Anisotropic interfacial stress at solid–liquid boundaries under uniaxial strain

We present a systematic atomistic investigation of solid–liquid interfacial excess stress in a model face-centered cubic metal under uniaxial strain. Molecular dynamics simulations with embedded-atom method potentials are used to quantify the orientation-dependent interfacial stress tensor and its Cartesian components for the (100), (110), and (111) interfaces. Even without applied strain, flat solid–liquid interfaces exhibit non-zero, orientation-specific excess stress, confirming the intrinsic mechanical character of equilibrium interfaces. Under uniaxial loading, the total interfacial stress exhibits pronounced orientation-dependent anisotropy, with variations exceeding 200 mJ/m², including sign reversals and non-monotonic trends. Decomposition into components reveals three distinct coupling modes: synchronized evolution of the in-plane excess stress components τ_xx and τ_yy for (100), a strain-dominated transverse in-plane response primarily reflected in τ_yy for (110), and compensating trends between τ_xx and τ_yy for (111). In contrast, the normal excess component τ_zz remains negligible across all cases, indicating that the mechanical response is confined to the lateral directions. These features arise despite the strain being strictly uniaxial and the liquid remaining hydrostatic, underscoring the interfacial origin of the stress anisotropy. Our results demonstrate that interfacial stress is more sensitive to orientation and strain than interfacial free energy, and must be treated as a tensorial, strain-dependent thermodynamic quantity. These findings provide quantitative benchmark data for materials-scale continuum and mesoscale modeling, including Ginzburg–Landau and phase-field crystal theories, that incorporate elastic and capillary effects. They also offer mechanistic insight for modeling microstructure evolution and interface morphology during solidification under mechanical loading.