A method for preparing a composite hard coating on the surface of a martensitic heat-resistant stainless steel

Abstract

The application discloses a kind of martensitic heat-resistant stainless steel surface preparation composite hard coating method, comprising the following steps: substrate is strictly cleaned and sand blasting pretreatment;Specific thickness WC-CoCr wear-resistant bottom layer is prepared using supersonic flame spraying process;The bottom layer is precisely ground and polished to surface roughness Ra≤0.2 μm;After ultra-precision cleaning, pure Cr transition layer and CrN surface layer are sequentially deposited in vacuum environment using physical vapor deposition technology.The application combines macroscopic strengthening HVOF technology with microscopic strengthening PVD technology, introduces a pure Cr transition layer with a thickness of 0.01 μm to 1.5 μm, and constructs a complete surface protection system, achieving strong and tough combination between heterogeneous coatings.The obtained composite coating system has excellent wear resistance, high toughness, strong interfacial bonding force and long-term corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of surface coating technology, specifically a method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel. Background Technology

[0002] In the fields of aviation, aerospace, and high-end equipment manufacturing, high-strength martensitic heat-resistant stainless steel serves as a key connecting and moving component. Its service environment is extremely harsh, often simultaneously subjected to high alternating loads, severe friction and wear, and corrosive media such as humid heat and salt spray. Currently, these core components are generally made of high-strength martensitic stainless steel such as 1Cr11Ni2W2MoV. While this material possesses excellent matrix strength and toughness, enabling it to withstand complex dynamic loads, its low surface hardness and inherent insufficient wear and corrosion resistance have become major bottlenecks restricting the overall lifespan and reliability of the components.

[0003] High-velocity oxygen fuel (HVOF) spraying is an advanced surface strengthening technique capable of producing metal-ceramic coatings, such as WC-CoCr. On the other hand, physical vapor deposition (PVD) can produce extremely dense, chemically stable nitride or carbide ceramic coatings, such as CrN and TiAlN, exhibiting extremely high hardness, low coefficient of friction, and excellent corrosion resistance.

[0004] While the two surface strengthening methods mentioned above can partially solve the single problem of wear resistance or corrosion prevention, they cannot achieve a perfect balance of comprehensive performance such as high wear resistance, high toughness, strong bonding, and long-term corrosion resistance on a single component. However, when the two surface strengthening methods are combined, the supersonic flame spraying technology is a rough bottom layer, while the physical vapor deposition technology is a dense top layer. These two surface strengthening methods are very different in physical morphology, chemical composition, and thermophysical properties. Due to factors such as interface mismatch and interface contamination, the bonding force is poor, and interface failure and early peeling are prone to occur under complex stress conditions. Therefore, there is an urgent need for a preparation method to effectively combine the two surface strengthening methods. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the above-mentioned technologies.

[0006] Therefore, the purpose of this invention is to propose a method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel. It innovatively and sequentially couples macroscopic strengthening HVOF and micro / nanoscale strengthening PVD technologies, and introduces a key functional gradient layer in between. The functional gradient layer is a pure Cr transition layer with a thickness of 0.01μm to 1.5μm, thus constructing a complete surface protection system. This achieves a strong and tough bond between heterogeneous coatings, making the bond strength stable above 80MPa and the critical scratch load Lc≥50N.

[0007] The technical solution of the present invention includes the following steps: The 1Cr11Ni2W2MoV steel martensitic heat-resistant stainless steel matrix was cleaned and roughened by sandblasting. A supersonic flame spraying process is used on the pretreated substrate surface to form a WC-CoCr wear-resistant underlayer, wherein the supersonic flame spraying material is WC-10Co-4Cr powder. The WC-CoCr wear-resistant substrate is ground and polished to make the surface roughness Ra of the WC-CoCr wear-resistant substrate ≤ 0.2μm; Clean the workpiece after grinding and polishing; The cleaned workpiece is placed in a physical vapor deposition apparatus and first subjected to ion bombardment cleaning, followed by the sequential deposition of a pure Cr transition layer and a CrN surface layer. The thickness of the pure Cr transition layer is 0.01 μm to 1.5 μm, and the thickness of the CrN surface layer is 3 μm to 8 μm.

[0008] Furthermore, the parameters of the supersonic flame spraying process are set as follows: oxygen pressure 140psi~160psi, fuel pressure 110psi~130psi, spraying distance 300mm~400mm, substrate preheating temperature 80℃~120℃, and powder feeding rate 80g / min~100g / min.

[0009] Furthermore, the precision cleaning is performed in a Class 100 cleanroom using a three-tank ultrasonic cleaning process. The cleaned workpiece is then placed in an oven to dry. The cleaning agents in the three-tank ultrasonic cleaning process are acetone, anhydrous ethanol, and deionized water, respectively.

[0010] Furthermore, the process parameters for the ion bombardment cleaning are as follows: argon gas at a flow rate of 70 sccm to 90 sccm is introduced under vacuum, a pulse bias voltage of -250V to -350V is applied, the cleaning time is 20 minutes to 40 minutes, the ion source power is 4kW, and the workpiece revolution speed is 0.5 rpm.

[0011] Furthermore, the CrN surface layer is deposited under a nitrogen atmosphere. The process parameters for depositing the CrN surface layer are: nitrogen flow rate of 250 sccm to 350 sccm, pulse bias voltage of -60V to -100V, target current of 90A to 110A, and deposition temperature of 200℃ to 300℃.

[0012] Furthermore, the thickness of the WC-CoCr wear-resistant underlayer is 150μm to 250μm.

[0013] Furthermore, the pretreated substrate undergoes two preheating treatments before formal spraying, with the number of spraying passes ranging from 16 to 22.

[0014] Furthermore, before the ion bombardment cleaning, the PVD equipment is evacuated to a high vacuum of ≤5.0×10⁻³Pa, and the cleaned workpiece is then heated to 200℃~300℃ and kept at that temperature for 2 hours.

[0015] Furthermore, the deposition of the pure Cr transition layer is carried out in a pure argon atmosphere. The process parameters for depositing the pure Cr transition layer are: argon flow rate of 100 sccm to 150 sccm, pulse bias voltage of -60 V to -100 V, target current of 90 A to 110 A, and deposition temperature of 200 °C to 300 °C.

[0016] The advantages of this invention compared to existing technologies are: 0. This invention provides a method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel. The HVOF spray coating is precisely ground and polished to Ra≤0.2μm to provide an atomically smooth substrate for PVD deposition, eliminating interface defects caused by the rough surface of the HVOF underlayer. Before depositing the PVD layer, a dual cleaning process of ultra-precision cleaning + high-energy argon ion bombardment cleaning is added to remove nanoscale contaminants, activate the surface, and introduce a pure Cr transition layer with a thickness of 0.01μm~1.5μm. This achieves a gradient transition in chemical composition and crystal structure between the WC-CoCr cermet underlayer and the CrN ceramic surface layer. The sequential coupling and precise parameter matching of HVOF and PVD technologies ensure that the surface state formed by the preceding HVOF process is compatible with the deposition requirements of the subsequent PVD process, while avoiding plastic deformation under high contact stress. 0. This invention provides a method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel. A pure Cr functional transition layer is introduced between the rough HVOF underlayer and the dense PVD top layer. The pure Cr transition layer can effectively fill the micropores and defects on the surface of the HVOF underlayer, further improving the overall density of the coating. At the same time, it achieves a smooth transition in composition and crystal structure from the metal ceramic underlayer to the ceramic top layer, eliminates interfacial stress concentration, improves the structural stability of the coating under alternating loads, and realizes a strong and tough bond between heterogeneous coatings. This completely solves the technical problem of easy peeling at the interface in multilayer coating systems. Attached Figure Description

[0017] Figure 1 This invention relates to the cross-sectional morphology of a wear-resistant and corrosion-resistant composite hard coating prepared on the surface of martensitic heat-resistant stainless steel.

[0018] Figure 2 This invention compares the surface hardness of the 1Cr11Ni2W2MoV steel after different surface treatments.

[0019] Figure 3 This is the appearance effect of the composite hard coating in Embodiment 1 of the present invention after 192 hours of neutral salt spray test. Detailed Implementation

[0020] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses consistent with some aspects of this disclosure as detailed in the appended claims.

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] like Figure 1 As shown, this embodiment proposes a method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel, including the following steps: The 1Cr11Ni2W2MoV steel martensitic heat-resistant stainless steel matrix was cleaned and roughened by sandblasting. A supersonic flame spraying process was used on the pretreated substrate surface to form a WC-CoCr wear-resistant underlayer. The supersonic flame spraying material was WC-10Co-4Cr powder. The WC-CoCr wear-resistant substrate is ground and polished to achieve a surface roughness Ra≤0.2μm. Clean the workpiece after grinding and polishing; The cleaned workpiece is placed in a physical vapor deposition apparatus and first subjected to ion bombardment cleaning. Then, a pure Cr transition layer and a CrN surface layer are deposited sequentially. The thickness of the pure Cr transition layer is 0.01 μm to 1.5 μm, and the thickness of the CrN surface layer is 3 μm to 8 μm.

[0023] It should be noted that, regarding the introduction of the transition layer in this invention, active metals such as Ti and Al have poor wettability with the WC-CoCr underlying layer, easily forming brittle phases and causing a sharp drop in bonding strength; metals such as Ni and Mo have low lattice matching with the CrN surface layer, resulting in weak interfacial bonding, and some materials are costly and difficult to deposit; alloy transition layers are prone to compositional segregation, failing to form a homogeneous transition interface, disrupting the Cr-CrN continuous phase structure, and increasing process complexity. Therefore, this invention uses pure Cr as the transition layer, and the thickness of the pure Cr transition layer is controlled at 0.01μm to 1.5μm, which is compatible with the lattice of the underlying CoCr bonding phase, has good wettability, and achieves atomic-level bonding; it forms a compositional gradient with the surface CrN, alleviating abrupt changes in physical properties and internal stress, and preventing delamination; it has excellent plasticity and toughness, with a thermal expansion coefficient between the two, buffering thermal expansion and modulus differences, offsetting stress and preventing cracking; at the same time, it seals the micropores of the underlying layer, improving corrosion resistance; it can be continuously deposited with CrN using PVD without changing the target or significantly adjusting parameters, avoiding secondary contamination.

[0024] Furthermore, the thickness of the WC-CoCr wear-resistant underlayer is 150μm to 250μm.

[0025] It should be noted that a thickness of <150μm can easily lead to early wear-through of the substrate, while a thickness of >250μm increases the spraying time and cost. This range achieves the best balance between performance and cost. This thickness range can withstand high contact stress and impact loads, while avoiding the problems of excessive internal stress or processing difficulties caused by excessively thick coatings. Within this thickness range, a surface roughness Ra≤0.2μm can be achieved through precision grinding, providing a smooth substrate for subsequent PVD deposition.

[0026] Furthermore, the parameters for the supersonic flame spraying process are set as follows: oxygen pressure 140psi~160psi, fuel pressure 110psi~130psi, spraying distance 300mm~400mm, substrate preheating temperature 80℃~120℃, and powder feeding rate 80g / min~100g / min.

[0027] It should be noted that optimized oxygen and fuel pressure ensure stable flame temperature and velocity, reduce WC particle decarburization and oxidation, maintain the original hardness of the powder, and preheating the substrate to 80℃~120℃ can reduce thermal stress, avoid coating cracking, and ensure consistent performance of each batch of products. Reasonable spraying distance and powder feeding rate enable molten particles to impact the substrate at high speed, forming a dense accumulation and significantly reducing porosity.

[0028] Furthermore, the pretreated substrate undergoes two preheating treatments before formal spraying, with 16 to 22 spray coats applied.

[0029] It should be noted that the two preheating passes allow the temperature to rise slowly, preventing rapid heating from causing changes in the substrate structure or stress concentration. The 16 to 22 spray passes correspond to a thickness range of 150μm to 250μm, which facilitates process control and avoids thickness deviation. The multiple spray passes allow each thin layer to be stacked alternately, reducing penetrating pores and improving the overall density and bonding strength of the coating.

[0030] Furthermore, the precision cleaning process involves three-tank ultrasonic cleaning in a Class 100 cleanroom. After cleaning, the workpieces are placed in an oven to dry. The cleaning agents in the three-tank ultrasonic cleaning are acetone, anhydrous ethanol, and deionized water, respectively.

[0031] It should be noted that ultrasonic oscillation combined with high-purity solvents can thoroughly remove residual micro-powder, oil stains, and electrostatically adsorbed particles from grinding. The Class 100 cleanroom environment ensures that the cleaned workpiece is not contaminated by airborne particles before being transferred to the PVD equipment. The ultra-clean surface is conducive to the nucleation and growth of Cr atoms, reduces coating defects, and improves the density and adhesion of the CrN surface layer.

[0032] Furthermore, before ion bombardment cleaning, the PVD equipment is evacuated to a high vacuum of ≤5.0×10⁻³Pa, and the cleaned workpiece is then heated to 200℃~300℃ and kept at that temperature for 2 hours.

[0033] It should be noted that the high vacuum environment removes active gases such as water vapor and oxygen to prevent oxidation or reaction contamination during the deposition of Cr and CrN. The 2-hour heat preservation ensures that the temperature of the substrate and the HVOF bottom layer is consistent, avoiding internal stress in the coating caused by differences in thermal inertia. The deposition temperature of 200℃~300℃ is conducive to the slight diffusion of Cr atoms on the WC-CoCr surface, forming a metallurgical bond to enhance the interface toughness.

[0034] Furthermore, the process parameters for ion bombardment cleaning are as follows: argon gas at a flow rate of 70 sccm to 90 sccm is introduced under vacuum, a pulse bias voltage of -250V to -350V is applied, the cleaning time is 20 minutes to 40 minutes, the ion source power is 4kW, and the workpiece revolution speed is 0.5 rpm.

[0035] It should be noted that high-energy argon ion bombardment can sputter away the extremely thin oxide film and adsorption layer on the bottom surface of HVOC, exposing a fresh active surface. Ion etching creates nanoscale unevenness on the surface, increasing the mechanical intercalation area of ​​the subsequent Cr transition layer and improving the bonding strength. The workpiece's revolution speed of 0.5 rpm ensures that all parts receive an equal amount of ion bombardment, avoiding incomplete cleaning in certain areas.

[0036] Furthermore, the deposition of the pure Cr transition layer was carried out in a pure argon atmosphere. The process parameters for the deposition of the pure Cr transition layer were: argon flow rate of 100 sccm to 150 sccm, pulse bias voltage of -60 V to -100 V, target current of 90 A to 110 A, and deposition temperature of 200 °C to 300 °C.

[0037] It should be noted that pure Cr atoms can enter the pores and microcracks on the surface of the HVOF bottom layer, block the penetration channels of corrosive media, and improve the overall corrosion resistance. This Cr layer serves as an intermediate transition, and its metallic properties are compatible with the bottom layer CoCr and homologous with the upper layer CrN, eliminating abrupt changes in physical properties and relieving internal stress.

[0038] Furthermore, the CrN surface layer was deposited under a nitrogen atmosphere. The process parameters for depositing the CrN surface layer were: nitrogen flow rate of 250 sccm to 350 sccm, pulse bias voltage of -60V to -100V, target current of 90A to 110A, and deposition temperature of 200℃ to 300℃.

[0039] It should be noted that a nitrogen flow rate of 250 sccm to 350 sccm ensures sufficient reaction to generate a stoichiometric CrN phase. The dense CrN surface layer acts as a barrier layer, effectively isolating corrosive media such as Cl⁻ and H⁺. A bias voltage of -60V to -100V puts the CrN layer into a compressive stress state, offsetting the tensile stress during service and delaying crack initiation and propagation. With the same target current, bias voltage, and temperature range as the Cr transition layer, it can be continuously deposited in the same equipment without switching parameters, avoiding interface contamination and process interruption.

[0040] Example 1 The workpiece was cleaned in two stages: alkaline solution (60℃, 15min) and acetone (ultrasonic, 15min). Then, it was sandblasted with No. 20 white corundum sand at a pressure of 0.25MPa until the surface was uniformly silver-gray and the roughness Ra was about 5.0μm.

[0041] A JP-5000 HVOF system was used. Process parameters were set as follows: oxygen pressure 150 psi, kerosene pressure 120 psi, spraying distance 350 mm, powder feeder speed 6 rpm, and powder feed rate approximately 90 g / min. The substrate was preheated twice to approximately 100℃, followed by 18 coats of the final coating. After coating, the WC-CoCr undercoat thickness was 205 ± 10 μm.

[0042] The grinding was performed on a precision CNC cylindrical grinding machine using a diamond grinding wheel. The wheel speed was set to 500 rpm, the workpiece speed to 200 rpm, and the feed rate to 0.02 mm / r. After grinding, the workpiece outer diameter met the drawing requirements, and the surface roughness Ra was reduced to 0.18 μm.

[0043] The workpiece is subjected to three-tank ultrasonic cleaning in a Class 100 cleanroom. The cleaning agents in the three tanks are acetone, anhydrous ethanol and deionized water, respectively, for 10 minutes in each tank. Finally, it is thoroughly dried in a 100°C oven.

[0044] Use a multi-arc ion plating system. Evacuate to a base vacuum ≤5.0×10⁻³Pa, then heat to 300℃ and hold for 2 hours. Then proceed with:

[0045] Introduce 80 sccm of high-purity argon gas, apply a -300V pulse bias, set the ion source power to 4kW, and the workpiece rotation speed to 0.5 rpm. Clean for 30 minutes. The argon flow rate was adjusted to 120 sccm, the bias voltage was -80V, and two high-purity Cr targets were turned on with a target current of 100A each. Deposition was carried out for 60 minutes. The Cr layer thickness was measured to be approximately 1.0 μm.

[0046] Argon gas was shut off, and 300 sccm of high-purity nitrogen gas was introduced. The bias voltage was maintained at -80V, and dual-target operation was enabled. The ion source power was reduced to 1 kW to assist ionization, and deposition was carried out for 60 minutes. The thickness of the CrN layer was measured to be approximately 4.0 μm.

[0047] Performance test results: The bonding strength between the HVOF layer and the substrate is 87 MPa; the critical scratch load Lc of the PVD layer is 58 N; the microhardness of the CrN surface layer is 1980; after 192 hours of neutral salt spray test, there is no red rust on the sample surface; the pin-disc wear test shows that its wear rate is only 1 / 13 of that of the untreated substrate.

[0048] Example 2 The workpiece was cleaned in two stages: alkaline solution (60℃, 15min) and acetone (ultrasonic, 15min). Then, it was sandblasted with No. 20 white corundum sand at a pressure of 0.25MPa until the surface was uniformly silver-gray and the roughness Ra was about 5.0μm.

[0049] A JP-5000 HVOF system was used. Process parameters were set as follows: oxygen pressure 150 psi, kerosene pressure 120 psi, spraying distance 350 mm, powder feeder speed 5.3 rpm, and powder feed rate approximately 80 g / min. The substrate was preheated twice to approximately 100℃, followed by 22 coats of the final coating. After coating, the WC-CoCr undercoat thickness was 255 ± 10 μm.

[0050] The grinding process was performed on a precision CNC cylindrical grinding machine using a diamond grinding wheel. The wheel speed was set to 500 rpm, the workpiece speed to 200 rpm, and the feed rate to 0.02 mm / r. After grinding, the workpiece outer diameter met the drawing requirements, ensuring a surface roughness Ra ≤ 0.2 μm.

[0051] Use a multi-arc ion plating system. Evacuate to a base vacuum ≤5.0×10⁻³Pa, then heat to 300℃ and hold for 2 hours. Then proceed with:

[0052] Introduce 80 sccm of high-purity argon gas, apply a -300V pulse bias, set the ion source power to 4kW, and the workpiece rotation speed to 0.5 rpm. Clean for 30 minutes. The argon flow rate was adjusted to 120 sccm, the bias voltage was -80V, and two high-purity Cr targets were turned on with a target current of 100A each. Deposition was carried out for 45 minutes. The Cr layer thickness was measured to be approximately 0.8 μm.

[0053] Argon gas was shut off, and 300 sccm of high-purity nitrogen gas was introduced. The bias voltage was maintained at -80V, and dual-target operation was enabled. The ion source power was reduced to 1 kW to assist ionization, and deposition was carried out for 75 minutes. The thickness of the CrN layer was measured to be approximately 5.0 μm.

[0054] Performance test results: Bond strength is 84 MPa; critical scratch load Lc is 55 N; microhardness of CrN surface layer is 1920; passed 500-hour salt water immersion test; wear resistance is 1 / 11 of the substrate. This solution has a thicker coating and performs better under long-term erosion and wear conditions.

[0055] Example 3 The workpiece was cleaned in two stages: alkaline solution (60℃, 15min) and acetone (ultrasonic, 15min). Then, it was sandblasted with No. 20 white corundum sand at a pressure of 0.25MPa until the surface was uniformly silver-gray and the roughness Ra was about 5.0μm.

[0056] A JP-5000 HVOF system was used. Process parameters were set as follows: oxygen pressure 150 psi, kerosene pressure 120 psi, spraying distance 350 mm, powder feeder speed 6.7 rpm, and powder feed rate approximately 100 g / min. The substrate was preheated twice to approximately 100°C, followed by 16 coats of the final coating. After coating, the WC-CoCr undercoat thickness was 185 ± 10 μm.

[0057] The grinding process was performed on a precision CNC cylindrical grinding machine using a diamond grinding wheel. The wheel speed was set to 500 rpm, the workpiece speed to 200 rpm, and the feed rate to 0.02 mm / r. After grinding, the workpiece outer diameter met the drawing requirements, ensuring a surface roughness Ra ≤ 0.2 μm.

[0058] Use a multi-arc ion plating system. Evacuate to a base vacuum ≤5.0×10⁻³Pa, then heat to 300℃ and hold for 2 hours. Then proceed with:

[0059] Introduce 80 sccm of high-purity argon gas, apply a -350V pulse bias, set the ion source power to 4kW, and the workpiece rotation speed to 0.5 rpm. Clean for 30 minutes. The argon flow rate was adjusted to 120 sccm, the bias voltage was -100 V, and two high-purity Cr targets were turned on with a target current of 100 A for 45 minutes. The Cr layer thickness was measured to be approximately 1.2 μm.

[0060] Argon gas was shut off, and 300 sccm of high-purity nitrogen gas was introduced. The bias voltage was maintained at -100V, and dual-target operation was enabled. The ion source power was reduced to 1kW to assist ionization, and deposition was carried out for 45 minutes. The measured thickness of the CrN layer was approximately 3.0 μm. The higher bias voltage promoted the ion bombardment effect during film growth, resulting in a denser film.

[0061] Performance test results: Bond strength is 89 MPa; critical scratch load Lc is significantly increased to 85 N; microhardness of CrN surface layer reaches 2100 HV; passed 240-hour salt water immersion test; wear resistance is 1 / 15 of the substrate. This solution is particularly suitable for working conditions with high contact stress and requiring extremely strong anti-stripping ability.

[0062] In summary, the HVOF coating is precisely ground and polished to Ra≤0.2μm to provide an atomically smooth substrate for PVD deposition, eliminating interface defects caused by the rough surface of the HVOF underlayer. Before depositing the PVD layer, a dual cleaning process of ultra-precision cleaning and high-energy argon ion bombardment cleaning is added to remove nanoscale contaminants, activate the surface, and introduce a pure Cr transition layer. This achieves a gradient transition in chemical composition and crystal structure between the WC-CoCr cermet underlayer and the CrN ceramic surface layer. The sequential coupling and precise parameter matching of HVOF and PVD technologies ensure that the surface state (composition, stress, roughness) formed by the preceding HVOF process is compatible with the deposition requirements of the subsequent PVD process.

[0063] A pure Cr functional transition layer is introduced between the rough HVOF substrate and the dense PVD topcoat. The pure Cr transition layer can effectively fill the micropores and defects on the surface of the HVOF substrate, further improving the overall density of the coating. At the same time, it achieves a smooth transition in composition and crystal structure from the metal ceramic substrate to the ceramic topcoat, eliminates interfacial stress concentration, improves the structural stability of the coating under alternating loads, and realizes a strong and tough bond between heterogeneous coatings. This completely solves the technical problem of peeling off at the interface in multilayer coating systems.

[0064] When the thickness of the pure Cr transition layer is too small, i.e. less than 0.01 μm, obvious functional failure problems will occur: the thin Cr layer cannot achieve uniform coverage of the entire WC-CoCr substrate surface, and the rough areas and micropores of the substrate are prone to leakage and breakpoints. The interface still has abrupt changes in physical properties and cannot effectively relieve internal stress. The role of the transition layer in improving the bonding force is basically lost. A continuous Cr-CrN transition phase cannot be formed, the uniformity of CrN surface deposition deteriorates, and the pores of the substrate cannot be effectively sealed. External corrosive media can still penetrate, and the overall coating bonding strength and corrosion resistance do not meet the design requirements. The coating is prone to failure problems such as microcracks and local peeling.

[0065] When the thickness of the pure Cr transition layer is too large, i.e., exceeding 1.5μm, the hardness of pure Cr metal is much lower than that of the WC-CoCr underlayer and CrN top layer. An excessively thick Cr layer will significantly reduce the overall surface hardness and wear resistance of the composite coating, which violates the core design requirement of heavy-duty wear resistance for the support pin. An excessively thick pure Cr layer has a large amount of plastic deformation, which will increase the overall internal stress of the coating. During service, the coating is prone to wrinkling, plastic flow, or even peeling. The toughness advantage is transformed into a failure factor.

[0066] Therefore, by using pure Cr as the transition layer and controlling the thickness from 0.01 to 1.5 μm, the technical problems of weak bonding, stress concentration, and difficulty in achieving synergistic corrosion resistance and wear resistance in heterogeneous coatings can be perfectly solved. This ensures that the composite coating has excellent bonding strength, wear resistance, and long-term corrosion resistance, which perfectly matches the actual service requirements of the support pin.

[0067] like Figure 2 As shown, through the triple interface strengthening technology of "sandblasting to create a macroscopic anchoring effect + ion cleaning to achieve nanoscale clean activation + introduction of a pure Cr transition layer to achieve a gradient transition of chemical composition and crystal structure", a strong and tough bond between heterogeneous coatings is achieved, which completely solves the technical pain point that multi-layer coating systems are prone to peeling at the interface. The bonding strength is stable at over 80MPa and the critical scratch load Lc≥50N.

[0068] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0070] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel, characterized in that, Includes the following steps: The 1Cr11Ni2W2MoV steel martensitic heat-resistant stainless steel matrix was cleaned and roughened by sandblasting. A supersonic flame spraying process is used on the pretreated substrate surface to form a WC-CoCr wear-resistant underlayer, wherein the supersonic flame spraying material is WC-10Co-4Cr powder. The WC-CoCr wear-resistant substrate is ground and polished to make the surface roughness Ra of the WC-CoCr wear-resistant substrate ≤ 0.2μm; Clean the workpiece after grinding and polishing; The cleaned workpiece is placed in a physical vapor deposition apparatus and first subjected to ion bombardment cleaning, followed by the sequential deposition of a pure Cr transition layer and a CrN surface layer. The thickness of the pure Cr transition layer is 0.01 μm to 1.5 μm, and the thickness of the CrN surface layer is 3 μm to 8 μm.

2. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 1, characterized in that: The thickness of the WC-CoCr wear-resistant underlayer is 150μm to 250μm.

3. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 1, characterized in that, The parameters for the supersonic flame spraying process are set as follows: oxygen pressure 140psi~160psi, fuel pressure 110psi~130psi, spraying distance 300mm~400mm, substrate preheating temperature 80℃~120℃, and powder feeding rate 80g / min~100g / min.

4. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 3, characterized in that: The pretreated substrate is subjected to two preheating treatments before formal spraying, with 16 to 22 spraying passes.

5. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 1, characterized in that: The precision cleaning is performed in a Class 100 cleanroom using a three-tank ultrasonic cleaning process, followed by drying of the cleaned workpiece. The cleaning agents in the three-tank ultrasonic cleaning process are acetone, anhydrous ethanol, and deionized water, respectively.

6. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 1, characterized in that: Before the ion bombardment cleaning, the PVD equipment is evacuated to a high vacuum of ≤5.0×10⁻³Pa, and the cleaned workpiece is then heated to 200℃~300℃ and kept at that temperature for 2 hours.

7. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 1, characterized in that, The process parameters for ion bombardment cleaning are as follows: argon gas at a flow rate of 70 sccm to 90 sccm is introduced under vacuum, a pulse bias voltage of -250V to -350V is applied, the cleaning time is 20 minutes to 40 minutes, the ion source power is 4kW, and the workpiece revolution speed is 0.5 rpm.

8. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 1, characterized in that, The deposition of the pure Cr transition layer was carried out in a pure argon atmosphere. The process parameters for the deposition of the pure Cr transition layer were: argon flow rate of 100 sccm to 150 sccm, pulse bias voltage of -60 V to -100 V, target current of 90 A to 110 A, and deposition temperature of 200 °C to 300 °C.

9. The method for preparing a composite hard coating on the surface of martensitic heat-resistant stainless steel according to claim 1, characterized in that, The CrN surface layer was deposited under a nitrogen atmosphere. The process parameters for depositing the CrN surface layer were as follows: nitrogen flow rate of 250 sccm to 350 sccm, pulse bias voltage of -60V to -100V, target current of 90A to 110A, and deposition temperature of 200℃ to 300℃.

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