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 variety of wear resistance applications due to the several advantages it offers. WC-Co coating is widely used for wear resistance applications. It is known 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 is considered to be a potential wear resistant coating material as compared to WC-Co coating. The thermally sprayed carbide coatings are in general surface finished by machining or grinding after the coating process. Therefore, it is imperative to understand the influence of the finishing operation on the characteristics and performance of carbide coatings. This work aims at 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 between two high velocity coating processes namely high velocity oxy-fuel (HVOF) and detonation gun spray process (DS). A WC-10Co-4Cr powder has been sprayed on a medium carbon steel using the above mentioned high velocity spray 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. The erosion experiments were carried out using an air-jet erosion test rig with silica erodents at a velocity of 80 m/s. It has been found that surface grinding improved the erosion resistance. This work presents detailed characterisation of the WC-Co-Cr coating in both 'as-coated' and 'as-ground' form. A detailed analysis indicates that the increase in residual stress in the ground specimen is a possible cause for the improvement in erosion resistance. (C) 2001 Elsevier Science B.V. All rights reserved.