Effect of morphology and content of nano-C on grain growth behavior of copper matrix composites

This study compares high-temperature grain growth behavior in copper matrix composites containing nano-carbons in the form of fullerenes, carbon nanotubes (CNTs), and graphene to investigate the effect of volume fraction and shape of nano-carbon reinforcement on grain growth suppression. The grain growth was significantly suppressed when the nano-carbon content was 5 vol%, but the suppression efficiency was reduced when nano-carbon particle loading increased above 20 vol%. Furthermore, CNTs induced better grain growth suppression than fullerenes and graphene. Grain growth was observed both near the nano-carbon interfaces and in the bulk matrix. The poor wetting ability between copper and the nano-carbons accelerates lattice diffusion at the reinforcement interface. Owing to differences in the thermal expansion coefficients and elastic moduli between copper and the nano-carbons, due to the presence of the reinforcement, stress distribution will be inhomogeneous. In composites containing discontinuous reinforcement, the stress is concentrated at the tip of the reinforcement and at its minimum at the center of the reinforcement. Inhomogeneous stress fields are formed in the far away from the reinforcement, which in turn causes the suppression of overall grain growth in the composites.