Cold/Hot Deformation Induced Recrystallization of Nickel-Based Superalloys for Molten Salt Reactors

A new special structural nickel-based alloy for use in molten fluoride salt environments in molten salt reactors (MSR) began to be developed by the COMTES FHT Company in the Czech Republic as early as 2001. The outcome of this development was the MoNiCr alloy, an alternative to Hastelloy-N. The present study was carried out on two experimentally-manufactured nickel alloys: MoNiCr and HN80MTY. Its purpose was to activate recrystallization processes in the as-cast microstructure of these alloys. In addition, experiments were performed to find a temperature which produces complete recrystallization. Static and dynamic recrystallization was studied in both alloys as well. An important aspect was to determine the lowest amount of deformation which still ensures complete recrystallization and provides as uniform recrystallized grains as possible. Such microstructure is well-suited for subsequent forming operations. Specimen microstructures were characterized using light microscopy (LM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD). Furthermore, corrosion tests of the MoNiCr alloy were conducted.