Microstructural characteristics and thermal stability of a NiAl-based near-eutectic alloy fabricated by water-cooled copper mold method

The microstructural characteristics and thermal stability of a rapidly solidified NiAl–Cr(Mo)–Hf near-eutectic alloy fabricated by water-cooled copper mold method were investigated by SEM, EDAX, TEM, and HIP treatment. Rapid solidification resulted in the following effects which encompass refinement of the microstructure: cell size, lamellar spacing and precipitates, deviation from the equilibrium composition, solubility extension, and a transition from a Heusler phase to a Hf-rich phase. With respect to thermal stability, it is proposed that the localized destabilization of the microstructure after hot isostatic pressing (HIP) treatment is closely related to the presence of primary NiAl dendrites.