Surface Modification of Graphene Oxide and Its Strengthening and Toughening Mechanism for Alumina-Based Ceramic Materials

This study investigated the effects of incorporating reduced-graphene-oxide-coated alumina (Al2O3–RGO) nanoparticles and unmodified graphene oxide (GO) onto the microstructure as well as the mechanical properties of Al2O3/TiB2 matrix ceramic materials. The microstructure observation revealed that, compared with GO addition, the addition of Al2O3–RGO nanoparticles significantly improved RGO dispersion in the ceramic materials and reduced defects such as pores caused by graphene agglomeration. In addition, the uniformly dispersed RGO nanosheets were interwoven with each other to form a three-dimensional grid structure due to grain growth and the disappearance of pores during sintering, which increased the contact area and interface-bonding strength between the RGO and ceramic matrix. According to the results of microstructure observation and analysis, the good interfacial strength not only facilitated load transfer from the ceramic matrix to the RGO but also induced the fracture mechanism of the RGO, which consumes more fracture energy than the traditional toughening mechanism. The results of mechanical properties analysis showed that the hardness, flexural strength, and fracture toughness of the obtained ATB–RG3.0 ceramic material was measured at 19.52 GPa, 1063.52 MPa, and 9.16 MPa·m1/2, respectively. These values are 16.82%, 27.92%, and 26.87% higher than those of the ceramic material with 3.0 vol.% GO.