Effect of spraying power on microstructure and properties of supersonic plasma sprayed A1_2O_3 coating on porous Si_3N_4 substrate

摘要

A1_2O_3 coatings were prepared using supersonic plasma spraying on the porous Si_3N_4 substrate at the spraying power of 52,54,58 and 60 kW, respectively. The effect of spraying power on the microstructures and properties of A1_2O_3 coating was investigated. The feedstock particles were sufficiently melted and A1_2O_3 coatings become more and more compact with the increasing spraying power. However, the defects, including the surface cracks, interlamellar cracks and needle-like particles, were produced within the coating when the spraying power was 60 kW due to the excessive power. As-received A1_2O_3 coatings sealed the surface pores of porous Si_3N_4, and decreased the water absorption obviously, but only with a slight decrease of the total porosity. Vickers hardness and flexural strength of porous Si_3N_4 with A1_2O_3 coating increased gradually as the spraying power increased from 52 to 58 kW, but it began to decrease when the spraying power was up to 60 kW due to the appearance of defects within the coating.