| Mold, known as “the heart of casting”, is a very important component forcontinuous casting in steelmaking process, while copper plate is the core component ofthe mold. The stability and reliability of copper affect not only the surface quality ofsemis, but also casting speed and operating rate of the continuous casting machine, andthe production costs and efficiency. However, previous researches revealed that thelifetime of the mold is limited to the thermal cracks, the thermal deformation at themeniscus and the severe wear at the bottom of the mold. Therefore, research anddevelopment of the longer lifetime of mold has become the key factor to improvesurface quality of casting semis, reduce costs, and promote the equipment level ofcontinuous casting machine.In order to develop a high thermal conductivity and the wear-resistant layer on thecopper of mold, ZrO2-MoSi2agglomerated composite powder used for plasma-sprayingwas prepared by spray drying and vacuum sintering, at the same time,high-performance supersonic atmospheric plasma spraying equipment (HEPJet-highefficiency supersonic atmosphere plasma spray system) was used for preparation ofZrO2-MoSi2/CoNiCrAlY on the surface CuCrZr Alloy Plates. The microstructure andcharacteristics of the powder and compound coating were characterized by scanningelectron microscopy(SEM) and X-ray diffraction(XRD), further more, the effects ofmilling time, slurry composition and the temperature of spray drying on the powdergranulation were studied by laser particle size analysos and viscosity tester. Moreover,the bonding strength, thermal shock resistance were tested by tensile experiment andthermal shock experiment, the wear resistance and thermal conductivity of theZrO2-MoSi2composite coating and Ni-Co plating were determined by the wearexperiment and thermal conductivity analysis at the room temperature. Furthermore, in order to improve the wear resiatance of ZrO2-MoSi2composite coating, the MoS2self-lubricating film was formed on the surface of the composite coating bysulphurizing method.The main conclusions can be drawed as following:(1)ZrO2-MoSi2composite powders are suitable for plasma spraing, whichpossesses good agglomeration degree and well flowability, the average size of thepowders is about42?m, apparent density is2.17g/cm3.(2)The coating exhibiteds two microstructure composed of well-melted regions andpartially-melted particles. The fracture morphology of the coating was a typicalwave-layered structure. The longitudinal section of the compound coating is verydifferent from fracture morphology, it's not the typical wave-layered structure.(3)The compound coatings possessed high thermal conductivity and combinedstrength. The average combined strength was32.21MPa. Thermal conductivity ofcomposite coating was1.7W/(m.K), which is similar to the currently used Ni-Coplating.(4)The the composite coatings showed excellent resistance thermal shock. Thethermal shock resistance was tested at500?,600?and700?by water quenchingmethod, the results showed that the coating from cracks to failure were experienced131.3times,66.3times,34times for bullet-type specimens, and147.3times,65.7times,48.3times for coin-type specimen.(5)The composite coating after sulphurizing has excellent self-lubricatingantifriction effect and can improve the wear resistance of the composite coating. Theaverage width of wear print was332.18?m, the average loss of wear volume was17.5×10-9m3and the friction coefficient was between0.58to0.62. |
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