Mechanism Of Action Of Sintering System And Additives On The Reaction Sintering Of Silicon Carbide

With the continuous development of science and technology,people’s requirements for materials performance are gradually increasing.Owing to their excellent performance,SiC materials have been widely concerned.Because of continuous optimization of its preparation technology to achieve performance improvement,silicon carbide materials are widely used in ceramic kilns,engines,optical mirrors and high-power lasers.Due to the strong covalent bond of SiC,most SiC ceramic materials require high temperature for sintering,which increases the preparation cost and limits its popularization and application.The SiC ceramic material prepared by reactive sintering method can be sintered at a lower temperature,but part of the free silicon will remain in the SiC ceramic material,affecting the high temperature performance of the SiC ceramic.In response to this problem,this article used SiC powders of different sizes as the main raw materials,and used compression molding to prepare ceramic green bodies to study the effect of two-step sintering method on the microstructure and properties of reactive sintered SiC ceramics under different heat treatment systems.The effect of two-step sintering method with different sintering temperatures on the microstructure and properties of SiC ceramics when 4wt%Al and 4wt%Al₄SiC₄were added respectively were studied,and the grain growth process of reactive sintered SiC ceramics during heat treatment and the effect mechanism of Al and Al₄SiC₄on the reaction of silicon carbide were studied.（1）The effects of different siliconizing time and sintering temperature in the two-step sintering method were studied.SiC ceramic after 2h siliconizing and sintered at 1650℃showed a net size change,and the relative content of Si was low,and the material obtained a good skeleton structure,higher volume density,lower apparent porosity and high normal temperature compressive strength.（2）When 4wt%Al was added as an additive,the liquid phase Al increased the liquid phase content in the system and accelerated the reaction sintering process,and hindered the growth of SiC grains.SiC ceramics were completely sintered at a sintering temperature of 1600℃,exhibiting slight shrinkage and good skeleton structure.When the sintering temperature reached 1700℃,SiC ceramics exhibited a continuous skeleton structure,with higher density higher normal temperature compressive strength..The second phase Al₄SiC₄generated by the reaction in the matrix was beneficial to strengthen the performance of SiC ceramics and improve the micro-morphology.（3）Adding 4wt%Al₄SiC₄as an additive,when the sintering temperature was low,it had a certain hindrance to the reaction sintering process.When the sintering temperature was higher than 1650℃,the SiC ceramic grains grew well,showing a continuous skeleton structure,greatly improved normal temperature compressive strength and high volume density.A small amount of Al decomposed by Al₄SiC₄accelerated the reaction sintering,and C decomposed by Al₄SiC₄could consume free silicon,and the reaction generated fine hexagonal SiC particles filled in the matrix,which was helpful to reduce the excess free silicon in the sample to improve the material strength.