Heat-affected coarsening of β grain in titanium alloy during laser directed energy deposition

The heat-affected coarsening of beta-grains in titanium alloy produced by additive manufacturing (AM), which would be important for the achievement of fine beta-grain like forging, was completely neglected in the past. Here, we reported that the significant coarsening of equiaxed beta-grain of Ti6Al4V happened under the instantaneous high-temperature (above beta-transus) thermal cycling during laser directed energy deposition process. Especially, the coarsening becomes more striking in the cases of smaller initial beta grain, larger energy density and higher preheating-temperature. Meanwhile, a modified model used to predict the size of the coarsened beta-grain of AM titanium alloy was proposed. These findings provide a more comprehensive understanding of the beta-grains of AM titanium alloy and a significant guidance for the composition design of AM titanium alloy with fine equiaxed beta-grains. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.