Improvement of mechanical properties in carbon nanotube/Al–Cu–Mg composites through introducing bioinspired tree-ring structure

Carbon nanotube (CNT) reinforced Al (CNT/Al) composites had much higher strength and modulus than the Al matrix, but the relatively low elongation restricted their application. To improve the strength-ductility of CNT/Al composites, a bioinspired tree-ring structure consisting of alternated ductile layers free of CNTs and brittle layers rich in CNTs was designed and fabricated by powder metallurgy route. The results indicate that the tree-ring composite showed higher strength and elongation, compared with those of the uniform composite. The extra strength enhancement of the tree-ring composite was the back-stress strengthening caused by the deformation mismatch between the ductile layers and brittle layers, as well as the coordinated deformation between the ductile core and the strong shell. The increase in elongation was the crack blunting and deflection caused by the ductile layers. The results provide a possible method to improve the strength-ductility of composites.