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.

Ti–Al3Ti laminated composites have been fabricated through reactive sintering in vacuum usingTi and Al foils with different initial thickness.The aluminum layer was completely consumed resulting in microstructures of well-bonded metal–intermetallic layered composites with Tiresidual metal layers alternating with the aluminide intermetallic layers. The MIL composites exhibit a very high degree of microstructuraldesign and control. Microstructure characterization by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersivespectroscopy (EDX) has shown that Al3Ti is the only titanium aluminide phase due to the thermodynamics and phase selection of the reactionbetween Ti and Al through mass diffusion in the presence of liquid Al. The mechanical properties and fracture behavior of the fabricatedlaminated composites were examined through three-point bending test. The results indicated that the composites exhibited anisotropic features.When the load perpendicular to the laminates was applied, they displayed a step-like or saw-tooth load-displacement response and superiorflexural strength as well as fracture toughness, which is also dependent on the number and thickness of individual layers. A non-catastropicfracture was observed in the laminated composites due to the deflection of cracks along the Ti/Al3Ti interface. The Ti layer failed by cleavagemode, showing extensive plastic deformation during the bending process.

Ti-Al3Ti laminated composites have been fabricated through reactive sintering in vacuum using Ti and Al foils with differentinitial thicknesses. The aluminum layer is consumed by forming a titanium aluminide intermetallic compound. Thus, the final microstructureconsists of alternating layers of intermetallic compound and unreacted Ti metal. Microstructural characterization by scanningelectron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectroscopy (EDX) has shown that only theintermetallic Al3Ti is formed, which can be rationalized in terms of thermodynamics and kinetics of phase selection, as well as by thediffusion processes occurring in the presence of liquid Al.

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.

Porous ceramic with a framework structure of aluminum borate (9Al2O3-2B2O3) whiskers was in situ synthesized by firing above 1150 8Ca green powder compact of a mixture of aluminum hydroxide, boric acid and an additive of nickel oxide. During sintering, the whiskers ofaluminum borate grew in situ in the compact, and were bonded together. The porous aluminum borate consisted solely of whiskers with aporosity of 54-58%. The average diameters of the whiskers increased from 0.2 to 2 mm with increasing sintering temperature from 1150 to1350 8C. However, the estimated whiskers aspect ratio decreased with increasing sintering temperature.