Study On Preparation And Properties Of Hydrogen Resistance Coatings Prepared With Ultra-low Oxygen Partial Pressure In Situ Oxidation

Energy is an extremely important strategy of the country.Among them,nuclear fusion energy is the preferred and ideal one to be applied for the human energy in the future.However,seepage and leakage of hydrogen and its isotopes are inevitable.In order to address this problem,the best solution is to prepare a ceramic hydrogen resistance coating on the surface of structural metal with irradiation resistance,high temperature chemical stability,and high permeability reduction factor（PRF）towards the hydrogen and its isotope.However,at present,nearly all the ceramic hydrogen resistance coating reported in recent literature needs to be prepared at the high temperature,which will cause easy cracking and peeling,resulting in the degradation of their anti-radiation performance,anti-high temperature performance and chemical stability.Up to now,ideal low temperature synthesis technology with higher and purer content of the ceramic hydrogen resistant coating has not been found,and the hydrogen resistance performance of the current coatings is not excellent and effective.This work mainly focused on the preparation technology of Ti C,Cr₂O₃andα-Al₂O₃ceramic hydrogen barrier coatings in low temperature with high purity and dense metal oxides or carbides as far as possible and obtaining the single composition coating far from the blocking problem.In-situ oxidation technology of ultra-low oxygen partial pressure coupled with pulsed electrochemical deposition,ionic liquid plating and ion implantation was designed and carried out for low temperature induction and preparation.Four kinds of composite coatings,TiO₂/TiC_x,Cr₂O₃-Y₂O₃,α-Al₂O₃and Al₂O₃/Cr_xO_y/Al_mO_n,were obtained.Their hydrogen resistance properties and mechanisms were investigated and analyzed.The main conclusions were obtained as follows:（1）Uniform and single Cr₂O₃ orα-Al₂O₃ coating shows exceptionally excellent resistance to hydrogen penetration.However,the phase transition temperature is much higher than that of sensitization of the stainless steel substrate,which is used as the structural material of nuclear fusion reactor.Therefore,it is very important to prepareα-Al₂O₃at low temperature.Therefore,in this work,the formation ofα-Al₂O₃was regulated,induced and promoted by in situ oxidation with ultra-low partial pressure of oxygen（Po₂）and ion implantation.The specific experimental operation process is to control the amount of Al doping by the way of ion implantation at a certain depth in the surface of pure Cr substrate.The experimental study of Al in the depth direction is Gaussian distribution.At the same time,by using in situ oxidation technology of ultra-low oxygen partial pressure（Po₂）,the formation ofα-Al₂O₃was successfully induced near the interface of Al₂O₃ and Cr₂O₃.Meanwhile,the content ofα-Al₂O₃gradually increased with the increase of the amount of Al ion implantation until reaching up to 17.0%,while gradually decreased with the depth direction.As a result,Al₂O₃/Cr_xO_y/Al_mO_n,a new type of dense hydrogen resistant composite coating,was formed at 600℃.The temperature is much lower than its phase transition temperature（1200℃）.The surface morphology evolution,phase composition,cross section structure of Al ion implantation dose,the stability and hydrogen resistance of Al ion implantation dose in hydrogen plasma environment was investigated in detail.The stability in the hydrogen plasma environment and resistance of hydrogen have been improved obviously,and the purpose of design and control has been achieved.（2）Becauseα-Al₂O₃ is formed by the lattice reconstruction ofγ-δ-θ-Al₂O₃at a high temperature above 1200℃,it’s thermodynamics is the most stable and its hydrogen permeability reduction factor（PRF）is also the highest.Therefore,it is expected to become one of the most promising hydrogen barrier material.However,such a severely high temperature will seriously weaken the mechanical properties of the matrix.Moreover,the thermal expansion coefficient difference between the coating and the substrate leads to the formation of a large number of cracks in the coating.Therefore,it is quite a challenge to prepareα-Al₂O₃at low temperature.Moreover,since Cr₂O₃andα-Al₂O₃have the same corundum crystal structure and similar lattice constants,Cr₂O₃can be used as the nucleation center and template ofα-Al₂O₃;So at the interface between Cr₂O₃andα-Al₂O₃,O^2-diffuses inward and V,_C,_r,diffuses outwardly to provide nucleation sites for the formation ofα-Al₂O₃,which induces and promotes the formation ofα-Al₂O₃.Therefore,considering that the formation of uniform and single Cr₂O₃andα-Al₂O₃should be closely related to the environment,and the formation of Cr₂O₃,which can be used as template effect and defect movement effect,the large formation ofα-Al₂O₃should be induced and promoted by using ultra-low oxygen partial pressure（Po₂）environment.Therefore,this part of the work is conducted on the basis of the previous using of ultra-low oxygen partial pressure（Po₂）In-situ oxidation technology combined with Al ion implantation technology to control the content ofα-Al₂O₃at 17.0%,the coupling technology of ultra-low oxygen partial pressure（Po₂）In-situ oxidation coupled with pulsed electrochemical deposition and ionic liquid plating technology is used,As a result,it effectively promotes the formation of near stoichiometric Cr₂O₃phase at 600℃,and the content of Cr₂O₃reaches up to 94.6%.The formation ofα-Al₂O₃successfully induced by the Cr₂O₃template effect,and the content ofα-Al₂O₃is up to 47.0%.which is176.5%higher than that of theα-Al₂O₃obtained by Al ion implantation on the surface of pure Cr matrix.（3）The presence of high-priced Cr ions seriously damages the hydrogen resistance of ceramic coatings.Also it is difficult to synthesize the homogeneous and single Cr₂O₃coating with low-price.In the process of exploring the synthesis technology and method of homogeneous and single Cr₂O₃coating,Cr is found to be easy to sublimate and diffuse outside at ultra-low oxygen partial pressure and high temperature,resulting in the formation of a large number of Cr vacancy and wrinkles.In order to solve this problem,Y³⁺（0.090 nm）,whose atomic radius is larger than Cr³⁺（0.062 nm）,is adopted.Therefore,to solve this problem,Y³⁺（0.090 nm）,whose atomic radius is larger than Cr³⁺（0.062 nm）,and the Y₂O₃has the characteristics of high melting point,high strength,high thermal chemical stability and high thermal conductivity.is adopted and chose to inhibit the sublimation and diffusion of Cr,using of ultra-low oxygen partial pressure（Po₂）In-situ oxidation technology.Therefore,Cr-Y coating has been formed on stainless steel substrate by pulsed electrochemical deposition and ion implantation.Then,the Cr₂O₃-Y₂O₃composite coating is prepared by using In-situ oxidation technology of ultra-low oxygen partial pressure（Po₂）at 600℃.The comprehensive performance analysis results show that the content of Cr₂O₃in the coating is up to 64.8%.Note that the content of Cr₂O₃is slightly lower than that of 74.7%prepared by pulse plating technology of our research group.However,the content of Y₂O₃increased by 1.3 at.%,which could compensate for the obvious decrease of Cr₂O₃and the increase of high-priced chromium CrO₃and CrO₂,and significantly inhibit the sublimation,migration,diffusion and wrinkle formation of chromium.（4）In order to prepare a TiC ceramic coating with uniform density,suitable thickness and high bonding force with the substrate is obtained without cracks and porosity defects.Coupling technology of In-situ oxidation in ultra-low oxygen partial pressure（Po₂）and ion implantation was designed.The TiC_xpassivation coating is formed on the surface of pure titanium substrate.Due to the carbon ion implantation,which is not limited by solubility and phase,the formation and existence of TiO₂and a non-stoichiometric TiC_xlayer with large hydrogen storage function are obtained（Note that the content of Ti C increases from 8.9%to 39.4%and the content of TiO₂decreases from 75.7%to 28.1%after hydrogen penetration）.The coating shows high stability,hydrogen absorption（Ti C）and hydrogen resistance（TiO₂）properties,further proving the reliability and versatility of the In-situ oxidation of ultra-low oxygen partial pressure（Po₂）and achieving the purpose of design and regulation.