Stress-assisted removal of conjugation boundaries in non-modulated Ni–Mn–Ga by coordinated secondary twinning
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Observations are presented, obtained by in situ straining and conventional TEM, of a transformation mechanism by coordinated secondary twinning predicted by Mullner and King. The material studied is the martensitic phase of a non-modulated Ni–Mn–Ga alloy, which exhibits a microstructure comprising domains of lamellar matrix/twin composites. Straining these specimens induced lamellar domains to transform into their conjugate counterparts. In this process, secondary twinning generates a change of misorientation between the matrix and twin lamellae of the initial domain by nearly 23°. The orientation evolves over a region behind the transformation front about 100 nm in extent.
We thank Nikki Kucza and Martika Flores-Ramos for assistance with the growth of single crystals. We acknowledge partial financial support from the National Science Foundation through grant DMR-1008167, and NSF MRI awards 0521315 (TEM) and 0619795 (XRD). The research described in this paper is part of the Chemical Imaging Initiative at Pacific Northwest National Laboratory under Contract DE-AC05-76RL01830 operated for DOE by Battelle. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.
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Conflict of interest
The authors declare that they have no conflict of interest.
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