Magnetron sputtered Ti–Si–C thin films prepared at low temperatures

Abstract

In this work, low temperature Ti–Si–C films were deposited onto silicon and polished stainless steel and high-speed steel substrates by DC magnetron co-sputtering from two Ti targets, one with C pellets and the other with Si pellets. The composition of the films was investigated by Electron Probe Micro-Analysis (EPMA), while structure was characterized using a conventional X-ray diffractometer. The hardness and residual stress were studied using depth-sensing indentation and substrate deflection measurements (using Stoney's equation), respectively. Plots of both C/Ti and Si/Ti atomic ratios as a function of the targets current ratio showed the existence of two distinct regions: (i) a silicon rich zone (target current ratios, I Ti–C/ I Ti–Si, up to 0.5, Si/Ti atomic ratios in the range of 0.21–0.27 and low C/Ti atomic ratio, < 0.17), and (ii) a carbon rich zone (films were prepared with target current ratios, I Ti–C/ I Ti–Si, between 1.4 and 2.9, with C/Ti atomic ratio in the range of 0.29–0.34 and low Si/Ti atomic ratio). These two composition regions were found to be of particular influence in all scanned properties. Structural analysis revealed the possibility of the coexistence of different phases in the prepared films, namely a sub-stoichiometric fcc NaCl-type TiC structure and a Ti metallic phase (α-Ti or β-Ti). The coatings with highest carbon content (carbon rich zone), exhibit mainly a sub-stoichiometric fcc NaCl TiC-type structure. The films within the silicon rich zone show a progressive tendency for amorphization. The existence of some C or even Si(C) amorphous tissues cannot be excluded. The residual stress states ( σ r) and the hardness values ( H) were relatively low, σ r < − 1 GPa and H = 7–11 GPa, respectively, which could be a consequence of the low crystallinity order exhibited by the coatings and/or due to the high amounts of Ti in the coatings.