LAUSR

Abstract In this paper, the microstructure evolution in NiCoCrAlYTa alloy powders at two different oxidation temperatures (900 and 1100 °C) was investigated. The results showed that higher oxidation temperature gave higher oxidation rate. Increasing temperature accelerated the diffusion of alloying elements outwards to the powder surface and oxide growth rate. Alumina was the main oxide when the Al content in the powder was high enough. With Al depletion, β phase was depleted by phase transformation of β-γ′-γ at 900 °C and β-γ at 1100 °C. When the Al content in the powder was not enough to maintain the growth of alumina layer, spinel phases were highly formed above the alumina layer and internal alumina begun to largely form. Y-rich and Ta-rich phases were detected beneath the oxide layers at long oxidation time. The diffusion behavior of alloying elements in the different oxidation stages was discussed.