3D Printing And Microstructure Design Of SiC Ceramic And Composites

SiC ceramics is an important structural material and has been widely used in industrial production and high technology fields.However,the traditional processing and molding technologies of SiC ceramics require the use of molds,which consumes more time and produces high cost in the whole production cycle.Ceramics parts with complex shapes and composite structures are limited in the manufacture.The emergence of ceramic 3D printing technology has overturned the traditional ceramic manufacturing methods.It has great potential in the preparation of ceramic parts with complex structure and composite performance,integrated molding,lightweight design,and can also shorten research cycle and reduce product costs.Direct ink writing and stereolithography apparatus are diffusely studied and concerned due to simple process,wide applicability of materials and high fabrication accuracy,respectively.Based on 3D printing technology and reaction infiltration sintering,two novel methods of fabricating SiC ceramic composites are proposed in this paper.Firstly,silicon carbide composite slurries for direct ink writing were investigated.Aqueous SiC ceramic slurries with shear thinning behavior were obtained by using sodium alginate as binder,chopped carbon fibers and carbon black as raw materials.The slurry with 2%sodium alginate had the highest modulus and the best adhesion property.The addition of carbon black barely influenced the viscosity of the slurries.When the carbon black content was 15vol%,the initial modulus of the slurry was the highest.With the increase of the chopped carbon fiber content,the viscosity of the slurry decreased and the shear stress first increased and then decreased.When the chopped carbon fibers content was25vol%,the viscosity of the slurry was the lowest.The slurries with different contents of carbon black and chopped carbon fibers had high dispersion,while showing typical shear thinning behavior.These slurries can meet the requirements of direct ink writing.Secondly,3D printing process was implemented through the self-assembly direct writing device.Reactive melt infiltration facilitated the densification of silicon carbide ceramic composites and near-net-forming in 1650?.The effects of printing conditions,slurries solid loading,the contents of carbon black and chopped carbon fibers on samples in process of forming and sintering were investigated.More printing layers and the plastic film substrate can effectively eliminate crack of dry samples.Chopped carbon fibers are continuous oriented distribution induced by extrusion shear force.The increase of slurries solid loading can improve the mechanical properties of 3D printed ceramic parts.The sintered samples with solid loading of 32.38vol%and 34.68vol%have maximum flexural strength of 238MPa and 300MPa,respectively,and maximum fracture toughness of 3.9MPa·m^1/2 and 4.6MPa·m^1/2,respectively.The sintering shrinkage of samples is less than 2%and of relative density is greater than 99%.The flexural strength first increased and then stabilized with the addition of carbon black,and the maximum flexural strength is 275.26MPa.When the content of chopped carbon fibers increased from 0vol%to 15vol%,the flexural strength of the sample gradually increased,and the maximum flexural strength is 252.53MPa.The flexural strength decreased sharply for samples with chopped carbon fibers content of 25vol%.Finally,the fabrication of SiC ceramic composites by digital light processing was explored.Photocurable chopped carbon fibers photosensitive slurry with a maximum solid loading of 20.86vol%was prepared.With the increase of exposure power and exposure time,curing thickness of photosensitive suspension was increased.The maximum curing thickness can reach 46?m.The chopped carbon fibers preform with complex grid structure was prepared after optimizing the exposure parameters.The curing adhesion of photosensitive resin and crisscrossed pinning of chopped carbon fibers have the synergistic effect to acquire tightly bonded adjacent layers.Debonding shrinkage rate of samples was anisotropy.The preform was densified by liquid silicon infiltration.Most of chopped carbon fibers were silicified in situ to form?-SiC.