A comparative study of HVAF-sprayed WC-based coatings with Co-free binders

Thermally sprayed tungsten carbide (WC)-based metal matrix composite coatings are popular candidates as wear resistant layers. Cobalt has been widely used to provide physical support for WC particles by acting as a tough binder and WC-Co formulations with and without Cr addition already find extensive industrial use. However, the price of Co has progressively increased while its potential environmental and health effects have simultaneously begun to deter its continued use. Consequently, the need for a substitute binder for WC-based coatings has assumed some urgency during recent years. In this paper, the wear performance of WC-based composite coatings with Co-free binders will be evaluated as an alternative to conventional WC-CoCr wear resistant layers. The High Velocity Air-Fuel (HVAF) process, which offers specific advantages in terms of high adhesion strength and minimal in situ degradation/oxidation of powder feedstock, will be used to deposit the coatings. The coatings will be comprehensively characterized for microstructure, phase constitution etc. and their performance under different wear modes (dry sand abrasion, erosion and sliding) will also be reported. All results from non-Co binder coatings will be compared using conventional WC-CoCr coatings as a reference.