Mechanisms of simultaneously enhanced strength and ductility of titanium matrix composites reinforced with nanosheets of graphene oxides

Types and sizes of nanoparticles as the secondary phases of metal matrix composites (MMCs) significantly affect their microstructures and mechanical properties. In literature, graphene nanoplates (GNPs) have been introduced into Ti matrix composites (TiMCs) but it is still a contradictory issue on how to simultaneously increase both the strength and toughness of the TiMCs using these graphene nanosheets. In the present work, graphene oxide nanosheets (GONs) were chosen as the reinforcement agent to prepare GONs/Ti matrix composites through a combined process of powder metallurgy and spark plasma sintering (SPS). Microstructures and mechanical properties of the TiMCs were investigated at both room temperature and high temperatures in order to evaluate strengthening and toughening effects of the GONs. It was revealed that 0.2% yield strength and ultimate tensile strength of the Ti-0.6 wt% GONs composite were increased by 7.44% and 9.65% as compared to those of pure Ti, though their elongation was slightly decreased to 22.9%, compared with 31.3% of the pure Ti. All the synthesized samples exhibited typical characteristics of ductile fracture with dimple patterns and pulling-out of the GONs. The Ti-0.6 wt% GONs composite demonstrated an enhancement of 31.66% in the 0.2% yield compressive strength measured at a temperature of 700 °C. Based on both theoretical analysis and experimental verification, the strengthening and toughening mechanisms of the nanocomposites were attributed to the synergistic effects of in-situ TiCx dispersion strengthening from the GONs and effective load transfer capability due to the well-formed interfacial structures.