High-temperature oxidation behavior and mechanism of a Co-50Ni-10Al-6Ta-8Cr-2W superalloy at 1000 °C

The high-temperature oxidation behavior of a Co-50Ni-10Al-6Ta-8Cr-2W alloy was investigated to clarify the role of W in oxide-scale evolution and stability. Oxidation in air at 1000 °C for up to 200 h followed predominantly parabolic kinetics, indicating diffusion-controlled growth. The parabolic rate constant was 1.51 × 10 −6 mg 2 cm −4 s −1 , lower than the previously reported value of 4.03 × 10 −6 mg 2 cm −4 s −1 for the W-free counterpart. At 25 h, the W-containing alloy had already developed an additional outermost (Co,Ni)Cr 2 O 4 spinel layer that was absent in the W-free counterpart. After 200 h, the W-containing alloy exhibited separate, continuous Cr 2 O 3 and (Al,Cr)TaO 4 layers instead of the interpenetrating Cr 2 O 3 + CrTaO 4 region observed in the W-free alloy. This reorganization is interpreted in terms of coupled changes in local elemental partitioning and tantalate chemistry: Al substitution may reduce Cr consumption by the Ta-rich oxide, while W-associated changes in the local chemical environment may favor Cr availability for separate chromia and outer spinel formation. Ab initio molecular dynamics calculations further showed that W in the γ phase selectively modifies local interfacial bonding, weakening Cr 2 O 3 /γ bonding while strengthening Al 2 O 3 /γ bonding. These results support an indirect role of W in reorganizing the multilayer scale and strengthening local Al 2 O 3 /γ bonding, contributing to improved long-term oxidation resistance.