The effect of particulate loading on the mechanical behaviour of Al2O3/Al metal-matrix composites

An investigation was made to determine the effect of particulate loading on the elastic, tensile, compressive and fracture properties of Al₂O₃/Al metal-matrix composites fabricated by a pressureless-liquid-metal-infiltration process. The elastic modulus was found to be strongly affected by the reinforcement content, falling within the Hashin-Shtrikman bounds. The Young's modulus of the most highly loaded composite was 170 GPa; compare with 65 GPa for the unreinforced alloy. The strength systematically increased with loading, and the rate of increase also increased with loading. The measured yield strengths were nominally the same in both tension and compression; however, the composites possessed far greater ultimate strengths and strains-to-failure in compression than in tension. At 52 vol % reinforcement, yield strengths in tension and compression of 491 and 440 MPa, respectively, were measured, whereas the associated ultimate strengths were 531 and 1035 MPa, respectively. In tension, the yield and ultimate strengths of the base alloy were found to be 170 and 268 MPa, respectively. The composites displayed a nearly constant fracture toughness for all particulate loadings, with values approaching 20 MPa m^1/2 compared to a value of 29 MPa m^1/2 for the base alloy. Using fractography, the tensile-failure mechanism was characterized as transgranular fracture of the Al₂O₃ particles followed by ductile rupture of the Al-alloy matrix, with no debonding at the matrix/reinforcement interfaces.