Investigation Of Oxidation And Corrosion Resistance At High Temperature For GH2135Fe-based Superalloy

The GH2135Fe-based superalloy was used as the substrate alloy. Chromateconversion passivating film with different processing condition was used to modifythe surface of experimental GH2135Fe-based superalloy, which lead to the improvingoxidation and corrosive resistance. Some measured method was employed to detectthe oxidation kinetic curves and microstructure of the oxidation scale. Theexperimental results revealed:The optimize prepared condition for chromate conversion passivating filmincluded: concentration of Na2CrO₃was0.5wt.%. The bathing time was30second.The temperature of vacuum heating treatment was600℃, and the time of vacuumheating treatment was3h. The microstructure of chromate conversion passivating filmwas consisted of Fe（Cr）O₃with rutile microstructure and small amount of Cr₂O₃. Theexchange from six valence chromium to three valence chromium was attributed to thevacuum heating treatment, which was in accord with the environmental issues.The spllation of oxidation scale led to the fluctuations of oxidation kinetic curvesat the range of experimental temperature for GH2135Fe-based superalloy. Therich-Fe oxidation phase was formated on the primary surface, and the rich-Croxidation phase with rutile microstructure was formated on the subsurface. Thecontinuous and density oxidation film, improving the oxidation resistance, wasformated, which was attributed to chromate conversion passivating film. and thesimilar content compared to oxidation scale on the subsurface was obtained.The improving of corrosive gain mass was obtained with elongation of corrosive timein Na₂SO₄corrosive media at500℃for GH2135superalloy. The decreasing gain massat primary corrosive stage and the existence of distinct pregnancy was obtained attemperature range of600～700℃. The best comprehensive corrosive propertied waschromate conversion passivating film prepared by Na2CrO4at tested condition.The corrosive kinetic curves were fit to the parabolic rule inNa₂SO₄+20wt.%NaCl corrosive media at500,600and700℃for all the testedsuperalloys. The oxidation scale of Fe₂O₃was obtained in the process of mix saltcorrosive media. With elongation of corrosive time, the microcrack was occur, whichled to the spallation. The residual stress was due to the quick grown of oxidation scale,which was the main reason. Alkaline fusion between the chromate conversion passivating film and the corrosive media occur at the primary corrosive stage until thedeplete of rich-Cr oxidation phase. And then the similar corrosive process as thesubstrate alloy occur.The corrosive mechanism was contingent on the moving direct for the differentalloyed elements in tested alloy. The alloyed element of Fe was outward diffusion,and then formated rich-Fe oxidation, which was the main reason for the formation ofrich-Fe oxidation phase. At the same time, the alloyed element of Ni was inwarddiffusion. The diffusion of Cr element was not clear.