Cr / CrN alternate multi-layer gradient slow-release stress coating and preparation method thereof

Abstract

The invention relates to the technical field of physical vapor deposition coatings, and particularly discloses a Cr / CrN alternate multilayer gradient slow-release stress coating and a preparation method thereof.The Cr / CrN alternate multilayer gradient slow-release stress coating comprises a plurality of Cr coatings and a plurality of CrN coatings, the Cr coatings and the CrN coatings are alternately arranged outwards from the surface of a substrate, the innermost layer is the Cr coating, and the outermost layer is the CrN coating; the Cr coatings and the CrN coatings are prepared through a magnetron sputtering method, the bias voltages of all the Cr coatings are the same, the bias voltages of all the CrN coatings are the same, and the bias voltages of the Cr coatings are smaller than the bias voltages of the CrN coatings. By adopting the technical scheme provided by the invention, the technical problem that an obvious stress concentration phenomenon still exists due to discontinuous stress gradients among layers of a Cr / CrN alternate multilayer structure in the prior art can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of physical vapor deposition coatings, and in particular to a Cr / CrN alternating multilayer gradient stress-relieving coating and a preparation method thereof. Background Art

[0002] Physical Vapor Deposition (PVD) is a technique that uses physical methods to evaporate or sputter a source material (such as a target) into atomic, molecular, or ionic particles under vacuum conditions, depositing them onto a substrate to form a thin film. PVD technology is widely used in machinery manufacturing, aerospace, electronics, medical devices, and other fields to improve surface hardness, wear resistance, corrosion resistance, and decorative properties.

[0003] Common PVD processes include: (1) magnetron sputtering: using a magnetic field to confine plasma, enhance ion bombardment efficiency, and improve deposition rate and film density; (2) arc ion plating: generating a high-density metal ion flow through a metal target, suitable for preparing high-hardness and high-adhesion coatings; (3) electron beam evaporation: using a high-energy electron beam to heat the material to achieve evaporation deposition, suitable for the preparation of high-purity thin films. Among the above processes, magnetron sputtering has become an important means of preparing functional coatings due to its advantages such as strong controllability, good film uniformity, and suitability for large-area deposition.

[0004] In industrial applications, CrN coatings are widely used for surface strengthening of key components such as aerospace engine blades, die stampings, and cutting tools due to their excellent hardness (>25GPa), wear resistance, and oxidation resistance. However, the high hardness achieved by traditional single-layer CrN coatings is often accompanied by high residual stress (>3GPa), limiting their thickness to less than 20μm. Increased coating thickness can easily lead to interfacial delamination or macrocracks, severely impacting the coating's bonding strength and service life, thus limiting its practical application under heavy-load friction and wear conditions.

[0005] To address these issues, existing technologies have proposed the use of a multilayer Cr / CrN coating structure. Through the combined action of a soft Cr layer and a hard CrN layer, this structure can, to a certain extent, release and optimize the distribution of residual stress, thereby improving the coating's toughness and crack resistance. However, existing multilayer coating designs often employ structures with abrupt changes in interlayer composition and thickness, resulting in discontinuous stress gradients between layers and significant stress concentration. This makes it difficult to meet the requirements for stable service of ultra-thick coatings (>50μm) under complex operating conditions.

[0006] In addition, most current Cr / CrN coating preparation processes use fixed bias parameters for deposition, and are unable to dynamically adjust the ion bombardment energy according to the requirements of each functional layer. Therefore, it is difficult to simultaneously achieve the coordinated optimization of comprehensive performance such as good interface adhesion, high hardness, and low residual stress under a single process condition.

[0007] Therefore, there is an urgent need for a Cr / CrN alternating multilayer gradient stress-relieving coating and its preparation method, which can effectively relieve interlayer stress concentration while ensuring high hardness and wear resistance of the coating, and improve the overall bonding strength and structural stability to meet the application requirements of high-performance and long-life surface engineering. Summary of the Invention

[0008] The present invention aims to provide a Cr / CrN alternating multilayer gradient stress-relieving coating and a preparation method thereof, so as to solve the technical problems of the prior art in which the stress gradient between the layers of the Cr / CrN alternating multilayer structure is discontinuous and obvious stress concentration phenomenon still exists.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions: A Cr / CrN alternating multilayer gradient stress-relieving coating comprises a multilayer Cr coating and a multilayer CrN coating, wherein the Cr coating and the CrN coating are alternately arranged from the surface of a substrate outward, and the innermost layer is the Cr coating and the outermost layer is the CrN coating; the Cr coating and the CrN coating are both prepared by a magnetron sputtering method, the bias voltage of all Cr coatings is the same, the bias voltage of all Cr coatings is the same, and the bias voltage of the Cr coating is smaller than the bias voltage of the CrN coating.

[0010] The preparation method of the Cr / CrN alternating multilayer gradient slow-release stress coating is used to prepare the above-mentioned Cr / CrN alternating multilayer gradient slow-release stress coating, comprising the following steps: S1. Substrate pretreatment: Polish the substrate to Ra < 0.1 μm, ultrasonically clean, and then use argon ion glow cleaning. S2. Alternating deposition: A Cr coating and a CrN coating are sequentially deposited on the substrate surface using a magnetron sputtering method, specifically comprising the following steps: S2-1. Cr coating deposition: in Ar atmosphere, apply -60 V bias, deposition for 10 minutes; S2-2. CrN coating deposition: in an Ar / N2 mixed atmosphere, apply a -120 V bias and deposit for 10 minutes; S2-3. Repeat steps S2-1 and S2-2 to form a 20-layer alternating structure.

[0011] The principles and advantages of this solution are: 1. This solution uses a lower bias voltage (-60V) when depositing the Cr layer, which reduces ion bombardment energy and minimizes damage to the underlying structure (substrate or underlying film layer), thereby effectively controlling residual stress accumulation (<1.5GPa). Using a higher bias voltage (-120V) when depositing the CrN layer enhances the ion bombardment effect, improves the ionization rate and density, and achieves higher hardness (>30GPa). Furthermore, layer-by-layer switching of the bias voltage allows each functional layer to be formed under optimal energy conditions, achieving a macroscopically coordinated optimization of hardness and toughness, ultimately resulting in a composite coating with a total thickness of 100μm that still exhibits excellent adhesion and crack resistance. This solution overcomes the limitations of traditional fixed bias processes, enabling ultra-thick coatings (>50μm) to maintain good adhesion and structural stability.

[0012] 2. The Cr layer has good plasticity and low hardness. As a buffer layer, it can relieve the compressive stress generated by the adjacent CrN hard layer. The CrN layer can provide high hardness and wear resistance. At the same time, its high thermal expansion coefficient will generate tensile stress during the cooling process. Without a buffer layer, it is easy to cause interfacial cracking. This solution forms a "soft-hard-soft-hard" multilayer structure through alternating Cr / CrN deposition, which helps to establish a continuous stress transition gradient, thereby significantly inhibiting the propagation of interfacial microcracks caused by thermal expansion mismatch and improving the overall service life of the coating.

[0013] 3. This solution utilizes magnetron sputtering technology, rather than more expensive methods like arc ion plating or electron beam evaporation, ensuring high quality while reducing equipment investment and operating costs. Furthermore, the CrN layer achieves higher density and crystal orientation consistency at a higher bias voltage (-120V) than the Cr layer, enabling excellent tribological properties (friction coefficient as low as 0.23) despite high hardness (>30 GPa). This solution boasts a rational overall coating structure, balancing performance and cost, and has promising prospects for industrial application.

[0014] Preferably, as an improvement, the thickness of the Cr coating is the same as that of the CrN coating, and the thickness of a single layer is 5±0.5 μm.

[0015] Beneficial Effects: 1) Achieve uniform stress distribution and alleviate interlaminar stress concentration: The Cr layer has lower hardness and higher plasticity, while the CrN layer has higher hardness but higher residual stress. A significant difference in thickness between the two layers can result in a significant stress mutation at the interface. This solution sets the thickness of the Cr and CrN coatings to the same value, ensuring that each layer has similar load-bearing and deformation capabilities across the thickness direction. This avoids localized stress concentration caused by excessively thick layers, facilitates layer-by-layer stress relief, reduces crack initiation, and improves coating toughness.

[0016] 2) Improved overall coating uniformity and process repeatability: In the magnetron sputtering process, deposition time and thickness are positively correlated. A uniform thickness design means that each layer takes a consistent deposition time (e.g., 10 minutes). Process parameters (bias voltage, gas pressure, flow rate, etc.) can be uniformly set and reused. Therefore, this solution significantly improves process controllability and repeatability, reduces thickness fluctuations caused by human error and equipment errors, facilitates industrial mass production, and improves yield.

[0017] 3) Ensure synergy between functional layers to enhance overall performance: The Cr layer serves as a buffer layer, and the CrN layer as a wear-resistant layer. Each layer has a distinct functional role. If a layer is too thin, its function will not be fully realized, while if it is too thick, the overall balance may be disrupted. This solution sets the thickness of each layer to 5±0.5μm, which can fully realize its respective functions without causing local stress accumulation. The functional layers work together well, achieving comprehensive optimization of hardness, toughness, and bonding strength, ultimately resulting in a composite coating with stable and reliable performance.

[0018] Preferably, as an improvement, the number of layers of the Cr coating and the CrN coating are both 10, with a total thickness of 100±5 μm.

[0019] Beneficial Effects: 1) Achieve stable deposition of ultra-thick coatings, breaking through traditional thickness limitations: Traditional CrN single-layer coatings are generally limited to thicknesses of no more than 20μm due to high residual stress. Multilayer structures can alleviate stress concentration by alternating soft and hard layers, but if the number of layers is too small (such as only 2-4 layers), effective stress relief is still not achieved. This solution, by creating a 20-layer multilayer system with an alternating Cr / CrN structure of 10 layers each, achieves an ultra-thick coating with a total thickness of 100μm, while each layer is 5μm thick. This significantly improves the coating's serviceability under heavy-load friction conditions, breaking through the existing technical limitations on the thickness of CrN coatings and expanding their application boundaries.

[0020] 2) Create a continuous stress gradient to improve crack resistance and interface stability: The Cr layer has low hardness and high plasticity, while the CrN layer provides high hardness and wear resistance. The alternating layers create a buffering mechanism for layer-by-layer stress release. The more layers, the more uniform the stress distribution. This solution's 10-layer Cr + 10-layer CrN structural design creates a stable stress gradient within the coating, preventing interfacial cracking caused by differences in thermal expansion coefficients between layers. This improves the coating's structural stability and durability under thermal cycling or impact loads.

[0021] 3) Ensure the full contribution of the functional layers, balancing hardness, toughness, and adhesion: A 5μm thickness for each layer allows for full utilization of its respective functions (Cr for cushioning, CrN for wear resistance). Too few layers (e.g., only 2-3) will hinder effective multi-layer synergy, while too many layers (e.g., over 20) may increase process complexity and cost. This solution utilizes a design with 10 layers each, achieving an optimal balance between performance and processability. This ensures the effective contribution of each functional layer while avoiding the process control difficulties associated with excessive layering, ultimately achieving the combined performance of high hardness (>30 GPa), low coefficient of friction (0.23), and strong adhesion.

[0022] Preferably, as an improvement, the bias voltage of the Cr coating is -60V, and the bias voltage of the CrN coating is -120V.

[0023] Beneficial effects: 1) Dynamic regulation of ion bombardment energy and optimization of each layer's performance: During magnetron sputtering, the bias voltage (substrate negative voltage) directly affects the energy of the deposited particles. A lower bias voltage (e.g., -60V) reduces the ion bombardment intensity, while a higher bias voltage (e.g., -120V) enhances the ion bombardment effect, improving density and hardness. This solution uses a -60V bias for the Cr layer, which can reduce damage to the substrate or underlying film layer and control residual stress accumulation (<1.5GPa), making it suitable as a buffer layer and bonding layer. Using a -120V bias for the CrN layer can increase the ionization rate and atomic migration ability, significantly improving the coating hardness (>30GPa), and facilitating the formation of a dense, wear-resistant surface structure. This bias layering control strategy enables each layer of material to be deposited under optimal energy conditions, resulting in better overall performance.

[0024] 2) Balancing hardness and toughness to achieve stable thick film deposition: While high bias voltage improves hardness, it also increases residual stress. Using high bias voltage for all layers can easily lead to excessive overall stress, causing cracking or spalling. Applying different bias voltages in layers allows for alternating "soft-hard" deposition, releasing stress layer by layer. In this solution, the Cr layer is deposited at a lower bias voltage to alleviate the compressive stress introduced by the upper CrN layer, while the CrN layer is deposited at a higher bias voltage to provide high hardness and wear resistance. By periodically switching the bias voltage, hardness and toughness are synergistically optimized, ultimately maintaining good adhesion and structural stability with a total thickness of up to 100μm.

[0025] 3) Improved coating tribological performance and service life: The CrN layer deposited at a -120V bias voltage is denser, with lower surface roughness and more ordered grain arrangement, which helps reduce the coefficient of friction and improve wear resistance. With a hardness greater than 30 GPa, the friction coefficient can be reduced to 0.23, significantly better than conventional single-layer CrN coatings (which typically have a friction coefficient greater than 0.3), extending the coating's service life under harsh operating conditions such as heavy loads and high temperatures.

[0026] Preferably, as an improvement, the single-layer deposition cycle of the Cr coating and the CrN coating is 10 minutes, and the bias voltage is automatically switched every 10 minutes.

[0027] Beneficial effects: This solution sets 10 minutes as a complete single-layer deposition cycle. The time window is reasonable, and the bias switching is strictly synchronized with the layer sequence, avoiding the deviation of functional layer performance from expectations due to time mismatch, and can improve the degree of automation and repeatability of the entire process.

[0028] Under the same power and pressure conditions, deposition time is positively correlated with film thickness. A 10-minute deposition time was used for all layers, ensuring consistent thickness across the layers (5±0.5μm). This prevented uneven thickness due to time differences, which could affect stress distribution. This significantly improved the overall uniformity and structural stability of the coating, reducing the formation of localized stress concentrations or weak areas, and contributing to maintaining excellent service performance even with a total thickness of 100μm.

[0029] The combination of fixed time (10 minutes) + fixed bias voltage (-60V / -120V) has simple and clear parameter settings and is easy to programmatically control, which significantly reduces operational difficulty, improves process repeatability, and has good industrial promotion value.

[0030] Preferably, as an improvement, in step S1, the ultrasonic cleaning time is 20 minutes; the bias voltage of the glow cleaning is -600V, and the time is 30 minutes.

[0031] Beneficial Effects: 1) This solution improves substrate surface cleanliness and strengthens the adhesion between the coating and the substrate. Substrate surface contaminants (such as grease, oxides, and dust) can significantly affect coating adhesion. Ultrasonic cleaning removes organic surface contaminants through cavitation, while glow cleaning utilizes high-energy Ar⁺ ion bombardment to remove adsorbed matter and oxide layers. This solution uses a 20-minute ultrasonic cleaning time to ensure that cleaning solutions such as deionized water, acetone, and alcohol are fully active and thoroughly remove surface contaminants. Glow cleaning at a -600V bias imparts sufficient kinetic energy to the Ar⁺ ions, effectively removing residual oxide layers and adsorbed gases from the substrate surface. Consequently, this solution significantly improves the interfacial bond between the coating and the substrate, reducing the risk of delamination or shedding during subsequent deposition.

[0032] 2) This solution improves initial nucleation conditions and enhances coating uniformity and density. Surface defects or contamination can affect the initial nucleation process, resulting in coarse or unevenly distributed grains. A clean and activated surface promotes ordered atomic arrangement and uniform nucleation. This solution utilizes optimized cleaning parameters (20 minutes of ultrasonic cleaning followed by 30 minutes of glow cleaning) to achieve a highly clean and active surface. This helps the Cr / CrN coating form a uniform, fine grain structure during the initial deposition phase, ultimately resulting in a denser, smoother, and more stable composite coating.

[0033] 3) This solution ensures the stability of subsequent thick film deposition and extends service life. In multilayer structures with a total thickness of up to 100μm, the bond between the substrate and the first Cr layer is particularly critical. If the initial bond is poor, overall flaking or crack propagation is likely to occur as the number of layers increases. The cleaning parameters used in this solution ensure a good bond between the innermost Cr layer and the substrate, providing a guarantee for the stable deposition of subsequent multilayer structures and significantly extending the service life of the coating in harsh environments such as high temperatures and heavy loads.

[0034] Preferably, as an improvement, in step S2, the target power of the magnetron sputtering is constant at 3 kW, and the working gas pressure is 0.6 Pa.

[0035] Beneficial Effects: 1) This solution achieves a stable plasma state, improving sputtering efficiency and film quality. A constant target power of 3kW provides sufficient sputtering energy to fully detach Cr atoms from the target surface and evenly distribute them. The operating gas pressure of 0.6Pa is within the ideal range for magnetron sputtering, ensuring efficient Ar⁺ ion bombardment while preventing excessive gas molecules from interfering with the deposition process. This results in a highly dense, well-adhesive, and uniform coating structure.

[0036] 2) This solution supports a dynamic bias alternation control strategy to ensure consistent performance across all layers. A constant 3kW power and 0.6Pa gas pressure ensure that each layer (whether Cr or CrN) is deposited under the same basic conditions. Combined with a bias switching strategy, this achieves layer-by-layer optimization and stable output of properties such as hardness, stress, and adhesion. Ultimately, a multilayer composite structure with excellent overall performance is achieved, even at a total thickness of 100μm.

[0037] 3) This solution offers reasonable cost control, balancing performance and economic efficiency. While excessively high target power (e.g., >5kW) can accelerate deposition, it also increases energy consumption and equipment wear. Excessively low power (<2kW) can result in slow deposition rates and looser films. 0.6Pa falls within the conventional sputtering pressure range and does not require specialized vacuum systems. 3kW + 0.6Pa represents an optimal compromise between performance and cost, reducing equipment investment and operating costs while ensuring coating quality, making it highly valuable for industrialization and promotion.

[0038] Preferably, as an improvement, in step S2, when the Cr coating is deposited, the Ar flow rate is 100 sccm; when the CrN coating is deposited, the Ar flow rate is 80 sccm and the N2 flow rate is 20 sccm.

[0039] Beneficial Effects: 1) This solution enables precise atmosphere control during the Cr and CrN deposition processes. The Cr layer is deposited by physical sputtering in a pure Ar atmosphere; the CrN layer is deposited in an Ar / N2 mixed atmosphere by reactive sputtering, where Cr atoms react with N2 to form nitrides. Ar is primarily used to maintain the plasma and the sputtering process, while N2 provides a nitrogen source, participating in the chemical reaction to form CrN. Using a higher Ar flow rate (100 sccm) for the Cr layer enhances plasma density, improves sputtering efficiency, and produces a dense, uniform metal layer. Using a lower Ar flow rate (80 sccm) + 20 sccm N2 for the CrN layer ensures a sufficient nitrogen source supply, promotes a thorough reaction between Cr and N, and forms a high-quality CrN layer. By precisely controlling the gas ratio, this solution enables controllable layer-by-layer deposition of Cr and CrN materials.

[0040] 2) This solution supports a dynamic bias alternation strategy to ensure consistent performance across all layers. During the bias switching process (-60V / 120V), if the gas environment is unstable, it will affect the particle energy distribution and film quality. Fixing the gas ratio for each layer helps maintain a consistent deposition basis under different bias conditions. A high Ar flow rate in the Cr layer can reduce plasma resistance and stabilize ion bombardment under low bias (-60V). Introducing N2+ in the CrN layer appropriately reduces the Ar flow rate, which can optimize the ionization rate and reaction efficiency under high bias (-120V). The two work together to ensure that each functional layer is formed under optimal atmosphere conditions, ultimately achieving layer-by-layer optimization and stable output of properties such as hardness, stress, and bonding strength.

[0041] 3) This solution offers reasonable cost control, balancing performance and economic efficiency. Excessively high N2 flow rates dilute the Ar and affect plasma stability; too low a flow rate results in incomplete CrN reaction, resulting in unreacted Cr or unstable phase composition. Properly adjusting the Ar to N2 ratio can achieve a balance between performance and cost. A ratio of 80 sccm Ar + 20 sccm N2 is both fully reactive and economically sound, producing CrN layers with high hardness (>30 GPa) and low friction coefficient (<0.25). This approach also avoids the problems of reduced deposition rate and equipment corrosion caused by excessive nitrogen, demonstrating promising prospects for industrial application.

[0042] Preferably, as an improvement, in step S2, the substrate rotates at a speed of 5 rpm.

[0043] Beneficial Effects: 1) This solution improves the uniformity of coating thickness and composition distribution. During magnetron sputtering, particles emitted from the target are distributed at an angle, creating a "shadow effect." If the substrate remains stationary, different areas receive inconsistent particle flux, resulting in uneven film thickness and composition. This solution rotates the substrate at 5 rpm, allowing different areas of the surface to alternately face the target, effectively eliminating the "shadow effect" and improving the spatial uniformity and consistency of the coating. This is particularly helpful for maintaining stable performance in each layer of multilayer structures with a total thickness of up to 100 μm.

[0044] 2) This solution improves ion bombardment uniformity and strengthens film-substrate bonding. During deposition, a bias voltage (-60V or -120V) is applied, ensuring continuous ion bombardment of the substrate surface. When the substrate is stationary, localized areas may be damaged or overheated due to prolonged bombardment. Rotation distributes the bombardment energy more evenly across the surface. A rotation rate of 5 rpm ensures uniform ion energy distribution without affecting the film formation process or causing centrifugal effects due to excessive rotational speed. This significantly improves the interfacial bonding strength between the coating and the substrate, reducing the risk of delamination.

[0045] 3) This approach optimizes atomic migration and surface diffusion, improving density and crystal quality. Matrix rotation increases the chances for deposited particles to find lower-energy positions on the surface, promoting orderly grain arrangement, densification, and optimized lattice orientation. During the alternating Cr / CrN deposition process, rotation contributes to the formation of a finer, more uniform, and denser grain structure, particularly in the CrN layer, significantly enhancing its hardness and wear resistance, ultimately resulting in a composite coating with excellent overall mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of coating samples of the embodiment of the present invention and the comparative example.

[0047] Figure 2 Schematic diagram of the indentation of an embodiment of the present invention under a load of 150 kgf using a Rockwell hardness tester.

[0048] Figure 3 Schematic diagram of the indentation of the comparative example of the present invention under a load of 150 kgf on a Rockwell hardness tester.

[0049] Figure 4 Schematic diagram of the indentation morphology of an embodiment of the present invention under a load of 0.25g on a micro-indenter.

[0050] Figure 5 Schematic diagram of the indentation morphology of the comparative example of the present invention under a load of 0.25g on a micro indenter.

[0051] Figure 6 Schematic diagram of the change of friction coefficient over time in the embodiments of the present invention and the comparative example.

[0052] Figure 7 Schematic diagram of scratch morphology according to an embodiment of the present invention.

[0053] Figure 8 Schematic diagram of the scratch morphology of the comparative example of the present invention. DETAILED DESCRIPTION

[0054] The following is further described in detail through specific implementation methods: Example The present invention provides a Cr / CrN alternating multilayer gradient stress-relieving coating, comprising multiple Cr coatings and multiple CrN coatings. The Cr coatings and CrN coatings are alternately arranged from the surface of a substrate outward, with the innermost layer being the Cr coating and the outermost layer being the CrN coating. The Cr coating and the CrN coating have the same thickness, with a single layer thickness of 5±0.5μm. The number of layers of both the Cr coating and the CrN coating is 10, with a total thickness of 100±5μm.

[0055] Both the Cr and CrN coatings were deposited using magnetron sputtering. The bias voltage for all Cr coatings was the same, and the bias voltage for all CrN coatings was smaller than that for the CrN coatings. Specifically, the bias voltage for the Cr coating was -60 V, and the bias voltage for the CrN coating was -120 V. The deposition cycle for each single layer of the Cr and CrN coatings was 10 minutes, with the bias voltage automatically switching every 10 minutes.

[0056] Table 1: Materials, thickness, bias voltage and function of each coating layer sequence Material thickness bias Function 1 Cr 5μm -60V Low stress bonding layer 2 CrN 5μm -120V High hardness layer 3 Cr 5μm -60V stress buffer layer …… …… …… …… …… 20 CrN 5μm -120V Wear-resistant surface The present invention also provides a method for preparing a Cr / CrN alternating multilayer gradient sustained stress relief coating, which is used to prepare the above-mentioned Cr / CrN alternating multilayer gradient sustained stress relief coating, comprising the following steps: S1. Substrate pretreatment: Pretreatment of the substrate includes the following steps: S1-1 Substrate preparation: Prepare 304 stainless steel as the substrate and polish the substrate to Ra < 0.1 μm to reduce the surface roughness of the substrate and improve the adhesion of the coating.

[0057] S1-2. Ultrasonic cleaning: Use deionized water, acetone, and alcohol to ultrasonically clean the substrate in sequence for a total of 20 minutes to remove oil, dust and other contaminants on the substrate surface.

[0058] S1-3. Install the substrate: Install the ultrasonically cleaned substrate on the substrate stage and confirm that the rotation function of the substrate stage is normal and can meet the rotation speed requirement of 5 rpm.

[0059] S1-4. Vacuuming: Use a vacuum pump to evacuate the vacuum chamber where the substrate stage is located to 9.9×10 -4Pa, to ensure that there is no air residue in the vacuum chamber to avoid oxidation and contamination.

[0060] S1-5. Glow cleaning: Glow cleaning is performed by bombardment with argon ions. The bias voltage of the glow cleaning is -600V and the duration is 30 minutes. + Ions bombard the substrate surface, remove adsorbents and oxide layers, and significantly improve the bonding strength between the coating and the substrate.

[0061] S2. Alternating deposition: A Cr coating and a CrN coating are sequentially deposited on the substrate surface using a magnetron sputtering method, specifically comprising the following steps: S2-1. Cr coating deposition: In an Ar atmosphere, a bias voltage of -60 V was applied and the deposition was carried out for 10 minutes; the target power was constant at 3 kW, the working pressure was 0.6 Pa, the Ar flow rate was 100 sccm, and the substrate was rotated at a speed of 5 rpm.

[0062] S2-2. CrN coating deposition: In an Ar / N2 mixed atmosphere, a -120 V bias was applied and the deposition was carried out for 10 minutes; the target power was constant at 3 kW, the working pressure was 0.6 Pa, the Ar flow rate was 80 sccm, the N2 flow rate was 20 sccm, and the substrate was rotated at a speed of 5 rpm.

[0063] S2-3. Repeat steps S2-1 and S2-2 to form a 20-layer alternating structure; after each layer is completed, the bias is automatically switched once.

[0064] S3. Cooling and sampling: After the deposition is completed, turn off the power, wait for the system to cool naturally, remove the substrate, and conduct subsequent testing on the sample.

[0065] Table 2: Deposition parameters of Cr coating and CrN coating in step S2 parameter Cr coating CrN coating Target power 3kW (DOMS) 3kW (DOMS) Working air pressure 0.6Pa 0.6Pa Ar flow 100sccm 80sccm <![CDATA[N2 flow rate]]> 0 20sccm bias -60V -120V Sedimentation time 10min / layer 10min / layer Base rotation 5rpm 5rpm Comparative Example A method for preparing a Cr / CrN alternating multilayer gradient stress-relieving coating is provided, which differs from the embodiment in that a single -60V bias process is adopted, that is, both step S2-1 and step S2-2 adopt a -60V bias.

[0066] The coating sample obtained in the comparative example is inferior to the coating sample obtained in the embodiment in terms of performance indicators such as surface hardness, bonding strength, fracture toughness, and residual stress, as shown in Table 3.

[0067] Table 3: Comparison of performance indicators of the coating samples obtained in the embodiment and the coating samples obtained in the comparative example Performance indicators Example Comparative Example Surface hardness 31.5±0.8GPa 25.2±0.5GPa Bonding strength (HF grade) HF1 HF2 fracture toughness <![CDATA[7.9MPa·m 1 / 2 ]]> <![CDATA[6.3MPa·m 1 / 2 ]]> residual stress 0.8±0.2GPa 1.2±0.3GPa Critical load Lc 75.3±1.2N 60.2±1.1N Friction coefficient 0.23 0.30 The coating samples obtained in the embodiments and comparative examples are shown in the attached Figure 1 As shown, attached Figure 1The left side of the figure is a coating sample obtained in the embodiment, and the right side is a coating sample obtained in the comparative example.

[0068] Experiment 1: HRC indentation bonding strength The coating samples obtained in the embodiment and the comparative example were loaded with a Rockwell hardness tester at a load of 150 kgf. Figure 2 As shown in the figure, the coating indentation is complete and has no cracks, indicating that the coating has a strong bonding force with the substrate. Figure 3 As shown in FIG, the coating has obvious cracks on the edge of the indentation and is partially peeled off, and the bonding strength is weaker than that of the coating sample obtained by alternating bias of -60 V / -120 V in Example.

[0069] Experiment 2: Microindentation Topography The micromechanical properties of the coating were tested using a microindenter. Under a load of 0.25 g, the coating sample obtained by alternating bias voltages of -60 V / -120 V in Example 1 was as shown in the attached figure. Figure 4 As shown in the figure, the coating indentation has no cracks; the coating sample obtained by the single -60V bias in the comparative example is as shown in the attached Figure 5 As shown in the figure, the coating has annular cracks, the coating stress is large, and the expansion coefficient does not match that of the substrate.

[0070] Experiment 3: Coefficient of Friction The changes of the friction coefficient over time of the coating sample obtained by the alternate bias voltage of -60 V / -120 V in the embodiment and the coating sample obtained by the single bias voltage of -60 V in the comparative example are shown in the attached figure. Figure 6 As shown in the figure, the coating sample obtained by the comparative example with a single -60 V bias voltage caused residual stress accumulation and microcrack propagation in the coating. This defect increased the surface roughness and easily generated abrasive particles during friction, resulting in a higher friction coefficient than the coating sample obtained by the alternating -60 V / -120 V bias voltage in the example.

[0071] Experiment 4: Scratch morphology The scratch morphology of the coating sample obtained by alternating bias voltage of 60 V / -120 V is shown in the attached figure. Figure 7 As shown; the scratch morphology of the coating sample obtained by single -60V bias is shown in the attached Figure 8 The scratch morphologies of the coating samples of the embodiment and the comparative example were analyzed, and the results are shown in Table 3.

[0072] Table 4: Analysis of scratch morphology characteristics of the coating samples obtained in the examples and the coating samples obtained in the comparative examples bias Critical load Lc Scratch morphology characteristics Example -60 V / -120 V alternating 75.3±1.2N The scratch edge is smooth, there is no significant peeling, and only slight plastic deformation on the surface. Comparative Example Single -60V 60.2±1.1N There are multiple transverse cracks on the edge of the scratch, and the coating is peeling off over a large area. Compared with the existing technology, the present invention has the following technical advantages: 1. A balance between hardness and toughness is achieved by periodically switching the bias voltage, enabling the preparation of a high-bonding, tough coating with a total thickness of 100 μm.

[0073] 2. The alternating transition between Cr and CrN effectively releases stress layer by layer and reduces the propagation of micro cracks on the interface caused by the difference in thermal expansion coefficient between layers.

[0074] 3. When the hardness is greater than 30GPa, the friction coefficient is reduced to 0.23, and the coating preparation cost is significantly reduced.

[0075] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. Cr / CrN alternating multi-layer gradient stress relief coating, characterized by: It includes a multi-layer Cr coating and a multi-layer CrN coating, wherein the Cr coating and the CrN coating are alternately arranged from the surface of the substrate outward, and the innermost layer is the Cr coating and the outermost layer is the CrN coating; The Cr coating and the CrN coating are both prepared by a magnetron sputtering method. The bias voltages of all Cr coatings are the same, the bias voltages of all CrN coatings are the same, and the bias voltage of the Cr coating is smaller than that of the CrN coating.

2. The Cr / CrN alternating multilayer gradient stress-relieving coating according to claim 1, characterized in that: The thickness of the Cr coating is the same as that of the CrN coating, and the thickness of a single layer is 5±0.5 μm.

3. The Cr / CrN alternating multilayer gradient stress-relieving coating according to claim 2, characterized in that: The Cr coating and the CrN coating both have 10 layers, and the total thickness is 100±5 μm.

4. The Cr / CrN alternating multilayer gradient stress-relieving coating according to claim 3, characterized in that: The bias voltage of the Cr coating is -60V, and the bias voltage of the CrN coating is -120V.

5. The Cr / CrN alternating multi-layer gradient stress-relieving coating according to claim 4, characterized in that: The single-layer deposition cycle of the Cr coating and the CrN coating is 10 minutes, and the bias voltage is automatically switched every 10 minutes.

6. A method for preparing a Cr / CrN alternating multilayer gradient stress-relieving coating, characterized by: The method for preparing the Cr / CrN alternating multilayer gradient stress-relieving coating according to any one of claims 1 to 5 comprises the following steps: S1. Substrate pretreatment: Polish the substrate to Ra < 0.1 μm, ultrasonically clean, and then use argon ion glow cleaning. S2. Alternating deposition: A Cr coating and a CrN coating are sequentially deposited on the substrate surface using a magnetron sputtering method, specifically comprising the following steps: S2-1. Cr coating deposition: in Ar atmosphere, apply -60 V bias, deposition for 10 minutes; S2-2. CrN coating deposition: in an Ar / N2 mixed atmosphere, apply a -120 V bias and deposit for 10 minutes; S2-3. Repeat steps S2-1 and S2-2 to form a 20-layer alternating structure.

7. The method for preparing the Cr / CrN alternating multilayer gradient stress-relieving coating according to claim 6, characterized in that: In step S1, the ultrasonic cleaning time is 20 minutes; the bias voltage of the glow cleaning is -600V, and the time is 30 minutes.

8. The method for preparing the Cr / CrN alternating multilayer gradient stress-relieving coating according to claim 7, characterized in that: In step S2, the target power of the magnetron sputtering is constant at 3 kW, and the working gas pressure is 0.6 Pa.

9. The method for preparing the Cr / CrN alternating multilayer gradient stress-relieving coating according to claim 8, characterized in that: In step S2, when the Cr coating is deposited, the Ar flow rate is 100 sccm; when the CrN coating is deposited, the Ar flow rate is 80 sccm and the N2 flow rate is 20 sccm.

10. The method for preparing the Cr / CrN alternating multilayer gradient stress-relieving coating according to claim 9, characterized in that: In step S2, the substrate is rotated at a speed of 5 rpm.

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