A method for preparing a crystalline alumina coating

Abstract

The application relates to the technical field of coating preparation, and discloses a preparation method of a crystalline alumina coating. In the preparation process of the crystalline alumina coating, a pretreated base body is placed in a vacuum environment, and the base body is heated to a first preset temperature under preset vacuum conditions; the base body is etched by using a medium-frequency power supply; target sputtering cleaning is carried out after etching; and the alumina coating is deposited by using a high-power pulsed magnetron sputtering technology; a specially set synchronous high-power pulsed magnetron sputtering power supply provides a bias for the base body, so that the crystallinity, compactness of the coating and the bonding force between the coating and the base body are improved; the application ingeniously sets a segmented energy providing process based on the magnetron sputtering technology, overcomes the technical prejudice that a large amount of energy can be provided only at high temperature, breaks through the technical difficulty that the existing magnetron sputtering technology cannot prepare the crystalline alumina coating at low temperature, and provides a new idea for stably preparing the crystalline Al2O3 coating at low temperature by using the magnetron sputtering technology.

Description

Technical Field

[0001] This invention relates to the field of crystalline ceramic coating materials technology, and specifically to a method for preparing a crystalline alumina coating. Background Technology

[0002] Alumina (Al2O3) coatings have been widely used in optics, reactor corrosion protection, high-temperature protection, and electronic insulation due to their excellent wear resistance, high-temperature oxidation resistance, corrosion resistance, transparency, and insulation properties, especially in the fields of cutting tools, optoelectronics, shipbuilding, fine ceramics, and composite materials.

[0003] Al2O3 coatings are divided into crystalline and amorphous structures. Compared with amorphous structures, although crystalline alumina coatings have better performance, the preparation technology is more demanding. In particular, higher energy is required during the coating growth process to crystallize, thus ensuring good performance and making the preparation more difficult.

[0004] Currently, the conventional method for preparing crystalline Al2O3 coatings is to heat the substrate to a very high temperature (1000℃) using chemical vapor deposition technology. This high temperature provides high energy for coating growth. However, this method faces the problem that the choice of substrate material for preparing crystalline Al2O3 coatings is greatly affected at such high temperatures, which limits the application range of crystalline Al2O3 coatings. Summary of the Invention

[0005] The present invention aims to provide a method for preparing crystalline alumina coatings to solve the technical problem of high temperature limiting the selection of substrate materials in the existing chemical vapor deposition technology for preparing crystalline Al2O3 coatings.

[0006] The basic invention provided by this invention is: a method for preparing a crystalline alumina coating, the method comprising the following steps:

[0007] S10: Matrix pretreatment;

[0008] S20: Preparation of crystalline alumina coating, including the following steps.

[0009] S201, the pretreated substrate is placed in a preset position in the chamber, and the substrate is heated to a first preset temperature under preset vacuum conditions;

[0010] S202 uses a medium-frequency power supply to etch the substrate;

[0011] S203, after the substrate etching is completed, the cathode power supply uses a DC power supply to sputter clean the target surface;

[0012] S204 employs high-power pulsed magnetron sputtering technology to deposit an alumina coating: sputtering gas and reactive gas are introduced, and the introduction rate of the reactive gas is controlled; simultaneously, a high-power pulsed magnetron sputtering power supply is used for the cathode power supply to sputter an aluminum target, and a synchronous high-power pulsed magnetron sputtering power supply set independently of the cathode power supply provides a high bias voltage to the substrate; after a preset coating growth time, a crystalline alumina coating is deposited.

[0013] Definition: High bias voltage refers to a bias voltage of -500 to -1000V.

[0014] Furthermore, in S201, the substrate is heated to a first preset temperature and maintained at the first preset temperature until the crystalline alumina coating is completed. The first preset temperature is 500-600°C.

[0015] Furthermore, in S201, the method for heating the substrate to a first preset temperature under preset vacuum conditions is to evacuate the chamber until the vacuum level drops to ≤3×10⁻⁶. -3 After Pa, the substrate is heated to the first preset temperature, and then vacuum is continued until the vacuum level drops to ≤2×10. -3 Pa.

[0016] Furthermore, in the S202 etching process, an etching gas with a preset flow rate is introduced; in the S203 sputter cleaning of the target surface, the etching gas is used as the sputtering gas, and the introduced flow rate is greater than the preset flow rate.

[0017] Furthermore, during the S202 etching process, the aluminum target baffle was opened, the voltage of the intermediate frequency power supply was set to 650V, and the frequency was set to 240kHz; argon was used as the etching gas, with an argon gas pressure of 180-250mPa; the etching time was 5-10min; and the sample stage rotation speed was 3-5r / min.

[0018] Furthermore, during the sputtering cleaning of the target surface by S203, the aluminum target baffle is closed, the power of the cathode power supply is 5000-8000W, a hollow cathode tube is used during the argon gas introduction process, the total argon gas flow rate is 500-700sccm, and the argon gas flow rate introduced from the hollow cathode tube is 550-600sccm; the target cleaning time is 2-10min.

[0019] Furthermore, in S204, the sputtering gas is krypton and the reaction gas is oxygen; when introduced, the oxygen partial pressure is 347-351 mPa and the krypton flow rate is 240-360 sccm.

[0020] Furthermore, in S204, the bias voltage provided by the synchronous high-power pulsed magnetron sputtering power supply is -500 to -1000V, and the pulse width is 60 to 80μs; ​​the power of the cathode power supply is 4000 to 6000W, the pulse width is 50μs, and the frequency is 1000 to 2500Hz; the sample stage rotation speed is 3 to 5 r / min.

[0021] Furthermore, in S10, the pretreatment includes ultrasonic cleaning, in which the substrate is sequentially immersed in deionized water and anhydrous ethanol for ultrasonic cleaning, with a cleaning time of 15 to 30 minutes.

[0022] Furthermore, the method also includes: S30, after the crystalline alumina coating is prepared, it is cooled to a second preset temperature and then removed from the furnace, the second preset temperature being 50-180°C.

[0023] The working principle and advantages of this invention are as follows: First, the substrate is pretreated; then, crystalline alumina is prepared. The pretreated substrate is placed on a workpiece holder in a chamber and heated to a first preset temperature under preset vacuum conditions. Then, the substrate is etched using a medium-frequency power supply, and the aluminum target is sputtered and cleaned after etching. Finally, an alumina coating is deposited using high-power pulsed magnetron sputtering technology. During the deposition process, sputtering gas and reactive gas are introduced, and the introduction rate of the reactive gas is controlled. At the same time, a high-power pulsed magnetron sputtering power supply is used to sputter the aluminum target, and a synchronous high-power pulsed magnetron sputtering power supply is used as a bias power supply to provide bias voltage to the substrate. After a preset coating growth time, a crystalline alumina coating is deposited.

[0024] In existing technologies, there are many methods for preparing alumina coatings, employing different equipment and preparation conditions. Commonly used techniques include chemical vapor deposition (CVD) and physical vapor deposition (PVD). Compared to CVD, which requires heating the substrate material to 1000°C, PVD sputtering can deposit alumina within a temperature range of 350–600°C, greatly expanding the application range of alumina. The lower deposition temperature also allows it to be coated on other materials such as high-speed steel and mold steel.

[0025] Physical vapor deposition (PVD) sputtering can solve the substrate material selection problem. However, conventional magnetron sputtering at low temperatures (below the 1000°C required for chemical vapor deposition) produces amorphous alumina. Preparing crystalline alumina coatings under these conditions is extremely difficult because crystalline Al2O3 coatings require high energy to form, and Al2O3 has a high dielectric constant. During preparation, the DC power supply used in magnetron sputtering cannot be used to provide the bias voltage to increase the energy of ion bombardment of the substrate, preventing the coating from crystallizing. Furthermore, when preparing Al2O3 coatings using magnetron sputtering, aluminum ions accumulated on the aluminum target surface react with oxygen to form Al2O3, which is deposited on the target surface. This leads to charge accumulation on the target surface, causing arcing and making the deposition process unstable.

[0026] This invention, based on magnetron sputtering technology, ingeniously sets up a segmented energy supply process, overcoming the technical bias that high temperatures are required to provide large amounts of energy. It also breaks through the technical difficulties of preparing crystalline alumina coatings at low temperatures using existing magnetron sputtering techniques, providing a new approach for the stable preparation of crystalline Al2O3 coatings under low-temperature conditions using magnetron sputtering. By selecting a substrate material that can be heated to 500–600°C and specifically using a synchronous high-power pulsed magnetron sputtering power supply independent of the existing cathode power supply for magnetron sputtering, a bias voltage is provided to the substrate during the coating deposition period. It was found that providing sustained high energy at critical moments of coating growth and structural changes improves the crystallinity, density, and adhesion between the coating and the substrate, promoting the formation of the crystalline structure of the Al2O3 coating. Simultaneously, the independence and synchronization of the synchronous high-power pulsed magnetron sputtering power supply and the cathode power supply enable selective acceleration of target ions, providing high energy more effectively. Tests have shown that controlling the rate of gas introduction during coating deposition can effectively slow down the poisoning rate of the aluminum target, prevent the target from arcing, ensure the stability of the coating deposition process, make the coating composition more uniform, and improve the repeatability of the experiment.

[0027] The crystalline alumina coating prepared by this invention exhibits a phase structure of a mixed phase of κ-Al2O3 and γ-Al2O3, with a nano-hardness value of 20-24.5 GPa. Compared with other amorphous alumina coatings, it has higher hardness and density. This coating can be alternately grown with other nitride ceramic coatings to form a composite coating that is applied to the tool surface for high-speed cutting and dry cutting of high-temperature alloy materials, thereby improving the tool's service life. Attached Figure Description

[0028] Figure 1 A flowchart illustrating a method for preparing a crystalline alumina coating according to an embodiment of the present invention;

[0029] Figure 2 The XRD pattern of the crystalline alumina coating provided in the embodiments of the present invention;

[0030] Figure 3 The XRD pattern of the crystalline alumina coating provided in the comparative embodiment of the present invention;

[0031] Figure 4 The fracture morphology diagram of the crystalline alumina coating provided in the embodiment of the present invention is shown.

[0032] Figure 5 This is a nanohardness diagram of the crystalline alumina coating provided in an embodiment of the present invention. Detailed Implementation

[0033] The following detailed explanation illustrates the specific implementation methods:

[0034] As attached Figure 1 As shown: This invention provides a method for preparing a crystalline alumina coating, the method comprising the following steps:

[0035] S10: Matrix pretreatment.

[0036] In the preparation method provided by the present invention, in S10, the substrate pretreatment includes substrate polishing, cleaning and drying. First, the substrate is polished by a polishing machine; then, sandblasting is performed to remove burrs from the substrate surface; next, the substrate is placed in deionized water and anhydrous ethanol for ultrasonic cleaning for 15 to 30 minutes, preferably 15 minutes, 20 minutes, 25 minutes or 30 minutes; finally, the substrate is dried by compressed air and placed on a workpiece holder; the whole process completes the substrate pretreatment, providing a good base material for the subsequent formation of crystalline alumina coating. The substrate can be a (100)-sided single-sided polished silicon wafer with a size of 20 mm × 20 mm × 0.5 mm. The target material used for sputtering is an aluminum target with a purity greater than 99%, but this is not limited.

[0037] S20: Preparation of crystalline alumina coating.

[0038] In the preparation method provided by the present invention, S20 includes the following steps:

[0039] S201, the pretreated substrate is placed in a preset position in the chamber, and the substrate is heated to a first preset temperature under preset vacuum conditions.

[0040] Specifically, the pretreated substrate is placed on the pre-set position of the chamber workpiece holder, the chamber door is closed, and the chamber is evacuated. When the vacuum level drops to ≤3×10 -3 After Pa, the substrate is heated to the first preset temperature, and then vacuum is continued until the vacuum level drops to ≤2×10. -3By performing a segmented vacuum reduction before and after substrate heating, the vacuum level inside the chamber can reach the preset value more quickly, avoiding the influence of impurity gases on the coating structure and performance during the deposition process. The substrate is heated to a first preset temperature and maintained at the first preset temperature until the crystalline alumina coating is prepared. The first preset temperature is 500-600℃, preferably 500℃, 550℃, or 600℃. Compared with chemical vapor deposition, this temperature range reduces the limitations on substrate materials and expands the application range of crystalline alumina.

[0041] The substrate can be heated by heating wires. The heating source consists of two sets of heating wires, one in front and one in back. The power can be set to 9000W and 14000W respectively when heating the substrate. After the substrate temperature reaches the first preset temperature, the power of the front and back heating sources is automatically adjusted to ensure the substrate temperature is stable.

[0042] S202 uses a medium-frequency power supply to etch the substrate.

[0043] Specifically, a medium-frequency power supply is used to perform glow discharge etching on the substrate by introducing an etching gas at a preset flow rate. During the etching process, the aluminum target baffle is opened to achieve glow extraction and enhance the etching effect. The voltage of the medium-frequency power supply is set to 650V and the frequency to 240kHz. Argon is used as the etching gas, and the argon flow rate is 180-250mPa, preferably 180mPa, 200mPa, 230mPa, or 250mPa. This is preferred because the argon flow rate depends on the substrate surface quality. This is to improve the coating adhesion and performance while avoiding excessive argon residue on the substrate surface, which would increase the residual stress of the coating. The etching time is 5-10min, preferably 5min or 10min. This etching time is also preferred to avoid the influence of the substrate on the coating performance. The sample stage rotation speed is 3-5r / min, preferably 3r / min, 4r / min, or 5r / min. In this process, the preferred sample stage rotation speed is mainly to ensure the uniformity of substrate heating.

[0044] S203, after the substrate etching is completed, the cathode power supply uses a DC power supply to sputter clean the target surface.

[0045] Specifically, after etching, the aluminum target baffle is closed, and the etching gas is used as the sputtering gas with a flow rate greater than the preset flow rate. The cathode power supply is then turned on, and a DC power supply is used to sputter and clean the aluminum target. The power of the cathode power supply is 5000–8000W, preferably 5000W, 6000W, 7000W, or 8000W. A hollow cathode tube is used during the argon gas introduction process, and the total argon gas flow rate is 500–700 sccm, preferably 500 sccm, 55 sccm, 600 sccm, 650 sccm, or 700 sccm. The argon gas flow rate introduced into the cathode tube is 550-600 sccm, preferably 550 sccm, 560 sccm, 570 sccm, 580 sccm, 590 sccm or 600 sccm; the target cleaning time is 2-10 min, preferably 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min. The selection of the above process parameters depends on the degree of target poisoning. Intentionally increasing the target cleaning power and cleaning time will cause unnecessary waste of target material.

[0046] S204, using high-power pulsed magnetron sputtering technology to deposit an alumina coating: a sputtering gas and a reactant gas are introduced, wherein the sputtering gas is krypton and the reactant gas is oxygen, and the introduction rate of the reactant gas is controlled. During introduction, the partial pressure of oxygen is 347-351 mPa, specifically selectable as 347 mPa, 348 mPa, 349 mPa, 350 mPa or 351 mPa; the krypton flow rate is 240-360 sccm, specifically selectable as 240 sccm, 280 sccm, 320 sccm or 360 sccm.

[0047] After testing, based on the high bias voltage range and substrate material heating temperature range set in this invention, this invention controls the oxygen injection rate during the coating deposition process through an oxygen pressure feedback controller in the magnetron sputtering equipment. From the results of the target peak current and the number of times the equipment arcs, it was found that within the above-mentioned oxygen partial pressure range, the poisoning rate of the aluminum target during the deposition process can be effectively slowed down, the "arc" phenomenon of the target material can be avoided, the stability of the coating deposition process can be ensured, the coating composition can be more uniform, and the repeatability of the experiment can be higher.

[0048] While introducing sputtering and reactive gases, a high-power pulsed magnetron sputtering power supply is used for sputtering an aluminum target at the cathode. A synchronous high-power pulsed magnetron sputtering power supply, independently set up from the cathode power supply, provides a high bias voltage to the substrate, ranging from -500 to -1000V, specifically selectable as -500V, -600V, -700V, -800V, -900V, or -1000V. The substrate pulse bias pulse width is 60–80μs, specifically selectable as 60μs, 70μs, or 80μs. The cathode power supply power is 4000–6000W, specifically selectable as 4000W, 4500W, 5000W, 5500W, or 6000W. The cathode power supply pulse width is 50μs. The cathode power supply frequency is 1000–2500Hz, specifically selectable as 1000Hz, 1500Hz, 2000Hz, or 2500Hz. The sample stage rotation speed during the deposition process is 3-5 r / min, preferably 3 r / min, 4 r / min or 5 r / min. The uniformity of the coating is controlled by the sample stage rotation speed. Under this preferred rotation speed control, the coating uniformity meets the usage conditions. The coating growth time is 40-120 min, preferably 40 min, 60 min, 80 min, 100 min or 120 min. The coating deposition time is optimized according to the cathode frequency and oxygen flow rate settings to ensure stable coating deposition before the target is severely poisoned.

[0049] Tests revealed that increasing the bias voltage altered the crystallinity of the coating, further confirming the benefits of the high bias voltage in this invention. This demonstrates that the high bias voltage provides energy for coating growth, leading to the formation of a crystalline coating. Furthermore, the test results show that a satisfactory crystalline alumina coating can be deposited after a suitable preset coating growth time.

[0050] S30, after the crystalline alumina coating is prepared, it is cooled to a second preset temperature and then removed from the furnace. The second preset temperature is 50 to 180°C.

[0051] For clarity, the following embodiments will be described in detail. S10 and S30 are basically the same as those described above, and will not be repeated in the embodiments. Each embodiment will focus on describing the content of S20 in detail.

[0052] Example 1

[0053] A method for preparing a crystalline alumina coating, S20: Preparation of a crystalline alumina coating includes the following steps:

[0054] The pretreated substrate is fixed on a special workpiece holder and sent into the coating chamber. The chamber door is closed, and a vacuum is drawn until the vacuum level reaches 3×10⁻⁶. -3Heating begins after Pa, with the heating temperature set at 550℃. After reaching the set temperature, vacuuming must continue for ≤2×10⁻⁶ seconds. -3 Pa, followed by glow discharge etching of the substrate using high-purity argon gas for 10 min, and finally deposition of an alumina coating. During the deposition process, the high-power pulsed magnetron sputtering power supply for the sputtering aluminum target was 4000 W with a pulse width of 50 μs and a frequency of 1000 Hz; a synchronous high-power pulsed magnetron sputtering power supply was used to provide a bias voltage to the substrate at -600 V with a pulse width of 60 μs; at the same time, the oxygen partial pressure was controlled at 349.5 mPa, the krypton flow rate at 360 sccm, the stage rotation speed at 3 r / min, and the coating growth time at 120 min.

[0055] like Figure 2 As shown in Example 1, the phase structure of the alumina coating is a mixed phase of κ-Al₂O₃ and γ-Al₂O₃, which meets the requirements for the crystalline properties of commonly used coatings. Furthermore, under these preparation process parameters, the alumina coating thickness is 1.2 μm, and the atomic percentages of oxygen and aluminum in the coating are close to the stoichiometric ratio. Figure 5 As shown in Example 1, the nanohardness of the alumina coating prepared in this example is 19.7 ± 1.2 GPa.

[0056] The above coating data demonstrates that a high-performance crystalline alumina coating was prepared using this invention. The substrate heating temperature was also reduced from 1000℃ required by conventional chemical vapor deposition technology to 550℃ in this embodiment of the invention. Based on this, the range of substrate materials that can be selected was expanded, verifying the feasibility of the new approach of preparing crystalline alumina coatings at low temperatures using magnetron sputtering technology.

[0057] Example 2

[0058] The pretreated substrate is fixed on a special workpiece holder and sent into the coating chamber. The chamber door is closed, and a vacuum is drawn until the vacuum level reaches 3×10⁻⁶. -3 Heating begins after Pa, with the heating temperature set at 600℃. After reaching the set temperature, vacuuming must continue for ≤2×10⁻⁶ seconds. -3 Pa, then high-purity argon gas was introduced to perform glow discharge etching on the substrate for 5 min. Finally, an alumina coating was deposited. During the deposition process, the cathode power was 4000 W, the pulse width was 50 μs, and the frequency was 1000 Hz. A synchronous high-power pulsed magnetron sputtering power supply was used for discharge, with a bias voltage of -700 V and a pulse width of 60 μs. At the same time, the oxygen partial pressure was controlled at 348 mPa, the krypton flow rate was 360 sccm, the sample stage rotation speed was 3 r / min, and the coating growth time was 120 min.

[0059] like Figure 2As shown in Example 2, the phase structure of the alumina coating is a mixed phase of κ-Al2O3 and γ-Al2O3. Figure 4 (a) shows the cross-sectional morphology of the coating in this embodiment. As can be seen from the figure, the coating structure is dense and has a clear boundary with the substrate, making it easy to distinguish. Figure 5 As shown in Example 2, the nanohardness of the alumina coating prepared in this example is 20.2 ± 1.8 GPa.

[0060] Compared with Example 1, the heating temperature was increased by 50°C and the bias voltage was increased by 100V. The resulting coating still has good crystalline structure properties and is harder than the coating generated in Example 1, indicating that the range of substrate material selection and bias voltage setting can be further expanded.

[0061] Example 3

[0062] The pretreated substrate is fixed on a special workpiece holder and sent into the coating chamber. The chamber door is closed, and a vacuum is drawn until the vacuum level reaches 3×10⁻⁶. -3 Heating begins after Pa, with the heating temperature set at 600℃. After reaching the set temperature, vacuuming must continue for ≤2×10⁻⁶ seconds. -3 Pa, then high-purity argon gas was introduced to perform glow discharge etching on the substrate for 8 min. Finally, an alumina coating was deposited. During the deposition process, the cathode power was 4000 W, the pulse width was 50 μs, and the frequency was 1000 Hz. A synchronous high-power pulsed magnetron sputtering power supply was used for discharge, with a bias voltage of -800 V and a pulse width of 60 μs. At the same time, the oxygen partial pressure was controlled at 350 mPa, the krypton flow rate was 360 sccm, the sample stage rotation speed was 3 r / min, and the coating growth time was 120 min.

[0063] like Figure 2 As shown in Example 3, the phase structure of the alumina coating is a γ-Al2O3 phase. Figure 4 (b) shows the cross-sectional morphology of the coating in this embodiment. As can be seen from the figure, the coating structure is dense and has a clear boundary with the substrate, making it easy to distinguish. Figure 5 As shown in Example 3, the nanohardness of the alumina coating prepared in this example is 24.5 ± 1.7 GPa.

[0064] Compared with Example 2, with the heating temperature unchanged, the bias voltage was further increased by 100V. It was found that the structure of the coating changed from a mixed phase to a γ-Al2O3 phase, which became more stable and accompanied by an increase in hardness, thus increasing the usability of the coating.

[0065] Comparative Example 1

[0066] The pretreated substrate is fixed on a special workpiece holder and sent into the coating chamber. The chamber door is closed, and a vacuum is drawn until the vacuum level reaches 3×10⁻⁶.-3 Heating begins after Pa, with a heating temperature of 500℃. After reaching the set temperature, vacuuming must continue for ≤2×10⁻⁶ seconds. -3 Pa was then introduced to perform glow discharge etching on the substrate for 5 min. Finally, an alumina coating was deposited. During the deposition process, the cathode power was 4000 W, the pulse width was 50 μs, and the frequency was 1000 Hz. A synchronous high-power pulsed magnetron sputtering power supply was used for discharge, with a bias voltage of -100 V and a pulse width of 60 μs. At the same time, the oxygen flow rate was controlled at 30 sccm, and the sputtering gas was changed to krypton and argon. The krypton flow rate was 120 sccm, the argon flow rate was 240 sccm, the sample stage speed was 3 r / min, and the coating growth time was 120 min.

[0067] like Figure 3 (As shown in Comparative Example 1), the phase structure of the alumina coating is a mixed phase of κ-Al2O3 and γ-Al2O3. Figure 4 (c) shows the cross-sectional morphology of the coating in this comparative embodiment. As can be seen from the figure, the coating structure is loose and has poor crystallinity, indicating that the bias voltage is too low and cannot provide enough energy for the crystal growth of the coating.

[0068] Comparative Example 2

[0069] The pretreated substrate is fixed on a special workpiece holder and sent into the coating chamber. The chamber door is closed, and a vacuum is drawn until the vacuum level reaches 3×10⁻⁶. -3 Heating begins after Pa, with a heating temperature of 500℃. After reaching the set temperature, vacuuming must continue for ≤2×10⁻⁶ seconds. -3 Pa, followed by glow discharge etching of the substrate using high-purity argon gas for 10 min, and finally deposition of an alumina coating. During deposition, the cathode power was 4000 W, the pulse width was 50 μs, and the frequency was 1000 Hz. A synchronous high-power pulsed magnetron sputtering power supply was used for discharge without bias voltage. At the same time, the oxygen flow rate was controlled at 40 sccm, the krypton flow rate at 360 sccm, the sample stage rotation speed at 3 r / min, and the coating growth time was 120 min.

[0070] like Figure 3 (As shown in Comparative Example 2), the phase structure of the alumina coating exhibits an amorphous structure. Figure 4 (d) shows the cross-sectional morphology of the coating in this comparative embodiment. As can be seen from the figure, the coating structure is loose and has poor crystallinity.

[0071] This demonstrates that magnetron sputtering technology can only prepare amorphous alumina under low-temperature, unbiased conditions. It also further verifies that, in the conventional understanding that existing magnetron sputtering technology cannot prepare crystalline alumina at low temperatures, this invention overcomes the technical difficulties by using a new bias application method, providing a new approach to preparing crystalline alumina at low temperatures using magnetron sputtering technology.

[0072] Table 1 Process parameters for the examples and comparative examples

[0073]

[0074] Based on the above embodiments and comparative embodiments, as well as the process parameters in Table 1, it can be concluded that crystallization transformation can be achieved by changing the bias voltage, further confirming the beneficialness of high bias voltage in this invention.

[0075] Compared with existing technologies, this invention overcomes the technical difficulties of preparing crystalline alumina coatings at low temperatures using existing magnetron sputtering techniques. It achieves stable preparation of crystalline Al2O3 coatings at low temperatures using magnetron sputtering, providing a new approach to bias voltage application during insulating coating deposition. Based on the problem of providing high energy, this invention discovers that applying a high bias voltage during alumina coating deposition can provide sufficient energy for its growth. However, due to the insulating nature of alumina coatings, ordinary DC power supplies cannot be used as bias power supplies during coating growth. Therefore, to complement the cathode, this invention uses a synchronous high-power pulsed magnetron sputtering power supply, independent of the cathode power supply. During alumina coating deposition, this synchronous high-power pulsed magnetron sputtering power supply is used as the bias power supply to apply a high bias voltage to the substrate. This causes the deposited ions to accelerate again before reaching the substrate, gaining more momentum to bombard the substrate surface, providing sufficient energy for coating growth, improving the crystallinity and density of the coating, and enhancing the adhesion between the coating and the substrate. This solves the problem that DC power supplies cannot provide bias voltage in existing magnetron sputtering processes.

[0076] Furthermore, the setup of two independent power supplies, besides utilizing the synchronous high-power pulsed magnetron sputtering power supply to provide high energy for coating growth, is also crucial in that the synchronous high-power pulsed magnetron sputtering power supply and the cathode power supply are independent and synchronized. This enables selective acceleration of target ions, allowing for more efficient high-energy delivery. Because in a vacuum environment, in addition to the desired target ions, other impurity gas ions exist, the independent and synchronized operation of the synchronous high-power pulsed magnetron sputtering power supply and the cathode power supply in this invention provides a solution for selectively accelerating target ions. Specifically, the time it takes for ions to reach the workpiece is estimated using conventional methods, and this time is used to set the bias pulse width and delay. By rationally controlling the bias voltage, the desired ions are biased onto the substrate just before reaching it, while unwanted ions are not biased, thus achieving selective acceleration of target ions.

[0077] The present invention has been tested and found that by controlling the introduction rate of the reactive gas during the coating deposition process, the poisoning rate of the aluminum target during the deposition process can be effectively slowed down, the "arc" phenomenon of the target material can be avoided, the stability of the coating deposition process can be ensured, the coating composition can be more uniform, and the repeatability of the experiment can be higher.

[0078] This invention prepares a crystalline alumina coating with a phase structure of κ-Al2O3 and γ-Al2O3 mixed phases. The nano-hardness value can reach 20-24.5 GPa, which has higher hardness and density than other amorphous alumina coatings. This coating can be alternately grown with other nitride ceramic coatings to form a composite coating that is applied to the tool surface for high-speed cutting and dry cutting of high-temperature alloy materials, thereby improving the tool life.

[0079] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, based on the guidance provided in this application, improve and implement the present invention in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for preparing a crystalline alumina coating, characterized in that, The method includes the following steps: S10, matrix pretreatment; S20, the preparation of crystalline alumina coating includes the following steps: S201, the pretreated substrate is placed in a preset position in the chamber, and the substrate is heated to a first preset temperature under preset vacuum conditions; S202 uses a medium-frequency power supply to etch the substrate; S203, after the substrate etching is completed, the cathode power supply uses a DC power supply to sputter clean the target surface; S204 employs high-power pulsed magnetron sputtering technology to deposit an alumina coating: sputtering gas and reactive gas are introduced, and the introduction rate of the reactive gas is controlled; simultaneously, a high-power pulsed magnetron sputtering power supply is used for sputtering an aluminum target, and a synchronous high-power pulsed magnetron sputtering power supply set independently of the cathode power supply provides a high bias voltage to the substrate; after a preset coating growth time, a crystalline alumina coating is deposited. In S201, the substrate is heated to a first preset temperature and maintained at the first preset temperature until the crystalline alumina coating is completed. The first preset temperature is 500~600℃. In S204, the sputtering gas is krypton and the reactant gas is oxygen; when it is introduced, the oxygen partial pressure is 347~351 mPa and the krypton flow rate is 240~360 sccm. In S204, the bias voltage provided by the synchronous high-power pulsed magnetron sputtering power supply is -500~-1000V, and the pulse width is 60~80μs; ​​the power of the cathode power supply is 4000~6000W, the pulse width is 50μs, and the frequency is 1000~2500Hz; the sample stage rotation speed is 3~5r / min.

2. The method for preparing a crystalline alumina coating according to claim 1, characterized in that, In S201, the method for heating the substrate to a first preset temperature under preset vacuum conditions is to evacuate the chamber until the vacuum level drops to ≤3×10. -3 After Pa, the substrate is heated to the first preset temperature, and then vacuum is continued until the vacuum level drops to ≤2×10. -3 Pa.

3. The method for preparing a crystalline alumina coating according to claim 1, characterized in that, In the S202 etching process, an etching gas with a preset flow rate is introduced; in the S203 sputter cleaning of the target surface, the etching gas is used as the sputtering gas, and the introduced flow rate is greater than the preset flow rate.

4. The method for preparing a crystalline alumina coating according to claim 3, characterized in that, During the S202 etching process, the aluminum target baffle is opened, the intermediate frequency power supply voltage is set to 650V and the frequency to 240kHz; argon is used as the etching gas, and the argon gas pressure is 180~250mPa; the etching time is 5~10min; and the sample stage rotation speed is 3~5r / min.

5. The method for preparing a crystalline alumina coating according to claim 4, characterized in that, During the sputtering cleaning of the target surface using S203, the aluminum target baffle is closed, the cathode power supply power is 5000~8000W, a hollow cathode tube is used during the argon gas introduction process, the total argon gas flow rate is 500~700sccm, and the argon gas flow rate introduced from the hollow cathode tube is 550~600sccm; the target cleaning time is 2~10min.

6. The method for preparing a crystalline alumina coating according to claim 1, characterized in that, In S10, the pretreatment includes ultrasonic cleaning, in which the substrate is sequentially placed in deionized water and anhydrous ethanol for ultrasonic cleaning, with a cleaning time of 15-30 minutes.

7. The method for preparing a crystalline alumina coating according to claim 1, characterized in that, Also includes: S30, after the crystalline alumina coating is prepared, it is cooled to a second preset temperature and then removed from the furnace. The second preset temperature is 50~180℃.

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