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

Acta Crystallogr B Struct Sci Cryst Eng Mater. 2020 Aug 1;76(Pt 4):563-571. doi: 10.1107/S2052520620006794. Epub 2020 Jul 8.


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.

Keywords: CoNiGa; in situ TEM; martensite; relaxation; shape memory alloy.