Effect of B-doping on the mechanical properties, thermal stability and oxidation resistance of TiAlN coatings.

In this study, boron was introduced into TiAlN coating to improve its performance. Ti 0.44 Al 0.56 N, Ti 0.42 Al 0.54 B 0.04 N, and Ti 0.36 Al 0.55 B 0.09 N coatings were synthesized by arc evaporation, and the effect of B on structure, mechanical and thermal properties of TiAlN coatings were investigated by detailed experiments. Furthermore, we studied the formation energy (E f) of cubic and wurtzite phases in Ti 1-x-y Al x B y N coatings by density functional theory (DFT) calculations. First-principle calculations indicate that the incorporation of B reduces the solid solubility of Al in cubic TiN, which is confirmed by the experimental results. Ti 0.44 Al 0.56 N coatings show a face-centered cubic structure while Ti 0.42 Al 0.54 B 0.04 N and Ti 0.36 Al 0.55 B 0.09 N exhibit a mixed structure of cubic and wurtzite phases. In addition, experimental results show that doping B by 4 at.% gives rise to an increase in hardness from 30.1 ± 0.4 GPa of Ti 0.44 Al 0.56 N to 32.7 ± 0.9 GPa of Ti 0.42 Al 0.54 B 0.04 N, while further increasing B content to 9 at.% triggers a dramatic decrease of the hardness down to 23.0 ± 0.6 GPa (Ti 0.36 Al 0.55 B 0.09 N). Alloying with B also significantly improves the oxidation resistance of TiAlN coatings by retarding the transformation of a-TiO 2 to r-TiO 2 and promoting α-Al 2 O 3 formation. • Ab initio calculations show that B-addition reduces the solubility of Al in c-TiN. • B-addition into TiAlN promotes the wurtzite AlN formation during deposition. • Adding 4 at.% B into TiAlN coating increases its hardness. • Alloying with B improves the oxidation resistance of TiAlN coatings. [ABSTRACT FROM AUTHOR]