Deposition of titanium nitride on surface-hardened structural steel by reactive magnetron sputtering

Abstract

High strength, low alloy steel of structural quality SIS-2172 (Swedish standard) was TiN deposited by a reactive d.c. magnetron sputtering process. The TiN deposition was performed on surface-hardened substrates. In this work we have studied the influence of the substrate deposition temperature on the TiN chemical composition at the interface as well as in the film. Also, the adhesion strength and hardness of the film and the substrate were measured. Several test methods were used: Auger electron spectroscopy, to estimate the chemical composition depth profiles from the upper parts of the TiN films at low, medium and high deposition temperatures; glow discharge optical spectrometry, to study the chemical composition depth profiles of the entire TiN film and the substrate; scratch test and micro and ultramicro hardness testers (Vickers' hardness), to study the critical load C L and the hardness of the TiN film and the substrate; electron microprobe analysis for quantitative chemical analysis of the depth profiles. As a result of decarborization, the substrate surface hardness drops from 820 to 600 HV after TiN deposition. This hardness was measured at a deposition temperature below 200°C. At the interface the C: Fe ratio decreases with increasing deposition temperature, while the C:N ratio increases with temperature up to 400°C and decreases at higher temperatures. The failure mechanism of the adhesion shows that the TiN film is adhesive at a deposition temperature below 300°C and cohesive at higher deposition temperatures up to 700°C. Both the critical load values and the TiN surface and bulk hardness correlate with the C:N ratio and reach a maximum between 300 and 400°C.