Toughening in Graphene Ceramic Composites

Abstract

The majority of work in graphene nanocomposites has focused on polymer matrices. Here we report for the first time the use of graphene to enhance the toughness of bulk silicon nitride ceramics. Ceramics are ideally suited for high-temperature applications but suffer from poor toughness. Our approach uses graphene platelets (GPL) that are homogeneously dispersed with silicon nitride particles and densified, at ∼1650 °C, using spark plasma sintering. The sintering parameters are selected to enable the GPL to survive the harsh processing environment, as confirmed by Raman spectroscopy. We find that the ceramic's fracture toughness increases by up to ∼235% (from ∼2.8 to ∼6.6 MPa·m(1/2)) at ∼1.5% GPL volume fraction. Most interestingly, novel toughening mechanisms were observed that show GPL wrapping and anchoring themselves around individual ceramic grains to resist sheet pullout. The resulting cage-like graphene structures that encapsulate the individual grains were observed to deflect propagating cracks in not just two but three dimensions.

Spark plasma sintering of Si3N4/multilayer graphene composites

“…Further increasing the graphene content did not cause significant change in the fracture toughness, which stayed around 5 MPa m 1/2 . It is in line with findings of Walker et al [24], who fabricated composite with 1.5 wt% of GPL and the achieved fracture toughness was of 6.6 MPa m 1/2 which is little higher than that of monolithic composite was not spectacular. Tapasztó et al [25] fabricated Si 3 N 4 with 3 wt% graphene and obtained a paltry 3.2 MPa m 1/2 value for the toughness.…”

Micromechanics of fracturing in nanoceramics

“…The new toughening micromechanisms and specific deformation modes operating in nanocrystalline ceramics are discussed in detail in §4. In order to enhance mechanical properties of ceramic materials, it is very effective to exploit graphene platelets/sheets as reinforcing structural elements in ceramic-matrix nanocomposites [24,25,[46][47][48][49][50][51][52]. This new approach is based on the unique mechanical characteristics (e.g.…”

“…More than that, in the first decade of the twenty-first century, ceramic-CNTs nanocomposites were viewed as the most promising ceramic materials for structural applications [21][22][23]. In recent years, however, graphene inclusions in the forms of multilayer graphene and GO platelets/sheets have been recognized as the most effective reinforcing fillers that dramatically enhance fracture toughness (and moderately improve strength) of ceramic-matrix composites [2,25,[46][47][48][49][50][51][52]. For instance, in one experiment [46], the mechanical characteristics (Young modulus, bending strength, hardness, fracture toughness) of silicon nitride reinforced by few-layer graphene sheets showed 10-50% enhancement when compared with those of silicon nitride reinforced by CNTs.…”

“…In particular, a silicon nitride nanocomposite containing 1.5 vol% graphene inclusions shows ≈235% increase in the fracture toughness (from ≈2.8 to ≈6.6 MPa m 1/2 ), when compared with monolithic Si 3 N 4 material. From a micromechanical viewpoint, toughening of the nanocomposite occurs through crack deflection, crack bridging by graphene sheets, their pull-out and necking (figure 5) [47]. It is important to note that cracks do not penetrate across graphene sheets which in fact form curved two-dimensional structures/surfaces along GBs.…”

Graphene and graphene oxide as nanomaterials for medicine and biology application

“…Notably, the properties of HAp and bioglass can be influenced by rGO which depends on the concentration. The improvements of mechanical properties of the bioceramic materials by graphene and other related materials are done by bridging, sheet pullout and three-dimensional crack deflection mechanisms [118,122,123]. The graphene has a surface area for contact.…”