<p>In this study, the NiTi components prepared by depositing Ti6Al4V and Inconel 718 wires were fabricated by a twin-wire arc additive. The microstructure and phase characteristics of Ti6Al4V/Inconel 718 composites were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Based on understanding the microstructure, the stability of the phase in the composite is calculated by the method of first principles, and the influence of the crystal structure of the phase on the hardness of the composite is discussed. The results show that the secondary dendrite arm spacing and grain size of the prepared composites decrease with the increase in printing height. The composite is mainly composed of the NiTi phase, with Cr₂Ti and NiTi on the dendrite axis, NiTi, Ni₃Ti, some granular Cr₂Ti, and a small amount of Ni₄Ti₃ among the dendrites. The crystal structure of the phase is discussed and the enthalpy of formation and cohesion energy of the phase are calculated by the method of first principles. The intermetallic compounds of NiTi, Ni₃Ti, and Cr₂Ti are thermodynamically stable, and the alloy-forming ability of Cr₂Ti is the strongest. The order of crystal structure stability from large to small is Cr₂Ti, Ni₃Ti, and NiTi. Their crystal structures are hexagonal crystal systems, close-packed hexagonal and body-centered cubic, respectively, and the crystal structure often affects the hardness of the material. The average microhardness of the prepared composite material is 918.92 HV.</p>