Microstructure and mechanical properties of Ni50.8Ti49.2 and Ni53Ti47 alloys prepared in situ by wire-arc additive manufacturing

In this study, polycrystalline Ni50.8Ti49.2 and Ni53Ti47 single-walled components were prepared by dual-wire-arc additive manufacturing (in-situ alloying) using TA1 and ER-Ni wires as feedstocks. The microstructural evolution in the building direction and the mechanical properties of the two components were also investigated. The phases of Ni50.8Ti49.2 and Ni53Ti47 change from NiTi + NiTi2 to NiTi + NiTi2+ Ni4Ti3 and from NiTi + NiTi2 through NiTi + Ni3Ti to NiTi + Ni3Ti + Ni3Ti2+ Ni4Ti3, respectively, with increasing distance from the substrate. The presence and absence of the NiTi(R) phase in the Ni50.8Ti49.2 and Ni53Ti47 components, respectively, were confirmed using differential scanning calorimetry. The two components have similar fracture stress values (i.e., 2.45 GPa); however, the fracture strain of Ni53Ti47 is 51.7% less than that of Ni50.8Ti49.2. The unrecoverable strain of Ni50.8Ti49.2 gradually approaches 4.5%, while that of Ni53Ti47 increases linearly during a cyclic compression test (15 load/unload cycles). This study reveals, for the first time, the phase evolution and mechanical properties of Ni53Ti47 components prepared using dual-wire-arc additive manufacturing and proposes a novel method for the fabrication of a NiTi shape memory alloy with a flexible composition that meets the needs of aerospace applications.