Characteristics of plasma-sprayed coatings using fine Al2O3 powder

The objective of this study was to investigate the characteristics of fine-Al2O3 coating after plasma spraying using fine-Al2O3 powder which has the particle size distribution of 1-12 mum and the mean particle size of 4.12 mum. The microstructure of the coating was very dense and the width of each splat of the fine alumina powder was approximately 10 mum. The average thickness of splats was approximately 1.4 mum, and this value was approximately 1/3 of mean particle size. The surface roughness of the coating was Ra = 5.2 mum and this result was approximately 30% lower than the surface roughness of other plasma-sprayed Al2O3 coatings. The main phase of the coating was gamma -Al2O3 and also a little of alpha -Al2O3 phase was observed. The fraction of alpha -Al2O3 in the coating was 8.39%. Micro-hardness ranged from 1030 to 890 depending on the indentation load and differed little from commercial Al2O3 coating but the hardness variation was relatively large. Nonetheless, it is expected that the fine-Al2O3 coating will be used as coating materials because it does not require post-surface finishing after spraying.