A ceramic coating and a method of making the same

Abstract

The application discloses a ceramic coating and a preparation method thereof, and belongs to the technical field of coating preparation. The ceramic coating comprises a NiCr / CoCrFeNiMo support layer and a (Ni-Cr3C2) x / (CoCrFeNiMo) 1‑x surface working layer arranged in sequence; in the (Ni-Cr3C2) x / (CoCrFeNiMo) 1‑x surface working layer, x is 70-90 wt%. The ceramic coating is prepared by combining the NiCr / CoCrFeNiMo support layer and the (Ni-Cr3C2) x / (CoCrFeNiMo) 1‑x surface working layer, the coating is combined with the base material closely, has low porosity, high toughness, and has excellent high-temperature wear resistance and electrochemical corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of coating preparation technology, and more specifically relates to a ceramic coating and its preparation method. Background Technology

[0002] Chromium carbide coatings are primarily used in power, energy, and aerospace industries due to their oxidation resistance and wear resistance. However, the NiCr binder in NiCr-Cr3C2 coatings softens at high temperatures and cannot effectively support the hard material. (NiCr has a coefficient of thermal expansion of approximately 13 × 10⁻⁶). -6 / ℃) and Cr3C2 (approximately 7×10) -6 The difference in temperature (°C) easily generates interfacial stress during high-temperature cycling, leading to delamination and peeling failure of the wear coating. Furthermore, the single Cr2O3 oxide film formed at high temperatures is brittle, porous, and has poor adhesion, limiting its application in high-temperature tribology. In corrosive environments, there is a significant potential difference (approximately 0.55V) between NiCr and Cr3C2. The low resistance and poor adhesion of the single Cr2O3 passivation film result in poor electrochemical corrosion resistance.

[0003] High-entropy alloys (HEAs), due to their unique multi-principal-element synergistic effect, possess high strength, high hardness, and excellent high-temperature stability, demonstrating great potential in enhancing the overall performance of coatings, surpassing traditional cemented carbides. In this context, HEAs have become a highly promising solution in the coating field, whether used alone or in combination with cemented carbides. Currently, research on HEAs in thermal spray coatings largely focuses on the influence of single-component addition on the coating microstructure. However, the interfacial interaction between HEAs and the Cr3C2 substrate, the evolution of the coating phase structure, and the regulation mechanism of multi-field coupled service performance after the gradient introduction of HEAs content remain unclear. Furthermore, existing coatings composed of Cr3C2 coatings and single HEAs components exhibit low hardness and toughness, and a low degree of hardness and toughness matching between the coating and the substrate, failing to meet the requirements of "surface wear resistance and internal crack resistance" in high-temperature wear. Therefore, developing a ceramic coating that optimizes coating hardness and toughness, optimizes the hardness and toughness matching between the coating and the substrate, and further enhances electrochemical corrosion resistance is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a ceramic coating and its preparation method to solve the problems existing in the prior art, optimize the hardness and toughness gradient of the coating from the surface to the substrate, meet the requirements of "surface wear resistance and inner crack resistance" in high temperature wear, and further improve the electrochemical corrosion resistance.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention is to provide a ceramic coating, the ceramic coating comprising a NiCr / CoCrFeNiMo support layer and a (Ni-Cr3C2) layer sequentially disposed thereon. x / (CoCrFeNiMo) 1-x Surface working layer; the (Ni-Cr3C2) x / (CoCrFeNiMo) 1-x In the surface working layer, x takes a value of 70~90 wt%.

[0007] Preferably, the thickness of the NiCr / CoCrFeNiMo support layer is 50~60 μm; the (Ni-Cr3C2) x / (CoCrFeNiMo) 1-x The thickness of the surface working layer is 150~180 μm.

[0008] Preferably, in the NiCr / CoCrFeNiMo support layer, the mass ratio of NiCr to CoCrFeNiMo is 1:1.

[0009] The second technical solution of the present invention provides a method for preparing the above-mentioned ceramic coating, comprising the following steps:

[0010] According to the specified dosage, NiCr powder and CoCrFeNiMo powder are mechanically mixed to obtain the support layer composite powder.

[0011] According to the specified dosage, Ni-Cr3C2 powder and CoCrFeNiMo powder are mechanically mixed to obtain the surface working layer composite powder.

[0012] The supporting layer composite powder and the surface working layer composite powder are sequentially sprayed onto the surface of the substrate to form the ceramic coating.

[0013] Preferably, the substrate comprises stainless steel and / or carbon steel.

[0014] Preferably, the mechanical mixing speed is 200~300 r / min and the time is 4~5 h.

[0015] Preferably, the spraying method is a supersonic flame spraying method; the spraying parameters are set independently as follows: powder feeding speed 55~60g / min, oxygen flow rate 1850~1900LPM, propylene flow rate 5~7 LPM, air flow rate 26~28 LPM, spraying distance 315~330 mm, and lateral speed 500~600 mm / s.

[0016] The CoCrFeNiMo high-entropy alloy described in this invention contains elements such as Co and Cr, which are highly compatible with the Cr3C2 coating system. The addition of Mo enhances the coating's corrosion resistance by forming a dense passivation film, while simultaneously refining the grain size to improve wear resistance. Increasing the Mo content shifts the corrosion potential positively, expands the passivation range, and improves high-temperature oxidation resistance. The introduction of CoCrFeNiMo in this invention significantly improves the surface hardness of the coating, ensuring excellent wear resistance. Furthermore, the multi-principal element characteristics of the CoCrFeNiMo high-entropy alloy suppress the formation of brittle phases in the coating, improving the toughness of traditional cermet coatings.

[0017] The NiCr / CoCrFeNiMo support layer of this invention not only enhances the adhesion between the outer coating and the substrate but also provides additional protection against oxidation and hot corrosion at high temperatures. By introducing a high-entropy alloy phase, the NiCr / CoCrFeNiMo support layer comprehensively outperforms a single NiCr support layer in terms of toughness, high-temperature mechanical properties, and corrosion resistance. Therefore, this invention utilizes the NiCr / CoCrFeNiMo support layer and (Ni-Cr3C2)... x / (CoCrFeNiMo) 1-x The combination of the surface working layer optimizes the hardness and toughness gradient of the coating from the surface to the substrate, ensuring that the coating can meet the requirements of "surface wear resistance and inner crack resistance" in high-temperature wear, while further improving its electrochemical corrosion resistance.

[0018] Furthermore, the NiCr / CoCrFeNiMo support layer and (Ni-Cr3C2) described in this invention x / (CoCrFeNiMo) 1-x The ceramic coating formed by the surface working layer avoids the drastic changes in interface composition in traditional coatings through "gradient transition," thereby reducing stress concentration and ensuring a tight bond between the coating and the substrate, significantly improving the coating's peel strength.

[0019] The present invention discloses the following technical effects:

[0020] This invention utilizes a NiCr / CoCrFeNiMo support layer and (Ni-Cr3C2) x / (CoCrFeNiMo) 1-x A ceramic coating was prepared by combining the surface working layer with the substrate. The coating has a tight bond with the substrate, low porosity, significantly improved average microhardness, high toughness, and excellent high-temperature wear resistance and electrochemical corrosion resistance. Attached Figure Description

[0021] Figure 1The images show the morphology and particle size distribution of NiCr powder, Ni-Cr3C2 powder, and CoCrFeNiMo powder described in Example 1. Specifically, a is the morphology of CoCrFeNiMo powder, b is the particle size distribution of CoCrFeNiMo powder, c is the morphology of NiCr powder, d is the particle size distribution of NiCr powder, e is the morphology of Ni-Cr3C2 powder, and f is the particle size distribution of Ni-Cr3C2 powder.

[0022] Figure 2 The images show the cross-sectional morphology and XRD patterns of the C0, C1, C2, and C3 coatings prepared in Example 1. Specifically, a represents the cross-sectional morphology of the C0 coating, b represents the XRD pattern of the C0 coating and C0 powder, c represents the cross-sectional morphology of the C1 coating, d represents the XRD pattern of the C1 coating and C1 powder, e represents the cross-sectional morphology of the C2 coating, f represents the XRD pattern of the C2 coating and C2 powder, g represents the cross-sectional morphology of the C3 coating, and h represents the XRD pattern of the C3 coating and C3 powder.

[0023] Figure 3 The porosity is the value of the C0, C1, C2, and C3 coatings prepared in Example 1.

[0024] Figure 4 The cross-sectional microhardness distribution and surface fracture toughness of the C0, C1, C2, and C3 coatings prepared in Example 1 are shown, where a represents the cross-sectional microhardness distribution and b represents the surface fracture toughness.

[0025] Figure 5 The friction coefficient curves for the CO, C1, C2, and C3 coatings prepared in Example 1 are shown.

[0026] Figure 6 The images show SEM images of the wear marks and corresponding elemental distribution diagrams of the C0, C1, C2, and C3 coatings prepared in Example 1, where a is the C0 coating, b is the C1 coating, c is the C2 coating, and d is the C3 coating.

[0027] Figure 7 The results of the component analysis of wear marks on the C0, C1, C2 and C3 coatings prepared in Example 1 are shown. (a) represents the C0 coating and (b) represents the C1, C2 and C3 coatings.

[0028] Figure 8 The three-dimensional morphology, depth, and wear data of the C0, C1, C2, and C3 coatings prepared in Example 1 under high-temperature friction and wear at 700°C are shown. In this figure, a represents the C0 coating, b represents the C1 coating, c represents the C2 coating, d represents the C3 coating, e represents the depth, and f represents the wear data.

[0029] Figure 9The electrochemical polarization curves of the CO, C1, C2, and C3 coatings prepared in Example 1 in 3.5 wt% NaCl solution are shown.

[0030] Figure 10 The images show the SEM morphology and corresponding elemental distribution of the C0, C1, C2, and C3 coatings prepared in Example 1 after etching, where a is the C0 coating, b is the C1 coating, c is the C2 coating, and d is the C3 coating.

[0031] Figure 11 Impedance diagrams of the CO, C1, C2, and C3 coatings prepared in Example 1 in 3.5 wt% NaCl solution, where a is the Nyquist diagram and b is the Bode diagram.

[0032] Figure 12 The equivalent circuit model of the C0, C1, C2, and C3 coatings prepared in Example 1 is shown, where a represents the C0 and C3 coatings and b represents the C1 and C2 coatings. Detailed Implementation

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0039] Unless otherwise specified, all raw materials used in the following embodiments and performance tests of this invention are commercially available products, and the source of these commercially available products does not affect the technical effect of this invention.

[0040] Example 1

[0041] This embodiment prepared three coatings with different surface working layers, the difference being (Ni-Cr3C2). x / (CoCrFeNiMo) 1-x The content of CoCrFeNiMo in the surface working layer varies. Furthermore, a 25NiCr-75Cr3C2 coating was prepared using the same process as a comparison; the specific parameter settings and preparation steps are as follows:

[0042] Parameter selection: In the NiCr / CoCrFeNiMo support layer, the mass ratio of NiCr to CoCrFeNiMo is 1:1 (Ni-Cr3C2). x / (CoCrFeNiMo) 1-x The contents of Ni-Cr3C2 and CoCrFeNiMo in the surface working layer are shown in Table 1. In addition, a coating labeled C0 (the support layer of the C0 coating is a NiCr layer and the surface working layer is 25NiCr-75Cr3C2) was prepared using commercially available sintered 25NiCr-75Cr3C2 powder as a comparative experimental coating. Its HVOF preparation process parameters are the same as those of other coatings.

[0043] Table 1 Parameter Selection

[0044]

[0045] Preparation steps for C1, C2, and C3 coatings:

[0046] Prepare NiCr powder (purchased from Chongyi Zhangyuan Tungsten Industry Co., Ltd.), Ni-Cr3C2 powder (purchased from Chongyi Zhangyuan Tungsten Industry Co., Ltd.), and CoCrFeNiMo powder (purchased from Beijing Yanbang New Materials Co., Ltd.) with a particle size range of 15~53 μm.

[0047] According to the specified dosage, NiCr powder and CoCrFeNiMo powder were placed in a planetary ball mill and mechanically mixed at a speed of 200 r / min for 4 h to obtain the support layer composite powder.

[0048] According to the specified dosage, Ni-Cr3C2 powder and CoCrFeNiMo powder were placed in a planetary ball mill and mechanically mixed at a speed of 200 r / min for 4 h to obtain the surface working layer composite powder.

[0049] A 20Cr13 stainless steel substrate was used. A JP8000 HVOF system was employed to sequentially spray the support layer composite powder and the surface working layer composite powder onto the substrate surface according to the process parameters described in Table 2, forming three different coatings, denoted as C1, C2, and C3. The thickness of the NiCr / CoCrFeNiMo support layer in each coating was 50 μm (Ni-Cr3C2). x / (CoCrFeNiMo) 1-x The thickness of the surface working layer is 150 μm.

[0050] Preparation steps of C0 coating:

[0051] Prepare NiCr powder with a particle size range of 15~53 μm (purchased from Chongyi Zhangyuan Tungsten Industry Co., Ltd.) and sintered 25NiCr-75Cr3C2 powder (purchased from Chongyi Zhangyuan Tungsten Industry Co., Ltd.).

[0052] According to the specified dosage, NiCr powder was placed in a planetary ball mill and mechanically mixed at a speed of 200 r / min for 4 h to obtain the support layer composite powder.

[0053] According to the specified dosage, sintered 25NiCr-75Cr3C2 powder was placed in a planetary ball mill and mechanically mixed at a speed of 200 r / min for 4 h to obtain the surface working layer composite powder.

[0054] A 20Cr13 stainless steel substrate was used. A JP8000 HVOF system was employed to sequentially spray the support layer composite powder and the surface working layer composite powder onto the surface of the 20Cr13 stainless steel substrate according to the process parameters described in Table 2, forming a coating denoted as C0. The thickness of the NiCr support layer in the coating was 50 μm, and the thickness of the 25NiCr-75Cr3C2 surface working layer was 150 μm.

[0055] Table 2 Process Parameters

[0056]

[0057] Performance testing:

[0058] 1. Microstructure and phase structure analysis:

[0059] The microstructure and composition of the raw material powder, coating structure, and surface features of the samples were observed using a Hitachi SU5000 scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS).

[0060] Phase analysis of the coating was performed using a Bruker D8 Advance X-ray diffractometer (XRD). The specific parameters were: Cu Kα rays (λ=1.54056Å), step size 0.02°, scanning angle 30°~90°, and scanning speed 2° / min. The porosity (area fraction) of the cross-sectional SEM images was quantitatively analyzed using ImagePro Plus 6.0 software.

[0061] Figure 1 The images show the morphology and particle size distribution of NiCr powder, Ni-Cr3C2 powder, and CoCrFeNiMo powder described in Example 1. Specifically, a is the morphology of CoCrFeNiMo powder, b is the particle size distribution of CoCrFeNiMo powder, c is the morphology of NiCr powder, d is the particle size distribution of NiCr powder, e is the morphology of Ni-Cr3C2 powder, and f is the particle size distribution of Ni-Cr3C2 powder.

[0062] from Figure 1 As can be seen from a, c, and e, CoCrFeNiMo powder exhibits a regular spherical shape, while NiCr powder is nearly ellipsoidal, with a smooth surface and good fluidity. It heats evenly during spraying, which is beneficial for forming a smooth and dense coating. Ni-Cr3C2 powder has a spherical cellular structure, with no obvious defects or flaws, and is a typical agglomerated-sintered powder. This structure has a uniform internal composition, effectively avoiding component segregation, and also possesses good fluidity, resulting in a tighter bond between powder particles, which is beneficial for improving the uniformity and density of the coating. From... Figure 1 As can be seen from b, d, and f, the average particle sizes of CoCrFeNiMo powder, NiCr powder, and Ni-Cr3C2 powder are 26.23±9 μm, 33.84±13 μm, and 26.19±8 μm, respectively. The particle size distribution is ideal and the size is uniform, which meets the particle size requirements of the HVOF spraying process. This ensures uniform melting and full spreading of the particles, significantly improving the spraying efficiency and coating performance.

[0063] Table 3. EDS elemental composition of NiCr powder, Ni-Cr3C2 powder, and CoCrFeNiMo powder described in Example 1

[0064]

[0065] The surface morphology and internal EDS surface scan results of each powder showed that each element had a low standard deviation value, indicating that the chemical composition was uniformly distributed, and there was no obvious elemental segregation or aggregation in the powder, indicating that the powder quality was stable.

[0066] Figure 2 The images show the cross-sectional morphology and XRD patterns of the C0, C1, C2, and C3 coatings prepared in Example 1. Specifically, a represents the cross-sectional morphology of the C0 coating, b represents the XRD pattern of the C0 coating and C0 powder, c represents the cross-sectional morphology of the C1 coating, d represents the XRD pattern of the C1 coating and C1 powder, e represents the cross-sectional morphology of the C2 coating, f represents the XRD pattern of the C2 coating and C2 powder, g represents the cross-sectional morphology of the C3 coating, and h represents the XRD pattern of the C3 coating and C3 powder.

[0067] The cross-sectional morphology of the coating shows that it bonds well to the substrate, with no obvious gaps or defects, indicating good density and uniformity. Analysis of the magnified image of the coating structure further reveals… Figure 2 As shown in a, c, e, and g, the C0 coating consists of a blocky gray-black A phase and small blocky gray-white B phase. The C1, C2, and C3 coatings with added CoCrFeNiMo consist of a blocky gray-black A phase, a smaller amount of small blocky gray-white B phase, and an ellipsoidal gray-white C phase. EDS spot scan analysis of the coatings (as shown in Table 4) revealed that the A phase is Cr3C2, the B phase is NiCr, and the C phase is FCC. Furthermore, the measured elemental chemical concentrations of the coatings are consistent with the nominal composition of the powder, indicating the thermal stability of the powder and the excellent composition retention capability of the HVOF process. Figure 2 From b, d, f, and h, it can be seen that compared to powder, the C0 coating, except for Cr... 0.7 Ni 0.3 Cr3C2 phase, and also a small amount of Cr 23 The C6 phase is caused by excessively high local flame temperature during the spraying process, leading to a decarburization reaction of the Cr3C2 phase: 23Cr3C2 → 3Cr 23 C6+14C. FCC diffraction peaks are formed in the C1, C2, and C3 coatings doped with CoCrFeNiMo, and the diffraction peaks intensify with increasing content, forming a composite structure of "carbide + FCC solid solution". XRD patterns show that the powder diffraction peaks are sharp, while the coating diffraction peaks are broadened. This is because the powder is crystalline, and the powder particles undergo rapid cooling and high-speed flattening during spraying, resulting in grain refinement and broadened diffraction peaks. Compared to the powder, the coating diffraction peaks shift to the left and decrease in height, indicating an increased interplanar spacing. This is attributed to the rapid solidification and flattening of particles at high temperature and speed during spraying, leading to residual compressive stress within the coating and localized amorphization or decreased crystallinity.

[0068] Table 4. Results of EDS energy dispersive spectroscopy composition analysis

[0069]

[0070] Figure 3 The porosity is the value of the C0, C1, C2, and C3 coatings prepared in Example 1.

[0071] The distribution characteristics and number of pores in the coating were statistically analyzed using ImageJ software. The results showed that the porosity of each coating was less than 2%, which indicates that the coating structure has excellent density and uniformity.

[0072] 2. Mechanical properties:

[0073] The fracture toughness of each coating was measured using a CSI-TE048 electric Brinell hardness tester. The load was 100 kg and held for 10 s. The fracture toughness was calculated by measuring the crack length of the Vickers hardness indentation angle and then using the Wilshaw formula. Each sample was measured 10 times, and the average value and standard deviation were calculated.

[0074] Wilshaw formula: In the formula, P is the load (N), a is half the length of the indentation diagonal (μm), c is the distance from the center of the indentation to the end of the crack (μm), and K... IC Fracture toughness (MPa·m) 1 / 2 ).

[0075] The cross-sectional microhardness of each coating was tested using an HXD-1000 micro Vickers hardness tester. The test load was 200 g, the holding time was 15 s, and at least 10 individual measurements were performed. The hardness value of each coating was obtained by averaging the 10 repeated measurements.

[0076] Figure 4 The cross-sectional microhardness distribution and surface fracture toughness of the C0, C1, C2, and C3 coatings prepared in Example 1 are shown, where a represents the cross-sectional microhardness distribution and b represents the surface fracture toughness.

[0077] Depend on Figure 4As shown in Figure a, the microhardness across the coating cross-section did not exhibit significant fluctuations, indicating that the composite coating possesses uniformity and consistency in composition and structure. With increasing CoCrFeNiMo content, the coating hardness decreased. This is due, on one hand, to the dilution of the Cr3C2 hard phase, leading to a reduction in coating hardness; on the other hand, the synergistic effect of porosity and defects resulted in a certain degree of decrease in the hardness test value. The microhardness of the support layer improved. The addition of CoCrFeNiMo and NiCr resulted in elemental diffusion, forming multi-element synergistic solid solution strengthening, which effectively improved the hardness of the NiCr support layer. This helps improve the matching of thermal expansion coefficients between coatings, promotes metallurgical bonding between coatings and the substrate, and enhances compatibility at the interface. (See Figure a). Figure 4 As shown in b, the surface fracture toughness of the coating is revealed. This parameter reflects the coating's cracking sensitivity and internal toughness characteristics. With increasing CoCrFeNiMo content, the surface fracture toughness of the coating first increases and then decreases. The fracture toughness of the C0 coating is 4.1 MPa·m. 1 / 2 The C1 coating has a strength of 5.73 MPa·m. 1 / 2 The CoCrFeNiMo content improved by 39.5% compared to the CO coating, indicating that the appropriate addition of CoCrFeNiMo can effectively enhance the fracture toughness of the coating. On one hand, at low contents, CoCrFeNiMo can uniformly dissolve in the NiCr substrate and Cr3C2 phase to form an interfacial solid solution layer. The lattice distortion of the solid solution atoms hinders dislocation movement, while refining the grains and increasing the number of grain boundaries. Grain boundaries, as physical barriers to crack propagation, can promote crack deflection or bifurcation, increasing the tortuosity of the crack propagation path, thereby consuming more fracture energy and improving toughness. On the other hand, when the CoCrFeNiMo content exceeds the solid solubility limit, the excess alloying elements Mo and Fe will form Co3Mo, FeNi3 intermetallic compounds or complex carbides, resulting in significant stress concentration and becoming preferential sites for crack initiation. Simultaneously, the excessive accumulation of CoCrFeNiMo leads to increased interfacial defects and porosity, resulting in a decrease in fracture toughness.

[0078] 3. High-temperature wear performance:

[0079] The tribological properties of each coating on an Al₂O₃ ball with a diameter of 6 mm were tested using an MPT-3G ball-disc tribological testing machine (Jinan Hengxu Testing Machine Technology Co., Ltd.) under a load of 15 N and a heating temperature of 700℃. The wear trajectory radius was 2 cm, the sample rotation speed was 200 r / min, and the high-temperature wear test lasted for 60 min. The depth and wear volume of each sample were measured on the wear trajectory using a three-dimensional optical interferometry (Leica DCM-8) instrument. Three tests were performed to obtain the average wear rate of the coating. The cross-sections of the worn samples were examined using SEM and EDS. The elemental valence states and composition of the coating surface after the high-temperature tribological test were analyzed by photoelectron spectroscopy (XPS).

[0080] The wear rate is calculated using the following formula:

[0081] In the formula, The wear rate of the sample (mm) 3 / N·m), V is the wear volume (mm). 3 L represents the grinding distance (m), and P represents the load (N).

[0082] Figure 5 The friction coefficient curves for the CO, C1, C2, and C3 coatings prepared in Example 1 are shown.

[0083] Depend on Figure 5 It is known that the coefficient of friction (COF) of the C0 coating exhibits unsteady oscillations during high-temperature friction at 700℃, showing instantaneous spikes and drops. This is due to the uneven formation of the mixed NiO and Cr3O2 oxide film. In some areas, the oxide film peels off due to the combined effects of thermal and frictional stress, exposing the bare NiCr substrate to direct contact with the mating part. This triggers intense adhesive friction, causing a sharp increase in the coefficient of friction. Subsequently, the substrate rapidly oxidizes to form a new film, and the coefficient of friction drops sharply due to the lubricating effect of the oxide film, forming a periodic oscillation of "peeling-regeneration," further disrupting the stability of the friction interface. In contrast, the COF curves of the C1, C2, and C3 coatings are smoother and more stable, with smaller fluctuations. Among them, the C1 coating has the highest coefficient of friction, followed by the C2 coating, and the C3 coating has the lowest. This indicates that the composite coating with added CoCrFeNiMo can effectively maintain interfacial continuity and improve the frictional stability of the coating. In high-entropy alloys, the synergistic oxidation of multiple principal elements (Co, Cr, Fe, Ni, Mo) forms a complex solid solution oxide film with Cr3C2. This multiphase synergistic effect keeps the friction interface in a state of "stable wear-gradual repair" and suppresses friction fluctuations.

[0084] Figure 6The images show SEM images of the wear marks and corresponding elemental distribution diagrams of the C0, C1, C2, and C3 coatings prepared in Example 1, where a is the C0 coating, b is the C1 coating, c is the C2 coating, and d is the C3 coating.

[0085] Figure 7 The results of the component analysis of wear marks on the C0, C1, C2 and C3 coatings prepared in Example 1 are shown. (a) represents the C0 coating and (b) represents the C1, C2 and C3 coatings.

[0086] It can be seen that the wear trace morphologies of the C1, C2, and C3 coatings with added CoCrFeNiMo are quite similar, while the wear trace morphology of the C0 coating without added CoCrFeNiMo is significantly different. The C0 coating shows the most severe plastic accumulation at the wear edge, with visible furrows up to 1000 μm wide. The wear surface contains island-like spalling areas, pits formed by hard particles, and wear debris, accompanied by obvious microcracks exhibiting brittle fracture characteristics, indicating that the coating underwent significant abrasive wear and spalling. EDS energy dispersive spectroscopy results show that the wear area in the figure is rich in Ni, Cr, and O elements, indicating that the coating surface underwent oxidation during high-temperature wear. XPS results further confirm that these oxides are mainly composed of Cr2O3 and NiO. Due to CTE mismatch and cyclic mechanical stress, the Cr2O3 layer fractured, forming local spalling areas and wear debris, exposing the unprotected softened NiCr binder phase to directly contact the mating part, inducing severe adhesive-shear wear, resulting in uneven Ni element distribution. Most oxides have lubricating properties and can improve the wear resistance of coatings to some extent. Cr2O3 has a certain protective effect, but NiO has a fast growth rate and a loose structure, making it prone to cracking and peeling, with poor adhesion. Furthermore, a single oxide film peels off under the cyclic action of thermal and frictional stresses, leading to discontinuity and accelerating oxidation-peeling cyclic wear. The main wear mechanisms of C0 coatings are fatigue wear, abrasive wear, and severe oxidation and adhesive wear. Compared to C0 coatings, the wear morphology of C1, C2, and C3 coatings is quite similar. The worn surface of the coating is mainly characterized by shallow, fine scratches and uniformly distributed fine wear debris, without obvious microcracks or significant peeling pits, indicating a significant reduction in abrasive wear and peeling. Moreover, with the increase of CoCrFeNiMo content, the wear track width decreases, and the wear resistance of the coating improves. On the one hand, CoCrFeNiMo forms a solid solution with NiCr, resulting in stronger hard phase-bonding adhesion. During wear, Cr3C2 is less prone to breakage, reducing internal thermal stress in the coating, inhibiting microcrack initiation, and reducing the risk of peeling. On the other hand, CoCrFeNiMo exhibits high-temperature resistance to softening and adhesion. Even at high temperatures, the binder phase maintains high hardness, reducing localized adhesion to the wear pair, improving resistance to ploughing, weakening abrasive wear, and mitigating adhesive wear. EDS energy dispersive spectroscopy results show that the wear region is rich in Co, Cr, Fe, Ni, Mo, and O elements, resulting in a denser and more uniform composite oxide film on the coating surface. XPS results further demonstrate that the synergistic effect of Co, Cr, and Mo elements inhibits the rapid growth of NiO, leading to the formation of a denser, continuous, and lubricating Cr2O3, Co3O4, MoO3, and Fe2O3 composite oxide film on the coating surface.On the one hand, the high-entropy Ni-based solid solution is suppressed to absorb frictional stress and inhibit microcrack propagation; on the other hand, the MoO3 lubricating phase reduces shear resistance, while oxides such as Fe2O3 and CoO form a solid solution with Cr2O3, resisting abrasive cutting and further hindering oxide film rupture, thus inhibiting the formation of large pieces of wear debris and reducing brittle spalling. This multiphase synergistic effect greatly reduces the degree of abrasive wear and adhesive wear, forming an oxidation-lubrication type wear mechanism, which significantly improves the durability of the coating under high-temperature extreme conditions.

[0087] Figure 8 The three-dimensional morphology, depth, and wear data of the C0, C1, C2, and C3 coatings prepared in Example 1 under high-temperature friction and wear at 700°C are shown. In this figure, a represents the C0 coating, b represents the C1 coating, c represents the C2 coating, d represents the C3 coating, e represents the depth, and f represents the wear data.

[0088] Depend on Figure 8 As can be seen from a, b, c, d, and e, the wear scratches of the C0 coating are deep and wide, with severe plastic deformation, forming a deep "U-shaped" groove with steep edges. The wear scratches of the C1, C2, and C3 coatings are "platform-shaped" with gentle edges, indicating that the wear process has changed from severe material removal to slight wear. This shows that the addition of CoCrFeNiMo significantly improves the wear resistance of the coating, and the high-temperature wear resistance of the coating increases with the increase of CoCrFeNiMo content. Figure 8 f represents the wear data of the coatings. The results show that the wear rate, wear volume, and average depth of the wear scratches of the C0 coating are much greater than those of the other three composite coatings. Furthermore, with the increase of CoCrFeNiMo, the wear scratch depth and width decrease. The wear rates of the C0, C1, C2, and C3 coatings are 6.95 × 10⁻⁶, respectively. -5 mm 3 / N·m, 2.11×10 -5 mm 3 / N·m, 1.99×10 -5 mm 3 / N·m, 0.95×10 -5 mm 3 Compared with the C0 coating, the wear rates of the C1, C2, and C3 coatings decreased by 69.64%, 71.37%, and 86.33%, respectively, indicating that the surface working layer of the present invention has better wear resistance under high-temperature extreme conditions compared with the Ni-Cr3C2 coating.

[0089] 4. Electrochemical corrosion resistance:

[0090] Electrochemical corrosion resistance tests were performed using an electrochemical workstation (Shanghai Chenhua CHI660E) in a conventional triode electrode cell. The test solution contained 1 cm³ of electrodes. 2The exposed surface of the coating was used as the working electrode (WE), and a saturated KCl calomel electrode and a platinum sheet were used as the reference electrode (RE) and counter electrode (CE), respectively. Before electrochemical testing, the coating was immersed in the test solution (3.5 wt% NaCl solution) for 1800 s to obtain a stable open-circuit potential (Eocp). All tests were performed at a constant temperature of 298 K maintained in a constant-temperature water bath. Potentiometric polarization measurements were performed on Eocp from ±250 mV at a scan rate of 0.1 mV / s. Potentiometric polarization and impedance measurements were performed on OCP, and an equivalent circuit was selected for fitting analysis. The accuracy and repeatability of the experimental results were ensured by performing three repeated experiments under the same settings. The morphology of the corroded surface was examined using SEM-EDS.

[0091] Figure 9 The electrochemical polarization curves of the CO, C1, C2, and C3 coatings prepared in Example 1 in 3.5 wt% NaCl solution are shown.

[0092] To evaluate the corrosion resistance of each coating in 3.5 wt% NaCl solution, the self-corrosion current density (Icorr), self-corrosion potential (Ecorr), and polarization resistance (Rp) were used to characterize their corrosion resistance. Here, Icorr represents the corrosion rate of the material in the corrosive medium, and Ecorr represents the equilibrium potential of the corrosion reaction, reflecting the material's corrosion tendency in the medium. The smaller the Icorr and the more positive the Ecorr, the better the corrosion resistance. The polarization resistance (Rp) was obtained by Tafel fitting the polarization curves. Polarization resistance (Rp) is a physical parameter of reaction kinetics, which can be used to represent the resistance to charge transfer on the material surface. Polarization resistance (Rp) can be calculated using the Stern-Geary formula: In the formula, βa is the anode Tarfel slope, βc is the cathode Tarfel slope, Icorr is the self-corrosion current density, and Rp is the polarization resistance.

[0093] Table 5. Corrosion resistance of the CO, C1, C2, and C3 coatings prepared in Example 1 in 3.5 wt% NaCl solution.

[0094]

[0095] As shown in Table 5, the C0 coating has the highest Icorr, at 6.412 μA·cm. 2 The Icorr values ​​for coatings C1, C2, and C3 are 0.508 μA·cm⁻¹, respectively. 2 0.725 μA·cm 2 3.484 μA·cm 2Among the coatings, C1 exhibited the lowest self-corrosion current density, indicating that the corrosion resistance of the coating initially increases and then decreases with increasing high-entropy alloy content. Adjusting the CoCrFeNiMo content can effectively reduce the corrosion rate of the coating. Simultaneously, the corrosion resistance of the coating is also related to the Ecorr and Rp indices. Comparing the Ecorr values ​​of the coatings in Table 5, the Ecorr of the C0 coating is -0.275 V, the Ecorr of the C1 coating is the lowest at -0.175 V, and the Ecorr of the C2 and C3 coatings are -0.241 V and -0.357 V, respectively. With increasing high-entropy alloy doping, the Ecorr of the composite material initially decreases and then increases. Adjusting the CoCrFeNiMo content can effectively reduce the corrosion tendency. By comparing the Rp index, the Rp of the C1 coating is more than 10 times higher than that of the C0 coating. Through systematic analysis of these three parameters, it can be concluded that the C1 coating has the best corrosion resistance. Adjusting the CoCrFeNiMo content can effectively improve the corrosion resistance of the coating, and with increasing high-entropy alloy doping, the corrosion resistance of the coating initially increases and then decreases.

[0096] Figure 10 The images show the SEM morphology and corresponding elemental distribution of the C0, C1, C2, and C3 coatings prepared in Example 1 after etching, where a is the C0 coating, b is the C1 coating, c is the C2 coating, and d is the C3 coating.

[0097] C0 coating, such as Figure 10 The surface shown in Figure a has many black corrosion grooves and pits, indicating severe pitting corrosion. This is partly due to the potential difference between the coating structure and composition. A significant potential difference (approximately 0.35 V) exists between the NiCr matrix (electrode potential approximately -0.25 V vs SHE) and the Cr3C2 hard phase (electrode potential approximately +0.1 V vs SHE), forming an "anodic (NiCr) - cathode (Cr3C2)" micro-battery in NaCl solution. This leads to preferential dissolution of the NiCr matrix, making the interface prone to crevice corrosion, forming corrosion trenches, and accelerating the detachment of Cr3C2 particles. Another factor is Cl... - The ions have small ionic radii and high electronegativity, making them readily adsorbed onto the Cr2C3 passivation film on the surface of the NiCr-Cr3C2 coating. -Ions replace oxygen ions in Cr2O3, forming soluble CrCl3, leading to localized film rupture, the formation of corrosion pits, and their propagation into the coating interior. The corrosion morphology of C1 and C2 coatings shows a significant reduction in pitting and corrosion severity, while the C3 coating exhibits black corrosion grooves and pits, indicating that the degree of pitting corrosion initially increases with decreasing high-entropy alloy reinforcement. On one hand, CoCrFeNiMo exhibits good miscibility with the NiCr matrix, forming a single face-centered cubic (FCC) solid solution (electrode potential approximately -0.1~0V vs SHE), reducing the potential difference with Cr3C2 to within 0.1V, thus decreasing the driving force for localized corrosion and suppressing the micro-cell effect by narrowing the potential difference. On the other hand, increasing the Cr2O3 content in the passivation film promotes Cr2O3 film formation while simultaneously increasing the Mo content, generating MoO3 or MoO4 within the film. 2- , for Cl - It exhibits stronger repulsive properties, which can inhibit pitting corrosion initiation. Simultaneously, the multi-element doping of the high-entropy alloy makes the passivation film composition more complex (Cr2O3-MoO4). 2- -Co(OH)2-Ni(OH)2 passivation film), the film has better density and conductivity, and can effectively hinder charge transfer and ion diffusion. However, excessive CoCrFeNiMo HEA increases the porosity of the coating and phase interface defects, Cl - Ions adsorb and replace oxygen atoms at defects such as pores and grain boundaries, causing local rupture of the passivation film, forming corrosion pits that extend into the coating, resulting in increased pitting corrosion of the C3 coating and a decrease in its corrosion resistance.

[0098] Figure 11 Impedance diagrams of the CO, C1, C2, and C3 coatings prepared in Example 1 in 3.5 wt% NaCl solution, where a is the Nyquist diagram and b is the Bode diagram.

[0099] Figure 11 Figure 'a' shows the Nyquist plot of EIS. The semicircle diameter reflects the charge transfer resistance (Rct). The larger the Rct, the more difficult the charge transfer and the stronger the corrosion resistance. The C1 coating has the largest semicircle, indicating its strongest ability to inhibit corrosion reactions, while the C0 coating has the smallest semicircle, indicating the worst corrosion resistance. Figure 11 Figure b shows the Bode plot of the coatings. A higher and wider phase angle peak indicates a stronger ability of the coating to impede ion diffusion. The phase angle peaks of the C1, C2, and C3 coatings are 66.7°, 62.7°, and 49.5°, respectively, significantly higher than the 38.2° peak of the C0 coating. In the low-frequency region... -2The higher the Hz modulus, the better the long-term corrosion resistance. The C0 coating has the lowest modulus and the worst corrosion resistance, while the C1 coating has the highest modulus in the low-frequency region and can resist the penetration of corrosive media for a long time. Electrochemical impedance spectroscopy (EIS) shows that the C1 coating has the best corrosion resistance, indicating that adding an appropriate amount of CoCrFeNiMo high-entropy alloy can effectively improve the impedance characteristics of the coating in corrosive environments and enhance its corrosion resistance.

[0100] Figure 12 The equivalent circuit model of the C0, C1, C2, and C3 coatings prepared in Example 1 is shown, where a represents the C0 and C3 coatings and b represents the C1 and C2 coatings.

[0101] To understand the electrode reactions during electrochemical corrosion, impedance data were fitted using Zview software. R1 represents the resistance generated in a 3.5 wt% NaCl solution, and R2 represents the charge transfer resistance between the composite material and the 3.5 wt% NaCl solution, i.e., the resistance between the solution and the working electrode. W represents the Warburg impedance, and the parameter W... 1-R For diffusion resistance, W 1-T W is the diffusion time constant. 1-P CPE is the phase angle parameter, representing an ideal capacitor or reactance element. 1-P CPE is the phase angle index. 1-T is the admittance coefficient.

[0102] Table 6. EIS fitting results of the C0, C1, C2, and C3 coatings prepared in Example 1.

[0103]

[0104] As shown in Table 6, the lowest R2 value for the C0 coating is 673.8 Ω·cm. 2 CPE 1-P The lowest is 0.66109Ω. -1 ·cm -2 ·s -1 This indicates that the coating is porous and has many defects, making it easy for electrolyte to penetrate and resulting in the worst corrosion resistance. As the doping amount of high-entropy alloy increases, the corrosion resistance of the coating first improves and then weakens. Among them, the C1 coating has the lowest CPE. 1-P The value is 0.73927, close to the ideal capacitance, indicating that the passivation film is uniform and has high density. The highest R2 is 42237 Ω·cm. 2 The resistivity is 63 times that of C0, indicating extremely high film resistivity and significant suppression of corrosion reaction. The results are consistent with the polarization curves and EIS analysis.

[0105] In summary, the surface fracture toughness of the CoCrFeNiMo high-entropy alloying agent first increases and then decreases with increasing dosage. The coating exhibits the best surface fracture toughness (5.73 MPa·m) when the agent dosage reaches 10 wt%. 1 / 2 The wear resistance was improved by 39.5% compared to the NiCr-Cr3C2 coating. The high-temperature wear resistance of the coating improved with the increase of the CoCrFeNiMo high-entropy alloy reinforcing agent. The best high-temperature wear resistance was achieved when the reinforcing agent content reached 30wt%, with a wear rate of 0.95×10⁻⁶. -5 mm 3 The corrosion resistance (R²) was reduced by 86.33% compared to the NiCr-Cr3C2 coating, and the wear mechanism changed from "oxidation-stripping type" to "oxidation-lubrication type". The corrosion resistance of the coating initially improved and then weakened with the increase of the CoCrFeNiMo high-entropy alloy reinforcing agent. The coating exhibited the best corrosion resistance with an R² of 42237 Ω·cm when the reinforcing agent content reached 10 wt%. 2 It is 63 times that of the NiCr-Cr3C2 coating.

[0106] This invention successfully prepared a ceramic coating with excellent mechanical properties, high-temperature wear resistance, and electrochemical corrosion resistance using HVOF technology.

[0107] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0108] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A ceramic coating, characterized in that, The ceramic coating comprises a NiCr / CoCrFeNiMo support layer and a (Ni-Cr3C2) layer arranged sequentially. x / (CoCrFeNiMo) 1-x Surface working layer; the ((Ni-Cr3C2)) x / (CoCrFeNiMo) 1-x In the surface working layer, x takes a value of 70~90 wt%; When x is 70wt%, the wear rate of the ceramic coating is 0.95×10⁻⁶. -5 mm 3 / N·m; When x is 90wt%, the fracture toughness of the ceramic coating reaches 5.7 MPa·m. 1 / 2 ; When x is 90wt%, the self-corrosion current density of the ceramic coating is 0.508 μA·cm. 2 The charge transfer resistance R2 reaches 42237 Ω·cm 2 ; In the NiCr / CoCrFeNiMo support layer, the mass ratio of NiCr to CoCrFeNiMo is 1:

1.

2. The ceramic coating according to claim 1, characterized in that, The thickness of the NiCr / CoCrFeNiMo support layer is 50~60 μm; the (Ni-Cr3C2) x / (CoCrFeNiMo) 1-x The thickness of the surface working layer is 150~180μm.

3. The method for preparing the ceramic coating according to any one of claims 1 to 2, characterized in that, Includes the following steps: According to the specified dosage, NiCr powder and CoCrFeNiMo powder are mechanically mixed to obtain the support layer composite powder. According to the specified dosage, Ni-Cr3C2 powder and CoCrFeNiMo powder are mechanically mixed to obtain the surface working layer composite powder. The supporting layer composite powder and the surface working layer composite powder are sequentially sprayed onto the surface of the substrate to form the ceramic coating.

4. The preparation method according to claim 3, characterized in that, The substrate includes stainless steel and / or carbon steel.

5. The preparation method according to claim 3, characterized in that, The mechanical mixing speed is 200~300 r / min, and the time is 4~5 h.

6. The preparation method according to claim 3, characterized in that, The spraying method is a supersonic flame spraying method; the spraying parameters are set independently as follows: powder feeding speed 55~60 g / min, oxygen flow rate 1850~1900 LPM, propylene flow rate 5~7 LPM, air flow rate 26~28 LPM, spraying distance 315~330 mm, and spraying lateral speed 500~600 mm / s.

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