Compressive response of nickel-rich NiTiHf high-temperature shape memory single crystals along the [1 1 1] orientation

Karaca, H.E.; Saghaian, Sayed M.; Başaran, B.; Bigelow, Glen S.; Noebe, R.D.; Chumlyakov, Yu. I.

doi:10.1016/j.scriptamat.2011.06.027

Cited by 63 publications

(43 citation statements)

References 17 publications

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“…However, in most cases, the addition of ternary elements (Cu, Fe, Pd) has reduced the transformation strain magnitudes compared to binary NiTi. Experimental results on NiTi20 Hf [5][6][7][8] also exhibit lower transformation strain than binary NiTi alloys [9]. In view of the inferior NiTiHf transformation strains measured at macroscale compared to the theoretical values, the question remains whether better agreement can be achieved if experimental strain measurements were made at smaller length scales.…”

Section: Introductionmentioning

confidence: 98%

Shape Memory Response of Polycrystalline NiTi12.5Hf Alloy: Transformation at Small Scales

Patriarca

et al. 2015

Shap. Mem. Superelasticity

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The transformation behavior of NiTiHf alloys is intriguing. In NiTiHf alloys, the experimental transformation strains have been reported to be considerably lower than theoretical transformation strains. In this study, the transformation strain is established with very careful strain measurements at small scales in isobaric and isothermal experiments. Because of the heterogeneity of strain distributions, the results depend on the sub-region considered. The measured local transformation strain can be as high as 6.0 % in compression which is in very good agreement with theoretical calculations for NiTi12.5Hf. The comprehension of NiTi12.5Hf alloy was furthered upon extensive microstructural characterization including high-resolution electron microscopy, establishing the volume fractions of precipitates and twin type. The volume fraction of precipitates is similar to that of Ni-rich binary NiTi alloys. Meanwhile, the twinning modes in the martensite are compound and Type I twins which were used in the theoretical calculations of transformation strains. This material also generates a high work output and represents a foundation for understanding higher Hf compositions.

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Section: Introductionmentioning

confidence: 98%

Shape Memory Response of Polycrystalline NiTi12.5Hf Alloy: Transformation at Small Scales

Patriarca

et al. 2015

Shap. Mem. Superelasticity

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“…Similarly, compressive testing was performed on the same alloy at temperatures above the austenite finish (A f ) temperature to study the effect of aging on the stress-induced transformation and plasticity, but also only for a few cycles [8]. In single crystal form, the effects of applied stress and testing temperatures were evaluated along the [111] orientation with stress levels up to 1000 MPa [9]. From a microscopic perspective, in situ neutron diffraction was used to investigate the role of the fine precipitates on texture, internal strains, and other microstructural features during tensile and isobaric thermomechanical testing [7].…”

Section: Introductionmentioning

confidence: 99%

Mechanical and functional behavior of a Ni-rich Ni50.3Ti29.7Hf20 high temperature shape memory alloy

et al. 2014

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a b s t r a c tThe mechanical and functional behaviors of a Ni-rich Ni 50.3 Ti 29.7 Hf 20 high temperature shape memory alloy were investigated through combined ex situ macroscopic experiments and in situ synchrotron X-ray diffraction. Isothermal tension and compression tests were conducted between room temperature and 260 C, while isobaric thermomechanical cycling experiments were conducted at selected stresses up to 700 MPa. Isothermal testing of the martensite phase revealed no plastic strain up to the test limit of 1 GPa and near-perfect superelastic behavior up to 3% applied strain at temperatures above the austenite finish. Excellent dimensional stability with greater than 2.5% actuation strain without accumulation of noticeable residual strains (at stresses less than or equal to À400 MPa) were observed during isobaric thermal cycling experiments. The absence of residual strain accumulation during thermomechanical cycling was confirmed by the lattice strains, determined from X-ray spectra. Even in the untrained condition, the material exhibited little or no history or path dependence in behavior, consistent with measurements of the bulk texture after thermomechanical cycling using synchrotron X-ray diffraction. Post deformation cycling revealed the limited conditions under which a slight two-way shape memory effect (TWSME) was obtained, with a maximum of 0.34% two-way shape memory strain after thermomechanical cycling under À700 MPa.Published by Elsevier Ltd.

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“…In the last years the interest on the mechanical behavior of NiTiHf is growing, and several studies have shown good SME, ISME and SE behaviors at temperatures above 250°C. Transformation strains up to 3.74% in polycrystal were obtained for the Ni 50.3 Ti 29.7 Hf 20 composition [71][72][73][74][75]. Remarkably, superelastic behavior was found at temperatures as high as 240°C [73].…”

Section: Overview Of Previous Nitihf Workmentioning

confidence: 91%

“…3. Previous works explored the transformation temperatures with change in Hf contents in the range 15-20 at.% [48][49][50]. Transformation temperatures less than 250°C have been reported depending on the Ni/Hf content.…”

Section: Transformation Strain-transformation Temperature Behavior Ofmentioning

confidence: 99%

“…In view of the promising results for the polycrystal, single crystals of Ni 50.3 Ti 29.7 Hf 20 alloy showed only comparable level of transformation strains. The Ni 50.3 Ti 29.7 Hf 20 [1 1 1] orientation was tested in isobaric compression experiments, and transformation strains up to 3.9% were measured [72]. However, further efforts in testing different crystal orientations ([0 0 1], [3 4 0], [6 7 8], [0 1 1]) did not lead to higher transformation strains.…”

Section: Overview Of Previous Nitihf Workmentioning

confidence: 99%

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Shape memory strains and temperatures in the extreme

Şehitoğlu

Patriarca

2017

Current Opinion in Solid State and Materials Science

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It is well known that the achievement of high transformation strains in shape memory alloys (SMAs) has been curtailed by plastic deformation mediated via dislocation slip. In particular, the utilization of SMAs at high temperatures is also hindered by plastic slip. In this paper, an overview of the most important SMAs is provided by constructing transformation strain, transformation temperature, and slip resistance plots to put existing works in perspective. To this plots, we added results on NiTiHf alloys which impart both high temperature capability and high slip resistance at unprecedented levels. The remarkable finding is that NiTiHf alloys can undergo transformation strains near 20% and transformation temperatures exceeding 400 °C

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Compressive response of nickel-rich NiTiHf high-temperature shape memory single crystals along the [1 1 1] orientation

Cited by 63 publications

References 17 publications

Shape Memory Response of Polycrystalline NiTi12.5Hf Alloy: Transformation at Small Scales

Shape Memory Response of Polycrystalline NiTi12.5Hf Alloy: Transformation at Small Scales

Mechanical and functional behavior of a Ni-rich Ni50.3Ti29.7Hf20 high temperature shape memory alloy

Shape memory strains and temperatures in the extreme

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