Effect of Depositing Particle Velocity on Microstructure and Mechanical Properties of Thermal Spray WC-Ni Coatings

YUAN Jingru; ZHU Xiaopeng; HE Jin; HU Peipei; LEI Mingkai

doi:10.16490/j.cnki.issn.1001-3660.2025.13.018

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Surface Technology ›› 2025, Vol. 54 ›› Issue (13) : 203-213. DOI: 10.16490/j.cnki.issn.1001-3660.2025.13.018

Thermal Spraying and Cold Spraying Technology

Effect of Depositing Particle Velocity on Microstructure and Mechanical Properties of Thermal Spray WC-Ni Coatings

YUAN Jingru, ZHU Xiaopeng^*, HE Jin, HU Peipei, LEI Mingkai^*

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Abstract

The thermal spraying process of WC-Ni coatings is investigated with the Ni bonding phase instead of Co, considering the application requirements of cemented carbide coatings in corrosive medium conditions of hydraulic mechanical equipment such as pumps and valves. To solve the complex problem of multi-objective optimization caused by the coupling of high-velocity oxy-fuel (HVOF) spraying process parameters and spraying materials, particle online monitoring equipment is used to derive the correlation between the high-temperature particle deposition velocity and the microstructure and mechanical properties of the coatings. The oxygen/kerosene stoichiometric ratio λ of HVOF spraying WC-Ni coatings is taken as the characteristic process quantity to study the effect of the process parameters on the microstructure and mechanical properties of the coatings. The kerosene and oxygen flow rate parameters are adjusted while keeping λ at a constant value of 1.05 to obtain coatings under different deposition velocities with similar deposition temperature of WC-Ni particles, and to analyze the change rule of porosity, phase structure, microhardness, elastic modulus and fracture toughness of the coatings. As the kerosene flow rate increases from 19.3 L/h to 23.8 L/h, the combustion chamber pressure of the spray gun increases from 0.66 MPa to 0.76 MPa, the average particle velocity increases from 847 m/s to 916 m/s with an average particle temperature about (1 682± 6) ℃ under the same spray distance of 350 mm. The particle velocity enhancement leads to reduction in the porosity of the coating surface and cross section, with the lower surface porosity values to the corresponding cross-sectional ones. The retention ratio of the WC phase increases from 71.4% to 82.3%, and the oxidation decomposition product metal W decreases from 9.5% to 3.4%. Accordingly, the microhardness values in the range of 7.8-10.3 GPa obtained from both the coating's surface and cross section increase as the particle velocity rises with a convergence tendency of the hardness values at higher velocities; while the elastic modulus of the coatings increases from 313 GPa to 405 GPa. In addition, the fracture toughness of the coating is tested with a large load Vickers hardness tester, and the correlation between the sprayed particle velocity and the fracture mechanical behavior of the coating is analyzed in conjunction with the different cracking characteristics of the indentation tips and edges. In the range of WC-Ni particle deposition velocity and temperature of this study, the faster particle has the higher impact kinetic energy for the deposition, which causes a sufficient flattening deformation of deposited particles and thus significantly reduces the interfacial defects between the flattened particles, increases the density of the coating, and improves the bonding strength between the deposited particles. At the same time, the increase in the velocity of in-flight particles shortens its heating time in the flame, reducing the oxidative decomposition of the WC phase and resulting in higher retention of the WC phase in the deposited coating. These two aspects contribute to the enhancement of the microhardness and elastic modulus of the coatings. The intrinsic correlation between the spraying process parameters and the surface integrity parameters of coated parts established in this study can provide a basis for process optimization and online monitoring for high-performance manufacturing of cemented carbide coated parts.

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high-velocity oxy-fuel spraying / WC-Ni coating / spray particle velocity / surface integrity / coating mechanical properties

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YUAN Jingru, ZHU Xiaopeng, HE Jin, HU Peipei, LEI Mingkai. Effect of Depositing Particle Velocity on Microstructure and Mechanical Properties of Thermal Spray WC-Ni Coatings[J]. Surface Technology. 2025, 54(13): 203-213 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.13.018

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