Cavitation erosion characteristics at various flow velocities in NaCl medium of carbide-based cermet coatings prepared by HVOF spraying

Abstract

This study aims to investigate the correlation between flow velocity and cavitation erosion (CE) characteristics of high-velocity oxygen-fuel (HVOF) sprayed Cr3C2-NiCr (CN) and WC-Cr3C2-Ni (WCN) coatings in 3.5 wt% NaCl medium, except for the microstructures, mechanical properties and electrochemical behaviors. In comparison with the CN coating, the WCN coating shows higher values of elastic modulus (E), hardness (H), H/E and H3/E2 as well as lower porosity, resulting in lower volume loss rate (VLR) and enhanced CE resistance in NaCl medium at each value of flow velocity. The VLR values of both coatings increase as the flow velocity increases. The change of the CE progresses in NaCl medium of the CN coating is the formation of cavitation pinholes, pits, craters and oxidation films coupled with the exfoliation of chromium carbide particles when the flow velocity is 23.4 and 33.5 m s−1 as well as the brittle fracture structure with layers delamination accompanied by the oxidation films when the flow velocity is 41.9 m s−1. In a wide flow velocity range, the formation of cavitation pinholes, pits and micro-cracks along with the oxidation films are addressed as the dominant CE mechanism in NaCl medium of the WCN coating.