The formation of Si/B-bearing innerlayer and its effect on the growth and adherence of chromia scale formed by pre-oxidation of cobalt-chromium based alloy

CoCr-based alloys are widely utilized in dental implants and serve as metallic frameworks for porcelain-fused-to-metal (PFM) restorations, owing to their cost-effective, excellent wear and corrosion. However, interfacial failure between the base alloy and the porcelain arose over extended periods of use in oral environments. Therefore, establishing a reliable metal-porcelain interface is of critically importance. This study investigates how the addition of boron impacts the pre-oxidation scale and its mechanical properties of Co-Cr-W-Cu-Si-(0, 0.5, 1.1 wt.%) B alloys at 928 °C for 10 mins in air. Surface analysis indicated that Si and B stabilized Cr 2 O 3 scale grown on the surface of CoCr based alloys. As the B concentration increased, the scale became thinner, and its morphology transformed from Cr 2 O 3 to a combination of outer CoCr 2 O 4 spinel and inner Cr 2 O 3 . Amorphous SiO₂ was detected along the scale-alloy interface together with B 2 O 3. The mechanical stability of the scale along with its adhesion to the matrix increases with increasing B concentration. The synergistic impact of Si and B is probably due to the amorphous innerlayer playing as an effective barrier to the transportation of reactants and slow down the oxide scale growth. Meanwhile, the morphology of pining-like arrangement for amorphous SiO 2 layer increases the factual contact area between the oxide scale and matrix, rendering it less susceptible to fracture.