Geometric principle of material strengthening by kink interfaces

Abstract Kink strengthening is a phenomenon in which kink microstructures significantly enhance the mechanical properties of long-period stacking ordered (LPSO) Mg alloys. However, the fundamental mechanism of kink strengthening has long remained elusive. Herein, we demonstrate, through geometric analysis based on a rank-1 connection, that the strengthening mechanisms arise from geometric constraints imposed at the intersection between the slip deformation and the kink interface. When deformation is governed by a single slip system, maintaining the continuity of the deformation necessitates the formation of disclinations at the intersection and the migration of kink interfaces, termed cooperative deformation, both of which enhance the material strength. Notably, even a small incident slip can trigger significant plastic work through cooperative deformation. Conversely, when the transmitted slip is constrained by the incident slip, cooperative deformation is geometrically suppressed and strengthening arises solely from disclination. In this regime, the kink interface acts as a damping medium that attenuates slip. This geometric principle of strengthening is not unique to LPSO Mg alloys but is broadly generalizable to layered materials with restricted slip systems. Our findings provide a geometrically grounded framework for kink strengthening.