Influence of Co addition on constituent phases and performance of a NiCrAlYRe alloy system

MCrAlY alloys can serve as stand-alone overlay coatings or bond coats in thermal barrier coating systems, and their phase constituents play a vital role in determining their performance. In the present investigation, the influence of Co addition on the constituent phases of a NiCrAlY alloy system containing 3wt.% Re in the temperature range of 800°C-1200°C was predicted through thermodynamic modeling. Based on the modeling results, four NiCrAlY alloy systems with different levels of Co (0, 10wt.%, 20wt.% and 30wt.%) were prepared and evaluated experimentally. Scanning electron microscopy and transmission electron microscopy results show that the additions of Co increase the fractions of γ-Ni and β-NiAl at the expense of γ'-Ni₃Al and α-Cr, and thus change the depletion scheme from β→γ'→γ to β→γ during 1100°C oxidation.