Study On Oxidation Failure Mechanism Of Cr20Ni80 Alloy During Heating

The high-resistance electric heating alloy is a key material of electric heating which is widely used in the fields of family and industry,and has a large market capacity.Gansu Province has rich nickel and other non-ferrous metal mineral resources,Jinchuan Group Nickel Alloy Co.,Ltd.is the first major enterprise to work in the production of ordinary high-resistance electric heating alloy.The long-life high-resistance electric heating alloy device for industrial furnace for deep processing of resources can improve the service life of the resource by improving the service life of the product.At present,our country has been able to produce various kinds of electric heating alloys and develop new type of electric heating alloys.However,it has been found that the life of Cr20Ni80 alloy produced in China is much lower than that of similar products abroad.The heating time and the temperature are two important influence factors for the performance of the Cr20Ni80 electric heating alloy material.For example,the formation and the destruction of the oxide film on alloy surface during the using process of the electric heating alloy plays an important role in the lifetime of alloy.In this paper,the damage mechanism of the oxide film of Cr20Ni80 alloy are investigated,in order to find the way to improve the oxidation resistance and increase the service life of the alloy.Therefore,this study has a certain degree of practical value.In this paper,the Cr20Ni80 electrothermal alloy wire is electrically heated by the equipment of high resistance electrothermal alloy rapid life meter to study the oxidation resistance of the alloy and the failure mechanism of the oxide film.The operating temperature of the Cr20Ni80 electrothermal alloy wire is 900¹100?.The rapid life measurement temperature of Cr20Ni80 electrothermal wire stipulated by the national standard?GB/T1234-2012?high resistance electrothermal alloy is 1200?.In this paper,the method of constant temperature continuous heating is used for the continuous oxidation of alloy samples in air.The oxidation temperature is 900¹100?.The surface morphology and the composition of the oxide film were analyzed by X-ray diffraction?XRD?,scanning electron microscopy?XRD?,scanning electron microscope?SEM?,and energy dispersive?EDS?.The failure mechanism of electrothermal alloy wire is also studied at 1200?.The curve of resistance changing with time is drawn at 1200?.The oxidation process of electrothermal alloy can be divided into three stages,the forming stage of oxide film.The stable stage of the oxide film,the failure stage of the oxide film.In the forming stage of the oxide film,the oxide NiO and NiCr₂O₄,formed by Cr and Ni elements on the surface of the alloy are mainly dense and uniform Cr₂O₃,to prevent the further oxidation of the alloy,and the failure stage of the oxide film is in the stable stage of the oxide film.During the oxidation process at high temperature,because of the stress in the oxide film of the alloy,the oxide film flakes a lot,and the loose porous matrix is exposed.The effective diameter of the alloy wire decreases due to the exfoliation of the oxide film,so the alloy wire quickly fails.The fracture surface of the alloy wire after failure was observed and analyzed,and it was found that there were many cracks and holes in the fracture surface of the alloy wire.Holes and cracks are important reasons for the failure of alloy wires.The formation of oxide film is determined by thermodynamics and kinetics.In this paper,the thermodynamics and kinetics of oxide film formation are studied,and the formation mechanism of oxide film is discussed.It is confirmed that the oxide film formed on the surface of the alloy is NiO,NiCr₂O₄,Cr₂O₃,SiO₂ from inside to outside.