Characteristics of microplasma spraying of Al₂O₃ ceramic coatings

Al₂O₃ coating was deposited by microplasma spraying system through axial powder injection at a low power level about 2 kW. The effects of plasma arc power, operating gas flow and spray distance on particle velocity during spraying, the microstructure and properties of the coatings were investigated. The coating microstructure was examined by optical microscopy, and the coating phase structure was examined by X-ray diffraction analysis. The coating property was characterized by abrasive wear loss. The particle velocity in flight was measured by the particle velocity/temperature measurement system based on thermal radiation. The results showed that the particle velocity was influenced significantly by plasma arc power, operating gas flow and spray distance. The velocity increased with increase of plasma arc power and operating gas flow, decreased with increase of spray distance. On the other hand, the abrasive wear loss of the coatings decreased with the increasing in arc power, and increased with increase of operating gas flow and spray distance. The abrasive wear loss of the coatings was significantly influenced by particle temperature. The abrasive wear loss of the Al₂O₃ coating deposited by microplasma spraying was comparable to that of the coating deposited by conventional plasma spraying system at 38 kW.