TY - JOUR

T1 - Underlying mechanism of dual hysteresis in NiMnGa single crystals

AU - Hamilton, R. F.

AU - Dilibal, S.

AU - Sehitoglu, H.

AU - Maier, H. J.

N1 - Funding information: The work received support from NSF under CMMI 09-26813 . The authors would like to acknowledge Yuri Chumlyakov from the Siberian Physical Technical Institute, Tomsk, Russia for providing the single crystals and fruitful discussions.

PY - 2010/10/22

Y1 - 2010/10/22

N2 - NiMnGa single crystals are compressed in the [001] orientation at room temperature. The stress-strain response exhibits multiple stages as the deformation proceeds. Initially, the response exhibits a stress drop in the stress-strain curve preceding a plateau stress. By contrast, the second transition, which occurs at five times the initial critical transformation stress, produces a work hardening like response. Complete pseudoelastic (PE) recovery ensues upon unloading with the reverse transformation exhibiting the same two-stages. Furthermore, for the dual hysteresis that results, the second hysteresis is nearly four times wider than the first. The underlying transformation path for each stage is ascertained from local strain analysis utilizing variable magnification in situ digital image correlation (DIC). We distinguish three different morphological transitions; band formation, phase front propagation, and heterogeneous growth. The morphologies can be attributed to austenite undergoing the successive transitions 10M→14M (modulated to modulated) and 10M→L10 (modulated to non-modulated). Differential critical stress and hysteresis levels are rationalized based on the initial modulated-to-modulated and successive modulated-to-non-modulated transition. The strain-temperature response is reported, as well, and exhibits a tiny thermal hysteresis (5°C), which is attributed to the modulated-to-modulated conversion.

AB - NiMnGa single crystals are compressed in the [001] orientation at room temperature. The stress-strain response exhibits multiple stages as the deformation proceeds. Initially, the response exhibits a stress drop in the stress-strain curve preceding a plateau stress. By contrast, the second transition, which occurs at five times the initial critical transformation stress, produces a work hardening like response. Complete pseudoelastic (PE) recovery ensues upon unloading with the reverse transformation exhibiting the same two-stages. Furthermore, for the dual hysteresis that results, the second hysteresis is nearly four times wider than the first. The underlying transformation path for each stage is ascertained from local strain analysis utilizing variable magnification in situ digital image correlation (DIC). We distinguish three different morphological transitions; band formation, phase front propagation, and heterogeneous growth. The morphologies can be attributed to austenite undergoing the successive transitions 10M→14M (modulated to modulated) and 10M→L10 (modulated to non-modulated). Differential critical stress and hysteresis levels are rationalized based on the initial modulated-to-modulated and successive modulated-to-non-modulated transition. The strain-temperature response is reported, as well, and exhibits a tiny thermal hysteresis (5°C), which is attributed to the modulated-to-modulated conversion.

KW - Digital image correlation

KW - Hysteresis

KW - Martensitic transformation

KW - Mechanical characterization

KW - Shape memory alloys

KW - Strain measurement

UR - http://www.scopus.com/inward/record.url?scp=78650175545&partnerID=8YFLogxK

U2 - 10.1016/j.msea.2010.10.042

DO - 10.1016/j.msea.2010.10.042

M3 - Article

AN - SCOPUS:78650175545

VL - 528

SP - 1877

EP - 1881

JO - Materials Science and Engineering A

JF - Materials Science and Engineering A

SN - 0921-5093

IS - 3

ER -