Preparation And Properties Of CoCrAlTaY-based Cermet Coating For High Temperature Furnace Roller

The high-temperature furnace roll is one of the key spare parts in the metallurgical continuous annealing furnace.However,high-temperature furnace rolls are prone to oxidation,abrasion and nodules under the high-temperature and harsh service environment,which leads to their premature failure.In view of the above-mentioned problems of high-temperature furnace rollers,Co Cr Al Ta Y-Al₂O₃ coatings were prepared by air plasma spraying(APS)technology,and the spraying process parameters,alumina doping amount on the coating microstructure,mechanical properties,friction and wear performance,high temperature oxidation resistance and anti-nodulation performance were studied respectively.The anti-oxidation mechanism of Co Cr Al Ta Y-Al₂O₃ coating at high temperature and the friction and wear mechanism was revealed.The research work has achieved some valuable results,which provides a theoretical basis for its application on high-temperature furnace rolls,which helps to improve the production efficiency and quality of metallurgical products.The main conclusions are as follows:(1)The preparation process parameters of plasma spraying Co Cr Al Ta Y-Al₂O₃ coating were optimized,and its microstructure and mechanical properties were studied.Plasma spraying Co Cr Al Ta Y-Al₂O₃ coating has two typical structures,Al₂O₃ phase and alloy phase,which exist alternately and are dispersed evenly.The coating is mainly composed of Al₅Co₂,Cr,?-Al₂O₃,?-Al₂O₃,and?-Al₂O₃ phases.The spraying power,spraying distance,main gas flow and powder feed rate have no obvious effect on the coating phase;the optimal process parameters for plasma spraying Co Cr Al Ta Y-Al₂O₃ coating are spraying power of 40 k W,spraying distance of120 mm,main gas flow of 40 L/min,powder feed rate of 32 g/min.The resulting coating had porosity of 3.69%,hardness of 664.9 HV_0.3,and tensile strength of 78.6 MPa.(2)The effect of Al₂O₃ doping amount on the microstructure,mechanical properties and friction and wear properties were studied.As the doping concentration of Al₂O₃ increases,the porosity and hardness of the coating increase;the doping concentration of Al₂O₃ has no significant effect on the type of coating phase.The coating mainly contains Al₅Co₂,Cr,?-Al₂O₃,?-Al₂O₃ and?-Al₂O₃ phase.At room temperature,the increase of Al₂O₃ doping concentration makes the wear mechanism of the coating mainly abrasive wear,the wear volume and wear rate of the grinding ball gradually increase.At 700°C,the wear mechanism of Co Cr Al Ta Y-30%Al₂O₃ coating is adhesive wear,local oxidation wear and slight abrasive wear;at this time the wear rate of the grinding ball is only 2.25×10^-6 mm³?N^-1?m^-1.(3)The anti-oxidation and anti-nodulation performance of Co Cr Al Ta Y-Al₂O₃ coating at high temperature were studied.The oxidation rate constants of the coating at 950°C and 1050°C are 0.013 mg²·cm^-4·h^-1 and 0.066 mg²·cm^-4·h^-1,respectively.The oxidation law conforms to the parabolic law;the oxide film is mainly composed of Co Al₂O₄,Co Cr₂O₄ spinel phase,Cr₂O₃phase,?-Al₂O₃ and?-Al₂O₃ phase;after the nodulation test at 1000°C,fine particulate matter is formed on the surface of the coating,and the particle size increase with the extension of the heat treatment time;and Mn is more likely to react with the coating to form particulate matter,while the reaction with Fe is less reactive.