Microstructure evolution and fracture behavior of Ti-6Al-4V fabricated by WAAM-LDM additive manufacturing

WAAM and LDM are two typical DED technologies. WAAM-LDM additive manufacturing technology can achieve the purpose of producing large and complex Ti-6Al-4V components, improving processing efficiency and precision. However, there is a lack of in-depth research on the microstructure evolution mechanism and the fracture behavior of WAAM-LDM samples. Therefore, horizontal and vertical WAAM samples were invoked as the substrate for LDM processes in this study, and the mechanical properties and tensile fracture behavior under different load directions were evaluated. The results show that the samples fabricated by WAAM-LDM manufacturing consist of four zones: WAAM zone, heat affected zone (HAZ), remelting zone (RZ) and LDM zone. WAAM zone mainly composed of coarse colony structure, HAZ and RZ are dominated by alpha colonies and fine basketweave structure, respectively, and LDM zone consists of acicular alpha phases and fine basketweave structure. The thickness of alpha laths shows a trend of 'WAAM > HAZ > LDM > RZ'. The strengths are greatly improved at the interfaces due to the good metallurgical bonding and finer microstructure. All the fractures locate at WAAM zone during tensile test and propagate along the basketweave structure. These strengths of WAAM-LDM samples under the action of horizontal loading are higher than that of WAAM samples, and all the elongations of WAAM-LDM samples are higher than 10 %.