Research On The Preparation Of Y₂O₃ Modified ZrB₂-SiC High Oxygen Barrier Coating And Oxygen Barrier Mechanism

As a desperately needed structural material for the aerospace strategies of major countries around the world,the poor oxidation resistance due to its sensitivity to oxygen greatly limits its engineering applications in aerospace vehicles.ZrB₂-SiC-based coatings are considered as coating materials that can provide effective oxidation protection for carbon structural materials because they produce glass films that effectively shield oxygen diffusion during oxidation.However,the bulk effect of the oxidation product crystal structure brings damage to the structural stability of the glass film and the coating,which directly weakens the synergistic oxygen barrier effect of the glass film and the oxidation products such as ZrO₂.In this thesis,based on ZrB₂-SiC-based composite coating,we add rare-earth oxide Y₂O₃ to the coating to stabilize the oxidation products and enhance the stability of the oxygen barrier structure of the complex glass film;we synthesize ZrB₂-ZrSi₂ composite powder by self-propagation at high temperature to achieve the effect of providing micro-zone repair for the oxygen barrier structure of the coating during the sintering process and reducing the oxidation activity of the coating,while strengthening the connection between the silicon-based elements and The composite ZrO₂ nanocrystalline particles are diffused to encapsulate the coating surface by solution combustion to weaken the high loss to the coating structure caused by the generation of self-generated glass film,and the"bionic glass film+self-generated glass film synergistic strengthening oxygen barrier mechanism"is proposed.The proposed"bionic glass film+self-generated glass film synergistic strengthening oxygen barrier mechanism"can provide all-round oxygen barrier protection for carbon structure materials and reduce the overall oxygen penetration rate.The main research contents are as follows.In this thesis,it was found that the production of glass films with a small amount of Y₂O₃ coating was more inclined to the parabolic oxidation mode,while the production of glass films with an excess or no Y₂O₃ coating was more in between the parabolic and linear oxidation modes,and Y₂O₃ promoted the production of more Y₂Si O₅ and Y₂Si₂O₇ in glass films,and Y³⁺replaced the ZrO₂ lattice with its atomic Y³⁺replaces the position of Zr⁴⁺in the ZrO₂ lattice,which has a similar radius,to form a solid solution,resulting in lattice distortion.At the same time,Y³⁺is a high field strength ion,which promotes the nucleation of oxidation product crystals and cuts off the continuous growth of crystals,and the crystal morphology evolves from dendrites to rounded granules of the coating.Compared with ZrB₂-SiC coating,the cumulative antioxidant protection efficiency of the coating added with 1%Y₂O₃ reached 99.142%,an improvement of 1.676%;the structure factor and inerting factor decreased by 22.600%and 53.352%,respectively;the final oxygen permeability and average oxygen permeability decreased by 87.853%and 65.578%,respectively,and several oxygen barrier performance indexes The final oxygen permeability and average oxygen permeability were reduced by 87.853%and 65.578%,respectively.The size of ZrB₂-ZrSi₂ composite powder prepared by self-propagating high-temperature synthesis technique is around 500-1000 nm,in which the bonding relationship between the two substances is different from mechanical mixing and there is also a chemical bonding mode.The appropriate amount of ZrSi₂ participates in the construction of high-quality glass films without destroying the oxygen barrier structure,preferentially generating ceramic phases such as ZrSi O₄;during the reaction process,the low melting point of ZrSi₂ leads to the formation of molten state while oxidizing ZrSi₂ at the beginning of the oxidation reaction,and at the same time,it works together with molten Si O₂ inside the coating to erode the zirconia particles,and the molten state material effectively The molten state effectively hinders the penetration of oxygen,which makes it difficult for the coating to be oxidized the closer it is to the carbon substrate,preserving the stability of the oxygen barrier structure.As the oxidation proceeded further until the end,the molten ZrSi₂ and glass were stripped from the coating surface due to volatilization,while the zirconium oxide particles grew out of the gradually depleted mother liquor in the form of nuclei,resulting in"coral dendrites",forming a structure with a large amount of oxide remaining on the coating surface and a large depletion zone in the glass film.The coating with a 9:1 ratio of the two substances in the self-propagating high-temperature synthetic ZrB₂-ZrSi₂ composite powder has more excellent oxygen barrier properties.After oxidation at 1700°C for 100min,the oxygen permeability of the coating is much lower than that of the coating without the addition of ZrSi₂,and its structure factor and inerting factor both exhibit the lowest values of 0.062%and 1.167%,respectively,compared with the coating without the addition of ZrSi₂ coating by 49.18%and 28.711%,respectively.Based on the characteristics of glass film at high temperature,we propose the biomimetic film technology of"biomimetic glass film+self-generated glass film to strengthen the oxygen barrier mechanism".The increase in electron cloud density of the outer layer of Zrin the Y₂O₃ partially stabilized ZrO₂ nanopowders prepared by solution combustion synthesis technique increased the shielding effect,weakened the attraction of the nuclear charge to the inner layer electrons and reduced the binding energy,and the oxygen vacancies generated led to a larger absolute value of the net charge of O in the powder,resulting in the decay of its binding energy;the geometric mean of the overall grain size of the powder was 79.28±1.21 nm,and the corresponding particle size was 74.53 nm when the cumulative percent size distribution reached 50%.The bionic film formation technology and the self-propagation high-temperature synthesis technology can improve the structural stability of the SHS powder composite coating by suppressing the structural defects in the oxygen barrier process of the SHS powder composite coating,with a higher degree of oxide dispersion on the coating surface and preferential generation of ceramic phases such as zirconium silicate on the coating surface,and the actual thickness of the B-element depletion layer is lower than that of the untreated SHS powder composite coating.The actual thickness of the B-element depletion layer was lower than that of the untreated SHS powder composite coating;the mass change rate decreased by 18.335%,the structure factor and inerting factor decreased by 28.095%and 6.349%,and the final oxygen permeation rate and the average oxygen permeation rate decreased by 26.270%and 31.389%,respectively,which showed that the biomimetic film-forming technology had further improved the oxygen barrier performance of the coating compared with the self-generated film-forming treatment technology.The thesis has 53 figures,3 tables and 122 references.