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Ceramic coatings with a thickness range of 1.5–5.5 μm were successfully prepared with polysilazane (PSN1) as a precursor and aluminum (Al) powder as an active filler. The effect of Al content on chemical composition, microstructure, and mechanical properties of the coatings was investigated. Chemical composition analysis revealed that Al powder was completely converted into Al 2 OC and AlN phases during the ceramization process, accompanied by volume expansion. Ceramic coatings derived from less Al powder containing PSN1/Al showed more compacted surface morphology and continuous microstructure. The surface hardness and elastic modulus of ceramic coatings decreased with the increase of the volume fraction of Al from 10% to 40% (Al/PSN1, v/v). The maximum surface hardness and elastic modulus of coatings were 6.38 GPa and 107.66 GPa, respectively.

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.