Study On The Surface Anti Oxidation Ablative Ceramic Coating Of Extreme Equipment Hot End Components

Refractory metals possess high melting points,excellent corrosion resistance,outstanding high-temperature mechanical properties,as well as ductility,thermal shock resistance,and creep strength,making them one of the most promising materials for extreme equipment applications.However,their performance in critical equipment parts is limited due to their inability to effectively resist high-temperature oxidation and erosion.To address this issue,the service performance of refractory metals can be improved by preparing anti-oxidation and erosion coatings on the surface of the matrix.This method can effectively reduce the damage caused by high-temperature gas flow to the material,prevent oxygen molecules from invading the interior of the matrix,and significantly improve its surface anti-oxidation and erosion resistance without affecting the basic properties of the alloy.The existing preparation technologies for thermal protection coatings on refractory metal surfaces mainly include plasma spraying,infiltration,slurry melting,and chemical vapor deposition.However,these technologies cannot simultaneously achieve the preparation of dense and thick ceramic coatings（≥200μm）.The existing material systems for thermal protection coatings on refractory metal surfaces mainly include precious metal,aluminum compound,and silicon compound coatings,but they cannot meet the long-term service requirements at higher temperatures（≥1800℃）.In recent years,ultra-high-temperature ceramic composite materials（typical coating system ZrB₂-Mo Si₂）have shown good resistance to oxidation and erosion.During the erosion process,it can not only generate a solid skeleton structure to resist gas flow erosion but also generate flowable oxides to improve the self-healing property of the coating.Therefore,it is a very promising anti-oxidation and erosion coating system for extreme equipment’s hot-end components.Based on this,this project proposes a new composite process for preparing ZrB₂-Mo Si₂ ultra-high-temperature ceramic coatings.Firstly,a gradient metal-ceramic coating（bottom layer 70wt%Mo-ZrB₂ and surface layer 32wt%Mo-ZrB₂）is prepared on the alloy matrix surface by plasma spraying to alleviate the thermal mismatch between the coating and the matrix.Then,the 32Mo-ZrB₂metal-ceramic surface layer is transformed into ZrB₂-Mo Si₂ composite pure ceramic coating by infiltration of silicon.Finally,the anti-oxidation and erosion properties of the ultra-high-temperature ceramic coating are evaluated using plasma beam technology.The specific research work is as follows:（1）Two types of Mo-ZrB₂ powders with 32wt%and 70wt%Mo content were prepared using spray granulation technology,and the powders had good sphericity and uniform element distribution.Plasma spraying technology was used to prepare a gradient metal-ceramic coating on the alloy matrix,with a surface layer of 32Mo-ZrB₂and a bottom layer of 70Mo-ZrB₂,using these spherical powders as raw materials.The spreading solidification process and microstructure evolution after a single droplet impact on the substrate were analyzed,and the effects of different process parameters on the surface,microstructure,and morphology of the final sprayed coating were studied to determine the process parameter window for high-quality coatings.（2）The plasma-sprayed Mo-ZrB₂ metal-ceramic coating’s surface layer was transformed into an ultra-high-temperature ceramic composite coating with a composite gradient structure（ZrB₂-Mo Si₂）using the infiltration of silicon process.The effects of different process parameters on the thickness,defects,microstructure,and phase composition of the obtained composite silicon infiltration coating were explored by changing the insulation time and temperature during the infiltration process.The process parameter window for the infiltration of silicon process was deduced.（3）The anti-oxidation and erosion performance of the samples prepared with the optimal process parameters were evaluated by plasma erosion at temperatures ranging from 1400℃to 2100℃.The surface phase composition,microstructure,and element distribution of the samples after oxidation and erosion treatment at different temperatures were comprehensively characterized and analyzed.The weight change data of the samples at each stage were recorded to intuitively reflect the differences in anti-erosion effects.Finally,by exploring the relationship between the cross-sectional morphology,phase composition,and element distribution in each temperature interval,the anti-oxidation and erosion performance and mechanism of the composite coating in each temperature interval were confirmed.In summary,this thesis uses a composite process of plasma spraying and infiltration of silicon to prepare a thick coating of ultra-high-temperature composite ceramics with few defects and reliable bonding for the first time.The dynamic erosion behavior and anti-oxidation and erosion mechanism of the coating at temperatures below 2100℃were revealed.The research in this thesis provides technical and material support for improving the surface thermal protection capability of refractory metal hot-end components in extreme equipment.This thesis includes 67 pictures,17 tables,and 107 references.