Abstract
The objective of this work is to simulate the superelasticity and shape-memory effect in a single-crystalline nickel-titanium (NiTi) alloy through a molecular dynamics (MD) study. Cooling and heating processes for this material are reproduced to investigate the temperature-induced phase transformation in its microstructure. It is found that the martensitic transformation and its reverse process occur accompanied by an abrupt volume change, and the transformed variants lead to the appearance of the (001) type compound twin. In addition, the transform temperatures for martensite start (Ms) and austenite finish (Af) are determined, respectively. The results indicate that when the temperature is beyond Af during the compressive loading-unloading, the superelastic behavior becomes pronounced, which is attributed to the role of nanotwins on the transformation from the austenitic phase (B2) to martensitic phase (B19′). Compared to existing experimental data, a reasonable agreement is achieved through the modeling results, highlighting the importance of the compound twins for dominating the superelasticity of nanostructured NiTi alloys.
Highlights
Shape-memory alloys (SMAs) have important applications involving miniactuators, microelectromechanical systems, robotics, biomedicine, and even smart clothing [1] because of their ability of recovering their original shape under heating conditions and sustaining large elastic strains
There is an evidence that demonstrates that the shape-memory effect (SME) and SE in the NiTi alloy are caused by the martensitic transition (MT) and its reversible one (i.e., austenitic transition (AT)) between cubic B2 and monoclinic B19, respectively [2], which are induced by environmental temperature and applied stress
The 2NN modified embedded-atom method (MEAM) potential is testified by a comparison of the calculated properties and experimental results, such as elastic constant, melting temperature, cohesive energy, and equilibrium lattice constant
Summary
Shape-memory alloys (SMAs) have important applications involving miniactuators, microelectromechanical systems, robotics, biomedicine, and even smart clothing [1] because of their ability of recovering their original shape under heating conditions and sustaining large elastic strains. Such two behaviors are recognized as the shape-memory effect (SME) and the superelasticity (SE), respectively. In recent years, these alloy materials are widely accepted and used as a functional material in the field of the automotive and aerospace industries. To meet the specific requirements of safe design, whether and how such behaviors occur in very small length scale system are of growing interest
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