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On the impact of nanometric γ’ precipitates on the tensile deformation of superelastic Co49Ni21Ga30

Reul, A. and Lauhoff, C. and Krooß, P. and Somsen, C. and Langenkämper, D. and Gutmann, M.J. and Pedersen, B. and Hofmann, M. and Gan, W.M. and Kireeva, I. and Chumlyakov, Y.I. and Eggeler, G. and Niendorf, T. and Schmahl, W.W.

ACTA MATERIALIA
Volume: 230 Pages:
DOI: 10.1016/j.actamat.2022.117835
Published: 2022

Abstract
Results are presented reporting on the martensite domain variant selection and stress-induced martensite morphology in [001]-oriented superelastic Co49Ni21Ga30 shape memory alloy (SMA) single crystals under tensile load. In situ neutron diffraction, as well as in situ optical- and confocal laser scanning microscopy were conducted focusing on three differently treated samples, i.e. in the as-grown, solution-annealed and aged condition. An aging treatment performed at 350 °C promotes the precipitation of nanoprecipitates. These second phase precipitates contribute to an increase of the number of habit plane interfaces, while reducing lamellar martensite plate thickness compared to the as-grown and solution-annealed (precipitate free) samples. During tensile loading, all samples show a stress-induced formation of martensite, characterized by one single domain variant (“detwinned”) and one set of parallel habit planes in a shear band. The results clearly show that γ’ nanoprecipitates do not necessarily promote multi-variant interaction during tensile loading. Thus, reduced recoverability in Co-Ni-Ga SMAs upon aging cannot be solely attributed to this kind of interaction as has been proposed in literature so far. © 2022

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