Study On Erosion Performance And Surface Protection Of 2D-C/C Composites For High Temperature Equipment

Due to the rapid development of manufacture technology for carbon/carbon?C/C?composites,its production cost reduced drastically and its application fields were also obtained great expand.Up to now,2D-C/C composites were widely used as thermal field parts in elevated-temperature equipment,such as protective materials for thermal insulation in high-pressure gas quenching vacuum furnace.However,during gas quenching,particulate matter may become entrained in the fast gas flows,and impingement with the C/C composites may result in material removal and reduce stabilization of the equipment.Therefore,the anti-erosion protection of 2D-C/C composites is necessary,and coating technology is an effective method.This paper first systematically studied solid particle erosion performance of 2D-C/C composites in different experiment conditions,including:impact time,impact angle,and impact particles velocity.It was found that the erosion mass loss of 2D-C/C composites increase linearly with erosion time,indicating that the erosion rate was stabilized.As the increase of impact angle,the erosion rate increases gradually,while the increment levels off.These two phenomena show that the erosion mode of 2D-C/C composites is typically brittle behavior.The impact velocity has a significant effect on the erosive wear of the 2D-C/C composites.The erosion rate?E?is related to particle velocity?V_p?as E = kV_pⁿ,and the value of n is 3.78?4.09 for different impact angle.At oblique impact angle,the ploughing grooves of fiber bundles and shearing of fibers are observed from the erosion morphology of 2D-C/C composites,while at normal impact angle,the characteristics of erosion morphology are matrix and fibers fracture,and fiber/matrix debonding.These indicate the erosion behavior of 2D-C/C composites is different in various impact angles.The major erosion mechanism of 2D-C/C composites are matrix fracture,fiber cracking,fiber breakage,and fiber/matrix debonding?and the additional polughing of fiber bundles and microcutting damage of fiber surface.Taking the research on erosion mechanism of the 2D-C/C composites as the foundation,the graphite coating was prepared by slurry method.The microstructure and erosion protective ability of the coating were investigated.The effect of graphite powder/phenolic resin powder with the different weight ratio on the microstructure and anti-erosion property was discussed.The results show that the coating slurry can be filled in the holes and cracks of surface of the composites,resulting in the densifying surface layer of the composites.With the increasing of graphite powder/phenolic resin powder weight ratio,the density of the coating increases while the flatness of the coating surface decreases,and the erosion protective ability of the coating increase firstly and decrease later.When the weight ratio is about 1:1,the coating shows the best erosion protective ability.Compared with the 2D-C/C composites,the coating improves anti-erosion property approximately 41.5%at the impact angle of 30� and 52.3%at normal impact.The improvement of the graphite coating on anti-erosion property can be explained that on the one hand the coating covers the surface of the substrate and replaces the substrate to erosion,on the other hand the coating slurry infiltrates into the substrate,enhancing the fibers bonding and increasing the phase interfaces,which can prevent the initiation and propagation of cracks during the erosion process.SiC particles were introduced into coating slurry to enhance the graphite coating.SiC particles increased the hardness of the coating,and improved the anti-erosion property.The effects of SiC particles content and size on the microstructure and erosion protective ability were investigated.With the increasing of the SiC particles content and size,the existent forms of SiC particles in the coating are from uniform embedding to local stacking,and the erosion protective ability of the coating exhibit the trend of increase first and decrease afterwards.The anti-erosion property of the coatings depends on supporting action and shadow effect.When the SiC particles content is 10%and the particle size is 75?m,the coating shows the best anti-erosion property.In this case,the erosion rate of the SiC particles enhanced graphite coating are 13.5 mg/g at the impact angle of 30� and 18.8 mg/g at the impact angle of 90�,improving the erosion protective ability of the coating without SiC particles enhanced approximately 21.5%and 18.9%,respectively.SiC coating was prepared by slurry and chemical vapor reaction method.The influence of the pre-coated carbon layer thickness on microstructure and anti-erosion property were investigated.The results reveal that with the increasing of the pre-coated carbon layer thickness,the density of SiC coating increases first and then decreases,while the thickness of SiC coating increases.The SiC coating is provided with excellent erosion resistant.The best coating can improve the erosion protective ability of the substrate about 30.9 times at the impact angle of 30� and 29.1 times at the impact angle of 90�.The improvement of SiC coating on anti-erosion property can be explained that SiC coatings form a harder and denser surface of the substrate,and the SiC coated the fibers can improve the cracking and breakage energy of the fibers.The anti-erosion property of the SiC coatings depends on the hardness and microstructure.By observing the erodent surface of SiC coated C/C composites,it can be found that the erosion mechanism consists coating cracking,fragmenting and brittle fracture,and the additional microplough and microcutting at oblique impact during the early stage of erosion,and subsequently fiber/matrix debonding,fiber breakage.In order to relieve the severe fragment of SiC coating during the erosion process,we added SiC whisker?SiCw?by silicon evaporation method to toughen the SiC coating.After introduction the SiCw,the nano-hardness and elastic modulus of the SiC coating are enhanced slightly,whereas fracture toughness of the SiC coating is enhanced to a great degree(from 3.43 MPa�m^-1/2 to 5.37 MPa�m^-1/2)due to the uniform distribution of the SiCw.The toughening mechanism includes microcrack bridging by the whiskers,whisker pullout,and crack deflection.Compared with the SiC coating without SiCw toughened,SiCw toughened SiC coating improves the erosion protective ability approximate 45.3%at the impact angle of 30� and 62.4%at the impact angle of 90�.2D-C/C composites were connected to rigid carbon fiber felt by adhension bonding method and chemical vapor deposition technique,and then the thermal insulative and erosion protective composites were obtained.The density of the composite is about 0.35 g/cm³,which includes the ttiermal insulative layer with density of 0.20 g/cm³ and the erosion protective layer with density of 1.20 g/cm³.The bonding strength between thermal insulative layer and the erosion protective layer is higher than the tensile strength of rigid carbon fiber felt,indicating that the composite material can meet the need of actual use.The erosion rates of the composite material are 3.96 mg/g at the impact angle of 30� and 6.60 mg/g at the impact angle of 90�,which improve the erosion protective ability of rigid carbon fiber felt about 20.1 times and 20.5 times,respectively.