Deformation behavior and strengthening mechanisms in a CNT-reinforced bimodal-grained aluminum matrix nanocomposite

Abstract

The aim of this study was to identify deformation behavior and strengthening mechanisms of a carbon nanotube (CNT)-reinforced bimodal-grained Al–Cu–Mg nanocomposite and its base alloy fabricated by two-step ball milling, powder metallurgy and extrusion. A superior strength-ductility synergy stemming from the concurrent presence of ultrafine grains (UFGs) and coarse grains (CGs) was achieved. Singly-dispersed CNTs in UFGs and sound CNT/Al interfacial bond contributed to a significant improvement in the strength of the nanocomposite. The predominant strengthening mechanism in the CNT-reinforced nanocomposite was identified to be Orowan looping due to severe shearing of CNTs into nano-sized fragments during ball milling, along with load-transfer and thermal mismatch-induced dislocation strengthening mechanisms. The predicted yield strength of the nanocomposite was in agreement with the experimental value obtained. The findings in this study help pave the way for developing high-performance lightweight materials with a superior strength-ductility synergy via incorporating CNTs with novel bimodal grain structures. • A novel bimodal CNT-reinforced 2009Al nanocomposite is successfully fabricated. • The concurrent presence of UFGs and CGs offers superior strength-ductility harmony. • CNTs are singly dispersed in the UFG regime with sound bond of CNT/Al interface. • 3 vol% CNTs in the nanocomposite lead to a significant strength improvement. • The predominant strengthening mechanism in the nanocomposite is Orowan looping.