Recent advances in coated carbon nanotube-reinforced metal matrix composites: Challenges, techniques, and performance enhancement

Carbon nanotubes (CNTs) have attracted considerable scholarly attention over the past few decades as reinforcement materials in metal matrix composites (MMCs). This increasing interest is mainly due to their unique structural characteristics and exceptional electrical, mechanical, and thermal properties. However, weak interfacial bonding and agglomeration of CNTs significantly reduce their reinforcement efficiency. These issues can be solved by surface functionalization and coating techniques. The effectiveness of MMC applications is contingent upon successfully addressing and overcoming the associated challenges. This paper aims to explore the recent advances in coated CNT-reinforced MMCs to address these issues. The pros and cons of using various coating materials, including nickel (Ni), copper (Cu), and metal oxides, for coated CNTs as reinforcement material are comprehensively reviewed in this article. Moreover, various coated CNT fabrication techniques such as physical vapor deposition, chemical vapor deposition, electrodeposition, and electroless deposition are illustrated along with their merits and demerits. Among these methods, electrodeposition has proven to be the most widely used coating technique. Research findings show that Ni-coated CNT/magnesium (Mg) composites and titanium dioxide (TiO₂)-coated CNT/aluminum (Al) composites exhibit enhanced mechanical properties. On the contrary, silver-coated CNT/Cu composites exhibit superior electrical conductivity. The study emphasizes that selecting the appropriate coating metal depends primarily on the desired final properties of the composite. In addition, the paper highlights current challenges in the field and suggests potential future research avenues aimed at improving the performance of coated CNT-reinforced MMCs.