Evolution of local strain bands of different orientation in single crystalline Ni–Mn–Ga foils under tension

Evolution of local strain bands of different orientation in single crystalline Ni–Mn–Ga foils under tension

► We investigate the tensile deformation of single crystalline Ni–Mn–Ga stripes by DIC. ► Mechanical constraints (fixation, bending) determine the type of twin boundary formed during training in a magnetic field. ► Orientation of strain bands (45° or 84° inclination) depends on the type of twin boun...

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Bibliographic Details
Published in:Journal of alloys and compounds Vol. 577; pp. S358 - S361
Main Authors: Pinneker, V., R.Yin, Eberl, C., Sozinov, A., Ezer, Y., Kohl, M.
Format: Journal Article
Language:English
Published: Elsevier B.V 15-11-2013
Subjects:
Bands
Crystal structure
Digital Image Correlation
Foils
Martensite
Nickel
Ni–Mn–Ga foil
Orientation
Strain
Strain band
Superplasticity
Training
Twinning
Training
Superplasticity
Digital Image Correlation
Strain band
Ni–Mn–Ga foil
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Summary:► We investigate the tensile deformation of single crystalline Ni–Mn–Ga stripes by DIC. ► Mechanical constraints (fixation, bending) determine the type of twin boundary formed during training in a magnetic field. ► Orientation of strain bands (45° or 84° inclination) depends on the type of twin boundary. ► The twinning stress is lower for twin boundaries inclined by 84° compared to the case of 45°. We investigate the mechanically induced local deformation effects in single crystalline Ni–Mn–Ga stripes by in situ Digital Image Correlation (DIC). Ni–Mn–Ga stripes of 100 and 200μm thickness and lateral dimensions of 15mm×3mm are fabricated by cutting and electropolishing a Ni–Mn–Ga bulk single crystal having a 10M martensite structure. Application of tensile stress causes reorientation of martensite variants being associated with the formation and growth of local strain bands. The true strain in the bands is determined to be about 6% indicating complete local variant reorientation. The stress–strain characteristics are strongly affected by the mechanical boundary conditions. (1) Fixation or clamping the foil specimens during training in a magnetic field results in the formation of a stationary twin boundary (TB) being oriented by 45° with respect to the specimen edge. Subsequent tensile loading causes formation of a strain band with 45° orientation extending in both lateral directions through TB motion. The corresponding twinning stress is about 2MPa. (2) Bending in out-of-plane direction causes formation of a stationary TB being oriented by about 84° with respect to the specimen edge. In this case, tensile loading causes formation of a strain band with 84° orientation. The corresponding twinning stress is reduced to about 0.7MPa.
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ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2012.03.004