The formation mechanisms and mechanical effects of lattice defects in carbon nanotube reinforced 2024Al composite

Lattice defects significantly affect the mechanical performance of metallic materials. In this study, lattice defects of a carbon nanotube reinforced 2024 aluminum alloy (CNT/2024Al) composite were systematically investigated and the contribution of carbon nanotubes was illustrated. The results showed that dislocations and grain boundaries were closely related to the deformation behavior and lead to discontinuous yielding phenomena. Moreover, the carbon nanotubes reduced the stacking fault energy, which was conducive to forming stacking faults and a small number of twins in the composite. The stacking faults, twin boundaries, and intragranular Al4C3 phases hindered dislocation motion, thus enhancing the mechanical properties of the composite. In addition, the novel formation mechanism of the 9R structure was revealed: the E3(111)/(151) incoherent twin boundary may dissociate into two tilt walls bounding a 9R structure (zone axis: [101]), which enriches understanding of the relationship between E3 twin boundaries and the 9R structure.