Formation of the orientation relationship-dependent interfacial carbide in Al matrix composite affected by architectured carbon nanotube
In-situ formed carbides at interface can enhance the interfacial bonding and load-transfer effect in nanocarbon/Al composites, but always sacrifice the structure integrity of reinforcement, inevitably degrading the strengthening efficiency. To alleviate such limitation, a novel hybrid leaf-like carbon nanotube (CNT)-graphene nanoribbon (GNR), architectured via partially longitudinal unzipping of multi-walled CNT (UZCNT), was adopted to reinforce Al matrix composites. Results show that the prominent mechanical properties of UZCNT/Al over CNT/Al were achieved, which originates from the in-situ formed interfacial Al4C3 together with the well-retained integrity of UZCNT. The regulated interfacial reaction between UZCNT and Al generates dense nano-sized Al4C3 (diameter: 14-19 nm, length: 36-82 nm), rather than its submicron-sized counterpart (diameter: 26-37 nm, length: 111-186 nm) with low number density which forms in unmodified CNT/Al composites. Systematic analysis indicates that the interfacial Al4C3 in UZCNT/Al forms via "nucleation-growth" pattern, contrary to the predominant epitaxial growth of Al4C3 in CNT/Al. It is revealed that UZCNT can stimulate Al4C3 nucleation via reducing the nucleation energy barrier and increasing the number of nucleation sites. Meanwhile, finite active C atoms and low-defective inner walls in UZCNT retard the fast growth of Al4C3 after nucleation. Such "nucleation-growth" pattern renders the formation of high number-density nano-sized Al4C3 at GNR margin in UZCNT/Al. Atomic-scale characterizations demonstrate that the coherent/semi-coherent Al4C3-Al interfaces in UZCNT/Al preferentially exhibit specific orientation relationships, most of which are reproducible by the edge-to-edge matching model. The present work is supposed to provide important insights on interfacial carbide formation in nanocarbon/metal composites.