Martensitic transformation of NiTi studied at the nanometer scale by local mechanical spectroscopy
Near-stoichiometric NiTi alloys exhibit a martensitic phase transformation between a low-temperature monoclinic phase, called martensite, and a high temperature cubic phase with B2 structure, called austenite. This transformation is responsible for the shape memory and pseudo-elastic effects in deformed NiTi alloys. Optical microscopy observation suggests that the transformation occurs very suddenly inside an austenite grain. This has led to the concept of military transformation. The width of the globally measured transformation would then be a sum of different narrow contributions coming from different places inside the sample. this image is, however, not universally accepted. A measurement inside one single grain of a polycrystal would be a way to address these questions. Both the special scale of the R phase distribution and the military character of the transformation will have an effect on the result of such a measurement. The martensitic transformation of such alloys has already been observed on bulk samples by mechanical spectroscopy, i.e., measurement of the inelastic part of the deformation induced by a cyclic stress. Such measurements, also called Internal Friction measurements, give access to the mechanical energy dissipation during the phase transition. However, they give an average behavior of all parts of the sample. This paper reports the first local (i.e., at a submicron scale) mechanical spectroscopy measurement of the martensitic transformation in thermally cycled NiTi alloys.
- Research Organization:
- Inst. de Genie Atomique, Lausanne (CH)
- OSTI ID:
- 20023107
- Journal Information:
- Scripta Materialia, Vol. 42, Issue 1; Other Information: PBD: 17 Dec 1999; ISSN 1359-6462
- Country of Publication:
- United States
- Language:
- English
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