Hot deformation behavior and processing workability of a Ni-based alloy

In the present work, the high-temperature deformation behavior of a U720LI alloy was investigated by means of hot compression tests at temperatures of 1060–1180 °C, strain rates of 0.001–10s⁻¹ under true strain of 0.8. The Arrhenius-type model, considering the dissolution of γ′ precipitates, was established on the basis of the friction and adiabatic heating corrected flow stress data. The hot deformation activation energies for quasi-γ phase and γ+γ′ dual-phase microstructures were determined as 417 kJ mol⁻¹ and 687 kJ mol⁻¹, respectively. The high activation energy for γ+γ′ dual-phase microstructures was mainly attributed to the precipitation hardening effect of γ' (Ni₃(Al,Ti)) particles which hindered dislocation slip via the pinning effect during hot deformation. The processing map was developed based on the dynamic material model. According to the detailed microstructural investigations, the optimum hot deformation domains of U720LI alloy were identified as 1080–1100 °C/0.01–0.3s⁻¹ for γ+γ′ dual-phase microstructure and 1140–1160 °C/0.01–0.1s⁻¹ for quasi-γ phase microstructure, respectively.