Microstructure evolution mechanisms of undercooled Ni80Cu20 alloys

Abstract

AbstractMicrostructure evolution mechanisms of undercooled Ni80Cu20 alloys were systematically studied, and two types of grain refinement were observed in the as-solidified microstructures. The first type of grain refinement appeared in a low undercooling range (i.e., 50 K ≤ ΔT ≤ 90 K). The remelting of primary dendrites during or after rapid solidification was due to liquid/solid interfacial tension and chemical superheating. The second type of grain refinement occurred in a high undercooling range (i.e., ΔT ≥ 165 K), in which the liquid phase pressure drop due to solidification contraction induced the flow of liquid in the inter-dendrite region and produced stress accumulation in the dendrites. At the slow solidification stage, i.e., post-recalescence period, recrystallization was observed. In addition, highly undercooled Ni80Cu20 alloy melts were quenched before rapid solidification by Ga–In liquid alloy, and partially recrystallized microstructures were obtained. Using electron backscattering diffraction and transmission electron microscopy techniques, the occurrence of recrystallization was verified experimentally.