Characterisation of Redmud Coatings Prepared by Plasma Spraying

Abstract

Plasma Spraying is a surface modification technique that combines particle melting, rapid solidification and consolidation in a single process. But as high cost of spray grade powders limits the adoption of this technique, exploring newer and cheaper materials suitable for plasma spray coating has drawn a lot of attention. This work reports an attempt to spray coat redmud (the waste generated in alumina producing plants) on different metal substrates. Plasma sprayed coatings of redmud have been developed at different operating power levels of the plasma gun on aluminium and copper substrates. Coating adhesion strength and deposition efficiency were studied at various operating conditions. Characterisation of the coatings was performed using micro hardness measurement and scanning electron microscopy (SEM). It was observed that the operating power appreciably influences the coating adhesion strength and coating thickness. Coatings deposited at very low and very high power levels show poor adhesion. Maximum interface adhesion strength of -8 MPa was recorded at an operating power of 9 kW. This work establishes 'redmud' as a potential coating material, which may be suitable for wear resistant applications. It also suggests a value added utilisation of this industrial waste.