Thermal Processing Map Study of the GH99 Nickel-Based Superalloy Based on Different Instability Criteria

Abstract

The thermal compression experiments of the GH99 alloy were carried out at different strains from 1020 °C to 1170 °C and 0.001 s−1–1 s−1 conditions using a Gleeble-3800 thermal compression simulation tester. Construction of thermal processing maps with four instability criteria were superimposed on Murty, Prasad, Gegel, and Malas at different strains based on stress-strain data. Based on the theoretical basis, prediction results, and EBSD microstructure characterization method of four instability criteria, the suitable forming processing region and rheological instability region of the alloy were predicted. It was found that the Prasad instability criterion had the most accurate prediction results. The instability range predicted by Murty was accurate under minor strains, but as the strain increased, the expected instability range slightly increased compared to the actual range. However, the Gegel and Malas criteria have biases in predicting alloys under low-rate conditions at different strains. A scientific and rational optimization was carried out to select hot working process parameters for GH99 alloy in response to the influence of strain on its hot deformation behavior.

Keywords

• GH99 alloy
• thermal compression simulation experiment
• thermal processing map
• rheological instability criterion
• microstructure