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

Khalil-Allafi, Jafar; Eggeler, Gunther; Dlouhy, A.; Schmahl, Wolfgang W. and Somsen, C. (2004): On the influence of heterogeneous precipitation on martensitic transformations in a Ni-rich NiTi shape memory alloy. In: Materials Science and Engineering A, Vol. 378, No. 1-2 SPEC. ISS: pp. 148-151

Abstract

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 Ni4Ti3 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.

• Item Type: Journal article
• Faculties: Geosciences > Department of Earth and Environmental Sciences > Crystallography and Materials Science
• Subjects: 500 Science > 550 Earth sciences and geology
• Language: English