Effect of dysprosium addition on the cyclic oxidation behaviour of CoNiCrAlY alloy

The cyclic oxidation behaviour of a Co32Ni21Cr8Al0.6Y (wt.%) alloy with and without the addition of 0.2 wt.% dysprosium was investigated at 800 and 1100 °C in static laboratory air. The Dy-containing alloy showed a faster θ- to α-alumina transformation and significantly less weight gain than Dy-free alloy. Under cyclic oxidation at 1100 °C, Dy addition produced a continuous and protective Al2O3 scale. The Dy-free alloy exhibited poor oxidation resistance. Scale spallation led to the development of a complex oxide scale and internal precipitation: (Al,Cr)2O3 on the surface, followed by a Al2O3 layer, then (Al,N) precipitates alone beneath the external scale.

Research highlights
► The cyclic oxidation behaviour of a CoNi-based alloy with small addition of Dy.
► Dy accelerated the θ- to α-Al2O3 Phase transformation.
► Dy refined the oxide grains and lowered the cyclic oxidation weight gain.
► At 1100 °C Dy-free alloy suffered severe oxidation and inward diffusion of nitrogen.
► No spallation or internal-precipitation was observed for Dy-containing alloy.