A new recrystallization at semi-coherent micro-lamella and its effect on tensile properties of wire arc additive manufactured titanium alloy

A new recrystallization without plastic deformation was observed at the semi-coherent micro-lamella (ML) of wire arc additive manufactured Ti6Al4V, which is driven by the interface energy and the dislocation-induced elastic strain energy. It was classified into three types according to nucleation site, which are the recrystallization at the boundary of colony structures, inside the colony structures, and at the boundary of basket weave structures, respectively. Some new behaviors in the nucleation and growth of this recrystallization were found. Firstly, the nucleation mechanism of one direction strain and interface induced grain boundary migration was found in the recrystallizations at colony boundary and inside the colony. Secondly, the recrystallized grains at colony boundary grew to be part of the original colony, while the others grew to be a new grain. Relevant mechanisms were discussed according to theoretical calculation of driving energy and grain growth behaviors. Because the continuous grain boundaries were broken by this recrystallization, not only the ultimate tensile strength was increased by 100 MPa or so, but also the ductility anisotropy was decreased from the 4.8% of as-deposited sample to the 0.2%. The results would provide a new approach without plastic deformation to improve the performances of additive manufactured components.