Study On Thermal Conductivity Of Diamond/Silicon Carbide Composites With Large Particle Size And High Proportion Of Diamond Prepared By HPHT

Diamond/silicon carbide composites have high thermal conductivity,high hardness,high modulus,high temperature resistance,high temperature oxidation resistance,thermal shock resistance and other excellent properties,widely used in aerospace,new energy-saving vehicles,abrasives,nuclear fusion and other fields.It has become one of the most ideal candidate systems for high temperature resistance,high thermal conductivity and high hardness functional materials.At present,diamond/SIC composites are synthesized by the following methods: high temperature and high pressure method,laser selective sintering method,true air phase sintering method,vacuum liquid phase melting method,spark plasma sintering.Diamond has a very high thermal conductivity,and as a functional enhancement phase of composite materials,the thermal conductivity will be significantly improved.Large and medium-sized diamond-size composite materials will provide a long-range ordered lattice structure for the internal transmission of phonons,open up internal thermal conductivity channels,and improve the overall thermal conductivity of the composite materials;The functional materials synthesized in high temperature and high pressure environment have high density and greatly reduce the thermal resistance caused by pores.In this paper,diamond/silicon carbide composites with large particle size and high proportion were synthesized by high temperature and high pressure method,and the effects of diamond surface treatment,diamond particle size,silicon carbide addition and silicon content on the forming and thermal conductivity of the composite were systematically investigated.(1)In the case of the same diamond mass ratio,we found that the larger the diamond particle size,the better the overall thermal conductivity of the composite material,which is applicable under the synthesis conditions of 5 GPa and 8 GPa.Double particle size(large particle size with small particle size)diamond has the effect of enhancing the bond of composite materials and improving the thermal conductivity of materials.The best proportion of large size diamond is 86 wt%～90 wt%in terms of material bonding strength and thermal conductivity.(2)nanoscale silicon carbide due to large specific surface area,high pressure melting point is reduced,and can fully fill the gap to wrap diamond particles.Therefore,using nanoscale silicon carbide as raw material can not only improve the bonding strength of composite materials but also improve the overall thermal conductivity.(3)At 8 GPa,the thermal conductivity of the sample with 91 wt% diamond of 1μm can also reach 533 W/m K,indicating that the high pressure conditions have a significant effect on the molding and high thermal conductivity of the fine diamond/silicon carbide sample.(4)The highest thermal conductivity of diamond/sic composite prepared at 8 GPa,1500℃ and30 min is 822 W/m·K,which is 4.9 times higher than that of the sample prepared by 5 GPa.The best group is divided into: diamond(300～250μm): 90 wt%,diamond(66～55μm): 3.8 wt%,Si C(1μm): Si(5μm)=7:3.In this experiment,diamond/silicon carbide composite materials were prepared by selecting large-particle size and high-proportion diamond under high temperature and pressure,which provided technical routes and guidance for subsequent experiments.