Hot deformation behaviors and three-dimensional processing map of a nickel-based superalloy with initial dendrite microstructure

Abstract

Investigating the initial upsetting process via inducing dynamic recrystallization (DRX) to update dendrite microstructure is of significant profound for obtaining homogeneous microstructure while avoiding defects such as cracking and severe texture etc. The hot deformation behaviors of an as-cast nickel-based superalloy with dendrite microstructure were investigated by uniaxial compression experiments performed at temperatures of 1040–1160 °C (across γˊ-solvus) and strain rates of 0.001–1 s−1. There exists a high positive correlation between peak flow stress and Zener-Hollomon parameter. The three-dimensional (3D) distributions of strain rate sensitivity (m) and power dissipation efficiency (η) were sequentially established, which facilitates thoroughly understanding the effect of deformation parameters (DPs) like temperature, strain rate and strain on them. Based on the processing map (PM) validated and microstructure evolution, the optimized hot working windows of studied alloy, in which an intense DRX happened, were identified as: 1040–1105 °C 0.0032–0.08 s−1, 1105–1124 °C 0.0018–0.16 s−1, and 1148–1160 °C 0.2–1 s−1. It provided a reasonable cogging operation process for homogenizing microstructure of the ingot. Worthy of note is that continuous dynamic recrystallization (cDRX) and discontinuous dynamic recrystallization (dDRX) concurrently occurred at low temperature, whilst the dDRX was predominant at sub-/super-solvus temperature, resulted in the discontinuous softening. The nucleation of γˊ nano-twin was implemented by the 1/6<112> type of twinning partials which dissociated from a perfect dislocation, gliding on (111) crystal plane at sub-solvus temperature. As a result, the γˊ precipitates were coherently embedded in γ matrix.