Influence of TiN and ZrN insertion layers on the microstructure, mechanical and thermal properties of Cr-Al-N coatings

Cr-Al-N coatings are widely used as wear protection for advanced machining and other high temperature applications due to their superior mechanical and thermal properties. Multilayer architecture to further optimize the properties of Cr-Al-N coatings attracts great attention. Here, we investigate the effect of TiN and ZrN insertion layers on the microstructure, mechanical and thermal properties of Cr-Al-N coatings by deposition of CrAlN/TiN and CrAlN/ZrN multilayer coatings with the same modulation period consisting of 7 nm CrAlN and 2 nm TiN (ZrN) sublayers. The CrAlN/TiN coating exhibits superlattice structure with coherent interfaces and thereby a high hardness value ~ 30.3 GPa, whereas only a hardness value of ~ 27.4 GPa is obtained by the CrAlN/ZrN coating with incoherent interfaces. The insertions of TiN and ZrN layers have a different influence on thermal decomposition process of Cr-Al-N coating during annealing due to the discrepancy of interfacial structure, where the TiN insertion layer improves the thermal stability of Cr-Al-N via deferring the w-AlN formation and N-loss, and the ZrN insertion layer has not obvious effect on the thermal stability. Nevertheless, CrAlN/TiN and CrAlN/ZrN coatings show a significantly inferior oxidation resistance than Cr-Al-N coating. After oxidation of 10 h at 900 °C the Cr-Al-N coating presents almost unaffected nitride layer thickness, whereas the CrAlN/TiN coating exhibits an oxide scale of ~ 0.9 μm and the CrAlN/ZrN coating has already been fully oxidized.