Microstructure and mechanical properties of reaction hot pressed AlxCoy/Al2O3 composites

Al2O3/AlxCoy composites have been fabricated by reaction hot-pressing of milled powder mixtures containing Al, Co2O3 and Al2O3 at 1450 °C in Ar atmosphere under 30 MPa. The intermetallic/ceramic ratio of Al2O3/AlxCoy composites was adjusted by adding Al2O3 to the starting mixture. The effect of Al to Co2O3 ratio in the starting powders on phase development, microstructure and mechanical properties has been investigated. The fracture modes are different with the increase of the Al content. The metal oxide (Co2O3) was in situ reduced by Al to form AlxCoy aluminides, dispersed in the ceramic matrix. The improvements in bend and fracture strength can be attributed to the ductile failure of the fine AlxCoy particles. The maximum bending strength and fracture toughness were 513 MPa and 5.2 MPa m1/2, respectively.