Formation of multilayer interfaces and the load transfer in graphene nanoplatelets reinforced Al matrix composites

Interfaces between graphene nanoplatelets (GNPs) and Al matrix in Al-GNPs composites prepared by ball milling, spark plasma sintering (SPS) and subsequent hot extrusion were investigated. 5-layered interfaces Al/Al2O3/GNPs/A1203/Al were observed in the as-SPSed composites and some fresh GNPs/Al interfaces formed after hot extrusion and led to the formation of 7-layered interfaces Al/Al2O3/GNPs/Al/GNPs/Al2O3/Al. The evolution of GNPs incorporated into the Al matrix after extrusion was also observed. No evidence of Al4C3 formed and/or detected in the interface. However, stacking faults were observed in the Al matrix near the interfaces in the as-SPSed composites. First principles calculations revealed that the unstable and metastable stacking fault energy (SFE) of Al matrix significantly decreased near the Al-GNPs interface, which further confirmed the formation possibility of stacking faults in the Al matrix. Load transfer across the interfaces were confirmed by strengthening analysis of the composites, which means the multilayered structure contribute much to the deformability and tensile strength of the Al-GNPs composites.