Influence of Si and Ta mixed doping on the structure, mechanical and thermal properties of Ti Al N coatings

Alloying with Si or Ta is an effective method to upgrade the properties of TiAlN coatings. In the present work, we prepared Ti0.54Al0.46N, Ti0.46Al0.45Si0.09N as well as Ti0.42Al0.43Si0.09Ta0.06N coatings, and then investigated the effect of Si and Ta mixed doping on the structure, mechanical and thermal properties of TiAlN coatings. The hardness of cubic Ti0.54Al0.46N coating is 28.6 ± 0.9 GPa, whereas the mixed cubic and wurtzite Ti0.46Al0.45Si0.09N coating presents a higher hardness of 29.1 ± 1.1 GPa. The Si and Ta mixed doping leads to a maximum hardness of 34.1 ± 0.8 GPa for cubic Ti0.42Al0.43Si0.09Ta0.06N coating. The thermal stability of TiAlN coatings is more beneficial from the Si and Ta mixed doping. After annealing at 1100 °C, the Ti0.42Al0.43Si0.09Ta0.06N coating reaches a peak hardness of 37.9 ± 1.1 GPa due to the age-hardening effect from the spinodal decomposition, whereas the hardness of Ti0.54Al0.46N and Ti0.46Al0.45Si0.09N coatings decrease to 30.4 ± 1.3 and 32.9 ± 0.9 GPa, respectively. Furthermore, the Ti0.42Al0.43Si0.09Ta0.06N coating shows the best oxidation resistance. After oxidation at 1000 °C for 15 h, the oxide scale thickness of Ti0.42Al0.43Si0.09Ta0.06N is only ∼0.56 μm, whereas ∼0.91 μm thick oxide scale is formed on the Ti0.46Al0.45Si0.09N coating.