Intermetallic formation and mechanical properties of Ni-Ti diffusion couples. (15th September 2017)

• Record Type: Journal Article
• Authors: Hu, Lifang; Xue, Yongzhi; Shi, Fangrong
• Is Part Of: Materials & design. Volume 130(2017)
• Page Start: 175
• Page End: 182
• Publication Date: 2017-09-15
• Subjects: Intermetallic -- Diffusion -- Interfaces -- Ni-Ti -- Shear strength; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2017.05.055
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: 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 Ni3 Ti, were formed at the Ni-Ti interface at 650 °C. Ni3 Ti first grew at the Ni substrate because of the diffusion of Ti into Ni, NiTi2 subsequently appeared, and NiTi finally developed between the NiTi2 -Ni3 Ti interface. As the thickness of the diffusion layers increased, a part of Ni3 Ti 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 Ni3 Ti matrix, which was immediately adjacent to NiTi, and this crystal then elongated at a direction perpendicular to the plane of the joint. Ni3 Ti 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 Ni3 Ti for the sample prepared at 650 °C. For the sample prepared at 900 °C, fractures were detected in NiTi2 . Graphical abstract: Highlights: The intermetallic Ni-Ti diffusion couples are formed in the following order: Ni3 Ti, NiTi2, and NiTi. NiTi2, NiTi, and Ni3 Ti coexisted at the diffusion interface at a diffusion temperature lower than 900 °C. Columnar crystal formed inside Ni3 Ti 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 Ni3 Ti.