Molecular dynamics study of the friction deformation mechanism and inverse Hall–Petch effect in Ni–Cr–Fe polycrystalline alloys with different grain sizes under tensile-vibrational friction coupling

Abstract

During service in critical components such as aircraft engine blades, nickel-based high-temperature alloys are subjected to the coupled effects of tensile stress and vibration friction. However, the failure mechanisms involved remain unclear. Grain refinement is a key method for improving the comprehensive mechanical properties of materials. However, as grain size decreases to the nanoscale, the plastic deformation mechanism of nanocrystals gradually shifts from dislocation slip-dominated to grain boundary-dominated, and the inverse Hall–Petch softening effect emerges. Based on the above background, this study employs molecular dynamics (MD) simulations to systematically analyze the mechanical response and microstructural deformation mechanisms of Ni–Cr–Fe polycrystalline models with average grain sizes of 8.6 nm, 12.7 nm, 17.1 nm, and 22.3 nm under tensile-vibrational friction coupling. The results indicate that the mechanical behavior and deformation mechanisms of the material exhibit size-dependent characteristics under tensile-vibrational friction coupling. Among these, the 17.1 nm model exhibits the optimal balance between tensile strength and wear resistance. Regarding microstructural deformation mechanisms, deformation in the 22.3 nm model is dominated by long-range dislocation slip within grains, with deformation concentrated locally in grains, leading to necking. In the 8.6 nm model, due to inverse Hall–Petch softening, continuous material removal occurs at the surface, while internal deformation is relatively uniform. The 12.7 nm and 17.1 nm models, situated near the transition range for the inverse Hall–Petch effect, exhibit transitional microstructural evolution characteristics. This study reveals the size-dependent nature of the mechanical behavior and deformation mechanisms of nickel-based polycrystalline materials under tensile-vibrational friction coupling conditions, providing a theoretical basis for the optimized design of alloy microstructures.