Effect of deposition temperature on the morphology, structure, surface chemistry and mechanical properties of magnetron sputtered Ti70–Al30 thin films on steel substrate

The present study investigates the effect of deposition temperature (ambient and liquid N2 temperatures) and sputtering power on the mechanical and chemical properties of magnetron sputtered Ti3Al thin films on 316 stainless steel substrates. Film structure and morphology are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Films deposited at liquid N2 temperature showed a dense nanocrystalline structure, whereas ambient temperature deposited films showed voids and discontinuities in their columnar grain morphology as evident from TEM analysis. A detailed analysis of the surface chemistry of DC-magnetron sputtered thin films is performed using X-ray photoelectron spectroscopy (XPS). Glancing angle XPS studies are carried out to study the chemistry at a few layers beneath the surface and monitor changes in thin film stoichiometry. Surface oxides are always present in the films and are more prominent in ambient temperature deposition. Higher power leads to an enhanced metallic Ti3Al component as detected from XPS Al(2p) and Ti(2p) lines. Films deposited at liquid N2 temperature are nanocrystalline and stoichiometric (Ti/Al∼3:1) and showed improved hardness than those deposited at ambient temperatures under similar sputtering conditions and constant film thickness. The hardness of the films increases with increased sputtering power at ambient temperature deposition.