Phase transformation and recrystallization kinetics in space-time domain during isothermal compressions for Ti-6Al-4V analyzed by multi-field and multi-scale coupling FEM

The spatio-temporal phase transformation and dynamic recrystallization (DRX) behaviors during isothermal compression including resistance heating, temperature-holding and compressing steps, would significantly influence the microstructure of materials. In order to understand these behaviors of Ti-6Al-4V alloy during isothermal compression, a finite element (FE) analysis model on the basis of multi-field coupling and multi-scale coupling methods was developed. A series of simulations for the compressions corresponding to different strain rates and temperatures were implemented. The results show that in the resistance heating process, the volume fraction of alpha-phase keeps constant till a certain alpha -> beta critical transformation moment, following which it decreases continuously till the heating process ends. The phase volume fraction in the radial direction is distributed uniformly, while in the axial direction it is distributed non-uniformly. At the beginning of temperature-holding process, the volume fraction of alpha-phase decreases sharply, following which increases gradually till the end. During isothermal compression, the volume fraction of alpha-phase is maintained, and the spatial distribution of alpha-phase gets more homogeneous. The DRX volume fraction increases with deformation at a certain strain rate, and decreases with increasing strain rate. Finally, the finite element (FE) analysis was validated by the microstructure observations. (C) 2016 Elsevier Ltd. All rights reserved.