αSiC - βSiC - graphene composites

Abstract

In this study, the mechanical properties of the pressureless sintered samples of α-SiC based composite containing 0–3 wt.% graphene and 0–15 wt.% nano β-SiC were investigated. Simultaneous usage of nano β-SiC and graphene and transformation of β-SiC (3C) to α-SiC (6H/4H) resulted in elongation of secondary α-SiC grains, which significantly improved the mechanical properties (e.g. fracture toughness) of SiC ceramics. According to the results, the highest Relative density of 99.04%, Young’s modulus of 537.76 GPa and fracture toughness of 5.73 MPa × m1/2 were obtained in the sample containing 5 wt.% nano β-SiC and 1 wt.% graphene (5B1G). In addition, two methods of measuring bending strength including three-point bending tests and biaxial tests (piston-on-three-ball) were compared. Strip-shaped specimens were prepared for three-point bending test and disc-shaped specimens were prepared for biaxial bending test. Each bending test was evaluated using a universal testing machine. The results showed that the biaxial bending strength is less than the three-point bending strength. Also, the maximum three-point bending strength of 582.01 MPa and biaxial bending of 441.56 MPa were obtained in 5 wt.% Nano β-SiC and 1 wt.% Graphene samples (5B1G). Studies have shown that in addition to the many advantages of using the biaxial bending method, the results have a very similar trend to the three-point bending strength. Also, the most-increased hardnesses of 28.03 GPa and 29.97 GPa were seen in the sample containing 5 wt.% nano β-SiC (5B) with forces of 10 N and 1 N, respectively. One of the effective mechanisms in improving the fracture toughness of α-SiC ceramics is crack deflection/bridging. Also, the difference in thermal expansion of the α-SiC matrix and the reinforcements, leading to the creation of residual stresses between the matrix grains and the reinforcement, is effective in improving the mechanical properties (e.g. strength and fracture toughness).

Modeling the Effect of Grain Boundary Segregations on the Fracture Toughness of Nanocrystalline and Ultrafine-Grained Alloys

“…The include brittle inclusions in GBs, such as graphene platelets, brittle amorphous f GBs embrittled due to the presence of hydrogen. For example, the results of th confirm that crack deflection in ceramic/graphene composites (where ceramic/g interfaces can be considered weak boundaries) contribute to the experimentall mented (e.g., [33][34][35][36][37]) toughening of ceramics due to the addition of graphene. T [23] via FE simulations for the normal tensile loading to the zigzag direction of the 2D hexagonal lattice of grain boundaries.…”