Effect of overlap distance on the microstructure and mechanical properties of in situ welded parts built by electron beam melting process

Electron Beam Melting (EBM), one of the powder bed-based additive manufacturing processes that is able to produce complex geometrical metal parts directly, has many application possibilities in various fields. However, an issue has been raised when we apply the EBM technology to fabricate medium volume components. Lack of energy when the scanning line is longer than 100 mm results in the lack-of-fusion pores, which degrades the mechanical properties of the printed part dramatically. Therefore, we propose an insitu welding process to overcome the issue. In order to further understand the microstructure and mechanical properties resulting from the insitu welded process with various overlap distances, we evaluate a series of overlap distances and successfully fabricate a big plate with dimensions of 200 × 200 × 4 mm3. It is suggested that the defects and microstructure vary according to the overlap distance. Optimized overlap distances are 0.25-0.75 mm for Ti-6Al-4V. Within this range, no microstructural variation is observed which results in constant microhardness and superior mechanical properties of the EBM-built component. An overlap distance ≥1.5 mm results in microstructure coarsening and mechanical property degradation in the overlap zone. Furthermore, the localized deformation mechanism is discussed based on the findings of the tensile properties and digital image correlation analysis.