On the Evolution of Primary Gamma Prime Precipitates During High Temperature and High Strain Rate Deformation and Subsequent Heat Treatment in the Ni-Based Superalloy, RR1000

Abstract

The microstructural evolution following compression and subsequent sub-solvus and super-solvus heat treatment was studied in the Ni-based superalloy, RR1000, typically used for rotor disc applications in aero-engines. For a low strain rate of 0.1 s−1 at close to solvus temperature, 1413 K (1140 °C), the flow stress is constant. For larger strain rates of 1 and 10 s−1 at sub-solvus temperature, 1373 K (1100 °C) dynamic re-crystallization (DRX) of γ grains occurs during forging with accompanying stress decay. Incoherent primary γ′ precipitates form mainly via meta-dynamic re-crystallization (MDRX) at 1 s−1 and are as intergranular. For 10 s−1, the coherently nucleated or existing precipitates present in the initial as-HIP condition become incoherent when the grain boundary sweeps past them during DRX and subsequent grain growth. The incoherent primary γ′ precipitates are mainly intragranular. During sub-solvus heat treatment at 1373 K (1100 °C), dissolution of the incoherent precipitates occurs through coarsening of the coherent intragranular population with only sporadic incoherent precipitates remaining. The prior induced deformation (strain and strain rate) influences the evolution of precipitate morphologies during cooling following heating to super-solvus temperature. Using numerical simulations, a quantitative calculation of the different precipitate morphologies was carried out during slow cooling from super-solvus temperature, 1443 K to 1373 K (1170 °C to 1100 °C).