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arXiv · 2610.08613

Grain-boundary segregation delays the onset of plastic flow in nanocrystalline Fe-18Cr-12Ni

Ashwinee Kumar
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Abstract

Grain-boundary (GB) segregation in austenitic Fe-Cr-Ni alloys has been studied mainly in irradiated or sensitised material, rarely in the nanocrystalline state. Hybrid molecular dynamics/Monte Carlo (MD/MC) simulations are used to segregate three independent nanocrystalline Fe-18Cr-12Ni polycrystals, which are compared with annealed and random controls on the same microstructures. Ni is depleted at the GB plane and Cr is enriched in the adjacent atomic shell; both directions are established at the production sampling budget and strengthen when one of the three microstructures is sampled further. The Cr enrichment is resolved only against the far-field grain interior; the common partition into face-centred-cubic (fcc) and non-fcc atoms places the enriched shell in its own reference. Under a constant uniaxial stress of 4.6 GPa at 300 K, the segregated polycrystals take about 16% longer than random ones to reach 50% strain; measured against annealed controls, boundary chemistry contributes about two-thirds of this gain and boundary relaxation the rest. The difference arises from a lower strain rate early in plastic flow, with no resolvable change in dislocation content. At a fixed strain rate the segregated state has a 6-7% higher peak stress than its annealed control at 300, 750 and 950 K, and at matched ratios of applied to flow stress the gain is the same at all three temperatures, decreasing only as that ratio rises. Early plastic flow is thus the stage at which GB chemistry acts, and simulated GB composition in nanocrystals depends strongly on the reference region.

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Ashwinee Kumar. 2026-10-06. Grain-boundary segregation delays the onset of plastic flow in nanocrystalline Fe-18Cr-12Ni. https://arxiv.org/abs/2610.08613

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