On the influence of heterogeneous precipitation on martensitic transformations in a Ni-rich NiTi shape memory alloy

Recently, a new explanation was given for the evolution of DSC chart features after ageing of Ni-rich NiTi alloys. It was shown that the 2–3–2 evolution of DSC chart features can be fully rationalised on the basis of a microstructural scenario, where metastable Ni-rich Ni 4Ti 3 particles precipitate...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2004-07, Vol.378 (1), p.148-151
Main Authors: Khalil-Allafi, J, Eggeler, G, Dlouhy, A, Schmahl, W.W, Somsen, Ch
Format: Article
Language:English
Subjects:
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
Heterogeneous precipitation
Martensitic transformations
Materials science
Microstructure
Multiple step martensitic transformations
NiTi shape memory alloys
Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
Physics
Precipitation
Thermal analysis
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Summary:Recently, a new explanation was given for the evolution of DSC chart features after ageing of Ni-rich NiTi alloys. It was shown that the 2–3–2 evolution of DSC chart features can be fully rationalised on the basis of a microstructural scenario, where metastable Ni-rich Ni 4Ti 3 particles precipitate on and near grain boundaries in a material, which was solution annealed and subsequently aged. A detailed description of the multiple step martensitic transformation has been given in the literature. However, this was only experimentally validated for one ageing temperature (500 °C). In the present study we show that heterogeneous precipitation is also a dominant microstructural feature when ageing is performed at 400 and 450 °C and that the microstructural scenario described previously also accounts for the phase transformation characteristics after lower temperature ageing. Long-term ageing results in large and widely spaced precipitates which no longer directly affect martensitic transformations.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2003.10.335