Atomic-scale study of the mechanical properties of dual-phase fcc/bcc crystallites: influences of alloying elements and phase boundaries

Y Jiao and LC Xu and WJ Dan and YS Xu and WG Zhang, JOURNAL OF MATERIALS SCIENCE, 57, 11111-11131 (2022).

DOI: 10.1007/s10853-022-07307-4

The present molecular dynamics (MD) study investigates the effect of Mn and C additions and phase boundaries on the deformation mechanism of fcc/bcc crystallites at an atomic scale. Dual-phase supercells that have various alloy contents in the fcc and at phase boundaries with an N-W orientation relationship are constructed and subjected to tensile simulation. The influence of alloy content on the mechanical response, plastic deformation mechanisms and microstructural evolution, martensitic transformation models, and local potential energy and atomic shear stress is studied in detail. For the supercell with a low Mn content (15 at%) in the fcc phase, metastable fcc atoms at the phase boundary tend to transform to bcc martensite, whereas with increasing Mn content, the fcc phase becomes stable, causing dislocation slip to occur first (25 at%). In the Mn cases, the phase boundary could be the martensite nucleation point (15 at%) or dislocation emission point (15 and 25 at%) due to the severe stress concentration in this region. Regarding the supercells containing interstitial C atoms, the pinning effect of C exceeds the mismatch effect of the phase boundary, causing the initiation points of martensitic transformation and dislocation slip to be scattered in the fcc matrix instead of at the phase boundary. The local potential energy analysis reveals that the alloy atoms could change the potential energy of the surrounding Fe atoms, which increases the critical shear stress of martensitic transformation; thus, martensitic transformation is inhibited. This could also explain why dislocation slip becomes preferred in supercells with a high alloy content.

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