Effect of Ta content on microstructure, hardness and oxidation resistance of TiAlTaN coatings

Abstract

Ti1−x−yAlxTayN coatings with various Ta contents (y=0.00–0.37) have been prepared by magnetron sputtering. Scanning electronic microscopy results show that the increased Ta content makes Ti1−x−yAlxTayN coatings more compact and exhibit a finer columnar structure. X-ray diffraction results show that the preferred orientation of Ti1−x−yAlxTayN coatings changes from (111) to (200) with increasing Ta content. Nanoindention results indicate that the hardness of the coatings sharply increases from 11GPa without Ta to 31.2GPa at y=0.21. Solution strengthening caused by doping Ta is the main reason for the rapid increase of hardness. After oxidation in ambient air, Ti0·44Al0.56N coating is fully oxidized to α-TiO2 and γ-TiO2 at 600°C. A significant increase of oxidation resistance for Ti0·37Al0.42Ta0.21N coating has been observed at 800°C. However, a higher Ta content (y=0.37) is not conducive to retard the formation of α-TiO2 phase at low temperature, but will increase lattice distortion. This can make the coating easy to spall during further oxidation.