Processing And Microstructure Of High Temperature Oxidation Protection Coatings On C_f/SiC Compsites

Because of the excellent combination properties under high-temperature circumstance,carbon fibers reinforced silicon carbide composites(Cf/SiC)can become a widely applied structure material in Aeronautics and Astronautics field.However,carbon fibers will oxidized under high temperature,which cause the performance reduction and limit the application of Cf/SiC.And make an anti-oxidization coating on the composites is an effective method to solve this problem.This paper use slurry combined with high-temperature melt infiltration to make a anti-oxidization coating with some thickness on the composites,and investigate the microstructure of precoating and coating.The slurry is mixed by phenolic resin and different powders(B4C and graphite),and homogeneously brushed on Cf/SiC substrate by self-made equipment which can effectively control the thickness of slurry.After curing and carbonization,the precoating is obtained.Then,use two kind silicon-zirconium mixed powders which contain 26.5wt%Zr and 50 wt%Zr to melt infiltrate on the precoating under high-temperature and vacuum environment,and got three kind anti-oxidization coatings(SiC coating,ZrC-SiC/SiC coating and ZrB2-ZrC-SiC/SiC coating).The coatings phase constitutes and microstructure characteristics were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM)with attached Energy Spectrum Analysis(EDX).The main results are as follows:(1)The as-prepared precoating which only use pure graphite powder possesses complete smooth surface and dense structure,while adding B4C on the basis of graphite,the surface is uniform and surface.The pores are mostly concentrated at the junction of B4C particles and C.(2)The thickness of SiC coatings which prepared by graphite is between 70～100μm。The increase of the thickness of the coating is enhanced with the content of graphite.but too many graphite content form defects in the coating.40wt%graphite is better content to prepare overall effect coating.(3)The main phases of ZrC-SiC/SiC coating which adding B4C and graphite are SiC and ZrC,containing a small amount of C.The morphology of the coating is characterized by the distribution of ZrC and SiC inclusions.Reaction is better when the cont of Zr is 50wt%than Zr is 26.5wt%.the main phases of ZrB2-ZrC-SiC/SiC coating which adding B4C and graphite are SiC,ZrB2 and ZrC,containing a small amount of C.The morphology of the coating is characterized by the distribution of SiC and ZrB2+ZrC inclusions.The coatings which adding 30wt%,50wt%,70wt%B4C are prepared respectively.the content of B4C is low,the amount of ZrB2+ZrC in the coatings is relatively small,while the SiC is relatively more,with the increase of B4C content,and increase the content of ZrB2+ZrC,and more obvious ZrC phase can be observed in ZrB2+ZrC..