A composite coating for cutting tool surfaces and a method of making the same

Abstract

The present application relates to the technical field of cutting tool protective coating, and discloses a composite structure coating on the surface of a cutting tool and a preparation method thereof. The composite structure coating comprises a CrN transition layer, an AlCrZrN gradient layer and an oxide film layer deposited on the surface of the tool substrate in sequence. The aluminum content and the chromium content of the AlCrZrN gradient layer continuously change along the thickness direction. The oxide film layer mainly comprises Al2O3, Cr2O3 and ZrO2, and the oxygen content decreases from the surface of the oxide film layer to the inside. The present application adopts the CrN transition layer and the AlCrZrN gradient layer with continuously changing Al / Cr composition, effectively buffers and releases the interface stress, greatly improves the critical bonding force of the coating, and avoids the peeling of the coating during cutting. The air oxygen infiltration post-processing utilizes the mild oxygen partial pressure in the air, and generates the dense composite oxide film layer mainly composed of nanocrystalline Al2O3, Cr2O3 and ZrO2 on the surface of the coating in situ through the programmed coordinated control of temperature and flow, which has high hardness, high wear resistance and high temperature oxidation resistance.

Description

Technical Field

[0001] This invention relates to the field of protective coating technology for cutting tools, and in particular to a composite structure coating on the surface of a cutting tool and its preparation method. Background Technology

[0002] Titanium alloys (such as Ti-6Al-4V) and high-temperature alloys hold an irreplaceable position in high-end manufacturing fields such as aerospace, medical devices, and precision components due to their excellent strength, heat resistance, and corrosion resistance. However, these materials exhibit extremely low thermal conductivity and extremely high chemical reactivity during cutting, leading to a sharp increase in temperature in the tool cutting edge area (often exceeding 600°C). This, in turn, causes problems such as rapid wear of the tool coating, workpiece material adhesion, and premature tool failure, severely restricting machining efficiency, accuracy, and tool life.

[0003] To improve the performance of cutting tools under high-temperature and high-load cutting environments, surface coating technology has become a key approach. Oxide coatings, due to their excellent high-temperature stability and chemical inertness, are considered an important alternative to traditional TiAlN and ZrN coatings. Among them, Al-Cr-Zr based oxide coatings ((AlCrZr)O x Because it can form a composite oxide structure of Al₂O₃, Cr₂O₃, and ZrO₂, it possesses both good oxidation resistance and wear resistance, showing great application potential. Currently, (AlCrZr)O x The coating is mainly prepared directly by magnetron sputtering or multi-arc physical vapor deposition (PVD) technology. However, such processes have obvious limitations: on the one hand, the difference in thermal expansion coefficients between the directly deposited oxide coating and the WC-Co cemented carbide substrate leads to significant interfacial stress, resulting in low coating bonding strength (critical load is often below 50N), which makes it easy to peel off during cutting. On the other hand, a loose microstructure is easily formed during the deposition process, with a large number of pores and defects, resulting in generally low coating hardness (usually below 35GPa), and the wear resistance is difficult to meet the requirements of high-speed and heavy-load cutting.

[0004] To further improve coating performance, existing technologies often employ vacuum annealing or inert gas-protected heat treatment as post-treatment. While these methods can release internal stress to some extent, they struggle to effectively control the phase composition and structural density of the oxides. Some studies have attempted to introduce oxygen for post-oxidation treatment, but due to insufficient consideration of the oxidation kinetic differences among elements such as Al, Cr, and Zr, and improper control of process parameters (such as oxygen concentration, temperature, and time), over-oxidation, embrittlement, or uneven oxidation of the coating often occurs, ultimately impairing the overall performance of the coating. Therefore, the key challenge is to achieve (AlCrZr)O₂ coating performance through a simple and controllable post-treatment process while ensuring good adhesion between the coating and the substrate. xThe optimization of coating structure and the synergistic improvement of performance have become key challenges that urgently need to be overcome in this field. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a composite structure coating for the surface of a cutting tool.

[0006] The second objective of this invention is to provide a method for preparing a composite structure coating on the surface of such a cutting tool.

[0007] The third objective of this invention is to provide a cutting tool.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a composite structure coating for the surface of a cutting tool, comprising a CrN transition layer, an AlCrZrN gradient layer, and an oxide film layer sequentially deposited on the surface of a tool substrate; wherein the aluminum content and chromium content of the AlCrZrN gradient layer change in a continuous gradient along the thickness direction; the oxide film layer is mainly composed of Al2O3, Cr2O3, and ZrO2, and the oxygen content decreases in a gradient from the outside to the inside of the oxide film layer surface.

[0009] In some embodiments of the present invention, the elemental composition of the oxide film layer conforms to (Al) 0.4 Cr 0.1 Zr 0.5 )O x Where x is the ratio of oxygen atoms to the total number of aluminum, chromium, and zirconium atoms, x = 1.5-2.0.

[0010] In some embodiments of the present invention, the aluminum content of the AlCrZrN gradient layer increases in the thickness direction, while the chromium content decreases in the thickness direction.

[0011] In some embodiments of the present invention, the elemental composition of the AlCrZrN gradient layer conforms to (Al y Cr z Zr 1-y-z )N, where y and z are atomic fractions, y = 0.2-0.4, z = 0.1-0.3.

[0012] In some embodiments of the present invention, the thickness of the CrN transition layer is 0.2-0.4 μm.

[0013] In some embodiments of the present invention, the thickness of the AlCrZrN gradient layer is 0.5-0.8 μm.

[0014] In some embodiments of the present invention, the thickness of the oxide film is 0.3-0.5 μm.

[0015] The inventive concept of this invention is as follows: The coefficients of thermal expansion of high-hardness oxides (such as Al2O3) and hard alloy substrates such as tungsten-cobalt (WC-Co) differ significantly. Direct deposition of these materials will generate high interfacial stress, leading to coating peeling. Therefore: a. In this invention, a CrN transition layer is used as a primary buffer. The thermal expansion coefficient of CrN is between that of the substrate and the upper coating layer, and it has good miscibility with metal elements (such as Co) in the substrate, which is beneficial to improving the interfacial bonding force. b. Using an AlCrZrN gradient layer as a secondary buffer, the Al content in the AlCrZrN gradient layer increases and the Cr content decreases in the thickness direction. On the side near the CrN transition layer, the low Al and high Cr design makes the thermal expansion coefficient of the gradient layer closer to that of CrN and the matrix, thus achieving good matching with the underlying CrN transition layer and the matrix, resulting in low interfacial stress. On the side near the surface layer, the low Cr and high Al design significantly reduces the thermal expansion coefficient of the gradient layer due to the high AlN content, making it closer to the top Al2O3-based oxide film. Because the Al content continuously increases and the Cr content continuously decreases, the thermal expansion coefficient of the coating also continuously changes in the thickness direction. In addition, Al has a strong affinity for oxygen, and after oxidation, it can form a very stable, dense and extremely hard Al2O3 film, which is the key to improving the surface hardness and oxidation resistance. By gradually increasing the Al content, the driving force of the oxidation reaction is gradually enhanced, which allows the oxidation front to advance into the coating more smoothly and uniformly. This avoids the violent reaction after the surface Al absorbs oxygen, which would lead to excessive internal stress in the oxide layer or the formation of a discontinuous oxide film. This achieves a smooth and continuous transition in the coefficient of thermal expansion and chemical potential from CrN to the top oxide layer, and evenly disperses the high stress originally concentrated in the oxide film layer to a thicker gradient functional region, thus inhibiting the peeling failure behavior of the coating from a mechanistic perspective. c. Directly deposited oxide coatings often have a loose structure, many defects, and insufficient hardness. Therefore, this invention uses the AlCrZrN gradient layer as a sacrificial layer, and its enriched Al, Cr, and Zr elements provide raw materials for the oxide film. Through controlled oxidation, a gradient of oxygen content is formed from the surface to the interior. Due to the different diffusion rates and oxidation activities of the three metal elements, a concentration gradient is formed in space, and they react simultaneously and in the same place, thereby generating an interwoven and mixed oxide film. Cr2O3 has a lower hardness than Al2O3, but it is equally dense and can improve corrosion resistance. ZrO2 has excellent toughness. Under the constraints of nanoscale and composite with Al2O3 and Cr2O3, its structural state is conducive to playing a phase transformation toughening and strengthening role. Therefore, the oxide film is dense and has high surface hardness, high corrosion resistance, high toughness, and oxidation resistance.

[0016] A second aspect of the present invention provides a method for preparing a composite structure coating on the surface of a cutting tool as described in the first aspect of the present invention, comprising the following steps: S1. The tool substrate is sequentially etched with argon ions and then with chromium metal ions. S2. Turn on the Cr target and use arc ion plating to deposit a CrN transition layer on the surface of the etched tool substrate. S3. Simultaneously turn on the Zr target, Al target and Cr target, and continuously adjust the target current respectively, and deposit an AlCrZrN gradient layer on the surface of the CrN transition layer by arc ion plating. S4. Perform air oxygen permeation treatment on the surface of the AlCrZrN gradient layer to form an oxide film layer in situ, thereby obtaining the composite structure coating on the surface of the cutting tool.

[0017] In some embodiments of the present invention, step S1 includes a pretreatment operation on the tool substrate before the argon ion etching.

[0018] In some embodiments of the present invention, the pretreatment includes sequentially performing surface polishing, roughening, ultrasonic cleaning, and vacuum drying on the tool substrate.

[0019] In some embodiments of the present invention, the surface polishing includes polishing with wet sandpaper to make the surface roughness Ra of the tool substrate ≤ 0.05 μm.

[0020] In some embodiments of the present invention, the roughening treatment includes sandblasting with Al2O3 sand particles at a pressure of 0.3-0.5 MPa.

[0021] In some embodiments of the present invention, the ultrasonic cleaning includes cleaning with acetone and ethanol for 15-20 minutes each.

[0022] In some embodiments of the present invention, the vacuum drying temperature is 110-130°C and the time is 25-35 min.

[0023] In some embodiments of the present invention, before the argon ion etching in step S1, the process further includes loading the pretreated tool substrate into the deposition chamber, evacuating the deposition chamber, heating and keeping it warm.

[0024] In some embodiments of the present invention, the distance between the tool substrate and the target material is 10-40 mm.

[0025] In some preferred embodiments of the present invention, the distance between the tool substrate and the target material is 30-40 mm.

[0026] In some embodiments of the present invention, the vacuum degree of the deposition chamber is less than 3.5 × 10⁻⁶. -3Pa.

[0027] In some preferred embodiments of the present invention, the vacuum degree of the deposition chamber is 2.0 × 10⁻⁶. -3 Pa-3.0×10 -3 Pa.

[0028] In some embodiments of the present invention, the temperature of the tool substrate is raised to 400-500°C and the holding time is not less than 30 minutes.

[0029] In some embodiments of the present invention, step S1, which involves sequentially performing argon ion etching and chromium metal ion etching on the tool substrate, specifically includes: introducing Ar at a flow rate of 80-120 sccm, adjusting the substrate bias voltage to -800V to -1000V, performing argon ion etching for 20-30 minutes; subsequently turning on the Cr target power supply, adjusting the target current to 100-120A, and adjusting the substrate bias voltage to -500V to -600V, performing chromium metal ion etching for 5-8 minutes.

[0030] In some embodiments of the present invention, in step S2, the process parameters for depositing the CrN transition layer include: Cr target current of 130-150A; substrate bias voltage of -120V to -150V; N2 to Ar partial pressure ratio of (1.5-4):1; total flow rate of 300-400sccm; and deposition time of 10-15min.

[0031] In some embodiments of the present invention, in step S3, the process parameters for depositing the AlCrZrN gradient layer include: a substrate bias voltage of -140V to -160V; a partial pressure ratio of N2 to Ar of (2.5-9):1; a total flow rate of 400-450 sccm; a deposition time of 25-35 min; during the deposition time, the Zr target current is maintained at 140-160 A, the Al target current increases from 120 A to 200 A, and the Cr target current decreases from 150 A to 80 A.

[0032] In some embodiments of the present invention, step S4 specifically includes: introducing air under a vacuum of 1-5 Pa to programmatically raise the temperature of the tool substrate from 400-500°C to 420-600°C, and simultaneously increasing the air flow rate at a ratio of 25-50 sccm / 100°C, controlling the total air flow rate to 50-150 sccm, holding the temperature for 10-30 minutes after the heating is completed, turning off the air source after the heating is completed, maintaining the vacuum environment and cooling at a rate of 3-6°C / min.

[0033] Specifically, the preparation method provided by this invention is based on the following principle: In step S1, the tool substrate is first argon ion etched to achieve atomic-level cleaning and activation of the substrate surface. Then, the substrate is further cleaned by bombarding with chromium metal ions, which are more reactive. At the same time, chromium atoms are injected / embedded into the substrate surface to form an extremely thin pre-diffusion layer, which enhances the subsequent physical bonding to a stronger metallurgical bonding. In step S3, by independently controlling the target currents of the Zr target, Al target, and Cr target, a controllable gradient change in the aluminum and chromium content within the AlCrZrN gradient layer can be achieved. In step S4, air (instead of pure oxygen) is used as the oxidation medium. Its constant oxygen partial pressure of approximately 21% provides a mild and controllable oxidation environment, avoiding the severe and uneven oxidation caused by pure oxygen. Furthermore, the main component of air is nitrogen, similar to the coating atmosphere, making the process conditions easier to control and less costly compared to introducing pure oxygen. Air is introduced at a temperature of 400-500°C to initiate oxidation at a lower activity level, ensuring the reaction starts uniformly from the surface. The temperature is then slowly increased to 420-600°C to accelerate atomic diffusion, promoting the oxide layer's depth and grain densification. As the temperature rises, the oxidation reaction rate increases. Increase airflow to maintain the required oxygen partial pressure and replenish consumed oxygen, thereby ensuring the oxidation reaction continues and is fully carried out. After heating, hold the temperature for a certain period of time to allow Al to preferentially oxidize into Al2O3 with high hardness, Cr to form Cr2O3 with oxidation resistance, and Zr to form ZrO2 with good toughness. The three combine to form a reinforcing phase and allow oxygen to diffuse from the surface to the interior, forming a gradient structure with gradually decreasing oxygen content. At the same time, because the oxidation process is accompanied by a certain volume expansion, it can effectively fill the micropores and grain boundaries generated by deposition, making the coating more dense. After holding the temperature, slowly cool at a rate of 3-6℃ / min to prevent new thermal stress from being generated by rapid cooling.

[0034] A third aspect of the present invention provides a cutting tool, comprising a tool substrate and a composite structure coating of the first aspect of the present invention deposited on the surface of the tool substrate.

[0035] In some embodiments of the present invention, the tool substrate comprises cemented carbide.

[0036] In some preferred embodiments of the present invention, the tool substrate is a tungsten-cobalt cemented carbide or a tungsten-titanium cemented carbide.

[0037] In some preferred embodiments of the present invention, the cutting tool is used for cutting titanium alloys or high-temperature alloys.

[0038] Compared with the prior art, the beneficial effects of the present invention are: 1) The composite structure coating on the surface of the cutting tool provided by the present invention adopts a CrN transition layer and an AlCrZrN gradient layer with a continuous gradient of Al / Cr composition, which realizes effective buffering and release of interfacial stress, and increases the critical bonding force of the coating to ≥65N, fundamentally avoiding coating peeling during the cutting process; the air oxygen infiltration post-treatment process utilizes the mild oxygen partial pressure in the air, and through programmed collaborative control of temperature and flow rate, generates a dense composite oxide film mainly composed of nanocrystalline Al2O3, Cr2O3 and ZrO2 on the coating surface in situ. This oxide film significantly increases the coating hardness to 42GPa, and its inherent oxygen content gradient structure further optimizes the stress distribution and forms a strong and tough bond with the gradient layer below; 2) The method for preparing the composite structure coating on the surface of the cutting tool provided by the present invention does not require expensive gases or complex equipment, and the air oxygen permeation post-treatment process is fully compatible with the existing arc ion plating production line, with short processing time and low cost. 3) The cutting tools provided by this invention have a composite structure coating with high adhesion, high hardness, high wear resistance and high temperature oxidation resistance deposited on the surface of the tool substrate such as cemented carbide. It is particularly suitable for high-speed and high-efficiency cutting of difficult-to-machine materials such as titanium alloys and high-temperature alloys, and shows broad application prospects in aerospace, precision manufacturing and other fields. Attached Figure Description

[0039] Figure 1 Here is a SEM image of the composite structure coating on the surface of the cutting tool in Example 1; Figure 2 This is an XPS image of the composite structure coating on the surface of the cutting tool in Example 1. Detailed Implementation

[0040] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0041] Example 1 This embodiment prepares a composite structure coating on the surface of a cutting tool, and the steps are as follows: S11. The WC-Co cemented carbide substrate is polished with water-jet sandpaper to reduce the roughness to below 0.05μm. Then, the smooth surface is sandblasted with Al2O3 abrasive (pressure 0.3MPa) to achieve controllable roughening. Finally, it is ultrasonically cleaned with acetone and ethanol for 15min each, and then vacuum dried at 120℃ for 30min to obtain the pretreated substrate. S12. The pretreated substrate is placed into the deposition chamber, with a spacing of 40 mm between it and the target. The deposition chamber is then evacuated to a vacuum level of 2.4 × 10⁻⁶.-3 Pa, heating to 400℃, holding at that temperature for 40 minutes; S13. Introduce Ar at a flow rate of 100 sccm, adjust the substrate bias voltage to -800V, and perform argon ion etching for 30 min. Then turn on the Cr target power supply, adjust the target current to 100A, and the substrate bias voltage to -500V to perform chromium metal ion etching for 5 min. S21. Introduce N2, adjust the Ar introduce flow rate to make the N2 to Ar partial pressure ratio 3:1, the total flow rate 400 sccm, adjust the Cr target current to 130 A, the substrate bias voltage to -130 V, deposit for 15 min, and obtain a 0.3 μm thick CrN transition layer. S31. Maintain the partial pressure ratio of N2 to Ar at 3:1, adjust the total flow rate to 450 sccm, and the substrate bias voltage to -150 V. Turn on the Zr target, Al target, and Cr target, and deposit for 30 min. During the 30 min, the Zr target current is maintained at 150 A, the Al target current is increased from 120 A to 200 A, and the Cr target current is decreased from 150 A to 80 A. After the deposition is completed, turn off the target power supply and gas source to obtain a 0.6 μm thick AlCrZrN gradient layer. S41. Control the vacuum degree of the chamber to 3 Pa and the substrate temperature to 400℃. Introduce dry air to perform air oxygen permeation treatment on the surface of the AlCrZrN gradient layer. The initial flow rate is 50 sccm. Then, heat the substrate to gradually increase the temperature to 500℃, and simultaneously increase the air flow rate at a ratio of 50 sccm / 100℃. After the heating is completed, keep the temperature for 20 min. After the treatment is completed, stop the air supply, maintain the vacuum environment and cool to room temperature at a rate of 5℃ / min to form an oxide film layer.

[0042] Figure 1 Here is a SEM image of the composite structure coating on the surface of the cutting tool in Example 1. Figure 1 It can be seen that the outermost layer (oxide film layer) of the composite structure coating has a dense structure and fewer defects.

[0043] Figure 2 This is an XPS image of the composite structure coating on the surface of the cutting tool in Example 1. Figure 2 It is known that the outermost layer (oxide film layer) of the composite structure coating does indeed contain four core elements: Al, Cr, Zr, and O, with Al mainly present in the form of Al. 3+ The presence of this state, corresponding to Al₂O₃, proves that the Al element has been fully oxidized, forming the target phase that provides high hardness; Cr mainly exists as Cr₂O₃. 3+The presence of the Cr2O3 state indicates that the Cr element forms a dense and stable Cr2O3, which helps to improve the coating's oxidation and corrosion resistance. The Zr element is oxidized to ZrO2, which is beneficial to improving the coating's toughness. In other words, this invention successfully generated a dense Al2O3-Cr2O3-ZrO2 oxide film layer in situ on the surface of the AlCrZrN gradient layer through air oxygen permeation post-treatment.

[0044] Example 2 This embodiment prepares a composite structure coating on the surface of a cutting tool, and the steps are as follows: S11. The WC-Co cemented carbide substrate is polished with water-jet sandpaper to reduce the roughness to below 0.05μm. Then, the smooth surface is sandblasted with Al2O3 abrasive (pressure 0.3MPa) to achieve controllable roughening. Finally, it is ultrasonically cleaned with acetone and ethanol for 15min each, and then vacuum dried at 120℃ for 30min to obtain the pretreated substrate. S12. The pretreated substrate is loaded into the deposition chamber, with a spacing of 40 mm between it and the target. The deposition chamber is then evacuated to a vacuum level of 2.4 × 10⁻⁶. -3 Pa, heating to 400℃, holding at that temperature for 40 minutes; S13. Introduce Ar at a flow rate of 100 sccm, adjust the substrate bias voltage to -800V, and perform argon ion etching for 30 min. Then turn on the Cr target power supply, adjust the target current to 100A, and the substrate bias voltage to -500V to perform chromium metal ion etching for 5 min. S21. Introduce N2, adjust the Ar introduce flow rate to make the N2 to Ar partial pressure ratio 3:1, the total flow rate 400 sccm, adjust the Cr target current to 130 A, the substrate bias voltage to -130 V, deposit for 15 min, and obtain a 0.3 μm thick CrN transition layer. S31. Maintain the partial pressure ratio of N2 to Ar at 3:1, adjust the total flow rate to 450 sccm, and the substrate bias voltage to -150 V. Turn on the Zr target, Al target, and Cr target, and deposit for 30 min. During the 30 min, the Zr target current is maintained at 150 A, the Al target current is increased from 120 A to 200 A, and the Cr target current is decreased from 150 A to 80 A. After the deposition is completed, turn off the target power supply and gas source to obtain a 0.6 μm thick AlCrZrN gradient layer. S41. Control the vacuum degree of the chamber to 3 Pa and the substrate temperature to 400℃. Introduce dry air to perform air oxygen permeation post-treatment on the surface of the AlCrZrN gradient layer. The initial flow rate is 50 sccm. Then, heat the substrate to rapidly increase the temperature to 600℃, and simultaneously increase the air flow rate at a ratio of 50 sccm / 100℃. After the heating is completed, keep the temperature for 15 min. After the treatment is completed, stop the air supply, maintain the vacuum environment and cool to room temperature at a rate of 5℃ / min to form a dense oxide film layer.

[0045] Example 3 This embodiment prepares a composite structure coating on the surface of a cutting tool, and the steps are as follows: S11. The WC-Co cemented carbide substrate is polished with water-jet sandpaper to reduce the roughness to below 0.05μm. Then, the smooth surface is sandblasted with Al2O3 abrasive (pressure 0.3MPa) to achieve controllable roughening. Finally, it is ultrasonically cleaned with acetone and ethanol for 15min each, and then vacuum dried at 120℃ for 30min to obtain the pretreated substrate. S12. The pretreated substrate is loaded into the deposition chamber, with a spacing of 40 mm between it and the target. The deposition chamber is then evacuated to a vacuum level of 2.4 × 10⁻⁶. -3 Pa, heating to 400℃, holding at that temperature for 40 minutes; S13. Introduce Ar at a flow rate of 100 sccm, adjust the substrate bias voltage to -800V, and perform argon ion etching for 30 min. Then turn on the Cr target power supply, adjust the target current to 100A, and the substrate bias voltage to -500V to perform chromium metal ion etching for 5 min. S21. Introduce N2, adjust the Ar introduce flow rate to make the N2 to Ar partial pressure ratio 3:1, the total flow rate 400 sccm, adjust the Cr target current to 130 A, the substrate bias voltage to -130 V, deposit for 15 min, and obtain a 0.3 μm thick CrN transition layer. S31. Maintain the partial pressure ratio of N2 to Ar at 3:1, adjust the total flow rate to 450 sccm, and the substrate bias voltage to -150 V. Turn on the Zr target, Al target, and Cr target, and deposit for 30 min. During the 30 min, the Zr target current is maintained at 150 A, the Al target current is increased from 120 A to 200 A, and the Cr target current is decreased from 150 A to 80 A. After the deposition is completed, turn off the target power supply and gas source to obtain a 0.6 μm thick AlCrZrN gradient layer. S41. Control the vacuum degree of the chamber to 2 Pa and the substrate temperature to 400℃. Introduce dry air to perform air oxygen permeation post-treatment on the surface of the AlCrZrN gradient layer. The initial flow rate is 50 sccm. Then, heat the substrate to slowly increase the temperature to 420℃, and simultaneously increase the air flow rate at a ratio of 50 sccm / 100℃. After the heating is completed, hold the temperature for 40 min. After the treatment is completed, stop the air supply, maintain the vacuum environment and cool to room temperature at a rate of 5℃ / min to generate an extremely fine and dense oxide film with a grain size of about 9-11 nm.

[0046] Comparative Example 1 This comparative example demonstrates the preparation of a composite structure coating on the surface of a cutting tool, using the following steps: S11. The WC-Co cemented carbide substrate is polished with water-jet sandpaper to reduce the roughness to below 0.05μm. Then, the smooth surface is sandblasted with Al2O3 abrasive (pressure 0.3MPa) to achieve controllable roughening. Finally, it is ultrasonically cleaned with acetone and ethanol for 15min each, and then vacuum dried at 120℃ for 30min to obtain the pretreated substrate. S12. The pretreated substrate is loaded into the deposition chamber, with a spacing of 40 mm between it and the target. The deposition chamber is then evacuated to a vacuum level of 2.4 × 10⁻⁶. -3 Pa, heating to 400℃, holding at that temperature for 40 minutes; S13. Introduce Ar at a flow rate of 100 sccm, adjust the substrate bias voltage to -800V, and perform argon ion etching for 30 min. Then turn on the Cr target power supply, adjust the target current to 100A, and the substrate bias voltage to -500V to perform chromium metal ion etching for 5 min. S21. Introduce N2, adjust the Ar introduce flow rate to make the N2 to Ar partial pressure ratio 3:1, the total flow rate 400 sccm, adjust the Cr target current to 130 A, the substrate bias voltage to -130 V, deposit for 15 min, and obtain a 0.3 μm thick CrN transition layer. S31. Maintain the partial pressure ratio of N2 to Ar at 3:1, adjust the total flow rate to 450 sccm, and the substrate bias voltage to -150 V. Turn on the Zr target, Al target, and Cr target, and deposit for 30 min. During the 30 min, the Zr target current is maintained at 150 A, the Al target current is increased from 120 A to 200 A, and the Cr target current is decreased from 150 A to 80 A. After the deposition is completed, turn off the target power supply and gas source to obtain a 0.6 μm thick AlCrZrN gradient layer. S41. Control the vacuum degree of the chamber to 3 Pa and the substrate temperature to 400℃. Introduce pure oxygen to perform air oxygen permeation treatment on the surface of the AlCrZrN gradient layer. The initial flow rate is 25 sccm. Then, heat the substrate to gradually increase the temperature to 500℃, and simultaneously increase the oxygen flow rate at a ratio of 25 sccm / 100℃. After the heating is completed, hold the temperature for 20 minutes. After the treatment is completed, stop the oxygen supply and maintain the vacuum environment to cool to room temperature with the furnace to form an oxide film layer with coarse oxide grains and microcracks in local areas.

[0047] Performance testing The performance of the composite coatings in Examples 1-3 and Comparative Example 1 was tested. The test items and reference standards are as follows: 1. Adhesion strength: Tested according to ASTM C1624-22, "Standard Test Method for Determining the Adhesion Strength and Mechanical Failure Mode of Ceramic Coatings by Single-Point Scratch Test with Quantitative Quantity"; 2. Coating hardness: Tested according to ISO 14577-1:2015 "Metallic materials - Instrumental indentation test for hardness and material parameters - Part 1: Test methods"; 3. Wear resistance: The wear on the tool surface after high-speed milling of titanium alloy Ti-6Al-4V for 250 minutes was tested according to ISO 3685:1993 "Tool life test using single-point turning tools". 4. High-temperature oxidation resistance: The coated sample was placed in an atmospheric environment and subjected to a static oxidation test at 600℃ for 150 minutes. After the oxidation was completed, the sample was made into a cross section, and the thickness of the surface oxide layer was observed and measured using a scanning electron microscope.

[0048] Table 1 Performance test results of the composite structure coatings in Examples 1-3 and Comparative Example 1

[0049] Table 1 shows the performance test results of the composite structure coatings in Examples 1-3 and Comparative Example 1. As can be seen from Table 1, the composite structure coatings in Examples 1-3 are significantly better than those in Comparative Example 1 in all core indicators such as adhesion, hardness, wear resistance, and high-temperature oxidation resistance. This is because Comparative Example 1 uses pure oxygen for post-treatment, and the high partial pressure of pure oxygen leads to a violent and uneven oxidation reaction, resulting in coarse oxide layer grains and microcracks, which seriously damages the density, bonding strength, and overall toughness of the coating. In contrast, the present invention uses an air oxygen permeation post-treatment method. By synergistically controlling the treatment temperature and gas flow rate parameters, a composite coating with uniform structure and coordinated performance can be obtained under relatively mild and controllable oxidation conditions. Example 1, based on a medium-temperature, medium-flow rate (500℃, 100 sccm) parameter setting, achieved the highest hardness (42 GPa) while maintaining excellent bonding strength and wear resistance. It exhibited a good balance between hardness and toughness, making it suitable for most high-speed finish milling and continuous turning operations. Example 2, based on a high-temperature, high-flow rate (600℃, 150 sccm) parameter setting, achieved the highest bonding strength (76 N) and optimal cutting wear resistance (0.030 mm), indicating that higher temperature conditions are beneficial for interfacial diffusion and metallurgical bonding, but are also accompanied by oxygen... The increased oxidation rate resulted in a relatively thick oxide layer (0.48 μm) with a slight decrease in hardness. This type of coating is suitable for heavy-duty, intermittent cutting, and high-impact machining scenarios. Example 3, based on low-temperature, low-flow-rate (420°C, 60 sccm) parameter settings, exhibited the best oxidation resistance, with the thinnest oxide layer (0.28 μm), demonstrating superior oxidation stability. This proves that a mild reaction can reduce coating stress and inhibit excessive oxidation, making it suitable for ultra-high-speed cutting, conditions extremely sensitive to oxidative wear, or for processing materials with higher chemical reactivity. Compared to pure oxygen post-treatment, the coating obtained by air oxygen infiltration post-treatment has better overall performance, easier process control, and lower cost.

Claims

1. A composite structure coating for the surface of a cutting tool, characterized in that, It includes a CrN transition layer, an AlCrZrN gradient layer, and an oxide film layer sequentially deposited on the surface of the tool substrate; wherein, the aluminum content and chromium content of the AlCrZrN gradient layer change in a continuous gradient along the thickness direction; the oxide film layer is mainly composed of Al2O3, Cr2O3 and ZrO2, and the oxygen content decreases from the outside to the inside of the oxide film layer surface.

2. The composite structure coating according to claim 1, characterized in that, The elemental composition of the oxide film layer conforms to (Al) 0.4 Cr 0.1 Zr 0.5 )O x Where x is the ratio of oxygen atoms to the total number of aluminum, chromium, and zirconium atoms, x = 1.5-2.

0.

3. The composite structure coating according to claim 1, characterized in that, The aluminum content of the AlCrZrN gradient layer increases in the thickness direction, while the chromium content decreases in the thickness direction.

4. The composite structure coating according to claim 3, characterized in that, The elemental composition of the AlCrZrN gradient layer conforms to (Al y Cr z Zr 1-y-z )N, where y and z are atomic fractions, y = 0.2-0.4, z = 0.1-0.

3.

5. The composite structure coating according to any one of claims 1-4, characterized in that, The thickness of the CrN transition layer is 0.2-0.4 μm; And / or, the thickness of the AlCrZrN gradient layer is 0.5-0.8 μm; And / or, the thickness of the oxide film is 0.3-0.5 μm.

6. The method for preparing the composite structure coating on the surface of the cutting tool according to any one of claims 1-5, characterized in that, Includes the following steps: S1. The tool substrate is sequentially etched with argon ions and then with chromium metal ions. S2. Turn on the Cr target and use arc ion plating to deposit a CrN transition layer on the surface of the etched tool substrate. S3. Simultaneously turn on the Zr target, Al target and Cr target, and continuously adjust the target current respectively, and deposit an AlCrZrN gradient layer on the surface of the CrN transition layer by arc ion plating. S4. Perform air oxygen permeation treatment on the surface of the AlCrZrN gradient layer to form an oxide film layer in situ, thereby obtaining the composite structure coating on the surface of the cutting tool.

7. The preparation method according to claim 6, characterized in that, In step S2, the process parameters for depositing the CrN transition layer include: Cr target current of 130-150A; substrate bias voltage of -120V to -150V; N2 to Ar partial pressure ratio of (1.5-4):1; total flow rate of 300-400sccm; and deposition time of 10-15min.

8. The preparation method according to claim 6, characterized in that, In step S3, the process parameters for depositing the AlCrZrN gradient layer include: substrate bias voltage of -140V to -160V; N2 to Ar partial pressure ratio of (2.5-9):1; total flow rate of 400-450 sccm; deposition time of 25-35 min; during the deposition time, the Zr target current is maintained at 140-160A, the Al target current increases from 120A to 200A, and the Cr target current decreases from 150A to 80A.

9. The preparation method according to claim 6, characterized in that, In step S4, the post-oxygenation treatment specifically includes: introducing air under a vacuum of 1-5 Pa to programmatically raise the temperature of the tool substrate from 400-500℃ to 420-600℃, while simultaneously increasing the air flow rate at a ratio of 25-50 sccm / 100℃, controlling the total air flow rate to 50-150 sccm, holding the temperature for 10-30 minutes after the heating is completed, turning off the air source after the heating is completed, maintaining the vacuum environment and cooling at a rate of 3-6℃ / min.

10. A cutting tool, characterized in that, It includes a tool substrate and a composite structure coating of any one of claims 1-5 deposited on the surface of the tool substrate.

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