Low‐temperature martensite relaxation in Co–Ni–Ga shape memory alloy monocrystal revealed using in situ cooling, transmission electron microscopy and low rate calorimetry

This work presents the results of research on a Co49Ni21Ga30 magnetic shape memory single crystal. Based on a literature review, it was identified that analyses of phase transformations have been limited to specific heating and cooling rates, which could lead to an incomplete description of the resu...

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Bibliographic Details
Published in:Acta crystallographica Section B, Structural science, crystal engineering and materials Structural science, crystal engineering and materials, 2020-08, Vol.76 (4), p.563-571
Main Authors: Żak, Andrzej, Dańczak, Anna, Dudziński, Włodzimierz
Format: Article
Language:English
Subjects:
Calorimetry
CoNiGa
Cooling
Cooling rate
Differential scanning calorimetry
Enthalpy
Heat measurement
Heating
in situ TEM
Literature reviews
Martensite
Martensitic transformations
Phase transitions
relaxation
shape memory alloy
Shape memory alloys
Single crystals
Temperature
Transmission electron microscopy
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Summary:This work presents the results of research on a Co49Ni21Ga30 magnetic shape memory single crystal. Based on a literature review, it was identified that analyses of phase transformations have been limited to specific heating and cooling rates, which could lead to an incomplete description of the resulting phenomena. Differential scanning calorimetry (DSC) performed with different heating/cooling rates enabled the precise determination of enthalpy values, which deviate from literature values. Weak and previously unnoticed thermal phenomena at temperatures below 190 K were also observed. Their presence was confirmed by low‐temperature in situ transmission electron microscopy (TEM). Through DSC measurements and TEM observations, a model of the discovered phenomenon was proposed, which may have an impact on a better understanding of the physics of magnetic shape memory materials. A Co49Ni21Ga30 magnetic shape memory single crystal was studied using in situ imaging and low‐temperature calorimetry. Both methods confirmed the occurrence of local reconstruction of the crystal lattice at temperatures below 190 K.
ISSN:2052-5206
2052-5192
2052-5206
DOI:10.1107/S2052520620006794