HVOF spray coating as well as preparation method and application thereof

Abstract

The invention discloses an HVOF spraying coating and a preparation method and application thereof, and belongs to the technical field of high-end equipment manufacturing, and the preparation method of the HVOF spraying coating comprises the following steps that hypersonic flame spraying is adopted, and a transition layer and a working layer are sequentially sprayed on the surface of a base body; the transition layer is made of NiCr (nickel chromium)-CoCrFeNiMo (cobalt chromium) or NiCr (nickel chromium); and the working layer is at least one of the following components: 10 < CoCr > FeNi < 18 > NiCr < 72 > Cr3 < C2 >, 20 < CoCr > FeNi < 16 > NiCr < 64 > Cr3 < C2 >, 75 < NiCr > < 25 > Cr3 < C2 >, 25 < NiCr > < 75 > Cr3 < C2 > and 50 < NiCr > < 50 > Cr3 < C2 >. According to the HVOF spraying coating prepared through the method, collaborative optimization of high-temperature wear resistance and corrosion resistance is achieved, and an effective path is provided for design of a high-performance protective coating under the complex working condition.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-end equipment manufacturing, and particularly relates to an HVOF sprayed coating and a preparation method and application thereof. BACKGROUND

[0002] The rapid development of high-end equipment manufacturing industry has posed unprecedented challenges to the service performance of key mechanical parts under different load, temperature, corrosion and other working conditions. Therefore, the development of high-performance protective coating with excellent wear resistance and outstanding corrosion resistance has become the core goal and major demand of the field of surface engineering. The high-velocity oxy-fuel (HVOF) spraying technology can prepare high-quality coating with low porosity, high bonding strength and low oxide content due to its high flame speed and moderate temperature, and is one of the most widely used wear-resistant coating preparation technologies. Among many thermal spraying materials, the NiCr-Cr3C2 cermet system has been widely used due to its good wear resistance and corrosion resistance in high-temperature, oxidation and corrosion environments. However, with the increasing complexity and harshness of the service conditions of different workpieces, the limitations of the traditional 25NiCr-75Cr3C2 coating in terms of insufficient toughness, limited high-temperature stability and weak ability to resist corrosion-wear synergistic effect have gradually become prominent, and it is difficult to fully meet the long-term service requirements under various complex working conditions. In addition, in recent years, as a new material system, high-entropy alloy breaks the traditional alloy design concept, and its unique four effects endow it with high strength, high hardness, excellent corrosion resistance and excellent high-temperature stability. Among them, CoCrFeNiMo series of high-entropy alloys show better comprehensive performance than traditional stainless steel and nickel-based alloy in many studies, providing a new idea for the design of a new generation of high-performance coating.

[0003] It is generally believed that the friction and wear properties and corrosion resistance mainly depend on the proportion of the binder phase (such as NiCr and NiAl) and the ceramic phase (Cr3C2 and WC), and especially the proportion of the ceramic phase seriously affects the improvement of the wear resistance of the coating. For example, Zhou et al. studied the high-temperature wear properties of HVOF sprayed Cr3C2-WC-NiCoCrMo and Cr3C2-NiCr hard alloy coatings, and the results showed that the wear resistance of the Cr3C2-WC-NiCoCrMo coating was better than that of the Cr3C2-NiCr coating in the wear test at 650℃. Fan et al. studied the effect of Cr3C2 content on the microstructure, mechanical properties and tribological properties of Ni3Al-based coatings, and the results showed that the friction coefficient and wear rate of the coating containing 15wt% Cr3C2 were the lowest in the friction and wear test at 25℃-800℃. Du et al. developed a new type of Cr3C2-NiCrCoMo (NCC) coating, which has a modified multi-element alloy binder phase. Compared with the traditional Cr3C2-NiCr (NC) coating, the newly designed NCC coating has a lower oxidation rate, better oxidation resistance, and improved interfacial compatibility between the oxidation layer and the coating. In addition, studies have shown that due to the uniform distribution of Cr3C2-25NiCr in a combined state, the corrosion-resistant element Cr is not easy to flow away at the atomic scale, and intermetallic compounds have better corrosion resistance than pure elemental metals. Matikainen et al. studied four different binder chemical compositions, contents and powder morphologies of Cr3C2-based coatings, and the results showed that the selection of the binder and its chemical composition affects the microstructure and properties of the coating, thereby determining the wear resistance level of the coating. The selection of the binder and its chemical composition affects the microstructure and properties of the coating, thereby determining the wear resistance level of the coating. Although the above studies discuss the effect of the proportion of the binder phase and the ceramic phase and the additives in the Cr3C2-NiCr coating on the performance of the coating, the adaptability of different types of binder phase and ceramic phase ratio schemes to different working conditions, and the influence mechanism of different temperatures on the formation and evolution of the oxidation film in the friction and wear process still need to be further explored. In particular, the regulation and mechanism of different addition ratios of high-entropy alloy as a new type of binder phase component on the wear resistance and corrosion resistance of the Cr3C2-NiCr coating still need to be further systematically studied. SUMMARY

[0004] In view of the above technical problems, the present application provides a HVOF sprayed coating and a preparation method and application thereof.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] A preparation method of a HVOF sprayed coating, comprising the following steps:

[0007] The transition layer and the working layer are sprayed on the surface of the substrate by high-velocity oxygen fuel spraying.

[0008] The transition layer is NiCr-CoCrFeNiMo or NiCr.

[0009] The working layer is at least one of 10CoCrFeNiMo-18NiCr-72Cr3C2, 20CoCrFeNiMo-16NiCr-64Cr3C2, 75NiCr-25Cr3C2, 25NiCr-75Cr3C2 and 50NiCr-50Cr3C2.

[0010] Optionally, the working layer of the HVOF sprayed coating is 10CoCrFeNiMo-18NiCr-72Cr3C2.

[0011] The transition layer is NiCr-CoCrFeNiMo.

[0012] Optionally, the thickness of the transition layer is 20-80 μm.

[0013] The thickness of the working layer is 200 μm.

[0014] Optionally, the substrate is a pretreated 20CrMo steel base.

[0015] Further, the pretreatment operation is that the substrate is sanded, ultrasonically cleaned with acetone to remove surface oil and impurities, and then subjected to sand blasting roughening treatment.

[0016] Optionally, the preparation process of 10CoCrFeNiMo-18NiCr-72Cr3C2 and 20CoCrFeNiMo-16NiCr-64Cr3C2 is as follows:

[0017] The NiCr-Cr3C2 and the NiCr powder are mixed in proportion to respectively prepare the composite powders 75NiCr-25Cr3C2 and 50NiCr-50Cr3C2.

[0018] The CoCrFeNiMo high-entropy alloy powder is mixed with the composite powders to obtain 10CoCrFeNiMo-18NiCr-72Cr3C2 and 20CoCrFeNiMo-16NiCr-64Cr3C2.

[0019] Optionally, the conditions of the high-velocity oxygen fuel spraying are as follows:

[0020] The powder feeding rate is controlled at 55-60 g / min, the oxygen flow is 1850-1900 LPM, the propylene flow is 6 LPM, the air flow is 21-26 LPM, the spraying distance is 310-360 mm, and the moving speed is 500 mm / s.

[0021] Further, compressed air is used for cooling the substrate throughout the HVOF spraying process.

[0022] An HVOF sprayed coating prepared by the above preparation method.

[0023] Application of the above HVOF sprayed coating in the field of high-end equipment manufacturing.

[0024] Compared with the prior art, the present application has the following advantages and technical effects:

[0025] The present application prepares a series of composite coatings by regulating the content of Cr3C2 in the NiCr-Cr3C2 system and introducing CoCrFeNiMo high-entropy alloy through the HVOF spraying technology. It is found that the 75NiCr-25Cr3C2 coating can form a stable oxide film at high temperature, showing the best wear resistance; while the coating added with high-entropy alloy has a significantly reduced wear rate at 500℃, greatly improved wear resistance, and better corrosion resistance than traditional coatings. That is, the present application realizes the synergistic optimization of high-temperature wear resistance and corrosion resistance, providing an effective path for the design of high-performance protective coatings under complex working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description are used to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0027] Figure 1 SEM morphologies and EDS analysis results of cross sections of NiCr coating and 25NiCr-75Cr3C2 coating; (a) and (b) are NiCr coating, (c) and (d) are 25NiCr-75Cr3C2 coating;

[0028] Figure 2 SEM-EDS analysis results of cross sections of 75NiCr-25Cr3C2 and 50NiCr-50Cr3C2 coatings; (a) and (b) are 75NiCr-25Cr3C2 coating; (c) and (d) are 50NiCr-50Cr3C2 coating;

[0029] Figure 3 SEM-EDS graph of cross section of 10CoCrFeNiMo-18NiCr-72Cr3C2 coating;

[0030] Figure 4 Cross-sectional SEM-EDS analysis results of 20CoCrFeNiMo -16NiCr-64Cr3C2 coating;

[0031] Figure 5 Microhardness distribution curves of cross-sections of coatings with different compositions;

[0032] Figure 6 Three-dimensional profile morphologies of wear traces of different coatings after friction and wear at 350°C;

[0033] Figure 7 Three-dimensional profile morphologies of wear traces of coatings with different composition ratios after friction and wear at 500°C;

[0034] Figure 8 Wear curves and wear rate column charts of different coatings after friction and wear at 350°C and 500°C;

[0035] Figure 9 SEM-EDS images of wear traces of coating samples after coating friction and wear at 350°C; (a) and (b) are NiCr coating; (c) and (d) are 25NiCr-75Cr3C2 coating;

[0036] Figure 10 SEM-EDS images of wear traces of coating samples after coating friction and wear at 500°C; (a) and (b) are NiCr coating; (c) and (d) are 25NiCr-75Cr3C2 coating;

[0037] Figure 11 SEM-EDS images of wear traces of coating samples after coating friction and wear at 350°C; (a) and (b) are 75NiCr-25Cr3C2 coating; (c) and (d) are 50NiCr-50Cr3C2 coating;

[0038] Figure 12 SEM-EDS images of wear traces of coating samples after coating friction and wear at 500°C;

[0039] Figure 13 SEM morphologies and EDS composition analysis results of wear traces of 10CoCrFeNiMo-18NiCr-72Cr3C2 (E) and 20CoCrFeNiMo-16NiCr-64Cr3C2 (F) coatings after friction and wear treatment at 350°C; (a) and (b) are 10CoCrFeNiMo-18NiCr-72Cr3C2 coating; (c) and (d) are 20CoCrFeNiMo-16NiCr-64Cr3C2 coating;

[0040] Figure 14 SEM morphology and EDS composition analysis results of 10CoCrFeNiMo-18NiCr-72Cr3C2 (E) and 20CoCrFeNiMo-16NiCr-64Cr3C2 (F) coating wear tracks after high temperature friction and wear at 500°C; (a) and (b) are 10CoCrFeNiMo-18NiCr-72Cr3C2 coating; (c) and (d) are 20CoCrFeNiMo-16NiCr-64Cr3C2 coating;

[0041] Figure 15 Electrochemical impedance Nyquist plots of coatings with different component ratios in 3.5 wt.% NaCl solution;

[0042] Figure 16 Potentiodynamic polarization curves of coatings with different component ratios in 3.5 wt.% NaCl solution. DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present application will now be described in detail, with reference to the figures. The detailed description is not to be regarded as limiting the application, but rather as an exemplification of certain aspects, features and embodiments of the application.

[0044] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Additionally, for a range of values of a parameter, unless otherwise stated, each intervening value of the parameter is also specifically included within the scope of the application. The intervening values of the parameter are combined with a stated value of the parameter in range form. These are only exemplary of the various values that can be used, and others will suggest themselves to those skilled in the art upon a reading of the disclosure. Also, various "combinations" can be included within the scope of the application. These combinations refer to the various feature combinations of the different embodiments described herein that are not necessarily available from the prior art. All such combinations are specifically included within the scope of the application and are disclosed herein as being among the intended benefits of the application.

[0045] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in further detail the methods and / or materials associated with the documents. In the case of conflict between the present specification and any document incorporated by reference, the present specification will control.

[0046] Various modifications and changes can be made to the specific embodiments of the application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples presented herein. The description and examples are illustrative of the application and are not intended to limit the scope of the application in any way.

[0047] As used herein, the terms "comprise", "comprising", "include", "including", "have" and "having" or the like are open-ended, that is, meaning "including but not limited to".

[0048] "Room temperature" as used herein, unless otherwise specified, refers to 20-30℃.

[0049] "Parts" as used herein, unless otherwise specified, refers to mass parts.

[0050] The raw materials used in the present application are all obtained by purchase on the market. The 25NiCr-75Cr3C2 and Ni80Cr20 (referred to as NiCr) powders used in the present application are provided by Chongyi Shanzhong Tungsten Industry Co., Ltd.; the CoCrFeNiMo high-entropy alloy powder is purchased from Beijing Yanbang New Material Technology Co., Ltd., and the specific composition is shown in Table 1; and the base material is 20CrMo steel.

[0051] Table 1 Composition of CoCrFeNiMo high-entropy alloy powder (at. %)

[0052]

[0053] The technical solutions of the present application are further illustrated by the following examples.

[0054] Example 1

[0055] A preparation method of an HVOF sprayed coating, comprising the following steps:

[0056] Step one: pretreatment of the substrate

[0057] The 20CrMo steel substrate (size 200x200x12 mm) was sequentially polished with sandpaper, ultrasonically cleaned with acetone to remove surface oil and impurities, and then subjected to sandblasting roughening treatment to improve the bonding strength of the coating and the substrate.

[0058] Step two: preparation of the powder

[0059] (1) Select commercially available 25NiCr-75Cr3C2 (wherein NiCr is Ni80Cr20, the ratio is weight percent), NiCr (Ni80Cr20) and CoCrFeNiMo high-entropy alloy powder as raw materials. Among them, the NiCr powder is elliptical, the particle size range is 10-100 μm, and the average particle size is 37.10 ± 15.19 μm; the NiCr-Cr3C2 powder is spherical, the particle size distribution is between 10-45 μm, and the average particle size is 22.19 ± 6.06 μm.

[0060] (2) The 25NiCr-75Cr3C2 and NiCr powders were mixed by mechanical mixing method to prepare two kinds of composite powders, 75NiCr-25Cr3C2 and 50NiCr-50Cr3C2;

[0061] (3) The CoCrFeNiMo high-entropy alloy powder was mixed with the two kinds of composite powders to obtain two new composite powders, 10CoCrFeNiMo-18NiCr-72Cr3C2 and 20CoCrFeNiMo-16NiCr-64Cr3C2.

[0062] Step three: preparation of the composite coating by supersonic flame spraying

[0063] (1) The powder prepared in step two was dried at 280°C for 6 hours to remove water and improve its flowability and dispersibility. A JP8000 supersonic flame spraying system was used for coating deposition. Before spraying, the substrate after sand blasting treatment was rapidly preheated.

[0064] (2) Then, a 50 μm-thick transition layer was sprayed on the surface of the substrate: for the NiCr, 25NiCr-75Cr3C2, 75NiCr-25Cr3C2 and 50NiCr-50Cr3C2 coatings, the transition layer was NiCr; for the 10CoCrFeNiMo-18NiCr-72Cr3C2 and 20CoCrFeNiMo-16NiCr-64Cr3C2 coatings, the transition layer was the composite powder of NiCr and CoCrFeNiMo;

[0065] (3) After the completion of the transition layer, a 150 μm-thick working layer was continuously sprayed, and the compositions were NiCr, 25NiCr-75Cr3C2, 75NiCr-25Cr3C2, 50NiCr-50Cr3C2, 10CoCrFeNiMo-18NiCr-72Cr3C2 and 20CoCrFeNiMo-16NiCr-64Cr3C2, respectively;

[0066] During the spraying process, the powder feeding rate was controlled at 55-60 g / min, the oxygen flow rate was 1850-1900 LPM, the propylene flow rate was 6 LPM, the air flow rate was 21-26 LPM, the spraying distance was 310-360 mm, and the moving speed was 500 mm / s. To prevent the substrate from overheating and deforming, compressed air was used to cool the substrate throughout the process. After the spraying was completed, the coating sample was processed into a 15×15×12 mm specimen using a wire cutting technique, which was used for subsequent testing and analysis of the microstructure, mechanical properties, friction and wear, and electrochemical corrosion performance. The specific spraying process parameters of the coatings with different compositions are shown in Table 2.

[0067] Table 2. Spray process parameters for different composition coatings

[0068]

[0069] Effect verification:

[0070] I. Cross-sectional microstructure analysis of the coating

[0071] Figure 1 SEM and EDS analysis results of the cross-section of NiCr coating (A) and 25NiCr-75Cr3C2coating (B). The overall NiCr coating is white, with uniform and dense structure, fewer defects, and porosity less than 0.5%, with a thickness of about 160 μm. Figure 1 (c) and (d) are SEM-EDS images of the 25NiCr-75Cr3C2working layer, which is about 150 μm thick and mainly composed of Cr3C2ceramic phase and NiCr binder phase, with a lot of defects inside and a porosity of not less than 1.8%. A 50 μm thick NiCr transition layer is provided between the 25NiCr-75Cr3C2coating and the substrate, which plays the following key roles: (1) relieving the mismatch of the thermal expansion coefficient: through gradient transition, the thermal stress is gradually released and redistributed, avoiding stress concentration on a single interface, significantly reducing the risk of coating cracking and peeling; (2) enhancing the bonding strength of the coating: NiCr alloy has excellent compatibility with metal substrates (such as steel or nickel-based alloy), and its toughness characteristics help to form a strong and tough metallurgical-mechanical composite bonding interface, providing reliable support for the coating system; (3) inhibiting element interdiffusion: the dense NiCr layer can act as an effective diffusion barrier, and its high stability can prevent the migration of C, Fe and other elements across the interface, preventing the formation of brittle harmful phases.

[0072] Figure 2 SEM-EDS analysis results of the cross-section of 75NiCr-25Cr3C2(C) and 50NiCr-50Cr3C2(D) coatings. The total thickness of the two coatings is about 150 μm, and each contains a 50 μm thick NiCr transition layer. In terms of phase distribution, the 75NiCr-25Cr3C2coating has a higher content of NiCr binder phase, while the 50NiCr-50Cr3C2coating has a relatively lower proportion of NiCr phase. It is worth noting that the NiCr phase and Cr3C2ceramic phase in the two coatings are alternately spaced, which helps to hinder the initiation and propagation of thermal cracks, effectively relieving the cracking tendency of the coating under thermal load.

[0073] Figure 3The image shows a cross-sectional SEM-EDS image of the 10CoCrFeNiMo-18NiCr-72Cr3C2(E) coating. The working layer thickness is approximately 200 μm, and the thickness of the CoCrFeNiMo-NiCr intermediate transition layer is between 20 and 80 μm. The working layer exhibits high overall density, few defects, and a porosity of approximately 1%. The high-entropy CoCrFeNiMo alloy phase displays a streamlined distribution in both the working and transition layers, appearing as white in the image, demonstrating good plastic rheological characteristics and structural compatibility.

[0074] Figure 4 The results of cross-sectional SEM-EDS analysis of the 20CoCrFeNiMo-16NiCr-64Cr3C2(F) coating are shown. Figure 4 As shown in (a), the working layer of the coating is approximately 180 μm thick, and the thickness of the CoCrFeNiMo-NiCr intermediate transition layer ranges from 45 to 90 μm. The working layer has a dense structure with few defects and a porosity of no more than 1%. The CoCrFeNiMo high-entropy alloy phase is mainly distributed in a streamlined shape in the working layer, with a few exhibiting ellipsoidal morphology; while in the transition layer, it is predominantly ellipsoidal with a secondary streamlined distribution. This high-entropy alloy phase is shown as white in the figure, reflecting its good plastic deformation adaptability in the coating and its compatibility with the substrate.

[0075] II. Friction and Wear Test

[0076] High-temperature tribological performance tests were conducted on six coating samples (A, B, C, D, E, and F). The experiments were performed on an MPT-3G high-temperature wear testing machine manufactured by Jinan Hengxu Testing Machine Technology Co., Ltd., which has a maximum load of 300 N and a maximum operating temperature of 1000℃. φ6 mm Al2O3 balls were used as the friction pair, and the sample size was uniformly 15×15×12 mm. Specific experimental parameters are shown in Table 3. Five repeated tribological tests were performed on each sample to ensure the reliability and accuracy of the experimental results. Wear volume and wear rate results are expressed as mean ± standard deviation. After the tests, a three-dimensional profilometer was used to measure the wear track morphology and wear volume, and the wear rate was calculated according to the following formula:

[0077] (1)

[0078] In equation (1), W represents the wear rate (mm³ / Nm), and Vc represents the wear volume (mm³ / Nm). 3 L represents the applied force (N), and S represents the sliding displacement (m).

[0079] Table 3 Friction and Wear Test Parameters

[0080]

[0081] Figure 5 Microhardness profiles of cross-sections of different composition coatings. It can be seen from the figure that the 25NiCr-75Cr3C2 coating (B coating) has the highest hardness, which is mainly due to its highest Cr3C2 ceramic phase content; followed by the 10CoCrFeNiMo-18NiCr-72Cr3C2 coating (E coating). With the decrease of ceramic phase content, the hardness decreases in turn, and the order is 20CoCrFeNiMo-16NiCr-64Cr3C2 coating (F coating), 50NiCr-50Cr3C2 coating (D coating), 75NiCr-25Cr3C2 coating (C coating) and NiCr coating (A coating). The hardness of the intermediate layer of all coatings is in the range of 450-520 HV 0.2 .

[0082] Figure 6 Three-dimensional profile morphologies of wear traces of different coatings after friction and wear at 350°C. It can be seen from the figure that the wear trace depth of coating C is the shallowest, and the wear volume is the smallest, indicating that it has the best wear resistance. In the order of wear volume from small to large, the order is C, F, B, A, D, and E coating (Fig. (a)). In the order of wear trace depth from shallow to deep, the order is C, F, E, A, D and B coating (Fig. (b)). The difference in wear performance is closely related to the composition and microstructure of the coating. Figure 6 Figure 6

[0083] Figure 7 Three-dimensional profile morphologies of wear traces of different composition ratio coatings after friction and wear at 500°C. It can be seen from the figure that the wear depth of coating C is the shallowest, and the wear volume is the smallest, indicating that it has the best wear resistance. The wear volume of the coating is in turn: C, E, F, B, D, A (Fig. (a)), and the depth is in turn: C, F, E, B, D, A (Fig. (b)). Figure 7 Figure 7 ​​​(b) It is noteworthy that, compared to 350°C, coating A exhibits a significantly increased wear mark depth at 500°C, leading to a substantial increase in wear volume, indicating poor resistance to high-temperature oxidation and softening. Although the wear mark depth of coating D does not change significantly, its width increases, also resulting in an increase in wear volume, reflecting its insufficient resistance to plastic deformation at high temperatures. In contrast, coatings B, C, E, and F show significantly reduced wear mark depths and wear volumes at 500°C. Coatings E and F, in particular, show a significant reduction in wear volume. This suggests that these coatings not only do not experience severe softening at high temperatures, but also, due to the formation of oxide films (such as dense Cr2O3, Al2O3, or composite oxides), may enhance surface hardness and lubricity, thus exhibiting excellent resistance to high-temperature wear and oxidation-coupled damage.

[0084] Next, the variation patterns of friction coefficient and wear rate of the six coatings at temperatures of 350℃ and 500℃ were compared and analyzed.

[0085] Figure 8 Wear curves and wear rate histograms for different coatings under triboelectric wear conditions at 350℃ and 500℃. At 350℃ ( Figure 8 In (a), coating C has the lowest coefficient of friction, approximately 0.15; coatings F and D are next, both around 0.31. The coefficient of friction for coating D gradually decreases as the test progresses, which may be related to the gradual formation of an oxide film on the surface and improved lubrication over time. Subsequently, coatings B (0.42), E (0.45), and A (0.50) show increasing coefficients of friction. Regarding wear rate ( Figure 8 In (b), coating C still performs best, with a value of 1.27 × 10⁻⁶. -5 The wear rate was mm³ / (N·m), followed by F (3.04), D (3.14), B (3.34) and A (3.75), while the wear rate of coating E was the highest, reaching 4.03 × 10⁻⁶ mm³ / (N·m). -5 mm³ / (N·m). At 500℃ ( Figure 8In the middle (c), the friction coefficient of the C coating is still the lowest, about 0.2~0.25; the friction coefficient of the F coating gradually decreases from 0.3 to 0.2, showing good operation adaptability; then, the friction coefficient increases in the order of D, B, A, E. Except that the friction coefficient of the A coating remains stable at about 0.3, the friction coefficients of the other coatings fluctuate, but are all lower than 0.4. More importantly, the wear rates of the coatings A and D increase at 500℃ compared with 350℃. Figure 8 In the middle (d), it indicates that these coatings may have experienced tribochemical reactions at high temperatures, thereby significantly improving their performance in resisting high-temperature wear-oxidation coupling damage.

[0086] In order to further reveal the influence of the wear mechanism of the coatings at different temperatures on the friction coefficient, wear rate and wear scar depth, and systematically compare and analyze the failure mechanism differences of the coatings at 350℃ and 500℃, the present application carries out systematic scanning electron microscope (SEM) observation and energy spectrum analysis (EDS) characterization on the surface morphology of the six kinds of coatings after the above temperature friction and wear test. Through micro-morphology comparison, composition distribution detection and damage characteristic analysis, the influence of temperature on the wear form, oxidation behavior and material removal mechanism of the coating is determined, so as to establish the internal correlation between the microstructure evolution and the macroscopic tribological performance, and provide theoretical basis and experimental support for optimizing the wear resistance of the coating in a wide temperature range.

[0087] Figure 9 The SEM-EDS diagram of the wear scar of the coating sample after the coating friction and wear at 350℃. From Figure 9 As shown in the middle (a) and (b), after the NiCr coating is subjected to 350℃ friction and wear, the wear scar surface mainly shows oxidation wear and adhesive wear mechanism, and the wear scar width reaches 1000μm. Moreover, the oxygen content in the wear scar area is as high as 48 at.%, indicating that a continuous and dense oxide covering layer has been formed on the surface, and the metal state is no longer present. However, due to the low hardness of the NiCr coating itself, it is difficult to effectively support the surface oxide layer, resulting in large-area peeling in the wear scar area, forming a "oxidation-wear-peeling-reoxidation" cycle mechanism. Although this mechanism leads to the highest wear rate and friction coefficient, the difference with other coatings is not significant. The wear scar morphology of the 25NiCr-75Cr3C2 coating after 350℃ friction and wear is as follows Figure 9As shown in (c) and (d), the wear track width is approximately 700 μm, and the wear mechanism is mainly abrasive wear and localized oxidative wear. The surface oxide layer is thin and unevenly distributed, failing to form a continuous and effective protective barrier. Therefore, abrasive wear dominates, leading to a significant increase in the wear rate and friction coefficient of this coating. Furthermore, excessive ceramic phase in the coating may increase its brittleness, making the oxide film prone to cracking and difficult to repair, thus accelerating abrasive wear.

[0088] Figure 10 The image shows the SEM-EDS image of the wear track after friction and wear of the coated sample at 500℃. When the friction and wear temperature increases to 500℃, the wear track morphology of the NiCr coating (coating A) changes significantly (e.g., ...). Figure 10 As shown in (a) and (b)). At this point, the width of the wear mark on the NiCr coating decreased to approximately 960 μm, and noticeably deeper furrows could be seen at the edges of the wear mark. Figure 10 In (a), this indicates that the material underwent severe plastic deformation and abrasive cutting; although a uniform oxide film formed in the middle of the wear mark, its surface has numerous parallel grooves, indicating that the mechanical properties of the oxide film are insufficient and cannot effectively resist abrasive action. Given its characteristics of high-temperature softening and poor oxidation resistance, the failure mechanism of coating A at 500℃ is mainly severe abrasive wear and oxidative wear. For coating B, the width of the wear mark is 600 μm, and the surface of the wear mark is covered with numerous small and parallel shallow furrows (…). Figure 10 (c) and (d) indicate that the wear mechanism is typical abrasive wear. Energy dispersive spectroscopy analysis shows that the oxygen content on the surface is relatively low ( Figure 10 In the middle (d), the oxide film is distributed in a dispersed patchy pattern and fails to form a continuous and dense protective layer.

[0089] In summary, compared to 350℃, the wear of the NiCr coating at 500℃ is significantly accelerated. The fundamental reason is that the coating softens considerably at high temperatures, leading to a decrease in its resistance to plastic deformation and load-bearing capacity, thus making it more susceptible to material migration and removal during friction. In contrast, the 25NiCr-75Cr3C2 coating exhibits a uniform wear morphology and slight plastic deformation characteristics under high-temperature conditions, indicating that it can maintain good high-temperature hardness and structural stability under the support of the high Cr3C2 ceramic phase, effectively suppressing the accelerated wear behavior caused by softening.

[0090] The Cr3C2 content in the 75NiCr-25Cr3C2(C) coating is approximately 25 wt.%, which can provide effective strength support to a certain extent.

[0091] Figure 11This is a SEM-EDS image of the wear track after friction and wear of the coated sample at 350℃. The wear track morphology of the coating at 350℃ is as follows. Figure 11 As shown in (a) and (b), the wear mark width of coating C is approximately 550 μm, which is significantly smaller than that of coatings A and B. Figure 11 EDS surface scan results in (b) show a dense oxide film with a high content. Its high oxygen content (40.2 at.%) indicates the presence of a continuous oxide layer (mainly Cr2O3), which possesses high hardness, low shear strength, and good solid lubrication, reducing the coefficient of friction to 0.16 and preventing oxygen diffusion and contact with wear particles. The 75 wt.% nickel-chromium binder provides toughness and thermal shock resistance, maintaining the integrity of the oxide layer, while the 25 wt.% Cr3C2 enhances hardness without causing excessive embrittlement. In contrast, the 50NiCr-50Cr3C2(D) coating exhibits a wider wear mark (approximately 750 μm) after friction and wear at 350°C, and a lower oxygen content (15 at.%), indicating an incomplete oxidation process and a lack of a protective oxide layer. Only localized oxide formation occurs, failing to isolate the friction components or prevent oxygen intrusion. Although the 50 wt.% NiCr binder provides some toughness, it cannot compensate for the brittleness introduced by the 50 wt.% Cr3C2. Under thermomechanical coupling, microcracks begin to form and propagate, while detached ceramic particles lead to three-body wear, scraping the surface and hindering the formation of a stable oxide layer. This results in a cyclical mechanism of "oxidation-crack spalling-wear-re-oxidation," thereby accelerating material loss.

[0092] Based on the changes in wear rate, wear track nitriding, and friction coefficient, it can be inferred that when the wear temperature rises to 500℃, the wear track morphology of the 75NiCr-25Cr3C2(C) coating and the 50NiCr-50Cr3C2(D) coating will inevitably undergo significant changes.

[0093] Figure 12 The image shows the SEM-EDS image of the wear track after friction and wear of the coated sample at 500℃. The wear track morphology of the C coating is as follows. Figure 12 As shown in (a)-(b), the wear marks on coating C are approximately 500 μm wide and relatively shallow. A relatively complete and continuous oxide film has formed on its surface, and no obvious furrows or peeling marks have been observed, indicating that the wear mechanism is mainly oxidative wear. Figure 12The middle (b) and its EDS element distribution map show that even in the area where the oxide film is locally damaged, a relatively high oxygen content is detected, indicating that the coating has strong dynamic regeneration and self-repairing ability of the oxide film. During the wear process, it can continuously form a new oxide layer, thereby effectively inhibiting abrasive wear and reducing material loss. In contrast, the wear trace width of the 50NiCr-50Cr3C2 (D) coating after friction and wear at 500°C is more than 800 μm, and the surface oxygen content is relatively low, and it fails to form a continuous and dense oxide protective layer. Parallel distribution of fine furrows is observed on the surface of the wear trace, which indicates that the main mechanism of wear is abrasive wear. This is related to the presence of a higher hard phase, which can form third body wear after surface wear, leading to rapid wear of the oxide film on its surface, thereby failing to effectively lubricate and protect.

[0094] Based on the above analysis, compared with the wear behavior at 350°C, the wear scar width of the 75NiCr-25Cr3C2 (C) coating at 500°C high temperature is significantly reduced, and the surface only shows slight plastic deformation characteristics, without deep furrows or peeling and other serious damage phenomena, indicating that its wear resistance is significantly improved in high temperature environment. This result confirms that the coating can effectively resist high temperature softening and the wear failure caused thereby, and exhibits good thermal stability and high temperature bearing capacity. In contrast, the surface of the 50NiCr-50Cr3C2 (D) coating after wear at 500°C shows severe wear morphology, accompanied by obvious peeling, and the wear scar depth and width are significantly greater than the wear results at 350°C. This indicates that the mechanical properties of the D coating degrade severely at high temperature, and its wear resistance decreases significantly, making it difficult to effectively inhibit the occurrence of high temperature softening and interface failure. The significantly different wear responses of the two coatings at high temperature highlight the key influence of the matching of ceramic phase content and matrix toughness on the high temperature performance of the coating, and provide an important basis for optimizing the composition design of wide temperature range wear-resistant coatings.

[0095] The introduction of high-entropy alloy CoCrFeNiMo will inevitably have a systematic effect on the microstructure and properties of the NiCr-Cr3C2 coating. From the significant changes in the friction coefficient, wear rate, and wear scar depth at different temperatures described in the foregoing, it can be inferred that the difference in the content of high-entropy alloy will directly cause obvious changes in the surface wear mechanism and wear scar morphology.

[0096] Figure 13SEM morphology and EDS composition analysis results of wear tracks of 10CoCrFeNiMo-18NiCr-72Cr3C2 (E) and 20CoCrFeNiMo-16NiCr-64Cr3C2 (F) coatings after friction and wear treatment at 350°C. The wear track width of E coating is about 1000 pm, and the wear track width of F coating is slightly narrower, about 850 pm. The oxygen content on the surface of the two coatings is similar (34.7 at.% and 35 at.% respectively), which indicates that both of them have formed an oxide layer mainly composed of Cr2O3, and may contain Co / Fe / Ni composite oxides, but their friction coefficient and wear rate are significantly different. This may be because the abrasive wear dominates the wear mechanism of E coating. While F coating has better toughness, oxidation wear and abrasive wear work together.

[0097] Figure 14 SEM morphology and EDS composition analysis results of wear tracks of 10CoCrFeNiMo-18NiCr-72Cr3C2 (E) and 20CoCrFeNiMo-16NiCr-64Cr3C2 (F) coatings after high-temperature friction and wear at 500°C. The wear track width of E coating is about 1000 pm, and the surface wear is uniform. At the same time, the energy spectrum analysis shows that the oxygen content on the surface is relatively high, which indicates that a relatively complete oxide film is formed at high temperature. The wear mechanism is the combined action of oxidation wear and abrasive wear. The oxide film effectively slows down the direct cutting of abrasive particles and inhibits the loss of material. The wear track width of F coating is about 580 pm, which is significantly smaller than that of E coating. This may be due to the formation of a thicker and more complete oxide film on the surface, which significantly reduces the wear rate and enhances the high-temperature wear resistance. Compared with 350°C, the wear resistance of E and F coatings is significantly enhanced at 500°C, and the wear depth and wear rate are significantly reduced. This is mainly due to the promotion of high temperature to form a denser and more stable oxide film (such as Cr2O3, MoO3 and their compounds), which has high hardness and lubricity, and can effectively prevent direct contact between friction components. At the same time, the CoCrFeNiMo multi-alloy phase enhances the strength and thermal stability of the coating at high temperature, maintaining its ability to resist deformation and softening. Therefore, E and F coatings exhibit excellent high-temperature tribological properties at 500°C and have the potential for application under high-temperature conditions.

[0098] In summary, in the low temperature stage (e.g. 350℃), the addition of appropriate amount of high-entropy phase can enhance the toughness of the coating, inhibit the abrasive wear, and promote the transition of wear mechanism to oxidation wear, which is manifested as shallow and uniform wear trace. In the medium-high temperature range (e.g. 500℃ and above), the high-entropy components can significantly improve the high-temperature oxidation resistance and softening resistance by promoting the formation of dense and stable composite oxide film (e.g. containing Cr, Mo oxides), making the wear morphology tend to be flat and the wear rate decrease significantly. However, when the content of high-entropy phase is too high, it may lead to a relative decrease in the proportion of ceramic phase or changes in interfacial compatibility, causing uneven microstructure, stress concentration or oxidation film embrittlement at high temperature, and thus inducing micro exfoliation or local collapse, which aggravates the wear. This series of phenomena shows that the addition of high-entropy alloy is not a simple linear improvement of coating performance, but a dynamic regulation of wear mechanism and surface morphology under temperature changes through the complex coupling of composition-structure-performance. Further micro characterization and simulation methods are needed to reveal the specific influence mechanism of high-entropy components on the wear path of the coating in a wide temperature range, and to provide a theoretical basis for the quantitative design of high-performance coatings.

[0099] Table 4 Results of EDS spectral composition analysis (atomic percentage)

[0100]

[0101] III. Electrochemical performance analysis

[0102] Figure 15 Nyquist plots of the electrochemical impedance of the coatings with different composition ratios in 3.5 wt.% NaCl solution. The size of the capacitive arc radius directly reflects the corrosion resistance of the coating, and the larger the capacitive arc radius, the better the corrosion resistance of the coating. As can be clearly seen from the figure, the capacitive arc radius of the coating 10CoCrFeNiMo-18NiCr-72Cr3C2 (E) is the largest, showing the best corrosion resistance; followed by the 75NiCr-25Cr3C2 coating (C); with the decrease of the capacitive arc radius, the corrosion resistance decreases in turn, in the order of: 20CoCrFeNiMo-16NiCr-64Cr3C2 (F), 25NiCr-75Cr3C2 (B), 50NiCr-50Cr3C2 (D), and the capacitive arc of the NiCr coating (A) is the smallest, with the worst corrosion resistance.

[0103] Figure 16 Potentiodynamic polarization curves of the coatings with different composition ratios in 3.5 wt.% NaCl solution, and Table 5 provides the corresponding electrochemical fitting parameters. Through analysis, the corrosion current density (i corr) highest, up to 11.8 nA / cm2, far higher than other coatings, indicating that it has the worst corrosion resistance. The corrosion current density of 10CoCrFeNiMo-18NiCr-72Cr3C2 coating (E) is the lowest, 2.08 nA / cm2, showing the best corrosion resistance. The corrosion current densities of the rest of the coatings are all in the range of 2-3 nA / cm2, in order of low to high corrosion resistance: 20CoCrFeNiMo-16NiCr-64Cr3C2 (F), 25NiCr-75Cr3C2 (B), 50NiCr-50Cr3C2 (D). This order is completely consistent with the size order of the capacitive arcs in the Nyquist plots of electrochemical impedance spectroscopy (EIS), which verifies the reliability of the experimental results. It is worth noting that the polarization curves of coatings B, C, D, E and F all show obvious passivation characteristics: the current density remains stable within a certain potential range, forming a platform, indicating that a protective passivation film is generated on the surface; then the current density rises rapidly, indicating that the passivation film has locally broken down and pitting has begun. This behavior reveals that the corrosion process of the coating includes two key stages: passivation film formation and pitting initiation.

[0104] The difference in corrosion behavior of coatings with different compositions is mainly due to the combined effect of coating composition and microstructure: the presence of CoCrFeNiMo high-entropy alloy phase in coating E promotes the formation of dense passivation films (such as Cr2O3, MoO3), effectively blocking the penetration of Cl - , and improving the pitting resistance; the 75% NiCr metal phase in coating C provides good toughness and continuity, and the 25% Cr3C2 ceramic phase enhances hardness and chemical stability, forming a uniform and less defective protective structure; the high ceramic phase content or single metal phase structure in coatings B, D and A easily leads to increased interface, increased porosity or uneven phase distribution, providing diffusion channels for the corrosion medium and accelerating local corrosion; the interface between high-entropy phase and carbide in coating F may have a microgalvanic effect, which reduces the corrosion resistance to some extent, but is still better than the traditional NiCr coating. In summary, the corrosion resistance of the coating not only depends on the composition design, but also is closely related to the uniformity of the microstructure, the interface characteristics and the stability of the passivation film. This result has important guiding significance for designing high-performance coatings suitable for marine corrosion environments.

[0105] Table 5 Fitting results of polarization curves of coatings with different composition ratios

[0106]

[0107] Summary: Six different composition coatings were prepared by HVOF technology. By systematically comparing their friction and wear-oxidation coupling behaviors at high temperature (350℃, 500℃) and electrochemical corrosion properties in 3.5 wt.% NaCl solution, the regulation mechanism of composition ratio on the microstructure, mechanical properties and service behavior of the coatings was revealed. The main conclusions are as follows:

[0108] (1) The 75NiCr-25Cr3C2 coating (C) can form a stable oxide film on the wear scar surface at 350℃ and 500℃, and the wear mechanism is mainly oxidative wear, so it shows the best tribological properties at both temperatures, with the lowest friction coefficient and wear rate.

[0109] (2) Compared with 350℃, the wear rate and wear scar depth of 75NiCr-25Cr3C2 (C), 25NiCr-75Cr3C2 coating (B), 10CoCrFeNiMo-18NiCr-72Cr3C2 (E) and 20CoCrFeNiMo-16NiCr-64Cr3C2 (F) coatings at 500℃ are significantly reduced, and the tribological properties are significantly improved. Among them, the wear rate of E and F coatings decreases by more than 50%, indicating that the addition of CoCrFeNiMo high-entropy alloy effectively enhances the high-temperature wear resistance of NiCr-Cr3C2 coating.

[0110] (3) At 350℃, B, D, E and F coatings are mainly abrasive wear, oxidative wear is auxiliary, and the protective effect of the oxide film is limited, and the wear is serious. At 500℃, B and D coatings are still mainly abrasive wear, but the oxide film plays a certain lubricating and protective role, and the wear resistance is improved. While E and F coatings change to oxidative wear dominated, and the wear resistance is significantly improved.

[0111] (4) In terms of electrochemical corrosion performance, coating E has the best corrosion resistance, followed by coating C, then F, B, D coatings, and coating A (NiCr) has the worst corrosion resistance.

[0112] The present application realizes the synergistic improvement of high-temperature wear resistance and corrosion resistance of the coating by regulating the content of Cr3C2 and introducing CoCrFeNiCr3C2Mo high-entropy alloy phase, providing a new idea for coating design facing high-temperature-corrosion coupling conditions.

[0113] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements easily thought of by those skilled in the art within the technical range disclosed by the present application should be covered within the protection scope of the present application.

Claims

1. A method for producing a HVOF sprayed coating, characterized in that, The method comprises the following steps: The transition layer and the working layer are sprayed on the surface of the substrate by using high-velocity oxygen fuel spraying; The transition layer is NiCr-CoCrFeNiMo or NiCr; The working layer is at least one of 10CoCrFeNiMo-18NiCr-72Cr3C2, 20CoCrFeNiMo-16NiCr-64Cr3C2, 75NiCr-25Cr3C2, 25NiCr-75Cr3C2 and 50NiCr-50Cr3C2.

2. A method of producing a HVOF sprayed coating according to claim 1, characterized in that The working layer of the HVOF sprayed coating is 10CoCrFeNiMo-18NiCr-72Cr3C2. The transition layer is NiCr-CoCrFeNiMo.

3. A method of producing a HVOF sprayed coating according to claim 2, characterized in that The thickness of the transition layer is 20-80 μm. The thickness of the working layer is 200 μm.

4. The method of claim 1, wherein the HVOF sprayed coating is prepared by using a feedstock powder having a particle size of 10-50 μm. The substrate is a pretreated 20CrMo steel substrate.

5. A method of producing a HVOF sprayed coating according to claim 4, characterized in that The pretreatment operation is as follows: the substrate is polished by sandpaper, cleaned by acetone ultrasonic cleaning to remove surface oil stains and impurities, and then subjected to sand blasting roughening treatment.

6. The method of claim 1, wherein the HVOF sprayed coating is prepared by using a feedstock powder having a particle size of 10-50 μm. The preparation process of 10CoCrFeNiMo-18NiCr-72Cr3C2 and 20CoCrFeNiMo-16NiCr-64Cr3C2 is as follows: The composite powders 75NiCr-25Cr3C2 and 50NiCr-50Cr3C2 are prepared by mixing NiCr-Cr3C2 and NiCr powders in a certain proportion, respectively; The 10CoCrFeNiMo-18NiCr-72Cr3C2 and 20CoCrFeNiMo-16NiCr-64Cr3C2 powders are obtained by mixing CoCrFeNiMo high-entropy alloy powders with the composite powders, respectively.

7. The method of claim 1, wherein the HVOF sprayed coating is prepared by using a feedstock powder having a particle size of 10-50 μm. The conditions of the high-velocity oxygen fuel spraying are as follows: The powder feeding rate is controlled at 55-60 g / min, the oxygen flow rate is 1850-1900 LPM, the propylene flow rate is 6 LPM, the air flow rate is 21-26 LPM, the spraying distance is 310-360 mm, and the moving speed is 500 mm / s.

8. A method of producing a HVOF sprayed coating according to claim 7, characterized in that During the high-velocity oxygen fuel spraying process, compressed air is used to cool the substrate.

9. A HVOF sprayed coating, characterized in that, The HVOF sprayed coating is prepared by the preparation method of any one of claims 1-8.

10. The HVOF sprayed coating of claim 9 is applied in the field of high-end equipment manufacturing.

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