The two way shape memory effect in CuZnAl single crystals: role of dislocations and stabilization

A Giant Magneto-Superelasticity of 5% Enabled by Introducing Ordered Dislocations in Ni34Co8Cu8Mn36Ga14 Single Crystal

Elasticity, featured by a recoverable strain, refers to the ability that materials can return to their original shapes after deformation. Typically, the elastic strains of most metals are well-known 0.2%. In shape memory alloys and high entropy alloys, the elastic strains can be several percent, as called superelasticity, which are all triggered by external stresses. A superelasticity induced by magnetic field, termed as magneto-superelasticity, is extremely important for contactless work of materials and for developing brand-new large stroke actuators and high efficiency energy transducers. In magnetic shape memory alloys, the twin boundary motion driven by magnetic field can output a strain of several percent. However, this strain is unrecoverable when removing the magnetic field and hence it is not magneto-superelasticity. Here, a giant magneto-superelasticity of 5% in a Ni34Co8Cu8Mn36Ga14 single crystal is reported by introducing arrays of ordered dislocations to form preferentially oriented martensitic variants during the magnetically induced reverse martensitic transformation. This work provides an opportunity to achieve high performance in functional materials by defect engineering.

Two-Way Shape Memory Effect Induced by Tensile Deformation in Columnar-Grained Cu71.7Al18.1Mn10.2 Alloy

Columnar-grained Cu_71.7Al_18.1Mn_10.2 shape memory alloy (SMA) was prepared by a directional solidification method and exhibited a high superelasticity of 8.18% and excellent ductility at room temperature, which provided the possibility of obtaining high shape memory. However, proper pre-deformation is an essential part of repeatedly obtaining large and stable shape change. In this paper, one-time uniaxial tensile pre-deformation was carried out at the temperature range −70–−80 °C. Then, the two-way shape memory effect (TWSME) of the alloy was evaluated by the martensitic transformation strain (ε_M) which was measured by a thermal expansion test to investigate the relationship between the pre-deformation strain (ε_T) and the TWSME. The results showed that ε_M of the columnar-grained Cu_71.7Al_18.1Mn_10.2 alloy increased at first and then decreased with the increase of ε_T. The maximum value 2.91% of the ε_M could be reached when ε_T was 6%. The effects of the ε_T on transformation temperatures were also measured by differential scanning calorimetry. Based on the variations of transformation temperatures, the relationship between the internal stress induced by the pre-deformation process and the ε_M, and the influence mechanism of the pre-deformation strain on the TWSME in columnar-grained Cu_71.7Al_18.1Mn_10.2 alloy, were discussed. The results obtained from this work may provide reference for potential applications of Cu-based SMAs, such as self-control components, fasteners, etc.

Observation of the two-way shape memory effect in an atomistic model of martensitic transformation

We study a system of classical particles in two dimensions interacting through an isotropic pair potential that displays a martensitic phase transition between a triangular and a rhomboidal structure upon the change of a single parameter. Previously it was shown that this potential is able to reproduce the shape memory effect and super-elasticity, among other well known features of the phenomenology of martensites. Here we extend those previous studies and describe the development of the more subtle two-way shape memory effect. We show that in a poly-crystalline sample, the effect is mostly due to the existence of retained martensite within the austenite phase. We also study the case of a single crystal sample where the effect is associated to particular orientations of the dislocations, either induced by training or by an ad hoc construction of a starting sample. Received: 16 January 2017,  Accepted: 23 March 2017; Edited by: L. Viña ; Reviewed by: J. Pons, Universitat de les Illes Balears, Palma  de Mallorca, Spain; DOI: http://dx.doi.org/10.4279/PIP.090004 Cite as: E. A. Jagla, Papers in Physics 9, 090004 (2017) This paper, by E. A Jagla, is licensed under the Creative Commons Attribution License 3.0.  

Deformable frequency selective surface structure with tuning capability through thermoregulating

We design and fabricate a deformable frequency selective surface (FSS) structure using shape memory alloys (SMA). The unit cell could "remember" two different geometrical shapes and the shapes convert to each other alternately during heating and cooling, that leads to the drift of resonant frequency. Qualitative analysis by equivalent circuit model and accurate numeric calculation are compared to display the character of the transmission. The measurements show that a tuning range of frequency from 13.07GHz to 16.29GHz is achieved when the morphology of the unit cell changes, making the deformable FSS an attractive choice for tunable filter in different frequency bands with the features of wide tuning range and sharp cut-off.

Universal symmetry property of point defects in crystals

Point defects (vacancies, solute atoms, and disorder) are ubiquitous in crystalline solids. With in situ transmission electron microscopy we find clear evidence for the existence of a universal symmetry property of point defects; i.e., the symmetry of short-range order of point defects follows the crystal symmetry when in equilibrium. We further show that this symmetry-conforming property can lead to various interesting effects including "aging-induced microstructure memory" and the associated "time-dependent two-way shape memory."