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

Abstract:

The presence of needle α′ martensite in the coarse columnar β grains is the main reason for the poor ductility of TC11 titanium alloys for wire-fed electron beam additive manufacturing (EBAM). In order to achieve the engineering fabrication of high-strength and ductile TC11 titanium alloy, a novel coaxial electron beam wire additive manufacturing (C-EBAM) process was used to improve the interaction state of electron beam, wire, and substrate during the EBAM process, and to improve the heat distribution of the melt pool. A detailed comparison between EBAM and C-EBAM was further made in terms of microstructure, grain morphology and mechanical properties. The effects of the transition state of the wire on the process stability, the martensitic transformation process, and the reasons for the difference and anisotropy of the tensile properties were discussed. The results show that C-EBAM achieves a strong lamellar α+β microstructure with almost no evaporation of Al elements via the pathway of slow cooling of the β phase field and in situ martensite decomposition at a lower cooling rate. Compared to EBAM, the improvement in ductility of C-EBAM can be attributed to a bi-lamellar microstructure and discontinuous grain boundaries α. This indicates the direction for further optimization of the beam source characteristics.