Ambient effects on the output strain of Ni–Mn-Ga single crystal magnetic shape memory alloy

Coexistence of five domains at single propagating interface in single-crystal Ni Mn Ga shape memory alloy

“…The superelasticity/pseudoelasticity and shape memory effect of shape memory alloys (SMAs) result from a 1 st -order solid-solid phase transformation (martensitic transformation) that can be induced by thermal, mechanical, and magnetic loadings (Kiefer and Lagoudas, 2005;Arndt et al, 2006;Karaca et al, 2006;Sehitoglu et al, 2012;Chen et al, 2014;Haldar et al, 2014;Kamarád et al, 2014;Pascan et al, 2015;Cisse et al, 2016;Heczko et al, 2016;Rogovoy and Stolbova, 2016;Yin et al, 2016;Bruno et al, 2017;Zhang et al, 2018b;Chen and He, 2020;Zhang et al, 2020). The high-temperature stable parent phase (austenite) has cubic symmetry whereas the lowtemperature stable product phase (martensite) has lower symmetry, such as tetragonal, orthorhombic, and monoclinic symmetry, depending on the chemical composition.…”

“…Martensite appears in the form of several variants with different orientations with respect to the austenite parent crystal, and therefore different characteristic transformation strains (Bain strains) are resulted (Ball and James, 1989; M. Pitteri and Zanzotto, 1998;James and Hane, 2000;Pitteri and Zanzotto, 2002;Bhattacharya, 2003). According to equilibrium thermomechanics (Ericksen, 1975;Falk, 1980;James, 1980;Abeyaratne and Knowles, 1991;He and Sun, 2009;Duval et al, 2011;Hallai and Kyriakides, 2013) and the experimental observations (Segui et al, 1996;Glatz et al, 2009;Seiner, 2015;Zhang et al, 2020;Qin et al, 2023;Zhang et al, 2023), the martensite variants and austenite with equal free energy can coexist during the phase transformation, among which there are twin boundaries (separating different martensite variants) and habit planes (separating austenite from martensite twins or variants). To guarantee the deformation reversibility of the phase transformation (avoiding plasticity), the twin boundaries and the habit planes must be compatible (coherent), meaning that the characteristic transformation strains of the different domains (martensite variants, twins, and austenite) must be accommodated without elastic strain (called "perfectly compatible" domain patterns) or with only small elastic strains (so-called "non-perfectly compatible" domain patterns).…”

Thermo-magnetic loading effects on high-frequency dynamic behaviour of magnetic shape memory alloys

“…Techapiesancharoenkil et al (2009, 2011 experimentally demonstrated the relationship between magnetic field and output strain in dynamic Ni-Mn-Ga actuators. Recent experiments in (Zhang et al, 2018a(Zhang et al, , 2018bZhang et al, 2020) focused on long-term (> 100 s) dynamic behaviour of MSMAs, revealed a new phenomenon: the accumulated heat from the intrinsic dissipation of the cyclic martensite reorientation induced by cyclic magnetic field can significantly increase the material's temperature. Under the weak ambient heat-transfer condition, the phase transformation temperature can be reached, and the martensite-to-austenite transformation can be triggered, leading to a sudden strain drop of the material.…”