Effect of hot deformation on grain refinement in a Re containing nickel-based superalloy

Abstract

Abstract Hot deformation experiments have been performed for a novel polycrystalline superalloy with a nominal composition Ni-12.5(Al,Ti,Nb,Ta)-37(Cr,Co,W,Mo,Re)-0.17(C,La,Y,Ce,B) (in wt. %) intended for disc applications in gas turbine engines. The as-cast superalloy was characterized by a higher amount of the γ’ phase, a coarse γ grain size and a high level of dendritic segregation. The as-cast superalloy was subjected to long-term annealing to homogenize and heterogenize the material prior to hot deformation. The hot working experiments were performed in a different manner. First, isothermal compression experiments at temperatures below and above the γ’ solvus temperature were performed. These experiments allowed us to determine the temperature-strain rate conditions providing improved workability. Second, unidirectional forging experiments were performed under quasi-isothermal conditions using a specially designed can made of a stainless steel. The use of the optimal temperature-strain conditions and the can provided reasonable hot workability and delocalized occurrence of recrystallization processes during hot forging. EBSD analysis of the forged workpieces revealed that the grain refinement resulted from continuous dynamic recrystallization. For the first time hot deformation processing was successfully developed for the rhenium containing ingot-metallurgy nickel-based superalloy.