Influence of spray distance on erosion wear resistance of plasma sprayed WC-12Co coating(2)

       The atmospheric plasma spraying (APS) process involves the extremely complex heat transfer and flow of the plasma arc, the interaction between the powder particles and the plasma jet, and the molten particles and the substrate. This makes the overall performance of the coating extremely important for the type of spray gun and the spraying distance. sensitive. Liu Yankuan and others used Fluent software to simulate HVOF flame flow, revealing the effect of flame flow velocity and temperature on particle velocity and temperature during spraying. Wen Kui et al. used the SprayWatch3i online monitoring system to measure the temperature and velocity of the Al2O3-3TiO2 particles in the plasma jet generated by the F6 atmospheric plasma spray gun under different nozzle conditions, and studied the degree of flattening of the particles and the coating performance. In the spraying process, the relationship between particle speed and temperature is contradictory. Under the same spraying distance, if you want to increase the flying speed of the particles, the heating time of the particles will be shortened, and the temperature of the particles will be reduced; if you want to increase the particles At higher temperatures, the speed of the particles will decrease. Therefore, in the spraying process, it is necessary to obtain a better particle temperature and speed coordination (that is, a suitable spraying distance) to obtain a high-quality coating.<br/>

WC-12Co hard coating is widely used in all aspects of industry due to its good wear and corrosion resistance. V·Bonache et al. used plasma spraying to prepare micro-structured and nano-structured powder WC-Co coatings. The study found that when the current is 625 A, the weight loss rate of the micro-structured WC-Co coating is greater than 90 at an erosion angle of 45°. °Erosion angle. Wang Haijun et al. used the HVOF method to prepare the WC-Co coating, and studied the erosion and wear properties of the WC-Co coating at an erosion angle of 30° and 90°. The study found that the weight loss rate was greater than 30° when the erosion angle was 90°. The failure form of the coating is the fatigue peeling of the coating. Li Yang et al. used the HVOF method to prepare the WC-Co-Cr coating, and analyzed the erosion behavior of the slurry at 15°, 45°, 75°, and 90° attack angles of defects such as pores and layered structure of the coating. At present, there are many reports on the performance of WC-Co coating prepared by plasma spraying with different process parameters, mainly focusing on the current and main gas flow; the research on the erosion resistance of the coating mainly focuses on the influence of different erosion angles on it . In this paper, Q235 steel is used as the substrate to prepare the WC-12Co coating by plasma spraying. The effect of different spraying distances on the microstructure, mechanical properties and erosion resistance of the coating is studied. By measuring the particle velocity and temperature at different spraying distances, it is revealed The effect of particle temperature and velocity on coating performance, and the mechanism of erosion and wear of WC-12Co coating is discussed.<br/>

1.1 Preparation of the coating The substrate is Q235 steel, the bond tensile test uses Φ20 mm×6 mm specimens, and the erosion and wear test uses 30 mm×40 mm×5 mm specimens. When spraying, the bonding layer is made of NiCr5Al powder with a particle size of 25~45 μm, and its mass fraction is: 5% Al, and the balance is NiCr. The WC-12Co spherical agglomerated powder was obtained by spray granulation. The SEM morphology of the powder is shown in Figure 1. The WC particles agglomerate into a spherical shape through the Co bonding phase. The particle size distribution of the WC-12Co powder is uniform, the surface is smooth, and the flowability is good. The particle size is 25~45 μm, the fluidity is 20.1 s/50 g, the bulk density is 4.4 g/cm3, and its composition (mass fraction/%) is: 88.0WC, 12.0Co. All powders are dried before spraying. See Table 1 for the parameters of sandblasting and plasma spraying. Before spraying, the surface of Q235 substrate should be smoothed and cleaned by ultrasonic cleaning for 30 minutes to remove oil and rust. Then use brown corundum with a particle size of 0.5~1.0 mm to roughen the surface. After sandblasting, use filtered clean compressed air to remove impurities on the surface of the substrate. And the floating dust is blown off, and the plasma spraying test is completed within 2 hours. The coating preparation adopts the DH-2080 plasma spraying system produced by Chengdu Jiupinweik Co., Ltd., and the inner diameter of the cylindrical nozzle is 6 mm.