On the small angle twist sub-grain boundaries in Ti3AlC2

Grain boundaries in MAX phases have been primarily studied with a focus on tilt boundaries. Twist grain boundaries, however, remain underexplored despite their potential role in deformation mechanisms. Existing knowledge suggests that MAX phases exhibit unique combinations of metallic and ceramic properties, but the atomic-scale behavior of twist boundaries is not well understood. Prior research has established that MAX phases deform through dislocation motion, but the specific role of twist boundaries remains unclear. This gap motivated the need to investigate twist sub-grain boundaries in Ti3AlC2. The study of such boundaries could clarify how atomic-level interactions influence macroscopic deformation. No prior work had resolved the structural details of twist boundaries in MAX phases. This lack of information limits the predictive power of deformation models. Understanding these boundaries may help refine simulation approaches for materials design.

The aim of this study is to examine small angle twist sub-grain boundaries in Ti3AlC2 under high-temperature compression. The specific problem is the lack of detailed structural and energetic information about twist boundaries in MAX phases. The motivation comes from the potential impact of these boundaries on deformation mechanisms. By analyzing dislocation networks and stacking fault energy, the study seeks to identify the location and behavior of twist boundaries. The researchers propose that these boundaries may form between specific atomic layers. This could inform future atomic-scale simulations of MAX phase deformation. The study also aims to quantify the twist angle as a function of deformation. The findings may help bridge the gap between macroscopic and atomic-level deformation understanding.

The study combines experimental observations with first-principles calculations. Small angle twist sub-grain boundaries were identified in Ti3AlC2 compressed at 1200 °C. Transmission electron microscopy was used to observe hexagonal screw dislocation networks. Basal dislocation reactions were analyzed to determine boundary formation. Atomic-scale deformation was simulated using density functional theory. Stacking fault energy landscapes were calculated to assess boundary stability. The location of twist boundaries was inferred from the interaction of Al and Ti4f layers. The twist angle was estimated based on deformation levels and dislocation spacing.

Small angle twist sub-grain boundaries were observed in Ti3AlC2 after compression at 1200 °C. These boundaries consist of hexagonal screw dislocation networks formed by basal dislocation reactions. First-principles calculations revealed that these boundaries are likely located between Al and Ti4f layers. The weakly bonded Al-Ti4f interaction is disrupted in these boundaries. The twist angle increases with deformation and reaches approximately 0.5° at 26% deformation. The stacking fault energy landscape supports the stability of these boundaries. The findings suggest that twist boundaries are a significant deformation mechanism in MAX phases. The results provide a structural basis for future atomic-scale simulations.

The study demonstrates that twist sub-grain boundaries in Ti3AlC2 are formed by hexagonal screw dislocation networks. These boundaries are most likely located between Al and Ti4f layers, with disruption of weak Al-Ti4f bonds. The twist angle increases with deformation and reaches about 0.5° at 26% strain. The findings may help refine atomic-scale simulations of MAX phase deformation. The researchers propose that these boundaries play a role in accommodating plastic deformation. The results suggest that twist boundaries are structurally distinct from tilt boundaries. The study highlights the importance of considering twist boundaries in deformation models. These conclusions are based on the observed dislocation networks and first-principles calculations.