Highly wear-resistant and low-friction Si3N4 composites by addition of graphene nanoplatelets approaching the 2D limit

Abstract

Graphene nanoplatelets (GNPs) have emerged as one of the most promising filler materials for improving the tribological performance of ceramic composites due to their outstanding solid lubricant properties as well as mechanical and thermal stability. Yet, the addition of GNPs has so far enabled only a very limited improvement in the tribological properties of ceramics, particularly concerning the reduction of their friction coefficient. This is most likely due to the challenges of achieving a continuous lubricating and protecting tribo-film through a high GNP coverage of the exposed surfaces. Here we demonstrate that this can be achieved by efficiently increasing the exfoliation degree of GNPs down to the few-layer (FL) range. By employing FL-GNPs as filler material, the wear resistance of Si3N4 composites can be increased by more than twenty times, the friction coefficient reduced to nearly its half, while the other mechanical properties are also preserved or improved. Confocal Raman spectroscopy measurements revealed that at the origin of the spectacular improvement of the tribological properties is the formation of a continuous FL- GNP tribo-film, already at 5 wt% FL-GNP content.

Thermodynamic Stability of Nano-grained Alloys Against Grain Coarsening and Precipitation of Macroscopic Phases

“…Substituting the values from above and from Table I into Eq. [12]: X gb ffi 37:6 kJ/mol, which is in agreement with Figure 3(b). As follows from Eq.…”

“…As follows from Eq. [12], at x = 0 and x = 1: X gb ¼ 1. As this is an unrealistic requirement, for pure metals r 0 is indeed impossible.…”

“…NANO-MATERIALS play an increasing scientific and social role. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In the past, nano-materials were simplified to single nano-particles. However, it has been clear for some decades that the real use of nanomaterials is expected if they form macroscopic articles with nano-structure inside.…”

Research on the interface properties and strengthening–toughening mechanism of nanocarbon-toughened ceramic matrix composites

“…Ultrasound can produce a strong shear force to disperse carbon nanoparticles in a liquid medium; however, this method can also damage the structure and reduce the aspect ratio of carbon nanotubes [23,38,48]. Therefore, the current research focuses on promoting nanocarbon dispersion by electrostatic interaction [42], hybrid particles [49] and designing the microstructures of ceramic matrix composites [50].…”

“…In the process, melamine will neither cause trauma nor form chemical bonds with the graphene scaffolds. Additionally, the surfaces of the materials form continuous GNP lubrication films and improve its frictional properties [49]. Akin et al proved that the GNP microstructures that surround matrix particles can promote their dispersion and improve the relative density and mechanical properties of composites [55].…”