Effect of flow velocity on cavitation erosion behavior of HVOF sprayed WC-10Ni and WC-20Cr3C2–7Ni coatings

Abstract

WC-10Ni and WC-20Cr3C2–7Ni coatings were deposited successively using high-velocity oxygen-fuel (HVOF) spraying. The microstructures and mechanical properties of the coatings were evaluated by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), Vickers microhardness tester, and Ultra nanoindentation tester. The cavitation erosion behaviors of the coatings at different flow velocities were investigated by a rotating disk rig facility with bolt cavitator and circulating system. The results showed that the main phases in the WC-10Ni and WC-20Cr3C2–7Ni coatings were WC, W2C, W, and WC, (W,Cr)2C, respectively. Both coatings were dense and well bonded to the steel substrate. Despite higher porosity and elastic modulus (E) as well as slightly lower hardness (H), the WC-10Ni coating showed lower H/E, H3/E2 and η values as well as cavitation erosion resistance at each flow velocity compared to the WC-20Cr3C2–7Ni coating. Both coatings exhibited an increase in the volume loss rates with increasing flow velocity, and the critical flow velocity of the WC-20Cr3C2–7Ni coating was in the region of 33.5 to 41.9 m·s−1. The cavitation erosion failure mechanism of the WC-10Ni coatings was the brittle detachment of the WC particles, while cavitation pinholes, pits, cracks, craters, and massive exfoliation contributed to the evolution of the cavitation erosion processes of the WC-20Cr3C2–7Ni coating with the increase of the flow velocity.