Performance and damage mechanism of TiN/ZrN nano-multilayer coatings based on different erosion angles

Nano-multilayer coating is an effective method for improving the sand erosion resistance of a material employed in any industrial field. However, very few studies have addressed this subject of research, especially in the aspects of the multi-angles erosion performance and the corresponding mechanism. In this study, a TiN/ZrN nano-multilayer coating was prepared on the Ti6Al4V substrate by employing physical vapor deposition; the nano-layer thickness of the alternating structure of this coating was less than 200 nm. The mechanical and erosion properties of TiN/ZrN were examined, accompanied by varying the erosion angles from 15° to 90°. The 3D surface topographies of the eroded surface were characterized by using a white-light interfering profilometer. The coating damage was examined by cross-sectioning the samples using the focused ion beam (FIB) method. The experiment shows that the maximum erosion rate occurs at 90°, which is approximately 3.1, 2.8 and 1.2 times larger than 15°, 45°, and 75° erosion angles, respectively. The diameter, depth and density of the erosion pit increases with a rise in the erosion angle. The erosion mechanism of the TiN/ZrN nano-multilayer coatings is governed by lateral cracks and the tensile stress of the coating itself at 15° and 45°; further, it is influenced by the longitudinal cracks at 75° and 90°. Lateral cracks in the erosion damage of coating are primarily Mode Ⅱ cracks. The average crack density in the effective FIB trenches reveals that the cracks are more probable to occur at high angles (75° and 90°); this further explains the results of a higher erosion rate at a high erosion angle.