[en] Highlights: • The intermetallic Ni-Ti diffusion couples are formed in the following order: Ni₃Ti, NiTi₂, and NiTi. • NiTi₂, NiTi, and Ni₃Ti coexisted at the diffusion interface at a diffusion temperature lower than 900 °C. • Columnar crystal formed inside Ni₃Ti matrix, immediately adjacent to NiTi at 900 °C, and changed into pure Ti subsequently. • The shear strength decreased in the following order: NiTi, NiTi₂ and Ni₃Ti. Samples of Ni-Ti diffusion couples were prepared by hot pressing in a furnace with a vacuum of 10^{− 1} Pa. Scanning electron microscopy (SEM) investigations indicated that three intermetallic compounds, namely, NiTi₂, NiTi, and Ni₃Ti, were formed at the Ni-Ti interface at 650 °C. Ni₃Ti first grew at the Ni substrate because of the diffusion of Ti into Ni, NiTi₂ subsequently appeared, and NiTi finally developed between the NiTi₂-Ni₃Ti interface. As the thickness of the diffusion layers increased, a part of Ni₃Ti was also consumed by Ti to form NiTi. The interfacial microstructure was changed by the current at 900 °C. A columnar crystal initially formed inside the Ni₃Ti matrix, which was immediately adjacent to NiTi, and this crystal then elongated at a direction perpendicular to the plane of the joint. Ni₃Ti vanished, and pure Ti was finally produced. The observed strength variations were discussed in relation to interfacial microstructures. Shear experiments showed that fractures were observed in Ni₃Ti for the sample prepared at 650 °C. For the sample prepared at 900 °C, fractures were detected in NiTi₂.