Effect of Coaxial Beam Wire Source Mode on Microstructure and Mechanical Properties of TC11 Titanium Alloy Fabricated by Wire-Fed Electron Beam Additive Manufacturing

The presence of needle-like alpha ' martensite within the coarse columnar beta grains is the primary reason for the poor ductility of TC11 titanium alloys produced by wire-fed electron beam additive manufacturing (EBAM). To enable the engineering fabrication of high-strength and high-ductile TC11 titanium alloys, a novel coaxial beam wire-EBAM (C-EBAM) process was developed, which could enhance the interaction between the electron beam, wire, and substrate, thereby improving the thermal distribution within the melt pool. Comparison between EBAM and C-EBAM samples was conducted, in terms of microstructures, grain morphologies, and mechanical properties. The impact of wire transition states on process stability, martensitic transformation, and the anisotropy of tensile properties was explored. The results reveal that C-EBAM facilitates the formation of strong lamellar alpha+beta microstructure with minimal evaporation of Al elements, which is achieved through slow cooling within the beta phase field and in situ martensite decomposition. Compared with EBAM, the enhanced ductility by C-EBAM is attributed to the development of the bi-lamellar microstructure and discontinuous alpha grain boundaries.