Microstructure and mechanical properties of machinable Al2O3/LaPO4 composites by hot pressing

Al2O3/LaPO4 composites were fabricated by hot-pressing, and the microstructure and mechanical properties were investigated. The layered LaPO4 grains inhibited densification of the composites and grain growth of Al2O3 due to the decreasing grain boundary diffusivity and mobility. Compared with monolithic Al2O3, the composite system possessed narrow and homogeneous grain size distribution, and this tendency became more obvious with increasing LaPO4 content. However, the fine and homogenous microstructure did not improve the fracture strength and elastic modulus due to formation of weak bonding between Al2O3 and LaPO4. Flexural strength and Vickers hardness of the Al2O3/LaPO4 composite added with 40 wt.% LaPO4 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 LaPO4.