As-cast microstructure and homogenization kinetics of a typical hard-to-deform Ni-base superalloy

Abstract

In this paper, the as-cast microstructure, microsegregation, and the kinetics of (γ+γ′) eutectic phase and Laves phase dissolution in GH4151 alloy were studied by the optical microscope (OM), scanning electron microscope (SEM), electron probe microanalysis (EPMA), differential scanning calorimetry (DSC), and high-temperature water quenching text. The results show that W and Al elements are segregated into the dendrites arm, while Mo, Nb, and Ti are segregated into the interdendritic region. The initial melting point temperature of the MB2 phase was near 1100 °C, the redissolution temperature range of γ′ phase is 1130–1160 °C, the obvious dissolution temperature of Laves phase was above 1145 °C and the γ + γ′ eutectic phase was redissolved obviously above 1165 °C. Based on the JMAK analysis, the activation energies of dissolution of Laves phase (266.3 kJ/mol) and γ+γ′ phase (279.5 kJ/mol) are close to the activation energy for the diffusion of Mo in Ni (288.15 kJ/mol) and Ti in Ni (288.15 kJ/mol), respectively. The back-diffusion of Mo and Ti into austenite is controlling the micro-mechanism for the dissolution of Laves phase and (γ+γ′) eutectic phase, respectively.

Keywords

• Ni-based superalloy
• Microstructure and microsegregation
• Residual segregation index
• Diffusion coefficient
• Activation energy