Competition between work-hardening effect and dynamic-softening behavior for processing as-cast GH4720Li superalloys with original dendrite microstructure during moderate-speed hot compression

Abstract

Competition between work-hardening effect and dynamic-softening behavior of as-cast GH4720Li superalloys with original dendrite microstructure during moderate-speed deformation was quantitatively investigated in this present paper. Flow behavior for processing the studied alloys with dendrite microstructure behaves typical three stages, caused by the competition effect between work-hardening and dynamic-softening. The relationships between work-hardening rate and true strain and true stress were derived from Kocks–Mecking dislocation relation. The work-hardening effect shows two obvious stages with strain, viz. steady fluctuations and linear decreasing. An obvious work-hardening effect was demonstrated under lower temperature and higher strain rate. The linear relationship of work-hardening rate θ on true stress ε was constructed with the slope only related to annihilation coefficient Ω. The microstructural mechanism of as-cast GH4720Li superalloys during moderate-speed deformation was referred to dislocation multiplication and dendrite fragmentation, and the latter was beneficial to dynamic recrystallization during moderate-speed deformation.