Effect of metal powder characteristics on structural defects of graphene nanosheets in metal composite powders dispersed by ball milling

Ball milling (BM) is the prime method to disperse graphene into metal powders; however, it inevitably introduces structural defects to graphene. The balance between dispersion quality and structural damage of graphene during BM is a significant issue for fabricating graphene/metal composite powders. In this study two metal powder characteristics, namely type and size, were investigated to understand the effect of the BM process on graphene structure in graphene/metal composite powders. Graphene nanosheets (GNSs) were added into commercial Ti-6Al-4V and pure Al powders with different diameters by three kinds of BM processes with distinct energy levels. According to the microstructure and Raman spectra, the results suggested that metal particle size had a minor influence in low-energy BM, while it played an important role in high-energy BM (HEBM). The structural defects of GNS crystals increase with increasing BM energy. However, increasing energy in BM has limited damage as the discrepancy in particle size is quite large. Furthermore, Al powders with lower hardness tend to deform with lower BM effect, which will cause less damage to GNSs compared to that in the harder Ti powder. Those findings may have implications for the development of high-performance metal matrix composites reinforced with nanocarbon materials.