Preparation Of Rare Earth Multicomponent Composite Oxidation Resistant Coating By Slurry Method

Molybdenum is a strategic metal with excellent properties.It has good corrosion resistance,excellent high temperature creep resistance and high hardness.It has good processing performance and is widely used in high temperature structural materials and heating elements in basic industries.As an important component of glass electric melting furnace electrodes,with the rapid development of glass manufacturing industry,the demand for molybdenum products in the glass electric melting industry has increased greatly.The molybdenum electrode needs to be exposed to the air at high temperature for up to a week during the temperature rise in the empty kiln,but the oxidation resistance of molybdenum is poor in the high temperature environment.The way to solve the problem of high temperature and easy oxidation of molybdenum electrode is to prepare a high temperature anti-oxidation coating on the surface of molybdenum electrode.Its main advantage is that the coating and the substrate can be processed separately without affecting each other.It can maintain the excellent performance of molybdenum substrate and the cost is low.The use of high temperature anti-oxidation coating is an effective solution.In this paper,MoSi₂ coating and Y₂O₃-glass coating was prepared on the surface of molybdenum substrate by slurry method.Then composite high temperature oxidation resistant coating was prepared on the surface of molybdenum substrate by slurry method.The interior of the composite coating is a Mo Si₂ coating and the exterior is a Y₂O₃-glass coating.The microstructure of the coating before and after oxidation was observed by SEM.The phase composition of the coating before and after oxidation was analyzed by XRD combined with EDS.The resistance of Mo Si₂coating,Y₂O₃-glass Coating and composite coating at high temperature was tested oxidation properties.The main conclusions are as follows:Adding La₂O₃ in the coating process can improve the preparation efficiency of Mo Si₂ coating and increase the thickness of the coating.With the increase of the amount of La₂O₃,the phase composition of the coating did not change,mainly consisting of the Mo Si₂ phase,and the thickness of coating increased first and then decreased.When the amount of La₂O₃ was 0.7 wt.%,the largest thickness of coating was 149.6?m.When the slurry composition is fixed,the thermodynamic formula is satisfied between the total coating thickness(h)and the heat treatment temperature(T):ln(^1/2h)=-_?+C₀(E_a is the activation energy of the coating growth process,R is the gas constant,and C₀ is the constant);At 1000?,the growth of the coating satisfies the kinetic curve formula:h=a^1?2+(7(the unit of h is?m,the unit of t is hour,and a and b are constant).The anti-oxidation mechanism of the coating is a consumption-reactive protection mechanism and an inert melt film shielding protection mechanism.The Mo Si₂ coating with a thickness of about 60?m prepared by slurry infiltration provides good oxidation protection to the molybdenum matrix at800-1200?,but with the further increase of oxidation temperature,at 1300?oxidation temperature,due to corner effect caused by the thermal expansion mismatch,and consumption of Mo Si₂ coating shortens the oxidation life of the coating.Adding Y₂O₃ to the coating can reduce the softening point temperature of the glass,refine the structure grains,increase the high-temperature stability of the glass coating,and adjust the thermal expansion coefficient of the glass.And it do not stain the glass.In addition,yttrium oxide can form yttrium silicate with silicon oxide at high temperature.and yttrium silicate is an anti-oxidation coating material.With the increase of the content of Y₂O₃,the temperature of the softening point of silicate glass is continuously reduced,and the crystallization exothermic peak is also getting lower and lower.After the Y₂O₃-glass coating with 10%Y₂O₃ content and a thickness of about 300?m is oxidized at 1200?,the coating surface is complete,the sample gains less,and the performance is excellent,which can meet the oxidation resistance requirements at the oven temperature.The surface of Y₂O₃-glass coating is complete and dense after oxidation.The cross section is divided into transition layer,middle layer and outermost layer.The transition layer is mainly Mo O₂ and Mo O₃,the middle layer is mainly Ba Mo O₄,and the outermost layer is mainly Si O₂.The anti-oxidation mechanism of Y₂O₃-glass coatings is a mutual-melt reaction type protection mechanism and an inert melt film shielding type protection mechanism.The MoSi₂ inner coating with a thickness of about 80?m was prepared on the surface of the molybdenum substrate by slurry infiltration method,and the Y₂O₃-glass coating with a thickness of about 300?m was prepared by slurry coating method to prepare the composite coating.The composite coating forms three layers in the oxidation resistance process,the outermost layer is mainly Si O₂,the middle layer is mainly Mo Si₂,and the innermost layer is mainly Mo₅Si₃.The composite coating can provide good oxidation protection to the molybdenum substrate below 1400?,and protect the substrate from oxidation for 36 h in an aerobic environment at 1500?.