Selective laser melting-wire arc additive manufacturing hybrid fabrication of Ti-6Al-4V alloy: Microstructure and mechanical properties

Selective laser melting (SLM) and wire arc additive manufacturing (WAAM) are two representative metal additive manufacturing technologies that fabricate the net shaping of small complex parts and near-net shaping of large components. To explore the feasibility of SLM-WAAM hybrid fabricating large and complex components, the preliminary hybrid SLM-WAAM process of Ti-6Al-4V is investigated. In this study, horizontal (H-) and vertical (V-) SLM samples are used as substrate for WAAM process to analyze microstructure and tensile properties, and to be compared with that of SLM samples and WAAM samples. The results show that Ti-6Al-4V sample formed by hybrid fabrication consists of three typical zones: SLM zone, WAAM zone and interface zone. The fine and short beta columnar grains consisting of primarily martensite alpha' exist in SLM zone, then these fine grains grow coarse in the about 3 mm-thick interface zone because of the repeated heating process, in contrast, the coarse beta columnar grains awash with a lamellae lead to epitaxial growth in WAAM zone. There is a good metallurgical bonding in the interface zone of both H-SLM-WAAM and V-SLM-WAAM specimens and all the fractures are located in the WAAM zone during the tensile test. The mean yield strength and ultimate tensile strength of the H-SLM-WAAM specimens are 850 MPa and 905 MPa, respectively. In comparison, the V-SLM-WAAM samples exhibited slightly higher tensile strengths; the mean yield strength and ultimate tensile strength are 890 MPa and 995 MPa, respectively. The elongations of different directions are both more than 10%, satisfying the requirements of engineering applications. These tensile properties of SLM-WAAM samples are comparable with or even better than that of WAAM samples.