Deformation mechanisms and crack routes of CrAlN coatings

CrAlN coatings possess high hardness and thermal stability, but also increased brittleness due to strong covalent AlN bonding. With poor plasticity due to frozen perfect dislocation activities, individual columnar grain acts as the fundamental deformation element that controls overall deformation via grain boundary activities. Damage tolerance can be thus improved by high compressive stress that hinders grain boundary glide and volume-dilation phase transition. By investigating deformation structure, we also found that zigzagged cracking modes might be attributed to atomic-scale hardening heterogeneity. Additionally, stress-induced nano-twinning was found, which also contributes to the improved fracture resistance. [Display omitted] •Grain boundary activities are the main deformation mechanisms.•High compressive stress impedes grain boundary glide.•Twinning and stress-induced phase transition contribute to crack resistance.•Local heterogeneity facilitates wavy cracking routes.