TY - JOUR
T1 - Shape Memory Response of Polycrystalline NiTi12.5Hf Alloy
T2 - Transformation at Small Scales
AU - Wu, Y.
AU - Patriarca, L.
AU - Li, G.
AU - Sehitoglu, H.
AU - Soejima, Y.
AU - Ito, T.
AU - Nishida, M.
N1 - Funding Information:
The work was supported by NSF-CMMI 1333884 which is gratefully acknowledged. The authors also acknowledge the Frederick Seitz Materials Research Laboratory and Dr. Mauro Sardela for assistance with X-ray diffraction.
Funding Information:
The work was supported by NSF-CMMI 1333884 which is gratefully acknowledged.?The authors also acknowledge the Frederick Seitz Materials Research Laboratory and Dr. Mauro Sardela for assistance with X-ray diffraction.
Publisher Copyright:
© 2015, ASM International.
PY - 2015/9/1
Y1 - 2015/9/1
N2 - 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.
AB - 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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U2 - 10.1007/s40830-015-0033-0
DO - 10.1007/s40830-015-0033-0
M3 - Article
AN - SCOPUS:84997515727
SN - 2199-384X
VL - 1
SP - 387
EP - 397
JO - Shape Memory and Superelasticity
JF - Shape Memory and Superelasticity
IS - 3
ER -