Thermal stability and oxidation resistance of Cr1−xAlxN coatings with single phase cubic structure

Abstract

Cr-Al-N coatings possessing excellent oxidation and wear resistance have been widely applied in cutting tools. Here, the thermal stability and oxidation resistance of Cr1−xAlxN coatings with single phase cubic structure are studied in detail. Incorporation of Al into CrN coating leads to an increased hardness from ∼14.9 GPa for CrN to 26.3 GPa for Cr0.48Al0.52N and to 27.6 GPa for Cr0.32Al0.68N. Increasing Al content of Cr1−xAlxN delays the N-loss, but promotes the wurtzite (w) AlN formation during thermal annealing. The Al-addition highlights a significant improvement in oxidation resistance of CrN coating due to the formation of a dense and protective Cr-Al-oxide scale. However, the Cr0.48Al0.52N coating with lower oxidation rate constant and higher activation energy exhibits better oxidation resistance compared with Cr0.32Al0.68N coating. After oxidation at 1100 °C for 15 h, the Cr0.48Al0.52N coating only exhibits a dense Cr-Al-oxide scale with a thickness of ∼0.4 μm whereas a ∼1.75 μm thick oxide scale with Cr-Al-oxide mixed top-layer and Al-rich porous precipitation sublayer is obtained by Cr0.32Al0.68N coating. Additionally, the formation of dense oxide scale on the surface of Cr1−xAlxN coatings has an obvious inhibited effect on the thermal decomposition process.