In order to investigate the effect of WC grain size on coatings’ properties and abrasive wear performance, a few WC-20Cr₃C₂-7Ni coatings with three different WC grain sizes were deposited by the high-velocity oxy-fuel (HVOF) thermal spray process. The phase compositions, microstructures, and mechanical properties of the coatings were investigated. Furthermore, the two- and three-body abrasive wear performances of the three coatings were tested by using SiC and SiO₂ abrasives, respectively. The results show that all the three coatings were composed of WC, Cr₃C₂, and the Ni binder as well as the (W,Cr)₂C phase. The abrasive wear resistance of the WC-20Cr₃C₂-7Ni coating monotonously increased with increasing WC grain size when the SiC abrasive was used in the two- and three-body abrasive wear tests. However, the wear resistance trend was reversed when the SiO₂ abrasive was used in the three-body abrasive wear test. The specific wear rate of the WC-20Cr₃C₂-7Ni coating exposed to the SiC abrasive under the two-body abrasive wear test was the largest. The wear resistance of the coatings was more significantly affected by the hardness of the abrasive particles than the size of carbides present within the coating. The high hardness of SiC can cut both the carbide and the binder phase of the WC-based cermet coatings, resulting in a high wear rate, whereas the low hardness of SiO₂ cuts and/or scratches the binder initially, and then it dislodges the carbides from the matrix. The dislodged carbides which were subsequently pulled out from the matrix by the repeated impact of the SiO₂ abrasives result in a milder wear rate.

Rare earth elements have been widely utilized in material manufacturing to enhance properties in various ways. In order to obtain the WC-10Co4Cr coating with uniform distribution of rare earths, CeO₂-modified powder was prepared by mixing 1 wt.% nano-sized CeO₂ during the initial ball-milling of the powder fabrication process. Bare and CeO₂-modified WC-10Co4Cr coatings were deposited via high velocity oxygen fuel spraying to investigate the impact of CeO₂ modification on the coating’s microstructure, mechanical properties and abrasive wear performance. The results show that the addition of CeO₂ increased the interface energy, inhibiting the formation of the Co₃W₃C phase during the powder sintering process, as well as the W₂C phase and CoCr alloy during the high-velocity oxy-fuel (HVOF) process. This led to a significantly decreased porosity and higher concentration of undissolved Cr-rich areas. The microhardness and fracture toughness of the CeO₂-modified coating were 1230 HV_0.3 and 5.77 MPam^1/2, respectively. The abrasive wear resistance of the CeO₂-modified coating was only 70.9% of that of the unmodified coating. Due to the weak cohesive strength between WC and Cr, Cr-rich areas were preferentially removed, resulting in an increased wear rate in the CeO₂-modified coating.

Cold spraying (CS), also known as cold gas dynamic spraying or supersonic cold spraying, is a process in which particles collide with the substrate at a speed greater than the critical value and deposit layer by layer to form a coating. As an emerging coating preparation technology that has been developed rapidly in recent years, CS is characterized by a low deposition temperature, a minimal thermal effect on substrate, and a high deposition efficiency. It has received extensive attention from industry. However, the inherent high strength and low plasticity of CS coatings and the numerous defects present limit their wider application to some extent. Therefore, various post-treatment technologies are successfully applied to the CS coatings to improve their comprehensive performance. This paper reviews the latest research progress of common post-treatment techniques for CS coatings, including five categories: thermal, mechanical, thermo-mechanical, chemical, and electrochemical processing. A considerable amount of experimental research has demonstrated that post-treatment can effectively enhance the microstructure and properties of CS coatings, and this can serve as a powerful approach to expand the application scope of CS technology. In addition, the relevant post-processing parameters and corresponding results are summarized and compared systematically.

To enhance the abrasive wear resistance of mechanical components operating in corrosive environments, this study fabricated WC-10Co-4Cr coatings using high-velocity oxygen-fuel (HVOF) thermal spraying technology. A L9 (3⁴) orthogonal array was designed to optimize four key process parameters (kerosene flow rate, oxygen flow rate, powder feed rate, and spraying distance) at three levels each, aiming for minimal porosity. The phase composition, microstructure, hardness, abrasive wear resistance, and corrosion resistance of the coatings were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), microhardness tester, wet sand rubber wheel abrasion tester, and electrochemical workstation. The results indicated that the optimal parameters were a kerosene flow rate of 0.0073 L/s, oxygen flow rate of 15.33 L/s, powder feed rate of 1 g/s, and spraying distance of 326 mm. The coating prepared under these conditions exhibited high density with a porosity of only 0.32% and a high microhardness of 1281 HV1. Compared to the AISI 1020 steel substrate, the optimized WC-10Co-4Cr coating demonstrated a 122-fold improvement in abrasive wear resistance and a better corrosion resistance, showcasing its excellent overall performance and great potential for wear-resistant surface protection in corrosive environments.

This study employed a high-pressure cold spray to apply a Zn30Al alloy coating to Q235 steel substrates to provide corrosion protection for steel in marine environments. The corrosion resistance of the coatings was investigated through full immersion tests, and the corrosion mechanisms were further analyzed using electrochemical experiments. The results were compared with those of traditional flame-sprayed Zn30Al alloy coating. The findings indicate that the high-pressure cold-sprayed Zn30Al alloy coating possesses a dense microstructure with a porosity of only 0.32%, providing effective cathodic protection to the substrate during the immersion tests. The cold-sprayed Zn30Al alloy coating maintained good integrity after 720 h immersion in 3.5 wt.% NaCl solution, whereas the flame-sprayed Zn30Al alloy coating exhibited significant pitting corrosion.