Abstract：The plastic behavior of single-crystal nickel critically governs its reliability and lifespan in aerospace and micro/nano-manufacturing applications. Consequently, understanding its plastic response and microscopic deformation mechanisms under localized indentation is essential for providing mechanistic and engineering guidance. In this study, molecular dynamics simulations are employed to investigate the spherical nanoindentation of single-crystal nickel, focusing on the influence of dislocation reactions on early-stage plastic deformation mechanisms. The study further examines the regulatory role of indentation speed on load drops and work-hardening behavior, while elucidating the intrinsic correlation between dislocation reactions and load drop phenomena. Results demonstrate that during the initial load drop stage, the propagation of Shockley partial dislocations on {111} slip planes forms semi-closed dislocation loops and intrinsic stacking faults, which triggers the first load drop. Increasing the indentation speed significantly alters dislocation evolution characteristics. Specifically, under low indentation speeds, dislocations organize into ordered V-shaped slip bands, whereas high indentations speeds promote the formation of disordered networks. Moreover, the indentation depth corresponding to the initial load drop increases with increasing speed. The work-hardening behavior exhibits pronounced rate dependence: under low indentation speeds, stable high-density dislocation networks form through Lomer-Cottrell locks and Hirth locks, whereas high speeds induce loose dislocation configurations due to non-equilibrium responses, suppressing the hardening effects. With increasing indentation depth, the load-depth curve exhibits multiple load drops accompanied by nonlinear increases in Shockley partial dislocation density. It is thus evident that the stability of resultant dislocation networks dictates the macroscopic mechanical response and extent of work hardening observed under different loading conditions. Elucidating these rate-dependent sessile lock formation mechanisms and gaining a deep understanding of defect evolution mechanisms not only contribute to the advancement of multiscale crystal plasticity modeling, but also provide significant guidance for optimizing micro-nano processing parameters, predicting the failure behavior of nickel-based superalloys in critical engineering components, and enhancing their surface integrity.
2026, Vol. 47 
