Study On Preparation Of Resistance To High Temperature Oxidation Coating For Porous Carbon Fiber Reinforced Ceramic Matrix Composite

Porous carbon fiber reinforced ceramic matrix composite materials are mainly used as insulation materials for thermal protection system in the field of aerospace,because of its low thermal conductivity and low density.But carbon fiber is easy to be oxidized,which limits the use of porous carbon fiber reinforced ceramic matrix composites at high temperature.In order to improve the oxidation and ablation resistance of Porous Carbon fiber reinforced ceramic matrix composite,ZrB₂-SiC/ZrB₂-MoSi₂ double layer coatings containing borosilicate glass were designed and successfully fabricated in this paper.The microstructures and phase composition of the coatings were characterized.The anti-ablation property and the oxidation mechanism of the coatings were evaluated.The Zr B₂-SiC-Glass coating was fabricated by slurry sintering process on porous carbon fiber reinforced ceramic matrix composite material.The optimize parameters of slurry preparation are:solid content 50%-60%,dispersant content 0.4%,binder content0.2%,ball milling time 6h.The better sintering parameter is 1300℃for 2h.The better content of borosilicate glass is 30%.The cracking problem of coating is solved by vacuum impregnation methods and adjustment process of slurry sintering methods.The ZrB₂-MoSi₂-Glass compound powder with spherical morphology and appropriate particle size was synthesized by spray-drying,which meets the requirements of plasma spraying.And induction plasma spheroidization（IPS）were selected to sintering the agglomerated powders in order to improve the density of the agglomerated powders.After IPS,the mobility and loose density of ZM-G30 powders are 49.1 s/50g and 1.72 g/cm³.Compared to the agglomerated powders,the mobility and loose density of ZM-G30powders increased 36.6%and 75.5%.The mobility and loose density of ZM-G15 powders are 46.3 s/50g and 1.86 g/cm³.Compared to the agglomerated powders,the mobility and loose density of ZM-G15 powders increased 32.1%and 61.7%.The ZrB₂-MoSi₂-Glass anti-ablation coatings were deposited by atmospheric plasma spraying（APS）on porous carbon fiber reinforced ceramic matrix composite material with ZrB₂-SiC-Glass as bond coatings.The microstructures and phase composition of the coatings were characterized by scanning electron microscopy（SEM）and X-ray diffraction（XRD）.The results show that the coating preserves the original composition and has a good bonding with the ZrB₂-SiC-Glass coatings.The anti-oxidation property of coating was tested by oxy-acetylene flame（OAF）.The results showed that the anti-ablation property of specimen improves significantly.With ablation distance 100mm-145mm（the temperature of OAF is about 1800℃-2400℃）,ablation time 200s-600s,the coating has no obvious loss of mass or thickness.when ablation distance is 100mm,after ablating 600s,mass ablation rate is merely-0.31×10^-4g/s.During the process of ablation,the coating forms a dense oxide layer,which is mainly consitituted by SiO₂ glass and mingled with some ZrO₂ and ZrSiO₄ ceramic particles in this oxide layer.Because the oxygen diffusion coefficient of SiO₂ glass is very low,the coating has good oxidation resistance.