Influence of Ti on the mechanical properties, thermal stability and oxidation resistance of Al–Cr–N coatings

Al0.68Cr0.32N, Al0.66Cr0.25Ti0.09N and Al0.62Cr0.20Ti0.18N coatings prepared by cathodic arc evaporation exhibit single phase cubic structure. Increasing Ti content from 0 to 18 at% causes a continuous hardness promotion from ∼27.4 to 33.2 GPa, however, a drop in elastic modulus from ∼481.8 to 337.1 GPa. Annealing of Al–Cr–N in Ar results in a transition into stable phases of wurtzite (w-) AlN and Cr via an intermediate phase Cr2N. Alloying with Ti into Al–Cr–N promotes the w-AlN formation, but retards the N-loss, where the finally stable phases of w-AlN, Cr and TiN after annealing are obtained. Nevertheless, the Ti-addition has a significantly inferior effect on the oxidation resistance of Al–Cr–N coating due to the higher affinity between Ti and oxygen, where the Al0.68Cr0.32N and Al0.62Cr0.20Ti0.18N coatings after oxidation at 1100 °C for 20 h reveal oxide scales of ∼1.3 and 4.0 μm, respectively.