Development and application of a Ni-Ti interatomic potential with high predictive accuracy of the martensitic phase transition

Abstract

Phase transitions in nickel-titanium shape-memory alloys are investigated by means of atomistic simulations. A second nearest-neighbor modified embedded-atom method interatomic potential for the binary nickel-titanium system is determined by improving the unary descriptions of pure nickel and pure titanium, especially regarding the physical properties at finite temperatures. The resulting potential reproduces accurately the hexagonal-close-packed to body-centered-cubic phase transition in Ti and the martensitic B2-B19 transformation in equiatomic NiTi. Subsequent large-scale molecular-dynamics simulations validate that the developed potential can be successfully applied for studies on temperature-and stress-induced martensitic phase transitions related to core applications of shape-memory alloys. A simulation of the temperature-induced phase transition provides insights into the effect of sizes and constraints on the formation of nanotwinned martensite structures with multiple domains. A simulation of the stress-induced phase transition of a nanosized pillar indicates a full recovery of the initial structure after the loading and unloading processes, illustrating a superelastic behavior of the target system.

Molecular Dynamics Modeling of the Effect of Nanotwins on the Superelasticity of Single-Crystalline NiTi Alloys

“…Additionally, it is evident that the average width of twin is in nanometer magnitude, which agrees well with experimental data [32]. However, it must be pointed out that the size effect on the transformation temperatures and the nanotwin formations disappears when the specimen is sufficiently large [21]. Figure 6 illustrates a resultant stress-strain response of the pillar subjected to longitudinal compressive deformations at 450 K. In this figure, the phase transition onset in loading/unloading is represented by an arrow.…”

“…Comparatively speaking, MEAM potentials are well suited for simulations of multicomponent systems composed of elements with different ground states, because they allow for characterizing a wide range of phases (fcc, bcc, hcp, diamondstructured, and even gases) using a common mathematical function [28]. However, Ko et al [21] strongly recommended the use of second nearest-neighbor modified embeddedatom method (2NN MEAM) when choosing an interatomic potential in the NiTi binary alloy. Furthermore, a comparison of the predicted results with the experimental ones [3] indicated that such a model could be available for representing the characteristics of the low temperature martensitic structure (B19 ).…”

“…The motivation behind previous investigations has been to study phase transformations in a single-crystalline NiTi alloy under uniaxial compression loading. It should be emphasized that our investigation is primarily focused on conducting numerical analysis for interatomic motions by using MD simulations coupled with an effective potential [21]. Considering that the twinning structure always appears inside the gain, an initial model is prepared as a single crystal NiTi with the B2 structure.…”

Superioniclike Diffusion in an Elemental Crystal: bcc Titanium

“…Supercell equilibrium volumes are taken from experiments [24]. CMD simulations are performed using LAMMPS [25], describing the Ti-Ti interactions via the second-nearest-neighbor modified embedded-atom method (MEAM) [26], as parameterized in [27], and integrating the equations of motion at 1-fs timesteps. The equilibrium volumes of supercells formed of 14×14×14 conventional bcc cells (5488 Ti atoms) are determined as a function of temperature via NPT sampling based on the Parrinello-Rahman barostat [28] and the Langevin thermostat.…”

Martensitic phase transformation in NiTi bi-crystals with symmetric ∑25 twist and tilt grain boundaries

“…The periodic boundary conditions are applied along the three orthogonal directions x, y and z of the cells. Atomic interactions in the Ni-Ti system are described by the modified embedded-atom method potential developed by Ko et al [24]. This interatomic potential can quite accurately predict the temperature-and stress-induced MT in NiTi alloys [24 -26].…”