Mo-Si-Al-C-based multiphase compounds and their composites reinforced by micro-SiC and TiC particulates were manufactured by meansof reactive hot-pressed sintering method. Their microstructure and room temperature mechanical properties were studied. The results showedthat Al addition and the ratio of Si/Al exerted a remarkable effect on the reaction products in the Mo-Si-Al-C systems. For the stoichiometricMo5(Si,Al)3C mixed powders with a molar ratio of Mo∶Si∶Al∶C as 5∶1.5∶1.5∶1, the sintered body contained Mo3Si, Mo3Al2C, and Mo5Si3C as themajor reaction products whereas and the minor phases consisted of MoSi2, Mo2C, and Mo(Si,Al)2 compounds. When the starting powder mixturewas off-stoichiometric with a small amount of excess Si, only Mo2C accounted for the minor product. Moreover, the relative contents of the formerthree major phases were affected by the changed Si/Al ratio, where the amounts of Mo3Al2C and Mo5Si3C compounds decreased and increased,respectively with increasing Si/Al ratio. The two multiphase alloys showed poor mechanical properties, due to the existence of residual porosity.In contrast, the composites exhibited superiority in both flexural strength and fracture toughness at room temperature to the Mo-Si-Al-C-basedmultiphase compounds. MSAC1/20 wt.%SiC and MSAC1/20 wt.%TiC composites had a respective flexural strength and fracture toughness of 454and 438MPa, 4.93 and 4.85MPa√m.

NiAl-based alloys and their composites reinforced with in situ formed TiC and externally added ceramic particles are fabricated by hot-pressing.Their microstructures and mechanical properties are evaluated. Comparatively, the Ti-and/or C-alloyed NiAl and the ceramic particulate reinforcedcomposites possess a significant improvement in both flexural strength fracture toughness at room temperature. Nevertheless, the NiAl-TiC-nano-Al2O3 composite has low strength, mainly due to the existence of residual porosity, inhomogeneous distribution and severe agglomeration ofnano-scaled Al2O3 particle within the NiAl matrix.

The processing, microstructures and mechanical properties of intermetallic alloy based on AleMoeZreCo (AMZC) and its composites reinforcedwith micro-sized TiC, partially stabilized zirconia (PSZ)-ZrO2 or SiC particulates were investigated. The results showed that the alloysystem exhibits multi-phase microstructures, composed of several aluminides including ZrAl2, Al5Co2, Al9Co2, AlMo3, Al8Mo3 and Zr2Al. TheAMZC/SiC composite showed poor mechanical properties, due to the existence of residual porosity and weak interfacial bonding. In contrast,the other two composites exhibited superiority in both flexural strength and fracture toughness at room temperature than the AleMoeZreCobasedmulti-phase alloy. Homogeneous distribution of ceramic particles and perfect interfacial bonding accounted for the improvement ofstrength. The addition of TiC or ZrO2 particle into the matrix alloy produced remarkable toughening effect.

Microstructures of Al45-Mo25-Zr25-Ge5 (in at.%, AMZG) alloy, produced by reaction hot pressing of elemental powder mixtures,have shown co-existence of AlMo3, Al3Mo8, ZrAl2, Zr2Al, MoGe2 and ZrGe2. In addition, its composites were fabricated through additionof micro-sized TiC, partially stabilized zirconia (PSZ-ZrO2) or SiC particulates into the pulverized multi-phase aluminide powders.The presence of SiC particulates showed a much less significant contribution to the strength/toughness enhancement of AMZG alloy,due to the existence of residual porosity and weak interfacial bonding. In contrast, the other two composites were superior in both flexuralstrength and fracture toughness to the AMZG multi-phase alloy, which is derived from the contribution of uniformly distributedand well-embedded harder particulates and the constrained plastic deformation of the matrix. The addition of hard ceramic particlessimultaneously yielded higher bulk Vickers hardness. The toughness enhancement in the composites was attributed to the increased tortuousityby crack deflection, branching and bridging. Moreover, the transformation of tetragonal zirconia particles into the monoclinicform might also partially contribute to the toughness enhancement in the AMZG/ZrO2 composite.

The ternary carbide Ti3AlC2 was reactively synthesized from the elemental powder mixtures of Ti, Al and activated carbon. Cu/Ti3AlC2 composites were fabricated by hot-pressing method. Their microstructures and properties were investigated. The resultsdemonstrated that Ti3AlC2 is a promising reinforcement for copper and the Cu/Ti3AlC2 composites exhibited lower electrical conductivityand much superior flexural strength to pure copper matrix without remarkable loss of fracture toughness.