Thermal and thermo-mechanical properties of Ti–Al–N and Cr–Al–N coatings

Metastable Ti–Al–N and Cr–Al–N coatings have been proven to be an effective wear protection due to their outstanding mechanical and thermal properties. Here, a comparative investigation of mechanical and thermal properties, for Ti–Al–N and Cr–Al–N coatings deposited by cathodic arc evaporation with the compositions (c-Ti0.52Al0.48N, c/w-Ti0.34Al0.66N and c-Cr0.32Al0.68N) widely used in industry, has been performed in detail. The hardness of Ti0.52Al0.48N and Ti0.34Al0.66N coatings during thermal annealing, after initially increasing to the maximum value of ~ 34.1 and 38.7 GPa with Ta up to 900 °C due to the precipitation of cubic Al-rich and Ti-rich domains, decreases with further elevated Ta, as the formation of w-AlN and coarsening of precipitated phases. A transformation to Cr2N and finally Cr via N-loss in addition to w-AlN formation during annealing of the Cr0.32Al0.68N coating occurs, and thus results in a continuous decrease in hardness. Among our coatings, the mixed cubic-wurtzite Ti0.34Al0.66N coating exhibits the highest thermal hardness, but the worst oxidation resistance. The Cr0.32Al0.68N coating shows the best oxidation resistance due to the formation of dense protective α-Al2O3-rich and Cr2O3-rich layers, with only ~ 1.4 μm oxide scale thickness, after thermal exposure for 10 h at 1050 °C in ambient air, whereas Ti–Al–N coatings are already completely oxidized at 950 °C.

► Thermal properties of c-Ti0.52Al0.48N, c/w-Ti0.34Al0.66N and c-Cr0.32Al0.68N coatings are researched.
► C-Ti0.52Al0.48N exhibits the best thermal stability.
► Mixed c/w-Ti0.34Al0.66N coating exhibits the highest thermal hardness, and the worst oxidation resistance.
► Cr0.32Al0.68N coating shows the best oxidation resistance, and the worst thermal stability.