Influence of oxygen addition on the structure, mechanical and thermal properties of CrN coating

In this study, the effect of oxygen addition on the structure, mechanical and thermal properties of CrN coatings was investigated. CrN, Cr0.50O0.07N0.43 and Cr0.47O0.22N0.31 coatings reveal a single-phase cubic structure, and further increasing oxygen content results in the formation of a corundum structured Cr2O3 coating. An increased hardness from ~16.9 GPa for CrN to ~21.9 GPa for Cr0.50O0.07N0.43, ~27.0 GPa for Cr0.47O0.22N0.31, and finally ~28.6 GPa for α-Cr2O3 is obtained. Cr0.50O0.07N0.43 and Cr0.47O0.22N0.31 coatings show a deferred onset temperature of nitrogen loss than CrN by ~100 °C. During annealing, the hardness value of the CrN coating decreases to ~11.3 GPa at 900 °C and then inversely increases to ~17.9 GPa at 1200 °C, while those of Cr0.50O0.07N0.43 and Cr0.47O0.22N0.31 coatings exhibit a continuous drop to ~14.5 and ~20.6 GPa at 1200 °C, respectively. The oxidation resistance of Cr-O-N coating is closely related to oxygen content. After oxidation at 800 °C for 20 h, the oxide scales of CrN, Cr0.50O0.07N0.43 and Cr0.47O0.22N0.31 coatings are ~0.22, ~0.16 and ~0.55 μm in thickness, respectively. In addition, the Cr2O3 coating always retains excellent mechanical and thermal properties regardless of in Ar or synthetic air. •O-addition into CrN causes a structural transformation from cubic to hexagonal.•The O-containing coatings reveal higher hardness than CrN coating.•Doping with O into CrN postpones the onset temperature of N-loss by ~100 °C.•The oxidation resistance of Cr-O-N coating is closely related to the O content.