Surface characterisation of Ni-free Co–Cr–W-based dental alloys exposed to high temperatures and the effects of adding silicon

• We study the effects of Si on surface oxide films of Ni-free Co–Cr–W dental alloys.
• Specimens of the alloys are oxidised in air at 1273 K for 15 min.
• A CoO phase is dominant at the outermost surface of all the alloys.
• Si hinders formation of Co oxides and stabilises the films, which contain Cr2O3.
• The Cr2O3 and SiO2 layers formed protect against oxygen diffusion.

We characterised the effects of the addition of Si on the surface oxide films formed on Ni-free Co–Cr–W-based dental alloys. The addition of Si prevented the formation of Co-containing oxides and stabilised the uniform oxide films, which primarily consisted of Cr2O3. Si segregation was noticed at the interface between the oxide films and the metal substrate. The Cr2O3 and SiO2 layers formed were observed to protect against oxygen diffusion, reducing the oxidation rate at elevated temperatures. Further, the addition of Si reduced the thickness and surface roughness of the oxide films.