| Silicon nitride ceramics have high hardness and high wear resistance,but possess brittleness,low bending strength.In order to improve the mechanical properties of silicon nitride,graphene/Si3N4 based ceramic was prepared by vacuum hot pressing sintering with graphene.Mechanical properties,microstructure and friction and wear behavior of graphene/Si3N4 based ceramic were studied.The different dispersants were used to study the dispersion of graphene.Ultraviolet visible spectrophotometer and optimization experiment was carried out to obtain the best dispersant.The results show that polyvinyl pyrrolidone was the best dispersant when the amount of polyvinyl pyrrolidone is the same as graphene.Graphene/Si3N4/TiC and graphene/Si3N4 ceramic were prepared by vacuum hot pressing sintering.The mechanical properties and microstructure were analyzed.The results show that the transformation from?-Si3N4 to?-Si3N4 is completed.The addition of graphene improved the mechanical properties.With the addition of 1wt%graphene,the hardness,fracture toughness and flexural strength of graphene/Si3N4ceramic are 13.9GPa,8.7MPa?m1/2 and 892MPa.With the addition of 0.75wt%graphene,the hardness,fracture toughness and flexural strength of graphene/Si3N4/TiC ceramic are 15.83GPa,9.39MPa?m1/2 and 928MPa.The mechanical properties of composites exhibit obvious anisotropy with the addition of graphene.With the addition of 1wt%graphene,the hardness,fracture toughness and flexural strength of graphene/Si3N4 ceramic perpendicular to the hot pressing direction are higher about 12.1%,14.5%and 20.2%in compared with that of parallel to the hot pressing direction.The hardness,fracture toughness and flexural strength of graphene/Si3N4/Ti C ceramic in perpendicular to the hot pressing direction are higher about 2.9%7.3%and 4.6%in compared with that of parallel to the hot pressing direction.Graphene is located at the boundaries of the grain boundaries and refines the grains.Crack deflection,crack bridging,crack branching and the bridging and pull-out of graphene are the main toughening mechanisms.The friction coefficient and wear rate in the surface perpendicular to the pressure direction of graphene/Si3N4 composite ceramic with 1wt%graphene are 0.67 and2.13×10-6mm3/N?m,respectively.However,the friction coefficient and wear rate in the surface parallel to the hot pressing are 0.73 and 2.56×10-6mm3/N?m,respectively.Based on the orientation of graphene/Si3N4 composite ceramic,it is found that graphene orientation angle has obvious influence on the friction coefficient and wear rate.When the angle is 30°,the effect of wear resistance of graphene is the best and the lowest friction coefficient and the wear rate are 0.46 and 4.29×10-6mm3/N?m,respectively.With the increase of load,the friction coefficient and wear rate was decreased first and then increased.When the load is 40N,the friction coefficient and wear rate were 0.41 and 1.75×10-6mm3/N?m.With the increase of speed,the friction coefficient and wear rate decreased gradually,when the speed is 400r/min,the friction coefficient and wear rate are lowest. |
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