Understanding, at the atomic scale, how microstructural architecture governs the tribological response of ferrite- and pearlite-based steels remains essential for designing wear-resistant alloys. In this work, molecular dynamics simulations are conducted to systematically compare nanoscale sliding friction in ferrite and pearlite polycrystals. Eight crystalline models (40 × 23 × 7 nm³) are constructed, comprising ferrite (I, I5, I10, I20) and pearlite (P, P5, P10, P20) with controlled grain numbers. A diamond hemispherical asperity (radius 7.5 nm) is indented to a depth of 20 nm and subsequently slid at 0.1 nm/ps under a constant-penetration protocol. Tangential force and friction coefficient are evaluated together with atomic shear strain, dislocation structures, and RMSD-based non-affine displacement statistics (φ and P99) to quantify the plastic activity and clarify how grain boundaries, phase boundaries, and their interconnected interfacial network regulate deformation and energy dissipation during sliding.
Pearlite exhibits a higher steady-state friction coefficient (0.6-0.8) than ferrite at comparable grain numbers (0.5-0.7). Its force-displacement curves show more frequent stick-slip events, indicating that Fe3C lamellae increase shear resistance and promote dissipation via fragmented local slip. With theincrease of grain numbers, ferrite dislocations are largely trapped at grain boundaries, consistent with their role as dislocation sinks that impede the spatial extension of plasticity. In contrast, pearlite develops substantially higher dislocation densities that penetrate into the interior (240 nm-460 nm), approximately 2-4 times those in ferrite of similar grain sizes. Intersections between Fe3C lamellae and grain boundaries act as preferred sites for dislocation multiplication and interaction, thereby amplifying plastic accommodation. High-strain regions in pearlite are distributed not only along grain boundaries but also continuously along Fe3C lamellae, forming a three-dimensional strain-bearing framework that conforms to the hard-phase geometry and serves as an efficient pathway for load transfer.
RMSD statistics corroborate the enhanced plastic rearrangement in pearlite. In the contact region, pearlite shows consistently higher φ (0.447-0.524) and P99 (46.6-49.1 pm) than ferrite (φ = 0.339-46.3; P99 = 45.2-46.9 pm). Models with intermediate interfacial connectivity (P5-P10) yield elevated φ and P99, suggesting an optimal connectivity window. By contrast, excessive interfacial density (P20) reduces the mean φ while increasing dissipation, resulting in an evident decoupling between φ and P99 (φ = 0.447, P99 = 48.1 pm) and implying a nonlinear dependence of plastic-transport efficiency on interfacial density and connectivity. Farregion RMSD distributions at pre-peak, peak, and post-peak stages largely overlap across all models, and farregion φ remains well below that in the contact region (ferrite: 0.139-0.213; pearlite: 0.310-0.383), indicating that irreversible deformation is primarily localized near the contact region. Notably, pearlite maintains a far region φ roughly twice that of ferrite, together with a higher farregion P99 (34.0-35.5 pm vs. 30.7-34.5 pm), demonstrating more effective transmission of shear perturbations into the far region and a larger dissipation volume.
Collectively, these results identify the microstructural origin of pearlite's superior wear resistance: a three-dimensional, interconnected interfacial network formed by alternating hard-soft Fe3C lamellae. This network pins dislocations and promotes finer-scale local slip, while simultaneously facilitating shear-strain redistribution across interfaces to suppress premature damage associated with severe localization. The quantitative linkage established between interfacial-network topology, plastic localization/transport, and macroscopic frictional response provides actionable guidance for tailoring lamellar spacing, orientation distributions, and interfacial connectivity in high-performance wear-resistant steels.
Key words
ferrite /
pearlite /
sliding friction /
interfacial network /
molecular dynamics simulation
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