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

• Published in: Journal of alloys and compounds 2019-01, Vol.772, p.247-255
• Main Authors: Wang, Pan, Nai, Mui Ling Sharon, Sin, Wai Jack, Lu, Shenglu, Zhang, Baicheng, Bai, Jiaming, Song, Jie, Wei, Jun
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Coarsening; Coordination compounds; Correlation analysis; Deformation mechanisms; Digital image correlation; Digital imaging; Electron beam melting; Mechanical properties; Microhardness; Microstructure; Powder beds; Tensile properties; Titanium alloy; Titanium alloys; Titanium base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.09.093

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 in situ welding process to overcome the issue. In order to further understand the microstructure and mechanical properties resulting from the in situ 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. •Overlap distance affects the microstructure and mechanical properties of in-situ welded EBM-built parts.•Graded microstructure, homogenous microstructure and lack of fusion were observed.•Optimized overlap distance was ranging from 0.25 mm to 0.75 mm.•Large overlap distance showed degraded mechanical properties caused by localized deformation.•Tensile deformation mechanism of graded microstructure was revealed by DIC.