Obtaining fine microstructure and unsupported overhangs by low heat input pulse arc additive manufacturing

Arc additive manufacturing can be used to fabricate large scale titanium alloy parts with high deposition rate and low costs. However, coarse columnar β grains in deposited Ti-6Al-4V components and unsupported overhangs fabrication are two challenges in arc additive manufacturing. In order to handle these issues, low heat input deposition using pulse current is investigated in this study. The results indicate that the reduction of heat input can increase the cooling rate, but has no significant effect on the refinement of β grain size due to the increasing temperature gradient and the preferred growth of β grain. Nonetheless, fine α plates can be obtained as the cooling rate increases. Tensile testing parallel to the deposition plane reveals that the ultimate tensile strength is between 963 and 1008 MPa and ductility is between 11.4% and 17.8%. With the decline of heat input, the ultimate strength and yield strength are improved. Besides, horizontal structures without supports are fabricated successfully using low frequency pulse current. According to the force conditions of the molten pool, a contact angle hysteresis model is applied to reveal the fabrication mechanism.