Microstructure and mechanical properties of machinable Al 2O 3/LaPO 4 composites by hot pressing

Abstract

Al 2O 3/LaPO 4 composites were fabricated by hot-pressing, and the microstructure and mechanical properties were investigated. The layered LaPO 4 grains inhibited densification of the composites and grain growth of Al 2O 3 due to the decreasing grain boundary diffusivity and mobility. Compared with monolithic Al 2O 3, the composite system possessed narrow and homogeneous grain size distribution, and this tendency became more obvious with increasing LaPO 4 content. However, the fine and homogenous microstructure did not improve the fracture strength and elastic modulus due to formation of weak bonding between Al 2O 3 and LaPO 4. Flexural strength and Vickers hardness of the Al 2O 3/LaPO 4 composite added with 40 wt.% LaPO 4 and sintered at 1450 °C reached 331 MPa and 4.69 GPa, respectively. It was shown that the machinability of alumina matrix materials could be greatly improved after introducing an interface dispersion phase of layer-structured LaPO 4.