| Fe-Cr-Al electrothermal alloy has the advantages of high resistance,small temperature coefficient of resistance and high temperature oxidation resistance.It is one of the most widely used electrothermal materials in Chinese industrial production and household appliances.However,the Al2O3 oxide film produced in air is not enough to protect the matrix from working in a complex environment for a long time,and its service life is still limited.Therefore,it is very important to improve the properties and service life of Fe-Cr-Al alloy by surface treatment.In this paper,the surface treatment of Fe-Cr-Al alloy by constant current anodic oxidation was used to form metal oxide ceramic film.The structure and properties of the anodized film were observed and evaluated by surface morphology,resistivity,electrochemical,mechanical and thermal fatigue tests.Firstly,the effect of oxidation time on the performance of anodized film in alkaline electrolyte was investigated.Secondly,the effect of adding different inhibitors to sulfuric acid electrolyte on the anodized film was studied.According to XPS test and voltage-time curve analysis of anodic oxidation in alkaline electrolyte,it can be known that anodizing can be divided into four stages.The elements involved in oxidation and the oxidizing substances generated are different in each stage.The resistivity of the anodized film was tested using a four-probe resistivity tester,and the results showed that the electrochemical anodized film has better insulation than the conventional heated oxide film.The anodic oxidation time was investigated by SEM,electrochemical test and nanoindentation test.It indicated that the film has the best surface morphology,corrosion resistance and mechanical properties when the oxidation time was 60min.After 1000 thermal fatigue cycles at a fatigue temperature above 700°C,no obvious fatigue cracks were found on the surface of the sample for 60min,indicating that the film has good high temperature resistance.Y2O3 was added to sulfuric acid solution as electrolyte to anodize Fe-Cr-Al alloy.The results showed that only Al2O3 and Cr2O3 oxides were produced in this electrolyte,Fe on the alloy surface was dissolved in the sulfuric acid electrolyte,and the film had conductivity.The addition of Y2O3 can significantly improve the corrosion resistance,hardness and Young's modulus of the alloy.When the amount of Y2O3 is 2.5g/L,there are no holes and other defects on the surface of the anodized film,which has the best surface morphology.At the same time,the electrochemical properties,mechanical properties and thermal fatigue results of the sample are better than other samples.Al2?SO4?3·18H2O was added to sulfuric acid solution as electrolyte to anodize Fe-Cr-Al alloy.The results showed that the addition of Al2?SO4?3·18H2O has no effect on the surface material composition of the film layer,and the film layer has conductivity.Adding Al2?SO4?3·18H2O to the electrolyte can increase the concentration of Al3+in the solution,reduce the precipitation of aluminum elements on the alloy surface,and promote the combination of Al and O to generate Al2O3.When the addition amount is20g/L,the film has the best performance and can work for a long time in a high temperature environment,which effectively prevents the alloy from further oxidation at high temperatures. |
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