WC-based composite coatings prepared by the pulsed gas dynamic spraying process: Effect of the feedstock powders

WC-based cermet coatings are typically produced using the HVOF process, due to high particle velocity and the lower heating characteristic of this technique. Despite the effort of optimisation of the coating process, degradation of the feedstock materials such as decarburisation of WC and amorphization of the metallic phase still occurs. It is known that the coating properties do not depend only on the spray process and its parameters, but also on the feedstock powder characteristics such as its chemistry, carbide size, particle morphology and production method. The work presented here is part of a research program aimed at exploring the possible advantages of the Pulsed Gas Dynamic Spray (PGDS) process, as an alternative technique for the preparation WC-based cermet coatings. In this paper, WC-based coatings have been prepared using six different types of cermets powders. In order to study the effects of the feedstock powder on the coatings microstructures and hardness, the selected starting powders differed not only in microstructural features such as size and morphology but also in the chemistry and phases. Using different analysis technique (OM, SEM, XRD, and HV), a detailed comparison of powders and coatings microstructures, phase compositions, and hardness are presented and discussed in detail. It was found that the PGDS process preserves the microstructure of the starting cermet powders in such a way that no significant degradation of the phase composition, even those that show the pre-existence of complex carbides, has been observed. Furthermore, although the same spray parameters were used, the thickness, deposition efficiency, porosity, and micro-cracks within the coatings are different from one type of cermet to another, suggesting that PGDS optimum process parameters are material dependant. (C) 2008 Elsevier B.V. All rights reserved.