Nano‑carbon-mediated microstructure evolution and superior performance in Ti-based nanocomposites

Nano‑carbon reinforced metal matrix composites have gained much interest in recent years to further develop the structural materials with high performance for engineering use. However, producing these composites is challenging, as most processing techniques involve agglomeration and high-temperature sintering induced severe interface reaction. This work provides a sintering-free approach via severe plastic deformation (SPD). Ti-based nanocomposites were creatively synthesized via high-pressure torsion (HPT) by introducing 0.6 wt% graphene nanoplatelets (GNPs) as reinforcements. Powders mixtures were directly compacted at ambient temperature and then deformed by HPT at three different pressures of 2GPa, 3GPa and 4GPa up to 5 turns. Nearly no interfacial reaction products could be observed in the fully dense bulk nanocomposites. More intriguingly, experiments and first-principles simulations revealed that a key benefit of incorporating nanoscale GNPs would be a reduction in the grain boundary energy (GBE) and stacking fault energy (SFE), thus enabling concurrent dislocation storage near the boundaries and inhibiting dislocation recovery during plastic deformation. We demonstrate that GNPs significantly increase the critical equivalent strain and texturing strengthening, leading to a remarkably enhanced saturation of microhardness. The present work emphasizes the uncovering of novel interaction between nano‑carbon and grain boundaries in metal matrix composites, and the current HPT approach is versatile and can open up a horizon of nano‑carbon/titanium combinations with an improvement of mechanical property.