Element accumulation beneath the scale/alloy interface of a CoNiCrAlReY alloy

In the present study, two types of subscale Cr and Re accumulation found at scale/alloy interface of two batches of Co32Ni21Cr10Al3.5ReY alloys are described. During oxidation, one alloy developed a supersaturated Cr-Re rich layer and another formed Cr-Re precipitates beneath the oxide in the subscale region. Diffusional and thermodynamic modelling showed the accumulation is a result of decreasing Cr and Re chemical potentials with Al depletion. The observed difference in accumulation forms is caused by the different phases in two alloys, with the former being γ, β, α and σ and the latter having only γ, β and σ.