A surface-pre-oxidized AlCrVTiSiON nanogradient coating and its preparation method

Abstract

This invention discloses a surface-pre-oxidized AlCrVTiSiON nanogradient coating and its preparation method, belonging to the field of coating technology. The AlCrVTiSiON nanogradient coating is prepared using arc ion plating technology. Specifically, the target materials selected are metallic Cr, V, AlCrSi, and AlTiSi targets. To further improve the coating's heat resistance and increase cutting parameters during service, pre-oxidation is performed on the coating surface, ultimately forming an AlCrVTiSiON nanogradient coating with an increasing O content from the inside out. The prepared coating exhibits good heat resistance, is suitable for high-speed cutting, and improves machining efficiency.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a surface-pre-oxidized AlCrVTiSiON nanogradient coating and its preparation method. Background Technology

[0002] Face-centered cubic (FCC) coatings possess high hardness, high wear resistance, and excellent thermal stability, making them widely used in industrial machining. Oxide (NOx) coatings, formed by adding oxygen, exhibit better oxidation resistance than nitride coatings. However, excessive O doping leads to the formation of amorphous oxide phases and a sharp decline in mechanical properties. V reacts readily with O to form V₂O₅, which has low shear strength at high temperatures and can be used as a solid lubricant. These oxides can significantly enhance the coating's oxidation resistance at high temperatures. However, lubricating oxide coatings cannot be directly used as protective coatings in mechanical applications. Most research focuses on adding oxide-forming elements to hard metal nitride coatings, aiming to achieve a low coefficient of friction while maintaining coating hardness. Vanadium oxide is one of the most studied lubricating oxides, especially the orthorhombic α-V₂O₅, which has a stable crystal structure. Additionally, Al and Cr elements in the coating can also improve oxidation resistance, but only when an α-phase aluminum-chromium oxide structure is formed in the coating can it effectively prevent high-temperature oxidation and improve wear resistance, thereby extending the service life of coated tools. These α-(Al,Cr)2O3-based coatings can withstand extremely high temperatures during dry milling of high-strength materials while exhibiting high wear resistance.

[0003] Oxygen doping leads to the formation of amorphous oxide phases, reducing the coating's friction coefficient, improving wear resistance, and affecting its mechanical properties. Introducing oxygen into AlCrN coatings results in the formation of a dense Al2O3 film on the coating surface, providing good protection and preventing microcrack propagation. Since most AlCrN-based coatings are prepared using arc ion plating, and the deposition rate of arc equipment is too high, introducing oxygen into Ti-containing coatings easily forms a highly brittle TiO2 layer, deteriorating coating performance. Current research on the effect of oxygen doping on coating oxidation resistance mainly focuses on the influence of O content. Higher oxygen concentrations lead to more oxygen-containing defects, such as stacking faults and polytype compounds described as octahedral coordination clusters of aluminum atoms. Furthermore, compared to single-layer coatings, multilayer composite coatings not only combine the strengthening mechanisms of single-layer coatings but also possess better structural control and strengthening mechanisms.

[0004] Current research on oxide layer thickness is scarce. This invention focuses on AlCrVTiSiN coatings, performing pre-oxidation with oxygen permeation for varying times at the end of deposition to investigate the effect of different oxide layer thicknesses on AlCrVTiSiN / AlCrVTiSiON bilayer coatings. Using arc ion plating technology, the oxygen permeation time on the coating surface was varied during the deposition process to prepare AlCrVTiSiN / AlCrVTiSiON gradient coatings with different oxide layer thicknesses. The influence of oxide layer thickness on the composition, phase composition, microstructure, mechanical properties, and tribological behavior of the AlCrVTiSiN coating was systematically studied. Summary of the Invention

[0005] To further improve the thermal stability and oxidation resistance of existing uniform AlCrVTiSiN coatings, the present invention aims to provide a pre-oxidized AlCrVTiSiON nano-gradient coating and its preparation method. The method employs arc ion plating technology to further pre-oxidize the surface of the AlCrVTiSiN gradient coating with varying V content. By controlling the V content and oxygenation time, an AlCrVTiSiON gradient coating with high hardness, high wear resistance, and high oxidation resistance is prepared.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A pre-oxidized AlCrVTiSiON nanogradient coating is deposited on a metal (hard alloy substrate or stainless steel sheet) or silicon wafer substrate. The oxide content of the coating gradually increases from the inside to the outside, and the surface of the coating is an AlCrVTiSiON oxide protective layer. The pre-oxidation of the coating surface improves its oxidation resistance and thermal stability.

[0008] The AlCrVTiSiON coating with surface pre-oxidation is separated from the substrate by a CrN transition layer. An AlCrVTiSiN functional layer is first deposited on the CrN transition layer and then pre-oxidized to obtain an AlCrVTiSiON nano-gradient coating. The total thickness of the formed nano-gradient coating is controlled between 2 and 5 μm.

[0009] The AlCrVTiSiON nanogradient coating includes fcc-(Al,Cr,V)N phase, fcc-TiO phase, hcp-Cr2N phase, bcc-TiVN phase, and a small amount of amorphous phase.

[0010] The AlCrVTiSiON nanogradient coating exhibits a hardness and elastic modulus of up to 28.0 GPa and 405.3 GPa, respectively, and H / E and H... 3 / E *2 The maximum values ​​can reach 0.069 and 0.111 GPa, at which point the critical load of the coating is 55.2 N.

[0011] In the AlCrVTiSiON nanogradient coating, the V element content is 19.0-27.0 wt.%, the O element content is 8.5-24.0 wt.%, and the O element content on the coating surface is 20.0-24.0 wt.%.

[0012] The AlCrVTiSiON nanogradient coating is deposited on a substrate using arc ion plating technology. The V content is controlled by linearly adjusting the V target current, and pre-oxidation is performed on the coating surface to form the AlCrVTiSiON nanogradient coating. Specifically, AlCrSi, AlTiSi alloy targets, and metallic V and Cr targets are selected. A CrN transition layer is first deposited on the substrate for 15–20 min, followed by the deposition of the AlCrVTiSiN functional layer and pre-oxidation. The base vacuum level during AlCrVTiSiN functional layer deposition and pre-oxidation is 3 × 10⁻⁶. -3 Above Pa, maintain a bias voltage of -100 to -110V (duty cycle 50% to 60%), and a deposition pressure of 2.8-2.9 Pa. Turn on the AlCrSi, AlTiSi, and V targets, keeping the target currents of the alloy targets constant. The AlCrSi target current ranges from 95 to 100 A, and the AlTiSi target current ranges from 80 to 85 A. The V target current increases linearly from a lower limit of 75 A to an upper limit of 80-95 A. Introduce Ar and N2. Set different target opening times and gas introduction times according to the required gradient coating thickness and target current. Introduce oxygen in the last 5-20 minutes of coating deposition to perform pre-oxidation and form an AlCrVTiSiON nano-gradient coating.

[0013] Furthermore, during the deposition of AlCrVTiSiN and AlCrVTiSiON layers, the flow rate of Ar was 50-60 sccm, the flow rate of N2 was 590-600 sccm, the total gas flow rate was 650 sccm, and the bias voltage was -100 to -110 V.

[0014] Preferably, during the deposition of the AlCrVTiSiON protective layer, the oxygen flow rate is 10-15 sccm, and the oxygenation time is preferably adjusted within the range of 5-12 min.

[0015] Furthermore, during the preparation of the AlCrVTiSiON nanogradient coating, as the oxygen purging time increased, the coating hardness and elastic modulus first increased and then decreased, while the coating friction coefficient and wear first decreased and then increased.

[0016] The preparation of the AlCrVTiSiON nanogradient coating specifically includes the following steps:

[0017] (1) Fix the cleaned substrate onto the rotating frame inside the coating chamber and evacuate the vacuum to 3×10. -3 Pa or above; AlCrSi, AlTiSi alloy targets and metal V targets and Cr targets are all used as cathode targets for arc ion plating.

[0018] (2) The substrate is subjected to glow discharge cleaning and ion bombardment cleaning in sequence. The glow discharge cleaning process is as follows: Ar is introduced, the Ar gas flow rate is set to 400-410 sccm, the working pressure is adjusted to maintain 2.4-2.5 Pa, the pulse bias voltage is set to -800 to -750 V (duty cycle 94-96%), and the glow time is 15-20 min. The ion bombardment cleaning process is as follows: after glow discharge cleaning, the bias voltage is turned off first, then the Ar gas flow rate is set to 100-110 sccm, the working pressure is adjusted to maintain 0.5-0.6 Pa, the Cr target is turned on, and the Cr target current is 90-95 A. The pulse bias voltage is sequentially set to -800 V, -600 V, -400 V and -200 V (duty cycle 94-96%) for 2 min each time.

[0019] (3) Deposit a CrN transition layer to improve the bonding strength between the working layer and the substrate. The process of depositing the CrN transition layer is as follows: turn off the target power supply and bias voltage in sequence, turn on the N2 gas cylinder, and set the argon and nitrogen flow rates to 50-60 sccm and 190-200 sccm, respectively. Adjust the working pressure to maintain it at 1.0-1.1 Pa, and set the pulse bias voltage to -100 to -90 V (duty cycle 60%). Turn on the Cr target to deposit the CrN transition layer. The Cr target current is 90-95 A, and the deposition time is 15-20 min.

[0020] (4) Deposition of AlCrVTiSiN functional layer

[0021] (5) Deposit AlCrVTiSiON protective layer.

[0022] The design mechanism of this invention is as follows:

[0023] This invention employs arc ion plating technology to deposit AlCrVTiSiON nanogradient coatings on cemented carbide sheets, SUS 304 stainless steel, and single-crystal Si wafers. The V element in the coating exhibits certain variations, while the O element gradually increases from the inside to the outside.

[0024] While AlCrVTiSiN coatings possess excellent mechanical properties and wear resistance, their poor thermal stability limits their application in high-speed machining of difficult-to-machine workpieces. To further enhance the coating's heat resistance and increase cutting parameters during service, pre-oxidation is performed on the coating surface, ultimately forming an AlCrVTiSiON nanogradient coating. This invention enhances the coating's thermal stability by varying the oxygen permeation time on the coating surface (range: 5 min-20 min) to form an oxide protective layer. The total coating thickness is controlled between 2 and 5 μm. This invention investigates the influence of process parameters such as oxide layer thickness on the coating composition, mechanical properties, and tribological behavior, obtaining the laws governing their impact on coating performance. By changing parameters such as the oxygen permeation time on the coating surface, the oxide layer on the prepared AlCrVTiSiON nanogradient coating surface exhibits excellent protective properties. Compared to AlCrVTiSiN coatings, the wear resistance of the coating is significantly improved, and its oxidation resistance and thermal stability are also significantly enhanced. The prepared AlCrVTiSiON gradient coating possesses superior wear resistance and high-temperature oxidation resistance.

[0025] The advantages and beneficial effects of this invention are as follows:

[0026] 1. The AlCrVTiSiON gradient coating prepared by this invention has excellent wear resistance, obvious anti-wear effect, and excellent high-temperature oxidation resistance and thermal stability.

[0027] 2. The AlCrVTiSiON coating of the present invention is based on an AlCrVTiSiN coating with a certain variation in V content. The surface of the coating is pre-oxidized, and the resulting AlCrVTiSiON nanogradient coating has the advantages of high oxidation resistance, thermal stability and high wear resistance.

[0028] 3. The AlCrVTiSiON gradient coating of this invention has broad application prospects and is suitable for high-speed dry cutting of various difficult-to-machine materials, which can significantly improve cutting efficiency and extend the service life of cutting tools.

[0029] 4. The AlCrVTiSiON gradient coating of this invention has excellent high temperature resistance, oxidation resistance, thermal stability, mechanical properties and tribological properties. The coated cutting tools are suitable for high-speed cutting and continuous heavy-duty machining. Attached Figure Description

[0030] Figure 1 The surface morphology of AlCrVTiSiON gradient coatings with different oxygen permeation times prepared by arc ion plating technology in Example 1 is shown below; where: (a) oxygen permeation time 0 min; (b) oxygen permeation time 5 min; (c) oxygen permeation time 10 min; (d) oxygen permeation time 15 min; (e) oxygen permeation time 20 min.

[0031] Figure 2 The cross-sectional morphology of the AlCrVTiSiON gradient coatings prepared by arc ion plating technology for different surface oxygen purging times in Example 1 is shown below: (a) oxygen purging for 0 min; (b) oxygen purging for 5 min; (c) oxygen purging for 10 min; (d) oxygen purging for 15 min; (e) oxygen purging for 20 min.

[0032] Figure 3 The XRD patterns of AlCrVTiSiON gradient coatings with different surface oxygen passage times prepared by arc ion plating technology in Example 1 are shown.

[0033] Figure 4 The hardness and elastic modulus of AlCrVTiSiON gradient coatings with different surface oxygen passage times prepared by arc ion plating technology in Example 1 are shown.

[0034] Figure 5 The H / E and H values ​​of AlCrVTiSiON gradient coatings with different surface oxygen permeation times prepared by arc ion plating technology in Example 1 are shown. 3 / E *2 .

[0035] Figure 6 The critical load for AlCrVTiSiON gradient coatings with different surface oxygen passage times prepared by arc ion plating technology in Example 1 is shown.

[0036] Figure 7 The friction coefficient and wear rate of AlCrVTiSiON gradient coatings with different surface oxygen passage times prepared by arc ion plating technology in Example 1 are shown.

[0037] Figure 8 The three-dimensional wear morphology of AlCrVTiSiON gradient coatings with different surface oxygen purging times prepared by arc ion plating technology in Example 1 is shown below: (a) oxygen purging for 0 min; (b) oxygen purging for 5 min; (c) oxygen purging for 10 min; (d) oxygen purging for 15 min; (e) oxygen purging for 20 min.

[0038] Figure 9 The composition of AlCrVTiSiON gradient coatings prepared by arc ion plating technology for different surface oxygen purging times in Example 1 is shown below: (a) test point; (b) oxygen purging for 0 min; (c) oxygen purging for 5 min; (d) oxygen purging for 10 min; (e) oxygen purging for 15 min; (f) oxygen purging for 20 min. Detailed Implementation

[0039] The present invention will be further described in detail below through embodiments.

[0040] In the following examples, the atomic ratio of Al, Cr and Si in the AlCrSi target is 6:3:1, and the atomic ratio of Al, Ti and Si in the AlTiSi alloy target is 6:3:1.

[0041] Example 1:

[0042] This embodiment prepared AlCrVTiSiON nanogradient coatings with different oxygen permeation times on the surface, resulting in five coatings in total. Specifically, the oxygen permeation times for depositing the AlCrVTiSiON coatings were 0 min, 5 min, 10 min, 15 min, and 20 min, respectively. The specific preparation process of the coatings is as follows:

[0043] In this embodiment, an AlCrVTiSiON coating is deposited on a single-crystal Si wafer (40mm×40mm×0.67mm), a cemented carbide wafer (25mm×25mm×3.0mm), and a stainless steel wafer (35mm×35mm×1.0mm) using arc ion plating technology. The specific operation steps are as follows:

[0044] (1) After polishing the cemented carbide substrate, to ensure good adhesion between the coating and the substrate, all substrates were cleaned for 15 minutes each using a solution of degreasing agent, acetone, and anhydrous ethanol after the polishing process, thereby maximizing the adhesion between the coating and the substrate. Subsequently, after drying with high-purity nitrogen, the treated substrates were suspended on the sample holder inside the furnace. This step not only helps to further remove any moisture and organic matter that may remain on the substrate surface, but also creates an ideal surface environment for the subsequent coating process. The substrates were fixed on the sample holder, and the AlCrSi, AlTiSi alloy targets, metal V targets, and Cr targets were all connected to the arc ion plating cathode; the fixture positions were adjusted, and the furnace door was closed.

[0045] (2) Vacuuming: Open the mechanical pump, roughing valve, holding pump, and holding valve sequentially. When the pre-vacuum level is less than 4 Pa, open the molecular pump to increase the pressure. When the furnace pressure is below 4 Pa, close the roughing valve and open the high-pressure valve for fine evacuation. Pre-evacuate the furnace pressure to 5 × 10⁻⁶ Pa. -3 Pa, turn on forward rotation and heating, rotor frequency 40Hz, heating temperature 450℃, furnace pressure as low as 3×10 -3 When the pressure is below Pa and the temperature reaches the set temperature, the experiment can begin.

[0046] (3) Glow discharge cleaning vacuum chamber: Open the Ar gas cylinder, set the gas flow rate to 400 sccm, adjust the throttle valve to keep the working pressure at 2.4 Pa, set the pulse bias voltage to -800 V, frequency to 10 kHz, pulse width to 6 μs (duty cycle 94%), and glow time to 20 min.

[0047] (4) Bombardment cleaning of target surface: First turn off the bias voltage, then set the Ar gas flow rate to 100 sccm, adjust the working pressure to maintain at 0.5 Pa, turn on the Cr target, and the Cr target current is 90 A; clean for 2 min each at pulse bias voltages of -800 V, -600 V, -400 V and -200 V, frequency 10 kHz, pulse width 6 μs (duty cycle 94%).

[0048] (5) Deposition of transition layer: Turn off the target power supply and bias voltage in sequence, turn on the N2 gas cylinder, the flow rates of argon and nitrogen are 50 sccm and 200 sccm respectively, adjust the working pressure to maintain 1 Pa, pulse bias voltage -100 V, frequency 50 kHz, pulse width 8 μs (duty cycle 60%), turn on the Cr target to deposit CrN transition layer, with Cr target current of 90 A and deposition time of 15 min.

[0049] (6) When preparing the AlCrVTiSiON nano-gradient coating, the Cr target power supply and bias voltage were turned off in sequence, argon gas was 50 sccm, nitrogen gas was 600 sccm, the working pressure was adjusted to be maintained at 2.8 Pa, the pulse bias voltage amplitude was -100 V, the frequency was 50 kHz, and the pulse width was 6 μs. The AlCrSi target was turned on, and the AlCrSi target current was 100 A. The AlTiSi target was turned on, and the AlTiSi target current was 80 A. The V target was turned on, and the target current was manually adjusted during the coating process to prepare the gradient coating. The V target current was gradually increased from the lower limit of 75 A to the upper limit of 90 A. Oxygen was introduced at 12 sccm at the last 0 min, 5 min, 10 min, 15 min and 20 min of coating deposition. The total deposition time of AlCrVTiSiON gradient coating was 180 min.

[0050] The morphology and performance of AlCrVTiSiON nanogradient coatings with different surface oxygenation times prepared in this embodiment were characterized and tested, as follows:

[0051] The surface and cross-sectional morphology of the coatings were observed using a Hitachi S-4800 field emission scanning electron microscope (SEM). The phase composition of the coatings was analyzed using a Brucker D8-Discovery X-ray diffractometer (XRD). Monochromatic Kα radiation (λ = 0.15418 nm) was used on a Cu target, and the spectra were recorded at a scanning rate of 0.02° / s within the diffraction angle range of 25–80° (2θ). The hardness and elastic modulus of the three coatings were tested using an Anton Paar TTX-NHT3 nanoindenter according to ISO 14577 standards. A Polkevik diamond indenter with a 142.3° apex angle was used to apply a load to the coating, with an indentation depth of 200 nm and a holding time of 10 s. Two sets of tests were performed for each sample, and the average value of 10 points in each set was taken. According to ISO 20502 standard, the critical load of different coatings was tested using an Anton Paar RST-3 scratch tester. The diameter of the spherical diamond tip was 200 μm, the load gradually increased from 1 N to 100 N, the scratch length was 3 mm, and the scratch rate was 6 mm / min. Each sample was tested three times and the average value was taken. The coefficient of friction of the coating was tested using an Anton Paar THT high-temperature tribometer. The friction pair used Al2O3 spheres with a diameter of 6 mm, the normal load was 4 N, and each sample was tested three times. The wear radii were 4 mm, 6 mm, and 8 mm, and the number of friction revolutions was 3000. After the friction experiment, the morphology of the coating wear was observed using a Contour GT-K white light interferometer, and the coating wear rate was calculated using formulas.

[0052] Figure 1 The surface morphology of AlCrVTiSiN gradient coatings with different surface oxygenation times is shown. With increasing oxygenation time, the number of large particles on the coating surface initially decreases and then increases. Compared to the AlCrVTiSiN coating, the number of large particles increases after surface oxygenation. This is attributed to the smaller active area on the target surface and the increased arc current density, leading to the formation of agglomerates of larger molten metal on the coating surface. These particles on the film surface are emitted from the small molten areas of the low-melting-point target. On the other hand, during oxygenation, oxygen atoms may react chemically with the metal elements (such as Al, Cr, V, Ti, etc.) on the coating surface to form oxides. These oxides may precipitate on the surface in particle form, forming a granular structure. The AlCrVTiSiN coating surface is densest after 10 min of surface oxygenation. This is attributed to the formation of a dense oxide layer on the coating surface, filling any pores and voids that may exist in the original coating, thus improving surface density. With shorter oxygenation times, a more uniform and dense oxide layer may form, suppressing the formation of large particles. Extending the oxygenation time may lead to more oxidation reactions, forming particulate oxides, thereby increasing the number and size of particles.

[0053] Figure 2 The cross-sectional morphology of AlCrVTiSiON coatings with different surface oxygenation times is shown. Due to the short oxygenation time and the similarity of elements between the two layers, the oxide layer interface is unclear. At an oxygenation time of 10 min, the coating cross-section exhibits a relatively smooth characteristic and the fewest embedded particles. In contrast, pores formed by particle detachment are observed in the coating cross-sections under other oxygenation time conditions. This phenomenon may be related to the oxidation reaction caused by oxygenation and its impact on the coating structure. With a shorter oxygenation time, the oxide layer formed on the coating surface is relatively uniform, effectively filling the gaps between surface particles, resulting in a smoother cross-section. However, with the extension of oxygenation time, the oxidation reaction may lead to particle detachment, forming pores, and the coating thickness also shows a significant decreasing trend. Notably, at oxygenation times of 5 min and 15 min, the coating thickness decreases sharply, even by half compared to the coating thickness at an oxygenation time of 10 min. Simultaneously, the interlayer interface becomes less clear, possibly due to structural changes in the coating caused by excessive oxidation.

[0054] Figure 3 The XRD patterns of AlCrVTiSiON coatings with five different surface oxygenation times are shown. All five coatings exhibit a predominantly face-centered cubic structure, and the thickness of the oxide layer has little effect on the coating phase structure. Unlike the AlCrVTiSiN gradient coating, the AlCrVTiSiON gradient coating shows a diffraction peak at 2θ = 37.19° for the bcc-TiVN2 (PDF#89-5212) phase formed by V atoms dissolved in TiN, and at 2θ = 43.27° for the fcc-TiO (PDF#89-5010) phase, but no TiO2 diffraction peak is detected. This may be attributed to the coating deposition temperature of 450℃, at which TiO is more readily formed. Since no silicon oxynitride peak was detected, it may exist as amorphous silicon oxynitride. In AlCrVTiSiN gradient coatings, silicon mainly exists as amorphous Si3N4, forming a nanocomposite coating structure. When oxygen is introduced during the deposition process, since ΔH(SiO2) = -910.86kJ / mol is higher than ΔH(Si3N4) = -760.00kJ / mol, silicon is more likely to react with oxygen first to form SiO2.

[0055] Figure 4The graphs show the changes in hardness and elastic modulus of five AlCrVTiSiON nanogradient coatings with different oxygen purging times. All exhibit a trend of first increasing and then decreasing. The coating hardness decreases from 33.4 GPa for the AlCrVTiSiN coating with 0 minutes of oxygen purging to 23.3 GPa for 20 minutes of oxygen purging. The hardness and elastic modulus reach their maximum values ​​of 28.0 GPa and 405.3 GPa, respectively, after 10 minutes of oxygen purging. With increasing oxygen purging time, the AlCrVTiSiON coating softens due to the increased oxide content and the relaxation of inherent compressive stress caused by oxygen incorporation. After oxygen doping, the coating hardness and elastic modulus generally show a trend of first increasing and then decreasing. Oxygen doping leads to the formation of a brittle oxide film on the coating surface, resulting in a decrease in hardness and elastic modulus. After 5 minutes of oxygen purging, the oxide film formed along the coating growth direction is not dense enough. During oxygen permeation for 10 minutes, the oxide layer, while maintaining the hardness of the AlCrVTiSiN functional layer, forms a dense protective coating of oxide films such as (Al,Cr)₂O₃ and V₂O₅ on the coating surface, preventing microcrack propagation. With further increases in oxygen permeation time, the thickness of the oxide film on the coating surface increases, leading to a sharp decrease in coating hardness and elastic modulus. Additionally, this may be due to vacancies in the cubic lattice; as oxygen permeation time increases, these vacancy defects may cause a decrease in indentation hardness and modulus.

[0056] Figure 5 H / E and H2 of five AlCrVTiSiON gradient coatings with different oxygen permeation times on the surface 3 / E *2 The graph shows that the higher the ratio of hardness to elastic modulus, the better the wear resistance of the coating. (H) 3 With E *2 The ratio represents the coating's resistance to plastic deformation. With increasing surface oxygenation time, the characteristic values ​​of the formed AlCrVTiSiON gradient coating first increase, reaching their maximum values ​​at 10 min of oxygenation, at 0.069 and 0.111 GPa respectively, higher than AlCrVTiSiON coatings prepared at other oxygenation times. Due to the periodic bombardment of high-energy ions during deposition, the crystal size is smaller, which also enhances the coating's resistance to plastic deformation, dispersing the applied external force over a larger volume and effectively reducing stress accumulation within the coating. Furthermore, the amorphous structure encapsulating nanocrystals formed in the coating also improves its toughness and strength. The characteristic value of the coating is lowest at 15 min of surface oxygenation, at which point the coating's toughness and fracture toughness are worst. When the oxygenation time is extended to 20 min, the characteristic value of the formed AlCrVTiSiON gradient coating shows an increasing trend again, possibly attributed to the increased thickness of the V2O5 film formed on the coating surface, leading to enhanced coating toughness.

[0057] Figure 6The graph shows the critical load variation of the AlCrVTiSiN gradient coating. With increasing oxygenation time, the critical load initially increases and then decreases. The coating / substrate adhesion is weakest at 43.6 N after 5 minutes of surface oxygenation. When the surface oxygenation time is 10 minutes, the critical load reaches its maximum value of 55.2 N, and cracks appear at the scratch boundary. Shell-shaped cracks and plastic deformation are observed at the edge of the scratch trajectory. Initially, the critical load is mainly affected by the needle tip compressive stress; later, the surface crack formation is due to the tensile stress at the indenter. With further increases in oxygenation time, a thicker oxide layer may form on the coating surface. This increase in oxide layer may lead to increased surface roughness, affecting the adhesion between the surface layer (the coating formed after oxygenation) and the AlCrVTiSiN functional layer (the coating formed before oxygenation), resulting in weakened adhesion between the coating and the substrate. Furthermore, prolonged oxygenation time may lead to more oxidation reactions occurring at the interface between the coating and the substrate. These interfacial reactions may alter the surface chemical composition and structure, changing the interaction properties between the coating and the substrate, thus affecting the adhesion.

[0058] Figure 7 The graph shows the variation of friction coefficient and wear rate of AlCrVTiSiON coatings with five different oxygenation times. The average friction coefficient of the AlCrVTiSiON coating is significantly lower than that of the AlCrVTiSiN coating without oxygenation. This is attributed to the formation of a Magnéli phase oxide film such as V₂O₅ on the coating surface during the friction process. In addition, the doping of O element during the coating process increases the oxide content on the coating surface. VO₂ forms on the coating surface. x The lubricating oxide phase significantly reduces the coefficient of friction and wear rate. The wear mechanisms are mainly abrasive wear, adhesive wear, and oxidative wear. Both the coefficient of friction and wear rate initially decrease and then increase. The average coefficient of friction and wear rate reach their minimum values ​​after 5 minutes of oxygen permeation to the surface, at 0.56 and 1.27 × 10⁻⁶, respectively. -9 mm 3 ·N -1 ·mm -1At this point, the oxide content on the coating surface is moderate, resulting in optimal wear resistance. As the surface oxygenation time increases further, the friction coefficient and wear rate increase. This is attributed to the rapid growth of porous, brittle TiO2 on the coating surface, whose formation is related to residual stress within the coating. This residual stress deteriorates the Al2O3 protective layer, and the Magnéli phase oxides such as V2O5 in the coating are insufficient for continuous supply, reducing the coating's wear resistance. Furthermore, hardness has always been considered a major property determining wear resistance; higher coating hardness generally corresponds to better wear resistance. Considering the changes in coating adhesion over different surface oxygenation times, the thickening of the oxide layer may alter the interfacial bonding between the coating and the substrate. The formation of the oxide layer after 5 minutes of surface oxygenation may help improve the bonding between the coating and the substrate, reducing friction and wear. However, excessive oxide layer thickening may weaken the interfacial bonding, leading to coating detachment and damage, causing a renewed increase in the friction coefficient and wear rate.

[0059] Figure 8 The three-dimensional wear track morphology of AlCrVTiSiON coatings with five different surface oxygenation times is shown. The worn surfaces are relatively smooth, with a small amount of adhesive debris present, indicating that the wear mechanism is mainly oxidative wear and slight adhesive wear. In the three-dimensional wear track morphology, the wear track is narrowest and shallowest after 10 minutes of surface oxygenation. Combined with XRD patterns, a relatively uniform and stable oxide layer structure is formed in the coating. This stable oxide layer can reduce spalling and wear during friction. Furthermore, the surface morphology suggests that 10 minutes of surface oxygenation may facilitate the formation of a smoother and denser surface structure, reducing surface roughness, lowering the coefficient of friction, and thus slowing down the wear process. As the surface oxygenation time increases further, the wear track of the AlCrVTiSiN / AlCrVTiSiON bilayer coating becomes wider and deeper, indicating a decrease in wear resistance. At 20 minutes of oxygenation, pores appear at the wear track, which may be due to the presence of large particles in the coating, which detach during the interaction between the coating and the friction pair. This observation is consistent with the SEM images of the coating surface, suggesting a potential correlation with the presence of a large number of particles on the coating surface.

[0060] Figure 9 The composition of the AlCrVTiSiON gradient coatings with different surface oxygen permeation times prepared in this embodiment; wherein: Figure 9 (a) is a schematic diagram of the coating test points. The corresponding component data are shown in Table 1 below.

[0061] Table 1. Composition (wt.%) of AlCrVTiSiON gradient coatings with different surface oxygen permeation times

[0062]

[0063]

[0064] Depend on Figure 9 As shown in Table 1, in the AlCrVTiSiON gradient coatings prepared in this embodiment, the O content in each coating gradually increases from the inside to the outside. With the increase of oxygen purging time, the O content in the coating first increases and then decreases. Although the V target power increases linearly during the deposition process, the V content in the coating changes to some extent but does not gradually increase with the increase of power.

[0065] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A surface-pre-oxidized AlCrVTiSiON nanogradient coating, characterized in that: The nanogradient coating is deposited on a metal or silicon substrate, with the O element content gradually increasing from the inside to the outside, and the coating surface is an AlCrVTiSiON oxide protective layer. The AlCrVTiSiON nanogradient coating is separated from the substrate by a CrN transition layer. An AlCrVTiSiN functional layer is first deposited on the CrN transition layer and then pre-oxidized to obtain the AlCrVTiSiON nanogradient coating. The total thickness of the formed nanogradient coating is controlled at 2~5 μm. The AlCrVTiSiON nanogradient coating includes fcc-(Al, Cr, V)N phase, fcc-TiO phase, hcp-Cr2N phase, bcc-TiVN phase, and a small amount of amorphous phase; In the AlCrVTiSiON nanogradient coating, the V element content is 19.0-27.0 wt.%, the O element content is 8.5-24.0 wt.%, and the O element content on the coating surface is 20.0-24.0 wt.%.

2. The AlCrVTiSiON nanogradient coating with surface pre-oxidation according to claim 1, characterized in that: The AlCrVTiSiON nanogradient coating exhibits a hardness and elastic modulus of up to 28.0 GPa and 405.3 GPa, respectively, and H / E and H... 3 / E *2 The maximum values ​​can reach 0.069 and 0.111 GPa, at which point the critical load of the coating is 55.2 N.

3. The method for preparing the surface-pre-oxidized AlCrVTiSiON nanogradient coating according to claim 1, characterized in that: The AlCrVTiSiON nanogradient coating was deposited on a substrate using arc ion plating technology. The V content was controlled by linearly adjusting the V target current, and pre-oxidation was performed on the coating surface to form the AlCrVTiSiON nanogradient coating. Specifically, AlCrSi, AlTiSi alloy targets, and metallic V and Cr targets were selected. First, a CrN transition layer was deposited on the substrate for 15–20 min, followed by the deposition of the AlCrVTiSiN functional layer and pre-oxidation. The base vacuum level during the deposition of the AlCrVTiSiN functional layer and pre-oxidation was 3 × 10⁻⁶. -3 Above Pa, maintain a bias voltage of -100 to -110 V, a duty cycle of 50% to 60%, and a deposition pressure of 2.8 to 2.9 Pa. Turn on the AlCrSi, AlTiSi, and V targets. The target currents of the AlCrSi and AlTiSi targets are kept constant, with the AlCrSi target current ranging from 95 to 100 A and the AlTiSi target current ranging from 80 to 85 A. The V target current increases linearly from a lower limit of 75 A to an upper limit of 80 to 95 A. Ar and N2 are introduced. The target turn-on time and gas introduction time are set according to the required gradient coating thickness and target current. Oxygen is introduced in the last 5 to 20 minutes of coating deposition to perform pre-oxidation and form an AlCrVTiSiON nano-gradient coating.

4. The method for preparing the surface-pre-oxidized AlCrVTiSiON nanogradient coating according to claim 3, characterized in that: When preparing the AlCrVTiSiON nanogradient coating, the flow rate of Ar was 50-60 sccm, the flow rate of N2 was 590-600 sccm, the total gas flow rate was 650 sccm, and the bias voltage was −100 ~ −110 V; during the pre-oxidation, the flow rate of oxygen was 10-15 sccm, and the oxygenation time was 5-20 min. During the deposition of AlCrVTiSiON nanogradient coating, as the oxygen purging time increases, the coating hardness and elastic modulus first increase and then decrease, while the coating friction coefficient and wear first decrease and then increase.

5. The method for preparing the surface-pre-oxidized AlCrVTiSiON nanogradient coating according to claim 3 or 4, characterized in that: The method specifically includes the following steps: (1) Fix the cleaned substrate onto the rotating frame inside the coating chamber and evacuate the vacuum to 3×10. -3 Pa or above; AlCrSi, AlTiSi alloy targets and metal V targets and Cr targets are all used as cathode targets for arc ion plating. (2) The substrate was sequentially subjected to glow discharge cleaning and ion bombardment cleaning; (3) Deposit a CrN transition layer to improve the bonding strength between the working layer and the substrate; (4) Deposition of AlCrVTiSiN functional layer; (5) Deposit AlCrVTiSiON protective layer.

6. The method for preparing the surface-pre-oxidized AlCrVTiSiON nanogradient coating according to claim 5, characterized in that: In step (2), the glow discharge cleaning process is as follows: Ar is introduced, the Ar gas flow rate is set to 400-410 sccm, the working pressure is adjusted to 2.4-2.5 Pa, the pulse bias voltage is set to −800~−750 V, the duty cycle is 94-96%, and the glow time is 15-20 min; The ion bombardment cleaning process is as follows: after glow discharge cleaning, the bias voltage is turned off first, then the Ar gas flow rate is set to 100-110 sccm, the working pressure is adjusted to 0.5-0.6 Pa, and the Cr target is turned on; the pulse bias voltage is sequentially set to −800 V, −600 V, −400 V, and −200 V with a duty cycle of 94-96%, and each cleaning is performed for 2 minutes; the Cr target current is 90-95 A.

7. The method for preparing the surface-pre-oxidized AlCrVTiSiON nanogradient coating according to claim 5, characterized in that: In step (3), the process of depositing the CrN transition layer is as follows: turn off the Cr target power supply and bias voltage, open the N2 gas cylinder, the flow rates of argon and nitrogen are 50-60 sccm and 190-200 sccm respectively, adjust the working pressure to maintain 1.0-1.1 Pa, the pulse bias voltage is −100~−90 V, the duty cycle is 60%, turn on the Cr target to deposit the CrN transition layer, the Cr target current is 90-95 A, and the deposition time is 15-20 min.

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