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ASM International 1059-9495/$19.00

Physical-Based Constitutive Modeling of Hot Deformation in a Hot-Extruded Powder Metallurgy Nickel-Based Superalloy Gang Tan, Hui-zhong Li, Yan Wang, Lei Yang, Zheng-qin Huang, Shi-chang Qiao, and Min-xue Liu Submitted: 22 February 2020 / Revised: 29 June 2020 / Accepted: 29 August 2020 For simulating the hot deformation behavior of a powder metallurgy nickel-base superalloy during isothermal forging, the hot compression tests were performed in the temperatures of 1020-1110 °C with the strain rates from 1023 to 1 s21. The thermoplastic deformation and dynamic recrystallization (DRX) behavior of the superalloy during thermocompression were systematically studied. It can be shown that the flow stress of the superalloy exhibits apparent characteristics of DRX. A relationship indicating the dependency of flow stress on deforming temperature and strain rates is built through introducing the Z parameter. The work-hardening rate (h) curves of the superalloy at various deformation conditions are obtained, and the values of h are found to decrease with decreasing Z parameter, i.e., decreasing strain rates and increasing deforming temperature. There exists a power exponential relationship between critical strain ec and Z parameter. Combining the experimental data, a two-stage constitutive model on the basis of the Estrin–Mecking constitutive model and the DRX kinetic model is set up to model the flow stress of the superalloy. The flow stresses obtained from the established model are well consistence with the measured values. Keywords

dynamic recrystallization, hot compression, physical-based constitutive model, powder metallurgy nickel-based superalloy, work-hardening rate

1. Introduction In aviation industry, PM nickel-based superalloys are widely used in manufacturing of air engine turbine disks since their fine grain size, uniform microstructure, good resistance to oxidation and corrosion, excellent high temperature strength and low crack growth rates (Ref 1–3). At present, the preparation process of PM nickel-based superalloys mainly includes powder atomization, hot isostatic pressing (HIP), and/ or hot extrusion (HEX), and/or isothermal forging (IF) and final heat treatment. Hot working is the key step in the preparation of the superalloys. However, the flow behavior and microstructural evolution of superalloys during hot forming processes (such as HIP, HEX and IF) are usually complicated (Ref 4).

Gang Tan, Hui-zhong Li, and Lei Yang, School of Materials Science and Engineering, Central South University, Changsha 410083, PeopleÕs Republic of China; and Yan Wang, National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, PeopleÕs Republic of China; and School of Aeronautics and Astronautics, Central South University, Changsha 410083, PeopleÕs Republic of China; Zheng-qin Huang and Shi-chang Qiao, School of Aeronautics and Astronautics, Central South University, Changsha 410083, PeopleÕs Republic of China; and Min-xue Liu, State Key Labor