| For the crystallizer of continuous casting,the bonding strength,wear resistance and thermal shock resistance of protective coatings are demanded.In this paper,the WC-12Co/Ni Cr BSi coatings were prepared on the mold copper plate by high velocity oxy-fuel spraying technology(HVOF).In order to solve the difference in thermal expansion coefficient between the substrate and the coatings,the Ni bonding layer was electroplated on the Cr Zr Cu substrate.The effects of spraying parameters on the microstructure of WC-12Co/Ni Cr BSi coatings were studied,and the high temperature tribological properties of the coatings were also evaluated.The influence of coatings'thickness on thermal shock resistance of WC based metal ceramic coatings were analyzed,and the effects of Ni Cr BSi content on the microstructure and properties of the coatings were investigated.The research results had provided the data base and theoretical basis for its engineering application.The results were listed as follows:1.WC-12Co/Ni Cr BSi coatings with different kerosene flow rates and spraying distances were prepared by high velocity oxy-fuel spraying technology.The results showed that the phases composition of different coatings were basically the same.W2C and a small amount of Cr7C3and Co3W3C phases were generated by decomposition and decarbonization to a certain extent during spraying.Dense structure and high hardness were conducive to improve the wear resistance of the coating.The coatings prepared by the process with kerosene flow rate of 26 L/h and spraying distance of 345 mm had the lowest porosity of 0.11%,the higher hardness of927.0 HV0.3,the lowest friction coefficient of 0.46,and the lowest wear rate of 2.83×10-15m3/(N·m).The wear mechanism was adhesive wear and oxidation wear2.The effects of coatings'thickness on thermal shock resistance of WC-12Co/Ni Cr BSi,WC-10Co4Cr and WC-12Co coatings were studied.The results showed that the residual compressive stress of the coatings decreased with the increase of the coatings thickness.The thermal shock resistance of the WC-based coatings decreased with the increase of the coating thickness.When the coatings thickness were 100?m,the thermal shock resistance of the coatings were the best.The thermal shock resistance of WC-12Co/Ni Cr BSi coatings were better than the WC-10Co4Cr and WC-12Co coatings,which is attributed to the improvement of fracture toughness and thermal expansion coefficient.3.The influence of Ni Cr BSi content on the microstructure and properties of the WC-12Co/Ni Cr BSi coating was studied.With the increase of Ni Cr BSi content,the hardness of the coating decreases and the fracture toughness increases.The high temperature friction and wear test results showed that the friction coefficient of the coating does not change much,but the wear rate gradually increases with the increase of Ni Cr BSi content.When the Ni Cr BSi content is 80%,the coating has the highest wear rate,which increased nearly 138%.The wear mechanism of the coating is adhesive wear and oxidative wear.The thermal shock test results showed that the thermal shock resistance of the coating gradually improved as the content of Ni Cr BSi increased.When the Ni Cr BSi content is 80%,the thermal shock resistance of the coating is the best,which is mainly due to the increase in the fracture toughness and thermal expansion coefficient of the coating.It can be seen that the influence of Ni Cr BSi content on the high-temperature friction and wear properties of the coating is greater than that of on the thermal shock resistance. |
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