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

Abstract Ti 1 − x − y Al x Ta y N 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 Ti 1 − x − y Al x Ta y N coatings more compact and exhibit a finer columnar structure. X-ray diffraction results show that the preferred orientation of Ti 1 − x − y Al x Ta y N coatings changes from (111) to (200) with increasing Ta content. Nanoindention results indicate that the hardness of the coatings sharply increases from 11 GPa without Ta to 31.2 GPa 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, Ti 0·44 Al 0.56 N coating is fully oxidized to α-TiO 2 and γ-TiO 2 at 600 °C. A significant increase of oxidation resistance for Ti 0·37 Al 0.42 Ta 0.21 N coating has been observed at 800 °C. However, a higher Ta content ( y = 0.37) is not conducive to retard the formation of α-TiO 2 phase at low temperature, but will increase lattice distortion. This can make the coating easy to spall during further oxidation.