Search

Al 2 O 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 2 O 3 due to the decreasing grain boundary diffusivity and mobility. Compared with monolithic Al 2 O 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 2 O 3 and LaPO 4 . Flexural strength and Vickers hardness of the Al 2 O 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 .

Layer structured LaPO4 was added to Al2O3 ceramic matrix to improve the machinability of the composites. Densification, hardness and microstructures of the Al2O3/LaPO4 ceramic composites have been studied at various sintering temperatures (1300, 1400, 1500, 1600 °C) and different LaPO4 contents (pure Al2O3, 10 wt.% LaPO4, 20 wt.% LaPO4, 30 wt.% LaPO4, 40 wt.% LaPO4, pure LaPO4). X-ray diffraction analysis showed that only Al2O3 and LaPO4 phases exist in the Al2O3/LaPO4 composites with different LaPO4 content even sintered up to 1600 °C. Bulk density, hardness and microstructures of the Al2O3/LaPO4 composites are largely dependent on the LaPO4 content and sintering temperature. Due to the layered structure of LaPO4 and the weak interface between the Al2O3 and LaPO4 phase, the 40 wt.% Al2O3/LaPO4 composite can be easily machined using cemented carbide drills instead of conventionally diamond tools.

This paper provides a new material design method for machinable ceramics within an overall methodology. Examples are provided to illustrate the use of the methodology in specific ceramic materials, and machinability of the materials is characterized with cemented carbide drills instead of diamond tools. This method enables the use of composition compound and structure design combination for the purposes of improving machinability of ceramics while allowing for retaining mechanical properties of the materials. At the same time, this method also provides the basic design principle for the other comparable, but intrinsically different, ceramic systems based on chemical compatibility and thermodynamic properties. Graded machinable Si3N4/h-BN and Al2O3/LaPO4 composites were designed, fabricated and characterized.