Study Of The Kinetics And Properties Of Ion Nitriding On High-temperature Alloy GH901

Superalloy has been used in high temperature components of many fields because of its excellent performance.In this paper,a new type of ion nitriding technology,which is named after the double cathode glow ion nitriding,was used to nitrify the superalloy GH901 to improve the surface properties of the alloy,so as to expand the application range of the alloy.In this paper,the alloy was nitrided at 510?,560?and 610?for 20h,40h,and 60h respectively.The microstructure,properties,morphology and element distribution of nitrided layer of superalloy were investigated by Metallgraphic microscope,microhardness instrument,friction and wear tester,scanning electron microscope?SEM?,X-ray diffraction?XRD?,energy dispersive spectroscopy?EDS?.The ion nitriding kinetics of GH901 was studied by tracking the mass change of GH901 before and after nitriding,and the hot corrosion properties of superalloy before and after nitriding were studied by salt coating test.The corrosion kinetics in the process of thermal corrosion were measured and the corrosion products were analyzed.The results show that:In the study of nitriding kinetics,it was found that the weight gain of the alloy in the nitriding process was obviously dependent on the nitriding temperature,and the weight gain of the alloy increased with the increase of nitriding temperature.It is calculated that the diffusion activation energy?Ea?of GH901 is 173.96 kJ/mol,which is much lower than that of pure nickel.There is a linear relationship between the increase of alloy mass and the thickness of nitriding layer in the process of ion nitriding,and the fitting line slope is 0.07696 mg/cm²/?m.The main phase of nitriding layer after nitriding is?phase corresponding to matrix and CrN phase,but the prolongation of nitriding time and the increase of nitriding temperature promote the formation of new phase of Ni₄N.After nitriding,the surface of the alloy is granular,and almost all the N elements are concentrated in the nitriding layer.At the same time,the content of Cr element in the nitriding layer is higher than that in the matrix,while the content of Ni,Fe in the nitriding layer is lower than that in the matrix.After nitriding,the thickness of nitriding layer increases with the increase of time and temperature.The hardness of the alloy surface is improved,and the wear resistance is enhanced.In the hot corrosion test,the corrosion occurred firstly from the edge area of the alloy sample surface.With the increase of corrosion time,the corrosion products were gradually removed from the sample surface from the edge area.When the corrosion product of the upper layer falls off,the exposed area of the alloy was subjected to a new corrosion reaction until the corrosion product was formed and removed by an external force.Before the corrosion time was less than 50 h,the mass loss of the nitrided alloy was less than that of theunnitrided sample;after the corrosion time was more than 50 h,the mass loss of the nitrided alloy increased greatly and was much larger than that of the unnitrided sample.The main phase??phase?of the matrix is retained after the alloy is corroded,the corrosion products of unnitrided samples are mainly Na₂S,NiO,Na₂CrO₄,NiCrO₄,FeCrO₄,TiO₂ and Cr₂O₃.The corrosion products of nitriding treated samples are mainly NiO,Na₂CrO₄,NiCrO₄,FeCrO₄,TiO₂,Cr₂O₃ and CrN.