Effects of deposition strategies on macro/microstructure and mechanical properties of wire and arc additive manufactured Ti–6Al–4V

In this study, Ti–6Al–4V was fabricated via wire and arc additive manufacturing (WAAM) using different deposition strategies. The effects of the travel direction and interlayer dwell time on the evolution of the prior-β grain morphology, microstructure, microhardness, and room-temperature tensile properties of the as-deposited walls were systematically investigated. The thermal and stress/strain field during the deposition process were also simulated to elucidate the macro/microstructural evolution during the deposition. When the interlayer dwell time was less than 24 s, there was a transition from equiaxed prior-β grains (EBGs) to columnar prior-β grains (CBGs) from the bottom to the top of the deposited wall. Vertical and tilted CBGs were obtained with bidirectional and unidirectional travel directions, respectively. With a dwell time of 120 s and unidirectional travel directions, full-equiaxed prior-β grains were obtained within the wall. The EBGs were formed not from the solidification of the molten pool but from the recrystallization induced by the large heat accumulation and high stress/strain during the WAAM process. The recrystallization nucleation rate of the EBG zone was the highest with a dwell time of 24 s. There were tilted layer bands when bidirectional travel strategies were used. There was a fine lamellar α in the layer band-free region and a basketweave α in the layer band region. The increase in the interlayer dwell time led to a decrease in the width of the α lath in the layer band region, but little changed in the layer band-free region. In addition, the hardness, yield strength, and tensile strength increased with the increase in the dwell time from 0 to 120 s.