Study On Preparation And Tribological Properties Of Graphene Reinforced Silicon Carbide Composites

Ceramic materials have high hardness and strength,good corrosion and abrasion resistance.As wear-resistant structural components,ceramic materials have extensive application prospects in many industrial areas.It has great significance to improve the tribological properties of ceramic materials and explore the tribological mechanism for the application of ceramic materials in tribology.In this dissertation,SiC ceramics were hot-press sintered by using Al₂O₃ and Y2O3 sintering additives.Research is conducted to understand the effects of content and mass ratio of sintering additives on relative density,phase composition,microstructure and mechanical properties of SiC ceramics.When the mass ratio of Al₂O₃ and Y2O3 was fixed in 1:2.5,the relative density,Vickers hardness,flexural strength and fracture toughness first increase and then decrease with the increasing of Al₂O₃ + Y2O3 content from 3 wt.% to 15 wt.%.SiC ceramic with 10 wt.% sintering additives exhibits the highest mechanical properties.The relative density,Vickers hardness,flexural strength and fracture toughness are 98%,26.7 GPa,617 MPa and 5.04 MPa·m1/2 respectively.The graphene reinforced SiC composites with different graphene content?1 wt.%,3 wt.%,5 wt.% and 7 wt.%?were prepared by hot-press sintering.The dispersion behavior and bonding mode of graphene in SiC matrix were studied.Effects of graphene content on relative density,microstructure and mechanical properties of composites were investigated.When the content of graphene increases from 0 to 7 wt.%,the relative density and Vickers hardness of the composites decrease continuously,relative density decreases from 98.0% to 94.5%,and Vickers hardness decreases from 26.7 GPa to 13.8 GPa.The axial pressure at the time of sintering leaded to the preferred orientation of the graphene,which caused anisotropy in flexural strength and fracture toughness.Flexural strength and fracture toughness parallel to the loading direction first increases and then decreases with the increase of graphene content.The main toughening mechanism of composite materials is graphene pull-out,bridging as well as crack deflection.Tribological properties of composites with different content of graphene were investigated.Three kinds of grinding balls: SiC,Al₂O₃ and Si3N4 were used and 10 N,20 N and 30 N were adopted as test loads.The wear mechanism of SiC ceramic is mainly brittle fracture and abrasive wear.The wear degree of SiC ceramics increases with the increase of load.When using SiC and Si3N4 balls,the worn surface is oxidized during the process of friction.Oxidation products content increases with increasing load.Oxidation products are compacted on the worn surface thereby reducing the coefficient of friction and wear rate.After adding graphene,the wear resistance of the composites increases,the wear mechanism of composite materials is mainly brittle fracture and delamination wear.On one hand,the addition of graphene to the composite material can enhance the mechanical properties of the composite material,inhibit the separation of the ceramic grains and weaken the micro-cutting caused by wear debris during wear.On the other hand,graphene and stripping debris together form a layer of glaze during the test.Graphene can reduce the frictional stress on the glaze layer,weaken the wear and tear of the glaze layer and improve the tribological properties of the composite.