Effects of grain size on martensitic phase transformations of NiTi alloy investigated by molecular dynamics simulation

RX Yan and PF Zou and ZY Hou and KF Li and QH Gao and G Shi and S Sha and C An and LX Liu, MATERIALS TODAY COMMUNICATIONS, 43, 111727 (2025).

DOI: 10.1016/j.mtcomm.2025.111727

Grain size has a significant impact on the functional performance of NiTi alloys, but the quantitative analysis of the effect on the martensitic phase transformation is few involved. In this work, the mechanical properties and deformation behavior of different grain-size NiTi are studied by molecular dynamics (MD) method. To investigate the mechanisms of martensitic phase transformation, the cluster analysis of the transformation process is conducted by the cluster type index method (CTIM). It is found that the hardness transforms from Hall-Petch (HP) relationship to inverse Hall-Petch (IHP) relationship with grain refinement at the critical grain size of dc = 14.9 nm. When the grain size is less than 14.9 nm, both the martensitic phase transformation and grain boundary activity contribute to the plastic deformation, with grain boundary activity playing a dominant role. Conversely, when the grain size exceeds 14.9 nm, the martensitic phase transformation predominantly governs the plastic deformation. Additionally, it reveals that the martensitic phase transformation occurs via a coherent shear mechanism and outlines two pathways of transition from BCC to HCP structure during the indentation process.

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