Synergistic manipulation of heat input and trace elements for equiaxed β-grains in high-efficiency additive manufacturing of titanium alloy

Distinguished by high deposition rates, cost efficiency, and superior material utilization, wire arc additive manufacturing (WAAM) is widely regarded as the premier technique for fabricating large-scale titanium aerospace components. However, the main technical bottleneck lies in obtaining fully β equiaxed grains while maintaining high deposition efficiency. In this study, we refined traditional coarse columnar grains through the synergistic regulation of heat input and Boron addition, while the hot-wire (HW) method was employed to ensure high feeding speed wire melting despite the significantly reduced arc heat input. The results demonstrate that this synergistic approach enables the fabrication of WAAM titanium alloy components featuring nearly fully equiaxed microstructures at the micron scale, with an average grain size of 124.5 μm. Furthermore, compared with samples deposited solely via the HW process, the α colonies and grain boundary α phases were significantly refined. Compared to WAAM samples without using the collaborative strategy, better comprehensive performance was obtained, especially achieving the improvement of tensile strength and a significant reduction in anisotropy while ensuring high deposition efficiency. This study provides a critical solution to the technical bottleneck of coarse columnar grains in titanium alloys and holds significant promise for advancing the application of WAAM-fabricated titanium structures in the aerospace sector.