INFLUENCE OF THERMAL SPRAYING PROCEDURES ON THE PERFORMANCE OF OVER LAYS DEPOSITED ON THE STEEL SUBSTRATES

Abstract

Thermal spraying is a process which is used to coat thin films of metallic or non metallic materials on to substrates. The study of these thermal sprayed coatings are useful, because these coatings are used to restore desired dimensions; to improve resistance to wear, corrosion, oxidation, or a combination of these; and to provide specific electrical or thermal properties. Three types of powders named Ni based WC (1002ET), Ni-Cr eutectic alloy (1004EN), and Co and Ni based CrC (1006EE) are used to develop coatings on mild steel substrate by flame spraying process. We added some carbide particles like WC, CrC to reinforce the coatings. Heat treatment was done for all modified and unmodified coatings to enhance wear resistance. It was studied the abrasive wear behavior of all coatings under different testing conditions like heat treatment, normal load, counter surface, percentage of hard carbide particles added. Tests like abrasive wear test, normal hardness test, microhardness test, SEM analysis of worn out surfaces, EPMA of coatings and microstructure study were carried out in order to understand wear behavior of coatings. Microstructures were obtained for all coatings to understand the distribution of secondary phases in the metal matrix. EPMA test (quantitative test) was done to get weight percentage of different elements present in the coating and in secondary phase. Microhardness test was carried out to get the hardness value at individual phases, to explain wear behavior under different conditions. SEM analysis of worn out samples was done to understand wear mechanism of wear. Heat treatment enhanced microhardness and reduced wear rates. Addition of carbide particles acts as reinforcement and so reduced wear rates. But heat treatment in modified powder coatings showed adverse effect on wear resistance.