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Sci Rep. 2016 Apr 6;6:23905. doi: 10.1038/srep23905.

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires.

Author information

1
State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China.
2
Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, 60208, USA.
3
School of Materials and Metallurgy, Northeastern University, Shenyang, 110819, China.
4
School of Engineering, Edith Cowan University, 270 Joondalup Drive, Joondalup, Perth, WA 6027, Australia.
5
School of Mathematics and Science, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu 212003, China.

Abstract

NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19' martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19' martensitic transformation, and (V) plastic deformation of the specimen.

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