Microstructure transformation and grain refinement during non-equilibrium solidification of a highly undercooled alloy system

Abstract

The rapid solidification of Ni-Cu alloy was systematically studied. It was found that the solidification interface became smoother and more random with the increase of undercooling. The results show that there are two grain refinements at the small and large undercooling, and the undercooling required for the second grain refinement increases with the increase of Cu mass fraction. In the study of grain refinement, it is found that there is no high-strength texture at large undercooling, and there are high-density high-angle grain boundaries, twin boundaries and a large number of undistorted grains, which preliminarily proves the occurrence of recrystallization. Some dislocations exist in microstructure at large undercooling, but the microhardness decreases sharply, which indicates that the stress accumulated during rapid solidification causes plastic strains and promotes recrystallization. It is further proved that the grain refinement at large undercooling is caused by stress-induced recrystallization.