THE EFFECT OF PARTICULATE LOADING ON THE MECHANICAL-BEHAVIOR OF AL2O3AL METAL-MATRIX COMPOSITES/

An investigation was made to determine the effect of particulate loadi ng on the elastic, tensile, compressive and fracture properties of Al2 O3/Al metal-matrix composites fabricated by a pressureless-liquid-meta l-infiltration process. The elastic modulus was found to be strongly a ffected by the reinforcement content, failing within the Hashin Shtrik man bounds. The Young's modulus of the most highly loaded composite wa s 170 GPa; compare with 65 GPa for the unreinforced alloy. The strengt h systematically increased with loading, and the rate of increase also increased with loading. The measured yield strengths were nominally t he same in both tension and compression; however, the composites posse ssed far greater ultimate strengths and strains-to-failure in compress ion than in tension. At 52 vol % reinforcement, yield strengths in ten sion and compression of 491 and 440 MPa, respectively, were measured, whereas the associated ultimate strengths were 531 and 1035 M Pa, resp ectively. In tension, the yield and ultimate strengths of the base all oy were found to be 170 and 268 MPa, respectively. The composites disp layed a nearly constant fracture toughness for all particulate loading s, with values approaching 20 MPa m1/2 compared to a value of 29 MPa m 1/2 for the base alloy. Using fractography, the tensile-failure mechan ism 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.