Hot deformation behavior and workability of a Ni–Co based superalloy

• Published in: Journal of alloys and compounds 2020-08, Vol.831, p.154618, Article 154618
• Main Authors: Liu, Peng, Zhang, Rui, Yuan, Yong, Cui, Chuanyong, Zhou, Yizhou, Sun, Xiaofeng
• Format: Article
• Language: English
• Subjects: Activation energy; Alloys; Aluminum; Chemical precipitation; Compression tests; Constitutive equation; Constitutive equations; Constitutive relationships; Deformation; Dynamic recrystallization; Flow stability; Hot deformation behavior; Microstructural evolution; Nickel base alloys; Ni–Co based Superalloy; Optimization; Precipitates; Process mapping; Process parameters; Processing map; Strain rate; Superalloys; True strain; Workability; Yield strength
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.154618

The hot deformation behavior of a new Ni–Co based alloy was investigated by the isothermal compression tests in a temperature range of 1060–1180 °C and a strain rate range of 0.01–10 s−1 under a true strain of 0.693. The results show that the flow stress, corrected by friction and adiabatic heating, increases with the decreasing temperature and increasing strain rate. Considering the dissolution of the γ′ precipitates during hot deformation, the Arrhenius-type constitutive equations were established segmentally via fitting the corrected flow stress data. The activation energies for the γ+γ′ dual-phase region and the γ single-phase region of the alloy are 671 and 391 kJ mol−1, respectively. The reason for higher activation energy of the γ+γ′ dual-phase region is that γ′ ((Ni,Co)3(Al,Ti)) precipitates hinder dislocation slip and harden the alloys during hot deformation. The processing map based on the dynamic material model (DMM) was also constructed. According to the analysis of microstructural evolution, dynamic recrystallization (DRX) occurs under all deformation conditions. The optimum hot deformation processing conditions for the γ+γ′ dual-phase region are 1060–1070 °C/0.01–0.02 s−1 or 1070–1141 °C/0.01–1 s−1. In addition, the optimal processing parameter for the γ single-phase region is 1141–1175 °C/0.01–10 s−1 (except a part of flow instability domain). •For the first time study on the hot deformation of the new Ni–Co based superalloy.•Constitutive model considering the dissolution of γ′ precipitates was established.•The optimum process parameters were validated by the deformed microstructure.•The new Ni–Co based alloy has a better hot workability than U720Li alloy.