Strengthening mechanisms of carbon nanotube-reinforced polycrystalline magnesium composites: A molecular dynamics study

Carbon nanotube (CNT)-reinforced magnesium (Mg) composites have emerged as promising lightweight structural materials due to their exceptional strength-to-weight ratio and potential for enhancing mechanical performance. However, the fundamental mechanisms governing the strengthening and plastic deformation of CNT/polycrystalline Mg composites remain insufficiently understood. In this work, large-scale molecular dynamics (MD) simulations were employed to systematically investigate the effects of crystallite size and grain number on the tensile response, dislocation evolution, atomic strain distribution, and microstructural stability of CNT/Mg composites. The results reveal pronounced size-dependent mechanical behavior: smaller crystallites exhibit higher strength but reduced ductility, governed by limited dislocation sources and strong grain boundary pinning, whereas larger crystallites promote dislocation slip, grain boundary sliding, and enhanced plasticity at the expense of strength. Increasing grain number initially improves strength through grain boundary strengthening, but excessive grain boundaries induce stress localization, grain boundary sliding, and brittle failure. CNTs play a crucial role in reinforcing the composites by pinning dislocations, promoting entanglement, and facilitating load transfer across grains. The synergistic interactions between CNTs, dislocations, and grain boundaries determine the strength–ductility balance. These findings provide atomistic insights into the deformation and strengthening mechanisms of CNT/polycrystalline Mg composites, offering valuable guidance for the microstructural design of high-performance lightweight metal matrix composites.