Improving toughness and oxidation resistance of TiB2 films by introducing W interlayer

This study employed alternating dcMS-TiB₂ and dcMS-W in a pure argon atmosphere to deposit TiB₂/W nanomultilayer films. The incorporation of the W metal interlayers facilitated atomic diffusion, interfacial mixing, and bonding effects, which effectively inhibited the segregation of B-rich phases and mitigated the stoichiometric deviation of TiB_x at the interfaces. The influence of varying the W interlayer thicknesses on mechanical properties and oxidation resistance of the TiB₂/W films was systematically investigated. The results revealed that the films exhibit a nanomultilayer structure, wherein the W interlayers disrupted the columnar growth of TiB₂ grains, resulting in a predominantly nanocrystalline morphology with smooth and dense cross-sectional features. The TiB₂/W film with 1.3-nm-thick W interlayer exhibits a hardness of 33.0 ± 0.9 GPa, while the TiB₂ single-layer film is 34.9 ± 1.2 GPa. The TiB₂/W film with a 3.2-nm thick W interlayer demonstrates a 27 % increase in scratch-derived toughness, a 40 % improvement in indentation-derived toughness, and a 57 % enhancement in adhesion strength compared to that of the TiB₂ single-layer film. Furthermore, oxidation tests at 500 °C revealed that the surface of the oxide scales of the TiB₂/W films was WO₃-rich, independent of the oxide scale thickness. The W prefers to form large WO₃ particles on the surface of the oxide scales of the TiB₂/W films. For the thickness of TiB₂/W film with W interlayers >4.9 nm, the formed WO₃-rich scale blocks oxygen interaction with B, thereby significantly retarding the oxidation kinetics.