Surface coating for prolonging fatigue life of metal and preparation method

Abstract

The invention discloses a surface coating for prolonging the fatigue life of metal and a preparation method of the surface coating. According to the coating, face-centered cubic structure layers and hexagonal system structure layers are alternately stacked to form a superlattice structure, the total thickness ranges from 1.0 micrometer to 1.5 micrometers, and a base material is titanium alloy. The thickness of the face-centered cubic structure layer is 4-6 nm, the thickness of the hexagonal system structure layer is 1-3 nm, the Mohs hardness difference between the two layers is not larger than 2, and the average grain size is 1-2 nm. According to the coating, a stable high-toughness interface phase is obtained through a specific crystal structure and thickness regulation and control, and dislocation slippage and crack propagation are effectively prevented. A magnetron sputtering method is adopted for preparation, and the process comprises the steps of substrate surface pretreatment, bias cleaning and alternate deposition. The coating shows excellent anti-fatigue performance under the cyclic load condition, and the service life of the titanium alloy component can be remarkably prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hard coating, and particularly relates to a surface coating for improving the fatigue life of metal and a preparation method. BACKGROUND

[0002] Titanium alloy is widely used in high-end manufacturing fields such as aerospace, automobile, medical device and marine engineering due to its excellent specific strength, corrosion resistance and high-temperature stability. However, during long-term service, titanium alloy is often subjected to high-frequency and low-strain cyclic loading, and its fatigue life faces severe challenges. In particular, under low-strain working conditions, fatigue cracks are prone to initiate and propagate in the material, which eventually leads to failure, and is one of the core problems restricting the service reliability of titanium alloy.

[0003] To improve the fatigue resistance of titanium alloy, surface coating technology has become an important means in current research and engineering application. Traditional coating systems mainly include metal coatings, ceramic coatings and their composite structures, which have achieved certain results in improving the wear resistance and corrosion resistance of materials. However, in the face of complex fatigue loading conditions, these coatings still have many technical bottlenecks: on the one hand, the high brittleness of the coating itself makes it prone to cracking in a low-strain fatigue environment. Once cracks occur, there is a lack of effective crack propagation inhibition mechanism between the coating and the substrate, and the cracks quickly propagate to the interior of the substrate, thereby accelerating the fatigue failure of the entire component. On the other hand, the interface between the traditional coating and the substrate is weakly bonded, which cannot effectively hinder dislocation slip and crack penetration, and is a key factor affecting the fatigue resistance of the coating.

[0004] In the prior art, for example, Chinese Patent Publication No. CN116356254A discloses a multilayer hard coating structure for improving the fatigue life of hard coating and a preparation method thereof. By introducing a large number of hard coating interfaces in the multilayer hard coating structure, fatigue microcracks propagated from the metal component can be effectively deflected at low stress levels, and the initiation and propagation of internal microcracks in the hard coating can be effectively inhibited at high stress levels, thereby significantly improving the fatigue life of the metal component. However, it still has the following deficiencies: first, the interlayer design is complex, and it is difficult to control during preparation; second, the toughness improvement is limited, and the H³ / E² value of the existing coating is only 0.35, and the plastic deformation resistance is insufficient; third, although the fatigue strength is improved, it is difficult to achieve a breakthrough in the order of magnitude from 10 6 to 10 7 cycles. SUMMARY

[0005] To solve the above problems, the application provides a surface coating for improving metal fatigue life and a preparation method.

[0006] To achieve the above object, the application adopts the following technical scheme:

[0007] The application provides a surface coating for improving metal fatigue life, characterized in that the surface coating is formed by alternately stacking a first layer and a second layer, the total thickness of the coating is 1.0-1.5 microns, the base material is titanium alloy, one of the first layer or the second layer is face-centered cubic structure, the other of the first layer or the second layer is hexagonal system, the layer of face-centered cubic structure is attached to the base material, the thickness of the layer of face-centered cubic structure is 4-6 nanometers, the thickness of the layer of hexagonal system is 1-3 nanometers, the difference between the Mohs hardness of the first layer and the second layer is not greater than 2, and the average grain size of the first layer and the second layer is 1-2 nanometers.

[0008] Further, the thickness of the layer of face-centered cubic structure and the thickness of the layer of hexagonal system away from the base material satisfy the following formula:

[0009] ;

[0010] wherein the thickness of the layer of face-centered cubic structure is t1, the thickness of the layer of hexagonal system is t2.

[0011] Further, the layer of face-centered cubic structure is TiN, and the layer of hexagonal system is AlN.

[0012] Further, in the surface coating, the thickness of the middle layer is greater than the thickness of the layers on both sides.

[0013] Further, in the surface coating, the thickness and the distance are in linear relationship.

[0014] The application further provides a preparation method of the surface coating, which comprises the following steps: surface treatment of the base material; and film plating on the surface of the treated base material by using a magnetron sputtering.

[0015] Further, the base material is titanium alloy, the base material is polished to a surface roughness of less than 0.16 microns, and then the polished base material is cleaned and dried.

[0016] Further, the sample is sequentially immersed in deionized water, anhydrous ethanol and acetone for 10-30 min by using an ultrasonic cleaner, and then dried.

[0017] Further, the magnetron sputtering process comprises: vacuumizing, bias cleaning and film coating; the vacuum degree after vacuumizing is not more than 2.0*10 -3 Pa; the bias cleaning process is: setting the preparation temperature to 180-220 DEG C to heat the substrate, when the vacuum degree in the chamber is not more than 1.8*10 -3 Pa, opening the stop valve, setting the flow valve parameter to 100 DEG, setting the argon flow to 30 sccm, setting the voltage to-900 V, keeping the pressure in the chamber above 1.0 Pa for bias cleaning, and the cleaning time is not less than 10 min.

[0018] Further, the film coating process is: setting the ratio of argon flow to nitrogen flow to 2-3, setting the chamber working pressure to 0.2-0.3 Pa, setting the deposition temperature to 380-420 DEG C, adjusting the bias voltage of the magnetron sputtering equipment to-100 V, and alternately depositing the first layer and the second layer.

[0019] The beneficial effects brought by the technical scheme provided by the embodiment of the present application include: the present application is based on the characteristics of face-centered cubic structure and hexagonal crystal structure, that is, the face-centered cubic structure has high brittleness, and the hexagonal crystal structure has good thermal shock resistance, the combination of the two with specific thickness and hardness can realize superstructure, that is, the fracture toughness and the anti-plastic deformation and crack propagation ability of the coating can be improved, and the reason for realizing the above effects is that the face-centered cubic structure has high brittleness, which can prevent dislocation from sliding on the surface of the substrate to form a slip step to the greatest extent, and the slip step is the source of fatigue cracks, but the face-centered cubic structure has poor thermal shock resistance, so the hexagonal crystal structure is introduced to reduce the influence of thermal shock, in order to well match the effects of the two, the thickness and Mohs hardness of the face-centered cubic structure and the hexagonal crystal structure are limited, so as to avoid poor coordination between the interfaces and large hardness difference, which in turn leads to an increase in crack propagation tendency. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical scheme in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Figure 1 The TEM cross-sectional micro-morphology diagram of the superlattice coating provided for the embodiment 1 of the present application;

[0022] Figure 2 HRTEM image of the superlattice coating provided for Example 1 of the present application;

[0023] Figure 3 Toughness test results of the superlattice coatings prepared for Examples and Comparative Examples of the present application;

[0024] Figure 4 Fatigue performance test results of the superlattice coatings prepared for Examples and Comparative Examples of the present application. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and specific examples.

[0026] The surface coating for improving metal fatigue life provided by the embodiment of the present application is formed by alternately stacking a first layer and a second layer, and the total thickness of the coating is 1.0 μm-1.5 μm; the base material is titanium alloy; one of the first layer or the second layer is face-centered cubic structure, and the other of the first layer or the second layer is hexagonal system; the layer of face-centered cubic structure is attached to the base material; wherein the thickness of the layer of face-centered cubic structure is 4 nm-6 nm, and the thickness of the layer of hexagonal system is 1 nm-3 nm; the difference between the Mohs hardness of the first layer and the second layer is not greater than 2; and the average grain size of the first layer and the second layer is 1 nm-2 nm.

[0027] The beneficial effects brought by the technical solution provided by the embodiment of the present application include: the present application is based on the characteristics of face-centered cubic structure and hexagonal system structure, i.e. the face-centered cubic structure has higher brittleness, and the hexagonal system structure has good thermal shock resistance effect, and the combination of the two with specific thickness and hardness can realize superstructure, i.e. can improve the fracture toughness and the ability of resisting plastic deformation and crack propagation of the coating, and the reason for realizing the above effects is that the face-centered cubic structure has higher brittleness, which can prevent dislocation from slipping on the surface of the base material to form slip steps to the greatest extent, and the slip steps are the source of fatigue cracks, but since the face-centered cubic structure has poor thermal shock resistance effect, the hexagonal system is introduced to reduce the influence of thermal shock, and in order to well match the effects of the two, the thickness and Mohs hardness of the face-centered cubic structure and the hexagonal system are limited, so as to avoid poor coordination between the interfaces and large hardness difference, which in turn leads to the increase of crack propagation tendency.

[0028] The present application significantly improves the fatigue life of titanium alloy materials under cyclic loading conditions by optimizing the surface coating design of the titanium alloy materials. Traditional coating materials usually exhibit high brittleness and are prone to crack under low strain conditions. Once the crack is formed, it tends to rapidly expand and may penetrate the coating into the substrate material, resulting in the appearance of fatigue crack sources inside the substrate, thereby significantly reducing the service life of the material. To solve the above problems, the present application proposes an innovative coating structure design: superlattice multilayer coating.

[0029] In the design of the superlattice multilayer coating, the material composition and microstructure of the coating are optimized to simultaneously improve its toughness and strength. A high-toughness coating can effectively slow down the crack propagation speed after crack initiation, preventing the crack from rapidly penetrating the coating and invading the substrate. Specifically, by precisely controlling the microstructure of the coating, such as grain size, phase composition, and interface characteristics, the resistance of the coating to crack propagation can be enhanced. In addition, increasing the strength of the coating helps to prevent dislocation slip on the substrate surface and avoid the formation of slip steps. Slip steps are an important source of fatigue crack initiation, and reducing their formation can effectively reduce the probability of fatigue crack generation, thereby prolonging the fatigue life of the material.

[0030] The strategy of alternately stacking multiple thin films on a nanoscale is also adopted, with each layer precisely controlled to a nanoscale range. The core advantage of this multilayer structure lies in the effective hindering effect of the interfacial layer on crack propagation and dislocation movement. When a crack initiates in the coating and attempts to propagate, the interfacial layer will hinder it, forcing the crack to deflect, passivate, or terminate, thereby reducing the likelihood of the crack propagating to the substrate. At the same time, the interfacial layer also limits the movement of dislocations, reducing the aggregation of dislocations on the substrate surface, and further inhibiting the formation of slip steps. In this way, the superlattice multilayer coating not only improves the overall toughness of the coating but also enhances its resistance to fatigue crack initiation and propagation.

[0031] By carefully designing a high-strength, high-toughness superlattice multilayer coating, the present application successfully suppresses the fatigue crack sources caused by slip steps and effectively reduces the risk of substrate crack propagation due to coating cracking. This innovative coating design strategy significantly improves the fatigue life of titanium alloy materials under cyclic loading conditions, providing reliable technical support for the application of high-performance titanium alloy materials.

[0032] For illustration purposes, in the embodiments of the present application, the material with face-centered cubic structure is TiN with a Mohs hardness of 8-9, and the material with hexagonal crystal structure is AlN with a Mohs hardness of 7-8, and the substrate is titanium alloy TC4.

[0033] Among them, the first layer or the second layer has the same crystal structure as the substrate to improve the bonding strength of the coating and the substrate.

[0034] Preferably, in order to coordinate the layers of face-centered cubic structure and hexagonal structure, the thickness of the layers of face-centered cubic structure and the thickness of the layers of hexagonal structure satisfy the following formula as far away from the substrate:

[0035] ;

[0036] wherein is the thickness of the layers of face-centered cubic structure, is the thickness of the layers of hexagonal structure. It should be noted that in the above formula, the thickness of the layers of face-centered cubic structure is calculated based on the thickness of the layers of hexagonal structure, and the thickness of the layers of hexagonal structure cannot be calculated based on the thickness of the layers of face-centered cubic structure. For example, if the thickness of the layers of hexagonal structure is 1 nm, the thickness of the layers of face-centered cubic structure on the side far away from the substrate is 4 nm, and the thickness of the layers of face-centered cubic structure on the side close to the substrate can be 4 nm-6 nm, and the thickness of the subsequent layers of hexagonal structure is not calculated based on the thickness of the layers of face-centered cubic structure on the side close to the substrate, and the thickness of the layers of hexagonal structure can be selected from 1 nm-3 nm.

[0037] Specifically, in the surface coating, the thickness of the middle layer is greater than the thickness of the layers on both sides. The thickness of the middle layer can coordinate the stress between the region close to the substrate and the region on the outer surface of the coating. For example, in the middle region of the coating, the thickness of the layers of hexagonal structure is selected to be 3 nm, and the thickness of the layers of face-centered cubic structure is selected to be 6 nm. Preferably, in the surface coating, the thickness is in a linear relationship with the distance. Specifically, in the region between the middle of the coating and the substrate, the thickness increases linearly with the distance away from the surface of the substrate; in the region between the middle of the coating and the outer surface of the coating, the thickness gradually decreases as far away from the substrate.

[0038] The embodiment of the present application also provides a preparation method of the above-mentioned surface coating, comprising: S1. surface treatment of the substrate; S2. film plating on the surface of the treated substrate by using a magnetron sputtering.

[0039] Specifically, the substrate is polished until the surface roughness is less than 0.16 μm; and then the polished substrate is cleaned and dried.

[0040] Specifically, the surface to be plated of the titanium alloy is polished step by step by using 400#-5000# SiC sandpaper until the surface is free of cavities and scratches, and then mirror polishing is performed by using 1.5 μm diamond polishing paste, the surface roughness of the prepared product is less than 0.16 μm, and finally the sample is immersed and cleaned in deionized water, anhydrous ethanol and acetone for 10 min-30 min by using an ultrasonic cleaner and then dried.

[0041] The magnetron sputtering process comprises: vacuumizing, bias cleaning and film plating; the vacuum degree after vacuumizing is not greater than 2.0×10-3 The bias cleaning process is: setting the preparation temperature to 180-220℃ to heat the substrate, when the vacuum degree in the chamber is not more than 1.8*10 -3 Pa, opening the stop valve, setting the flow valve parameter to 100°, setting the argon flow to 30sccm, setting the voltage to-900V, keeping the pressure in the chamber above 1.0Pa for bias cleaning, and the cleaning time is not less than 10min. Ensure that the contaminants on the surface of the substrate can be removed, the surface of the substrate is activated, and the adhesion of the coating is ensured.

[0042] The coating process is: setting the ratio of argon flow to nitrogen flow to 2-3, the chamber working pressure to 0.2-0.3Pa, the deposition temperature to 380-420℃, adjusting the bias voltage of the magnetron sputtering equipment to-100V, and alternately depositing the first layer and the second layer. In the embodiment of the application, the argon flow is set to 17sccm. The deposition time is about 10-20min, and the specific deposition time is adjusted based on the layer thickness. The above process parameters are very critical. First, not only the deposition thickness needs to be considered, but also the grain size of the prepared layered material needs to be 1-2nm. It is known that the grain size has a great influence on the mechanical properties of the layered material. If an amorphous structure is formed, although the hardness and strength are high, the crack propagation trend is large. If the grain size is large, the toughness is large, which affects the plastic deformation and deformation capacity. Therefore, by limiting the small layer thickness and small grain size, the plastic deformation and crack propagation resistance is enhanced, and the service life of the coating under cyclic loading conditions is improved.

[0043] The target material used in magnetron sputtering is a metal Ti target (φ76.2*5mm 3 ) with a purity of 99.995% manufactured by Zhongnuoxin Material Technology Co., Ltd. and a metal Al target (φ76.2*5mm 3 ) with a purity of 99.995%.

[0044] In order to better illustrate the embodiments of the application, the application will be further described in detail through specific examples.

[0045] Example 1

[0046] The application provides a surface coating for improving metal fatigue life and a preparation method, which comprises:

[0047] S1, surface treatment of the substrate. The surface to be combined of TC4 titanium alloy is treated.

[0048] S2, coating the surface of the treated substrate by magnetron sputtering. The vacuum degree after vacuumizing is 2.0*10 -3Pa, the stop valve is opened, the flow valve parameter is set to 100°, the argon flow is set to 30sccm, the voltage is set to -900V, the pressure in the chamber is kept above 1.0Pa for bias cleaning, and the cleaning time is 10min. -3 Pa, the stop valve is opened, the flow valve parameter is set to 100°, the argon flow is set to 30sccm, the voltage is set to -900V, the pressure in the chamber is kept above 1.0Pa for bias cleaning, and the cleaning time is 10min.

[0049] The coating process is as follows: the ratio of argon flow to nitrogen flow is set to 2.43, that is, the argon flow is set to 17sccm, the nitrogen flow is set to 7sccm, the chamber working pressure is 0.2Pa-0.3Pa, the deposition temperature is 400℃, the bias voltage of the magnetron sputtering device is adjusted to -100V, and the first layer and the second layer are alternately deposited. The first layer is TiN, the second layer is AlN, the thickness of each layer in the TiN layer is the same, the thickness of each layer in the AlN layer is the same, the thickness of the TiN layer is 4nm, the thickness of the AlN layer is 2nm, and the total thickness of the coating is 1.0μm.

[0050] The prepared coating has an average grain size of 1.5nm, as shown in Figure 1 and Figure 2 The prepared coating has an average grain size of 1.5nm, as shown in

[0051] Embodiment 2

[0052] The embodiment of the present application provides a surface coating for improving metal fatigue life and a preparation method thereof, which comprises the following steps:

[0053] S1, surface treatment is performed on the substrate. The surface to be combined of the TC4 titanium alloy is treated.

[0054] S2, the surface of the treated substrate is coated by magnetron sputtering. After vacuumizing, the vacuum degree is 2.0x10 -3 Pa, the substrate is heated by setting the preparation temperature to 180℃, when the vacuum degree in the chamber is not greater than 1.8x10 -3 Pa, the stop valve is opened, the flow valve parameter is set to 100°, the argon flow is set to 30sccm, the voltage is set to -900V, the pressure in the chamber is kept above 1.0Pa for bias cleaning, and the cleaning time is 15min.

[0055] The film coating process is: setting the ratio of argon flow and nitrogen flow as 2, that is, setting the argon flow as 17sccm, setting the nitrogen flow as 8.5sccm, setting the chamber working gas pressure as 0.2Pa-0.3Pa, setting the deposition temperature as 380℃, adjusting the bias voltage of the magnetron sputtering device as-100V, and alternately depositing the first layer and the second layer. The first layer is TiN, the second layer is AlN, the thickness of each layer in the TiN layer is the same, the thickness of each layer in the AlN layer is the same, the layer thickness of TiN is 6nm, the layer thickness of AlN is 1nm, the average grain size is 1nm, and the total thickness of the coating is 1.3μm.

[0056] Example 3

[0057] The embodiment of the application provides a surface coating for improving metal fatigue life and a preparation method.

[0058] S1, performing surface treatment on a base material. The surface to be combined of TC4 titanium alloy is treated.

[0059] S2, performing film coating on the surface of the treated base material by using a magnetron sputtering. The vacuum degree after vacuumizing is 2.0*10 -3 Pa, the preparation temperature is set as 220℃ for heating the base material, when the vacuum degree in the chamber is not greater than 1.8*10 -3 Pa, the stop valve is opened, the parameter of the flow limiting valve is set as 100°, the argon flow is set as 30sccm, the voltage is set as-900V, the pressure in the chamber is kept above 1.0Pa for bias cleaning, and the cleaning time is 10min.

[0060] The film coating process is: setting the ratio of argon flow and nitrogen flow as 3, that is, setting the argon flow as 17sccm, setting the nitrogen flow as 6sccm, setting the chamber working gas pressure as 0.2Pa-0.3Pa, setting the deposition temperature as 420℃, adjusting the bias voltage of the magnetron sputtering device as-100V, and alternately depositing the first layer and the second layer. The first layer is TiN, the second layer is AlN, the thickness of each layer in the TiN layer is the same, the thickness of each layer in the AlN layer is the same, the layer thickness of TiN is 4nm, the layer thickness of AlN is 3nm, the average grain size is 2nm, and the total thickness of the coating is 1.5μm.

[0061] Example 4

[0062] Different from example 1, in the embodiment, the layer thickness of TiN is 6nm, the layer thickness of AlN is 3nm, and the average grain size is 1.5nm.

[0063] Example 5

[0064] Different from example 1, in the embodiment, the layer thickness of TiN is 4nm, the layer thickness of AlN is 1nm, and the average grain size is 1.5nm.

[0065] Example 6

[0066] Different from Example 1, in this example, the thickness of the TiN layer combined with the substrate is 4 nm, and the thickness of the adjacent AlN layer is 1 nm; in the middle region of the coating, the thickness of the TiN layer is 6 nm, and the thickness of the adjacent AlN layer is 3 nm; in the outer region of the coating, the thickness of the TiN layer is 4 nm, and the thickness of the adjacent AlN layer is 1 nm, and the thickness of the TiN layer and the thickness of the AlN layer in the remaining regions are set in a linear relationship.

[0067] Comparative Example 1

[0068] Compared with Example 1, in this comparative example, the thickness of the TiN layer is 3 nm, and the thickness of the AlN layer is 4 nm.

[0069] Comparative Example 2

[0070] Compared with Example 1, in this comparative example, the first layer is a TiC layer with a Mohs hardness of 10, and the second layer is an AlN layer with a Mohs hardness of 7.

[0071] Comparative Example 3

[0072] Compared with Example 1, in this comparative example, the coating process is as follows: the ratio of argon flow rate to nitrogen flow rate is 2-3, the chamber working pressure is 0.2 Pa-0.3 Pa, the deposition temperature is 450°C, the bias voltage of the magnetron sputtering device is adjusted to -100 V, the TiN layer and the AlN layer are alternately deposited, and the average grain size is 2.5 nm.

[0073] In order to characterize the effect of the technical scheme, the following indexes are used for judgment:

[0074] (1) The toughness index of the prepared coating is measured, H 3 / E 2 , H is the hardness, and E is the elastic modulus.

[0075] (2) Fatigue performance measurement. In the high-cycle fatigue experiment, the initial stress of the sample (substrate) is set to 50% of its yield strength, i.e. about 500 MPa, in order to more accurately evaluate the fatigue resistance of the material in actual use.

[0076] The measurement results are shown in Figure 3 and Figure 4 , and the specific detection values are shown in Table 1.

[0077] Table 1 Detection results of each example and comparative example

[0078] Item H 3 / E 2 ]]> Fatigue cycle Example 1 0.47 8.3 x 10 7 ]] Example 2 0.48 8.7 x 10 7 ]] Example 3 0.48 8.6 x 10 7 ]] Example 4 0.53 9.5 x 10 7 ]] Example 5 0.54 9.8 x 10 7 <!-- 6 -->]]> Example 6 0.60 1.4 x 10 8 ]]> Comparative Example 1 0.32 3.5 x 10 6 ]]> Comparative Example 2 0.31 4.1 x 10 6 ]]> Comparative Example 3 0.35 4.3 x 10 6 ]]>

[0079] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A surface coating for improving the fatigue life of metals, characterized in that, The surface coating is formed by alternating layers of a first layer and a second layer, and the total thickness of the coating is 1.0 μm-1.5 μm; The base material is a titanium alloy; One of the first layer or the second layer is a face-centered cubic structure, and the other of the first layer or the second layer is a hexagonal crystal system, wherein the face-centered cubic layer is bonded to the substrate; The layer thickness of the face-centered cubic structure is 4nm-6nm, and the layer thickness of the hexagonal crystal system is 1nm-3nm. The difference in Mohs hardness between the first layer and the second layer is no greater than 2; The average grain size of the first and second layers is 1nm-2nm.

2. The surface coating according to claim 1, characterized in that, As the distance from the substrate increases, the layer thickness of the face-centered cubic structure and the layer thickness of the hexagonal crystal system satisfy the following equation: ； in The layer thickness of a face-centered cubic structure The thickness is the layer thickness of the hexagonal crystal system.

3. The surface coating according to claim 1, characterized in that, The face-centered cubic layer is TiN, and the hexagonal crystal system layer is AlN.

4. The surface coating according to claim 1, characterized in that, In the surface coating, the thickness of the middle layer is greater than that of the two sides.

5. The surface coating according to claim 4, characterized in that, In the surface coating, the layer thickness has a linear relationship with the distance.

6. The method for preparing the surface coating according to any one of claims 1-5, characterized in that, include: Surface treatment of the substrate; Magnetron sputtering is used to coat the surface of the treated substrate.

7. The preparation method according to claim 6, characterized in that, The substrate is selected from titanium alloy; The substrate is polished until the surface roughness is less than 0.16 μm; The polished substrate is then cleaned and dried.

8. The preparation method according to claim 7, characterized in that, The samples were then soaked and cleaned in deionized water, anhydrous ethanol, and acetone for 10-30 minutes each using an ultrasonic cleaner, and then dried.

9. The preparation method according to claim 6, characterized in that, The magnetron sputtering process includes: vacuuming, bias cleaning, and coating. The vacuum level after evacuation is no greater than 2.0 × 10⁻⁶. -3 Pa; The bias cleaning process is as follows: the substrate is heated at a preparation temperature of 180℃-220℃, and the vacuum degree in the chamber is no greater than 1.8×10⁻⁶. -3 When the pressure reaches Pa, open the shut-off valve, set the flow limiting valve parameter to 100°, the argon flow rate to 30 sccm, and the voltage to -900V, so that the pressure in the chamber is maintained above 1.0Pa for bias cleaning, and the cleaning time is not less than 10 minutes.

10. The preparation method according to claim 9, characterized in that, The coating process is as follows: the ratio of argon flow rate to nitrogen flow rate is set to 2-3, the working pressure of the chamber is 0.2Pa-0.3Pa, the deposition temperature is 380-420℃, the bias voltage of the magnetron sputtering equipment is adjusted to -100V, and the first and second layers are deposited alternately.

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