CNT-induced heterogeneous matrix grain structure in CNTs/Al composites

Ductility collapse is a stubborn issue for developing high-strength Al matrix composites reinforced with carbon nanotubes (CNTs). In order to solve this problem, here we manipulated the fabrication process and crafted a heterostructured CNTs/Al composite consisting of fine-grained zone (FGZ) and quasi-continuously networked coarse-grained zone (CGZ). Such heterostructured CNTs/Al composite with CGZ in a quasi-continuously networked fashion has never been reported before. Microstructural analysis showed that the majority of CNTs resides in FGZ, which stimulated dynamic recrystallization of Al during hot deformation and resulted in the formation of FGZ. Tensile tests showed that the heterostructured composite possesses a tensile property of 549 MPa of strength and 11.2% of ductility, which is superior to those in literatures. Further in-situ tensile EBSD and post-tensile TEM analyses revealed that during tensile deformation, the stiff FGZ undertook most of the stress, whereas the CGZ facilitated hetero-deformation induced hardening, which helped to resist the high flow stress of FGZ and assisted the ductility retention. This study may provide some guidance for the development of strong yet ductile CNTs/Al composites.