DEVELOPMENT OF WEAR RESISTANT COATINGS ON METALLIC COMPONENTS

Abstract

Detonation gun spraying is one of the most promising thermal spray variants for depositing high quality wear resistant coatings .Of. all these coating materials that can be d-gun sprayed, alumina, WC-Co-Cr and Cr3C2-NiCr are the most widely established and these coatings have already gained industrial acceptance for diverse applications. Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction was used for characterization. Coating qualities are discussed with respect to hardness, porosity and microstructure. Sand erosion studies of thermally sprayed coatings and substrates have been undertaken using an air sand erosion test rig. SEM studies indicates that erosion is caused by the anisotropic microstructure of the thermally sprayed coating with preferred crack propagation parallel to coating surface followed by crack interlinking and spalling. This is the dominant erosion mechanism present. The coatings also have defects (especially plasma sprayed) including stress induced transverse cracks, voids and pores. Such defects accelerate the erosion process considerably because they aid crack initiation.