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 3 wt.% 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, 10 wt.%, 20 wt.% and 30 wt.%) 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.

Research highlights
► The influence of Co on the phases of a NiCrAlY alloy system was evaluated.
► Co additions reduce γ′-Ni3Al formation and increase fractions of β-NiAl and γ-Ni.
► It changes the depletion scheme from β → γ′ → γ to β → γ during oxidation at 1100 °C.
► The stabilization of β caused by Co leads to an improvement in oxidation resistance.