Influence of Al2O3 layer thickness on high-temperature stability of TiAlN/Al2O3 multilayers

TiAlN/Al2O3 multilayers which have constant TiAlN layer thickness (10 nm) and various Al2O3 layer thicknesses ranging from 0.5 nm to 4.5 nm were synthesized on alumina substrate by magnetron sputtering. The effects of annealing on the mechanical and structural properties of the multilayers were investigated using X-ray diffractometry (XRD), X-ray reflection (XRR), X-ray photoelectron spectroscopy (XPS), and Nanoindenter. It was found that the hardness for the multilayers with Al2O3 layer thickness from 0.5 nm to 4.5 nm was much higher than TiAlN or Al2O3 monolayer and their hardness values were over 36 GPa. The annealed multilayers displayed high-temperature stable hardness and elastic modulus. The hardness increases from 36 GPa of as-deposited to 39 GPa of annealed multilayer at 700 °C in the case of lAl2O3=1.2nm. It also indicates the highest elastic modulus of 560 GPa after 700 °C annealing. The multilayers had polycrystallines of TiAlN(1 1 1) and TiAlN(2 2 2) textures. Compared with as-deposited multilayers, the annealed multilayers exhibited unchanged textures. The interface and layered structure also showed good high-temperature stability.