Modeling the effect of thermal-mechanical processing parameters on the density and length fraction of twin boundaries in Ni-base superalloy RR1000

Enhancement of the physical and mechanical properties of polycrystalline Ni-base superalloys may be achieved through control of the grain boundary structure and is dependent on the optimization of the thermal-mechanical processing parameters. Superalloys containing grain boundary networks that are comprised with a sufficiently high fraction of Σ3/twin boundaries have been reported to exhibit enhanced creep and fatigue properties. In this report, the density and length fraction of twin boundaries in annealed samples of powder processed Ni-base superalloy RR1000 were quantified and expressed as a function of the average grain diameter. The results were found to be consistent with classical models relating density and length fraction to grain size. The effects of varying hot deformation parameters on twin density and length fraction were also quantified and modified models were derived to describe the relationships.