Multi-laser powder bed fusion of Ti–6Al–4V alloy: Defect, microstructure, and mechanical property of overlap region

As an emerging additive manufacturing technology, multi-laser powder bed fusion (ML-PBF) can be used for the rapid fabrication of large-size Ti–6Al–4V components with complex shapes. However, researches regarding the overlap quality control of the relevant products are insufficient. In this study, a self-developed ML-PBF system was used to produce a series of Ti–6Al–4V samples. The defect, microstructure, and mechanical property of the overlap regions obtained from different process conditions were researched. It is demonstrated that the overlap region can be nearly fully dense regardless of whether the scanning paths of the corresponding two lasers are the same or different. However, if the two lasers scan the overlap region simultaneously and their incident points encounter with each other, a large number of keyhole defects may form. All the overlap regions possess an acicular martensite microstructure, which is essentially the same as that of the single-laser PBF material. However, crystallographic texture intensities of the overlap regions are relatively stronger compared with that of the single-laser PBF material. When the encounter of two different laser incident points is avoided during the ML-PBF process, basic mechanical properties of the overlap region such as microhardness and tensile strength can be comparable to those of the single-laser PBF material. The results can help to improve the performance consistency of large-size Ti–6Al–4V components fabricated by ML-PBF.