Refinement Mechanism of Microstructure of Undercooled Nickel Based Alloys

Abstract

Through the use of purification and recirculation superheating techniques on molten glass, the Ni65Cu33Co2 alloy was successfully undercooled to a maximum temperature of 292 K. High-speed photography was employed to capture the process of interface migration of the alloy liquid, allowing for an analysis of the relationship between the morphological characteristics of the alloy liquid solidification front and the degree of undercooling. Additionally, the microstructure of the alloy was examined using metallographic microscopy, leading to a systematic study of the microscopic morphological characteristics and evolution laws of the refined structure during rapid solidification. The research reveals that the grain refining mechanism of the Ni-Cu-Co ternary alloy is consistent with that of the binary alloy (Ni-Cu). Specifically, under low undercooling conditions, intense dendritic remelting was found to cause grain refinement, while under high undercooling conditions, recrystallization driven by accumulated stress and plastic strain resulting from the interaction between the liquid flow and the primary dendrites caused by rapid solidification was identified as the main factor contributing to grain refinement. Furthermore, the study highlights the significant role of the Co element in influencing the solidification rate and reheat effect of the alloy. The addition of Co was also found to facilitate the formation of non-segregated solidification structure, indicating its importance in the overall solidification process.

Keywords

grain refinement / recalescence / recrystallization / undercooling

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