Unraveling the impact fracture behavior of Ti-1300 alloy: α phase morphology-dependent interface damage and crack propagation behavior

This study systematically investigates the paradoxical relationship between exceptional strength-ductility synergy and deteriorated impact toughness in Ti-5Al-4Mo-4V-4Cr-3Zr (Ti-1300) alloys by elucidating the microstructural mechanisms underlying damage tolerance in bimodal (BM) and lamellar microstructures (LM). Although α-phase strengthening contributes to remarkable quasi-static tensile properties, the findings reveal that the intrinsic spatial configurations of α-phases play a critical role in governing the degradation of impact performance. Notably, despite similar deficiencies in impact resistance, BM demonstrates higher absorbed energy compared to LM due to its unique hierarchical structure, which integrates αp-necklaces, αp-rods, and βt matrix with pronounced crystallographic misorientations. Furthermore, the study highlights that geometrically necessary dislocation (GND) density at V-notch tips in BM exceeds that of LM, thereby enhancing local plasticity through orientation-dependent dislocation pile-ups at multi-phase interfaces—a stress-buffering mechanism absent in LM's randomly distributed αs-lamellae weave structure. Crack propagation analysis reveals a significant paradigm shift: BM facilitates crack deflection along αp/βt interfaces, resulting in an increase in path tortuosity compared to LM, whereas LM exhibits brittle trans-lamellar fracture with minimal deflection. These insights establish a novel microstructure-design paradigm that prioritizes energy dissipation pathways over traditional strength-ductility metrics for improving the impact resistance of titanium alloys.