Investigations of cavitation erosion and wear resistance of cermet coatings manufactured by HVOF spraying

Abstract

This work studies the effect of mechanical properties and microstructure on sliding wear and cavitation erosion behaviors of cermet coatings deposited via high velocity oxy-fuel (HVOF) spraying on AZ31 magnesium substrate. Cavitation tests indicated that WC-Co-Cr cermet had superior resistance to cavitation erosion than WC-Cr3C2-Ni, WC-Co coatings, and far better resistance than the AZ31 expressed by the volume material loss 3.74 mm3, 6.99 mm3, 10.30 mm3, and 108.82 mm3, respectively. WC-Co-Cr coating’s erosion mechanism exhibited uniform material removal, which slows the erosion rate. The CoCr binder prevented severe surface pitting and the detachment of the WC-Co-Cr cermet material in massive chunks which was observed for WC-Co and WC-Cr3C2-Ni coatings. Cermet coatings microstructure discontinuities such as pores and ceramic-metallic phase interfaces are the centers of material erosion. No clear correlation between the erosion behavior and mechanical properties of coatings was revealed. Contrary to that, sliding wear results were strongly related to the mechanical properties. The WC-Co-Cr and WC-Co samples exhibited higher hardness and higher values of Young’s modulus than the WC-Cr3C2-Ni one. The generated stresses with lower values of hardness and Young’s modulus for the WC-Cr3C2-Ni sample resulted in a higher wear factor, approx. 1·10−7 mm3·N−1·m−1. For the harder samples, which exhibited higher stiffness (WC-Co-Cr and WC-Co), this type of wear resulted in lower values of the wear factor: 6·10−8 mm3·N−1·m−1 and 9·10−8 mm3·N−1·m−1, respectively. Deposition of the cermet coatings effectively protected the magnesium substrate, which shows low resistance to cavitation erosion and sliding wear when uncoated.