Tension-compression fatigue behaviors of uniform and bimodal carbon nanotube/Al-Cu-Mg composites

Abstract

By introducing the ductile-zones (DZs) without carbon nanotubes (CNTs) into the brittle-zones (BZs) containing CNTs, constructing the bimodal structure, can effectively improve the toughness of CNT reinforced Al (CNT/Al) composites. However, to be applied in the field of aerospace, CNT/Al composites will be required to have high toughness, as well as high fatigue strength. At the present study, the fatigue behaviors of uniform and bimodal CNT/Al composites under the tension-compression state with the stress ratio of −1 were investigated. It was found that CNT rich zones could keep grains stable after the fatigue loading. However, for the bimodal CNT/Al composites, the preferential local deformation occurred in the DZs, which resulted in much lower fatigue strength as compared to the uniform composite. By reducing the grain size of DZs to ultra-fine grain (UFG) level, the large number of grain boundaries within the DZs hindered the directional movement of slip bands, which significantly enhanced the fatigue strength and achieved a higher toughness of bimodal CNT/Al composites. This discovery provides a new strategy for the preparation of high performance CNT/Al composites, and the bimodal CNT/Al composite with UFG DZs is expected to be applied in the aerospace field. • The grain size of CNTs rich zones keeps stable after fatigue loading due to the pinning effect of CNTs on grain boundaries. • The introduction of bimodal structures decreases the tension-compression fatigue life of the CNT/Al-Cu-Mg composites. • The fatigue performance of bimodal CNT/Al-Cu-Mg composite can be improved by refining the grains in the CNT free zones.