Facile formation of a superalloy-like microstructure in Ni77Ga23 alloys by rapid solidification processing

Abstract

Ni77Ga23 alloys were undercooled and rapidly solidified using glass fluxing treatment. An in situ diagnosis of dendrite growth velocity during rapid solidification processing suggests crystallization of a disordered solid solution from low to high undercoolings. While this diagnosis is consistent with an X-ray diffraction analysis, a neutron diffraction analysis suggests the formation of Ni3Ga phase in addition to the disordered solid solution. An EBSD analysis shows the formation of an equiaxed microstructure at a high undercooling. A HAADF-STEM study of equiaxed grains reveals a superalloy-like substructure, where cuboidal coherent precipitates of Ni3Ga phase are dispersed in the matrix of the disordered solid solution. A HRTEM study further reveals disordered nanodomains in the lattice of Ni3Ga phase. It is concluded that rapid solidification processing can lead to facile formation of a superalloy-like microstructure without an aging treatment.