Third element diffusion induced amorphization of NiTi in a NiTi-Nb nanocomposite

S Bakhtiari and A Agrawal and H Yang and R Mirzaeifar and LS Cui and DQ Jiang and YN Liu, ACTA MATERIALIA, 257, 119180 (2023).

DOI: 10.1016/j.actamat.2023.119180

The paper reports a unique and rare phenomenon observed in a NiTi-Nb nanowire in-situ composite system. The phenomenon is the amorphization of the B2 NiTi matrix caused by the diffusion of Nb through the B2 lattice. The diffusion of Nb through the NiTi matrix is driven by the effect of Oswald ripening associated with the fragmentation and granulation of Nb nanowires at elevated temperatures and the amorphization of the NiTi matrix is attributed to the effect of Ni-Ti atomic swapping, i.e., the formation of anti-site defects in the B2 structure, caused by the substitutional diffusion of a third element, Nb in this case. The phenomenon is observed by transmission electron microscopy examination and x-ray diffraction measurement and the hypothesis of explanation is supported by molecular dynamic simulation studies.

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