Effect of V-addition on the thermal stability and oxidation resistance of CrAlN coatings

Abstract Since the superiority of tribological properties, V-containing coatings, with the potential to generate lubricious Magneli oxides at elevated temperatures, are regarded as excellent candidates for machining applications. Here, a study was conducted to shed light on the intrinsic thermal stability, mechanical properties and oxidation resistance of V-alloyed CrAlN coatings deposited by cathode arc evaporation. The hardness of Cr0.48Al0.52N and Cr0.44Al0.50V0.06N coatings with a single-phase face-centered cubic structure is 30.8 ± 0.9 and 33.0 ± 1.3 GPa, respectively. Upon annealing in Ar atmosphere, Cr0.44Al0.50V0.06N coating reveals a retarded precipitation of wurtzite AlN as well as a postponement in Cr–N disintegration as compared to V-free Cr0.48Al0.52N coating, owing to the solid solution of V with a stronger binding capacity with nitrogen. The improved structural stability of Cr0.44Al0.50V0.06N coating contributes to the mild decline in hardness and elastic modulus upon annealing. When exposed to air, the incorporation of V into CrAlN promotes the formation of (Al, Cr)2O3 mixed oxide as well as additional V2O5, leading to a significantly lower onset temperature for oxidation. The existence of V2O5 degrades the protective of (Al, Cr)2O3 oxide layer and causes a complete oxidation of Cr0.44Al0.50V0.06N coating at 950 °C, where only a dense and thin oxide scale can be detected in Cr0.48Al0.52N coating.