Study On Forming Process And Properties Of Boron Carbide Composite Ceramic Materials

Gel casting B₄C ceramics is a new method to form three-dimensional skeleton network by using polymer organic monomer cross-linked in situ polymerization and to immobilize B₄C ceramic particles in it.The ceramic blank prepared by gelcasting process has the advantages of uniform distribution of each component phase and low volume shrinkage after drying.In the traditional carbon black-ammonium persulfate?APS?system,carbon black has an inhibitory effect on the polymerization of monomers.Compared with other B₄C sintering methods,such as pressureless sintering and hot pressing sintering,reaction sintering has the advantages of low sintering temperature,high densification degree of sintered ceramic products and simple production process.In this paper,by introducing white sugar as a carbon source for gel casting B₄C ceramic slurry and reducing carbon black incorporation,experimental parameters such as solid content,particle gradation,and ball milling time that affect the rheological properties of B₄C ceramic water-based slurry were studied.In order to solve the problems of high viscosity of water-based slurry and low mechanical strength of ceramic plain.B₄C ceramic green body was prepared by a gel casting method,and silicon carbide whisker?SiC_w?and titanium diboride?TiB₂?were used as reinforcements to prepare a reactive sintered B₄C ceramic composite material.The effects of the addition of SiC_w and TiB₂on the rheological properties of B₄C ceramic water-based slurry were studied.The changes in the microstructure,microstructure and mechanical properties of the composite materials were analyzed and tested,and the toughening and strengthening mechanisms were discussed.Research indicates:?1?The rheological property of the slurry can be improved by using the soft white sugar as the carbon source to reduce the amount of carbon black,but excessive soft white sugar will destroy the structure of the blank and reduce material mechanical properties.When the amount of dispersant PVP is 3 wt%of B₄C powder,the mass ratio of B₄C powder W3.5 to W10 is 3:7,the milling time of slurry is 150 min,the mass ratio of carbon black to soft white sugar is 1:2,the solid content is 54 vol%,the fluidity can meet the requirements of injection molding process,and the structure of ceramic blank and sintered body after curing is complete and the mechanical properties are good.?2?Using SiC_w as the toughening body,the reaction-sintered SiC_w/B₄C ceramic material was successfully prepared at 1500°C by gel casting progress.With the increase the content of SiC_w,the viscosity of water-based slurry is increasing.However,the hardness,bending strength and fracture toughness of SiC_w/B₄C composite increased first and then decreased.When the content of SiC_w is 12wt%,the maximum bending strength is 201MPa;when the content of SiC_w is 8wt%,the fracture toughness of the material is 3.42MPa·m^1/2.SiC Whisker pullout is the main mechanism for toughening of composite materials.?3?Using TiB₂ as the reinforcement,the reaction sintered TiB₂/B₄C ceramic material was prepared at 1500?by gel casting process.When TiB₂ content is less than 4wt%,the viscosity of water-based slurry after mixing has little change.When TiB₂ content is more than 16wt%,the viscosity of water-based slurry will be more than 1000m Pa·s.With the increase the content of TiB₂,the fracture toughness of the composite increases,while the bending strength of the composite increases first and then decreases.When the content of TiB₂ is 12wt%,the maximum bending strength is 227MPa;when the content of TiB₂ is16wt%,the fracture toughness is 3.37MPa·m^1/2.The phenomenon that the crack tip of the composite material encounters the residual stress field and the deflection of the TiB₂particles is the main reason for the reinforcement and toughening of the material properties.