The material development cycle is becoming too slow if compared with other technologies sectors like IT and electronics. The materials scientists’ community needs to bring materials science back to the core of human development. ICME (Integrated Computational Materials Engineer) is a new discipline that uses advanced computational tools to simulate material microstructures, processes and their links with the final properties. There is the need for a new way to design tailor-made materials with a faster and cheaper development cycle while creating products that meet “real-world” functionalities rather than vague set of specifications. Using the ICME approach, cutting edge computational thermodynamics models were employed in order to assist the microstructure characterization and refinement during the TIG welding of a functionally graded composite material with outstanding wear and corrosion resistance. The DICTRA diffusion model accurately predicted the carbon diffusion during sintering, Thermo-Calc and TC-PRISMA models described the thermodynamic and kinetics of harmful carbide precipitation, while COMSOL Multhiphysic furnished the temperature distribution profile at every timestep during TIG welding of the material. Bainite transformation and the influence of chromium and molybdenum was studied and modelled with MAP_STEEL software. The simulations were then compared with experimental observations and a very good agreement between computational works and experiments was found for both thermodynamic and kinetics predictions. The use of this new system proved to be a robust assistance to the classic development method and the material microstructures and processes were carefully adjusted in order to increase corrosion resistance and weldability. This new approach to material development can radically change the way we think and we make materials. The results suggest that the use of computational tools is a reality that can dramatically increase the efficiency of the material development.

The aim of this study is to investigate the mechanical behavior and its relation with processing and microstructure of the silicon carbide particulate (SiCp) reinforced aluminum matrix composite. Aluminum 7075 alloy is chosen as matrix alloy, in which zinc is the main alloying element. Four different additions of SiCp were used and the weight fractions were 10%, 15%, 20% and 30%. Composites were processed by with squeeze casting and the applied pressure during casting was 80 MPa. The mould is specially designed to produce both specimens ready for tensile and three point bending tests. Both as-cast and heat treated aluminum composites were examined and T6 heat treatment was applied. Three point bending tests were performed to reveal the fracture strength of aluminum composites. 10wt% SiCp aluminum composites showed the maximum flexural strength in both as-cast and heat treated composites. The mechanical test results revealed that precipitated phases in heat treated composites, behaved like fine silicon carbide particulates and they acted as barriers to dislocation motion. Maximum flexural strength increased about 40 MPa (10%) in as-cast and 180 MPa (44%) in heat treated composites. Tensile testing was also conducted to verify the results of the three point bending tests. Hardness tests were done to find the effect of silicon carbide addition and to find the peak hardness in heat treatment. For as-cast specimens hardness values increased from 133 to 188 Vickers hardness (10 kg.) with increase in SiCp content from 0 to 30wt% and for heat treatment specimens hardness values increased from 171 to 221 Vickers hardness (10 kg.). The peak hardness values were obtained at 24 hours precipitation heat treatment. SEM studies were carried out to examine the heat treated composites, to take SEM photographs and to obtain a general elemental analysis. Theoretical volume percentage addition of SiCp was checked with Clemex Image Analyzer program. Distribution of SiCp was determined by mettalographic examination. Second phases that were formed during heat treatment was searched by x-ray analysis.

Silver is a precious metal that has traditionally been used for jewellery and money. It also possesses desirable properties such as being corrosion resistant and having good electrical conductivity, resulting in its use for industrial applications. Furthermore, it is also recognised for its tribological properties in non-cost prohibitive applications. Silver can be used as a surface coating and can be deposited using an electroplating process. The utilisation of silver as a surface coating is advantageous and sustainable, as the substrate material properties are enhanced while usage of silver is kept to a minimum. On the other hand, electroplating has been used for over a century. It is a process which is able to produce a layer of uniform and dense coating that adheres well to the substrate metal, thus modifying the properties of the substrate. It benefits from being relatively low cost and is scalable. Silver is electroplated onto stainless steel threaded compression fittings to prevent galling. Traditional silver electroplating, which contains the use of cyanide as a complexing agent in the electroplating bath, is still in use within industry, even to this day. Cyanide, in its various forms can be poisonous, toxic and even lethal, which presents a risk during the silver electroplating process. Furthermore, the toxic wastes created during the cyanide silver electroplating process are detrimental to the environment. The aim of this work is to develop a self-lubricating non-cyanide silver PTFE composite coating suitable for use in threaded compression fittings of the ferruled type. The composite can be considered self-lubricating when a concentration of 8% or more by volume of the self-lubricating PTFE substance is incorporated. My original contribution to knowledge is firstly the successful development and characterisation of a self-lubricating non-cynanide Ag-PTFE coating on stainless steel without a strike resulting in improved CoF of 0.06 from the CoF of 0.6 based on an unlubricated surface. Secondly is the application of a non-cyanide Ag-PTFE MMC for threaded compression fittings. Thirdly is the characterisation of the make-up process of threaded compression fittings through the proposed use of the torque-angle slope in assessing coating performance for threaded compression fittings during make-up. Conclusions that can be drawn for the work are that the performance non-cyanide Ag-PTFE coating exceeded the performance of the pure Ag coating made using the same non-cyanide process. Moreover, the performance of the Ag-PTFE coating shows promising results when compared to the performance of the commercial silver cyanide coating. As a viable replacement to the current silver cyanide process, the self-lubricating non-cyanide Ag-PTFE coating, will improve the working conditions and have a positive contribution to the environment. Moreover, a thinner coating with has the potential to reduce raw material usage and electroplating waste disposal costs.

Made available in DSpace on 2014-06-11T19:32:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-24Bitstream added on 2014-06-13T20:08:31Z : No. of bitstreams: 1 ranieri_k_dr_guara.pdf: 3032038 bytes, checksum: 78d562848610f76e621250d9538e5ad3 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O estudo do processamento de compósitos de matriz metálica pelo método de fundição com agitação é de grande interesse em engenharia pelo seu baixo custo e possibilidade de utilizar equipamentos convencionais de fundição. Nesse trabalho é feito o estudo do processo de síntese de compósitos da matriz da liga A356 reforçada com partículas de alumina, focalizando a influência dos fatores de processo na fração de partícula incorporada. Foram sintetizados lingotes de compósitos variando as condições de processo. Foram desenvolvidos métodos específicos de amostragem estatística associados à análise e processamento de imagens e utilizados na obtenção de estimativas confiáveis da fração volumétrica. Para investigar a influência dos fatores e suas interações foi projetado um experimento fatorial com 4 fatores, definidos em ensaios preliminares. Os resultados confirmam achados teóricos e experimentais anteriores e indicam novos caminhos para se obter uma melhor incorporação de partículas, além de um entendimento do mecanismo da molhabilidade da liga no estado semissólido. Compósitos com maior grau de partículas incorporadas foram examinados por microscópio eletrônico de varredura e microscópio óptico, mostrando que a partícula se aloja preferencialmente na região interdendrítica da matriz. / The study of metal matrix composite processing through stir casting method is of great interest for engineering because of its low cost and possibility of using conventional casting equipment as well. The synthesis of hypoeutectic A356 matrix alloy reinforced with alumina particle was done in this work focusing the influence of the processing factors on the incorporated particle fraction. Ingots of composites were synthesized by varying the process conditions. Methods of statistic sampling connected to the analysis and processing images were developed and used for reliable estimate of volumetric fraction. To investigate the influence of the factors and their interactions, a factorial experiment was planned with four factors defined in a preliminary test. The results confirm theorical and experimental findings and points to a new way of getting better particle incorporation and an insight of the wettability mechanism. Composites with high level of particle incorporation were checked through electronic and optical microscopes showing that the particle stays mainly in interdendritic regions.

Este trabalho versa sobre a caracterização de uma junta soldada em cheio (bead-onplate) de liga AA356 reforçada com partículas de SiC, soldada por um Laser de fibra de alta potência. A soldagem foi realizada em duas amostras com diferentes condições térmicas, tratadas termicamente T6 (solubilização e envelhecimento) antes da soldagem (amostra A) e após a soldagem (amostra B). Nas amostras A e B foram realizadas as análises de materialográfia via Microscopia Óptica de luz reflexiva (M.O) e Microscopia Eletrônica de Varredura (MEV), também foram realizadas análises microquímica por Energia Dispersiva de Raios-X (EDX), ensaio mecânico de microdureza e difração de Raios-X. Os corpos de prova submetidos ao ensaio de tenacidade em Flexão três pontos tinham condições térmicas iguais a da amostra A, pois essa condição térmica é a condição que normalmente o Compósito de Matriz Metálica (CMM) exibe em serviço. A inspeção materialográfica por M.O identificou a interferência do tratamento térmico T6 realizado na amostra A, fazendo que fosse possível identificar a baixa proporção das partículas de Si na matriz, conforme análise se aproximava da zona fundida (ZF), e a presença de uma estrutura metaestável com a presença dendritas na ZF, aos quais foram diretamente correlacionados com os resultados da microdureza. A amostra B exibiu uma microestrutura bem homogênea em relação à amostra A, em termos de dispersão das partículas de Si e presença de dendritas na ZF. A fratográfia por MEV em modo de imageamento por elétrons secundários, permitiu analisar as superfícies de fratura do compósito em estudo (AA356+SiC), fraturado após o ensaio de tenacidade em Flexão três pontos, identificando a presença de muitos dimples que formavam uma estrutura alveolar, conhecida como uma estrutura típica de um regime dúctil. Por meio desta técnica, também foi possível detectar os principais mecanismos de tenacificação nos CMM, tais como: trincamento, descolamento ou destacamento das partículas de SiC, e o crescimento e coalescência de dimples na estrutura da matriz, os quais foram identificados e correlacionados com o desempenho mecânico dos corpos de prova analisados. A microanálise química por EDS permitiu o mapeamento dos elementos químicos presentes nas regiões do Metal Base (MB) e na Zona Termicamente Afetada (ZTA) do CMM. Por meio desta técnica, foi possível identificar a presença das partículas de Si e SiC, os elementos químicos presentes nas regiões dendriticas, os elementos fragilizantes presentes na microestrutura do CMM, tais: como Fe, Cr e Mn, e a presença de carbeto de Aluminio-Silício (Al4SiC4) presentes nas ZF, em forma de agulhas. A microanálise química foi realizada tanto nas regiões das juntas soldadas quanto nas superfícies de fraturas provenientes do ensaio de tenacidade em Flexão três pontos. / This work focuses on the characterization of a joint welded bead-on-plate of SiC particulate-reinforced A356-alloy welded by high power fiber laser. The welding was achieved in two samples with different conditions, both with T6 applied, before (sample A) and after (sample B) the welding process respectively. Samples A and B were performed materialographic analysis by Optic Microscopy of light reflected (O.M) and scanning electron microscopy (SEM), were also performed chemical microanalysis by energy dispersive X-ray , mechanical testing microhardness and X-ray diffraction. Specimens submitted to the three point bending toughness test present a thermal condition similar to sample A, because this thermal condition is the condition that normally the Metal Matrix Composite (MMC) exhibits in service. The inspection metallographic by (O.M) identified heat treatment T6 interference in the sample A, and though this is it was possible to identify low proportion of Si particles in the matrix, while the analysis was approaching fused zone, and the presence of a metastable structure with formation of dendrites in the fused zone, were which promptly correlated with results of microhardness. The sample B exhibited more homogenous a microstructure in terms of dispersion of Si particles. SEM fractography in secondary electron imaging mode allowed to analyze fracture surface of MMC, identifying the presence of more microvoids creating an alveolar structure typical of an ductile regime. Through this technique, it also was possible to detect main toughening mechanisms for MMC, such as, cracking, debonding and growth and coalescence dimples in the structure the of matrix which were identified and correlated with performance of specimens analyzed. EDS micro-chemical analysis allowed to map chemistry elements present in various regions of CMM, such as, Base Metal (BM), heat affected zone (HAZ) and Fused Zone (FZ). Through this technique, it was possible to identify and quantify the presence of Si and SiC particles, the elements present in the dendrites and presence of embrittlement elements in the microsctructure of MMC, such as, Fe,Cr and Mn and presence of needle-shapped Aluminium-Silicon carbides (Al4SiC4) in the FZ of sample A. Chemical microanalyses were performed both in regions of welded joints and in surface of fracture from the three points bending toughness test.

Made available in DSpace on 2014-06-11T19:28:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-01Bitstream added on 2014-06-13T19:48:08Z : No. of bitstreams: 1 ranieri_k_me_guara.pdf: 3916943 bytes, checksum: 88678d123d4709bfb7b9722e94a20ebd (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / Este trabalho apresenta o projeto e a construção de um equipamento para a produção de lingotes de compósitos de matriz metálica, com ligas de baixo ponto de fusão, e material de reforço na forma de pó cerâmico. O equipamento pode operar em temperaturas de até 1000 °C e carga de aproximadamente 800 g de metal. Possui um sistema para agitação do metal fundido e a possibilidade de controle dos principais parâmetros, térmicos e mecânicos, do processo de fundição com agitação mecânica. São descritas as diferentes partes do equipamento, e apresentados resultados utilizando a liga Al7%Si com reforço de alumina, sem recobrimento, e em granulações diferentes. A rota utilizada envolve a fusão do metal, seguida pelo seu resfriamento até temperaturas entre as linhas liquidus e solidus, seguida pela mistura da alumina, por determinado tempo, e o reaquecimento para vazamento. O equipamento mostrou-se eficiente na obtenção de compósitos particulados. Os lingotes obtidos foram analisados por microscopia eletrônica de varredura, EDS e microscopia óptica. / This work presents the project and construction of an equipment for synthesis of particulated metal matrix composite ingots, with low melting point, and ceramic as reinforcement material, using mechanical stir casting. The equipment can operate in temperatures up to 1000° C and loading of about 800g of metal. It has a system to stir the metal with the possibility of controling the main, thermal and mechanical, parameters of the process. Different parts of the equipament are described and results are presented by using the Al 7% Si alloy, with alumina, without recovering, and with different granulation. The process used was melting the metal followed by its cooling up to temperatures between liquidus and solidus lines, followed by the mixing of alumina and the reheating for pouring . The equipment was efficient in the obtainment of particulated metal matrix composite. The ingots obtained were analysed through electronic microscopy, EDS and optical microscopy.

Compósitos de matriz metálica (CMM) reforçados com dois tipos de particulado cerâmico foram produzidos por meio do processo ARB (Accumulative Roll Bonding) a fim de estudar os efeitos destes no que diz respeito às propriedades mecânicas e microestruturais. ARB é um processo de deformação plástica severa aplicada originalmente a uma pilha de lâminas metálicas, a qual é laminada, seccionada em duas metades, as quais são empilhadas e novamente laminadas, e assim por diante, desenvolvido com o propósito de reduzir o tamanho de grão e aumentar a resistência mecânica do produto final. O processo é econômico e capaz de produzir de folhas ultrafinas a placas espessas, sem que haja restrição de quantidade. Confeccionou-se CMM de alumínio reforçados com partículas de carbeto de silício (Al+SiCp) e alumina (e Al+Al2O3p) com granulometria média de 40µm, as quais foram caracterizadas microestruturalmente e ensaiadas em tração até a falha, cuja análise foi conduzida via microscopia eletrônica de varredura. Ambas as amostras obtiveram ganho em sua resistência mecânica, comparadas ao alumínio monolítico (sem adição de partículas de reforço) e alumínio recozido. Foram ensaiados em tração corpos de prova com e sem presença de entalhe, sendo que as peças entalhadas apresentaram comportamento esperado de aumento de resistência mecânica e baixo alongamento e fratura de aspecto frágil. De acordo com análise feita por fratografia houve boa ancoragem e dispersão das partículas de reforço na matriz. / Metal matrix composite (CMM) reinforced with two types of ceramic particles have been produced through the process ARB (Accumulative Roll Bonding) in order to study their effect as regards the mechanical and microstructural properties. ARB is a severe plastic deformation process originally applied to a stack of metal sheets, which is laminated, sectioned into two halves, which are stacked and rolled again, and so on, developed with the purpose of reducing the grain size and increase the mechanical strength of the final product. The process is economical and capable of producing ultrafine sheets to thicker plates without much restriction. Were fabricated CMM of the aluminum reinforced with particles of silicon carbide (Al + SiCp) and alumina (and Al + Al2O3p) with an average particle size of 40μm, which are characterized microstructurally and tested in tension until failure, whose analysis was conducted via scanning electron microscopy. Both samples were successful in its mechanical strength compared to the monolithic aluminum (without addition of reinforcing particles) and annealed aluminum. They were tested for tensile specimens with and without the presence of notch, and the carved pieces showed strength-enhancing behavior and low elongation and frail fracture. According to analysis by fractography was good anchoring and reinforcement particles dispersed in the matrix.

Les composites à matrice titane (CMTi) sont des matériaux attractifs pour des applications aéronautiques, en raison de leurs performances mécaniques à haute température et de leur faible densité. La difficulté d’usiner ce type de matériaux rend les procédés de fabrication additive intéressants pour la fabrication de pièces complexes en trois dimensions. Cette étude porte sur l'élaboration de composites à matrice titane par le procédé de fabrication additive par fusion laser de poudre projetée. Dans un premier temps, différents types de poudres- renfort et de préparations de poudre ont été utilisés pour faciliter la mise en œuvre du procédé additif, dans le but d’obtenir des microstructures homogènes. Dans un second temps, l’étude s’est concentrée sur le mélange Ti-6Al-4V / B4C formant des renforts TiB et TiC par voie in-situ dans une matrice de Ti-6Al-4V. Les mécanismes de formation des microstructures obtenues ont pu être expliqués puis une étude des propriétés mécaniques (dureté, module d’Young et comportement sous une sollicitation en traction à chaud et à l’ambiante) a été réalisée afin d’évaluer l’effet du renforcement sur les propriétés mécaniques du matériau. Parmi les résultats importants ce cette étude, la présence de taux de carbone élevés en solution solide dans la matrice de titane a été évoqué comme étant le facteur prédominant dans l'augmentation des propriétés mécaniques avec le taux de B4C. / Titanium matrix composites are attractive materials for aeronautical applications, mainly because of their superior mechanical resistance at elevated temperature, combined with a low density. The critical machinability of such composites makes additive manufacturing processes particularly adapted for building complex 3D shapes. This study has been focused on the Direct Metal Deposition (DMD) of Metal matrix composites. In a first step, various powders and powder blends have been carried out in order to facilitate the DMD process and to obtain homogeneous microstructures. Following this, Ti-6Al-4V / B4C powder blends, allowing to obtain TiB + TiC particles distributed in the Ti matrix were more specifically considered. Metallurgical mechanisms involved in the formation of microstructures were identified prior to an investigation on mechanical properties at ambient and elevated temperature for various DMD process conditions and particle concentrations. Among the most interesting results of this study, the influence of a high carbon content solubilized in the Ti-matrix was considered as a dominant factor to explain the evolution of mechanical properties with increased amounts of reinforcements.

No description available.

<p>Aluminum alloys have broad applications in aerospace, automotive, and defense industries as structural material due to the low density, high-specific strength, good castability and formability. However, aluminum alloys commonly suffer from problems such as low yield strength, low stiffness, and poor wear and tear resistance, and therefore are restricted to certain advanced industrial applications. To overcome the problems, one promising method is the fabrication of aluminum matrix composites (AMCs) by introducing ceramic reinforcements (fibers, whiskers or particles) in the metal matrix. AMCs typically possess advanced properties than the matrix alloys such as high specific modulus, strength, wear resistance, thermal stability, while remain the low density. Among the AMCs, particulate reinforced aluminum matrix composites (PRAMCs) are advantageous for their isotropic properties, ease of fabrication, and low costs. Particularly, the PRAMCs with in-situ particulate reinforcements have received great interest recent years. The in-situ fabricated particles are synthesized in an aluminum matrix via chemical reactions. They are more stable and finer in size, and have a more uniform distribution in the aluminum matrix and stronger interface bonding with aluminum matrix, compared to the ex-situ particulate reinforcements. As a consequence, the in-situ PRAMCs have superior strength and mechanical properties as advanced engineering materials for a broad range of industrial applications.</p> <p>This dissertation focuses on the investigation of high strength aluminum matrix composites reinforced with in-situ particulates. The first chapter provides a brief introduction for the studied materials in the dissertation, including the background, the scope, the significance and the research questions of the study. The second chapter presents the literature review on the basic knowledge, the fabrication methods, the mechanical properties of in-situ PRAMCs. The strengthening mechanisms and strategies of in-situ PRAMCs are summarized. Besides, the micromechanical simulation is introduced as a complementary methodology for the investigation of the microstructure-properties relationship of the in-situ PRAMCs. The third chapter shows the framework and methodology of this dissertation, including material preparation and material characterization methods, phase diagram method and finite element modelling. </p> <p>In Chapter 4, the microstructures and mechanical properties of in-situ Al₃Ti particulate reinforced A356 composites are investigated. The microstructure and mechanical properties of in-situ 5 vol. % Al₃Ti/A356 composites are studied either taking account of the effects of T6 heat treatment and strontium (Sr) addition or not. Chapter 5 studies the evolution of intermetallic phases in the Al-Si-Ti alloy during solution treatment, based on the work of Chapter 4. The as-cast Al-Si-Ti alloy is solution treated at 540 °C for different periods between 0 to 72 h to understand the evolution of intermetallic phases. In Chapter 6, a three-dimensional (3D) micromechanical simulation is conducted to study the effects of particle size, fraction and distribution on the mechanical behavior of the in-situ Al₃Ti/A356 composite. The mechanical behavior of the in-situ Al₃Ti/A356 composite is studied by three-dimensional (3D) micromechanical simulation with microstructure-based Representative Volume Element (RVE) models. The effects of hot rolling and heat treatment on the microstructure and mechanical properties of an in-situ TiB₂/Al2618 composite with minor Sc addition are investigated in Chapter 7. TiB₂/Al2618 composites ingots were fabricated <i>in-situ</i> via salt-melt reactions and subjected to hot rolling. The microstructure and mechanical properties of the TiB₂/Al2618 composite are investigated by considering the effects of particle volume fraction, hot rolling thickness reduction, and heat treatment. </p>