Structure analysis of a precipitate phase in an Ni-rich high-temperature NiTiHf shape memory alloy

Thermal aging of the high-temperature shape memory alloy 50.3Ni–29.7Ti–20Hf (at.%) introduces a novel precipitate phase that plays an important role in improving shape memory properties. The precipitate phase was investigated by conventional electron diffraction, high-resolution scanning transmissio...

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Bibliographic Details
Published in:Acta materialia 2013-05, Vol.61 (9), p.3335-3346
Main Authors: Yang, F., Coughlin, D.R., Phillips, P.J., Yang, L., Devaraj, A., Kovarik, L., Noebe, R.D., Mills, M.J.
Format: Article
Language:English
Subjects:
Ab initio electron theory
Applied sciences
Crystal structure
Exact sciences and technology
High-angle annular dark field (HAADF)
Joining, thermal cutting: metallurgical aspects
Metals. Metallurgy
Precipitation
Shape memory alloys (SMAs)
Welding
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Summary:Thermal aging of the high-temperature shape memory alloy 50.3Ni–29.7Ti–20Hf (at.%) introduces a novel precipitate phase that plays an important role in improving shape memory properties. The precipitate phase was investigated by conventional electron diffraction, high-resolution scanning transmission electron microscopy (STEM) and three-dimensional atom probe tomography. An unrelaxed orthorhombic atomic structural model is proposed based on these observations. This model was subsequently relaxed by ab initio calculations. As a result of the relaxation, atom shuffle displacements occur, which in turn yields improved agreement with the STEM images. The relaxed structure, which is termed the “H phase”, has also been verified to be thermodynamically stable at 0K.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2013.02.023