Cavitation-erosion behavior and mechanism of high-velocity oxygen-fuel sprayed CuAlNiTiSi medium-entropy alloy coating

Abstract

In this paper, a novel Cu55Al20Ni12Ti8Si5 (at.%) medium-entropy alloy (MEA) coating was fabricated on the 316L stainless steel substrate by high-velocity oxygen-fuel (HVOF) spraying technology. Phase composition, microstructure, microhardness and nano-mechanical properties of the as-sprayed coating were characterized by X-ray diffractometer (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and transmission electron microscope (TEM) techniques, Vickers microhardness tester and nano-indenter, respectively. The cavitation-erosion (CE) behavior of the coating in the distilled water was investigated by using gravimetric and volumetric with the comparison of the Al-bronze, and the CE damage mechanism of the coating was proposed by analyzing the cavitation-eroded morphologies. The results illustrated that the coating consisted of primarily body centered cubic (BCC) solid solution phase and a mixture of a few NiTi-rich and nanocrystalline phases. The coating exhibited higher microhardness and better mechanical properties than the Al-bronze. After being cavitation-eroded for 16 h, the cumulative mass loss and volume loss of the Al-bronze are both much higher than those of the coating, indicating the more excellent CE resistance of the coating as compared with the Al-bronze. The superior CE resistance of the coating was attributed to its unique microstructure and excellent mechanical properties. The CE damage was preferentially occurred at or around the pre-existing pores on the coating surface, followed by the initiation and propagation of craters and cracks. The CE damage mechanism of the coating can be summarized as fatigue failure and lamellar spalling, while the material removal mechanism of the Al-bronze was plastic deformation and fatigue fracture.