Compressive behavior of CNT-reinforced aluminum matrix composites under various strain rates and temperatures

Carbon nanotubes (CNTs) have been attractively used as reinforcement in metal matrix composites (MMCs) for advanced mechanical properties. However, the effects of loading rate and temperature on such materials are still to be resolved. In the present study, aluminum-based MMCs reinforced with CNTs of different contents were investigated under various loading rates and temperatures, along with microstructural examination by electron microscopy. It is found that the strengthening capability of CNTs/Al in comparison to PBM Al decreased with the temperature increasing and loading rate decreasing. However, microstructure characterization showed that CNTs played an essential role on hindering dislocation movement and stabilizing the microstructure, thus yielding an increased strength in Al-based MMCs at temperatures up to 603 K, regardless of the loading rate. A constitutive model that takes into the effect of temperature and microstructures account is then established to illuminate the role of CNTs. In addition, experimental results showed that the CNTs-reinforced Al composites exhibited an enhanced value of strain rate sensitivity and a reduced activation volume than the Al counterpart under all the tested temperatures. It is also found that the increased temperature softened the matrix and reduced the amounts of interactions of mobile dislocations with CNTs and forest dislocations, which led to the enhanced thermal activation volume of the CNTs/Al with temperature.