SUPERIOR HIGH-TEMPERATURE RESISTANCE OF ALUMINUM NITRIDE PARTICLE-REINFORCED ALUMINUM COMPARED TO SILICON-CARBIDE OR ALUMINA PARTICLE-REINFORCED ALUMINUM

Aluminium-matrix composites containing AlN, SiC or Al2O3 particles were fabricated by vacuum infiltration of liquid aluminium into a porous particulate preform under an argon pressure of up to 41 MPa. Al/AlN had similar tensile strengths and higher ductility compared to Al/SiC of similar reinforcement volume fractions at room temperature, but exhibited higher tensile strength and higher ductility at 300-400 degrees C and at room temperature after heating at 600 degrees C for 10-20 days. The ductility of Al/AlN increased with increasing temperature from 22-400 degrees C, while that of Al/SiC did not change with temperature. At 400 degrees C, Al/AlN exhibited mainly ductile fracture, whereas Al/SlC exhibited brittle fracture due to particle decohesion. Moreover, Al/AlN exhibited greater resistance to compressive deformation at 525 degrees C than Al/SiC. The superior high-temperature resistance of Al/AlN is attributed to the lack of a reaction between aluminium and AlN, in contrast to the reaction between aluminium and SiC in Al/SlC. By using Al-20Si-5Mg rather than aluminium as the matrix, the reaction between aluminium and SiC was arrested, resulting in no change in the tensile properties after heating at 500 degrees C for 20 days. However, the use of Al-20Si-5Mg instead of aluminium as the matrix caused the strength and ductility to decrease by 30% and 70%, respectively, due to the brittleness of Al-20Si-5Mg. Therefore, the use of AlN instead of SiC as the reinforcement is a better way to avoid the filler-matrix reaction. Al/Al2O3 had lower room-temperature tensile strength and ductility compared to both Al/AlN and Al/SiC of similar reinforcement volume fractions, both before and after heating at 600 degrees C for 10-20 days. Al/Al2O3 exhibited brittle fracture even at room temperature, due to incomplete infiltration resulting from Al2O3 particle clustering.