Well-Dispersion of Multi-walled Carbon Nanotubes in Aluminum Matrix Composites by Controlling the Mixing Process

Abstract

One of the major obstacles to the effective use of carbon nanotube (CNT) as a reinforcement in metal matrix composites is its agglomeration and poor dispersion within the metallic matrix. In order to obtain a homogeneous product, good control of the milling process parameters is essential. In fact, the control of the ball motion during the milling leads to a reduction in grinding energy and a more homogeneous product. Also, the critical inner diameter of the milling container at a particular rotational speed can be calculated. In the present work, we use conventional and modified mechanical alloying to generate a homogenous distribution of 2wt% CNT within Al powders. We used 99% purity aluminium powder (Acros, 200mesh) along with two different types of multi-walled carbon nanotubes having different aspect ratios to produce Al-CNT composites. The composite powders were processed into bulk material by compaction, and sintering using a cylindrical compaction and tube furnace. Field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and Vickers macro hardness tester were used to evaluate CNT dispersion, powder morphology, CNT damage and mechanical properties. Despite the success of ball milling in dispersing CNTs in Al powder, it is often accompanied with considerable strain hardening of the Al powder, which may have implications on the final properties of the composite. The results show that particle size and morphology vary with milling time. Also, by using the mixing process and sonication before mechanical alloying and modified ball mill, dispersion of the CNTs in Al matrix improves.