Study On Microstructure Of Plasma Nitriding Layer Of Superalloy

The iron-base superalloy GH2132 and nickel base superalloy GH33 are prepared to be plasma nitrided at different temperature:400 ℃、450 ℃、500 ℃.The phase composition,chemical composition and microstructure of the nitrided layer were investigated by X-ray diffraction(XRD),optical microscope(OPM)and scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS).The tribological properties of nitrided and untreated alloy were evaluated comparatively.The article had analyzed the microstructure and properties of the nitriding layer of iron base superalloy and Ni base superalloy at the same nitriding temperature.The following conclusions are reached:Nitriding of iron-base superalloy:1.The nitriding layer is mainly composed of N saturated solid solution in iron-base superalloy at different temperatures.And the double layer structure produced in iron-base superalloy(γN1 and γN2)and the N content in the surface layer γN1 and the sublayer γN2 is 18.98%～11.49%and 5.87%～5.32%.In addition.2.XRD results showed that large lattice expansion and lattice distortion occurred on γN1,but low expansion and less distortion on the γN2,relative to an ideal fcc structure.3.Discontinuous precipitation of γN1→CrN +γ-Fe occurs at the phase boundary of N saturated solid solution.4.The nitrided superalloy surface exhibited high hardness and wear resistance.And both the γN1 and γN2 layers showed better corrosion resistance than the untreated substrate.Nitriding of nickel base superalloy:1.The nitriding layer is mainly composed of N saturated solid solution and nitrides phase of(Cr,Al,Ti)N.2.Obviously,the lattice parameter of the γN phase is increased,but there is no obvious change in the lattice parameters of the γN phase at different penetration depth,that is,relative to an ideal fcc structure.3.The nitrided superalloy surface exhibited high hardness and wear resistance.