The influence of aging on critical transformation stress levels and martensite start temperatures in NiTi. Part 2: Discussion of experimental results
- Univ. of Illinois, Urbana, IL (United States). Dept. of Mechanical and Industrial Engineering
- Siberian Physical and Technical Inst., Tomsk (Russian Federation). Physics of Plasticity and Strength of Materials Lab.
- Univ.-GH-Siegen (Germany). Inst. fuer Werkstofftechnik
An experimental study was performed to determine the effect of aging on martensitic transformations in NiTi. Polycrystalline and single crystal NiTi ([100], [110], and [111] orientations) were both considered. Stress-induced transformations in single crystals of the [110] and [111] orientations. Solutionized and over-aged single crystals exhibited a strong orientation dependence of the critical stress required to trigger the transformation, {sigma}{sub cr}. The Schmid law was able to accurately predict the orientation dependence of {sigma}{sub cr} in the solutionized and over-aged single crystals. Peak-aged single crystals demonstrated a much weaker orientation dependence of {sigma}{sub cr} and in general, the Schmid law was not obeyed. By considering the local stress fields outside of the semi-coherent precipitates, the decrease in the orientation dependence of {sigma}{sub cr} was accounted for. The martensite start temperatures, M{sub s}, in aged single crystal and polycrystalline NiTi were much higher than in solutionized samples. In peak-aged NiTi the increase was primarily attributed to the local stress fields outside the coherent precipitates which create preferential nucleation sites for the martensite. In the over-aged NiTi the increase in M{sub s} was primarily attributed to the decrease in the average Ni concentration of the matrix surrounding the coarsened precipitates.
- Sponsoring Organization:
- USDOE, Washington, DC (United States); Russian Foundation for Basic Research (Russian Federation)
- DOE Contract Number:
- FG02-93ER14393
- OSTI ID:
- 329106
- Journal Information:
- Journal of Engineering Materials and Technology, Journal Name: Journal of Engineering Materials and Technology Journal Issue: 1 Vol. 121; ISSN 0094-4289; ISSN JEMTA8
- Country of Publication:
- United States
- Language:
- English
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