Structure, mechanical, and thermal properties of Ti 1‐x Al x N/CrAlN ( x = 0.48, 0.58, and 0.66) multilayered coatings

Nano‐multilayered TiAlN/CrAlN coatings combining advantages of Ti‐Al‐N and Cr‐Al‐N are considered to be promising candidates for advanced machining processes. Here, the structure and thermal properties of Ti 1‐ x A l x N/CrAlN ( x  = 0.48, 0.58, and 0.66) multilayered coatings as well as referential Ti 1‐ x A l x N and Cr 0.32 Al 0.68 N monolithic coatings were investigated. Ti 1‐ x A l x N coatings show a structural transformation from cubic structure for x  = 0.48 to mixed cubic and wurtzite structure for x  = 0.58 and 0.66, and Cr 0.32 Al 0.68 N coating exhibits a single cubic structure. Through a multilayer arrangement with Cr 0.32 Al 0.68 N layers, the Ti 0.52 Al 0.48 N and Ti 0.42 Al 0.58 N layers can be stabilized in their metastable cubic structure, but the Ti 0.34 Al 0.66 N layer still tends to crystallize in the mixed cubic and wurtzite structure. The hardness of Ti 0.52 Al 0.48 N/CrAlN and Ti 0.42 Al 0.58 N/CrAlN coatings is higher than that of corresponding monolithic coatings regardless of as‐deposited and annealed states. Especially, after annealing at 800°C, the Ti 0.52 Al 0.48 N/CrAlN and Ti 0.42 Al 0.58 N/CrAlN coatings reach their peak hardness of ~34.2 and 32.8 GP a due to the spinodal decomposition of Ti 1‐ x A l x N layers. However, the oxidation resistance of Ti 1‐ x A l x N/CrAlN coatings is mainly up to the Al content of Ti 1‐ x A l x N layers, where only the Ti 0.34 Al 0.66 N/CrAlN coating can survive the 10 h exposure to air at 1000°C.