CN120666303A - Cr/CrN alternating multilayer gradient slow-release stress coating and preparation method thereof - Google Patents

Abstract

The present invention relates to the technical field of physical vapor deposition coatings, specifically disclosing a Cr/CrN alternating multilayer gradient stress-relieving coating and a preparation method thereof. The coating comprises a multilayer Cr coating and a multilayer CrN coating, wherein the Cr coating and the CrN coating are alternately arranged from the surface of a substrate outward, with the innermost layer being the Cr coating and the outermost layer being the CrN coating. The Cr coating and the CrN coating are both prepared using a magnetron sputtering method, with all Cr coatings having the same bias voltage, and all CrN coatings having the same bias voltage, and the bias voltage of the Cr coating is less than that of the CrN coating. The technical solution provided by the present invention can solve the technical problem of the existing Cr/CrN alternating multilayer structure having discontinuous stress gradients between layers and the presence of significant stress concentration.

Description

Cr/CrN alternating multilayer gradient slow-release stress coating and preparation method thereof

Technical Field

The invention relates to the technical field of physical vapor deposition coatings, in particular to a Cr/CrN alternating multilayer gradient slow-release stress coating and a preparation method thereof.

Background

Physical vapor deposition (Physical Vapor Deposition, PVD) is a technique in which a source of material (e.g., a target) is physically vaporized or sputtered into atomic, molecular, or ionic particles under vacuum conditions and deposited on a substrate surface to form a thin film. PVD technology is widely used in the fields of machine manufacturing, aerospace, electronics, medical devices, etc., for improving hardness, wear resistance, corrosion resistance, decorative properties, etc. of material surfaces.

The common PVD process comprises (1) magnetron sputtering, which utilizes a magnetic field to restrain plasma, enhances ion bombardment efficiency, improves deposition rate and film compactness, (2) arc ion plating, which generates high-density metal ion flow through a metal target material, is suitable for preparing a high-hardness and high-binding force coating, and (3) electron beam evaporation, which utilizes a high-energy electron beam to heat a material to realize evaporation deposition, and is suitable for preparing a high-purity film. In the process, magnetron sputtering is an important means for preparing the functional coating due to the advantages of strong controllability, good uniformity of a film layer, suitability for large-area deposition and the like.

In industrial application, crN coating has excellent hardness (> 25 GPa), wear resistance and oxidation resistance, and is widely applied to surface strengthening treatment of key parts such as aeroengine blades, die stamping parts, cutting tools and the like. However, conventional single layer CrN coatings tend to be accompanied by higher residual stresses (> 3 GPa) while achieving high hardness, resulting in a thickness limited to within 20 μm. Once the thickness of the coating is increased, interfacial peeling or macrocracks are easily caused, and the bonding strength and service life of the coating are seriously affected, so that the practical application of the coating under the heavy-duty friction and wear working condition is limited.

In order to solve the problems, the prior art proposes to adopt a multi-layer Cr/CrN coating structure, and release and distribution optimization of residual stress are realized to a certain extent by the combined action of a Cr soft layer and a CrN hard layer, so that the toughness and the crack resistance of the coating are improved. However, most of existing multilayer coating designs adopt a structure form with abrupt changes of interlayer components and thickness, so that stress gradients among layers are discontinuous, obvious stress concentration phenomenon still exists, and stable service requirements of the ultra-thick coating (> 50 μm) under complex working conditions are difficult to meet.

In addition, the current preparation process of most Cr/CrN coatings adopts fixed bias parameters for deposition, and the ion bombardment energy cannot be dynamically adjusted according to the requirements of each functional layer, so that the cooperative optimization of the comprehensive properties such as good interfacial binding force, high hardness, low residual stress and the like is difficult to realize simultaneously under a single process condition.

Therefore, a Cr/CrN alternating multilayer gradient slow-release stress coating and a preparation method thereof are needed at present, and can effectively relieve interlayer stress concentration and improve the overall bonding strength and structural stability while ensuring the high hardness and wear resistance of the coating so as to meet the application requirements of high-performance and long-service-life surface engineering.

Disclosure of Invention

The invention aims to provide a Cr/CrN alternating multilayer gradient slow-release stress coating and a preparation method thereof, so as to solve the technical problem that the stress gradient between layers of a Cr/CrN alternating multilayer structure in the prior art is discontinuous, and the phenomenon of obvious stress concentration still exists.

In order to achieve the above purpose, the invention adopts the following technical scheme:

the Cr/CrN alternating multilayer gradient slow-release stress coating comprises a plurality of layers of Cr coatings and a plurality of layers of CrN coatings, wherein the Cr coatings and the CrN coatings are alternately arranged outwards from the surface of a substrate, the innermost layer is the Cr coating, the outermost layer is the CrN coating, the Cr coatings and the CrN coatings are prepared by adopting a magnetron sputtering method, the bias voltages of all the Cr coatings are the same, the bias voltages of all the CrN coatings are the same, and the bias voltage of the Cr coatings is smaller than the bias voltage of the CrN coatings.

The preparation method of the Cr/CrN alternating multilayer gradient slow-release stress coating is used for preparing the Cr/CrN alternating multilayer gradient slow-release stress coating and comprises the following steps of:

s1, preprocessing a matrix, namely polishing the matrix to Ra <0.1 mu m, and carrying out argon ion glow cleaning after ultrasonic cleaning;

s2, alternately depositing a Cr coating and a CrN coating on the surface of the substrate in sequence by adopting a magnetron sputtering method, wherein the method specifically comprises the following steps of:

s2-1.Cr coating deposition, namely, applying-60V bias voltage in Ar atmosphere, and depositing for 10 minutes;

s2-2.CrN coating deposition, namely applying-120V bias voltage in Ar/N ₂ mixed atmosphere, and depositing for 10 minutes;

s2-3, repeating the step S2-1 and the step S2-2 to form a 20-layer alternating structure.

The principle and the advantages of the scheme are as follows:

1. The scheme uses lower bias (-60V) when the Cr layer is deposited, can reduce ion bombardment energy and damage to a lower layer structure (a substrate or a lower layer film layer), thereby effectively controlling residual stress accumulation (< 1.5 GPa), and uses higher bias (-120V) when the CrN layer is deposited, can enhance ion bombardment effect, improve ionization rate and compactness, and obtain higher hardness (> 30 GPa). And the bias voltage is switched layer by layer, so that each functional layer can be formed under the optimal energy condition, thereby realizing the cooperative optimization of hardness and toughness in a macroscopic sense, and finally obtaining the composite coating with the total thickness of 100 mu m and excellent bonding force and crack resistance. The scheme breaks through the limitation of the traditional fixed bias voltage process, so that the ultra-thick coating (> 50 μm) can still keep good binding force and structural stability.

2. The Cr layer has good plasticity and low hardness, can be used as a buffer layer to relieve compression stress generated by adjacent CrN hard layers, can provide high hardness and wear resistance, can generate tensile stress in the cooling process due to high thermal expansion coefficient, and can easily cause interface cracking if no buffer layer exists.

3. The scheme uses magnetron sputtering technology instead of more expensive methods such as arc ion plating or electron beam evaporation, and the like, so that the equipment investment and the operation cost are reduced while the high quality is ensured. And the CrN layer can realize higher compactness and crystal orientation consistency under the (-120V) bias voltage higher than that of the Cr layer, so that the CrN layer still has excellent tribological performance (the friction coefficient is as low as 0.23) under the premise of high hardness (30 GPa). The whole coating of this scheme structural design is reasonable, takes into account performance and cost, has good industrialization application prospect.

Preferably, as a modification, the Cr coating and the CrN coating have the same thickness, and the monolayer thickness is 5+/-0.5 mu m.

The method has the beneficial effects that 1) the stress distribution is uniform, the stress concentration between layers is relieved, the Cr layer has lower hardness and higher plasticity, the CrN layer has high hardness and is accompanied with higher residual stress, and if the thickness difference between the Cr layer and the CrN layer is larger, obvious stress mutation can be formed at the interface. According to the scheme, the thicknesses of the Cr coating and the CrN coating are set to be the same, so that each layer of material has similar bearing capacity and deformability in the thickness direction, local stress concentration caused by overlarge thickness of a certain layer is avoided, gradual release stress is favorably realized, crack initiation tendency is reduced, and the toughness of the coating is improved.

2) The overall uniformity and the process repeatability of the coating are improved, wherein in the magnetron sputtering process, the deposition time and the thickness are positively correlated, and the equal thickness design means that the deposition time of each layer is consistent (for example, 10 minutes), and the process parameters (bias voltage, air pressure, flow rate and the like) can be uniformly set and recycled. Therefore, the method can obviously improve process controllability and repeatability, reduce thickness fluctuation caused by artificial or equipment errors, be easier to realize industrialized mass production and improve the yield.

3) The synergistic effect of the functional layers is ensured, the comprehensive performance is enhanced, the Cr layer is taken as a buffer layer, the CrN layer is taken as a wear-resistant layer, each layer bears a definite function role, if one layer is too thin, the function of the layer is difficult to fully play, and if the layer is too thick, the whole balance can be destroyed. According to the scheme, the thickness of the single layer is set to be 5+/-0.5 mu m, so that the respective functions can be exerted, local stress accumulation can not be caused, the synergy among the functional layers is good, the comprehensive optimization of hardness, toughness and binding force is realized, and the composite coating with stable and reliable performance is finally obtained.

Preferably, as a modification, the number of layers of the Cr coating and the CrN coating is 10, and the total thickness is 100+/-5 mu m.

The method has the beneficial effects that 1) stable deposition of the ultra-thick coating is realized, the limitation of the traditional thickness is broken through, the thickness of the traditional CrN single-layer coating is generally not more than 20 mu m due to the limitation of high residual stress, the stress concentration can be relieved through soft and hard alternation, and if the number of layers is too small (for example, only 2-4 layers), the effective stress release can not be realized. According to the scheme, a multi-layer system with 20 layers is formed by arranging 10 layers of Cr/CrN alternating structures, on the premise of 5 mu m of each layer, an ultra-thick coating with the total thickness of 100 mu m is realized, the service capacity of the coating under a heavy-load friction working condition can be remarkably improved, the limitation of the prior art on the thickness of the CrN coating is broken through, and the application boundary of the CrN coating is expanded.

2) The Cr layer has lower hardness and higher plasticity, the CrN layer provides high hardness and wear resistance, a buffer mechanism for releasing stress layer by layer can be formed alternately between layers, and the stress distribution is more uniform as the number of layers is more. The structural design of the 10 Cr+10 CrN layers ensures that stable stress gradient distribution is formed in the coating, interface cracking caused by difference of thermal expansion coefficients between layers is avoided, and the structural stability and durability of the coating under thermal cycle or impact load are improved.

3) The full effect of the functional layers is ensured, the hardness, the toughness and the binding force are considered, the thickness of each layer of 5 mu m can fully exert the respective functions (Cr is used as buffer and CrN is used as wear resistance), if the number of layers is too small (for example, only 2-3 layers), the effective multilayer synergistic effect is difficult to form, and if the number of layers is too large (for example, more than 20 layers), the process complexity and the cost can be increased. The scheme adopts the design of 10 layers, obtains the best balance between the performance and the process, ensures the effective contribution of each functional layer, avoids the process control difficulty caused by excessive layering, and finally realizes the comprehensive performance of high hardness (30 GPa), low friction coefficient (0.23) and strong binding force.

Preferably, as a modification, the bias voltage of the Cr coating is-60V, and the bias voltage of the CrN coating is-120V.

The method has the beneficial effects that 1) the dynamic regulation and control of ion bombardment energy is realized, the performance of each layer is optimized, in the magnetron sputtering process, the bias voltage (matrix negative voltage) directly influences the energy of deposited particles, the lower bias voltage (such as-60V) reduces the ion bombardment intensity, the higher bias voltage (such as-120V) enhances the ion bombardment effect, and the density and hardness are improved. The scheme adopts-60V bias to the Cr layer, can reduce damage to a substrate or a lower film layer, controls residual stress accumulation (< 1.5 GPa), is suitable for being used as a buffer layer and a bonding layer, and adopts-120V bias to the CrN layer, can improve ionization rate and atom migration capacity, remarkably improves coating hardness (> 30 GPa), and is beneficial to forming a compact and wear-resistant surface structure. This bias layering control strategy achieves deposition of each layer of material under optimal energy conditions, resulting in a more excellent overall performance.

2) The hardness and toughness are balanced, stable deposition of thick films is realized, namely, although the hardness can be improved by high bias voltage, residual stress is increased, if all layers are high bias voltage, the overall stress is easily overlarge to crack or peel, different bias voltages are applied to layers, and the alternate deposition of soft and hard can be realized, so that the stress is released layer by layer. According to the scheme, the Cr layer is deposited at a lower bias voltage, so that compression stress brought by the upper CrN layer is relieved, the CrN layer is deposited at a higher bias voltage, high hardness and wear resistance are provided, the cooperative optimization of hardness and toughness is realized through periodic switching of the bias voltage, and finally, good binding force and structural stability can be kept under the condition that the total thickness reaches 100 mu m.

3) The friction performance and service life of the coating are improved, the CrN layer is more compact to deposit under the bias of-120V, the surface roughness is lower, the grain arrangement is more ordered, the friction coefficient is reduced, and the abrasion resistance is improved. On the premise of the hardness of >30 GPa, the friction coefficient can be reduced to 0.23, which is obviously superior to the traditional CrN single-layer coating (the friction coefficient is usually > 0.3), and the service life of the coating under severe working conditions such as heavy load, high temperature and the like is prolonged.

Preferably, as a modification, the monolayer deposition period of the Cr coating and the CrN coating is 10 minutes, and the bias voltage is automatically switched every 10 minutes.

The method has the beneficial effects that 10 minutes is set as a complete single-layer deposition period, the time window is reasonable, the bias voltage switching and the layer sequence are strictly synchronous, the deviation of the performance of the functional layer from the expected performance caused by time mismatch is avoided, and the automation degree and the repeatability of the whole process flow can be improved.

Under the same power and air pressure conditions, the deposition time is positively correlated with the thickness of the film, and all layers are deposited for 10 minutes, so that the thickness of each layer is basically consistent (5+/-0.5 mu m), and the influence on stress distribution caused by uneven thickness due to time difference is avoided. Thereby remarkably improving the overall uniformity and structural stability of the coating, reducing the formation of local stress concentration or weak areas, and being more beneficial to maintaining good service performance under the condition that the total thickness reaches 100 mu m.

The combination of fixed time (10 minutes) +fixed bias voltage (-60V/-120V) is simple and clear in parameter setting and convenient for programmed control, so that the operation difficulty is remarkably reduced, the process repeatability is improved, and the method has good industrialized popularization value.

Preferably, in the step S1, the ultrasonic cleaning time is 20min, the glow cleaning bias voltage is-600V, and the time is 30min.

The technical scheme has the beneficial effects that 1) the surface cleanliness of the substrate can be improved, and the binding force between the coating and the substrate is enhanced. Contaminants on the surface of the substrate (such as grease, oxide and dust) can obviously influence the adhesive force of the coating, organic contaminants on the surface are removed by cavitation effect through ultrasonic cleaning, and the adsorbed substances and the oxide layer are removed by high-energy Ar+ ion bombardment through glow cleaning. The scheme adopts ultrasonic cleaning time of 20 minutes to ensure that cleaning liquid such as deionized water, acetone, alcohol and the like fully acts to thoroughly remove surface pollutants, adopts glow cleaning under-600V bias to enable Ar+ ions to have enough kinetic energy, and effectively removes residual oxide layers and adsorbed gas on the surface of a substrate. Therefore, the method can obviously improve the interface bonding strength between the coating and the substrate and reduce the risk of peeling or falling off in the subsequent deposition process.

2) The scheme can improve initial nucleation conditions and promote uniformity and compactness of the coating. Surface defects or contamination can affect the initial nucleation process, resulting in coarse or maldistribution of grains, and clean and activated surfaces facilitate ordered arrangement and uniform nucleation of atoms. The optimized cleaning parameters (20 min ultrasonic+30 min glow cleaning) are adopted to obtain a highly clean and high-activity surface state, so that the Cr/CrN coating can form a uniform and fine grain structure at the initial stage of deposition, and the composite coating with higher compactness, flatness and stable performance is finally obtained.

3) The scheme can support the deposition stability of the subsequent thick film and prolong the service life. In a multilayer structure with a total thickness of up to 100 μm, the bonding between the matrix and the first layer Cr is particularly critical, and if the initial bonding is poor, the overall spalling or crack propagation tends to occur with an increase in the number of layers. The cleaning parameters adopted by the scheme ensure that the innermost Cr layer and the matrix have good bonding foundation, provide guarantee for stable deposition of a subsequent multilayer structure, and remarkably prolong the service life of the coating in severe environments such as high temperature, heavy load and the like.

Preferably, as a modification, in the step S2, the target power of the magnetron sputtering is constant at 3kW and the working air pressure is 0.6Pa.

The method has the beneficial effects that 1) the scheme can realize stable plasma state and improve sputtering efficiency and film forming quality. The constant target power of 3kW can provide enough sputtering energy to enable Cr atoms to be fully separated from the surface of the target material and uniformly distributed, and the working air pressure of 0.6Pa is in an ideal interval of magnetron sputtering, so that the Ar+ ion bombardment efficiency is ensured, excessive gas molecules are prevented from interfering the deposition process, and a coating structure with high density, good adhesive force and uniformity is integrally realized.

2) The scheme can support a bias dynamic alternate control strategy and ensure the performance consistency of each layer. The constant 3kW power and the 0.6Pa air pressure ensure that each layer (whether Cr or CrN) can be deposited under the same basic condition, and the bias voltage switching strategy is combined to realize the layer-by-layer optimization and stable output of the performances of hardness, stress, binding force and the like, so that the multilayer composite structure with the total thickness of 100 mu m and excellent comprehensive performance is finally obtained.

3) The scheme can reasonably control the cost, and has both performance and economy. Too high target power (e.g., >5 kW) can increase deposition rate but can increase energy and equipment loss, and too low power (< 2 kW) can result in slow deposition rate and loose film, 0.6Pa is in the conventional sputtering pressure range, without special vacuum system support. 3kW+0.6Pa is the best compromise point between performance and cost, can reduce equipment investment and running cost on the premise of guaranteeing coating quality, and has good industrialized popularization value.

Preferably, in the step S2, the flow rate of Ar is 100sccm when the Cr coating is deposited, the flow rate of Ar is 80sccm when the crn coating is deposited, and the flow rate of n ₂ is 20sccm.

The technical scheme has the beneficial effects that 1) the scheme can realize the accurate atmosphere regulation and control of the Cr and CrN deposition process. The Cr layer is deposited by physical sputtering in a pure Ar atmosphere, and the CrN layer is formed by reacting Cr atoms with N ₂ in a mixed Ar/N ₂ atmosphere by reactive sputtering. Ar is mainly used for maintaining plasma and sputtering process, N ₂ provides nitrogen source and participates in chemical reaction to form CrN. The Cr layer uses higher Ar flow (100 sccm), so that the plasma density can be enhanced, the sputtering efficiency can be improved, and a compact and uniform metal layer can be obtained. The CrN layer uses a low Ar flow rate (80 sccm) +20sccmN ₂, which can ensure sufficient nitrogen source supply, promote the sufficient reaction of Cr and N, and form a high quality CrN layer. The scheme can realize the layer-by-layer controllable deposition of Cr and CrN materials by precisely controlling the gas proportion.

2) The scheme supports a bias dynamic alternating strategy and ensures the performance consistency of each layer. During the bias switching process (-60V/120V), if the gas environment is unstable, the particle energy distribution and the film forming quality can be affected, and the gas proportion of each layer is fixed, so that the uniform deposition foundation can be maintained under different bias conditions. The Cr layer has high Ar flow, can reduce the plasma resistance and stabilize ion bombardment under low bias (-60V). The CrN layer is introduced with N ₂ + to properly reduce Ar flow, so that the ionization rate and the reaction efficiency under high bias (-120V) can be optimized. The two are cooperated to ensure that each functional layer is formed under the optimal atmosphere condition, and finally the layer-by-layer optimization and stable output of the performances of hardness, stress, binding force and the like are realized.

3) The scheme can reasonably control the cost, and has both performance and economy. Too high flow of N ₂ can dilute Ar to affect the stability of plasma, too low flow of N ₂ can cause incomplete CrN reaction, unreacted Cr or unstable phase composition, and reasonable adjustment of the ratio of Ar to N ₂ can realize balance between performance and cost. The 80sccmAr+20sccmN ₂ is a mixture ratio which is fully reacted and economical and reasonable, can obtain a CrN layer with high hardness (30 GPa) and low friction coefficient (0.25), simultaneously avoids the problem of deposition rate reduction or equipment corrosion caused by excessive nitrogen, and has good industrialized application prospect.

Preferably, in the step S2, the substrate is rotated at a speed of 5 rpm.

The beneficial effects are that 1) the scheme can improve the uniformity of the coating thickness and the component distribution. In the magnetron sputtering process, particles emitted by the target material are distributed in an angle, a shadow effect exists, and if a substrate is static, particle flux received by different areas is inconsistent, so that the thickness and the composition of a film layer are uneven. In the scheme, the substrate rotates at 5rpm, so that all areas on the surface of the substrate face the target in turn, the shadow effect is effectively eliminated, the uniformity and consistency of the coating in space are improved, and the multilayer structure with the total thickness of 100 mu m is particularly beneficial to maintaining the performance stability of each layer.

2) The scheme can improve the uniformity of ion bombardment and strengthen the binding force of the film base. Bias voltage (-60V or-120V) is applied in the deposition process to enable the ions to continuously bombard the surface of the substrate, when the substrate is static, local areas can be damaged or overheated due to long-time bombardment, and bombardment energy can be distributed on the surface more uniformly through rotation. The rotation speed of 5rpm can ensure the even distribution of ion energy, can not influence the film forming process or cause centrifugal effect due to the overhigh rotation speed, obviously improves the interface bonding strength between the coating and the matrix, and reduces the peeling risk.

3) The scheme can optimize atom migration and surface diffusion, and improve compactness and crystal quality. The substrate rotates to make the deposited particles have more machines on the surface to find the position with lower energy, which is favorable for ordered arrangement of crystal grains and promotes densification and optimization of lattice orientation. In the Cr/CrN alternate deposition process, the rotation is helpful to form finer, uniform and compact grain structures, especially in the CrN layer, the hardness and wear resistance of the CrN layer can be obviously improved, and finally the composite coating with excellent comprehensive mechanical properties is obtained.

Drawings

FIG. 1 is a schematic representation of a coating coupon of examples and comparative examples of the present invention.

FIG. 2 is a schematic representation of the indentation of an embodiment of the present invention under a load of 150kgf of a Rockwell hardness tester.

FIG. 3 is a schematic representation of the indentation of the comparative example of the present invention under a load of 150kgf of Rockwell hardness tester.

FIG. 4 is a schematic representation of the indentation morphology of an embodiment of the present invention under a load of 0.25g for a micrometer indenter.

Fig. 5 is a schematic representation of the indentation morphology of the comparative example of the present invention under a load of 0.25g for a micrometer indenter.

Fig. 6 is a schematic representation of the coefficient of friction over time for the examples and comparative examples of the present invention.

Fig. 7 is a schematic view of scratch morphology according to an embodiment of the present invention.

FIG. 8 is a schematic representation of the scratch morphology of a comparative example of the present invention.

Detailed Description

The following is a further detailed description of the embodiments:

Examples

The invention provides a Cr/CrN alternating multilayer gradient slow-release stress coating, which comprises a plurality of layers of Cr coatings and a plurality of layers of CrN coatings, wherein the Cr coatings and the CrN coatings are alternately arranged outwards from the surface of a substrate, the innermost layer is the Cr coating, and the outermost layer is the CrN coating. The Cr coating and the CrN coating have the same thickness, and the single-layer thickness is 5+/-0.5 mu m. The number of layers of the Cr coating and the CrN coating is 10, and the total thickness is 100+/-5 mu m.

The Cr coating and the CrN coating are prepared by a magnetron sputtering method, the bias voltages of all the Cr coating are the same, the bias voltages of all the CrN coating are the same, and the bias voltages of the Cr coating are smaller than those of the CrN coating. Specifically, the bias voltage of the Cr coating is-60V, and the bias voltage of the CrN coating is-120V. The single layer deposition cycles for both the Cr coating and the CrN coating were 10 minutes, with the bias voltage being switched automatically every 10 minutes.

TABLE 1 materials, thicknesses, biases and functions of the layers of the coating

Sequence of layers	Material	Thickness of (L)	Bias voltage	Function of
					1	Cr	5μm	-60V	Low stress bonding layer
2	CrN	5μm	-120V	High hardness layer
					3	Cr	5μm	-60V	Stress buffer layer
......	......	......	......	......
					20	CrN	5μm	-120V	Wear-resistant surface layer

The invention also provides a preparation method of the Cr/CrN alternating multilayer gradient slow-release stress coating, which is used for preparing the Cr/CrN alternating multilayer gradient slow-release stress coating and comprises the following steps:

S1, preprocessing a matrix, namely preprocessing the matrix, wherein the method specifically comprises the following steps of:

S1-1, preparing a 304 stainless steel serving as a matrix, polishing the matrix to Ra <0.1 mu m, reducing the surface roughness of the matrix and improving the adhesive force of the coating.

S1-2, ultrasonic cleaning, namely sequentially carrying out ultrasonic cleaning on the substrate by using deionized water, acetone and alcohol for 20min, and removing pollutants such as greasy dirt, dust and the like on the surface of the substrate.

S1-3, installing the substrate, namely installing the substrate after ultrasonic cleaning on a substrate table, and confirming that the rotation function of the substrate table is normal, so that the requirement of a rotation speed of 5rpm can be met.

And S1-4, vacuumizing, namely vacuumizing a vacuum chamber where the substrate table is positioned to 9.9X10 ^-4 Pa by a vacuum pump, so as to ensure no air residue in the vacuum chamber and avoid oxidization and pollution.

S1-5, glow cleaning, namely carrying out glow cleaning by argon ion bombardment, wherein the bias voltage of the glow cleaning is 600V, and the duration time is 30min. The high-energy Ar ⁺ ions are utilized to bombard the surface of the matrix, so that adsorbates and oxide layers are removed, and the bonding strength between the coating and the aggregate is remarkably improved.

S2, alternately depositing a Cr coating and a CrN coating on the surface of the substrate in sequence by adopting a magnetron sputtering method, wherein the method specifically comprises the following steps of:

S2-1.Cr coating deposition, namely, applying-60V bias voltage in Ar atmosphere, depositing for 10 minutes, wherein the target power is constant at 3kW, the working air pressure is 0.6Pa, the Ar flow is 100sccm, and the substrate rotates at the speed of 5 rpm.

S2-2.CrN coating deposition, namely applying-120V bias voltage in Ar/N ₂ mixed atmosphere, depositing for 10 minutes, wherein the target power is constant at 3kW, the working air pressure is 0.6Pa, the Ar flow is 80sccm, the N ₂ flow is 20sccm, and the substrate rotates at a speed of 5 rpm.

S2-3, repeating the step S2-1 and the step S2-2 to form a 20-layer alternating structure, and automatically switching the bias voltage once after each layer is completed.

S3, cooling and sampling, namely turning off a power supply after the deposition is finished, taking out a matrix after the system is naturally cooled, and carrying out subsequent detection on the sample.

TABLE 2 deposition parameters of Cr coating and CrN coating in step S2

Parameters (parameters)	Cr coating	CrN coating
			Target power	3kW(DOMS)	3kW(DOMS)
Working air pressure	0.6Pa	0.6Pa
			Ar flow rate	100sccm	80sccm
N 2 flow	0	20sccm
			Bias voltage	-60V	-120V
Deposition time	10 Min/layer	10 Min/layer
			Rotation of the substrate	5rpm	5rpm

Comparative example

A preparation method of a Cr/CrN alternating multilayer gradient slow-release stress coating is different from the embodiment in that a single-60V bias process is adopted, namely, a step S2-1 and a step S2-2 are both biased by-60V.

The coating blocks obtained in the comparative examples are inferior to the coating blocks obtained in the examples in terms of the surface hardness, binding force, fracture toughness, residual stress and other performance indexes, and are shown in Table 3.

TABLE 3 comparison of the various Performance indices of the coating swatches obtained in the examples and the coating swatches obtained in the comparative examples

Performance index	Examples	Comparative example
			Surface hardness	31.5±0.8GPa	25.2±0.5GPa
Binding force (HF grade)	HF1	HF2
			Fracture toughness	7.9MPa·m1/2	6.3MPa·m1/2
Residual stress	0.8±0.2GPa	1.2±0.3GPa
			Critical load Lc	75.3±1.2N	60.2±1.1N
Coefficient of friction	0.23	0.30

Examples and comparative examples the coating slips obtained are shown in fig. 1, in which the left side of fig. 1 is the coating slip obtained for the examples and the right side is the coating slip obtained for the comparative examples.

Experiment 1 HRC indentation binding force

The coating coupons obtained in the examples and comparative examples were ballasted separately using a Rockwell hardness tester load of 150 kgf. The coating sample block obtained by alternating bias voltage of the example-60V/-120V is complete in appearance and free of cracks after one circle of coating indentation, as shown in figure 2, and shows that the bonding force between the coating and the substrate is strong. The coating sample obtained by the single-60V bias voltage of the comparative example is shown in figure 3, obvious cracks and partial falling off occur at the edges of the coating indentation, and the binding force is weaker than that of the coating sample obtained by the alternating bias voltage of the example-60V/-120V.

Experiment 2 micron indentation morphology

The micro-indentation instrument is used for testing the micro-mechanical property of the coating, under the load of 0.25g, the coating sample block obtained by alternately biasing the sample block in the embodiment-60V/-120V is shown in the figure 4, the coating indentation is crack-free, and the coating sample block obtained by biasing the sample block in the comparative example by single-60V is shown in the figure 5, the coating is ring-shaped crack, the coating stress is large, and the expansion coefficient is not matched with the matrix.

Experiment 3 coefficient of friction

The change in coefficient of friction over time for the coating swatches from example-60V/-120V alternating bias and the coating swatches from comparative example single-60V bias is shown in figure 6. The comparative example single-60V bias resulted in a coating coupon, the-60V fixed bias induced residual stress build-up and microcrack propagation in the coating, which increased surface roughness and was prone to abrasive grain generation during rubbing, resulting in a higher coefficient of friction than the coating coupon obtained with the example-60V/-120V alternating bias.

Experiment 4 scratch morphology

Examples-60V/-120V were alternately biased to give a coating coupon with a scratch profile as shown in figure 7, and comparative examples were biased to give a coating coupon with a single-60V bias with a scratch profile as shown in figure 8. The scratch morphologies of the example coating swatches and the comparative coating swatches were characterized and the results are shown in table 3.

TABLE 4 scratch morphology characterization of the coating coupons obtained in the examples and the coating coupons obtained in the comparative examples

	Bias voltage	Critical load Lc	Scratch topographical features
				Examples	-60V/-120V alternates	75.3±1.2N	The scored edges were smooth, without significant flaking, with only slight plastic deformation of the surface.
Comparative example	Single-60V	60.2±1.1N	The edges of the scratches have transverse cracks, and the coating is peeled off in a large area.

Compared with the prior art, the invention has the following technical advantages:

1. the balance of hardness and toughness is realized through periodical switching of bias voltage, and the preparation of the high-binding force and toughness coating with the total thickness of 100 mu m is realized.

And 2.Cr and CrN are alternately transited, so that the stress is effectively released layer by layer, and the micro-crack expansion of interfaces caused by difference of thermal expansion coefficients between layers is reduced.

3. The friction coefficient is reduced to 0.23 when the hardness is more than 30GPa, and the preparation cost of the coating is obviously reduced.

The foregoing is merely exemplary of the present application, and specific technical solutions and/or features that are well known in the art have not been described in detail herein. It should be noted that, for those skilled in the art, several variations and modifications can be made without departing from the technical solution of the present application, and these should also be regarded as the protection scope of the present application, which does not affect the effect of the implementation of the present application and the practical applicability of the patent. The protection scope of the present application is subject to the content of the claims, and the description of the specific embodiments and the like in the specification can be used for explaining the content of the claims.

Claims (10)

1. The Cr/CrN alternating multilayer gradient slow-release stress coating is characterized by comprising a plurality of layers of Cr coatings and a plurality of layers of CrN coatings, wherein the Cr coatings and the CrN coatings are alternately arranged outwards from the surface of a substrate, the innermost layer is the Cr coating, the outermost layer is the CrN coating, the Cr coatings and the CrN coatings are prepared by adopting a magnetron sputtering method, the bias voltages of all the Cr coatings are the same, the bias voltages of all the CrN coatings are the same, and the bias voltage of the Cr coatings is smaller than the bias voltage of the CrN coating.
2. 2. The Cr/CrN alternating multilayer gradient slow-release stress coating according to claim 1, wherein the thickness of the Cr coating is the same as the thickness of the CrN coating, and the single-layer thickness is 5+/-0.5 μm.
3. 3. The Cr/CrN alternating multilayer gradient slow-release stress coating according to claim 2, wherein the number of layers of the Cr coating and the CrN coating is 10, and the total thickness is 100+ -5 μm.
4. 4. The Cr/CrN alternating multilayer gradient slow-release stress coating according to claim 3, wherein the bias voltage of the Cr coating is-60V and the bias voltage of the CrN coating is-120V.
5. 5. The Cr/CrN alternating multilayer gradient slow-release stress coating according to claim 4, wherein the single layer deposition cycles of the Cr coating and the CrN coating are each 10 minutes, and the bias voltage is automatically switched every 10 minutes.
6. The preparation method of the Cr/CrN alternating multilayer gradient slow-release stress coating is characterized by comprising the following steps of:

   s1, preprocessing a matrix, namely polishing the matrix to Ra <0.1 mu m, and carrying out argon ion glow cleaning after ultrasonic cleaning;

   s2, alternately depositing a Cr coating and a CrN coating on the surface of the substrate in sequence by adopting a magnetron sputtering method, wherein the method specifically comprises the following steps of:

   s2-1.Cr coating deposition, namely, applying-60V bias voltage in Ar atmosphere, and depositing for 10 minutes;

   s2-2.CrN coating deposition, namely applying-120V bias voltage in Ar/N ₂ mixed atmosphere, and depositing for 10 minutes;

   s2-3, repeating the step S2-1 and the step S2-2 to form a 20-layer alternating structure.
7. 7. The method for preparing a Cr/CrN alternating multilayer gradient slow release stress coating according to claim 6, wherein in the step S1, the ultrasonic cleaning time is 20min, the glow cleaning bias voltage is 600V, and the glow cleaning time is 30min.
8. 8. The method of claim 7, wherein in the step S2, the target power of the magnetron sputtering is 3kW, and the working air pressure is 0.6Pa.
9. 9. The method for preparing a Cr/CrN alternating multilayer gradient slow-release stress coating according to claim 8, wherein in the step S2, ar flow is 100sccm when the Cr coating is deposited, ar flow is 80sccm when the CrN coating is deposited, and N ₂ flow is 20sccm.
10. 10. The method for preparing a Cr/CrN alternating multilayer gradient slow-release stress coating according to claim 9, wherein in the step S2, the substrate is rotated at a speed of 5 rpm.