High-velocity oxy-fuel (HVOF) spray coating plays a major role in many surface treatment methods, which tend to improve erosion and corrosion resistance properties. HVOF is well known for its dense and high-quality coating ability. This is due to the less in-flight exposure time, which tends to have less oxide content because of its high-velocity properties. Among the number of process parameters, porosity and hardness are predominant factors while considering wear rate and corrosion behaviour analysis. The current study aims to optimise HVOF process parameters to obtain low levels of porosity and high hardness values in the WC-10Ni-5Cr coating sprayed on 35 Mo Cr steel. The flow rates of oxygen, LPG, coating powder feed rate and spray distance are selected in this study as these have a superior influence on the final condition of the coating. Statistical tools such as the design of experiments (DoE), analysis of variants and response surface methodology (RSM) were used to achieve the desired results. As per the result analysis, the oxygen flow rate has a higher effect on the porosity value and microhardness value of the coating.

The paper summarizes the current development of high-velocity oxygen–fuel coupled physical vapor deposition (HVOF-PVD) duplex coatings as protective candidates. Following a detailed historical overview of HVOF and PVD technologies, the fabrication methods for duplex protective coatings are presented. The duplex coating superimposes the synergistic advantages of coatings deposited by HVOF and PVD, where the traditional weaknesses of each technique are modified to a great certain extent. Subsequently, the relation between structural characteristics of the duplex coatings and their mechanical, tribological, and corrosive behavior is described in detail. It is demonstrated that the duplex coatings show more excellent overall performance than coatings deposited by both HVOF and PVD separately. Finally, we summarize the protective performance and promising potential of HVOF-PVD duplex coating for applications as well as the research prospects of challenges in future.

To improve the corrosion resistance of Mg alloy, Al alloy/alumina metal matrix composite (MMC) coatings were formed by low pressure cold spraying (LPCS) technology followed by post friction stir processing. The phase structure, microstructure, and corrosion properties of the cold-sprayed metal matrix composite coatings before and after friction stir processing were investigated. The effect of the friction stir process (FSP) on the corrosion characteristics of MMC coatings at 3.5 weight percent of NaCl solution was explored using a Tafel polarisation plot. Microstructural studies were examined to investigate the electrochemical behaviour of the cold spray (CS) and FSPed MMC coatings. The results demonstrated that an enhancement in corrosion protection of the MMC deposits occurred at the 1st and 2nd runs of FSP, with superior corrosion performance observed at the 2nd run of FSP. The enhanced surface state is the primary enhancement mechanism of the electrochemical properties of the FSPed MMC coatings. For the higher run of FSP (3rd run), the electrochemical performance of the specimens was lower owing to the amalgamate action of the enhanced surface state with the aggravated interface of interior deposits.

To explore the Co/Cr ratio impact on the high-velocity oxygen fuel (HVOF)-sprayed WC-Co-Cr coatings microstructure and performances, three kinds of WC-Co-Cr coatings, namely WC-4Co-10Cr, WC-7Co-7Cr, and WC-10Co-4Cr, were prepared by using a high-velocity oxygen fuel (HVOF) spraying process. The three coatings’ phase composition, microstructure, basic mechanical properties, abrasive wear, and corrosion resistance were investigated. The results show that all three WC-Co-Cr coatings comprise the main phase WC, minor W₂C, and amorphous W-Co-Cr phase, besides the WC-4Co-10Cr coating containing a small amount of Cr_xC_y phase. In addition, WC-7Co-7Cr coating exhibited the highest hardness and abrasive wear resistance, followed by WC-10Co-4Cr and WC-4Co-10Cr coatings. The corrosion resistance as a hierarchy was found to be WC-10Co-4Cr > WC-7Co-7Cr > WC-4Co-10Cr.

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.

To enhance the surface of a material with the desired qualities for diverse applications in service, a variety of thermal and thermo-chemical surface treatment processes are used. Due to the high-velocity impact inherent in the process, high-velocity oxy-fuel (HVOF) spray is now frequently employed in industrial applications for its ability to generate a high-quality coating with appropriate hardness and low oxide content. In this investigation, a high-velocity oxy-fuel (HVOF) thermal spraying process was utilized to coat WC-10Co powders on a 35CrMo steel substrate. A water jet erosion test was also used to examine the substrate and coated samples’ erosion behavior. The erosion rate was systematically investigated using water jet variables such as the angle of impingement, water jet velocity, standoff distance, and erodent discharge. For the development of multiple regression models, experiments were performed utilizing the central composite rotatable design and the response surface methodology. The angle of impingement had the most impact on the rate of coating erosion, leading to the water jet velocity, standoff distance, and erodent discharge.