The co-regulation mechanism for the indentation size effect and the interface in Nb–NiTi–Nb nano-multilayer films

Abstract This study presents a systematic investigation into the nanoindentation behavior of Nb–NiTi–Nb (BCC/B2/BCC) nanomultilayers at 400 K through molecular dynamics simulations. The findings reveal that a small-radius indenter ( R = 50 Å) induces localized stress concentration and pronounced dislocation fluctuations, leading to a highly confined plastic zone. In contrast, a larger-radius indenter ( R = 60 Å) facilitates more extensive plastic deformation and promotes coordinated deformation behavior. This observed size effect underscores the substantial influence of indenter geometry on the material’s deformation mode. Further analysis indicates that the intrinsic origin of this size effect can be attributed to a synergistic regulation mechanism at the BCC-Nb/B2-NiTi interface. Owing to its unique confinement effect, the interface significantly delays the initiation depth of dislocation nucleation from 5.6 Å to 9.9 Å, thereby effectively localizing plastic deformation within the upper Nb layer and preserving the structural integrity of the intermediate NiTi functional layer. Dislocation analysis demonstrates that at 400 K, the interfacial constraint suppresses martensitic transformation, thereby rendering dislocation activity the primary deformation mechanism. This conclusion is further corroborated by the evolution of dislocation density and slip system activation analysis. The present study elucidates the synergistic interplay of ‘interfacial constraint-dislocation activity-transformation suppression’ at the atomic scale, and the developed analytical methodology provides critical theoretical underpinnings for the interface design and performance optimization of high-performance composite materials.