An internal-oxidation-based strategy induced high-density alumina in-situ nanoprecipitation and carbon nanotube interface optimization for co-reinforcing copper matrix composites

Achieving high strength and ductility for copper matrix composites reinforced by carbon nanofillers remains challenging due to secondary agglomeration, few intragranular distributions, and poor interfacial bonding in carbon/copper system. Here, we report an internal-oxidation-based fabrication strategy to simultaneously facilitate high-density in-situ nanoprecipitation into matrix grain interior as well as interfacial optimization between carbon nanotubes (CNTs) and copper matrix. Comprehensive experimental results show that in-situ generation of high-density coherent gamma-Al2O3 nanoparticles with intragranular distribution and formation of amorphous copper oxides (CuxOy) between CNTs and Cu are attributed to oxygen diffusion and in-situ solid reaction ascribing to thermodynamic driving force during internal oxidation. The co-strengthening effect of high density gamma-Al2O3 nanoparticles and interface optimized CNTs is corroborated to contribute to the high mechanical properties of the composite, which exhibits a high tensile strength of up to 510 MPa and excellent ductility of 20.2%. Mechanism analysis indicates that both high-density intragranular gamma-Al2O3 nanoparticles and interface optimized CNTs co-render high strength of the hybrid composite with regard to Orowan strengthening and highly effective load transfer strengthening respectively, which greatly agrees with theoretical quantitative and experimental values of corresponding strength contributions. Meanwhile, cooperation of the dislocation accumulation caused by intragranular gamma-Al2O3 nanoparticles and cracking resistance enhanced by interfacial bonding optimized CNTs collectively maintains tensile ductility. The present design concept may provide a promising strategy for achieving the remarkable co-strengthening effect of nanoscale dual-reinforcements, contributing to high strength and ductility in other carbon nanofillers reinforced metal matrix composites.