High-volume-fraction Si3N4-Al-based composites have been fabricated by high-pressure casting method. The effects of chemical compositionof infiltrated Al alloys, microstructures of Si3N4 preforms, and test temperature on the mechanical properties were investigated.The maximum four-point bending strength and fracture toughness of the composites reached 924 and 8.2MPa(√m), respectively. Increasingsintering temperature above 1650℃ for Si3N4 preforms resulted in an enhancement of fracture toughness at the expense of degradation inflexural strength. However, an increase in sintering time for Si3N4 preforms at moderately sintering temperature yielded an improvement inboth flexural strength and fracture toughness of the corresponding composites. Both flexural strength and fracture toughness decreased withincreasing temperature and CIP pressure due to inhomogeneous distribution of Al phase and some defects introduced into the preforms duringthe casting process. The Si3N4–6061 Al composite exhibited the lowest strength, which may be attributed to the presence of porosities andinterfacial reactions.

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.

Fe3Al-based composites reinforced with micron-sized titanium carbide, tetragonal zirconia and nano-scaled alumina particles were hot-pressed, and the room temperature mechanical properties were investigated. Results show that nano-Al2O3 is not an efficient ceramic for the enhancementof mechanical properties of Fe3Al, primarily due to its inhomogeneous distribution and severe agglomeration within the matrix as well as the weakinterfacial bonding. By contrast, Fe3Al/5 wt.% ZrO2 composite had a strength as high as 1361 MPa and a fracture toughness of 19.0 MPa ffiffiffiffi mp. Theenhancing effect is attributed to the low thermal expansion mismatch between ZrO2 and Fe3Al matrix, and to the stress-induced transformation ofZrO2 particles. The flexural strength and fracture toughness for Fe3Al/10 wt.% TiC composite was 1086 and 20.0 MPa ffiffiffiffi mp, respectively. Themechanical properties of Fe3Al/TiC composites decreased with TiC content above 10 wt.% due to the suppression of plastic deformation, residualporosity and interfacial debonding.

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.

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.