Study On High Temperature Oxidation Behavior Of Inconel740H Alloy Used In Ultra Supercritical Unit

With the continuous improvement of the operating parameters of the thermal power unit,the service environment of the boiler reheater and superheater tubes need to face becomes more and more severe.The materials used to produce these components must be equipped with good resistance to high temperature oxidation as well as corrosion of soot.It is of great significance to investigate the high temperature oxidation resistance and and the oxidation corrosion performance of Inconel740 H.In this paper,the high temperature air oxidation experiment of Inconel740 H alloy was carried out.Experimental study on the high temperature oxidation of airwater vapor mixture and the oxidation corrosion of high temperature coal gas were carried out by using self-designed devices.The weight gain of the samples were measured by the method of discontinuous increasing weight,and the kinetic curves were drawn.The morphology and structure of the surface and cross section oxide film were observed by scanning electron microscope?SEM?after high temperature experiment.The composition of oxide layer was analyzed by energy dispersive spectrometer?EDS?.The phase composition of the surface oxide layer was analyzed by X ray diffraction?XRD?.The law of oxidation kinetics of Inconel740 H in different environments were studied.And the influences of temperature and time to oxidation corrosion products were studied as well.The experimental results show that the oxidation rate of Inconel740 H increases with the increase of temperature and time.However,the specific kinetics of oxidation corrosion is different.The oxidation kinetics curves in the air vapor at 700? and800? follow the parabolic law.The water vapor oxidation kinetics curves in 900?follows the linear law.For air oxidation,the linear rule is observed at 700? 100 h,while the parabolic law is observed at 800? and 900?.The corrosion of coal flue gas at 700? and 900? follows the parabolic law.Water vapor can accelerate the oxidation.Under the same temperature,the oxidation weight gain of water vapor environment is greater than that of air environment.The corrosion of coal flue gasincludes two processes: the formation of oxide film and the corrosion of oxide film.Therefore,the oxidation corrosion of the sample increases slowly or even decreases.It is found that the surface oxide film is mainly composed of Cr₂O₃ after short time oxidation.With the extension of oxidation time,the phase of the oxide film transites.The film is mainly composed of spinel NiCr2O4 and chromium titanium oxide.After long time oxidation,Al₂O₃ and TiO₂ are formed.After the corrosion of high temperature coal flue gas at700?and 800?,the oxides are mainly composed of Cr₂O₃ and SiO₂,also contain some Ni C and sulfur.After a long time of corrosion,the Al₂O₃ based oxide exists.The porosity of the oxidation corrosion product exists in the layer after 300 h coal gas corrosion at 800?.After 900 h of coal flue gas corrosion,the compounds include Cr₂O₃,Al₂O₃,Ni C,SiO₂ and mixed oxides of chromium and titanium.After long time air oxidation at 900?,the surface oxide film spalling phenomenon occurs.After the oxidation of 120 h at 900?,the oxide film on the surface of the sample was broken.Oxide film spalling was observed after long time air oxidation and air-water vapor oxidation.The material can not meet the requirements of long-term service at 900?.