Molecular dynamics study on microscopic mechanism for phase transformation of Ni–Ti alloy

Abstract

Molecular dynamics simulation (MDS), using the embedded atom method for interatomic interactions, is performed to reveal the microscopic mechanism of stress-induced martensitic transformation of Ni–Ti alloys. Stress-induced martensitic transformation was observed for tensile simulation using four different strain rates. The relationship between stress and martensite ratio does not depend on the strain rate. Investigation of the results of MDS for the transformation pathway makes it clear that there are multiple pathways between the parent phase and the martensite phase regardless of the strain rate. Multiple pathways appear owing to differences in the relationship (angle) between the tensile direction and the specific lattice lengths of the parent or martensite unit cell. Increase and decrease in the martensite ratio during tensile simulation varies according to the pathways, depending on the strain rate.

Atomistic Study on Size Effects in Thermally Induced Martensitic Phase Transformation of NiTi

“…It has been confirmed that structurally stable B2 and B19 phases are obtained with low potential energy. In particular the cohesive energy of B19 variants is found to be more stable than that of B2 [57,58].…”

“…An effective MD simulation framework for NiTi binary alloy based on the Finnis-Sinclair many-body interatomic potential has been proposed and examined in detail [11,23,24,31,39,44,45,53,[57][58][59]. For self-containment, a brief and relevant description of this semiempirical interatomic MD potential is provided here, yet more detailed information can be found elsewhere [11,23,24,31,39,44,45,53,[57][58][59]. Lai and Liu [53] developed this semiempirical interatomic potential based on experimental data and first principal calculations.…”

Simulation of the shape memory effect in a NiTi nano model system

“…Strong zigzag behavior of the stress-strain curve upon loading due to abrupt stress releases was shown to be smoothed by differently oriented martensitic grains as starting configuration [10], which fits the realistic situation in a better way. Concerning nanosized systems, the austenite-martensite transformation upon loading, which is the origin of SE, has been studied by MD by straining a NiTi nanocrystal with free surfaces, leading to stress decrease if martensite nucleates heterogeneously in the sample [11]. By applying MD, several characteristics of structural phase transformations in NiTi model systems have been investigated in the past by Suzuki and coworkers [12][13][14] with a pair potential, as well as by Ishida and Hiwatari [15], who used the modified embedded atom method.…”

Simulation of structural phase transitions in NiTi

“…With a potential originating from the second-moment approximation of the tight-binding model (TBSMA), Lai and Liu 20 studied crystalline-to-amorphous transitions of nickel/titanium solid solutions as well as the amorphization of several NiTi compounds upon ion irradiation. Since this potential predicts a monoclinic structure to have a higher cohesive energy than the cubic state, it was adopted by Sato et al 21 to perform MD on the stress induced martensitic phase transformation, whereby multiple B2-B19 ′ pathways could be identified. Until today, there is a lack of studies regarding the temperature driven structural changes in NiTi with simulations.…”