Transformation strains and temperatures of a nickel–titanium–hafnium high temperature shape memory alloy

Stebner, Aaron P.; Bigelow, Glen S.; Yang, Jin; Shukla, Dhwanil; Saghaian, Sayed M.; Rogers, Richard B.; Garg, A.; Karaca, H.E.; Chumlyakov, Yuriy; Bhattacharya, Kaushik; Noebe, Ronald D.

doi:10.1016/j.actamat.2014.04.071

Cited by 98 publications

(40 citation statements)

References 38 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: 99%

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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: 99%

“…The most recent publications in Hf alloyed NiTi have been focused primarily on 20 at.% Hf [8] and recently on 25 at.% Hf compositions [10]. The experimental transformation strains for 20 at.% Hf are less than 4 % in most cases compared to theoretical values at 8 %.…”

Section: Introductionmentioning

confidence: 99%

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

Patriarca

et al. 2015

Shap. Mem. Superelasticity

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“…As previously discussed, the recent body of work on NiTiHf alloys [50,72,75,83] has considered both polycrystals and single crystals for Hf contents less than 20 at.%. These recent works on compression have shown that the transformation strains fall far below the theoretical values [75].…”

Section: Discussion Of Resultsmentioning

confidence: 95%

“…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: 81%

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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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