In-situ TEM Dynamic Observation and Multi-scale Dissipation Mechanisms of Damage Evolution at Crack Tips in Hard Domains of Heterostructured Al-Cu Alloys

The damage initiation and propagation mechanisms within the "hard domains" of heterostructured Al-Cu alloys under load are crucial for their service performance. This study employed in-situ TEM tensile testing to dynamically observe crack propagation behavior within these hard domains at the atomic scale. It was found that inside the hard domains, the crack tip continuously emits dislocations. These dislocations interact with grain boundaries and second-phase particles, establishing a dynamic "emission-pile-up-annihilation" equilibrium. This process is identified as the core micro-mechanism for stress relaxation and crack-tip blunting. Notably, within the hard domains, which typically possess high SFE, the extreme local stress/strain gradients at the crack tip drive the anomalous dynamic nucleation and annihilation of stacking faults. This unconventional deformation mode directly releases the stress singularity and can induce crack deflection by generating localized shear strain. Furthermore, this in-situ study captured the critical moment of nano-void coalescence for the first time. These results indicate that the hard domains are not merely zones of brittle fracture. Instead, they achieve effective toughening dissipation through coordinated micro-nano mechanisms. Meanwhile, this research has deepened the understanding of the damage tolerance and the intrinsic strengthening-toughening synergy in heterostructured materials.