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The effects of oxidation in the thermomechanical response of porous titanium diboride have been investigated. An in-house quasi-static material point method tool was used to perform two -dimensional plane strain simulations on unoxidized hexagonal representative volume elements (RVEs) with macroporosity volume fractions of 10%, 40% and 70% to establish a baseline for the response due to geometric effects. Compressive strains of up to 30% were applied at room temperature. The 10% and 40% RVEs showed shear banding and subsequent shear failure of the inter-pore struts, while shear banding in 70% RVE weakened the struts, which lead to buckling failure. A snapshot oxidation model was then applied to the hexagonal RVEs in place of a transient, diffusion-based oxidation solver. Compressive strain simulations were performed on RVEs with oxide layers ranging from 5 to 50 μm. In RVEs with porosity of 40% or higher, oxide percolation in the struts reduced the effective elastic modulus and compressive strength, though further oxidation beyond the percolation point did not have a significant impact. Ramped and cyclic thermal loads were applied and the damage due to thermal expansion coefficient mismatch at the oxide-substrate interface decreased as the oxide layer was increased. Finally, the snapshot oxidation modeling approach was applied to large porous RVEs derived from micro-computed tomography images of titanium diboride foam. The effective elastic modulus decreased by 47% when the 5 μm layer was applied due to many thin, flexible struts becoming fully oxidized. Subsequent oxidation did not have a significant impact on the thermomechanical response. / Master of Science / Thermal loading experienced by hypersonic flight vehicles has posed significant design challenges in the development of platforms for military and re-entry applications. The advent of hypersonic strike weapons and waveriders has led to an interest in utilizing ceramics with melting points above 3000°C, called ultra-high temperature ceramics (UHTCs), that offer improved resistance to high-temperature oxidation. Beyond load-carrying applications, UHTCs imbued with macroscale porosity have been introduced as candidates for providing thermal insulation of sensitive on-board components. This thesis presents a first pass at modeling the coupled effects of oxidation and continuum damage in the thermomechanical response of such materials. Using an in-house material point method tool, two-dimensional compressive strain simulations were performed on hexagonal representative volume elements (RVEs) of titanium diboride foam with varying levels of macroporosity, along with large porous RVEs derived from micro-computed tomography images of titanium diboride foam. A snapshot oxidation model was applied to these RVEs in place of a transient, diffusion-based oxidation solver, then simulations with applied compressive strains of up to 30% were performed on RVEs with oxide layers ranging from 5 to 50 μm. Ramped and cyclic thermal loads were applied to explore the effects of thermal expansion mismatch between the substrate and oxide phases. The oxide layers were shown to reduce the effective stiffness, compressive strength, and thermal conductivity of the RVEs, with the oxidation state of the inter-pore struts having a large impact on the overall material response.

The research focus was to determine diffusion mechanisms responsible for densification behavior of SHS produced Al2O3/TiB2 Ceramic Matrix Composites (CMCs). Previous research has shown SHS produced Al₂O₃/TiB₂ composites exhibited unique microstructural properties that contributed to high strength, fracture toughness, and hardness properties. Pressureless densification of SHS produced Al₂O₃/TiB₂ composites would provide a cost savings because the equipment for pressureless densification is less expensive and less complicated than equipment required for densification with pressure. Models for sintering of CMCs and calculation of Sintering Time Constants (STC) were used to predict the densification behavior of the SHS produced Al2O3/TiB2 composite. The Levin, Dirnfeld, Shwam equation was used to determine the Rate Controlling Diffusion Mechanism (RCDM) and activation energy for sintering. X-Ray Diffraction (XRD) analysis of the as-milled reaction product powder revealed the presence of an aluminum borate (Al₁₈B₄O₃₃) as a third phase, as well as, in pressureless heat treated samples. Based on experimental results and analysis, it seemed possible the Al₁₈B₄O₃₃ compound may have formed by reaction of Al₂O₃ with TiB2 along their interfaces. Aluminum borates have been observed to form Al₁₈B₄O₃₃ (s) + B₂O₃ (l) at temperatures above 1000°C. The RCDM for densification of SHS produced Al₂O₃/TiB₂ was found to be liquid phase diffusion with volume diffusion also likely being active during densification. In addition, Al₁₈B₄O₃₃ seemed to be the preferred compound formed during oxidation. Further research should be performed to control formation of Al₁₈B₄O₃₃; as well as, on the oxidation behavior of the SHS produced Al2O3/TiB2. / Master of Science

The use of electrospun polystyrene (PS) fibers to create continuous long range ordered multi-scale porous structures in titanium diboride (TiB2) is investigated in this work. The introduction of electrospun PS fibers as a sacrificial filler into a colloidal suspension of TiB2 allows for easy control over the pore size, porosity, and long range ordering of the porous structures of the sintered ceramic. Green bodies were formed by vacuum infiltrating an electrospun-fiber-filled mold with the colloidal TiB2 suspension. The size, volume, distribution, and dispersion of the pores were optimized by carefully selecting the sacrificial polymer, the fiber diameter, the solvent, and the solid content of TiB2. The green bodies were partially sintered at 2000 C in argon to form a multiscale porous structure via the removal of the PS fibers. Aligned continuous cylindrical pores were derived from the PS fibers in a range of ~5 - 20 μm and random porosity was revealed between the ceramic particles with the size of ~0.3 - 1 μm. TiB2 near-net-shaped parts with the multi-scale porosities (~50 to 70%) were successfully cast and sintered. The multi-scale porous structure produced from electrospun fibers was characterized both thermally and mechanically, at room temperature. The conductivity ranged from 12-31 W m^(-1) K^(-1) at room temperature and the compressive strength ranged from 2-30 MPa at room temperature. Analytical thermal and mechanical models were employed to understand and verify he processing-structure-properties relationship. Finally, a method was devised for estimating the effective thermal conductivity of candidate materials for UHTC applications at relevant temperatures using a finite difference model and a controlled sample environment. This low-cost processing technique facilitates the production of thermally and mechanically anisotropic structures into near-net shape parts, for extreme environment applications, such as ultra high temperature insulation and active cooling components. / MS / Society is on the cusp of hypersonic flight which will revolutionize defense, space and transport technologies. Hypersonic flight is associated with conditions like that of atmospheric re-entry, high heat and force or specific locations of a space craft. The realization of hypersonic flight relies on innovative materials to survive the harsh conditions for repeated flight. We have created a new material with tiny holes that can help prevent heat flow from the harsh atmosphere from damaging the hypersonic craft. Thesis tiny holes are made from placing a polymer fiber in an advanced ceramic (which withstand high temperatures) and removing the fiber to leave holes. The tiny hole’s effect on strength and heat flow have been studied, to understand how the tiny holes can be made better. It is difficult to test materials in the harsh atmosphere associated with hypersonic flight, so a program has been written to estimate thermal properties of candidate materials for hypersonic flight.

Made available in DSpace on 2017-07-21T20:42:42Z (GMT). No. of bitstreams: 1 Cristiano da Silva.pdf: 5271302 bytes, checksum: 25a5bdf4a3671c9a497d93fa788662df (MD5) Previous issue date: 2014-01-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work aims at verifying the influence of processing by high energy ball milling of titanium diboride (TiB2), to increase the effect of grain refining of high-purity aluminum. Various mills were carried out by varying the ratio of the initial TiB2 and aluminum charges. After obtaining the milling products, they were compressed in a cylindrical array as a uniaxial compressive stress of 100MPa, some were later sintered at 600°C for 30 minutes. The tablets were introduced in the metal bath of aluminum and castings at 800°C in thermal analysis cups. In metal baths, experiments with and without the presence of titanium as a solute, in addition to the variation of the content of TiB2 (0.15 and 0.30 wt%) can be observed. The results indicate a significant reduction in grain size, especially in the samples were nucleated with pellets which were sintered before being added to the bath. / Este trabalho, tem por objetivo, verificar a influência do processamento por moagem de alta energia em moinho de bolas, do diboreto de titânio (TiB2), visando aumentar o efeito de refino de grãos do alumínio de alta pureza. Várias moagens foram realizadas, variando-se a razão de alumínio e TiB2 das cargas iniciais. Após a obtenção dos produtos de moagem, os mesmos foram compactados em uma matriz cilíndrica uniaxial como uma tensão de compressão de 100MPa, algumas posteriormente foram sinterizadas à 600°C por 30 minutos. As pastilhas foram introduzidas no banho metálico de alumínio e vazadas à 800°C em copos para análise térmica. Nos banhos metálicos, experimentos sem e com a presença de titânio como soluto, além da variação do teor de TiB2 (0,15 e 0,30%p) também podem ser observados. Os resultados indicam uma redução significativa no tamanho de grão, especialmente nas amostras que foram nucleadas por pastilhas que foram sinterizadas antes de serem adicionadas ao banho.

The mechanical properties of boron carbide (B4C) with 10 and 20 vol% particulate inclusions of commercially available nano-sized alpha-phase silicon carbide (a-SiC) or micron-sized titanium diboride (TiB2) were investigated so as to produce a fine-grained material with high hardness, toughness, and overall strength in order to increase the effectiveness of B4C as a structural ceramic, whose use in the field has been limited because of the extreme brittle nature of the material. Full density sintering of the ceramics (≥99% theoretical) was completed using the novel Plasma Pressure Compaction (P²C®) technique, which limited grain growth due to a reduced processing temperature and a significantly reduced consolidation time. The reinforced ceramic composites had particulate grains homogeneously distributed within the B4C matrix. X-ray diffraction patterns confirmed that the constituents did not interdiffuse. The four-point flexure strength for the monolithic B4C ceramic was found to be significantly larger than any recorded value found in scientific literature, and was most likely attributed to the fine-grained microstructure resulting from the P²C® processing. The mechanical properties of the nano-sized a-SiC-B4C ceramics showed a slight increase in the Chevron-notched four-point bend fracture toughness due to the crack deflection toughening mechanism. A slight decrease in the Vickers microhardness and the static elastic modulus values were also observed. A significant increase in the fracture toughness as well as a slight increase in the microhardness and elastic modulus of the micron-sized TiB2-B4C materials was found. The toughening mechanism of this composite was attributed to the slight chemical bond between the B4C matrix and the ultra-small, ultra-tough TiB2 particulates, which forced a propagating crack to completely rip apart the TiB2 reinforcing particles. This cleaving nature resulted in significant amounts of energy being absorbed by the micron-sized particulates. It was concluded that the composite with 20 vol% TiB2 allowed for the largest gain in toughness because it possessed the largest number of ultra small, ultra tough particulate-cracktip interactions.

This work presents a systematic study of the mechanochemical processes leading to chemical reactions occurring due to effects of high-strain-rate deformation associated with uniaxial strain and uniaxial stress impact loading in highly heterogeneous metal powder-based reactive materials, specifically compacted mixtures of Ti/Al/B powders. This system was selected because of the large exothermic heat of reaction in the Ti+2B reaction, which can support the subsequent Al-combustion reaction. The unique deformation state achievable by such high-pressure loading methods can drive chemical reactions, mediated by microstructure-dependent meso-scale phenomena. Design of the next generation of multifunctional energetic structural materials (MESMs) consisting of metal-metal mixtures requires an understanding of the mechanochemical processes leading to chemical reactions under dynamic loading to properly engineer the materials. The highly heterogeneous and hierarchical microstructures inherent in compacted powder mixtures further complicate understanding of the mechanochemical origins of shock-induced reaction events due to the disparate length and time scales involved. A two-pronged approach is taken where impact experiments in both the uniaxial stress (rod-on-anvil Taylor impact experiments) and uniaxial strain (instrumented parallel-plate gas-gun experiments) load configurations are performed in conjunction with highly-resolved microstructure-based simulations replicating the experimental setup. The simulations capture the bulk response of the powder to the loading, and provide a look at the meso-scale deformation features observed under conditions of uniaxial stress or strain. Experiments under uniaxial stress loading reveal an optimal stoichiometry for Ti+2B mixtures containing up to 50% Al by volume, based on a reduced impact velocity threshold required for impact-induced reaction initiation as evidenced by observation of light emission. Uniaxial strain experiments on the Ti+2B binary mixture show possible expanded states in the powder at pressures greater than 6 GPa, consistent with the Ballotechnic hypothesis for shock-induced chemical reactions. Rise-time dispersive signatures are consistently observed under uniaxial strain loading, indicating complex compaction phenomena, which are reproducible by the meso-scale simulations. The simulations show the prevalence of shear banding and particle agglomeration in the uniaxial stress case, providing a possible rationale for the lower observed reaction threshold. Bulk shock response is captured by the uniaxial strain meso-scale simulations and is compared with PVDF stress gauge and VISAR traces to validate the simulation scheme. The simulations also reveal the meso-mechanical origins of the wave dispersion experimentally recorded by PVDF stress gauges.

Ce travail est dédié á l´étude de l´influence de nano-particules de alumina (Al2O3) et de di-borure de titane (TiB2) sur la solidification, la microstructure et les propriétés thermiques et mécaniques de l´alliage d´aluminium renforcés, Al-Si9Cu3Fe1. Les matériaux ont été obtenus par un procédé de fonderie à haute pression en coulant les alliages dans les mêmes conditions que les alliages non renforcés correspondants.On a constaté que les particules de Al2O3 et de TiB2 ont une influence directe sur les caractéristiques de l´alliage telles que la microstructure, la précipitation des phases pendant la solidification et les propriétés mécaniques et électriques. On a ainsi montré que les particules de Al2O3 et de TiB2 peuvent être utilisées pour ajuster les caractéristiques des alliages et obtenir des propriétés spécifiques pour des applications dans les secteurs de matériaux légers. / The work has been focused on the study of the influence of TiB2 and Al2O3 nano-particles (up to 1 wt. %) on the properties and physical features of an aluminium casting alloy, Al-Si9Cu3Fe1.Samples have been obtained through the High Pressure Die Casting (HPDC) process and compared with unreinforced samples obtained at the same conditions. It has been observed that the Al2O3 and TiB2 particles have a direct influence on several features of the alloy such as the microstructure and precipitating phases as well as in the improvement of the soundness and mechanical and electrical properties. Al2O3 and TiB2 particles can be used to tailor the properties of the alloy and to match the specifications of light weight applications

Zirconium- and titanium- based compounds (borides, carbides and nitrides) are of importance because of their attractive properties including: high melting temperature, high-temperature strength, high hardness, high elastic modulus and good wear-erosion-corrosion resistance. The ultra high temperature ceramics (UHTCs) - zirconium diboride (ZrB2) and zirconium carbide (ZrC) in combination with SiC are potential candidates for ultra-high temperature applications such as nose cones for re-entry vehicles and thermal protection systems, where temperature exceeds 2000°C. Titanium nitride (TiN) and titanium diboride (TiB2) composites have been considered for cutting tools, wear resistant parts etc. There are problems in the processing of these materials, as very high temperatures are required to produce dense composites. This problem can be overcome by the development of composites through reactive hot processing (RHP). In RHP, the composites are simultaneously synthesized and densified by application of pressure and temperatures that are relatively low compared to the melting points of individual components. There have been earlier studies on the fabrication of dense ZrB2-ZrC, ZrB2-SiC and TiN-TiB2 composites by the following methods: Pressureless sintering of preformed powders at high temperatures (1800-2300°C) with MoSi2, Ni, Cr, Fe additions Hot pressing of preformed powders at high temperatures (1700-2000°C) with additives like Ni, Si3N4, TiSi2, TaSi2, TaC Melt infiltration of Zr/Ti into B4C preform at 1800-1900°C to produce ZrB2-ZrC-Zr and TiB2-TiC composites RHP of Zr-B4C, Zr-Si-B4C and Ti-BN powder mixtures to produce ZrB2-ZrC, ZrB2-SiC and TiN-TiB2 powder mixtures at 1650-1900°C Spark plasma sintering of powder mixtures at 1800-2100°C There has been a lack of attention paid to the conditions under which ceramic composites can be produced by simple hot pressing (~50 MPa) with minimum amount of additives, which will not affect the mechanical properties of the composites. There has been no systematic study of microstructural evolution to be able to highlight the change in relative density (RD) with temperature during RHP by formation of sub-stoichiometric compounds, and liquid phase when a small amount of additive is used. The present study has been undertaken to establish the experimental conditions and densification mechanisms during RHP of Zr-B4C, Zr-B4C-Si and Ti-BN powder mixtures to yield (a) ZrB2-ZrC, (b) ZrB2-SiC, (c) ZrB2-ZrC-SiC and (d) TiN-TiB2 composites. The following reactions were used to produce the composites: (1) 3 Zr + B4C → 2 ZrB2 + ZrC (2) 3.5 Zr + B4C → 2 ZrB2 + 1.52rCx- 0.67 (3) (1+y) Zr + C → (1+y) ZrCx- 1/ (1+y) (y=0 to 1) (4) 2 Zr + B4C + Si → 2 ZrB2 + SiC (5) 2.5 Zr + B4C + 0.65 Si → 2 ZrB2 + 0.5 ZrCx + 0.65 SiC (6) 3.5 Zr + B4C + SiC → 2 ZrB2 + 1.5 ZrCx + SiC (5 to 15 vol%) (7) (3+y) Ti + 2 BN → (2+y) TiN1/(1+y) + TiB2 (y=0 to 0.5) (a) ZrB2-ZrC Composites: The effect of different particle sizes of B4C (60-240 μm, <74 μm and 10-20 μm) with Zr on the reaction and densification of composites has been studied. The role of Ni addition on reaction and densification of the composites has been attempted. The effect of excess Zr addition on the reaction and densification has also been studied. The RHP experiments were conducted under vacuum in the temperature range 1000-1600°C for 30 min without and with 1 wt% Ni at 40 MPa pressure. The RHP composites have been characterized by density measurements, x-ray diffraction for phase analysis and lattice parameter measurements, microstructural observation using optical and scanning electron microscopy. Selected samples have been analyzed by transmission electron microscopy. The hardness of the composites has also been measured. The results of the study on the effect of different particle sizes B4C and Ni addition on reaction and densification in the stoichiometric reaction mixture as follows. With the coarse B4C (60-240 μm and <74 μm) particles the temperature required are higher for completion of the reaction (1600°C and above). The microstructural observation showed that the material is densified even in the presence of unreacted B4C particles. The composite made with 10-20 μm B4C and 1 wt% Ni showed completion of the reaction at 1200°C, whereas composite made without Ni showed unreacted B4C (∼3 vol%) and the final densities of both the composites are similar (5.44 g/cm3). Increase in the temperature to 1400°C resulted in the completion of the reaction (without Ni) accompanied with a relative density (RD) of 95%. The composites produced with and without Ni at 1600°C had similar densities of 6.13 g/cm3 and 6.11 g/cm3 respectively (~97.3% RD). The Zr-Ni phase diagram suggests that the addition of Ni helps in formation of Zr-Ni liquid at ~960°C and leads to an increase in the reaction rate up to 1200°C. Once the reaction is completed, not enough Zr is available to maintain the liquid phase and further densification occurs through solid state sintering. The grain sizes of ZrB2 and ZrC phases after 1200°C are 0.4 μm and 0.3 μm, which are much lower than those reported in literature (2-10 μm), and may be the reason for reducing the densification temperature to 1600°C for stoichiometric ZrB2-ZrC composites. The effect of excess Zr (0.5 mol), over and above the stoichiometric Zr-B4C powder mixture, on reaction and densification of the composites is as follows. The formation of ZrB2 and ZrC phases with unreacted starting Zr and B4C is observed at 1000°C and with increase in temperature to 1200°C the reaction is completed. Since microstructural characterization reveals no indication of free Zr, it is concluded that the excess Zr is incorporated by the formation of non-stoichiometric ZrC (ZrCx-0.67). This observation is supported by lattice parameter measurements of ZrC in the stoichiometric and non-stoichiometric composites which are lower than those reported in the literature. X-ray microanalysis of ZrC grains in the stoichiometric and non-stoichiometric composites using transmission electron microscopy confirmed the presence of carbon deficiency. The composite produced at 1200°C showed the density of 6.1 g/cm3 (~97% RD), whereas addition of Ni produced 6.2 g/cm3 (~99% RD). The reduction in densification temperature for the non-stoichiometric composites is due to the presence of ZrCx even in the absence of Ni. The mechanism of densification of the composites at 1200°C is attributed to the lowering of critical resolved shear stress with increasing non-stoichimetry in the ZrC, which leads to plastic deformation during RHP. An additional mechanism may be enhanced diffusion through the structural point defects created in ZrC. The hardness of the composites are 20-22 GPa, which is higher than those of reported in literature due to the presence of a dense and fine grain microstructure in the present work. In order to verify the role of non-stoichiometric ZrC the study was extended to produce monolithic ZrC using various C/Zr ratios (0.5-1). Here again, stoichiometric ZrC does not densify even at 1600°C, whereas non-stoichiometric ZrC can be densified at 1200°C. (b) ZrB2-SiC Composites: Since ZrB2 and ZrC do not have good oxidation resistance unless they are reinforced with SiC, the present study has been extended to produce ZrB2-SiC (25 vol%) composites using Zr-Si-B4C powder mixtures. The samples produced at 1000°C showed the formation of ZrB2, ZrC and Zr-Si compounds with unreacted Zr and B4C and as the temperature is increased to 1200°C only ZrB2 and SiC remained. A fine grain (~0.5 μm) microstructure has been observed at 1200°C. During RHP, it was observed that the formations of ZrC, Si-rich phases and fine grain size at low temperatures was responsible for attaining the high relative density at a temperature of ~1600°C. The relative densities of the composites produced with 1 wt% Ni at 40 MPa, 1600°C for 30 min is 97% RD, where as composites without Ni showed a small amount of partially reacted B4C; extending the holding time to 60 min eliminated the B4C and produced 98% RD. The hardness of the composites is 18-20 GPa. (c) ZrB2-ZrC-SiC Composites: Since ZrC plays a crucial role in densification of ZrB2-ZrC and ZrB2-SiC composites, the study has been extended to reduce the processing temperature for ZrB2-ZrCx-SiC composites by two methods. In one of the methods, Si is added to the non-stoichiometric 2.5Zr-B4C powder mixture which is resulted in ZrB2-ZrCx-SiC (15 vol%) composites with ~98% RD at 1600°C. In another method, SiC particulates are added to the non-stoichiometric 3.5Zr-B4C powder mixture to yield ZrB2-ZrCx-SiCp (5-15 vol%) composites at 1400°C. The density of the 5 vol% SiC composite is 99.9%, whereas addition of 15 vol% SiC reduced the density to 95.5% RD. The mechanisms of densification of the composites are similar to those observed in ZrB2-ZrC composites. The hardness of the composites is 18-20GPa (d) TiN-TiB2 Composites: ZrB2, ZrC, TiB2, and TiN are members of the same class of transition metal borides, carbides and nitrides; however, their densification mechanisms appear to be different. In earlier work, the RHP of stoichiometric 3Ti-2BN powder mixtures yielded dense composite at 1400-1600°C with 1 wt% Ni addition, whereas composites without Ni required at least 1850°C. The major contributor to better densification at 1600°C (with Ni) appeared to be the formation of local Ni-Ti liquid phase at ~942°C (Ti-Ni phase diagram). The present work explores the additional role of non-stoichiometry in this system. It is shown that Ti excess can lead to a further lowering of the RHP temperature, but with a different mechanism compared to the Zr-B4C system. Excess Ti allows the transient alloy phase to remain above the liquidus for a longer time, thereby permitting the attainment of a higher relative density. However, eventually, the excess Ti is converted into a non-stoichiometric nitride. Thus, the volume fraction of a potentially low melting phase is not increased in the final composite by this addition. The contrast between these two systems suggests the existence of two classes of refractory materials for which densification may be greatly accelerated in the presence of non-stoichiometry, either through the ability to absorb a liquid-phase producing metal into a refractory and hard ceramic structure or greater deformability. Conclusions: The study on RHP of ZrB2-ZrC, ZrB2-SiC, ZrB2-ZrC-SiC and TiN-TiB2 composites led to the following conclusions: • It has been possible to densify the ZrB2-ZrC composites to ~97 % RD by RHP of stoichiometric Zr-B4C powder mixture with or without Ni addition. The role of B4C particle size is important to complete both reaction as well as densification. • Excess Zr (0.5 mol) to stoichiometric 3Zr-B4C powder mixtures produces dense ZrB2-ZrCx composite with 99% RD at 1200°C. The densification mechanisms in these non-stoichiometric composites are enhanced diffusion due to fine microstructural scale / stoichiometric vacancies and plastic deformation. • In the case of ZrB2-SiC composites, the formation of a fine microstructure, and intermediate ZrC and Zr-Si compounds at the early stages plays a major role in densification. • Starting with non-stoichiometric Zr-B4C powder mixture, the dense ZrB2-ZrCx-SiC composites can be produced with SiC particulates addition at 1400°C. • Non-stoichiometry in TiN and ZrC is route to the increased densification of composites through enhanced liquid phase sintering in TiN based composites that contain Ni and through plasticity of a carbon-deficient carbide in ZrC based composites.