Investigation Of HVOF Sprayed Wear-resistant Coating For Metallurgical Parts

In this study, two kinds of carbide coating(WC-Co＆Cr3C2-NiCr) wereprepared by HVOF technique using different spray parameters. Sealing process andthe effect of parameters on coating performance were investigated for thedevelopment of practical process and application in metallurgical roller.Microstructure and phase composition of the coatings have been examined by opticalmicroscope, scanning electron microscope (SEM, including EDS microanalysis) andX-Ray Diffraction. The porosity, bonding strength micro-hardness, nano-indentionand high temperature wear resistance were tested respectively. The sealing treatmentof coating was also investigated.The adjustment of parameters has little effect on coating compostion. The resultshows that HVOF sprayed Cr3C2-25NiCr coating is mainly comprised of Cr3C2、Cr7C3and little NiCr and Cr2O3phase. The coating porosity decreases with the increasing ofcombustion pressure, while the micro-hardness is opposite. With the increase ofpowder feed rate, the porosity and micro-hardness decrease at first and then increase.The coating sprayed at10.6bar combustion pressure and33.5g/min powder feed rateshows better basic properties and best high temperature wear resistance. The wearmechanism is abrasive wear and slight adhesive wear.The service life of furnace rolleris prolonged3times by HVOF sprayed Cr3C2-25NiCr coating.The imported WC-12Co powder was sprayed using different spray distance. Thespray distance has little effect on coating phase. The main components of HVOFsprayed WC-12Co coating is WC、η and W2C phase. HVOF sprayed WC-12Cocoating possesses low porosity(＜1%) and high hardness(HV11000). The coatingsprayed at340mm spray distance exhibits best performance. The repair of sink rollerand stabilizing roller using HVOF sprayed WC-12Co coating has proved to beefficient. And the service life of sink roller and stabilizing roller is prolonged3~4timesby HVOF sprayed WC-12Co coating.Four domestic WC-12Co powders with different particle size were sprayed byHVOF. Coatings all show low porosity、 high bonding strength and highmicro-hardness.And WC-1and WC-3coating, which have smaller particle size, have best structure propetties. HVOF sprayed WC-12Co coating possesses well hightemperature wear resistance, which shows low wear rate and rarely oxidation andpeeling. The wear mechanism of WC-12Co coating is abrasive. WC-1and WC-3,which have better microstructure properties, possess best wear resistance.The sealant shows well bonding performance, which enrich in surface layer butreduce in inner coating. There are little pits and scratch in worn surface of sealedcoating due to the protection of sealant against particle peeling. The frictioncoefficient of sealing coating is lower than unseling coating. And the result provesthat it is beneficial of sealant to coating wear resistance. Two kinds of sealant all showbetter performance in the decreasement of coating porosity and have better bondingperformance, which could avoid peeling during the proccess.