Investigation of short-term, high-temperature oxidation of AlCrN coating on WC substrate

A surface analysis was performed on an aluminum chromium nitride (AlCrN) coating formed on a tungsten carbide (WC) substrate subjected to short-term (in minutes) oxidation at an elevated temperature (900 degrees C) using focused ion beam (FIB), X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GI-XRD), and laser-induced breakdown spectroscopy (LIBS). To separately analyze a coating with a thickness of several micrometers, the GI-XRD method was used. For cross-sectional imaging, the samples were milled using an FIB system, and chemical bonding states and surface elemental concentrations were analyzed by XPS. Within just a few seconds, the color of the AlCrN coating surface changed irregularly and, after 10 min, the entire coating layer surface changed. The entire coating surface oxidation as discoloration progressed in partial areas after 30 min. Based on the GI-XRD and XPS results, after 1 min, alumina and chromium oxides formed on the outermost surface, and after 10 min, Cr-W and Co-W oxide phases appeared, resulting from a reaction with WC near the interface. The atomic concentration of nitrogen in the AlCrN coating decreased after few seconds on the outermost surface and was almost eliminated after 10 min; oxygen showed the opposite trend. Finally, the FIB and LIBS results showed that voids formed within the coating layer and interface at high temperatures, and diffusion of Al and Cr in subsequent reactions was identified. This work demonstrates interesting results from various analyses that differ from previously reported AlCrN coating oxidation behaviors, and could provide a better understanding of long-term reactions for the surface oxidation of AlCrN coatings at high temperatures.