Overcoming strength-ductility trade-off by building a micro-nano laminated structure based on an ultralow amount of single-dispersed carbon nanotubes

CNTs/Ti composites (Carbon nanotube reinforced titanium matrix composites) with a novel micro-nano laminated structure consisting of alternating CNTs nanolayers and Ti microlayers were successfully prepared by electrophoretic deposition combined with spark plasma sintering and temperature-controlled rolling. The CNTs/Ti composites exhibited a simultaneous enhancement in both strength and ductility compared to pure Ti fabricated by the same methods, despite the addition of CNTs being an ultra-low 0.02 weight percent (wt.%). The improvement in strength was attributed to (i) the high strengthening efficiency of individually dispersed, structurally intact CNTs and (ii) Heterogeneous deformation-induced (HDI) strengthening resulting from the heterogeneous deformation between soft Ti microlayers and hard CNTs nanolayers. Furthermore, the HDI hardening induced by the micro-nano laminated structure led to extra work hardening, enhancing the uniform deformability of CNTs/Ti composites. Consequently, strain localization was suppressed, as observed by in-situ tensile experiments, thereby preventing the initiation of interfacial. Additionally, interfacial crack propagation was significantly delayed due to CNTs bridging and crack tip blunting by ductile Ti microlayers, thereby promoting the total elongation to failure. Moreover, a progressive fracture process consisting of three stages was proposed, based on three-dimensional visualization and quantitative analysis of crack volumes. This provided a new strategy for overcoming the strength-ductility trade-off of traditional metal (Ti, Al, Fe, Ni, etc.) matrix composites through the reasonable design of a hierarchical architecture based on an ultra-low amount of high-quality nanoscaled reinforcements.