Forming Mechanism of Refined Granular Microstructure of Undercooled Cu70Ni30 Melts
The microsturctural evolution of Cu70Ni30 alloy melts was systematically investigated in wide undercooling range of 20 K to 270 K by using glass fluxing technique. Experiment results of solidified microstructural evolution show that two kinds of refined granular grains and two kinds of dendrites appear under different undercooling ranges. Under 38 K ～ 120 K undercooling range,the first granular crystalline formed from dendrite with increasing undercooling. It is show that the grain refindment mechanism consists of two stages. The dendrite formed in rapid solidification is firstly disintegrated into fragments owing to the remelting during the recalescence and the subsequent normal solidification. And then the fragments, under the driving force of their surface energy, merge through the boundary migration,thus leading to the first granular crystalline.