Mechanical and microstructural characterization of Cu/CNT nanocomposite layers fabricated via friction stir processing

In this study, the effect of incorporation of carbon nanotubes into pure copper was investigated through friction stir processing (FSP). To this end, FSP has been performed using one and three passes. Moreover, the changes in peak temperature of one-pass friction stir processing performed by tools with different shoulder diameters have been recorded. It was found that for the tool with smaller shoulder, the process temperature peak has been significantly reduced. Remarkable reduction in grain size of Cu/carbon-nanotube nanocomposites was observed as compared with the pure copper. Raman spectroscopy results proved a higher extent of degradation of carbon nanotubes upon increasing the friction stir processing passes. On the other hand, microhardness and wear results showed that as the carbon nanotubes are introduced to the pure copper, hardness of composites processed via one- and three-friction stir processing passes showed enhancements of 65 and 105 %, respectively, and the weight losses were also decreased 31 and 68 %, respectively. It was also observed that friction coefficient of one-pass processed composite is lower than that of the pure copper due to the presence of carbon nanotube clusters. Whereas, the friction coefficient of three-pass processed composite was increased regarding to the pure copper. The reduction in slope of wear weight loss upon increasing the applied force at the wear test signified the higher efficiency of the processed composites under harsh conditions.