| The process and anti-ablation property of ZrB2/SiC coatings deposited on C/C by APSwere researched in the paper. The Induction Plasma Spheroidization (IPS) was selected tosintering the ZrB2/SiC agglomerated powders in order to obtain the ZrB2/SiC complexceramic powders fit for the Atmosphere Plasma Spraying (APS), the mechanism andcontrolling method of sintering process for the ZrB2/SiC agglomerated powders treated byIPS were researched; according the theory of creation of plasma plume character, theplasma plume field was controlled in order to fix the request of ZrB2/SiC powders melting,and obtain the ZrB2/SiC coating with low porosity and high bonding strength, and therelation between character of plasma plume and character of coatings was also researched;the anti-ablation property of ZrB2/SiC coating under different ablating flame was evaluated,the development of coating character was revealed and the failure mechanism wasdiscussed.When the ZrB2/SiC agglomerated powders was treated by IPS, as the temperatureelevated, the eutectic of ZrB2and SiC occurred, the slag covered the particles and pour thedefects of the powders, and after the rapid freezing, the rapid melting&freezingorganization formed. The rapid melting&freezing organization could modify the bondstyle of particles and pour the defects to improve the density and strength of the ZrB2/SiCpowders. The powder could be feed steady and obtain the integral deformed particles afterAPS. During IPS process, the parameters of device and the size of agglomerated powderswill affect the sintering ratio of ZrB2/SiC powders. The optimized parameters for IPSsintering the ZrB2/SiC agglomerated powders is: size of agglomerated powders5～70μm;flow rate of H26SCFH; flow rate of Ar65SCFH; chamber pressure12Psig; the rotatingspeed of powder feeder4rpm，and the last sinter rate of ZrB2/SiC agglomerated powders is71.3%.According the theory of pinch process of plasma plume, the plasma field controllingdevice (PFC) was designed. The lost energy of plasma plume will be reduced after thepinch process was prolonged, and the space range for heating and accelerating powders wasexpended. After the PFC was loaded, the temperature and speed of plasma plume was elevated compare to APS. The temperature and speed of powders after fly through thecontrolled plasma plume were also elevated uncommonly, and the density and bondingstrength of coating improved significantly. The optimized parameters of PFC-APS obtainedby orthogonal test design is: spraying distance65mm、power950A、Ar flow rate90SCFH、He flow rate55SCFH，protect gas pressure0.5MPa, and the porosity of coating is8.76%，the bonding strength of coating is13.12MPa.The property of anti-ablation of ZrB2/SiC coating was test by Oxy-acetylene flame(OAF) and supersonic combustion flame (SCF).The result showed that the anti-ablationproperty of C/C was improved significantly, it can enduring higher temperature flame andhave longer lifetime during ablation. The ZrB2/SiC coating with25vol%SiC mixtureratio could persist600s at50mm ablated distance during OAF test, and persist180sat140mm ablated distance during SCF test. Although the flames obtained fromOAF and SCF have different character, but the ZrB2/SiC coating changed along thesame process. There were three stage during the development process of ZrB2/SiCcoating under ablation test including: the passive oxidation of SiC, the activeoxidation of SiC and evaporation of SiO2.The passive oxidation of SiC occurred atthe surface of the ZrB2/SiC coating, and the melted SiO2will pour the defects ofcoating surface blocking the penetration of O2from outer position to inside coating.The active oxidation of SiC will make the Si atoms collected at the surface ofcoating and formed film. The evaporation of SiO2will cause the absence of meltingfilm, and the detects will not be sealed, the coating will failure rapidly. |
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