Molecular dynamics simulation of mechanical behavior and phase transformation of nanocrystalline NiTi shape memory alloy with gradient structure

• Published in: Computational materials science 2022-03, Vol.204, p.111186, Article 111186
• Main Authors: Wang, Man, Jiang, Shuyong, Sun, Dong, Zhang, Yanqiu, Yan, Bingyao
• Format: Article
• Language: English
• Subjects: Mechanical behavior; Molecular dynamics simulation; NiTi alloy; Phase transformation; Shape memory alloy
• ISSN: 0927-0256; 1879-0801
• DOI: 10.1016/j.commatsci.2022.111186

[Display omitted] •Superelasticity of gradient-structure nanocrytalline NiTi is investigated based on MD.•The maximum tensile stress decreases with the increase of surface average grain size.•The irrecoverable strain decreases with the increase of surface average grain size.•Plastic deformation of amorphous phase and GB leads to degradation of superelasticity. Severe plastic deformation can lead to surface amorphization of nickel-titanium shape memory alloys (NiTi SMAs), and amorphous layer can be transformed into nanocrystalline layer by means of appropriate heat treatment. Consequently, molecular dynamics simulation is used to investigate mechanical behavior and phase transformation of nanocrystalline NiTi shape memory alloy with gradient structure, where surface layers possess the average grain sizes of 6, 9, 12 and 15 nm, respectively, and the middle layer possesses the average grain sizes of 20 nm. The maximum tensile stress and the irrecoverable strain decrease with the increase of the average grain size in the surface layers. As for the maximum tensile stress, the maximum value is 2.46 GPa and the minimum value is 1.92 GPa. As for the irrecoverable strain, the maximum value is 0.5%, and the minimum value is 0.25%. Amorphous phase and grain boundaries (GBs) have an important influence on the superelasticity of NiTi SMA. The degradation of superelasticity is mainly attributed to plastic deformation of the amorphous phase and the GBs.