Study on microsegregation and homogenization process of a novel nickel-based wrought superalloy

Abstract

In this paper, the as-cast microstructure, microsegregation, precipitates and suitable homogenization process of a novel Ni-based wrought superalloy prepared by vacuum induction melting (VIM) + vacuum arc remelting (VAR) were investigated by optical microscope (OM), scanning electron microscope (SEM), electron probe microanalysis (EPMA), differential scanning calorimetry (DSC), high temperature confocal laser scanning microscope (HT-CLSM) and thermal simulation compression. The results show that severe element segregation exists in the ingot. Nb, Ti and Al are mainly segregated in the interdendritic region, while W is mainly segregated in the dendrite arm. The precipitates in the alloy mainly include non-uniform γ′ strengthening phase, coarse (γ + γ′) eutectic phase and MC carbide, among which, the redissolution temperature range of γ′ phase is 1060–1220 °C; the (γ + γ′) eutectic phase can be redissolved obviously above 1180 °C but melted into liquid at 1250 °C; the redissolution temperature range of MC carbide is 1349–1358 °C, exceeding the solidus temperature of the alloy. After homogenization at 1220 °C/10 h, all the γ′ phase and most of the (γ + γ′) eutectic phase can be redissolved, and the element segregation can be significantly alleviated, moreover, the hot deformation resistance of the alloy is lower and the dynamic recrystallization (DRX) degree is higher, indicating that 1220 °C/10 h is an ideal single-stage homogenization process.

Keywords

• Ni-based superalloy
• As-cast microstructure
• Microsegregation
• Precipitates
• Homogenization
• Hot deformation