Reaearch Of Direct Ink Writing Reaction Bonded SiC-based Ceramics And Its Properties

As a functional and structural ceramic with high thermal conductivity,high wear resistance,low coefficient of thermal expansion and high mechanical strength,silicon carbide(SiC)ceramics have been used in a wide range of engineering applications,but technological innovations have also posed new challenges in the preparation of SiC ceramic components,but traditional methods of preparing SiC ceramic products are difficult to meet for the production of special shapes.For example,in the manufacturing of semiconductors and infrared emitters,a large number of complex-shaped SiC ceramic components are used,requiring not only precise special structural shapes,but also excellent properties such as high thermal conductivity and good mechanical properties to meet the necessary requirements for heat transfer and support.As a new production process for ceramic materials,Direct Ink Writing(DIW)3D printing and forming technology has become a hot topic of research in recent years,which can achieve a good combination of function and shape design of ceramic parts.In this paper,SiC ceramics were prepared using a DIW process and a reactive sintering process for near-net size forming.The optimal design of SiC ceramic slurry for printing was explored,and the DIW process of SiC ceramics as well as the reactive sintering and composite properties of the printed parts were investigated.The effects of different content carbon black,sodium alginate(SA)binder and polyvinylpyrrolidone(PVP)dispersant on the rheological properties of the slurry were first investigated.At 10 wt%to 20 wt%carbon black content,the modulus and yield stress of the slurry increase as the increases as the inter-particle force changes.The dispersant helps to reduce the viscosity of the slurry,the shear stress at the flow point of the slurry with 1 wt%dispersant is only 19 Pa.The addition of binder helps to improve the stability of the slurry.The thixotropic properties of the slurry were tested and it was found that the viscosity of the slurry with 1 wt%binder and 1 wt%dispersant recovered immediately after one shear interval and that the modulus recovered to approximately 66%of the original storage modulus after 100 s.The forming process of DIW SiC blanks was investigated with different nozzle diameter,blank drying behavior,complex structure forming parameters and the effect of solid phase content on the blanks.A larger nozzle diameter gives a higher modulus of paste extrusion,which helps to support the superstructure and allows the printing of solid or hollow complex shapes.The drying of the printed blanks is controlled to maintain consistent drying at the top and bottom,and slurries in the 72 wt%-77 wt%solid phase content range are suitable for printing.The effect of carbon black content on the microstructure and properties of DIW reaction bonded SiC ceramics was investigated and it was found that the internal microstructure of the sintered ceramics could be controlled by adjusting the carbon black content.As carbon black content increased,the SiC grains in the ceramics grew,and when the carbon black content was 20 wt%,the sintered SiC grains interconnected with each other and the thermal and mechanical properties of the material improved,with the flexural strength and hardness of the ceramics being 229 MPa and 14.9 GPa respectively,and the thermal conductivity being as high as 132 W/(m·K).The DIW reaction bonded BN/SiC composite ceramics were prepared and the effect of BN content on the microstructure and properties of the composite ceramic materials was investigated.When the BN content was 1 wt%,the powder was well dispersed in the billet,which inhibited crack expansion in the fracture section of the composite,and the mechanical properties of the composite ceramics were significantly improved,with a flexural strength of 283 MPa,an increase of 24%compared to the matrix.