The Research On Argon-Arc Melt Injection NiCr-Cr₃C₂ Surface Composite Coating

In order to overcome problems with methods to produce composite coating, the argon-arc melt injection was used to make NiCr-Cr₃C₂ composite coating on the surface of Q235 steel. The microstructures and composition of the coatings were analyzed by means of optical microscope, SEM, XRD and EDS. Microhardness,wear resistance, erosion resistance and corrosion resistance of the composite coating and substrate were investigated by means of respective equipments.The results show that the argon-arc melt injection NiCr-Cr₃C₂ composite coating has a good shape and without macroscopical defects. The composite coating and substrate integrate metallurgical joint. Complex microstructure is found in the argon-arc melt injection NiCr-Cr₃C₂ composite coating, which consists of Cr₃C₂,Cr7C3,M7C3 and ion-based solid solution. The difference of morpology in different zone of the composite coating is remarkable. Un-dissolved Cr₃C₂ + fine rich-chromium carbides M7C3 in the top of the composite coating, A number of un-dissolved Cr₃C₂ + rich-chromium radial carbides M7C3 with the un-dissolved Cr₃C₂ as the core in the middle of the composite coating and a few un-dissolved Cr₃C₂ particles + bundles of rich-chromium rhabditiform carbides M7C3 in the bottom of the composite coating.The microhardness of the composite coating is much higher than the substrate, on average, about 1490 HV0.1/10. The wearing capacity of the composite coating is much less than the substrate. The major wear mechanism is abrasive wear. The erosion resistance of the composite coating is far better than that of the substrate under the same erosion condition. The protecting effect of the un-dissolved Cr₃C₂ and the supporting effect of the substrate cooperate and increase the erosion resistance of the composite. The erosion rate of the composite coating increases then turns to decrease with increase of eosion angles, increases again at last. The composite coating reveals some typical features between plastic material and brittle material. The corrosion resistance of the composite coating is better than that of the substrate under the same corrosion condition. The addition of Cr can increase the electrode potential of the substrate,decrease the number of the microbattery,improve the corrosion resistance of the substrate effectively. Un-dissolved Cr₃C₂ and the rich-chromium carbides M₇C₃ have well corrosion resistance themselves,and on the other hand, they can reduce the number of primary cell and the electromotance is also decreased. The existence of carbide can improve the corrosion resistance of the composite coating.