Effect of grinding on the erosion behaviour of a WC-Co-Cr coating deposited by HVOF and detonation gun spray processes

There is a growing interest on the use of thermal spray coatings for a vari ety of wear resistance applications due to the several advantages it offers . WC-Co coating is widely used for wear resistance applications. It is know n that addition of Cr to WC-Co improves binding of the metallic matrix with the WC grains and provides better wear resistant coating. Thus, WC-Co-Cr i s considered to be a potential wear resistant coating material as compared to WC-Co coating. The thermally sprayed carbide coatings are in general sur face finished by machining or grinding after the coating process. Therefore , it is imperative to understand the influence of the finishing operation o n the characteristics and performance of carbide coatings. This work aims a t investigating the effect of grinding on the erosion behaviour of a WC-Co- Cr coating. As a part of this work a comparison has also been brought out b etween two high velocity coating processes namely high velocity oxy-fuel (H VOF) and detonation gun spray process (DS). A WC-10Co-4Cr powder has been s prayed on a medium carbon steel using the above mentioned high velocity spr ay processes. Some of the coated specimens were further ground by a diamond wheel with controlled parameters. The coating in both 'as-coated' and 'as- ground' conditions has been tested for solid particle erosion behaviour. Th e erosion experiments were carried out using an air-jet erosion test rig wi th silica erodents at a velocity of 80 m/s. It has been found that surface grinding improved the erosion resistance. This work presents detailed chara cterisation of the WC-Co-Cr coating in both 'as-coated' and 'as-ground' for m. A detailed analysis indicates that the increase in residual stress in th e ground specimen is a possible cause for the improvement in erosion resist ance. (C) 2001 Elsevier Science B.V. All rights reserved.