt%. High nickel concentrations in AISI 410L stainless steel expand the austenite phase field at the expense of -ferrite and alter the solidification mode from ferritic to austenitic-ferritic. The addition of up to 5.5 wt% nickel, or combinations of nickel and manganese, to the nitrogen-alloyed AISI 410L powder feed raised the deposit nitrogen content, but not to the same extent as those deposits alloyed with manganese only. Since more austenite is present on cooling in nickel-alloyed AISI 410L deposits, less nitrogen is rejected to the liquid phase on solidification, resulting in higher nitrogen contents and less porosity in the room temperature microstructures. The amount of dilution during single-track laser cladding is mainly influenced by the specific energy per unit mass delivered by the laser beam. The clad height is strongly influenced by the powder deposition rate, whereas the bead width is influenced by the wettability of the deposits during laser cladding. During multi-track cladding, the observed percentage porosity is a function of the aspect ratio of the individual beads making up the clad layer, the deposition rate and the clad height. High deposition rates result in thicker layers, increasing the distance that N2 gas bubbles have to travel to escape to the atmosphere, while a high aspect ratio favours interbead porosity. The results suggest that in-situ nitrogen alloying during laser cladding should preferably be performed at low deposition rates to ensure higher clad nitrogen contents and hardness, lower clad heights, less dilution and less porosity.
Dissertation (MEng)--University of Pretoria, 2016.
Materials Science and Metallurgical Engineering
MEng
Unrestricted

The laser technology of the fusion of the working surface of details changes the surface properties, decreasing the microroughness of the processing surface, increasing wear resistance and microhardness. This work is intended for analyzing the differences in technological processes of fusion, alloying and the synthesis of material. Synthesis of material, fusion, and introduction into the matrix they were carried out using different compositions of powders under the action of laser emission. Investigated the minimum power density of laser emission for the melting of the covering is established its dependence on the chemical composition of coating and base of material. Evaluated the dependence of the temperature distribution in basis and coverage of layer on the thermal parameters of the basis of material and power of laser radiation.

Orientador: João Batista Fogagnolo
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Titânio e suas ligas são amplamente utilizados como biomateriais devido a propriedades como alta resistência específica, alta resistência à corrosão e baixo módulo de elasticidade. As ligas de titânio apresentam diferentes estruturas cristalinas, as quais possuem diferentes módulos de elasticidade. Esta característica permite que o módulo de elasticidade seja manipulado através do controle da composição química da peça, o que por sua vez possibilita a fabricação de peças com gradientes de rigidez, abrindo-se um amplo campo de pesquisa e novas aplicações. Este trabalho utiliza a técnica de modificação superficial por laser e adição de nióbio com o objetivo de obter peças de titânio com revestimentos constituídos por fases com menores módulos de elasticidade, ou seja, peças com revestimentos menos rígidos que o substrato. Inicialmente foram caracterizados cordões isolados obtidos com diferentes densidades de energia do feixe de laser, através da variação da potência, do diâmetro e da velocidade de varredura do feixe de laser. Nos cordões isolados, observou-se que a potência do feixe de laser é o parâmetro de maior influência e que densidades de energia intermediárias possibilitaram obter cordões com zonas fundidas com dimensões e formato adequados para a posterior etapa de obtenção de recobrimento contínuo por sobreposição de cordões. As composições dos cordões isolados, apesar de apresentar heterogeneidade, permitiram a estabilização da fase ?. No entanto, uma fração significativa dos cordões apresentou também a fase ? com microestrutura dendrítica, indicando que essa fase foi resultado da solidificação, o que pode ter ocorrido pela contaminação por oxigênio, que é um forte estabilizador dessa fase. Dessa forma, mesmo com a formação da fase ?, não se observou uma redução do módulo de elasticidade. Em todos os casos, a dureza apresentou um significativo aumento, também devido a forte contaminação por oxigênio. A formação de revestimentos contínuos foi obtida através da sobreposição de 50% da largura dos cordões. Os revestimentos contínuos assim obtidos apresentaram segregação de soluto, com fase ? estabilizada nas regiões com maiores teores de nióbio e agulhas de martensita nas regiões com menores teores de nióbio. A contaminação por oxigênio foi reduzida em comparação com os cordões isolados. Os revestimentos contínuos apresentaram aumento de dureza e diminuição do módulo de elasticidade, conforme o objetivo proposto
Abstract: Titanium and its alloys are commonly used as biomaterials due to their properties as high specific strength, high corrosion resistance and low elastic modulus. Titanium alloys show differents crystalline structures, which have different elastic modulus. This characteristic allows the manipulation of the elastic modulus through chemical composition control, which allows the manufacture of pieces with stiffness gradients, spreading a large research field and new applications. This work use the laser surface alloying technique with addition of niobium powder to obtain titanium pieces with coatings composed by phases with lower elastic modulus, in other words, pieces with coatings less stiff than the substrate. Firstly, isolated tracks obtained by different beam laser energy densities, by varying laser beam power, diameter and scan speed were characterized. In this case, the laser beam power was the most important parameter and the intermediaries energy densities allowed to obtain tracks with melted zones with dimensions and shape suitable to obtain a continuous coating by overlapping tracks. The isolated tracks compositions, despite their chemical heterogeneities, showed the stabilization of the ? phase. However, a significant fraction of tracks showed also ? phase with dendritic microstructure, indicating that this phase was the result of solidification, which may have occurred due oxygen contamination, which is a strong ? stabilizer element. Thus, despite the stabilization of the ? phase, a reduction in elastic modulus was not observed. In all the cases the hardness showed a significant increase, also because of the high contamination by oxygen. The continuous coating formation was obtained by overlapping 50% of the tracks width. The continuous coatings obtained showed solution segregation, with ? phase stabilized in the regions with higher niobium content and needle like traces of martensite in the regions with less niobium content. The oxygen contamination was reduced in comparison with isolated tracks. The continuous coatings showed high hardness with a decrease of the elastic modulus, in accordance with the proposed objective
Mestrado
Materiais e Processos de Fabricação
Mestra em Engenharia Mecânica

Die Arbeit beschäftigt sich im ersten Teil mit der Untersuchung des Einflusses der Prozessgrößen auf die Zielgrößen, Randschichthärtetiefe und die Oberflächenhärte beim Laserhärten. In einem weiteren Kapitel werden die Ergebnisse von verschiedenen Möglichkeiten der laserbasierten Härteverfahren zur Steigerung der Prozessgrenzen dargestellt. Eine Möglichkeit ist das Laserlegieren von kohlenstoffhaltigen Zusatzwerkstoffen, wie zum Beispiel mit Eisencarbid, Eisenchromcarbid oder Glaskohlenstoff. Dazu sind die Einflussgrößen auf die Einhärtetiefe sowie die Schmelzbaddynamik der jeweiligen Werkstoffe analysiert worden. Auf der Basis der neu erworbenen Kenntnisse ist ein Model zur Schichtdickenberechnung und eine numerische Simulation des Laserlegierprozesses entwickelt worden. Eine andere Möglichkeit die Prozessgrenzen zu erweitern ist, in der Arbeit durch das Laserauftragschweißen beschrieben worden. Dabei sind unterschiedliche Düsen und Beschichtungsstrategien zum Einsatz gekommen. Die letzte in der Arbeit beschriebene Methode zur Steigerung der Prozessgrenzen ist das Gaslegieren. Dabei sind Versuche zum Laserhärten unter Stickstoffatmosphäre sowie zum Lasercarbonitrieren als auch Lasercarburieren gemacht worden. Im letzten Kapitel werden konkrete Anwendungsgebiete zum Laserhärten von Powertrain-Komponenten vorgestellt. Dabei werden unterschiedliche Lösungsansätze zum Laserhärten von Bohrlöchern in Flanschwellen und zum Laserhärten der Hohlkehlen von Kurbelwellen aufgezeigt.

Des alliages de surface renforces par des carbures mixtes fer-chrome m#7c#3 (m = fe, cr) d'une part, et par du carbure de titane d'autre part, ont ete elabores par irradiation laser sur l'acier inoxydable austenitique aisi 316l (z2 cnd 17-12) afin d'ameliorer sa resistance a l'usure. L'utilisation de differents precurseurs (graphite, carbure de silicium, carbure cr#3c#2 seul ou associe a du chrome, tic submicronique et micronique, melange de poudres de titane et de carbure sic) a permis d'obtenir des revetements presentant une large variete de microstructures et de compositions. Les microduretes correspondantes, comprises entre 350 hv et 900 hv temoignent d'un durcissement significatif de l'acier 316l (200 hv). La confrontation des phases presentes dans les differents alliages de surface avec celles des diagrammes d'equilibre des systemes correspondants a mis en evidence le caractere metastable des carbures m#7c#3 et la bonne stabilite thermique des carbures de titane. La resistance a l'oxydation a haute temperature des divers alliages de surface a ete caracterisee par thermogravimetrie. Les resultats obtenus ont montre le role essentiel des elements chrome et silicium dans le processus d'oxydation. Ainsi, les revetements elabores par irradiation d'un melange de carbure cr#3c#2 et de chrome, et ceux obtenus a partir d'un predepot constitue d'un melange de titane et de carbure de silicium, presentent une excellente resistance a l'oxydation a 1000c, equivalente a celle de l'acier 316l. D'autre part, le maintien prolonge a 1000c des alliages contenant des carbures m#7c#3 conduit a la precipitation des phases d'equilibre ce qui provoque une nette baisse de durete. Aucune modification structurale n'est observee dans les alliages contenant des carbures de titane. Les tests de corrosion intergranulaire effectues ont confirme le role preponderant du chrome sur le comportement a la corrosion. Enfin, les tests d'usure par frottement effectues sur ces differents alliages de surface ont montre que le durcissement obtenu permet une amelioration significative du comportement tribologique de l'acier 316l

L'objectif du travail presente ici est d'augmenter, par un traitement de surface, la tenue a l'oxydation a temperature elevee et la durete d'aciers ferritiques faiblement allies. Nous presentons les resultats obtenus avec les aciers 35ncd16 et z38cdv5 par irradiation laser assurant l'incorporation superficielle et la dissolution de predepots de nitrures (aln, si#3n#4) ou de carbures (sic, cr#3c#2). Nous precisions les conditions d'obtention d'alliages de surface exempts de fissures, d'amas ou de porosites. La durete de ces alliages depend principalement de la formation de martensite et (ou) de la precipitation de carbures ou de nitrures. L'excellente tenue a l'oxydation en conditions isothermes jusqu'a 950c de quelques alliages de surface dans une atmosphere d'oxygene resulte essentiellement de la formation d'une couche d'oxyde de chrome cr#2o#3. Dans les alliages contenant du silicium et relativement peu de chrome, la croissance de cette couche de cr#2o#3 n'intervient qu'apres celle, initiale, d'une tres mince pellicule de silice qui inhibe l'oxydation du fer et rend possible le developpement de la couche protectrice de cr#2o#3. Le bon comportement en cyclage thermique des alliages de surface etudiees sur l'acier z38cdv5 resulterait de la croissance de cr#2o#3 par diffusion anionique. La petite taille de grains de cet oxyde permettrait une bonne relaxation de contraintes thermiques par deformation plastique. Nous avons donc montre que le traitement laser avec ajout peut constituer un procede efficace pour conferer aux aciers peu allies un comportement en oxydation a haute temperature tout a fait comparable a celui des aciers inoxydables avec l'avantage d'une durete plus elevee

[ES] Dentro del sector biomédico, el titanio y sus aleaciones han desplazado a otros materiales como el acero inoxidable 316L y las aleaciones Co-Cr por ofrecer un módulo elástico más cercano al hueso cortical, lo que reduce sustancialmente el efecto de apantallamiento de tensiones. Una manera de disminuir aún más el módulo elástico es estabilizando la fase cúbica beta (bcc) del titanio a temperatura ambiente mediante la adición de elementos como el Nb y Mo, cuya biocompatibilidad ha sido comprobada en numerosos estudios. La ruta convencional para el procesado de estas aleaciones es la fundición y/o forja, pero en esta investigación se ha optado por la pulvimetalurgia ya que el desperdicio de material es mínimo y se reducen las etapas posteriores de tratamientos térmicos y mecanizado, facilitando el procesado en general y reduciendo los costos. Además, el carácter refractario de los elementos estabilizadores beta justifica aún más el empleo de un método de consolidación en estado sólido como la pulvimetalurgia donde no es necesario alcanzar temperaturas tan elevadas. Por tanto, en una primera aproximación se han procesado aleaciones de Ti-xNb-yMo (x = 13, 20, 27, 35 ; y = 12, 10, 8, 6; % en peso) mediante pulvimetalurgia convencional para estudiar el efecto del Nb y Mo en la microestructura y propiedades mecánicas de las aleaciones. A fin de atacar otros problemas inherentes del proceso como la porosidad y la falta de homogeneidad en la microestructura se ha acudido a la mezcla mecánica de polvos de la aleación Ti-35Nb-6Mo, evaluando también el efecto de diferentes agentes controladores de proceso en la molienda. Por último, se ha tratado la superficie de las aleaciones Ti-27Nb-8Mo y Ti-35Nb-6Mo mediante fusión por láser con diferentes parámetros para estudiar la capacidad del proceso de cerrar la porosidad abierta, mejorar la homogeneidad superficial, y evaluar su efecto en la microestructura y propiedades mecánicas de las aleaciones. Pese a aumentar la porosidad en función del contenido de Nb, las aleaciones Ti-27Nb-8Mo y Ti-35Nb-6Mo de las obtenidas por mezcla elemental exhibieron las mejores propiedades en general, con una microestructura casi beta en su totalidad y un módulo de elasticidad de 67 - 74 GPa, que se acerca más al presentado por el hueso cortical en comparación con la aleación comercial Ti-6Al-4V ELI. Por su parte, la mezcla mecánica mejoró considerablemente la homogeneidad química de la aleación Ti-35Nb-6Mo, pero promovió la formación de la fase alfa y deterioró la resistencia y deformación mecánica debido a la ganancia en acritud del polvo y el aumento de la porosidad. No obstante, la microdureza de las aleaciones aumentó significativamente. En cuanto al agente controlador de proceso, el cloruro de sodio (NaCl) exhibió los mejores resultados en términos de rendimiento y distribución de tamaño de partícula, mientras que el ácido esteárico indujo la contaminación del polvo mediante la formación de la fase no deseada TiC. El tratamiento de fusión superficial por láser consiguió cerrar efectivamente la porosidad abierta de las aleaciones y mejorar la homogeneidad microestructural. Adicionalmente, promovió un aumento de la resistencia y la deformación mecánica y una leve disminución del módulo elástico en ambas aleaciones. Por último, la aleación Ti-27Nb-8Mo tratada superficialmente a 1000W y 6,67 mm/s exhibió una microestructura beta casi en su totalidad y las mejores propiedades mecánicas desde un punto de vista biomédico, con una resistencia de 1467 MPa, una deformación de 7% y un módulo de elasticidad de 67 - 72 GPa.
[CA] Dins del sector biomèdic el titani i els seus aliatges han desplaçat a altres materials com l'acer inoxidable 316L i els aliatges Co-Cr per oferir un mòdul elàstic inferior i més pròxim a l'os cortical, la qual cosa redueix substancialment l'efecte d'apantallament de tensions. Una manera de disminuir encara més el mòdul elàstic és estabilitzant la fase cúbica beta; (bcc) del titani a temperatura ambient mitjançant l'addició d'elements altament biocompatibles com el Nb i Mo. La ruta convencional per al processament d'aquests aliatges és la fosa i/o forja, però en aquesta recerca s'ha optat per la pulvimetalurgia ja que el desaprofitament de material és mínim i es redueixen les etapes posteriors de tractament tèrmics i mecanitzat, facilitant el processament en general i reduint els costos. A més, el caràcter refractari dels elements estabilitzadors beta justifica encara més l'ús d'un mètode de consolidació en estat sòlid com la pulvimetalurgia on no és necessari aconseguir temperatures tan elevada. Per tant, en una primera aproximació s'han processat aliatges de Tu-xNb-yMo (x = 13, 20, 27, 35 ; i = 12, 10, 8, 6; % en pes) mitjançant pulvimetalurgia convencional per a estudiar l'efecte del Nb i Mo en la microestructura i propietats mecàniques dels aliatges. A fi d'atacar altres problemes inherents del procés com la porositat i la falta d'homogeneïtat en la microestructura s'ha acudit a la mescla mecànica de pólvores de l'aliatge Tu-35Nb-6Mo, avaluant també l'efecte de diferents agents antiadherentes en la mòltaa. Finalment, s'ha tractat la superfície dels aliatges Tu-27Nb-8Mo i Tu-35Nb-6Mo mitjançant fusió per làser amb diferents paràmetres per a estudiar la capacitat del procés per a tancar la porositat oberta, millorar l'homogeneïtat superficial, i avaluar el seu efecte en la microestructura i propietats mecàniques dels aliatges. Malgrat augmentar la porositat en funció del contingut de Nb, els aliatges Tu-27Nb-8Mo i Tu-35Nb-6Mo van exhibir les millors propietats en general. La mescla mecànica va millorar l'homogeneïtat química de l'aliatge Tu-35Nb-6Mo però va deteriorar les propietats mecàniques amb excepció de la microdureza. El tractament de fusió superficial per làser va aconseguir tancar efectivament la porositat oberta dels aliatges i va millorar l'homogeneïtat microestructural i les propietats mecàniques. Finalment, l'aliatge Tu-27Nb-8Mo tractada superficialment a 1000W i 6,67 mm/s va exhibir una microestructura beta gairebé íntegrament i les millors propietats mecàniques des d'un punt de vista biomèdic.
[EN] Within the biomedical sector, titanium and its alloys have replaced other materials such as 316L stainless steel and Co-Cr alloys due to a lower elastic modulus, closer to the cortical bone, which significantly reduces the stress shielding effect. An alternative to decrease the elastic modulus even more is to stabilize the cubic beta phase (bcc) of titanium at room temperature by adding highly biocompatible elements such as Nb and Mo. These alloys are normally processed by casting and/or forging, but in this work powder metallurgy was conducted due to lower material waste and less subsequent stages of heat treatments and machining, reducing costs significantly. Moreover, the refractory nature of beta stabilizing elements justifies even more the use of a solid-state consolidation method such as powder metallurgy where it is not necessary to reach meting point temperatures. Therefore, in a first approach, Ti-xNb-yMo alloys (x = 13, 20, 27, 35; y = 12, 10, 8, 6;% by weight) were processed by conventional powder metallurgy to study the effect of Nb and Mo in the microstructure and mechanical properties of the alloys. In order to attack other powder metallurgy inherent problems, such as porosity and inhomogeneity in the microstructure, mechanical mixing was carried out for the Ti-35Nb-6Mo powder, evaluating the effect of different non-stick agents on the milling process. Finally, the surface of Ti-27Nb-8Mo and Ti-35Nb-6Mo alloys were treated by laser surface melting under different parameters to reduce open porosity, improve surface homogeneity, and evaluate its effect. in the microstructure and mechanical properties of alloys. Despite increasing porosity with the increase of Nb content, Ti-27Nb-8Mo and Ti-35Nb-6Mo alloys exhibited the best overall properties, consisting of a beta phase microstructure. Mechanical mixing improved the chemical homogeneity of the Ti-35Nb-6Mo alloy but deteriorated the mechanical properties with the exception of microhardness. The laser surface melting treatment effectively closed the open porosity in the alloys and improved the microstructural homogeneity and mechanical properties. Lastly, the Ti-27Nb-8Mo alloy which surface was treated at 1000W and 6.67 mm/s exhibited a beta microstructure and the best mechanical properties from a biomedical point of view. Despite increasing porosity with Nb addition, Ti-27Nb-8Mo and Ti-35Nb-6Mo alloys exhibited the best overall properties, both consisting of a beta phase microstructure and an elastic modulus of 67 - 74 GPa, which is closer to the cortical bone in comparison to the commercial Ti-6Al-4V ELI alloy. On the other hand, the mechanical mixing significantly improved the chemical homogeneity of the Ti-35Nb-6Mo alloy, but induced the formation of alfa phase and deteriorated the resistance and mechanical deformation due to the increase in porosity and the hardening effect produced during the milling process. Therefore, the microhardness increased significantly. Regarding the process control agent, sodium chloride (NaCl) exhibited the best results in terms of powder yield and particle size distribution, while stearic acid induced contamination by the formation of the undesired TiC phase. The laser surface melting treatment was able to effectively close the open porosity of the alloys and improve microstructural homogeneity. Moreover, it promoted an increase in strength and mechanical deformation and a slight decrease in the elastic modulus in both alloys. Finally, the surface-treated Ti-27Nb-8Mo alloy at 1000W and 6.67 mm/s exhibited almost an entirely beta phase microstructure and the best mechanical properties from a biomedical point of view, with a resistance of 1467 MPa, a deformation of 7% and a modulus of elasticity of 67 - 72 GPa.
El trabajo se realizó en el Instituto de Tecnología de Materiales y en el Departamento de Ingeniería Mecánica y de Materiales de la Universitat Politècnica de València, bajo la ayuda del proyecto MAT2014-53764-C3-1-R del Ministerio de Economía y Competitividad de España, y la subvención 2016/020 del programa SANTIAGO GRISOLIA, enmarcada en la convocatoria del 2015 de la Conselleria de Educación, Cultura y Deporte de la Generalitat Valenciana.
Viera Sotillo, M. (2020). Desarrollo de aleaciones ß Ti-Nb-Mo mediante pulvimetalurgia para aplicaciones biomédicas [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/156194
TESIS

La problématique initiale part du constat que les échecs d’implants sont souvent causés par une inadéquation entre les propriétés élastiques de l’os et celles de l’implant. Aujourd’hui, ce problème de biocompatibilité mécanique suscite un intérêt croissant et a conduit au développement d’alliages de titane β-métastables qui possèdent un module d’élasticité faible, moitié moindre que celui de l’alliage Ti-6Al-4V classiquement utilisé dans les applications d’implantologie. De plus, les structures architecturées ou treillis font, elles aussi, l’objet d’intenses recherches dans le but de réduire le module d’élasticité et de maximiser la résistance. Leur mise en forme, avec une maîtrise précise de l’architecture, est possible grâce à la fabrication additive et les nombreuses possibilités qu’elle offre : liberté de design, gain matière, pièces complexes, customisation de masse... Ce travail de thèse porte sur la mise en œuvre de l’alliage de titane à bas module d’élasticité Ti-26Nb(%at.) par la technologie de fusion laser sur lit de poudres. Une stratégie d’élaboration in situ de ces alliages à partir de poudres élémentaires de Ti et de Nb est explorée, à la fois pour permettre d’éventuels ajustements de composition, et pour pallier au manque de disponibilité des alliages de titane sous forme de poudres. La démarche est réalisée avec deux morphologies de poudre, irrégulière et sphérique. Les effets des nombreux paramètres de ce procédé (puissance du laser, vitesse et stratégie de balayage...) sur l’homogénéité et la porosité des pièces élaborées sont quantifiés. Un alliage homogène peut être obtenu sous réserve de l’utilisation d’une densité d’énergie adaptée et d’une granulométrie de poudre tenant compte des températures de fusion respectives des éléments. La caractérisation de la microstructure met en évidence une texture marquée, dépendante de la stratégie de balayage. Les pièces élaborées présentent un bas module d’élasticité associé à une résistance mécanique élevée, avec une déformation élastique favorable par rapport à un alliage de référence coulé. Par ailleurs, un algorithme d’optimisation est développé et permet de contrôler les propriétés mécaniques d’une structure architecturée à partir de ses paramètres géométriques (rayon, longueur et orientation des poutres). La combinaison de cet alliage de titane à bas module d’élasticité et d’une structure architecturée développée à partir ce cet algorithme a été appliqué à une prothèse totale de hanche, qui a fait l’objet de simulations par éléments finis. L’évaluation du phénomène de stress-shielding montre que, comparativement à un modèle massif plus rigide, ce type de prothèse permet de réduire de façon significative la déviation des contraintes. En se rapprochant du modèle dit physiologique, cette prothèse peut être qualifiée de « biomimétique » sur le plan du comportement mécanique
The initial problematic arises from the fact that implant failure is often caused by a mismatch between the elastic properties of the bone and those of the implant. Nowadays, an increasing interest is given to this mechanical biocompatibility and led to the development of β-metastable titanium alloys that possess low Young’s modulus, about half that of the conventionally used Ti-6Al-4V alloy. Moreover, lattice structures are currently being the subject of many investigations with the aim of achieving low Young’s modulus and high strength. Their fabrication, with accurate control over the architecture, is made possible thanks to additive manufacturing processes and the several possibilities they offer: design freedom, reduced material usage rate, complex shapes, mass customisation... The present work focuses on the implementation of low modulus titanium alloy Ti-26Nb(at.%) by the means of selective laser melting. An in situ elaboration strategy, based on a mixture of elemental powders, is explored in order to allow potential composition adjustments and to overcome the unavailability of titanium alloy powders. The approach is carried out using two distinct powder morphologies, spherical and irregular. The effects of the numerous parameters of the process (laser power, speed, scanning strategy...) on homogeneity and porosity of the manufactured parts is quantified. A homogeneous alloy can be obtained subject to the use of suitable energy density levels and powder size distributions that take into account the respective fusion temperatures of both elements. Microstructure characterisation highlights a pronounced texture resulting from the scanning strategy. The elaborated samples display a low Young’s modulus associated with a high strength, and hence a favourable strength to elastic modulus ratio compared to the reference cast alloy. Furthermore, an optimization algorithm is developed and allows controlling the mechanical properties of a lattice structure with its geometrical parameters (radius, length and orientation of struts). The combined use of this low Young’s modulus titanium alloy with a lattice structure developed through this algorithm was applied to the design of a total hip prosthesis that was subjected to finite element simulations. Stress-shielding evaluation shows that, compared to a solid design, this kind of prosthesis permits to reduce stress-shielding significantly. By getting closer to a physiological model, this prosthesis can be qualified as “biomimetic” in terms of mechanical behaviour

La fusion sélective par laser (Selective Laser Melting, SLM), une des techniques de la fabrication additive (AM), permet la production de pièces en trois dimensions (3D) de formes complexes directement à partir de poudres métalliques. Elle présente de nombreux avantages significatifs par rapport aux méthodes traditionnelles de fabrication mais se heurte encore à une faible disponibilité des matériaux en poudre.Le travail effectué dans cette étude a donc consisté à étudier et à développer un nouveau moyen pour réaliser in situ des pièces en alliages et en composites à partir de mélanges de poudres.Au niveau expérimental le choix s'est porté sur le système Fer-Aluminium et sur un renforcement par des particules de SiC.Les essais ont permis de constater que dans le processus de fabrication de pièces par SLM la puissance du laser et la vitesse de balayage déterminent au premier chef la densité, la microstructure, la composition de phase et les propriétés mécaniques.À partir d'un mélange de poudres, des phases intermétalliques ont été obtenues en contrôlant les paramètres SLM. Un traitement thermique ultérieur influence les paramètres cristallins, le degré d'ordre et les propriétés mécaniques des pièces ainsi formées.Avec l'utilisation de poudres préalliées, un phénomène de texture a été observé prenant la forme de grains allongés/colonnaires orientés dans la direction de construction.Le renforcement de la matrice de fer par des particules de SiC de différentes tailles conduit à une modification structurale avec la formation de produits d'interaction, perlitie et martensite, conduisant à une amélioration de la résistance à la traction par rapport au Fe pur.

Thesis (Ph.D.)--Worcester Polytechnic Institute.
Keywords: composite Pd and Pd/Ag membranes, alloying, Pd/Ag barrier, intermetallic diffusion, bi-metal multi-layer BMML deposition, electroless plating kinetics, high temperature x-ray diffraction, aluminum hydroxide surface grading, porous sintered metal supports, hydrogen separation. Includes bibliographical references (leaves 279-296 ).

碩士
國立中正大學
機械系
92
Laser surface alloying with Ni- and Fe-based powder on the surface of squeeze casing A390 aluminum alloy was conducted utilizing Nd-YAG laser. Powder deposition on the surface of A390 Al alloy prior to laser alloying was carried out by using plasma-spraying method. Through laser remelting of the surface coating and the base metal the mixture of the coating and substrate will form an alloyed layer with compounds. The laser alloyed coating exhibits improved wear and corrosion resistance. Relationship between laser processing parameters including laser power/scanning speed and the characteristics of Ni- and Fe-based alloyed layers on the surface of A390 Al alloy including hardness and geometrical features was investigated. Concentration of the beam energy by decreasing laser beam diameter would achieve completely molten surface. In general the hardened depth increased with increasing laser power and decreasing scanning speed. For multi-pass alloyed layer, the hardness decreases with increasing overlap between passes due to heat accumulation. A shallow hardened layer with hardness value higher than HV600 on the surface of A390 Al alloy can be achieved. Four different microstructures such as acicular structure, snow-flake structure, columnar dendrite and irregular lump existed in the single-pass Ni-based alloyed layer. The former three microstructures were formed to be Ni2Al3 intermetallic compound and the last was NiAl intermetallic compound identified by EDS and EPMA. However, acicular Ni2Al3 and irregular-shaped NiAl compounds mainly formed in multi-pass Ni-based alloyed layer, which was identified by XRD results. The NiAl compound is much harder than Ni2Al3 compound The microstructure of single-pass Fe-based alloyed layer mainly consisted of cellular dendrite and irregular lump, which were identified as Fe2Al5 and FeAl compounds respectively. Due to overlap and higher dilution, the upper and bottom of the multi-pass Fe-based alloyed layer consisted of Al-rich needle-like structure and Fe-rich irregular lump, which were identified as FeAl3 and FeAl compounds respectively by EDS and EPMA. XRD results also revealed that FeAl3 and FeAl compounds indeed existed in the multi-pass Fe-based alloyed layer. The adhesive wear of the Al substrate and the abrasive wear of Fe- and Ni-based alloyed layers was observed using SEM and OM. The wear loss of Ni-based alloyed layer was twice higher than that of Fe-based alloyed layer, indicating a superior wear resistance of Fe-based alloyed layer. Therefore, Fe-based alloyed layer could be applied in wear components to prolong the service life.

M. Tech. Metallurgical Engineering
Martensitic stainless steel (MSS) metal matrix composite coatings that can accommodate most applications were developed using TiC and stellite 6 as reinforcement powders and Nd: YAG solid state laser for surface alloying. The alloyed surfaces were characterized by means of optical microscopy (OM), scanning electron microscopy (SEM/EDS) and x-ray diffraction (XRD). The microstructures of the alloyed zones show even distribution and super saturation of titanium carbide and other complex carbides of chromium (Cr23C6), niobium (Nb6C5), and iron (Fe7C3) in the matrix of the MSS A significant increase in the hardness was achieved by the addition of stellite 6, although with cracks in the alloyed layer. The cracks formation was due to high heat build-up during the laser alloying process. As a result of the addition of TiC powder in the form of premixed ratio, the heat build-up in the work-piece was minimized. This is due to the high absorptance of laser irradiation by the TiC powder. The alloyed zone of the premixed ratio was free from cracks with microhardness increase of more than 150% of that of the substrate. Multiple tracks of 50% and 75% overlap were fabricated. Three-body abrasive wear study of the overlapped coatings revealed the wear mechanism of the laser coatings to be adhesion, mild abrasive and less degree of deformation showing less plastic ploughing and cutting compared to the as-received. The wear mechanism of the as-received is adhesion, severe abrasive and plastic deformation, showing distinct grooves and damaged spots in the form of craters. The wear resistance of the MMC obtained by alloying with the TiC powder was significantly improved with the 75% overlap, about 90% better than the native material.

D. Tech. Chemical and Metallurgica Engineering.
Discusses the development highly corrosion resistant multi-functional materials for automobile applications by using laser surface alloying of aluminium substrate with a combination of metallic and ceramic powdery materials.

碩士
國立成功大學
材料科學及工程學系碩博士班
93
Aluminum alloys have been considered to be one of the most versatile useful materials because of to interesting mechanical properties, such as high strength-weight ratio, high electrical conductivity, good themal conductivity, easy to shape, and relatively inexpensive. However, the low hardness, low melting point of such alloys result in poor friction properties and heat resistance. The YAG laser alloying is one of the efficient method to improve the surface wear resistance. This paper is using YAG laser alloying Ni-based and Co-based powder on the surface of 6061 alloy and then to discuss the wear resistance property, microstructure, composition, and hardness throughout the alloying layers. As experimental result, we can find alloying layer can be divided into four layers, such as surface layer, subsurface layer, middle layer, and interface layer. The main reason to cause the variation of the alloying layer is due to different cooling rate and density. The Ni-based of the surface layer has the Al3Ni, the subsurface layer has Al3Ni2 feather-like microstructure, and the middle layer is AlNi . The Co-based of the surface layer has the Al9Co2, the subsurface layer is Al13Co4, and the middle layer is needle-like Al5Co2,and after laser alloying treatment, the hardness of middle layer of Ni-based and Co-based are 10 times higher than substrate. We can find transition from mild wear to severe wear point from SEM of wear surface and wear debris, and from results, we can find the wear resistance of Ni-based alloy is 8 times better than substrate’s, and Co-based alloy is 5 times better than substrate. And after heat treatment, because the middle layer of Ni-based Al3Ni will segregate to reduce the hardness, it results in that the transition from mild wear to severe wear point reduce to 500m, and so is Co-based alloy, The optimum specimen of wear resistance is Ni-based alloy without heat treatment.

博士
國立成功大學
材料科學及工程學系碩博士班
94
The surface microstructures of 6061 Al-Mg-Si alloy coated with laser surface alloyed (LSA) pure Ni, Ni base and Co base powder and the microstructure, hardness, and sliding wear performance have been investigated. Experimental results show that there are three regions, as region I, region II and region III in LSA Ni base powder treated specimen. Two regions, IV and V are observed in the LSA Co base treated specimen. The Al3Ni and Al3Ni2 compounds appear in the region I and region II, respectively. The Al-Ni-Cr amorphous structure can be observed in the region III. The Al9Co2 particles with a network structure are present in region IV and block-like Al13Co4 and Al7Cr are distributed in region V. The hardness of the LSA Ni and Co base specimens is much higher than the Al-matrix. Compared with the Al-matrix, the LSA Ni and Co base specimens have excellent sliding wear performance. They have lower friction coefficient and wear rate. The critical temperature of sliding wear resistance of LSA specimen is higher than that of Al-matrix by about 50°C.

碩士
國立臺灣科技大學
機械工程研究所
83
A 1500 W CW-CO2 laser was used to surface remelt and alloy nickel coated aluminum powder on W-Mo-Co high speed steel , then post heat treated at 560 ℃ for two hours and three times. Optical metallography (OM) , scanning electron microscope (SEM) , Vicker's microhardness (Hv) , energy- dispersive spectrometer (EDS) , electron probe microanalyzers (EPMA , and transmission electron mircroscope (TEM) were employed to characterize the remelted and alloyed layer. The microstructure of the remelted layer was a preponderance of cells. The hardness of laser=remelted layer was increased from 750-900Hv to 1100-1200Hv and the alloyed layer was increased from 550Hv to 620Hv after the 560 ℃ post heat treatment. And the EDS and EPMA results reveal that the cells were composed of Fe,Al,Ni and the cellular seregaations of W,Mo,V,Cr were observed in the laser-alloyed zone. And from the electron diffraction crystal structure determination , a B2 (Fe,Ni)Al superlattice structure was identified and its lattice parameter is 2.876A.

博士
國立臺灣科技大學
機械工程系
91
This study examined the laser alloying of NiAl powder, with addition of 0, 10, 20, 30, and 40 wt% ZrO2, upon Ti-6Al-4V by 1200 W CO2 laser. The experimental results show that a well-shaped alloying layer was obtained with pre- placed 0.1 mm thick powder at a traverse speed of 1 mm/sec. The microstructures, micro hardness, X-ray spectrum, SEM/EDS, TEM, impact, and wear tests of the alloying layers were investigated. The results indicate that the microstructures were finer, and microhardness was double or triple than that of the base material. The absorption of vibration was enhanced with increasing addition of ZrO2. During laser processing, NiAl and ZrO2 powders were dissolved in the molten pool, reacted with other elements, and formed new phases such as AlZr3、NiAlZr、Ti2Ni、Ti3Al and Al2O3. In the present work, a carbon steel was chosen as the base metal for relative studies.

To decrease fuel consumption and environmental impact, the use of more aluminum-based alloys in automobiles is the current trend which necessitates reliable aluminum - steel dissimilar joint. For this, traditional fusion joining techniques due to their high heat input which promotes the excessive formation of thick intermetallics at the interface of the joint that leads to low strength and premature failure. Brazing is a probable solution which utilizes a filler material and eliminates the melting of the steel and can potentially avoid/decrease intermetallics formation but requires careful selection of the filler metal and process parameters. In the present study laser brazing technique was employed to weld-braze 2 mm thick galvanized interstitial free (IF) steel (mentioned as GI) with 2 mm thick aluminum alloys (i.e., AA6082 (AlMg-Si) and AA5082 (Al-Mg)) in flange joint configuration, using 2 mm diameter solid AlSi12 (4047) filler wire. Experiments were performed with a constant spot size (1.7 mm) and varying other laser parameters, i.e., laser power (2.0-4.0 kW), wire feed rates (2.0 – 3.6 m/min) and at a scan speed of (2-2.5 m/min). Subsequently, the joints were subjected to phase evaluation study (microstructure, XRD), mechanical characterization (hardness, tensile and low cycle fatigue) and corrosion studies (immersion, salt-spray, potentiodynamic polarization, EIS). From macrographs, it was noticed that the size and shape of the weld-braze joint appearance vary with respect to the laser parameters. Microstructural observation of the etched specimens under SEM demonstrated columnar dendritic structure at the brazed zone, while eutectic structure at the inter-dendritic region. At the aluminum side, epitaxial growth was noticed, and a two-layered (planar and needle structured) interface towards the galvanized steel in both the compositions (i.e., AA6082/GI and AA5083/GI). EDS point analysis and X-ray diffraction technique were used to study the interface, and the results confirmed that the planar and needle structures are comprised of ternary Alx-Fey-Siz and binary Alx-Fey intermetallic phases respectively in both the combinations (i.e., AA6082/GI and AA5083/GI). The asymmetrical hardness profile throughout the braze joint with the lowest value in the brazed region was noted. In the case of nanoindentation testing, intermetallics have shown higher hardness values compared to base materials. From the tensile testing, it was pointed out that joints produced with AA6082/GI has exhibited higher strength and failed at the base material (aluminum-side). AA503/GI joints demonstrated marginally lower strength and recorded interfacial failure. The fatigue life of the laser brazed joints (AA6082/GI and AA5083/GI) at lower stain amplitude recorded higher fatigue life, and it was close to aluminum base material value. Fatigue tested specimens recorded brazed zone failure and revealed flow lines, intergranular cracking, and typical fatigue striations. From the salt spray test, it was revealed that galvanized steel was highly susceptible to corrosion compared to the Al-rich phase in both the joint combinations (i.e., AA6082/GI and AA5083/GI). Polarization results showed a substantial change in corrosion resistance from the steel interface to the brazed region due to variation in the microstructure. AA5083/GI brazed joints have shown marginally higher corrosion resistance as compared to the joints made with AA6082/GI. Post corrosion microstructure revealed pit formation at the brazed region

碩士
國立中正大學
機械工程所
96
Finite element modeling for single and multi-pass laser surface alloying (LSA) process with plasma sprayed coating layer was established. The finite element computation is carried out with SYSWELD commercial FEM packaging. Based on the previous research Al-Si aluminum alloy was chosen as the substrate and the coating powder was commercial iron based powder METCO 42C. Finite element with half-disc shape geometry was established for modeling the single-pass LSA process with axis-symmetric condition, while solid-rectangular and full-disc shaped geometries were established for the multi-pass LSA process. The adopted moving heat source used for modeling the laser power on those geometries was Goldak double ellipsoid heat source. This research was started from establishing an FEM model for single-pass LSA processing on a half-disc shape specimen was established due to its simplicity. Two stages of FEM computation using SYSWELD were carried out, which were thermal-metallurgical and thermal-mechanical computation. After confirming the appropriate temperature distribution between FEM result and previous experimental result, the computation for thermal-mechanical stages was carried out for predicting the residual stress distribution. An experiment for plasma sprayed-LSA process on a solid rectangular shaped specimen was then carried out for multi-pass FEM computation verification purpose. The selected substrate was also an aluminum alloy but with different series and slightly different composition compared with the aluminum in a previous work. Material for coating layer was the same as previous one. The chosen experimental parameters were based on the optimal parameters from previous work. An LSA treated specimens for both single and multi-pass process were then successfully accomplish with acceptable results compared to previous experimental results. The next effort was to apply the established finite element modeling setup for multi-pass LSA process to model the present experimental work which is in solid shape geometry. A small change of the Goldak parameters was done in order to adjust the size of heat source in order to synchronize the temperature distribution with the molten zone of the rectangular shape element. Thermo-Mechanical computation was also performed to predict the maximum residual stress on the geometry. Finally, the FEM simulation of multi-pass plasma sprayed LSA process on a disc-shaped specimen was established based on previous modeling technique. Some modification of Goldak parameters was done in order to ensure a good agreement between computation results and experimental results that were also conducted previously. Extracted data from thermal-mechanical analysis was only the residual stress distribution in the geometry. Similar residual stress distribution can be observed from those three FEM computation that the stress is accumulated on the area interacted with heat source for the very final time and in HAZ.

This thesis describes the novel laser surface alloying of aluminium AA1200 with various combinations of Ni, Ti and SiC powders, using a 4.4kW Rofin Sinar Nd:YAG laser in order to improve its mechanical and tribological properties. The laser alloying parameters were optimized on the breakdown systems of the complex Al-Ni-Ti-SiC system. Various analytical techniques were used to study the microstructures produced. Wear testing was conducted under sliding and abrasion conditions while the fracture mechanisms were investigated using impact tests. Aluminium surfaces reinforced with metal matrix composites and intermetallic phases were achieved. The phases present depended on the composition of the alloying powder mixture. Al reacted with Ni to form Al3Ni and Al3Ni2 intermetallic phases while Ti reacted with Al to form an Al3Ti intermetallic phase. Some of the SiC particles dissociated and reacted with either Al or Ti to form Al4C3, Al4SiC4, TiC or Ti3SiC2 phases. Si reacted with Ti to form a Ti5Si3 phase. An increase in surface hardness was achieved, up to a maximum of 13 times that of aluminium when alloying with 80wt%Ni + 15wt%Ti + 5wt%SiC. The increase in hardness was attributed to the intermetallic phases especially the Al3Ni2 phase. Alloying led to a 4-38% improvement in the wear resistance of the pure aluminium under sliding wear conditions and a 19-82% improvement under three body abrasion wear conditions. The predominant wear mechanisms for both wear types were groove formation by ploughing and cutting action of the abrasive particles, smearing, material pile-up, extensive cracking of the intermetallic phases and fracturing of the embedded SiC particles in the MMCs. Alloying led to a 31-50% decrease in the impact resistance of the pure aluminium. Brittle fracture of the SiC particles and transgranular cracking of the intermetallic phases were observed for the laser alloyed surfaces while ductile fracture was observed for the bulk aluminium.

Yes
The mass production of polymeric parts with functional surfaces requires economically viable manufacturing routes. Injection moulding is a very attractive option however wear and surface damage can be detrimental to the lifespan of replication masters. In this research, the replication of superhydrophobic surfaces is investigated by employing a process chain that integrates surface hardening, laser texturing and injection moulding. Austenitic stainless steel inserts were hardened by low temperature plasma carburising and three different micro and nano scale surface textures were laser fabricated, i.e. submicron triangular LaserInduced Periodic Surface Structures (LIPSS), micro grooves and Lotus-leaf like topographies. Then, a commonly available talc-loaded polypropylene was used to produce 5000 replicas to investigate the evolution of surface textures on both inserts and replicas together with their functional response. Any wear orsurface damage progressively built up on the inserts during the injection moulding process had a clear impact on surface roughness and peak-to-peak topographies of the replicas. In general, the polymer replicas produced with the carburised inserts retained the wetting properties of their textured surfaces for longer periods compared with those produced with untreated replication masters.
European Union’s H2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 675063 (www.laser4fun.eu). The work was also supported by three other H2020 projects, i.e. “HighImpact Injection Moulding Platform for mass-production of 3D and/or large micro-structured surfaces with Antimicrobial, Self-cleaning, Anti-scratch, Anti-squeak and Aesthetic functionalities” (HIMALAIA, No. 766871), “Process Fingerprint for Zero-defect Net-shape Micromanufacturing” (MICROMAN, No. 674801) and “Modular laser based additive manufacturing platform for large scale industrial applications” (MAESTRO, No. 723826). Further support was provided by the UKIERI DST programme “Surface functionalisation for 18/20 Accepted in the journal Tribology – Materials, Surfaces & Interfaces. food, packaging, and healthcare applications”
The full-text of this article will be released for public view at the end of the publisher embargo on 13 Jul 2021.

碩士
國立成功大學
材料科學及工程學系碩博士班
96
The microstructure, Vicker’s microhardness, and electrochemical property on 7075 Al-Zn-Mg-Cu alloy surface coated by Nd: YAG laser surface alloying (LSA) with Ni base and Co base powder have been investigated. The experimental results showed that the Al3Ni, Al3Ni2 dendrites existed in the Ni base alloy layer, and the Al9Co2, Al13Co4, Al11Cr2 dendrites existed in the Co base alloy layer respectively. The microstructure was decided by the cooling rate and distribution of alloy elements in LSA layers. The microhardness was raised to HV 900 for Ni base and Co base specimens, which is nine times to the matrix. The OCP was -0.9 V for Ni base and Co base alloyed layers in 3.5 wt% NaCl solution. The results of potentiodynamic polarization test showed that corrosion potential and protection potential were increased for Ni base and Co base alloyed layers, but the pitting potential was similar with 7075 alloy. The SEM images after PD test showed the aluminum in the Ni base and Co base alloyed layers flow away. The Al-Ni, Al-Co and Al-Cr IMCs were remained on the surface after PD test. Ni base specimen showed the minimum weight loss of 0.08 g at velocity for 900 mm/min and power for 1400 W. And, Co base specimen showed the minimum weight loss of 0.06 g at velocity for 600 mm/min and power for 1400 W.

碩士
國立高雄第一科技大學
機械與自動化工程所
91
Aluminum alloys have been considered to be one of the most versatile useful materials because of their interesting mechanical properties, such as high strength-weightratio, high electrical conductivity, good thermal conductivity, easy to shape, and relatively inexpensive. However, the low hardness, low melting point of such alloys result in poor friction properties and heat resistance. The Co2 laser alloying is one of the efficient method to improve the surface wear resistant.This paper is using CO2 laser alloying Ni-based and Co-based powder on the surface of 6061 Al-Mg-Si alloy and than to discuss the wear resistance property on high temperature. In this study we also will discusses the variation of composition, hardness,and the microstructure throughout the alloying layers after heat treatment. As Experimental result；we can find alloying layer can be divided into four layers, such as surface layer, subsurface layer, middle layer, and interface layer. The main reason to cause the variation of the alloying layer is due to different cooling rate and density. The Ni-based of the surface layer has the Al3Ni oriented microstructure due to rapid fast cooling rate, the subsurface layer has bigger Al3Ni2 dendritic microstructure, and the middle layer has Al-Ni-Cr amorphous microstructure. The Co-based of the surface layer has the Al9Co2 microstructure, the subsurface layer is Al13Co4 microstructure, and the middle layer is strip-like Al5Co2 microstructure. About the hardness test, the surface layer and the interface layer of Ni-based and Co-based after the laser alloying are influenced by effect of substrate.So the hardness is not increasing obviously. The middle layer is belonging to amorphous structure, and its hardness is 20 times than substrate. The life of the Ni-based and Co-based laser alloying treatment is 3 times as the based material after the wear resistance test under the 250 ℃. After the heat treatment, the α-Al of the alloying surface layer appears the nodulizing precipitation, the hardness is twice than original one. It can also improve the hardness gradient of the Ni-based alloying layers, and decrease the stress concentration. But the wear resistance property does not increase obviously since decreasing of the hardness in the middle layer. The Co-based alloying has better heat-resistance property.After heat treatment, the hardness of surface layer alloying increases. And the milled layer alloying is hard to solution precipitating Al9Co2 microstructure, it can keep the original hardness（Hv501038）. So the Co-based heat-treatment sample alloying has the best wear resistance during high temperature (200℃) of this research.

Die Arbeit beschäftigt sich im ersten Teil mit der Untersuchung des Einflusses der Prozessgrößen auf die Zielgrößen, Randschichthärtetiefe und die Oberflächenhärte beim Laserhärten. In einem weiteren Kapitel werden die Ergebnisse von verschiedenen Möglichkeiten der laserbasierten Härteverfahren zur Steigerung der Prozessgrenzen dargestellt. Eine Möglichkeit ist das Laserlegieren von kohlenstoffhaltigen Zusatzwerkstoffen, wie zum Beispiel mit Eisencarbid, Eisenchromcarbid oder Glaskohlenstoff. Dazu sind die Einflussgrößen auf die Einhärtetiefe sowie die Schmelzbaddynamik der jeweiligen Werkstoffe analysiert worden. Auf der Basis der neu erworbenen Kenntnisse ist ein Model zur Schichtdickenberechnung und eine numerische Simulation des Laserlegierprozesses entwickelt worden. Eine andere Möglichkeit die Prozessgrenzen zu erweitern ist, in der Arbeit durch das Laserauftragschweißen beschrieben worden. Dabei sind unterschiedliche Düsen und Beschichtungsstrategien zum Einsatz gekommen. Die letzte in der Arbeit beschriebene Methode zur Steigerung der Prozessgrenzen ist das Gaslegieren. Dabei sind Versuche zum Laserhärten unter Stickstoffatmosphäre sowie zum Lasercarbonitrieren als auch Lasercarburieren gemacht worden. Im letzten Kapitel werden konkrete Anwendungsgebiete zum Laserhärten von Powertrain-Komponenten vorgestellt. Dabei werden unterschiedliche Lösungsansätze zum Laserhärten von Bohrlöchern in Flanschwellen und zum Laserhärten der Hohlkehlen von Kurbelwellen aufgezeigt.:Einleitung Motivation Stand der Technik Umwandlungskinetik eisenhaltiger Werkstoffe Versuchsaufbau Versuchsauswertung Einfluss der Prozessgrößen auf die Randschichthärtetiefe und die Oberflächenhärte Erweiterung der Prozessgrenzen durch die Anwendung verschiedener Laseroberflächenverfahren Laserhärten von Powertrain-Komponenten Zusammenfassung Anhang

In the present investigation, surface coatings employing laser surface alloying (LSA) and plasma electrolytic oxidation (PEO) processes have been prepared on Mg alloys. The coatings have been investigated for corrosion and wear behaviour. Two important Mg alloys based on Mg–Al system were selected namely, MRI 230D and AM50 as substrates. LSA coatings have been prepared employing Al and Al2O3 as precursors using different laser scan speeds. PEO coatings were prepared in standard silicate and phosphate based electrolytes employing unipolar, pulsed DC. Hybrid coatings using a combination of the two processes were also produced and investigated for corrosion and wear behaviour. Hybrid coatings of LSA followed by PEO (LSA+PEO) were investigated for effectiveness of sealing the cracks in the LSA coatings by subsequent PEO process and consequent improvement in the corrosion resistance. Hybrid coatings of PEO followed by LSA (PEO+LSA) were prepared with an objective of sealing the pores in the PEO coating LSA treatment. In an attempt to produce more compact PEO coatings, electrolyte containing montmorillonite clay additives was employed for the PEO process of AM50 Mg alloy. The coatings were produced employing different current densities and the effect of current density on the microstructure and corrosion behaviour of coating was investigated. Electrochemical corrosion tests of uncoated and coated alloys were carried out in 3.5 wt.% (0.6M)NaCl, neutral pH, solution with an exposed area of 0.5 cm2 for a time duration of 18.5 h. For the PEO coatings with clay additives, corrosion tests were conducted additionally in 0.5 wt.% (0.08 M) NaCl, neutral pH, solution for a time duration of 226.1 h. Wear behaviour of LSA coatings was analyzed by employing a pin on disc tribo–tester conforming to ASTM G–99 standard at ambient conditions with ground EN32 steel disc of hardness Rc 58 as the counterface. Tests were conducted under dry sliding conditions for a sliding distance of 1.0 km at a sliding velocity of 0.837 m/s employing normal loads of 10, 20, 30 and 40 N. Friction and wear behavior of PEO and PEO+LSA coatings were analyzed at ambient conditions by employing a ball−on−flat linearly oscillating tribometer conforming to ASTM G–133 standard. AISI 52100 steel ball of diameter 6 mm was employed as the friction partner. Wear tests were conducted under dry sliding conditions for a total sliding distance of 100 m at normal loads of 2 N and 5 N with oscillating amplitude of 10 mm and mean sliding speed of 5 mm/s. LSA coatings could not improve the corrosion resistance of MRI 230D Mg alloy. This was attributed to the presence of cracks in the LSA coating, which resulted in the accelerated galvanic corrosion of the substrate. LSA coatings improved the wear resistance at all loads. The improved wear resistance was attributed to β (Mg17Al12) phase and Al2O3 particles in the coating which increased the hardness of the LSA layer. No trend in corrosion and wear resistance with laser scan speed was observed for LSA coatings. PEO coatings improved the corrosion resistance of the MRI 230D Mg alloy significantly. The improved corrosion resistance was attributed to the enhanced barrier protection provided by dense barrier layer formed at the substrate/coating interface and to the insoluble phase constituents in the coatings. PEO coating was effective in improving the wear resistance at low loads/contact pressures. At higher loads, the coating underwent micro–fracture as a result of the porosity in the coatings. Hybrid coatings of LSA followed by PEO (LSA+PEO) in silicate based electrolyte improved the corrosion resistance of LSA coatings. However, the corrosion resistance was not improved to the extent of PEO coatings on as–cast alloy as a result of cracks in the primary coatings, which were not fully sealed by the plasma conversion products. No trend in corrosion resistance with laser scan speed was observed for LSA+PEOcoatings. In hybrid coatings of PEO followed by LSA (PEO+LSA), primary PEO coating was completely melted and mixed with applied precursor to form a single composite LSA layer. The corrosion resistance of the hybrid coatings was observed to be lower than that of the as–cast alloy. The presence of solidification cracks reduced the barrier properties and resulted in the accelerated galvanic corrosion of the substrate similar to LSA coatings. Hybrid (PEO+LSA) coatings exhibited improved wear resistance as compared to as–cast alloy at lower loads as a result of increase in the hardness due to β (Mg17Al12) phase and oxide/ceramic particles in the hybrid layer. At higher loads, hybrid coatings exhibited higher wear rate as compared to as–cast alloy and PEO coatings. This was attributed to three–body abrasive wear as a result of dislodged hard oxide/ceramic particles in the wear tracks. No trend in corrosion and wear resistance with laser scan speed was observed for PEO+LSA coatings. PEO coatings on AM50 Mg alloy by employing clay additives in the electrolyte resulted in the reactive uptake of clay particles producing a predominantly amorphous coating at low current density. Clay additives were effective in improving the compactness of the coating at lower current density. At higher current densities, the porosity of the coatings increased. The clay particles got re–constituted producing increasing amount of crystalline phases with increase in current density. Long term impedance measurements showed that clay addition as well as increased current density employed for the PEO process was not effective in improving the corrosion resistance of the coatings. At low current density, even though the coating with clay additives was more compact, it was deficient in MgO and consisted predominantly of an amorphous phase, which underwent fast dissolution in electrolyte thereby resulting in an early loss of barrier properties. At higher current densities, even though the coatings consisted of increased amount of MgO and crystalline phases, which resist dissolution in the electrolyte, the increased porosity and defective barrier layer resulted in easy permeation of the electrolyte into the substrate/coating interface, which resulted in much earlier loss of barrier properties and inferior corrosion resistance.

In the present investigation, surface coatings employing laser surface alloying (LSA) and plasma electrolytic oxidation (PEO) processes have been prepared on Mg alloys. The coatings have been investigated for corrosion and wear behaviour. Two important Mg alloys based on Mg–Al system were selected namely, MRI 230D and AM50 as substrates. LSA coatings have been prepared employing Al and Al2O3 as precursors using different laser scan speeds. PEO coatings were prepared in standard silicate and phosphate based electrolytes employing unipolar, pulsed DC. Hybrid coatings using a combination of the two processes were also produced and investigated for corrosion and wear behaviour. Hybrid coatings of LSA followed by PEO (LSA+PEO) were investigated for effectiveness of sealing the cracks in the LSA coatings by subsequent PEO process and consequent improvement in the corrosion resistance. Hybrid coatings of PEO followed by LSA (PEO+LSA) were prepared with an objective of sealing the pores in the PEO coating LSA treatment. In an attempt to produce more compact PEO coatings, electrolyte containing montmorillonite clay additives was employed for the PEO process of AM50 Mg alloy. The coatings were produced employing different current densities and the effect of current density on the microstructure and corrosion behaviour of coating was investigated. Electrochemical corrosion tests of uncoated and coated alloys were carried out in 3.5 wt.% (0.6M)NaCl, neutral pH, solution with an exposed area of 0.5 cm2 for a time duration of 18.5 h. For the PEO coatings with clay additives, corrosion tests were conducted additionally in 0.5 wt.% (0.08 M) NaCl, neutral pH, solution for a time duration of 226.1 h. Wear behaviour of LSA coatings was analyzed by employing a pin on disc tribo–tester conforming to ASTM G–99 standard at ambient conditions with ground EN32 steel disc of hardness Rc 58 as the counterface. Tests were conducted under dry sliding conditions for a sliding distance of 1.0 km at a sliding velocity of 0.837 m/s employing normal loads of 10, 20, 30 and 40 N. Friction and wear behavior of PEO and PEO+LSA coatings were analyzed at ambient conditions by employing a ball−on−flat linearly oscillating tribometer conforming to ASTM G–133 standard. AISI 52100 steel ball of diameter 6 mm was employed as the friction partner. Wear tests were conducted under dry sliding conditions for a total sliding distance of 100 m at normal loads of 2 N and 5 N with oscillating amplitude of 10 mm and mean sliding speed of 5 mm/s. LSA coatings could not improve the corrosion resistance of MRI 230D Mg alloy. This was attributed to the presence of cracks in the LSA coating, which resulted in the accelerated galvanic corrosion of the substrate. LSA coatings improved the wear resistance at all loads. The improved wear resistance was attributed to β (Mg17Al12) phase and Al2O3 particles in the coating which increased the hardness of the LSA layer. No trend in corrosion and wear resistance with laser scan speed was observed for LSA coatings. PEO coatings improved the corrosion resistance of the MRI 230D Mg alloy significantly. The improved corrosion resistance was attributed to the enhanced barrier protection provided by dense barrier layer formed at the substrate/coating interface and to the insoluble phase constituents in the coatings. PEO coating was effective in improving the wear resistance at low loads/contact pressures. At higher loads, the coating underwent micro–fracture as a result of the porosity in the coatings. Hybrid coatings of LSA followed by PEO (LSA+PEO) in silicate based electrolyte improved the corrosion resistance of LSA coatings. However, the corrosion resistance was not improved to the extent of PEO coatings on as–cast alloy as a result of cracks in the primary coatings, which were not fully sealed by the plasma conversion products. No trend in corrosion resistance with laser scan speed was observed for LSA+PEOcoatings. In hybrid coatings of PEO followed by LSA (PEO+LSA), primary PEO coating was completely melted and mixed with applied precursor to form a single composite LSA layer. The corrosion resistance of the hybrid coatings was observed to be lower than that of the as–cast alloy. The presence of solidification cracks reduced the barrier properties and resulted in the accelerated galvanic corrosion of the substrate similar to LSA coatings. Hybrid (PEO+LSA) coatings exhibited improved wear resistance as compared to as–cast alloy at lower loads as a result of increase in the hardness due to β (Mg17Al12) phase and oxide/ceramic particles in the hybrid layer. At higher loads, hybrid coatings exhibited higher wear rate as compared to as–cast alloy and PEO coatings. This was attributed to three–body abrasive wear as a result of dislodged hard oxide/ceramic particles in the wear tracks. No trend in corrosion and wear resistance with laser scan speed was observed for PEO+LSA coatings. PEO coatings on AM50 Mg alloy by employing clay additives in the electrolyte resulted in the reactive uptake of clay particles producing a predominantly amorphous coating at low current density. Clay additives were effective in improving the compactness of the coating at lower current density. At higher current densities, the porosity of the coatings increased. The clay particles got re–constituted producing increasing amount of crystalline phases with increase in current density. Long term impedance measurements showed that clay addition as well as increased current density employed for the PEO process was not effective in improving the corrosion resistance of the coatings. At low current density, even though the coating with clay additives was more compact, it was deficient in MgO and consisted predominantly of an amorphous phase, which underwent fast dissolution in electrolyte thereby resulting in an early loss of barrier properties. At higher current densities, even though the coatings consisted of increased amount of MgO and crystalline phases, which resist dissolution in the electrolyte, the increased porosity and defective barrier layer resulted in easy permeation of the electrolyte into the substrate/coating interface, which resulted in much earlier loss of barrier properties and inferior corrosion resistance.

Вєніков В. О. Формування високоентропійних структур в системі Fе-Nі-Со-Сг-А1 при лазерному легуванні : кваліфікаційна робота магістра спеціальності 104 "Фізика та астрономія" / наук. керівник О. В. Смоляков. Запоріжжя : ЗНУ, 2020. 55 с.
UA : В роботі 55 сторінок, 22 рисунків, 2 таблиць та було використано 65 літературних джерел. Об’єкт дослідження – поверхня зразків технічно чистого алюмінієвого сплаву марки А-8 після лазерного легування. Мета роботи: встановлення закономірностей формування структурно–фазового стану при лазерному легуванні алюмінію сумішшю порошків Fe, Ni, Co та Cr. Метод дослідження – рентгенівський фазовий, металографічний, растрова електронна мікроскопія. За допомогою наведених методів була досліджена структура зразків у вихідному стані та після лазерного легування еквіатомною сумішшю порошків Fe, Ni, Co та Cr на повітрі. Встановлено, що лазерне легування технічно чистого алюмінієвого сплаву А8 сумішшю перехідних металів групи заліза на повітрі, призводить до значного зростання мікротвердості поверхневих шарів алюмінію приблизно в 20 раз, що обумовлено формуванням фаз з ОЦК та ГЦК ґратками, фази Al13Me4 та підвищенням ступеня дисперсності структури.
EN : In the work 55 pages, 2 tables and 22 figures, was used 65 literary sources. The object of research is the surface of samples of technically pure aluminum alloy grade A-8 after laser alloying. Purpose: to establish the patterns of formation of the structural phase state after laser alloying of aluminum with a mixture of Fe, Ni, Co and Cr powders. Research method – X-ray phase, metallographic, scanning electron microscopy. Using the given methods, was investigated the structure of the samples in the initial state and after laser alloying with an equiatomic mixture of Fe, Ni, Co and Cr powders in air. Was found, that laser alloying of technically pure aluminum alloy A8 with equiatomic mixture transition metals of iron in air, leads to a significant increase in microhardness of aluminum surface layers nearly 20 times, what conditioned to the formation of phases with BCC and fcc lattices, Al13Me4 phase and increasing the degree of dispersion of the structure.

Ралко А. В. Структурно-фазовий стан поверхневих шарів армко-заліза після лазерного легування сумішшю порошків нікелю, кобальту та хрому : кваліфікаційна робота магістра спеціальності 104 «Фізика та астрономія» / наук. керівник О. В. Смоляков. Запоріжжя : ЗНУ, 2020. 53 с.
UA : В роботі 53 сторінок, 13 рисунків, 2 таблиць та було використано 60 літературних джерел. Об’єкт дослідження – стрктурно-фазовий стан поверхневих шарів армко-заліза, після лазерного легування сумішшю порошків металів групи заліза. Мета роботи: встановити можливість створення за допомогою метода лазерного легування високоентропійного сплаву в поверхневих шарах армко-заліза. Метод дослідження – рентгенівський фазовий, металографічний, вимірювання мікротвердості та метод растрової електронної мікроскопії. В кваліфікаційній роботі за допомогою рентгенівського фазового аналізу було досліджено фазовий склад зразків у вихідному стані та після лазерної обробки на повітрі. Проаналізували структуру та фізико-механічні властивості при поверхневого шару зразків після лазерного легування та визначили значення мікротвердості за глибиною в зоні лазерної дії.
EN : In the work 53 pages, 2 tables and 13 figures, was used 60 literary sources. The object of the study is the structural-phase state of the surface layers of armco-iron, after laser doping with a mixture of powders of metals of the iron group. Purpose: to establish the possibility of creating a high-entropy alloy in the surface layers of armco-iron using the method of laser doping. The research method is X-ray phase, metallographic, microhardness measurement and scanning electron microscopy method. In the qualification work with the help of X-ray phase analysis, the phase composition of the samples in the initial state and after laser treatment in air was investigated. The structure and physico-mechanical properties of the surface layer of the samples after laser doping were analyzed and the values of microhardness in depth in the laser action zone were determined.

碩士
遠東科技大學
機械工程研究所
107
The microstructure and corrosion characteristics of spheroidal graphite cast iron surface were modified by discharge alloying process (EDA) and wide peenig cleaning (WPC). The microstructure and corrosion characteristics of the spheroidal graphite cast iron surface are improved after surface modification.The experi-mental results show that the WPC treatment can reduce thesurface roughness and the microstructure refinement of the EDA modified layer. The hardness value of EDA+WPC composite treatment is higher than that of EDA, therefore, WPC pro-cess can effectively improve the hardness of EDA surface modification layer. The Ra value of surface roughness is lower than that of EDA after WPC treatment. The WPC process uses micro-particles for surface modification to make the surface pits that can be used to conserve lubricating fluids to improvelubrication. The WPC process can effectively improve the surface hardness, surface roughness and mi-crostructure refinement of chromium EDAed layer and zirconium EDAed layer.

碩士
國立中興大學
材料科學與工程學系所
104
In this study, electrical discharge alloying (EDA) was used for surface modifying on AA6082 alloy. EDA process is the reverse-electrode method of electrical discharge machining (EDM). Pure iron was used as negative electrode in this process to improve tribology performances of AA6082 alloy through the differences in EDA steps and parameters. The experimental results show the surface roughness (Ra) was approximately 7.24 m after two-step alloying, the hardness of alloyed layer could achieve at least 1400 HV and the appearance of graphite in X-ray diffraction patterns. According to the reference, graphite have excellent lubricating performance. Then, after a shorter time of the third-step alloying, the surface roughness was decreased to 6.90 m and the alloyed layer could also achieve at least 1400 HV. The contents of graphite phase, graphitization and its crystallinity also increased with this third-step alloying. However, we gave a relative movement between iron electrode and AA6082 workpiece in the third-step alloying, experimental results show that the effect of smoothing surface was achieved with a significantly decreasing in the surface roughness (Ra) to 5.23 m and the hardness of alloyed layer could keep at least 1400 HV. This relative movement also could make the EDS mapping signal of aluminum, iron and carbon uniformly dispersed in the alloyed layer. The contents of graphite phase, graphitization and its crystallinity had a greater increasing than the third step alloying without the relative movement, and graphene structure was observed in the surface of alloyed layer after the third-step alloying with the relative movement. In tribology performance, the friction coefficient was decreased from the range about 0.5~0.6 in AA6082 substrate to 0.1~0.2 after three-step alloying with the relative movement. Among the experimental results, three step alloying with the relative movement can effectively improve the tribology performance of AA6082 alloy with the collocation of the hard alloyed layer and the excellent lubrication effect of graphite and graphene.

碩士
遠東科技大學
機械工程研究所在職專班
101
In the study, surface modification of SG cast iron by electrical discharge alloying is used to examine the effect of machining parameters (discharge current, pulse duration and duty factor) on the thickness and surface roughness of the surface modified layer on ferric spheroidal graphite (SG) cast iron while the electrode polarity (anode) and the electrode composition (Zr) are fixed. EPMA composition analysis reveals that the zirconium element in the electrode effectively dissolves and passes into the substrate of SG cast iron, forming an alloyed layer, and the amount of dissolved zirconium element decreases as the distance from the surface increases. X-ray diffraction results of the zirconium alloyed layer show that α-Fe, ZrC and FeSiC are the main constituent phases. According to the results of an experiment that explores the effect of changes in conditions for single-stage electrical discharge alloying on the characteristics of the alloyed layer, the thickness and hardness of the layer generated by discharge alloying using the pure Zr electrode as well as the corrosion potential of the ZrC alloyed layer increase together with the discharge current. To examine the changes in conditions for two-stage discharge alloying, particularly pulse duration and duty factor, on the characteristics of the ZrC alloyed layer, the first-stage process continued for 10 minutes in the fixed conditions of 50A discharge current, 500 s pulse duration and 50% duty factor. The experimental results show that individual specimens subjected to two-stage discharge alloying process using varying parameters (changes in pulse duration and duty factor) have better surface states (including number of defects and roughness) than their counterparts subjected to single-stage discharge alloying. The thickness of ZrC alloyed layers tend to increase with pulse duration with the maximum thickness of about 55m when DF = 33%, but tends to decreases when DF > 33%. During two-stage discharge alloying, each alloyed layer resulted from each variance in pulse duration has higher corrosion potential than the substrate of SG cast iron and the maximum corrosion potential is achieved when pulse duration = 750 s. Also, each alloyed layers resulted from each variance in duty factor has higher corrosion potential than the substrate of SG cast iron although changes in duty factor have no significant effect on the corrosion potential of the alloyed layers.

碩士
國立中興大學
材料科學與工程學系所
106
ABSTRACT This study experimentally investigates the surface modification of 6082 Al alloy by the electrical discharge alloying EDA process. EDA process is the reverse-electrode method of electric discharge machine. pure iron was used as negative electrode in this process to improve friction properties of AA6082 alloy. Samples were analyzed by internal grander machine and infrared thermograph. The internal grinder experimental result show the base metal (6082 Al alloy) on the wear-resisting is rated current 5.6 A of 12 % (friction current 0.672 A) and electric power is 147 W. The general hard anodizing and super hard anodizing of specimen, the wear-resisting is show rated current 5.6 A of 11% (friction current 0.616 A) and electric power is 135 W. EDA alloyed layer of the wear-resisting is show rated current 5.6 A of 10% (friction current 0.56 A) and electric power is 123 W. EDA alloyed layer the specimen surface due to has pyrolytic graphite, can effectively reduce the wear-resisting and friction current, according to the reference, graphite have excellent lubricating performance. Then, the infrared thermography experimental result show the friction temperature on base metal (6082 Al alloy) is 29.46 degrees. Hard anodizing of the friction temperature is 31.41 degrees. super hard anodizing of the friction temperature is 32.46 degrees . EDA alloyed layer the specimen the friction temperature dropped to 27.91 degrees. The infrared thermography of EDA alloyed layer was evidently lower than that of the base metal (6082 Al alloy) and hard and super hard anodizing of specimen. Among the experimental result, pyrolytic graphite can effectively improve the friction properties of AA6082 alloy with the collocation of the hard alloyed layer and the excellent lubrication effect of graphite.