Structure/mechanical properties relationship of titanium–oxygen coatings reactively sputter-deposited

Ti–O coatings are DC sputter-deposited on HSS substrates from titanium targets in various Ar–O2 reactive mixtures leading to different structural states, from pure titanium to TiO2 films. These coatings are structurally (X-ray diffraction measurements) and mechanically (micro hardness and intrinsic stress measurements) characterised as a function of the inlet oxygen flow rate. Special attention is paid to the case of FCC TiOx (0.9<x<1.5) sub-oxide which presents an interesting level of hardness. TiOx layers composition and internal stress are found to depend on deposition parameters like oxygen flow rate, substrate bias and its position with respect to magnetron axis. The intrinsic stress of TiO films is shown to control the cracking damage under high-load Vickers indentation as well as in single pass and multi-pass scratch testing operation. Finally, coating delamination is likely to occur by interface cracking triggered by ‘coalescence along the interface’ from two neighbouring through-thickness crack tips.