Effect of heat treatment on the structure and properties of ion-plated TiN films

Heat treatment processes were widely applied to improve the properties of hard coatings. However, the mechanisms that enhance thin film properties are still unclear. In this study, titanium nitride (TiN) films were deposited on 304 stainless steel using a hollow cathode discharge ion-plating technique. The specimens were heat-treated at 400 and 700 °C for 1 h under controlling atmosphere to reduce the oxidation of the thin films. After heat treatment, the microstructure and packing factor inside the TiN thin films were not significantly changed; however, the surface grain size was enlarged and surface roughness decreased. The variation of texture coefficient was more distinct at 700 than 400 °C. The hardness of heat-treated specimens increased 10–30% more than the as-deposited specimens with corresponding thickness. The 400 °C-treated specimens were all slightly harder than those treated at 700 °C, except one specimen. This can be attributed to the fact that the specimens treated at 400 °C have higher residual stress than those treated at 700 °C. The higher residual stress may be from the insufficient supply of thermal energy at 400 °C such that the rearrangement of atoms is incomplete in the processing time, which may lead to the poor accommodation of the atoms, and thereby increasing the residual stress.