Hot Deformation Behavior and Workability of a New Ni–W–Cr Superalloy for Molten Salt Reactors

Abstract

The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800 °C molten salt reactors (MSRs) was looked into by isothermal compression tests in the temperature range of 1050–1200 °C with a strain rate of 0.001–1 s⁻¹ under a true strain of 0.693. An Arrhenius-type model for the Ni–W–Cr superalloy was constructed by fitting the corrected flow stress data. In this model, the effect of dispersion of solid solution elements during thermal deformation on microstructure evolution was considered, as well as the effects of friction and adiabatic heating on the temperature and strain rate-dependent variation of flow stresses. The hot deformation activation energy of the Ni–W–Cr superalloy was 323 kJ/mol, which was less than that of the Hastelloy N alloy (currently used in MSRs). According to the rectified flow stress data, processing maps were created. In conjunction with the corresponding deformation microstructures, the flow instability domains of the Ni–W–Cr superalloy were determined to be 1050–1160 °C/0.03–1 s⁻¹ and 1170–1200 °C/0.001–0.09 s⁻¹. In these deformation conditions, a locally inhomogeneous microstructure was caused by flow—i.e., incomplete dynamic recrystallization and hot working parameters should avoid sliding into these domains. The ideal processing hot deformation domain for the Ni–W–Cr superalloy was determined to be 1170–1200 °C/0.6–1 s⁻¹.