Microstructure And Properties Of Ion Plating Gradient CrN_x Film

Solid particles erosion(S.P.E.) is one of failure forms of the steam turbine blades,and the plating treatment on the materials surface of steam turbine blades with erosion-resistance coatings is a main method to improve the properties of solid particle erosion-resistance.The gradient CrN_x film was deposited on 2Cr10MoVNbN substrate using Ion-plating technique.The component,structure and properties of coatings were examined.The chemical compositions,phases and microstructures of CrN_x coating were determined by the electron-probe X-ray microanalysis(EPMA),X-ray diffractometer(XRD),X-ray photoelectron spectroscope(XPS) as well as transmission electron microscope(TEM) and scanning electron microscope(SEM).The residual stress and surface roughness were measured by X-350A X-ray stress testing instrument and TR2000 surface roughness instrument,respectively.The bonding strength between coating and substrate was examined by scratch test.The nanohardness and elastic modulus of CrN_x coating were measured by nanoindentation technology.The properties of both electrochemical corrosion and oxidation resistance on the high temperature were evaluated by the experiments of electrochemistry and oxide resistance, respectively.The S-N curves of the plated samples and substrate samples were measured using the three-point bending method,and took the fractographic analysis of the fatigue samples,finally analyzed the influence of the CrN_x gradient film on the fatigue properties of substrate.The results show that the microstructures of Ion-plating CrN_x gradient coating were compact,having few defects;The coating was composed of CrN and Cr₂N phases,which distributed gradiently.The phase distributions from the surface to the interface of the film-substrate were CrN+Cr₂N,Cr₂N+Cr, Cr₂N+Cr+Fe-Cr,respectively.The elements of Cr and N distributed with a certain variation of gradient,and the interface was Cr-rich and N-rich.The interfacial adhesion was relatively higher due to the preparation of the transient layer.The surface roughness of the plating samples had a little increment,and all of them were approximately 0.70μm.It had high compressive residual stress in the surface of the CrN_x film,which was above 1.3GPa,decreasing gradually with the increment of the depth from the surface.The nanohardness of the CrN_x film was up to 23.12GPa,and the interfacial nanohardness was 10.95GPa.The average value of elastic modulus of the CrN_x film was 326.24GPa.The higher hardness of the CrN_x film had significant effect on the property of solid particles erosion-resistance.The CrN_x coatings show excellent properties of corrosion resistance, superior oxidation resistance and thermal fatigue behavior.The results showed that the influence of the fluctuating stress on plated samples was greater than that of substrate samples.The CrN_x film obviously increased the fatigue life at low fluctuating stress due to its strengthening to the samples,and the fatigue limit increased by 7.3%;The CrN_x film made the fatigue life decrease,and datas of fatigue test was largely dispersive at high fluctuating stress due to the relatively high sensitivity of CrN_x film to the notches.The fatigue cracks of the ion-plated samples nucleated on the surface of samples and propagated by the Close - Wedge mechanism in the CrN_x film.The analysis show that the CrN_x film can adapt to the working environment of the steam turbine blades,so it can be used on the surface of steam turbine blades to increase the solid particle erosion resistance.