Thermal oxidation, mechanical response and tribological performance of WS2 coatings deposited by magnetron sputtering

In this work, the thermal stability, oxidation behavior, and tribological performance of WS 2 coatings deposited by magnetron sputtering on AISI D2 steel and Si substrates were investigated. In situ X-ray diffraction analyses from room temperature to 700 °C showed that the hexagonal 2H-WS 2 phase remained dominant during intermediate-temperature exposure, while minor WO 3 formation was detected by Rietveld refinement at 300 °C and became distinguishable in the diffraction patterns around 400 °C. WO 3 became the predominant phase above 600 °C. Scanning electron microscopy revealed homogeneous and defect-free coatings in the as-deposited condition, whereas thermal treatment at 700 °C produced increased roughness, microcracks, and local delamination due to thermal stresses and oxidation. Cross-sectional observations confirmed the designed coating architecture, consisting of a dense columnar WS 2 coating deposited on a Ti interlayer intended to promote adhesion to the substrate. Nanoindentation results indicated moderate hardness (6.75 ± 0.4 GPa) and a relatively low elastic modulus (121.03 ± 10.45 GPa), suggesting adequate stress redistribution capability. Scratch tests showed a transition from cohesive cracking to delamination with increasing load. Tribological tests demonstrated a significant reduction in friction at room temperature compared with the substrate, attributed to the interlaminar sliding of WS 2 . At elevated temperatures, oxidation degraded the lubricating behavior, although friction stabilized at 600 °C due to the formation of oxidized phases. Wear rate evolution showed a non-monotonic response associated with coating degradation at intermediate temperatures and the formation of stable tribo-oxidative layers at higher temperatures.