Annealing studies and oxidation tests of a hybrid multilayer arrangement of cathodic arc evaporated Ti-Al-N and reactively sputtered Ta-Al-N coatings

A multilayer architecture of cathodic arc evaporated Ti1-xAlxN and reactively sputtered Ti1-yAlyN layers is investigated in terms of thermal stability, thermo-mechanical properties, and oxidation resistance. In a recent study, Ti1-xAlxN/Ti1-yAlyN multilayers demonstrated increased hardness and stability upon annealing treatments as compared with their monolithically grown counterparts. However, the respective coatings prepared by arc/arc configuration were deficient in oxidation tests. The present work emphasises on an improvement in oxidation resistance taking advantage of a hybrid processes using cathodic arc evaporation for Ti1-xAlxN layers and reactive sputter deposition for Ti1-yAlyN. Variations in Ti1-yAlyN layer thicknesses are realised by varying the Ta0.75Al0.25 cathode powering between 3, 4, and 5 kW, respectively. Multilayers of thin arc evaporated Ti1-xAlxN (supersaturated cubic structure, similar to 18 nm layer thickness) and reactively sputtered Ti1-yAlyN (super-saturated cubic structure, similar to 2 nm layer thickness) layers exhibit as-deposited hardness values of similar to 30.7-34.6 GPa. Upon vacuum annealing a hardness increase to peak values of similar to 33.6-36.4 GPa at 800 degrees C is triggered by spinodal decomposition of the matrix as well as slight intermixing of the individual layer interfaces. The hardness is of still similar to 31.4-33.5 GPa even after annealing at 1000 or 1100 degrees C. For all Ti1-xAlxN/Ti1-yAlyN multilayers, 80-90% of the initial similar to 2.6 mu m thin multilayer remains unaffected even after 20 h exposure to ambient air at 850 degrees C, highlighting the significant increase in oxidation resistance with respect to monolithically grown Ti1-xAlxN and Ti1-yAlyN coatings. (C) 2015 Elsevier B.V. All rights reserved.