Layer control method and mechanical anisotropy of titanium alloy based on double-hot-wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is an important manufacturing technology for fabricating large-size titanium alloy parts, which has important application prospects in aerospace and other fields. However, the grain size and mechanical anisotropy of WAAM materials have a certain impact on the application. In this paper, the influence of two kinds of layer control methods based on DHWAAM on grain size is studied. The β grain morphology of the layer cooling method is mostly the mixed morphology of small-size short columnar grain and equiaxed grain, while the continuous deposition method is coarse columnar grain. The layer cooling method is beneficial to grain refinement. The tensile results show that the ultimate tensile strength (UTS) of the layer cooling method is 6.5 % higher than that of the continuous deposition method, but the elongation has no significant change. In addition, the mechanical anisotropy of the titanium alloy fabricated by DHWAAM was also studied. The mechanical properties of the tensile samples at different angles were different. The% in plane anisotropy (%IPA) of UTS was 4.48. The fracture mode is quasi cleavage fracture. The pore defects (unfused pores and gas pores) in DHWAAM were characterized by XCT. The formation mechanism of different pore types is analyzed as well.