Grain morphology evolution and texture characterization of wire and arc additive manufactured Ti-6Al-4V

In this study, four straight walls of Ti-6Al-4V titanium alloy were fabricated by wire and arc additive manufacturing (WAAM) to investigate the effect of deposition parameters on grain morphology evolution and texture characterization in the building direction. A certain volume fraction of equiaxed β grain appeared at the bottom of the wall and can be controlled by deposition parameters, while the columnar β grain zone was on the equiaxed β grain zone. It is indicated that the formation of equiaxed β grains at the bottom of the wall initiated from the recrystallization. There were the large residual stress, strain, and high heating rate when depositing the first several layers near the substrate, which can induce the recrystallization of the already-deposited layers. However, the preferred crystallographic orientations along the building direction formed gradually during the deposition process, then the β grains began to grow epitaxially from the already-deposited layers, and changed to columnar β grains, which lead to a strong 〈001〉 fiber texture in the building direction. In addition, there are also some equiaxed β grains at the top surface of the wall due to the occurrence of the columnar to equiaxed grain transition (CET) in the molten pool.