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[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.