Performance of Flame Sprayed Ni-WC Coating under Abrasive Wear Conditions

This paper describes the influence of a post spray heat treatment on the microstructure, microhardness and abrasive wear behavior of the flame sprayed Ni-WC (EWAC 1002 ET) coating deposited on the mild steel. Coatings were deposited by using an oxy-acetylene flame spraying torch (Superjet Eutalloy L & T, India). The wear behavior of the coating was evaluated using a pin on disc wear system against SiC abrasive medium of 120 and 600 grades at 5, 10, 15, and 20 N normal load. Results revealed that the influence of normal load on wear is governed by the microstructure, hardness and abrasive grit size. The heat treatment increased average microhardness of the coating. However, it was found that the hardness does not correctly indicate the abrasive wear resistance of Ni-WC coating in an as sprayed and heat treated condition. The heat treatment of the coating improved its abrasive wear resistance against fine abrasive medium while the wear resistance against coarse abrasive was found to be a function of a normal load. At low-normal load (5 and 10 N) the heat treated coating showed lower-wear rate than as spayed coating while at high-normal loads (15 and 20 N) heat treated coating was subjected to higher-wear rate than as sprayed coating. In general, an increase in normal load increased the wear rate. The scanning electron microscopy study indicated that the wear largely takes place by groove formation and scoring of eutectic matrix and the fragmentation of the carbide particles.