Microstructure and property of Al₂O₃ coating microplasma-sprayed using a novel hollow cathode torch

Al₂O₃ coating is deposited using a novel microplasma torch of a hollow cathode through axial powder injection under low power, up to several kilowatts. The microstructure of the coating is characterized using optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. The property of the coating is characterized by dry rubber wheel abrasive wear test. The velocity of in-flight particles is measured using a velocity/temperature measurement system for spray particles based on thermal radiation. The effect of plasma power on particle velocity during spraying, and the microstructure and property of the coating are examined. The comparison of the velocity of in-flight particles, and microstructure and property of the coating deposited by the microplasma spraying with those of conventional plasma spraying is carried out. The results reveal that Al₂O₃ coating, of comparable performance to that deposited by conventional plasma jet under a power of about 40 kW, can be deposited by the present microplasma spray torch.