Metal Matrix Composites (MMCs) are used as structural materials because of their ability to have a combination of high strength and good ductility. A common problem with MMCs utiliz-ing vastly different materials is the difficulty in forming a strong matrix/reinforcement interface without suffering extensive dissolution, debonding, or chemical reactions between the compo-nents. In this work, a nickel base amorphous particulate reinforced crystalline nickel matrix composite is processed. The reinforcement, an equimolar NiW amorphous powder, was synthe-sized using the mechanical alloying process. The amorphous and crystalline nickel powders were blended in varying volume fractions and then consolidated using hot-isostatic pressing (HIP). This work reveals that the amorphous NiW reinforcement provides strength and hardness to the ductile Ni matrix while simultaneously maintaining a strong interfacial bond due to the similar chemistry of the two components. The strengthening achieved in the composite is attrib-uted to the particulate/matrix boundary strengthening. / Master of Science

Titanium been used industrially for nearly a century. Ever since it was first reduced to its elemental form, concerted efforts have been made to improve the material and to reduce the cost of production. In this thesis, titanium is mechanically alloyed with cellulose nanocrystals followed by powder consolidation and sintering to form a solid titanium metal matrix composite. Cellulose nanocrystals (CNCs) were chosen as the particle reinforcement as they are a widely abundant and natural material. Additionally, the nanocrystals can be derived from waste materials such as pistachio shells. This offers a unique advantage to act as a green process to enhance the mechanical properties of the titanium as well as to reduce to cost of production. Vibrational milling using a SPEX 8000M mill was used to mechanically alloy titanium powder with varying concentrations of CNCs. Additionally, the milling time was varied. This process showed that varying the concentrations of CNCs between 0.5% - 2% by weight did not noticeably alter the microstructural or mechanical properties of the materials. Conversely, changing the milling time from 0.5 hours to 5 hours proved to greatly alter the microstructural and mechanical properties of the titanium matrix metal composites. Further increasing the milling time to 10 and 25 hours caused the materials to become exceedingly brittle thus, the majority of experiments focused on samples milled between 0.5 hours and 5 hours. The hardness values for the Ti-1%CNC materials increased from 325-450-600-800 for the samples milled for 0.5, 1, 2, and 5 hours respectively. The other concentrations used were found to yield similar values and trends. SEM micrographs showed that small precipitates had formed within the grains except materials milled at 5 hours, which showed the production of very coarse particles at the grain boundaries. Similarly, an attrition mill was used to mechanically alloy titanium with varying CNC concentrations. Milling time was also varied. The powders were consolidated, sintered and characterized. It was found that increasing CNC content at low milling times caused a reduction in hardness. The X-ray diffractograms also showed a trend in that the diffraction patterns shifted to the lower angle with increasing CNC concentration, thereby suggesting that the increase in CNC content facilitated the removal of oxygen atoms housed within the interstitial sites. The oxygen was observed to diffuse and precipitate platelet titanium dioxide particles. These particles were found to be located within the titanium grains and coarsened with milling time. Generally, increasing the milling time to 15 hours was found precipitate particles at the grain boundaries as well as to excessively dissolve oxygen into the titanium lattice leading to embrittlement. The materials milled for 5 hours showed the best increase in strength while maintaining good ductility. / Master of Science / Titanium has only been used industrially since the early 1940’s thanks in large to the modern advances to reduce titanium ore to its elemental state. Titanium gained much interest as a structural material because of its corrosion resistance and its exceptional strength for a lightweight metal, making the material ideal for medical and aerospace applications. Pure titanium was found to be soft and had poor wear resistance, therefore, efforts were made to create titanium alloys which mitigated these weaknesses. Often titanium is alloyed with costly and toxic elements to enhance its strength properties, making it dangerous to use in the medical field. One way to enhance the strength properties of titanium without the addition of these harmful alloying elements is to create a titanium composite by adding strong inert particles to a titanium matrix. One method to create titanium metal matrix composites is to violently mix titanium powder with the reinforcement material, through a process called mechanically alloying. Following the mixing process the powder is then compacted and heated to form a solid part through a process called sintering. While these powder processing methods are known and viable for forming titanium metal matrix composites, some of the reinforcement materials can be expensive. In this thesis, cellulose nanocrystals (CNCs) will be added as reinforcement to titanium by means of two mechanical alloying processes, vibratory milling (shaking) and attrition milling (stirring). CNCs can be derived from plant matter which is widely abundant and inexpensive. The viability of CNCs to be used as a reinforcement material, as well as the mechanical alloying processes were investigated to determine the effect on the titanium strength properties. The powder processing steps were found to cause the CNCs to react with the surrounding titanium matrix which caused beneficial oxides to form as the reinforcement materials. In general, it was found that vibratory milling caused the final titanium metal matrix composite to be hard and brittle. Attrition milling was found to be more favorable as some materials were observed to be strong yet ductile.

Reinforcing metals with compositionally similar amorphous particles has been found to create composites with good interfacial bonding. It is conceivable that significant additional strengthening in amorphous reinforced composites can be realized by creating high-aspect ratio reinforcements; attritor milling holds promise in this regard. In this work, mechanical alloying was used to produce equimolar Ni-W powder that became a composite of amorphous Ni-W with undissolved W crystallites. A mixture of nickel powder and ten volume percent amorphous Ni-W powder was blended by attritor milling for either one or three hours, compacted by combustion-driven compaction and sintered for up to fifty hours at 600ºC. Prolonged times at elevated temperatures led to crystallization of the amorphous reinforcement particles and dissolution of tungsten into the matrix. Vickers macrohardness tests on the sintered composites yielded lower-than-expected values. Microscopy after hardness testing revealed sliding of particles at their boundaries, indicating poor bonding between them. It is believed that the sintering process was compromised by contamination from organic vapor present in the tube furnace used. While attritor milling effected smaller reinforcement particles, the small increase in aspect ratio would likely have been insufficient to cause significant strengthening by shear load transfer. / Master of Science

Metal matrix composites offer unique opportunities for achieving multi-functionality in materials. In an attempt to investigate the possibility of enhancing damping characteristics of structural metals, copper was reinforced with tetragonal ferroelectric BaTiO3 particulates (Cu-BaTiO3 composites) using powder metallurgy techniques. The effect of particulate size and three processing conditions, sintering atmosphere, cooling rate and, uniaxial compaction pressure on the tetragonality and hence the ferroelectric properties of barium titanate powder were investigated using differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The results show that sintering atmosphere and cooling rates have little effect on the tetragonality of barium titanate powder. Tetragonality of barium titanate powder decreased gradually with decreasing particle size. The decrease in tetragonality with decreasing particle size, however, was only severe in the very fine powders. Although no direct relationship was found between uniaxial compaction pressure and tetragonality, uniaxial pressure may also decrease the tetragonality of barium titanate. Three Cu-BaTiO3 composites, D1, D2 and D3 reinforced with 40vol% barium titanate particles of average sizes 209μm, 66μm and 2μm were respectively fabricated. The retention of the ferroelectric tetragonal phase of barium titanate after composite processing was confirmed by DSC. Composite microstructures observed using optical and scanning electron microscopy revealed uniform dispersions of barium titanate particles in D1 and D2. In D3, the barium titanate formed a chain-like structure because of extensive agglomeration of the fine reinforcement particles. Damping characteristics of the composites were evaluated between 25oC and 165oC at a frequency of 1Hz using dynamic mechanical analysis (DMA). The relative damping capacities (tanδ) in the composites were higher than the unreinforced metal. The damping capacity of composites D1 and D2 was also found to be dependent on temperature. Damping capacity was high from room temperature up to the Curie point of barium titanate, after which there was a slight drop in damping values probably due to a loss in ferroelectric properties. The small drop in damping values recorded in excess of the Curie temperature is an indication that ferroelectricity contributes little to the overall damping capacity of the Cu-BaTiO3 composites. This results from either a reduced ferroelectric damping in barium titanate particles or, poor stress transfer from matrix to reinforcement because of the weak and porous copper-barium titanate interface. / Master of Science

A Local Load Sharing (LLS) model recently developed by Curtin and co-workers for the numerical simulation of tensile stress-strain behavior in fiber-reinforced composites is used to predict the tensile strength of metal matrix composites consisting of a Titanium matrix and unidirectionally aligned SiC fibers. This model is extended to include the effects of free boundary conditions and non-constant load gradients and then used to predict the strength of a Ti-6Al-4V matrix reinforced with Sigma SiC fibers under 4-point flexure testing. The predicted tensile and flexure strengths agree very well with the values measured by Gundel and Wawner and Ramamurty et al. The composite strength of disordered spatial fiber distributions is investigated and is shown to have a distribution similar to the corresponding ordered composite, but with a mean strength that decreases (as compared to the ordered composite) with increasing Weibull modulus. A modified Batdorf-type analytic model is developed and similarly extended to the case of non-uniform loading to predict the strength of composites under tension and flexure. The flexure model is found to be inappropriate for application to the experimental materials, but the tensile model yields predictions similar to the Local Load Sharing models for the experimental materials. The ideas and predictions of the Batdorf-type model, which is essentially an approximation to the simulation model, are then compared in more detail to a simulation-based model developed by Ibnabdeljalil and Curtin to more generally assess the accuracy of the Batdorf model in predicting tensile strength and notch strength versus composite size and fiber Weibull modulus. The study shows the Batdorf model to be accurate for tensile strength at high Weibull moduli and to capture general trends well, but it is not quantitatively accurate over the full range of material parameters encountered in various fiber composite systems. / Master of Science

Particulate reinforced Al alloy composites (AlMCs) are recognized as important structural materials due to their lightweight, high modulus and strength and high wear resistance. In order to understand the effect of matrix, reinforcement and secondary processing techniques on the microstructure development and mechanical properties of AlMCs produced by powder metallurgy routes, Al alloy composites reinforced with three types of reinforcements by different secondary processing techniques have been produced and examined. Fabrication of Al or 6061Al alloy based composites reinforced with nano-sized SiC particles (~500nm), micro-sized (<25µm) quasicrystalline alloy particles (hereinafter referred to as “NQX”) and micro-sized Nb particles (~130µm) has been carried out by powder metallurgy routes followed by extrusion or cold rolling. After extrusion, a homogeneous distribution of secondary particles has been obtained with rare interfacial reaction products. The 6061Al/SiC composites exhibit superior mechanical properties than either monolithic alloys or composites reinforced with micro-sized particles with retained ductility while the 6061Al/NQX and 6061Al/Nb composites show limited improvement in tensile strength mainly due to their reinforcement size and poor interfacial bonding. After cold rolling, the evolution in microstructure, texture and strength has been analysed. A typical near β fibre texture with highest intensities near Copper and Brass orientations has been developed for 6061Al/NQX and 6061Al/Nb composites. For 6061Al/SiC composites, a randomized texture with very small grains has achieved due to the presence of the non-deformable SiC particles. Mechanical property tests including microhardness, three-point bending tests and tensile tests have been carried out on cold rolled samples and the results exhibit some level of improvement when compared with as-extruded samples due to work hardening. Finally, the work moves on to the general discussion based on the previous result chapters. The microstructural development related to reinforcement, matrix and interfacial areas during extrusion and cold rolling has been summarised and the correlation between microstructure and mechanical properties has been discussed. The thesis provides a thorough understanding of AlMCs produced by powder metallurgy routes in terms of matrix, reinforcement and processing techniques. It can provide reference to the future development of AlMCs for high strength applications.

Automobile and aero industries have an increasing interestin materials with improved mechanical properties. However, manyof these new materials are classified as difficult-to-cut withconventional tools. It is obvious that tools, cutting processesand cutting models has to be devel-oped parallel to materialsscience. In this thesis rotary cutting tools are tested as analternative toexpensive diamond or cubic bore nitridetools. Metal matrix composites mostly consist of a light metalalloy (such as aluminium or titanium) reinforced with hard andabrasive ceramic parti-cles or fibres. On machining, thereinforcement results in a high rate of tool wear. This is themain problem for the machining of MMCs. Many factors affect thelife length of a tool, i.e. matrix alloy, type, size andfraction of the reinforcement, heat treatment, cuttingconditions and tool properties. In tests, the Al-SiC MMC formed a deformation layer duringmilling, probably affected by lack of cooling. The dominatingfactor for tool life was the cutting speed. Water jet or CO2cooling of turning did not provide dramatic increase in toollife. With PCD, cutting speeds up to 2000 m/min were usedwithout machining problems and BUE formation. Tool flank wearwas abrasive and crater wear created an "orange-peel type" wearsurface. PCD inserts did not show the typical increase in flankwear rate at the end of its lifetime. The use of self-propelled rotary tools seems to be apromising way to increase tool life. No BUE was formed on therotary tool at high cutting data. The measurements indicatethat the rotary tool creates twice as good surface as PCDtools. The longest tool life was gained with an inclinationangle of 10 degrees. Tool costs per component will beapproximately the same, but rotary cutting tool allows higherfeeds and therefore a higher production rate and thus a lowerproduction cost. The rotary cutting operation might have a potential toincrease productiv-ity in bar peeling. The lack of BUE withrotary cutting gives hope on higher tool life. The test resultsshow that tool wear was 27% lower with rotary cutting tools.Increase of cutting speed from 22 to 44 m/min did not affectcutting forces. This indicates that the cutting speed canincrease without significant change in tool wear rate. Issues related to rotary cutting like cutting models,cutting processes, standards, tools and models have beendiscussed. A tool wear model with kinetic energy has beendiscussed. KEYWORDS:Difficult-to-Cut material, Metal MatrixComposite (MMC), Machining, Machinability, Rotary Cutting Tool,Acoustic Emission / <p>QCR 20161026</p>

O presente trabalho tem como objetivo o estudo e aproveitamento de cinzas leves da queima de carvão mineral em termoelétrica, como reforço para o Compósito de Matriz Metálica de cobre. Foram estudados diferentes percentuais de cinzas leves como reforço para o cobre, sendo misturados estes pós através de m , compactando os pós em diferentes pressões e sinterizando os corpos de prova obtidos pela compactação. A amostra sinterizada que apresentou a maior dureza entre todos os corpos de prova sinterizados, atingindo 89 HV, foi utilizada como base para a formulação e obtenção de novos corpos de prova, que foram estudados sob condições de moagem dos pós por moinho de bolas e moagem de alta energia. A fabricação do compósito seguiu os padrões industriais do processo de Metalurgia do Pó, como a mistura e moagem dos pós, compactação dos pós e sinterização em atmosfera controlada. Foi realizado o estudo das propriedades físicas e elétricas do compósito formado por cobre e cinzas leves, que comprovou o aumento da dureza para 122 HV, mantendo a condutividade do cobre puro. Este trabalho proporciona uma nova aplicação para as cinzas leves, utilizando estes resíduos de usinas termoelétricas como matéria prima para reforço mecânico na composição de peças à base de cobre, na indústria metalmecânica. / This paper aims to study and use fly ash from coal-fired thermal power plant, as reinforcement for copper Metal Matrix Composite. Different fly ash percentage were studied as reinforcement for copper. The powders were mixed by "Twin V Mixer'', were compacted at different pressures and the compacted samples were sintered. The sintered sample with the highest hardness among all samples reached 89 HV and was used as basis for the formulation and obtaining of new samples, which were studied under controlled conditions of ball milling and mechanical alloying. The manufacture of the composite was made using Powder Metallurgy processes like mixing and milling of powders, compacting of the powders and sintering at controlled atmosphere. A study on the physical and electrical properties of the composite formed by copper and fly ash was carried out proving the hardness increase to 122 HV and maintaining the conductivity of pure copper. This work provides a new application for fly ash using these power plants waste as raw material for mechanical reinforcement in the composition of copper parts in the metalworking industry.

Orientador: Carlos Kiyan / Banca: Messias Borges da Silva / Banca: Luis Rogério de Oliveira Hein / Banca: Olivério Moreira de Macedo Silva / Resumo: 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. / Abstract: 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. / Doutor

Tungsten carbide-based metal matrix composite coatings are deposited by PTAW (Plasma Transferred Arc Welding) on production critical components in oil sands mining. Homogeneous distribution of the reinforcement particles is desirable for optimal wear resistance in order to reduce unplanned maintenance shutdowns. The homogeneity of the coating can be improved by controlling the heat transfer, solidification rate of the process and the volume fraction of carbide. The degree of settling of the particles in the deposit was quantified using image analysis. The volume fraction of carbide was the most significant factor in obtaining a homogeneous coating. Lowering the current made a modest improvement in homogeneity. Changes made in other operational parameters did not effect significant changes in homogeneity. Infrared thermography was used to measure the temperature of the surface of the deposit during the welding process. The emissivity of the materials was required to acquire true temperature readings. The emissivity of the deposit was measured using laser reflectometry and was found to decrease from 0.8 to 0.2 as the temperature increased from 900C to 1200C. A correction algorithm was applied to calculate the actual temperature of the surface of the deposit. The corrected temperature did increase as the heat input of the weld increased. A one dimensional mathematical model of the settling profile and solidification of the coatings was developed. The model considers convective and radiative heat input from the plasma, the build-up of the deposit, solidification of the deposit and the settling of the WC particles within the deposit. The model had very good agreement with the experimental results of the homogeneity of the carbide as a function of depth. This fundamental model was able to accurately predict the particle homogeneity of an MMC deposited by an extremely complicated process. It was shown that the most important variable leading to a homogeneous coating is to operate at the packing saturation limit of the reinforcement. In the case of the MMC explored, a fully homogeneous coating was obtained with 50 vol% WC in a NiCrBSi matrix. / Materials Engineering