| The sintered material of MoSi2 intermetallic compound ceramic is widely used as high-temperature components for high temperature thermocouple,tail nozzle of rocket,heating element,and so on due to its excellent high temperature oxidation resistance.To obtain a protective coating with high temperature oxidation resistance,the excellent property of MoSi2 has been fully exploited by spraying its powder with plasma spraying equipment.In this paper,MoSi2-Al2O3 composite powder which was suitable for thermal spraying was prepared by spraying dry technology.By using these powder,MoSi2-Al2O3 high temperature protective coating was successfully prepared on the surface of 310S alloy by thermal spraying process.By analyzing the effects of spraying parameters,powder structure,powder ratio,preparation process on microstructure,mechanical properties,high temperature oxidation resistance of coating were studied.The main results are as follows:1.Study on spraying powder.The effects of powder modification with sintered,ratio of MoSi2-Al2O3 powder on microstructure,high temperature oxidation resistance of coating were investigated.The results showed that,after powder modification with sintered,agglomerated powder got nice sphericity,cohesion and physical properties,its phase transition degree of coating was lower which retain more t-MoSi2.The addition of Al2O3 could improve the toughness and reduce the phase transition of coating.The MoSi2-Al2O3 coating kept excellent microstructure and high temperature oxidation resistance because of complete SiO2 film was produced when ratio was 9:1 of MoSi2-Al2O3 composite powder.2.Study on spraying parameters.The effects of spraying distance and H2 gas flow rate on microstructure of MoSi2-Al2O3 coating were investigated.The results showed that,the better microstructure of coating were obtained with 140mm spraying distance,which came to conclusion by analysed the morphologies of powder sprayed in water and coating.By analysed morphologies,phase composition,porosity of coating,The results showed that powder melting degree and coating density increased when H2 gas flow rate increased,the better microstructure of coating were obtained with H2 gas flow rate of 15L·min-1.3.Study on preparation process.The effects of flame spraying and plasma spraying on microstructure,mechanical properties,high temperature oxidation resistance of coating were investigated.Results showed that,plasma spraying coating were superior to flame spraying coating in microstrcture because of excellent powder melting degree,uniform distribution of Si,O phase composition and good lamellar structure.The bonding strength of plasma spraying coating was 24.25MPa,increased by about 68%than flame spraying coating.The microhardness of plasma spraying coating were much higher than flame spraying coating.After high temperature oxidation test for 25h at 1200?,flame spraying coating was transform into powder with severe oxidation and spalling,plasma spraying coating wasn't transform into powder and showed better performance in oxidation resistance at high temperature because of high temperature production SiO2 sealed the cracks which prevented the oxygen spreading into coating. |
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