Effect of overheating treatment on the microstructure of NiAl-based alloy

The effect of melt overheating treatment on the microstructure of the alloy NiAl–28Cr–5.9Mo–0.1Hf(at.%)–0.05Ho(wt.%) has been investigated. Overheating treatment resulted in the decrease of the amount of primary NiAl from 12% in the normal sample to 8% in the overheated sample and in the refinement of NiAl/Cr(Mo) lamellar. The size of eutectic cell was increased from 37μm to 63μm after the treatment. Another significant change of the microstructure was the morphological instability of precipitates: the morphology of Cr(Mo) precipitates in primary NiAl was dendritic in the normal alloy but was cubic/spherical in the overheated alloy. The mechanisms responsible for these changes were discussed.