Identification of crystal variants in shape-memory alloys using molecular dynamics simulations

Wu, Jo Fan; Yang, Chia Wei; Tsou, Nien‐Ti; Chen, Chuin Shan

doi:10.12989/mmm.2016.1.3.271

Cited by 4 publications

(2 citation statements)

References 13 publications

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“…The procedures of the martensite variant identification method is illustrated in Figure 1. The method identified the phases and variants by examining each group of eight cubic unit cells (Figure 1a) in the model, which consisted with six distorted tetragonal unit cells (two for each of the x , y , z axes, as shown in Figure 1b–d) [21] under the given loads. The transformation matrices of the distorted tetragonal unit cells can be determined, i.e., Uboldxbold1,Uboldxbold2,⋯,Uboldzbold2, as shown in Figure 1e.…”

Section: Methodsmentioning

confidence: 99%

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The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics

Chen

Tsou

2018

Materials

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Superelasticity in shape memory alloys is an important feature for actuators and medical devices. However, the function of the devices is typically limited by mechanical bandwidth and fatigue, which are dominated by the microstructures. Thus, in order to correlate the mechanical response and the microstructures, the microstructural evolution in NiTi single crystals under the compression, tensile, and shearing tests is simulated by molecular dynamics (MD) in the current study. Then, the martensite variant identification method, which identifies the crystal variants/phases of each lattice based on the transformation matrix, is used to post-process the MD results. The results with the detailed information of variants and phases reveal many features that have good agreement with those reported in the literature, such as X-interfaces and the transitional orthorhombic phase between the austenite and monoclinic phases. A new twin structure consisting of diamond and wedge-shaped patterns is also discovered. The macroscopic behavior, such as stress-strain curves and the total energy profile, is linked with the distribution of dislocation and twin patterns. The results suggest that the loading cases of shear and compression allow a low critical strain for the onset of martensitic transformation and a better superelasticity behavior. Therefore, the two loading cases are suitable to apply to the NiTi actuators. The current work is expected to provide insight into the mechanical responses and design guideline for NiTi shape memory alloy actuators.

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Section: Methodsmentioning

confidence: 99%

“…The algorithm described above has been implemented as a plug-in in the visualization tool OVITO. The detailed post-processing procedures can be found in the authors’ previous work [17,21].…”

Section: Methodsmentioning

confidence: 99%

The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics

Chen

Tsou

2018

Materials

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Microstructural Evolution of Superelasticity in Shape Memory Alloys

Lai

Tsou

2019

Multiscale Sci. Eng.

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Superelasticity in shape memory alloys (SMAs) is an important feature which caused by martensitic transformation and microstructural evolution. The composition of crystal variants and microstructures during the superelasticity process are simulated by molecular dynamics in the current work. Then, a computational post-processing scheme, which can identify variants type and interface orientation are proposed. This method reveals that the crystal adopts a multi-phase mixture during the superelsticity process, including many crystal systems, such as orthorhombic (O), R-phase (R), monoclinic (M) and body-centered-orthorhombic (BCO). In addition, the interface normal vectors between two different variants are examined by the compatibility equation, and the result has good agreement. The stress-strain curve, volume fraction for present variants and total energy diagram are illustrated. The microstructural evolution shows that R phase can serve as the transitional region between pairs of BCO variants. The variants O, BCO, M phase coherent between each other with specific pattern to form twinned arrangement. Furthermore, different random seeds for the initial velocity of the atoms, are used in the simulation to obtain equivalent microstructural evolution paths. The corresponding macroscopic properties are analyzed. The microstructural evolution path can have different energy barrier of initialization, which also leads to different present variant in the crystal. The results discovered in the current work are expected to provides design guidelines for the applications in SMAs.

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Microstructural analysis and molecular dynamics modeling of shape memory alloys

Yang

Tsou

2017

Computational Materials Science

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Identification of crystal variants in shape-memory alloys using molecular dynamics simulations

Cited by 4 publications

References 13 publications

The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics

The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics

Microstructural Evolution of Superelasticity in Shape Memory Alloys

Microstructural analysis and molecular dynamics modeling of shape memory alloys

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