A novel magnetic field assisted powder arc additive manufacturing for Ti60 titanium alloy: Method, microstructure and mechanical properties

Due to the rapid heating-cooling process and unstable keyhole, pore defects are easily formed during the high energy beam-powder additive manufacturing (AM) process, posing great challenges to the high-performance manufacturing of aerospace components. Using an arc with lower energy density as a heat source can effectively avoid these defects, but its matching raw materials are limited to wire. In this paper, a novel magnetic field assisted powder arc additive manufacturing (MFA-PAAM) method has been proposed, which combines arc heat source and powder raw material to achieve dense metal parts. A transverse magnetic field (TMF) was introduced to solve the powder spattering problem which impacts the stability of the PAAM process, by regulating the direction of the arc plasma flow and the arc pressure. The unique melting behavior of the powder under arc heating was captured by a high-speed camera, which can be summarized into two steps: balling and adsorption by the molten pool. And the well-formed and fully dense Ti60 high-temperature titanium alloy wall components were successfully manufactured using the self-developed equipment. The microstructure of the thin-wall component is dominated by basket-weave distributed α laths and few β sheets remaining at their boundaries. A layered periodic distribution along the building direction was observed, which is mainly distinguished from the content and morphology of the β phase. The average ultimate tensile strength (UTS) and elongation to failure in the travelling direction are 1003.2 MPa and 15.1%, while the average UTS and elongation along the building direction are 1009.3 MPa and 16.6%, respectively. The fracture morphologies in both directions are characterized by ductile fracture. The MFA-PAAM technique shows great potential for fabricating materials that are difficult to be drawn into wires with high efficiency and performance.