Phase field simulation of the stress-induced α microstructure in Ti-6Al-4 V alloy and its CPFEM properties evaluation

Variant selection under specific applied stresses during precipitation of alpha plates from prior-beta matrix in Ti-6Al-4 V was investigated by 3D phase field simulations. The model incorporates the Burgers transformation path from beta to alpha phase, with consideration of interfacial energy anisotropy, externally applied stresses and elastic interactions among alpha variants and beta matrix. The Gibbs free energy and atomic mobility data are taken from available thermodynamic and kinetic databases. It was found that external stresses have a profound influence on variant selection, and the selection has a sensitive dependence, as evidenced by both interaction energy calculations and phase field simulations. Compared with normal stresses, shear stresses applied in certain directions were found more effective in accelerating the transformation, with a stronger preference to fewer variants. The volume fractions of various alpha variants and the final microstructure were determined by both the external stress and the elastic interaction among different variants. The alpha clusters formed by variants with Type2 misorientation ([1 1 -2 0]/60 degrees) relation were found more favored than those with Type4 ([-10 5 5 -3]/63.26 degrees) under certain applied tensile stress such as along < 111 >(beta). The mechanical properties of different microstructures from our phase field simulation under different conditions were calculated for different loading conditions, utilizing crystal plastic finite element simulation. The mechanical behavior of the various microstructures from phase field simulation can be evaluated well before the alloys are fabricated, and therefore it is possible to select microstructure for optimizing the mechanical properties of the alloy through thermomechanical processing based on the two types of simulations. (C) 2021 Published by Elsevier Ltd on behalf of Chinese Society for Metals.

Automated summary

The study investigated variant selection under specific applied stresses during precipitation of alpha plates from prior-beta matrix in Ti-6Al-4V through 3D phase field simulations. It was found that external stresses have a profound influence on variant selection, with a stronger preference for fewer variants under shear stresses in certain directions. This study provides insights into optimizing the mechanical properties of the alloy through thermomechanical processing based on the findings from phase field simulations and crystal plastic finite element simulation.