Deformation and strengthening mechanisms of a carbon nanotube reinforced aluminum composite

The objective of this study was to characterize microstructure, texture, and deformation behavior of a carbon nanotube (CNT) reinforced aluminum composite via electron backscatter diffraction (EBSD), X-ray diffraction (XRD), scanning and transmission electron microscopy. The addition of 2.0 wt.% CNTs in a 2024Al alloy led to considerable grain refinement, with a bi-modal distribution of grain misorientation angles positioned at ∼7° for low-angle grain boundaries and ∼50° for high-angle grain boundaries. The CNTs were observed to be uniformly dispersed in the matrix while some CNT shortening occurred during ball milling. The grain size reduction and compressive micro-strains in the composite broadened X-ray peaks and resulted in lattice shortening. The macro-texture determined via XRD and micro-texture via EBSD were in good agreement, revealing that the composite contained stronger {112} <111> Copper texture and {110} <001> Goss texture in comparison with 2024Al base alloy. The deformation resistance of the composite at both room and elevated temperatures was effectively enhanced due to the CNT addition. This was mainly attributed to the role of underlying strengthening mechanisms: Hall-Petch strengthening (significant grain refinement involving the Zener pinning effect of CNTs), and composite strengthening including load transfer, thermal mismatch and Orowan looping.