Effect of melt superheat treatment on solidification behavior and microstructure of new Ni–Co based superalloy

Abstract

A new type of Ni–Co based superalloy was prepared by vacuum induction melting (VIM), and the effects of superheat on element distribution, dendrite segregation, and solidification microstructure refinement of the new Ni–Co based superalloy are revealed. The effect of solidification structure treatment under different conditions was quantitatively studied by differential scanning calorimetry (DSC), scanning electron microscope (SEM), and electron probe micro analyzer (EPMA). The results indicated that the nucleation undercooling increased and the crystallization temperature interval decreased with the rise of the melt temperature; As the superheat temperature rised, the size of the phase was refined; the secondary dendrite arm spacing of the alloy decreased continuously; and the dendritic segregation of the alloy decreased. It was found that the critical temperature of melting energy for the new Ni–Co based superalloy clusters is about 1550 °C. The maximum positive segregation element of the new Ni–Co-based superalloy is Ti, and the maximum negative segregation element is W; When the temperature increased from 1450 °C to 1600 °C, the segregation coefficient of Ti increased from 0.54 to 0.63, and the segregation coefficient of W decreased from 1.9 to 1.5. When the superheat was increased, the atomic cluster size decreases, and the effect of refining the solidification structure of the new Ni–Co-based superalloy is more significant.