P96] Experimental investigations and simulations of the effect of Ta content on formation of fcc-free surface layers in graded cemented carbides

Abstract

The deteriorative wurtzite (w) AlN formation and N-loss of Cr–Al–N coatings while exposed to high temperature limit their high temperature applications. Here, the Cr0.32Al0.68N, Cr0.30Al0.68Zr0.02N and Cr0.29Al0.66Zr0.05N coatings with high Al content as well as Cr0.48Al0.52N and Cr0.44Al0.50Zr0.06N coatings with low Al content were deposited by cathodic arc evaporation in order to study the effect of Zr on structure, mechanical and thermal properties on Cr–Al–N coatings. Zr-addition results in a structural transition from single phase cubic structure for Cr0.32Al0.68N to mixed cubic-wurtzite structure for Cr0.30Al0.68Zr0.02N and Cr0.29Al0.66Zr0.05N, whereas both Cr0.48Al0.52N and Cr0.44Al0.50Zr0.06N low Al-content coatings exhibit a single phase cubic structure. Zr is very effective in increasing the hardness of the Cr–Al–N, where Zr-containing coatings exhibit a higher hardness than Cr–Al–N coatings by 4–6 GPa. Alloying with Zr into cubic Cr–Al–N effectively retards the thermal decomposition process including the w-AlN and especially N-loss during thermal annealing. However, Zr-addition causes a drop in oxidation resistance of Cr–Al–N coatings. The Cr0.29Al0.66Zr0.05N and Cr0.44Al0.50Zr0.06N coatings are already completely oxidized after oxidation of 20 h at 1100 °C, other coatings still exhibit intact nitride layer. Additionally, the Cr0.29Al0.66Zr0.05N and Cr0.44Al0.50Zr0.06N coatings with high Zr content shows the best oxidation resistance at 1000 °C in the range of 900–1000 °C.