Study On Graphene-coated Silicon Carbide Reinforced Silicon Nitride Ceramic Tool

To address the issue of poor mechanical properties of single matrix Si₃N₄ ceramic tool materials,Si₃N₄/SiC@G ceramic tool materials were prepared by SPS sintering in this thesis,and the sintering process and sintering aid system were optimized.Graphene-coated silicon carbide（SiC@G）nanoparticles were prepared using liquid-phase laser irradiation technique,and Si₃N₄/SiC@G ceramic tool materials were prepared by incorporating SiC@G nanoparticles into the Si₃N₄ ceramic matrix.The graphene content in the SiC@G nanoparticles was determined by thermogravimetric analysis,and control experimental groups were set up to prepare Si₃N₄/SiC@G,Si₃N₄/SiC/G and Si₃N₄/SiC ceramic tool materials to analyse the toughening mechanism of the encapsulated particles.The optimum sintering process and sintering aid content were determined experimentally.Ceramic tool materials with a Vickers hardness of 15.91 GPa,a flexural strength of 798.92 MPa and a fracture toughness of 7.79 MPa·m^1/2 was prepared at a sintering temperature of 1650°C,a holding time of 6 min,a sintering pressure of 30 MPa and a sintering aid content of 9 wt.%.The Si₃N₄/SiC@G ceramic tool material was prepared by incorporating SiC@G nanoparticles into a Si₃N₄ ceramic matrix.This special encapsulation structure can combine the advantages of both materials,improving the wear resistance of the ceramic tool and solving the problem of difficult dispersion of SiC and graphene.the SiC@G nanoparticles are tightly bonded in the ceramic matrix,and the outer layer of graphene is embedded between the grains,enhancing the bond strength between the grains.It was experimentally verified that the Vickers hardness,fracture toughness and flexural strength of Si₃N₄/SiC@G ceramic tools increased by 2.7%（16.34 GPa）,32.7%(10.34 MPa·m^1/2)and 13.7%（907.31 MPa）compared to Si₃N₄ ceramic tool material when SiC@G nanoparticles were added at 5 wt.%.The loss of graphene mass by SiC@G nanoparticles was calculated to be about 15%by thermal weight loss analysis,and a control experimental group was set up to investigate the toughening mechanism of SiC@G.The experimental results demonstrated that the Vickers hardness of the graphene-added ceramic tools decreased and the flexural strength and fracture toughness increased.11.7%（16.3 GPa）increase in Vickers hardness,1%（907.31 MPa）increase in flexural strength and 11.1%(10.34 MPa·m^1/2)increase in fracture toughness were observed for the Si₃N₄/SiC@G ceramic tool material compared to the Si₃N₄/SiC/G ceramic tool material(10.34 MPa·m^1/2).When the Si₃N₄/SiC@G flakes prepared by FIB were observed by HRTEM,the SiC@G nanoparticles remained intact in the cladding structure during the SPS sintering process,and the SiC@G nanoparticles filled between the silicon nitride particles and the glass phase formed by the sintering aid,strengthening the bonding ability between the particles and increasing the relative density of the ceramic tool material.the SiC@G nanoparticles and the matrix.The strong and weak interfacial bond between the SiC@G nanoparticles and the substrate material can effectively consume the fracture energy propagation and improve the fracture toughness of the ceramic tool material.Comparing the cutting performance of the three ceramic tool materials,the cutting distance（2000 m）of the Si₃N₄/SiC@G ceramic tool was improved by 25%and 12.5%compared to the effective cutting distance of the Si₃N₄/SiC and Si₃N₄/SiC/G ceramic tools at v_c=200 m/min,a_p=0.1 mm and f=0.102 mm/r,respectively.The coefficient of friction on the front tool face was reduced by 18.9%compared to the Si₃N₄/SiC/G ceramic tool.The addition of SiC@G nanoparticles improves the dispersion and wear resistance of the SiC@G nanoparticles by the special encapsulation structure compared to the addition of graphene and silicon carbide respectively,effectively increasing the cutting life of the ceramic tools.