Synthesis and characterization of hardness-enhanced multilayer oxide films for high-temperature applications

Multilayer oxide coatings consisting of amorphous Al2O3 and crystalline TiO2 nanolayers have been deposited using reactive pulsed d.c. magnetron sputtering at different partial pressures of oxygen. Hardness enhancement has been observed in oxide multilayer coatings with amorphous Al2O3 as the majority component. These coatings had greater hardness-to-modulus ratios and showed greater resistance to wear over monolithic Al2O3 and TiO2 majority phase multilayers. Multilayer films retain their high hardness up to ~ 800 °C in air; some hardness enhancement in the Al2O3 majority phase multilayer coating remains even after 1 h of air annealing at 1000 °C. The hardness decrease at elevated temperatures is due to the roughening of interfaces between nanolayers, which can be attributed to the annealing-driven change of crystallographic texture of TiO2 layers.