Grain boundaries in the refined solidification structure of undercooled Ni75Pd25

Abstract: When a single-phase alloy solidifies in a low-undercooling range or above a critical undercooling, grain-refined structures are obtained. Taking Ni75Pd25 alloy as an example, the microscopic orientation of the refined grains was investigated by electron backscattered diffraction technology. It is revealed that the refined grains at low undercooling are completely randomly distributed. In the refined structure at high undercooling, certain grain boundaries with misorientation angles less than 5° can be observed, while most of the grain boundaries have large misorientation angles. The inverse pole figure indicates that the refined grains at high undercooling have a textured crystallographic orientation. The fact that twins exist in the refined structure at high undercooling and the dendritic substructure arms exhibit no misorientation supports such an argument that the grain refinement at high undercooling results from the recrystallization of the solidification dendrites. [Copyright &y& Elsevier]