High strength and high ductility copper matrix composite reinforced by graded distribution of carbon nanotubes

The mutual exclusion between strength and ductility has been a long-standing problem in the field of materials science, especially in metal matrix composites (MMCs). Here we report the discovery of an unprecedented combination of high strength and high ductility within the copper matrix composites reinforced by super-aligned carbon nanotube (SACNT) films distributed with a gradient. The high strength (302 MPa) and high ductility (11.5%) are simultaneously achieved in this gradient-structured MMCs. The SACNT volume fraction gradient induces a plastic strain gradient and subsequent development of geometrically necessary dislocations (GNDs) near the boundaries. High back stress and extra strain hardening derived from the pile-up of GNDs are responsible for the superior mechanical properties. These observations shed light on the development of strong and ductile MMCs by architecting gradient structures.