In-situ neutron diffraction study on the high temperature thermal phase evolution of wire-arc additively manufactured Ni53Ti47 binary alloy.

In the present research, to further reduce the fabrication and forming cost of NiTi alloy, an innovative wire-arc additive manufacturing process (WAAM), which is simultaneously an in-situ alloying process, has been applied to fabricate polycrystalline Ni 53 Ti 47. The as-fabricated alloy is subsequently subjected to a necessary post-production annealing for additively manufactured metals. During the thermal cycle, to characterize the obtained phases in the Ni 53 Ti 47 alloy and provide dynamic lattice evolution information, neutron diffraction is conducted to the heated sample in real time. It is found that the metastable Ni 4 Ti 3 phase is only obtained in the heat-treated alloy while the as-fabricated NiTi alloy produced by WAAM contains only NiTi and Ni 3 Ti. The generated Ni 4 Ti 3 precipitates have increased the NiTi phase micro strains. The hcp -Ni 3 Ti lattice evolution is found inducing converse lattice shrinkage and expansion in bcc -NiTi lattice during the dissolution and precipitation of Ni 3 Ti, respectively. The WAAM induced residual stress in the as-fabricated alloy is tensile and during the residual stress relief, the thermal expansion rate of Ni and Ni 3 Ti are reduced. In addition, the thermal expansion coefficient of NiTi and Ni 3 Ti is measured according to the neutron Rietveld refinement as 0.040 × 10−3 °C−1 and 0.036 × 10−3 °C−1, respectively. Image 1 • Neutrons are conducted in-situ to the phase evolutions in additively manufactured Ni 53 Ti 47 alloy. • The as-fabricated Ni 53 Ti 47 alloy contains only NiTi and Ni 3 Ti without Ni 4 Ti 3 phase. • Responses of bcc-NiTi and hcp-Ni 3 Ti phase lattice strains to temperature are calculated. [ABSTRACT FROM AUTHOR]