Mechanical and thermal properties of AlN/Ti1-xAlxN (x=0, 0.45 and 0.62) multilayers

Ti1-xAlxN coatings with face-centered cubic structure are widely used as wear-resistant protective materials. Construction of multilayer architecture is an efficient method to tailor the properties of Ti1-xAlxN coatings. In this work, the structure, mechanical and thermal properties of AlN/Ti1-xAlxN (x = 0, 0.45 and 0.62) multilayers as well as corresponding monolithic coatings are studied. Monolithic TiN, Ti0.55Al0.45N and Ti0.38Al0.62N coatings exhibit single cubic structure, corresponding to their hardness of similar to 26.4, 28.6 and 32.7 GPa, respectively. The epitaxial growth between AlN and TiN (Ti0.55Al0.45N) layers increases the hardness to similar to 30.5 and similar to 31.4 GPa, whereas the AlN/Ti0.38Al0.62N multilayer with incoherent interface only has a hardness of similar to 24.2 GPa. Even if the AlN insertion layer promotes the thermal decomposition of Ti0.55Al0.45N coating, the AlN/Ti0.55Al0.45N coating still present a higher hardness than Ti0.55Al0.45N coating during annealing up to 1000 degrees C. The AlN insertion layer has a positive effect on the Ti1-xAlxN coatings regardless of coherent and incoherent interfaces. Especially, the oxidation resistance of AlN/Ti1-xAlxN multilayers is predominantly influenced by the total Al content rather than the interfacial states. The AlN/Ti0.38Al0.62N multilayer with incoherent interface behaves the best oxidation resistance.