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Article

Comparison of Microstructure, Mechanical Properties, and Wear Properties of Cold Sprayed and HVOF WC-10Co4Cr Coatings on 4340 Steel Substrates

by
Jiamin Zeng
1,
Xiankun Ji
1,
Yingjing Yuan
1,
Yonghong Wang
1,
Li Liu
1,
Nanyang Su
1,
Zhuang Qian
2,*,
Xin Chu
2,
Yingchun Xie
2 and
Chunming Deng
2
1
AECC Hunan Aviation Powerplant Research Institute, Zhuzhou 412002, China
2
Guangdong Provincial Key Laboratory of Modern Surface Engineering Technology, Guangdong-Hong Kong Joint Laboratory of Modern Surface Engineering Technology, Institute of New Materials, Guangdong Academy of Sciences, Guangzhou 510651, China
*
Author to whom correspondence should be addressed.
Coatings 2025, 15(10), 1227; https://doi.org/10.3390/coatings15101227
Submission received: 30 June 2025 / Revised: 23 July 2025 / Accepted: 25 July 2025 / Published: 20 October 2025
(This article belongs to the Special Issue Cold-Spray Coatings: Microstructure, Mechanical Properties and Applications)
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Versions Notes

Abstract

This paper investigates WC-10Co4Cr coatings on 4340 steel prepared by conventional HVOF and novel cold spraying (CS) under optimal process parameters to address low wear resistance. The results show that the CS WC-10Co4Cr coating porosity is less than 0.1%, while the HVOF WC-10Co4Cr coating porosity is about 0.3%. The WC phase in the CS coating did not change, whereas the WC phase in the HVOF coating underwent decarburization and a new W2C phase was formed. The microhardness of the CS WC-10Co4Cr coating reaches 1617.2 HV0.3, which is about 50% higher than that of HVOF WC-10Co4Cr coating of 1061.3 HV0.3. The sliding wear rate of the CS WC-10Co4Cr coatings is 0.17 × 10−5 μm3/N·m, which is 40% of that of the HVOF coatings. The CS coating’s fretting wear rate is 1.28 μm3/N·m, which is 40% faster than that of HVOF coating. However, the bond strength of the CS WC-10Co4Cr coating (35 MPa) is lower than that of the HVOF coating (73.5 MPa). Overall, the WC-10Co4Cr coatings prepared by the CS process have higher hardness, denser coating microstructure, and better sliding wear resistance than those prepared by the conventional HVOF process.

1. Introduction

4340 steel with high strength and toughness is widely used in the rotor shafts of large machines, drive shafts, and crankshafts in automobiles, as well as universal joint shafts and other shaft parts of industrial standard parts. However, 4340 steel has relatively poor wear resistance under high load and high speed conditions, leading to failure and short life of the parts, which cannot fully meet the increasing service requirements of, e.g., the new generation of large machines [1]. Spraying wear-resistant coating on the surface of 4340 steel to improve its friction and wear performance is an effective means to solve the above problems.
WC-10Co4Cr is a kind of metal–ceramic composite material consisting of 86% tungsten carbide (WC) particles as well as 10% cobalt (Co) and 4% chromium (Cr) metal bonding phases. WC particles provide a very high hardness (over 1500 HV0.3), giving the material excellent wear resistance, and Co acts as a bonding phase giving the material a certain toughness [2,3,4]. WC-10Co4Cr coatings can be used as a repair and reinforcement coating for aerospace parts, and high velocity oxy-fuel (HVOF) is a common technology for preparing WC [5]. HVOF is a thermal spraying technology that produces a high temperature, high speed gas stream by combusting fuel with high purity oxygen, accelerating the powder material to supersonic speeds and ejecting it onto the surface of the substrate to form a coating [6,7,8,9,10]. Although HVOF WC-10Co4Cr coating has the advantages of dense coating and high bonding strength, there are still some disadvantages, such as decarburization of WC-10Co4Cr and limited coating thickness due to large thermal stresses (up to 1 mm) [11,12,13]. For example, the literature showed that as the HVOF process temperature decreased, the dissolution of carbides in WC-10Co4Cr decreased, resulting in a significant increase in the hardness of the coating [14,15].
Grabowski et al. used nitrogen as a propellant gas to prepare WC-10Co4Cr coatings on H13 steel substrates using CS and HVOF techniques, respectively [16]. Although the WC-10Co4Cr coatings prepared using CS had a denser microstructure with fewer surface defects, their hardness was only about 800 HV0.3, which is lower than that of the WC-10Co4Cr coatings prepared using HVOF [16]. Moreover, the literature did not investigate the bond strength of WC-10Co4Cr coatings on H13 steel substrate, nor the mechanical properties of the coatings, such as friction and wear. 4340 steel has a higher hardness than H13 steel, and very few researcher has reported successful deposition of well bonded and dense WC-10Co4Cr coatings on the steel surface using CS [17,18,19].
In this study, WC-10Co4Cr coatings were successfully prepared on steel substrates by high pressure cold spray under optimal parameters. The objective of this paper is to investigate the microstructure, mechanical and wear properties of WC-10Co4Cr coatings prepared on 4340 steel substrate under CS, and compare to the conventional HVOF WC-10Co4Cr coatings. The feasibility, advantages and disadvantages of preparing WC-10Co4Cr coatings on 4340 steel surfaces by cold spraying technology are investigated.

2. Materials and Methods

2.1. Experimental Materials

4340 steel was used as the substrate, and the feedstock powder was WC-10Co4Cr prepared by sintering and fragmentation method. SEM morphology of the powder is shown in Figure 1a and the powder particles are nearly spherical, with a porous structure. The particle size distribution of WC-10Co4Cr powder is shown in Figure 1b and the d50 is 15.5 μm, d10, and d90 are 10 μm and 20 μm, respectively.

2.2. Spraying Process

2.2.1. Cold Spray (CS)

The equipment used for cold spraying (CS) is a high-pressure cold spraying equipment CX580 made and equipped at the Institute of New Materials, Guangdong Academy of Sciences. It has a maximum spraying gas pressure of 5 MPa, a maximum gas pressure of 1000 °C, and can continuously spray for more than 30 min. The substrate was ultrasonically cleaned using acetone/anhydrous alcohol and blown dry before cold spraying. The cold sprayed WC-10Co4Cr coatings were prepared on the substrate surface using nitrogen and helium as the propellant gas, respectively. However, the trial tests using helium as a propellant gas all led to WC-10Co4Cr coating failure during spray and no successful deposition can be achieved on 4340 steel substrate; therefore research efforts were turned to nitrogen propellent gas hereafter. The specific process parameters are shown in Table 1.

2.2.2. High Velocity Oxygen Fuel (HVOF)

HVOF was performed using the HVOF spraying system GTV-K2 (GTV, Luckenbach, Germany). The surface of the substrate needs to be cleaned before coating preparation, and the surface was subsequently pretreated by sandblasting. The air gun was continuously used to cool down the substrate during the thermal spraying process, and when the temperature of the substrate increased to 70–80 °C, the spraying was stopped to cool down the substrate for 1 min, and the spraying continued after the temperature of the substrate was cooled down to 40–50 °C, and the parameters of the thermal spraying are shown in Table 2.

2.3. Characterization of Coating Microstructure and Properties

Metallographic specimens with a size of 10 mm × 10 mm were cut on the prepared cold/thermal sprayed substrates using a wire-cutting machine. The metallographic specimens after cold mounting were polished by using 120, 1200, 2000, and 4000 mesh diamond grinding disks, 3 μm diamond mol polishing solution, and finally nanoscale diamond polishing solution with a particle size of 0.25 μm. An optical microscope was used to observe the microstructure of the coating cross-section, and a SU8600 SEM (Hitachi, Tokyo, Japan) was used to observe the coating cross-section and top surface, and the coating surface was sprayed with gold before observation.
An X-ray diffractometer SmartLab 9 kW (Rigaku, Tokyo, Japan) was used to characterize the CS/HVOF coatings and WC-10Co4Cr powder, and the phases of the coatings were analyzed for different parameters at a scanning speed of 5°/min over a diffraction angle (2θ) scanning range of 10–90°.
ImageJ1 software was used to calculate the porosity based on the proportion of pore pixels to the total pixels in the image according to the gray value; each coating was selected for three areas and these averEMOages were recorded. The deposition efficiency is calculated by weighing the amount of powder consumed in the powder feeder divided by the difference in the mass of substate before and after spray. Microhardness tests were performed on polished specimens using a Vickers microhardness tester Dura Scan 70G5 (EMCOTEST, Kuhl, Austria) with an applied load of 300 g and a loading time of 15 s. Five randomly selected points in the coated cross-section were tested, and the average value was calculated.
For bonding strength measurements, the specimens after spraying were cut into φ25.4 mm disks using an EDM wire-cutting machine, and both sides of the disks were sandblasted according to the ASTM C633 test standard, and the coating was connected to the dyadic parts using E7 adhesive with a fixture loading torque of 2.15 N∙m, and was heated at heating and holding at 100 °C for 200 min, cooled to room temperature with the furnace, and a tensile test was carried out using a universal testing machine (GOPOINT, Shenzhen, China) with a tensile rate of 1 mm/min.
Circumferential wear tests were carried out using UMT-3 friction and wear tester for both cold sprayed and thermal sprayed coatings and for the substrate (4340 steel) using Si3N4 friction balls with a diameter of 4 mm, with the test parameters of 500 g load, 600 RPM rotational speed, and friction radius of 7.5 mm, and the test time of 30 min, and the coefficient of friction was recorded and plotted on the images. The wear rate is calculated based on Equation (1) below:
Wear rate = V/(F × L)
where V is wear volume; L is path length; and F is applied normal load.
To better monitor the wear conditions of rotors during operation, both coatings were also subjected to fretting wear tests using CFT-1 type material surface property universal tester. The fretting wear test conditions are a grinding ball of GCr15, a Hertzian contact stress of 600 MPa, a test length of 30 min, and an amplitude of 0.6 mm.
The wear tracks were characterized using a DEKTAK XT contact 3D profiler (Bruker, MA, USA). The scanning rate was 100 μm/s and 200 passes were scanned in the area by three-dimensional contouring. The wear rate was also calculated according to Equation (1), and the interfering data of the uneven surface in the data were removed to draw the three-dimensional contour map. The sliding wear and fretting wear tracks were also observed by SU8600 SEM (Hitachi, Tokyo, Japan) for microstructure.

3. Results and Discussion

3.1. Microstructure

Figure 2 shows top surface and cross-sectional SEM images of CS and HVOF WC-10Co4Cr coatings. No obvious pores were found in the top surface of CS coatings shown in Figure 2a, while the cross-sections of CS coatings shown in Figure 2b,c show a clear aggregation of CoCr phases. An SEM image of HVOF coating top surface is shown in Figure 2d, where obvious pores can be seen. SEM images of the cross-sections of HVOF coating are shown in Figure 2e,f, where interfacial contamination can be seen in the coating–substrate interfaces in Figure 2e.
During HVOF, the particles melt at high temperatures and form a “pancake-like” structure upon impact, with incomplete overlap or gas trapping between layers, and some WC decomposes at high temperatures, generating CO2/CO and porosity [20]. At the same time, the decarburized phase will accumulate at the interface between the substrate and the coating, resulting in interfacial contamination. The absence of the CoCr phase in HVOF coatings is possibly due to the high temperature of WC-10Co4Cr powder during the HVOF process; the melting point of the CoCr phase in the powder is lower than that of the WC phase and it is easier to melt, oxidize, or evaporate, which leads to a reduction in the Cr content in the original powder and a reduction in the CoCr phase [21].
The deposition efficiency and porosity of CS/HVOF WC-10Co4Cr coatings are shown in Table 3, with a deposition efficiency of 5% for CS and 40% for HVOF. The deposition principle of CS is that the sprayed particles are accelerated by high-temperature and high-pressure gas and then impacted onto the substrate at supersonic speed, and the particles and the substrate undergo intense deformation to form the coating. The particles remain solid state during the spraying process, and due to the high velocity of the WC-10Co4Cr powder, a large amount of powder bounces in all directions when it hits the substrate or the previously formed coating [22], resulting in an inefficient deposition of only 5%. The deposition principle of HVOF is to hit the molten state powder to the substrate with supersonic speed, the molten state WC-10Co4Cr powder is more likely to produce deformation, more powder attached to the substrate, the splash phenomenon is not obvious, and the deposition efficiency can be up to 40% [23].
The porosity of CS WC-10Co4Cr coating is less than 0.1%, while the porosity of HVOF WC-10Co4Cr coating was calculated to be 0.3%. This is due to the fact that during the CS process, the powder particles impact the substrate entirely in solid state at high speeds, causing strong plastic deformation of the substrate and the powder, while at the same time, the subsequent flying solid particles will exert a strong tamping effect on the previously formed coatings, resulting in a fuller deformation and a reduction in porosity [24]. While in the HVOF process, the particles are melted and sprayed on the surface of the substrate, the WC-10Co4Cr powder tends to oxidize in the high-temperature flame flow, and the molten powder particles splash and shrink, forming more pores [25]. It is worth noting that the differences in porosity are negligible in terms of their influence on the overall microstructure and performance of the final coatings. This is because the porosity is below 1% in all cases and cannot be reliably quantified by simple image analysis.

3.2. Phase Composition

XRD diagrams of CS/HVOF WC-10Co4Cr coatings and WC-10Co4Cr powder is shown in Figure 3. XRD diagrams of WC-10Co4Cr powder exhibit two diffraction peaks, which are WC and CoCr phases. The CoCr phase occurs because WC-10Co4Cr is prepared by sintering and the fragmentation method, and Cr and Co powders in the mixed powder will form a CoCr phase during the sintering process. The diffraction peaks in CS coatings are identical to that of the powders. Researchers have successfully prepared WC coatings by high-pressure cold spraying and confirmed that no decarburization occurred in cold sprayed WC coatings [26]. In the HVOF coating, a new W2C phase was produced, and in the WC phase, the quantity ratio of W to C is 1:1, while in the W2C phase, the quantity ratio of W to C reaches 2:1. Since the original CS coating is identical to that of the HVOF feedstock powder, it can be determined that the W2C phase is decarburized from the WC phase [27]. This is because in the process of thermal spraying, the particles are heated to a very high temperature; the particles in the high-temperature state and the oxygen in the spraying environment react, transforming the C element into CO2 or CO escape, resulting in decarburization [28]. The C element in the HVOF layer decreases and some WC phases recombine to form a new W2C phase, while other elements in the coating dope the coating by generating oxides with oxygen. The diffraction peaks of the CoCr phase disappear from the XRD images of the HVOF coating because during rapid cooling, CoCr phase transforms to an amorphous phase and thus is not observable in the XRD spectra of the coating [27].

3.3. Microhardness

The microhardness of CS/HVOF WC-10Co4Cr coatings and WC-10Co4Cr powder is shown in Figure 4. The average microhardness of the cold sprayed coating is 1617.2 HV0.3, and the microhardness of the thermal sprayed coating is lower than the cold sprayed coating at 1061.3 HV0.3. The average hardness of the 4340 steel substrate is 399 HV0.3.
The process characteristics of CS are completely different from HVOF. Its particle velocity is much higher (up to 1000–1200 m/s) and the particle is always kept in the solid state [29]. High-speed particle impact will produce a significant tamping effect, resulting in the formation of high-density dislocations in the internal structure of the material and fine crystalline structure, and thus a significant work-hardening effect. Although the particle flight velocity of the HVOF process is usually high (up to 600–1000 m/s), its particle temperature often exceeds the phase transition temperature of the material (the melting point of WC is about 2870 °C and Co is about 1495 °C), which triggers a phase transition [30]. At high temperatures, the sprayed particles not only undergo significant oxidation reactions, forming oxide inclusions on the surface (e.g., CoO, Cr2O3, etc.), but also gas entrainment in the molten state leaves pores in the coating [27]. These defects significantly reduce the densification of the coating and generate large tensile stresses due to the rapid cooling process after high temperature deposition, which in turn affects the hardness of the coating [31]. The high temperature environment will also lead to an annealing effect on the coating material, especially for the cobalt-based bonding phase; its lattice structure will recover and recrystallize at high temperatures, thus reducing the work-hardening effect of the material and the overall hardness [32].

3.4. Bonding Strength

The bond strength results of the CS/HVOF WC-10Co4Cr coating are shown in Figure 5. The cold sprayed coating was fractured within the coating and the average value of bonding strength was measured to be 35 MPa. The HVOF coating was fractured within the coating and the average value was measured to be 73.5 MPa, but the coating was not separated from the substrate, so the actual bond strength was greater than the measured value. The bonding strength of the WC-10Co4Cr coating on 4340 steel substrates by thermal spraying is much tighter than that of cold spraying.
Mechanical interlocking and metallurgical bonding are the primary bonding mechanisms in cold spray. Mechanical bonding is the capture of hard particles by a soft substrate to form interlocking, and metallurgical bonding is the result of high pressure contact between the particles and the coating/substrate interface, and metallurgical bonding will provide high bond strength [33]. When spraying high melting point particles, mechanical interlocking dominates and the cohesive strength of the coating is relatively low, thus the bond strength of cold sprayed WC-10Co4Cr coatings is relatively low at 35 MPa [34]. While during the thermal spraying process, the molten particles cool down quickly when they hit the substrate/coating and generate a large adhesive force with the substrate/coating, and this strong cohesive force makes the bonding strength of the WC-10Co4Cr coatings usually ≥55 MPa [35]. According to the XRD results (Figure 3), the difference in bonding strength is primarily attributed to the phase transformation behavior of WC-10Co4Cr [34]. Studies have shown that during the HVOF spraying process, molten particles at high temperature are rapidly deposited onto the 4340 steel substrate, forming a metallurgical diffusion layer at the interface, thereby achieving strong interfacial bonding [2]. Although the WC-10Co4Cr coating prepared by HVOF tends to experience a certain degree of decarburization, which is unfavorable for enhancing bonding strength [36]. The strong interfacial metallurgical bonding not only offsets the adverse effect of decarburization, but also significantly promotes the interfacial diffusion and bonding mechanism dominated by metallic bonding forces [10]. In addition, local tensile stress fields induced by the phase transformation volume effect reduce the grain boundary bonding energy and lead to the formation of dislocation pile-ups, thereby enhancing the cohesive strength of the coating. In contrast, cold spray deposition relies mainly on mechanical interlocking of solid-state particles, where bonding is governed by kinetic energy-driven plastic deformation, without any metallurgical bonding. Given the inherently hard and brittle nature of WC-10Co4Cr particles, the bonding strength is intrinsically limited. Therefore, the bonding strength is significantly inferior to that of coatings prepared by HVOF [37,38]. This, to some extent, reflects the limitation of cold spray processes dominated by plastic deformation, which are less effective in depositing coatings involving high-strength particles and substrates. The inherent weakness in bonding strength imposes significant limitations on the application of such coatings. For instance, WC-10Co4Cr coatings fabricated by cold spray exhibit the advantage of high hardness, but suffer from insufficient bonding strength, making them suitable for applications such as cutting tools, low-load sliding bearings/components, and temporary protective coatings [39,40].

3.5. Sliding Wear Tests

The 3D contour scans and SEM images of wear tracks of CS/HVOF WC-10Co4Cr coating and 4340 steel substrates are shown in Figure 6. The wear tracks of CS coating are shown in Figure 6a,d and the scratch is very shallow with no material peeling. Figure 6b,e show the wear tracks of the HVOF coating, and a small amount of the coating surface is peeled off, and the depth of the wear tracks is shallow. Figure 6c,f show the wear tracks of the 4340 steel substrate, and there are chunks of coating peeling off the surface of the coating, and the wear tracks are deeper. The friction coefficients and calculated wear rates of CS/HVOF coatings and the 4340 steel substrate are shown in Table 4. The wear rate is 0.17×10−5 μm3/N·m for the CS coating, 0.43×10−5 μm3/N·m for the HVOF coating, and 1.62×10−4 μm3/N·m for the 4340 steel substrate. The CS/HVOF coatings both show much superior wear rates compared with the 4340 steel substrate, and the wear rate of the CS coating is only 40% that of the HVOF coating.
In HVOF coatings, the compressive stresses exerted on the coating by friction couple causes surface wear tracks, and when the wear tracks extend to defects such as porosity, material exfoliation occurs, and the exfoliated WC hard phases form new wear particles, leading to further wear of WC-10Co4Cr coatings [41]. In contrast, CS coatings with higher surface hardness is less prone to shedding of WC hard phases, which is conducive to delaying the generation and further development of wear tracks.

3.6. Fretting Wear Tests

Figure 7a–c show 3D contours of the wear tracks of the CS/HVOF WC-10Co4Cr coatings and 4340 steel substrate, respectively. The 4340 steel substrate has the most obvious wear tracks and maximum depth of 10 μm, followed by the CS coating, and the narrowest and shallowest scratches are those of the HVOF coatings. Figure 7d–f shows the SEM image of the scratches of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrate, respectively. There is obvious and deep material detachment on the surface of the coating of the CS WC-10Co4Cr coating; there is relatively shallow material detachment of the HVOF WC-10Co4Cr coating, and there are large areas of material detachment on the surface of the substrate of the 4340 steel substrate. Table 5 shows the fretting wear rates of CS/HVOF coating and 4340 steel substrates, and the results are consistent with the results in Figure 7, in which the wear rate of HVOF coating is the smallest at 0.93 m3/N·m, followed by 1.28 μm3/N·m for CS coating, and both have a significant improvement in wear rate compared with 120 μm3/N·m for 4340 steel substrates.
Fretting wear is different from circumferential sliding wear, the coating surface is subjected to cyclic stress during fretting friction, although the microhardness of the CS coating is greater than that of the HVOF coating, the cohesion of the CS coating is weaker than that of the HVOF coating, and the hard phase of WC in the CS coating is more likely to be dislodged under the stress of the high-frequency cycling, and the dislodged hard phase is retained in the previously formed wear tracks, which aggravates the wear of the coating. The wear of the coating is exacerbated [42,43].

4. Conclusions

In this study, WC-10Co4Cr wear-resistant coatings were prepared on 4340 steel substrates by CS and compared to HVOF in terms of microstructure, hardness, sliding and fretting wear performance of the coatings, and the related mechanisms were analyzed. The main conclusions are as follows:
1.
Compared to the 0.3% porosity of the HVOF coating, the CS coating has a porosity of ≤0.1%, and there is no delamination at the interface between the two coatings and the substrate.
2.
XRD shows that the WC in the HVOF coating undergoes a phase transition, while the CS coating does not undergo any phase transition.
3.
The average hardness of the CS coating was 1617.2 HV0.3, the average hardness of the HVOF coating was 1061.3 HV0.3, and the CS coating had the higher hardness.
4.
The bonding strength of the HVOF coating reached 73.5 MPa, whih was higher than that of the CS coating, which was 35 MPa.
5.
The sliding wear performance of the CS coating is about twice as high as that of the HVOF coating. The fretting wear performance of the two coatings is similar, with the HVOF coating being slightly higher than the CS coating.

Author Contributions

Writing-original, data curation, J.Z. and X.J.; methodology Y.Y.; pro-ject administration, Y.W. and N.S.; funding acquisition, L.L.; Writing-review, editing, Z.Q., L.L. and X.C.; supervision, Y.X. and C.D. All authors have read and agreed to the published version of the manuscript.

Funding

Financial support was received from the National Key R&D Program of China (2024YFB4609600), Guangdong Province Science and Technology Plan Projects (2023B1212060045, 2023B1212120008), Guangdong Academy of Sciences Special Fund for Comprehensive Industrial Technology Innovation Center Building (2022GDASZH-2022010107), Key R&D Program of Guangxi Province, China (GKAB23026101), Guangdong Provincial Key Laboratory of Modern Surface Engineering Technology and Guangdong-Hong Kong Joint Laboratory of Modern Surface Engineering Technology Open Project Support Project (2024KFKT04), and Guangxi Natural Science Foundation, China (2023GXNSFBA026287).

Institutional Review Board Statement

No applicable.

Informed Consent Statement

No applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. SEM image and particle size distribution of WC-10Co4Cr powder: (a) SEM image of WC-10Co4Cr powder; (b) particale size distribution of WC-10Co4Cr powder.
Figure 1. SEM image and particle size distribution of WC-10Co4Cr powder: (a) SEM image of WC-10Co4Cr powder; (b) particale size distribution of WC-10Co4Cr powder.
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Figure 2. SEM images of WC-10Co4Cr coatings: (a–c) Cold spray; (d–f) HVOF; (a,d) are top surfaces; (b,c,e,f) are cross-sections.
Figure 2. SEM images of WC-10Co4Cr coatings: (a–c) Cold spray; (d–f) HVOF; (a,d) are top surfaces; (b,c,e,f) are cross-sections.
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Figure 3. XRD diagrams of CS/HVOF WC-10Co4Cr coatings and WC-10Co4Cr powder.
Figure 3. XRD diagrams of CS/HVOF WC-10Co4Cr coatings and WC-10Co4Cr powder.
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Figure 4. Microhardness of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates.
Figure 4. Microhardness of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates.
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Figure 5. Bonding strength of CS/HVOF WC-10Co4Cr coatings on 4340 steel substrates.
Figure 5. Bonding strength of CS/HVOF WC-10Co4Cr coatings on 4340 steel substrates.
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Figure 6. Three-dimensional contour views and SEM images of sliding wear tracks of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates: (a) Three-dimentional contour view of CS coating, (b) Three-dimentional contour view of HVOF coating, (c) Three-dimentional contour view of 4340 substrate (d) SEM image of CS coating, (e) SEM image of HVOF coating, and (f) SEM image of 4340 substrate.
Figure 6. Three-dimensional contour views and SEM images of sliding wear tracks of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates: (a) Three-dimentional contour view of CS coating, (b) Three-dimentional contour view of HVOF coating, (c) Three-dimentional contour view of 4340 substrate (d) SEM image of CS coating, (e) SEM image of HVOF coating, and (f) SEM image of 4340 substrate.
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Figure 7. Three-dimensional contour views and SEM images of fretting wear tracks of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates: (a) Three-dimentional contour view of CS coating, (b) Three-dimentional contour view of HVOF coating, (c) Three-dimentional contour view of 4340 substrate (d) SEM image of CS coating, (e) SEM image of HVOF coating, and (f) SEM image of 4340 substrate.
Figure 7. Three-dimensional contour views and SEM images of fretting wear tracks of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates: (a) Three-dimentional contour view of CS coating, (b) Three-dimentional contour view of HVOF coating, (c) Three-dimentional contour view of 4340 substrate (d) SEM image of CS coating, (e) SEM image of HVOF coating, and (f) SEM image of 4340 substrate.
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Table 1. CS process parameters.
Table 1. CS process parameters.
CoatingGas Pressure/MPaGas Temperature/°CSpray Speed/mm s−1Spray Distance/mmPowder Feed Rate/g min−1
CS585030030~50
Table 2. HVOF process parameters.
Table 2. HVOF process parameters.
CoatingKerosene Flux/L•h−1Oxygen Flux/L•min−1Powder Feed Rate/g•min−1Spray Distance/mm
HVOF26920105380
Table 3. Deposition efficiency and porosity of CS/HVOF WC-10Co4Cr coatings on 4340 steel substrates.
Table 3. Deposition efficiency and porosity of CS/HVOF WC-10Co4Cr coatings on 4340 steel substrates.
CoatingDeposition Efficiency, %Porosity %
CS50.1
HVOF400.3
Table 4. Friction coefficient and sliding wear rates of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates.
Table 4. Friction coefficient and sliding wear rates of CS/HVOF WC-10Co4Cr coatings and 4340 steel substrates.
CoatingCOFWear Rate
(μm3/N·m)
CS coating0.510.17 × 10−5
HVOF coating0.480.43 × 10−5
4340 steel0.261.62 × 10−4
Table 5. Fretting wear rates of CS/HVOF WC-10Co4Cr coatings and 4340 steel.
Table 5. Fretting wear rates of CS/HVOF WC-10Co4Cr coatings and 4340 steel.
CoatingCOFWear Rate
(μm3/N·m)
CS coating0.511.28
HVOF coating0.480.93
4340 steel0.26120
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MDPI and ACS Style

Zeng, J.; Ji, X.; Yuan, Y.; Wang, Y.; Liu, L.; Su, N.; Qian, Z.; Chu, X.; Xie, Y.; Deng, C. Comparison of Microstructure, Mechanical Properties, and Wear Properties of Cold Sprayed and HVOF WC-10Co4Cr Coatings on 4340 Steel Substrates. Coatings 2025, 15, 1227. https://doi.org/10.3390/coatings15101227

AMA Style

Zeng J, Ji X, Yuan Y, Wang Y, Liu L, Su N, Qian Z, Chu X, Xie Y, Deng C. Comparison of Microstructure, Mechanical Properties, and Wear Properties of Cold Sprayed and HVOF WC-10Co4Cr Coatings on 4340 Steel Substrates. Coatings. 2025; 15(10):1227. https://doi.org/10.3390/coatings15101227

Chicago/Turabian Style

Zeng, Jiamin, Xiankun Ji, Yingjing Yuan, Yonghong Wang, Li Liu, Nanyang Su, Zhuang Qian, Xin Chu, Yingchun Xie, and Chunming Deng. 2025. "Comparison of Microstructure, Mechanical Properties, and Wear Properties of Cold Sprayed and HVOF WC-10Co4Cr Coatings on 4340 Steel Substrates" Coatings 15, no. 10: 1227. https://doi.org/10.3390/coatings15101227

APA Style

Zeng, J., Ji, X., Yuan, Y., Wang, Y., Liu, L., Su, N., Qian, Z., Chu, X., Xie, Y., & Deng, C. (2025). Comparison of Microstructure, Mechanical Properties, and Wear Properties of Cold Sprayed and HVOF WC-10Co4Cr Coatings on 4340 Steel Substrates. Coatings, 15(10), 1227. https://doi.org/10.3390/coatings15101227

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