Tension-compression asymmetry of the stress-strain response in aged single crystal and polycrystalline NiTi
- 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.
The purpose of this work is to thoroughly understand tension-compression asymmetry in precipitated NiTi using unique experimental results and micro-mechanical modeling. For the first time, tensile and compressive stress-strain behaviors were established on aged single crystals ([100], [110], and [111] orientations) and polycrystalline NiTi. The single crystal and polycrystalline Ti-50.8 at.% Ni materials were given both peak aged and over aged heat treatments. The drawn polycrystalline NiTi has a strong texture of the {l_angle}111{r_angle}{l_brace}110{r_brace} type, thus it deformed in a manner consistent with the [111] single crystals. In contrast to the phenomenological theory of martensitic transformations (analogous to Schmid`s law), the critical resolved shear stress required to trigger the transformation, {tau}{sub crss}, in the peak-aged single crystals was dependent on both the stress direction and crystallographic orientation. Using micro-mechanical modeling, the deviation from Schmid`s law was attributed to the unique orientation relationship that exists between the Ti{sub 3}Ni{sub 4} precipitates (their coherent stress fields) and the 24 martensite correspondence variant pairs. The over-aged single crystals generally obeyed Schmid`s law within experimental error, consistent with the proposed micro-mechanical model. Qualitatively, the tension-compression asymmetry and orientation dependence of the recoverable strain level, {var_epsilon}{sub 0}, was consistent with the phenomenological theory for martensitic transformations. However, the peak- and over-aged single crystals generally both demonstrated smaller {var_epsilon}{sub 0} magnitudes than predicted. The differences for both crystals were attributed to the inhibition of martensite detwinning coupled with several unique microstructural effects.
- Sponsoring Organization:
- USDOE, Washington, DC (United States); Russian Foundation for Basic Research (Russian Federation)
- DOE Contract Number:
- FG02-93ER14393
- OSTI ID:
- 338425
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 4 Vol. 47; ISSN 1359-6454; ISSN ACMAFD
- Country of Publication:
- United States
- Language:
- English
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