Oxidation behavior of the B2-phase-strengthened FBB8 alloy under various surface roughness conditions

The effect of surface roughness on the oxidation behavior of the FBB8 (Fe-9.96Ni-10.7Cr-6.49Al-0.25Zr-3.49Mo-0.0094B) alloy in air at 900°C was investigated in this study. The results indicated that the parabolic rate constants ( K _p ) for the samples with arithmetic roughness average (Ra) values of 0.2 µm, 1.2 µm and 2.1 µm were 3.68×10⁻¹³ g²·cm⁻⁴·s⁻¹, 5.26×10⁻¹³ g²·cm⁻⁴·s⁻¹ and 7.91×10⁻¹³ g²·cm⁻⁴·s⁻¹, respectively. This positive correlation revealed that the increasing of surface roughness accelerated the mass gain in the early oxidation stage. When the substrate Al content was depleted below a critical level, the B2 phase acted as an “aluminum reservoir” to replenish consumed Al. The sample with Ra of 0.2 µm exhibited severe internal oxidation due to its lower surface area to volume ratio. In contrast, the ground sample with Ra of 2.1 µm reduced internal oxidation by introducing a stress-induced scale at the surface that promoted outward diffusion of Al. This study elucidates the influence of surface roughness on the oxidation behavior of FBB8 alloy through its effects on element diffusion and oxide film formation, offering key insights for optimizing surface treatment processes.