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

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

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.

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.

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.

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