The sintering behavior to form TiC-Ni-Mo cermet using a nano-size TiC powders was investigated in flowing Argon gas at 1500°C. Nano-sized titanium carbide powders with high purity, high surface area, and low cost were synthesized from carbon coated Ti containing precursors utilizing a patented process. The sintering studies showed that an increase in theoretical density (TD) with increasing molybdenum content. TiC based cermets were characterized using X-ray diffraction (XRD), Vickers hardness, and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Mechanical properties, electrical conductivity and oxidation resistance results shows potential applications as interconnect for Low/Intermediate Temperature Solid Oxide Fuel Cells (SOFC) and machining tool tips.

In the present study / the effects of the powder metallurgical parameters such as the mixing method, compaction pressure, initial tungsten (W) particle size, composition, sintering temperature and sintering time on the sintering behavior of selected high density W-Ni-Cu alloys were investigated. The alloys were produced through conventional powder metallurgy route of mixing, cold compaction and sintering. The total solute (Ni-Cu) content in the produced alloys was kept constant at 10 wt%, while the copper concentration of the solutes was varied from 2.5 wt% to 10 wt%. Mainly liquid phase sintering method was applied in the production of the alloys. The results of the study were based on the density measurements, microstructural characterizations including optical and scanning electron microscopy and mechanical characterizations including hardness measurements. The results showed that the nature of the mixing method applied in the preparation of the powder mixtures has a considerable effect on the final sintered state of W-Ni-Cu alloys. Within the experimental limits of the study, the compaction v pressure and initial W particle size did not seem to affect the densification behavior. It was found that the sintering behavior of W-Ni-Cu alloys investigated in this study was essentially dominated by the Ni content in the alloy and the sintering temperature. A high degree of densification was observed in these alloys with an increase in the Ni content and sintering temperature which was suggested to be due to an increase in the solubility and diffusivity of W in the binder matrix phase with an increase in these parameters, leading to an increase in the overall sintering kinetics. Based on the results obtained in the present study, a model explaining the kinetics of the diffusional processes governing the densification and coarsening behavior of W-Ni-Cu alloys was proposed.

Recently, the evolutions of wireless communication systems are growing rapidly to satisfy the personal communication requirements. Compact, small size, low cost, and multi-function are the major developing trends among these modern wireless communication devices. The use of ceramic materials with high permittivity can effectively reduce the sizes of microwave devices. This thesis consists of two parts: the research of microwave dielectric materials and the implementation of microstrip ceramic antennas. In the first part of the dissertation, the systematic investigations of the microstructure and microwave dielectric properties in respect of BiNbO4-based ceramics and MCAS glass-added Al2O3-TiO2 ceramics have presented. By the addition of CuO, V2O5, or CuO-V2O5 mixture, the BiNbO4 ceramics can be densified at lower sintering temperatures less than 940¢J. The excellent microwave dielectric properties are obtained as 0.5 wt% CuO or V2O5 are added as sintering aids. The exceeded additive amount or sintering temperatures will result in the appearance of abnormal grain growth and the increase of grain boundary inclusions, which will decrease the microwave dielectric properties including the quality factor (Q) and the temperature coefficient of resonant frequency (£nf). The CuO-added BiNbO4 ceramics reveal a negative £nf value and V2O5-added BiNbO4 ceramics reveal a positive one. The £nf values can be reduced to near 0 ppm/¢J by controlling the weight ratio of CuO/V2O5. Another method to reduce the £nf values to near 0 ppm/¢J is the substitution of Sm for Bi. For the (Bi1-xSmx)NbO4 ceramics, the presence of the £]-form of (Bi1-xSmx)NbO4 ceramics will affect the grain growth, density, Q¡Ñf values and £nf values, but that has no apparent effect on £`r values. On the whole, a high permittivity, an acceptable quality factor, and the temperature stable BiNbO4-based ceramic can be obtained. As for (1-x)Al2O3-xTiO2 ceramics, the addition of MCAS glass can lower the sintering temperatures of (1-x)Al2O3-xTiO2 ceramics from 1500¢J to 1300¢J. And the £nf value can be adjusted to near zero by controlling the TiO2 content and sintering temperature. The appearance of Al2TiO5 phase, resulted from the consumption of TiO2, exhibits intense effect on the microwave dielectric properties of (1-x)Al2O3 -xTiO2 ceramics. The major contributions in this research would be the lower sintering temperatures and the near 0 ppm/¢J of £nf value. The 2wt%- MCAS-added (1-x)Al2O3-xTiO2 ceramics sintered at 1300¢J and x = 0.12 has a minimum £nf value of ¡V0.6 ppm/¢J. In the second part of the dissertation, the microstrip antennas with high permittivity BiNbO4 ceramics (£`r = 43) substrate are fabricated. The bandwidths obtained are narrow and insufficient for the WLAN application. The techniques of U-slots patch and stacked structure are used to enhance the bandwidth of the microstrip ceramic antennas by combining the two adjacent resonant modes. The results indicate that the impedance bandwidth can be enhanced from 2.3% to 5.3% by embedding double U-shaped slots in the rectangular patch, or to 4.5% by using stacked patches.

The objective of this research was to design aluminum powder metallurgy (PM) alloys and processing strategies that yielded sintered products with thermal properties that rivaled those of the cast and wrought aluminum alloys traditionally employed in heat sink manufacture. Research has emphasized PM alloys within the Al-Mg-Sn system. In one sub-theme of research the general processing response of each PM alloy was investigated through a combination of sintering trials, sintered density measurements, and microstructural assessments. In a second, the thermal properties of sintered products were studied. Thermal conductivity was first determined using a calculated approach through discrete measurements of specific heat capacity, thermal diffusivity and density and subsequently verified using a transient plane source technique on larger specimens. Experimental PM alloys achieved >99% theoretical density and exhibited thermal conductivity that ranged from 179 Wm-1K-1 to 225 Wm-1K-1. Thermal performance was largely dominated by the amount of magnesium present within the aluminum grains and in turn, bulk alloy chemistry. Data confirmed that the novel PM alloys were highly competitive with even the most advanced heat sink materials such as wrought 6063 and 6061. Two methods of thermal analysis were employed in order to determine the thermal conductivity of each alloy. This first consisted of individual analysis of the specific heat capacity (Cp), thermal diffusivity (?) and density (?) as a function of temperature for each alloy. The thermal conductivity (K) was subsequently determined through the relationship: K=C_p ??. The second means of thermal analysis was a direct thermal conductivity measure using a transient plane source (TPS). The thermal diffusivity and density of samples were both found to decrease with temperature in a linear fashion. Conversely, the specific heat capacity was found to increase with temperature. The only measured thermal property that appeared to be influenced by the alloy chemistry was the thermal diffusivity (and subsequently the calculated thermal conductivity). Both means of thermal analysis showed high thermal conductivity in alloys with low concentrations of magnesium, demonstrating the significance of having alloying elements in solid solution with aluminum. Overall, several alloys were developed using a press and sinter approach that produced higher levels of thermal conductivity than conventional aluminum heat sink materials. The highest thermal conductivity was achieved by alloy Al-0.6Mg-1.5Sn with a calculated value of 225.4 Wm-1K-1. This novel aluminum PM alloy was found to exceed both wrought 6061 and 6063 (195 and 217 Wm-1K-1 respectively). Furthermore, PM alloy Al-0.6Mg-1.5Sn was found to have a significant advantage over die-cast A390 (142 Wm-1K-1).

Homogenization of alloying elements is desired during sintering of powder metallurgy components. The redistribution processes such as penetration of liquid phase into the interparticle/grain boundaries of solid particles and subsequent solid-state  diffusion of alloy element(s) in the base powder, are important for the effective homogenization of alloy element(s) during liquid phase sintering of the mixed powders. The aim of this study is to increase the understanding of alloy element redistribution processes and their effect on the dimensional properties of the compact by means of numerical and experimental techniques. The phase field model coupled with Navier-Stokes equations is used for the simulations of dynamic wetting of millimeter- and micrometer-sized metal drops and liquid phase penetration into interparticle boundaries. The simulations of solid particle rearrangement under the action of capillary forces exerted by the liquid phase are carried out by using the equilibrium equation for a linear elastic material. Thermodynamic and kinetic calculations are performed to predict the phase diagram and the diffusion distances respectively. The test materials used for the experimental studies are three different powder mixes; Fe-2%Cu, Fe-2%Cu-0.5%C, and Fe-2%(Cu-2%Ni-1.5%Si)-0.5%C. Light optical microscopy, energy dispersive X-ray spectroscopy and dilatometry are used to study the microstructure, kinetics of the liquid phase penetration, solid-state diffusion of the Cu, and the dimensional changes during sintering. The wetting simulations are verified by matching the spreading experiments of millimeter-sized metal drops and it is observed that wetting kinetics is much faster for a micrometer-sized drop compared to the millimeter-sized drop. The simulations predicted the liquid phase penetration kinetics and the motion of solid particles during the primary rearrangement stage of liquid phase sintering in agreement with the analytical model. Microscopy revealed that the C addition delayed the penetration of the Cu rich liquid phase into interparticle/grain boundaries of Fe particles, especially into the grain boundaries of large Fe particles, and consequently the Cu diffusion in Fe is also delayed. We propose that the relatively lower magnitude of the sudden volumetric expansion in the master alloy system could be due to the continuous melting of liquid forming master alloy particles. / <p>QC 20140515</p>

Apatite containing bioceramic materials are considered to be potentially useful for replacement or repair of natural bone. In the present study, the aim was to produce a new composite bioceramic containing crystalline apatite and wollastonite phases with a bimodal grain size distribution. The manufacturing scheme was based on the liquid phase sintering process in which the compacts pressed from powders of apatite (HAP or Si&shy / HAP) and pseudowollastonite was sintered in the presence of a liquid phase. Three distinct fluxing agents, magnesium flux (MCAS), sodium feldspar and sodium frit (NCAS), were prepared to act as additives for generating the liquid phase during sintering. Among those, the use of sodium frit resulted in the expected bimodal microstructural assembly. During the sintering studies, it was discovered that the apatite component of the ceramic was prone to compositional modifications by reaction with the liquid phase. This interaction resulted in a formation of siliconized HAP which crystallized in the form of rod-like grains. Meanwhile wollastonite grains tended to exhibit faceted equiaxed morphology and bonded to rod-like apatite grains with the help of a glassy phase. The results showed significant enhancement in the mechanical properties of apatite-wollastonite composites compared to phase pure hydroxyapatite. For example, the sample with 47.5 wt% Si-HAP2 + 47.5 wt% W + 5 wt% NCASfrit had the highest value of flexural strength, 83.6 MPa, which was almost twice that of hydroxyapatite, 46.3 MPa. The results for other properties such as compressive strength, hardness and fracture toughness also demonstrated the benefit of apatite-wollastonite composite approach.

O comportamento dos materiais cerâmicos quanto à resistência ao choque térmico é um tema de grande interesse, devido às aplicações em que a confiabilidade frente a variações bruscas de temperatura é necessária. Neste trabalho foi estudado como a variação na proporção dos aditivos Y2O3:Al2O3 e diferentes parâmetros no processamento do carbeto de silício sinterizado via fase líquida como, tipo e temperatura de sinterização, podem influenciar na resistência ao choque térmico deste material. As misturas foram preparadas com 90%SiC+10%Y2O3:Al2O3 em mol, variando as proporções molares dos óxidos entre 2:1 e 1:4, com e sem prévia reação dos aditivos. As misturas foram compactadas e sinterizadas em forno resistivo de grafite nas temperaturas de 1750°C, 1850°C e 1950°C e, por prensagem a quente, a 1750°C e 1850°C, sendo avaliadas quanto à densificação. Após análise dos resultados preliminares, a sinterização sem pressão e as misturas com proporções 1:3 e 1:4 de Y2O3:Al2O3 previamente reagidos foram selecionadas para o estudo da resistência ao choque térmico. Os ciclos térmicos foram realizados com aquecimento em temperaturas de 600°C, 750°C e 900°C e resfriamento brusco em água em temperatura ambiente. A avaliação das amostras quanto à resistência ao choque térmico, feita por meio da determinação de módulo de elasticidade, porosidade, resistência à flexão e por análise microestrutural de trincas. As amostras sinterizadas na temperatura de 1950°C são as que apresentam o melhor desempenho em relação à resistência ao choque térmico, enquanto a variação na proporção Y2O3:Al2O3 de 1:3 para 1:4 não altera significativamente esta propriedade. Nas condições utilizadas, a temperatura máxima de aplicação do SiC sinterizado via fase líquida deve ser limitada a 750°C, permitindo seu uso como trocadores de calor, rolamentos, mancais de bombas submersas, turbinas a gás e sensor de motores automotivos e aeronáuticos. / The behavior of ceramic materials towards thermal shock resistance is a topic of great interest, due to applications in which the reliability against sudden temperature variations is required. In this thesis, it was studied how the variation in the proportion of Y2O3:Al2O3 additives and different parameters on the processing of liquid phase sintered silicon carbide may influence thermal shock resistance of this material. Samples were prepared with molar composition 90%SiC+10%Y2O3:Al2O3, by varying oxides molar proportion between 2:1 and 1:4, with and without previous reaction of the additives. Mixtures were compacted and sintered in a resistive graphite furnace at 1750, 1850 and 1950°C, and by hot pressing at 1750 and 1850°C, and evaluated for densification. After analysis of the first results, pressureless sintering and the mixtures with proportions of 1:3 and 1:4 of previously reacted Y2O3:Al2O3 were selected for the study of thermal shock resistance. Thermal cycles were performed by heating at temperatures of 600, 750 and 900°C and sudden cooling in water at room temperature. The evaluation of samples regarding thermal shock resistance was conducted by determination of elasticity modulus, porosity, flexural strength and microstructural analysis of the cracks. The samples sintered at 1950°C temperature are those that exhibit the best performance in relation to thermal shock resistance, while the variation in the proportions Y2O3:Al2O3 from 1:3 to 1:4 do not significantly change this property. Under the conditions used, the maximum temperature for liquid phase sintered SiC application must be limited to 750°C, which allows its use as a component of heat exchanges, bearings, pump bearings, gas turbines and sensors of automotive and aeronautical engines.

O comportamento dos materiais cerâmicos quanto à resistência ao choque térmico é um tema de grande interesse, devido às aplicações em que a confiabilidade frente a variações bruscas de temperatura é necessária. Neste trabalho foi estudado como a variação na proporção dos aditivos Y2O3:Al2O3 e diferentes parâmetros no processamento do carbeto de silício sinterizado via fase líquida como, tipo e temperatura de sinterização, podem influenciar na resistência ao choque térmico deste material. As misturas foram preparadas com 90%SiC+10%Y2O3:Al2O3 em mol, variando as proporções molares dos óxidos entre 2:1 e 1:4, com e sem prévia reação dos aditivos. As misturas foram compactadas e sinterizadas em forno resistivo de grafite nas temperaturas de 1750°C, 1850°C e 1950°C e, por prensagem a quente, a 1750°C e 1850°C, sendo avaliadas quanto à densificação. Após análise dos resultados preliminares, a sinterização sem pressão e as misturas com proporções 1:3 e 1:4 de Y2O3:Al2O3 previamente reagidos foram selecionadas para o estudo da resistência ao choque térmico. Os ciclos térmicos foram realizados com aquecimento em temperaturas de 600°C, 750°C e 900°C e resfriamento brusco em água em temperatura ambiente. A avaliação das amostras quanto à resistência ao choque térmico, feita por meio da determinação de módulo de elasticidade, porosidade, resistência à flexão e por análise microestrutural de trincas. As amostras sinterizadas na temperatura de 1950°C são as que apresentam o melhor desempenho em relação à resistência ao choque térmico, enquanto a variação na proporção Y2O3:Al2O3 de 1:3 para 1:4 não altera significativamente esta propriedade. Nas condições utilizadas, a temperatura máxima de aplicação do SiC sinterizado via fase líquida deve ser limitada a 750°C, permitindo seu uso como trocadores de calor, rolamentos, mancais de bombas submersas, turbinas a gás e sensor de motores automotivos e aeronáuticos. / The behavior of ceramic materials towards thermal shock resistance is a topic of great interest, due to applications in which the reliability against sudden temperature variations is required. In this thesis, it was studied how the variation in the proportion of Y2O3:Al2O3 additives and different parameters on the processing of liquid phase sintered silicon carbide may influence thermal shock resistance of this material. Samples were prepared with molar composition 90%SiC+10%Y2O3:Al2O3, by varying oxides molar proportion between 2:1 and 1:4, with and without previous reaction of the additives. Mixtures were compacted and sintered in a resistive graphite furnace at 1750, 1850 and 1950°C, and by hot pressing at 1750 and 1850°C, and evaluated for densification. After analysis of the first results, pressureless sintering and the mixtures with proportions of 1:3 and 1:4 of previously reacted Y2O3:Al2O3 were selected for the study of thermal shock resistance. Thermal cycles were performed by heating at temperatures of 600, 750 and 900°C and sudden cooling in water at room temperature. The evaluation of samples regarding thermal shock resistance was conducted by determination of elasticity modulus, porosity, flexural strength and microstructural analysis of the cracks. The samples sintered at 1950°C temperature are those that exhibit the best performance in relation to thermal shock resistance, while the variation in the proportions Y2O3:Al2O3 from 1:3 to 1:4 do not significantly change this property. Under the conditions used, the maximum temperature for liquid phase sintered SiC application must be limited to 750°C, which allows its use as a component of heat exchanges, bearings, pump bearings, gas turbines and sensors of automotive and aeronautical engines.

This thesis work focus on evaluating the metallurgical bonding between the TiB2 andiron grains in the Fe-TiB2 composite. The starting materials were commercial materialsin form of Ferro-boron and Ferro-titanium that together with pure TiB2 powder formeda material with the composition seen below:FeB + FeTi + TiB2  52.3TiB2 + 45.7Fe + 2TiDuring sintering an iron liquid phase is formed where the boron from the FeB diffuse tothe titanium in FeTi which enables the formation of TiB2. The temperature used in theliquid phase sintering was chosen just above the three phase region, Fe-TiB2-liquid inthe phase diagram, to get an adequate densification of the samples. However, thetemperature could not be too high because of the internal stress and deformation thesamples would have been exposed to.After sintering the material properties and microstructure were examined throughPalmqvist indentations, Fargo and Transverse-Rupture-Strength tests and SEM studiesincluding EBSD.Through these tests the hardness was measured to 1323 HV and the microstructureconsidered to be fine with well distributed phases. The EBSD also showed that thebrittle Fe2B phase is present close to the TiB2 grains and that the porosity givesunreliable results for the Fargo and TRS-tests. The composite was impregnated withcopper to show that it may be possible to achieve wetting of the TiB2 phase by castingand to perform new tests on the material with less porosity.

No description available.