CN109898051B - Wear-resistant and corrosion-resistant DLC/SiNxComposite film and preparation method thereof - Google Patents

Abstract

A wear-resistant and corrosion-resistant DLC/SiN _x composite film and a preparation method thereof; the composite film prepares an amorphous metal or alloy modified layer on the surface of a metal or alloy substrate, and sequentially prepares SiN _x by using a magnetron sputtering technology Film, DLC film. The preparation method is as follows: placing a metal or alloy substrate in a magnetron sputtering device, bombarding the surface of the metal or alloy substrate with plasma, and performing ion etching on the surface of the metal or alloy substrate or performing ion implantation at the same time as ion etching to obtain a surface modification. After the property layer was formed, the SiN _x thin film and the DLC thin film were prepared in situ on the surface modified layer by magnetron sputtering. The diamond-like thin film prepared by the invention has the advantages of high cost and high efficiency. The substrate can be ion-cleaned, and the ionization rate of the carbon-containing atmosphere can be improved. At the same time, the substrate bias can be applied to effectively improve the overall performance of the composite film. In particular, the RF substrate bias will not greatly reduce the bias with the increase of the film thickness. Pressure effect, suitable for large-scale applications.

Description

A kind of wear-resistant and corrosion-resistant DLC/SiNx composite film and preparation method thereof

technical field

The invention discloses a wear-resistant and corrosion-resistant DLC/ _SiNx composite film and a preparation method, which belong to the technical field of diamond-like film material preparation.

Background technique

Diamond-like carbon films have excellent mechanical, friction resistance, corrosion resistance, and can be deposited at low temperature, and have great application potential in tribology, biomedical and other fields. However, the diamond-like carbon film has a characteristic - high internal stress, which makes the bonding force of the film base very weak and its own thickness is very limited. A transition layer or doping must be added for such diamond films. Doping, on the other hand, may weaken the performance of a certain aspect of the diamond-like carbon film. Therefore, finding a suitable transition layer is the key to promoting the application of diamond-like carbon films. The transition layer not only affects the bonding force of the diamond-like carbon film, but also has a great influence on the corrosion resistance. Therefore, in addition to the high bonding strength with the matrix and the diamond-like carbon film, it also has a high corrosion resistance and does not accelerate the corrosion of the film or substrate.

At present, there are three main preparation methods for diamond-like carbon films: cathodic arc deposition, plasma enhanced CVD (PECVD) and magnetron sputtering.

Cathodic arc is one of the earliest methods used to deposit diamond-like carbon films. It is to deposit carbon atoms on the substrate under the action of a strong electric field. The main defects are: 1. The prepared diamond-like carbon films have extremely high internal The stress limits the thickness of the diamond-like carbon film to the nanometer level, and it is difficult to add a transition layer or doping; 2. The strong electric field causes a large number of graphite particles to be bombarded and finally deposited on the substrate, so high-quality diamond-like carbon film cannot be obtained. Adding a magnetic filter device to reduce graphite particles will filter a large part of carbon ions or atoms at the same time and reduce the deposition efficiency, and the filter device is complicated and costly. Although magnetic filtration cathodic arc can prepare diamond-like carbon films with high sp3C content, it cannot be applied industrially and is not favored by enterprises.

The deposition efficiency of the diamond-like carbon film prepared by PECVD is high, and the sp3C content of the diamond-like carbon film is relatively low, and the internal stress is relatively low, and the comprehensive performance is excellent. However, its doping elements must be input in the form of atmosphere, which greatly hinders the preparation of metal-doped films diamond film.

Magnetron sputtering mainly includes ion source assisted magnetron sputtering and DC bias magnetron sputtering; ion source assisted magnetron sputtering can prepare diamond-like carbon films with high bonding strength and many types, but the overall performance is slightly worse. Source and maintenance costs are high. When DC bias magnetron sputtering is used to prepare diamond-like carbon films, the metal target is insulated due to the formation and accumulation of carbides on the target surface during sputtering, and the positive ions bombarding the target surface will accumulate on the target surface, resulting in the potential of the target. The electric field between the electrodes gradually decreases until the glow discharge is extinguished and the sputtering stops. At the same time, due to the poor conductivity of the DLC film itself, the DC bias effect will weaken or even no longer work, resulting in limited film deposition thickness. . In the three different preparation methods, the substrate bias is essential, but since the conductivity of the diamond-like carbon film is extremely low, and the prior art usually uses a DC bias, the substrate bias increases with the increase of the deposition thickness. The effect on the structure of the diamond-like carbon film is weakened, and it fails completely when the thickness reaches 4 μm.

In addition, due to the defects of the DLC film, the electrolyte diffuses to the substrate along the defects, resulting in corrosion of the microbattery, and the corrosion rate is very fast even exceeding the substrate without film protection, resulting in poor long-term corrosion resistance of the substrate protected by the DLC film. Although the prior art adopts the structure of the transition layer, it does not solve the potential problem between the film layer, the transition layer and the substrate, and its corrosion resistance performance is not satisfactory.

To sum up, the prior art has the defects of unsatisfactory film-base bonding force, large internal stress of the film layer, unsatisfactory corrosion resistance, and high preparation cost. Therefore, an effective solution is urgently needed.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a DLC/ _SiNx composite film with low process cost, reasonable film structure, good wear and corrosion resistance and a preparation method.

The radio frequency bias-assisted magnetron sputtering preparation technology proposed in the present invention has the advantages of low cost and high efficiency for preparing diamond-like thin films with excellent comprehensive properties. RF bias can be used to ion clean the substrate to improve the bonding force, and RF bias can be used to increase the ionization rate of carbon-containing atmosphere while applying substrate bias to improve mechanical properties, and the magnetron target can deposit transition layers. Doping elements can also be provided, or a graphite target can be used to prepare intrinsic diamond-like carbon films. In particular, the RF substrate bias will not greatly decrease the bias effect with the increase of the film thickness, which is suitable for large-scale applications.

The invention is a DLC/SiN _x composite film with wear resistance and corrosion resistance. After the amorphous metal or alloy modified layer is prepared on the surface of the metal or alloy substrate, the magnetron sputtering technology is used to prepare the SiN _x film and the DLC film in turn; In the SiN _x film, the value of x is in the range of 0-1.5, excluding 0. 2. The wear-resistant and corrosion-resistant DLC/SiN _x composite film according to claim 1 is characterized in that, a metal or alloy substrate is bombarded by plasma Surface, ion etching and ion implantation are performed on the surface of the metal or alloy substrate to obtain a surface modification layer.

The anti-wear and corrosion-resistant DLC/SiN _x composite film of the invention can be applied to specific products such as hard alloy circular saw discs and PCB circuit board milling cutters; the saw blade of the hard alloy circular saw disc product is a steel plate such as spring steel Material, the thickness of the steel plate material is 2.5-4.0mm, and the diameter is mainly D300-D600mm. There are 120-140 serrations on the outer circle of the saw blade, and a carbide cutter head is inlaid on the serrations; the specifications of the PCB circuit board milling cutter are 20-315mm in outer diameter, 5-40mm in aperture, and 0.2-6.0mm in thickness.

The invention is a DLC/SiN _x composite film with wear resistance and corrosion resistance. The metal or alloy substrate is placed on the sample base of the magnetron sputtering equipment. The sample base is insulated from the grounded vacuum chamber and connected to the radio frequency power supply. The metal or alloy substrate is biased, and the surface of the metal or alloy substrate is bombarded by plasma, and ion etching and ion implantation are performed on the surface of the metal or alloy substrate to obtain a surface modification layer; the surface modification layer is an amorphous layer.

The anti-wear and anti-corrosion DLC/SiN _x composite thin film of the present invention, the applied bias voltage is 500-1000V, the plasma is selected from Ar plasma, a mixed plasma of Ar and N; the plasma bombardment time is 10- 20min; the thickness of the surface modification layer is 5-100nm.

The invention is a wear-resistant and corrosion-resistant DLC/SiN _x composite thin film, and the thickness of the SiN _x thin film + DLC thin film is 0.0001-0.1 mm.

The invention is a wear-resistant and corrosion-resistant DLC/SiN _x composite film, the metal matrix is selected from one of metal magnesium, aluminum, titanium, copper and iron; the alloy matrix is selected from metal magnesium, aluminum, titanium, copper and iron. one of the alloys.

A method for preparing a wear-resistant and corrosion-resistant DLC/SiN _x composite thin film is to place a metal or alloy substrate in a magnetron sputtering device, bombard the surface of the metal or alloy substrate with plasma, and perform ion etching on the surface of the metal or alloy substrate. Ion implantation is carried out at the same time as etching or ion etching, and after obtaining the surface modification layer, the SiN _x film and the DLC film are prepared in situ on the surface modification layer by magnetron sputtering;

A method for preparing a wear-resistant and corrosion-resistant DLC/SiN _x composite film, the preparation of the surface modification layer is that a metal or alloy substrate is placed on a sample base of a magnetron sputtering device, and the sample base is connected to a grounded vacuum chamber Insulate and connect the radio frequency power supply, apply a bias voltage to the pure metal or alloy substrate, use plasma to bombard the surface of the metal or alloy substrate, and perform ion etching or ion implantation on the surface of the metal or alloy substrate to prepare the surface modification. layer; the applied bias voltage is 500-1000V, the plasma is selected from Ar plasma, Ar and N plasma; the plasma bombardment time is 10-20min; the thickness of the surface modification layer is 5-100nm. The implanted ions are selected from at least one of N, C, Cr, O, Si, and Ti.

A method for preparing a wear-resistant and corrosion-resistant DLC/SiN _x composite thin film, the in-situ preparation of the SiN _x thin film and the DLC thin film on the surface modification layer is as follows:

SiN _x thin films are prepared by reactive magnetron sputtering, using Si or Si ₃ N ₄ as the sputtering target, the sputtering source is radio frequency, intermediate frequency or DC power supply, and the sputtering atmosphere is a mixture of Ar and N ₂ or Ar and NH ₃ Atmosphere; magnetron sputtering process parameters are:

In the mixed atmosphere, the flow ratio of Ar and N ₂ or Ar and NH ₃ is 1-8, the target power density is 3.5-18.5 W·cm ^-2 , the working pressure is 0.5-10Pa, and the deposition time is 5-60min;

When the DLC film is prepared, a graphite target or metal is used as the sputtering target;

When sputtering with graphite as the target:

The sputtering atmosphere is argon, and the sputtering source is radio frequency, intermediate frequency or DC power supply;

The magnetron sputtering process parameters are:

The target power density is 3.5-18.5W·cm ^-2 , the working pressure is 0.25-5Pa, the deposition time is 5-60min, the initial bias voltage is 20-25V, and the increase is every 5-10 minutes during the magnetron sputtering process Bias voltage, the bias voltage adjustment rate is 5-30V, when the bias voltage reaches 300V, the bias voltage adjustment is stopped;

When sputtering with a metal target as the target:

The sputtering atmosphere is a mixed atmosphere of Ar and C ₂ H ₂ or Ar and CH ₄ , and the sputtering source is radio frequency, intermediate frequency or DC power supply;

The metal target is selected from one of W, Mo, Ti, Cr, Si, Al or its alloy;

The magnetron sputtering process parameters are:

The flow ratio of Ar and C ₂ H ₂ or Ar and CH ₄ in the mixed atmosphere is 0.5-6, the target power density is 3.5-18.5W·cm ^-2 , the working pressure is 0.5-10Pa, the deposition time is 5-60min, and the initial The bias voltage is 20-25V. During the magnetron sputtering process, the bias voltage is adjusted every 5-10 minutes. The bias voltage adjustment increment is 5-30V. When the bias voltage reaches 300V, the bias voltage adjustment is stopped; It has gradient hardness increasing from inside to outside (the bias voltage increases, the content of hard phase SP ³ C in the film increases), the residual stress in the film is reduced, and the wear resistance of the film is improved.

According to various defects of the prior art, the present invention proposes a radio frequency bias-assisted magnetron sputtering deposition of DLC, which can apply radio frequency bias voltages of different sizes to the substrate, and can efficiently prepare a film substrate with high bonding strength, mechanical properties and friction resistance. Diamond-like carbon film with excellent performance and corrosion resistance. By changing the RF bias, the ratio between sp2 and sp3 in the diamond-like carbon film can be changed, and the structure of the diamond-like carbon film can be effectively controlled in a wide range. Because of the present invention, the DLC can be doped or the transition layer can be prepared by using a gas doping source or a metal target. In the present invention, the SiNx transition layer is selected as the buffer layer between the DLC film and the substrate, which solves the problem of excessive stress in the DLC film and further improves the DLC performance. At the same time, before preparing the SiNx transition layer, we use a high radio frequency bias Under certain conditions, the substrate was bombarded with Ar, N plasma, and an amorphous modified layer was prepared on the substrate. The advantages such as corrosion potential between the small matrix and the second phase confirm that the amorphous layer/SiNx/DLC film has excellent mechanical properties and corrosion resistance.

The present invention has the following advantages due to the adoption of the above-mentioned process method and film structure:

1. The use of radio frequency bias-assisted magnetron sputtering preparation technology has the advantages of low-cost and high-efficiency preparation of diamond-like carbon films with excellent comprehensive properties. This technology can not only use RF bias to ion clean the substrate to improve the bonding force, but also use RF bias to improve the ionization rate of the carbon-containing atmosphere while applying substrate bias to improve the mechanical properties, and the magnetron target can not only Deposition of transition layers can also provide doping elements, or use graphite targets to prepare intrinsic diamond-like carbon films.

An additional advantage of RF substrate biasing is that there is no significant reduction in biasing effect with increasing film thickness. Because the radio frequency power supply is alternating current, the cycle acts on the target alternately, when the sputtering target is in the positive half cycle, the electrons flow to the target surface, neutralize the positive charge accumulated on the surface, and accumulate electrons, making the surface present a negative bias. The negative half cycle of the RF voltage attracts positive ions to bombard the target, so that the sputtering process can continue, reducing or preventing the occurrence of target poisoning; in addition, the RF voltage can pass through any kind of impedance, so when the DLC film is deposited thicker When the DLC film itself has a weak shielding effect on the RF power supply, the bias voltage can continue to be applied without being affected by the thickness.

2. Prepare an amorphous transition layer to effectively improve the bonding force of the film base

1) The amorphous modified layer improves the surface state of the substrate and makes the surface denser;

Due to the uniform single phase of the amorphous layer, the composition and structure are more uniform, the composition fluctuates less, there is no obvious grain boundary, no second phase particles or dislocations, etc., so the preparation of the amorphous modified layer on the surface of the substrate can greatly improve the Improve the unevenness of the surface of the base metal or alloy, and eliminate existing defects such as holes or pores, cracks, and pinholes on the base surface, thereby greatly reducing the number of core corrosion defects on the base surface and improving the corrosion resistance of the composite film structure. .

2) The amorphous modified layer reduces the corrosion potential between the matrix and the second phase;

The ion bombardment or etching during the preparation of the amorphous layer can chemically combine the matrix or its impurity elements with the same ions to generate a new phase with similar structure, which increases the chemical uniformity of the surface of the matrix and reduces the original matrix. and the corrosion potential between the second phase. In addition, the amorphous layer can inhibit the diffusion of impurity elements in the matrix to the surface of the matrix, and avoid the situation that the impurities diffuse to the surface of the matrix and become the pitting core.

3) During the preparation of the amorphous modified layer, a new corrosion-resistant phase is produced in the matrix:

During the process of ion bombardment or ion implantation, a new phase will be formed by combining with the matrix atoms. For example, N plasma bombardment or N ion implantation on the surface of the magnesium alloy substrate will generate a new phase of Mg3N2, which is a corrosion-resistant phase, which is a corrosion-resistant phase, thereby improving the corrosion resistance of the substrate surface.

4) Due to the disorder of the structural atoms of the amorphous layer itself, the amorphous layer itself has good corrosion resistance, and at the same time, it is very difficult for impurity ions or ions in the electrolyte to move in the amorphous layer, thus hindering the The occurrence of substrate corrosion.

The present invention uses plasma to bombard the metal or alloy surface. Because of the use of a bias voltage of several hundred volts or even thousands of volts, the plasma bombardment is completed under the condition of a relatively large bias voltage, which causes the surface temperature of the substrate to rise rapidly, and the surface composition of the substrate is different from that of the substrate. The plasma composition will undergo a certain metallurgical bond at a higher temperature, or the composition of the surface layer of the matrix will be re-dissolved. After the plasma bombardment ends, the bias voltage is suddenly reduced to a very low value or the transition layer is directly turned off to start the deposition of the transition layer. The whole process on the surface of the substrate only lasts about 10-20 minutes, so the temperature of the surrounding environment will not increase significantly when the substrate rapidly rises to high temperature. In the surrounding environment, it cools rapidly, so the plasma bombardment is approximately a process of rapid melting and solidification, which satisfies the rapid cooling conditions required for the formation of an amorphous layer. In addition, when plasma bombards the surface of the substrate under the action of a high bias voltage, high-energy particles strike the surface of the substrate to generate a large number of vacancies or interstitial atoms. These point defects will continuously migrate and form dislocations under the action of thermal activation. Under high-energy bombardment for a longer time, higher dislocation density will be caused. Due to the inherent limit of the dislocation density that can be maintained on the surface of each metal or alloy, when the dislocation density caused by plasma bombardment on the surface of the substrate exceeds When this inherent limit is reached, the internal lattice collapse on the surface of the matrix will cause a disordered state and eventually an amorphous layer will be formed on the surface of the matrix.

3. Through the amorphous transition layer, the film base potential can be effectively improved

The present invention uses the plasma immersion ion implantation technology as the pretreatment method for depositing thin films, which is very suitable for implanting N ions because of its low energy requirement, high efficiency, and easy realization of compounding with other vacuum preparation technologies. In addition to changing the composition, the corrosion resistance can also be improved by changing the structure of the metal or alloy; so that the metal or alloy has long-term stable corrosion resistance.

To sum up, the radio frequency bias-assisted magnetron sputtering technology of the present invention solves various defects existing in the prior art, and has obvious advantages.

Detailed ways

The present invention will be described in further detail below through examples and comparative examples.

The performance indexes of the samples prepared in the embodiment of the present invention and the comparative example are shown in Table 1.

Example 1:

(1) Preparation of Ar plasma modified layer

The AZ31 magnesium alloy with poor corrosion resistance is used as the substrate, and the cleaned AZ31 magnesium alloy substrate is placed in the sputtering chamber. , the power supply is 37W, the working pressure is 1.1pa, the substrate bias voltage is 700V, and the bombardment time is 15min, and an amorphous modified layer is obtained on the surface of the substrate.

(2) Preparation of SiNx thin films

Rotate the target so that the AZ31 magnesium alloy substrate faces the silicon target, and at the same time, argon and nitrogen are introduced, the flow ratio is 4:1, the sputtering power source is radio frequency power source, the radio frequency power is 200W, the working pressure is 0.75pa, and the deposition time is 60min.

(3) Preparation of diamond-like carbon films

Rotate the substrate so that the AZ31 magnesium alloy substrate is facing the graphite target, the substrate is connected to a radio frequency power supply, a bias voltage of 50 V is applied, and argon and acetylene are fed at the same time. The flow ratio is 8:3. The air pressure was 1.3pa, and the deposition time was 6min.

Example 2:

(1) Preparation of Ar, N plasma modified layer

Using AZ31 magnesium alloy with poor corrosion resistance as the substrate, put the cleaned AZ31 magnesium alloy substrate into the sputtering chamber. 1. The sputtering power supply is a DC power supply, the power supply is 37W, the working pressure is 1.1pa, the substrate bias is 700V, and the bombardment time is 15min to obtain an amorphous modified layer on the surface of the substrate.

(2) Preparation of SiNx thin films

The substrate was rotated so that the AZ31 magnesium alloy substrate was facing the silicon target, and argon and nitrogen were introduced at the same time, the flow ratio was 4:1, the sputtering power was RF power, the RF power was 200W, the working pressure was 0.75pa, and the deposition time was 60min.

(3) Preparation of diamond-like carbon films

Rotate the target so that the AZ31 magnesium alloy substrate is facing the graphite target, the substrate is connected to a radio frequency power supply, a bias voltage of 50 V is applied, and argon and acetylene are fed at the same time. The flow ratio is 8:3. The working pressure is 1.3pa, and the deposition time is 6min.

Example 3:

(1) Preparation of Ar, N plasma modified layer

Using AZ31 magnesium alloy with poor corrosion resistance as the substrate, put the cleaned AZ31 magnesium alloy substrate into the sputtering chamber. 1. The sputtering power supply is a DC power supply, the power supply is 37W, the working pressure is 1.1pa, the substrate bias is 700V, and the bombardment time is 15min to obtain an amorphous modified layer on the surface of the substrate.

(2) Preparation of SiNx thin films

The substrate was rotated so that the AZ31 magnesium alloy substrate was facing the silicon target, and argon and nitrogen were introduced at the same time, the flow ratio was 4:1, the sputtering power was RF power, the RF power was 200W, the working pressure was 0.75pa, and the deposition time was 60min.

(3) Preparation of gradient diamond-like carbon films

Rotate the target so that the AZ31 magnesium alloy substrate is facing the graphite target, the substrate is connected to the RF power supply, and argon and acetylene are introduced at the same time. During the deposition process, the argon flow rate is fixed at 16sccm, and the acetylene flow rate is slowly increased from 0 (sccm) to 8 (sccm). ), while linearly increasing the substrate bias from 25V to 140V. The sputtering power supply is a DC power supply, the power supply is 150W, the working pressure is 1.1pa, and the deposition time is 20min.

Comparative Example 1:

(1) Preparation of SiNx thin films

The AZ31 magnesium alloy with poor corrosion resistance was used as the substrate, and the cleaned AZ31 magnesium alloy substrate was placed in the sputtering chamber, the substrate was facing the silicon target, and argon gas and nitrogen gas were introduced at the same time, and the flow ratio was 4:1. The power source is radio frequency power, the radio frequency power is 200W, the working pressure is 0.75pa, and the deposition time is 60min.

(2) Preparation of diamond-like carbon films

Rotate the target so that the AZ31 magnesium alloy substrate is facing the graphite target, the substrate is connected to a radio frequency power supply, a bias voltage of 50 V is applied, and argon and acetylene are fed at the same time. The flow ratio is 8:3. The working pressure is 1.3pa, and the deposition time is 6min.

The properties of the obtained diamond-like carbon composite films were tested, and the test results are shown in Table 1.

Tested by electrochemical method (using a three-electrode system, the reference electrode is a saturated Ag/AgCl electrode, the counter electrode is a Pt sheet (15mm×15mm×0.1mm), the sample is a working electrode (exposed area 0.25cm2), and the electrolyte is 3.5wt. %NaCl solution) and its corrosion resistance, the corrosion current is obtained by testing the Tafel polarization curve; the wear resistance is characterized by the reciprocating friction and wear test method, and the counterpart is a silicon nitride ball (diameter 4.2mm), sliding The distance is 8mm, the load is 8N, and the frequency is 8Hz.

Performance testing

Table 1:

Performance comparison: From the data in Table 1, it can be seen that:

Coefficient of friction (COF.): Example 3 < Example 2 < Example 1 < Comparative Example 1;

Corrosion current density: Example 3<Example 2<Example 1<Comparative Example 1.

It can be seen from the data in Table 1 that the friction coefficient of the diamond-like composite films prepared in Examples 1-3 of the present invention is smaller than that of the films prepared by the comparative example; the maximum corrosion current density is only 1/4 of the comparative example.

Claims (8)

1. a wear-resistant and corrosion-resistant DLC/SiN composite film, _is characterized in that, after preparing amorphous metal or alloy modified layer on metal or alloy substrate surface, adopt magnetron sputtering technology to prepare _SiN film successively, DLC film; in the SiN _x film, the value of x is 0-1.5, excluding 0; the surface of the metal or alloy substrate is bombarded by plasma, and ion etching and ion implantation are performed on the surface of the metal or alloy substrate to obtain a surface modification layer . 2. The wear-resistant and corrosion-resistant DLC/SiN composite film according to claim ₁ , wherein the metal or alloy substrate is placed on the sample base of the magnetron sputtering equipment, and the sample base is connected to a grounded vacuum The chamber is insulated and connected to a radio frequency power supply, a bias voltage is applied to the pure metal or alloy substrate, the surface of the metal or alloy substrate is bombarded with plasma, and ion etching and ion implantation are performed on the surface of the metal or alloy substrate to obtain a surface modification layer. 3. The wear-resistant and corrosion-resistant DLC/SiN composite film according to claim ₁ and 2, wherein the applied bias voltage is 500-1000V, and the plasma is selected from the mixed plasma of Ar plasma, Ar and N One of them; the plasma bombardment time is 10-20min; the thickness of the surface modification layer is 5-100 nm. 4. The wear-resistant and corrosion-resistant DLC/ _SiNx composite film according to claim 3, wherein the thickness of the _SiNx film+DLC film is 0.0001-0.1 mm. 5. a kind of DLC/ _SiN composite film for wear-resistant and corrosion-resistant metal or alloy surface according to claim 4, is characterized in that, metal matrix is selected from one of metal magnesium, aluminum, titanium, copper, iron The alloy matrix is selected from one of the alloys of metal magnesium, aluminum, titanium, copper and iron. 6. the method for preparing a kind of wear-resistant and corrosion-resistant DLC/SiN composite film as claimed in claim 5 _is to place metal or alloy substrate in magnetron sputtering equipment, and use plasma to bombard the metal or alloy substrate surface, The surface of the metal or alloy substrate is ion-etched or ion-implanted at the same time as ion-etching to obtain a surface-modified layer, and then magnetron sputtering is used to in-situ prepare SiN _x film and DLC film on the surface-modified layer. 7. the preparation method of a kind of wear-resistant and corrosion-resistant DLC/SiN composite thin film according to claim 6, _is characterized in that: the preparation of surface modification layer is to place metal or alloy matrix in magnetron sputtering equipment On the sample base, the sample base is insulated from the grounded vacuum chamber and connected to a radio frequency power supply. A bias voltage is applied to the pure metal or alloy base, and the surface of the metal or alloy base is bombarded with plasma to perform ion etching or ion etching on the surface of the metal or alloy base. Ion implantation is performed at the same time of etching to prepare a surface modification layer; the applied bias voltage is 500-1000V, and the plasma is selected from one of Ar plasma, Ar and N plasma; the plasma bombardment time is 10-20min; The thickness of the modified layer is 5-100 nm. 8. the preparation method of a kind of anti-wear and corrosion-resistant DLC/SiN _x composite thin film according to claim 7, is characterized in that: on the surface modification layer, the in-situ preparation of SiN _x thin film and DLC thin film technology is as follows: SiN _x thin films are prepared by reactive magnetron sputtering, using Si or Si ₃ N ₄ as the sputtering target, the sputtering source is radio frequency, intermediate frequency or DC power supply, and the sputtering atmosphere is a mixture of Ar and N ₂ or Ar and NH ₃ Atmosphere; magnetron sputtering process parameters are: In the mixed atmosphere, the flow ratio of Ar and N ₂ or Ar and NH ₃ is 1-8, the target power density is 3.5-18.5 W·cm ^-2 , the working pressure is 0.5-10Pa, and the deposition time is 5-60min; When the DLC film is prepared, a graphite target or metal is used as the sputtering target; When sputtering with graphite as the target: The sputtering atmosphere is argon, and the sputtering source is radio frequency, intermediate frequency or DC power supply; The magnetron sputtering process parameters are: The target power density is 3.5-18.5 W·cm ^-2 , the working pressure is 0.25-5Pa, the deposition time is 5-60min, the initial bias voltage is 20-25V, and the increase is every 5-10 minutes during the magnetron sputtering process Bias voltage, the bias voltage adjustment rate is 5-30V, when the bias voltage reaches 300V, the bias voltage adjustment is stopped; When sputtering with a metal target as the target: The sputtering atmosphere is a mixed atmosphere of Ar and C ₂ H ₂ or Ar and CH ₄ , and the sputtering source is radio frequency, intermediate frequency or DC power supply; The metal target is selected from one of W, Mo, Ti, Cr, Si, Al or its alloy; The magnetron sputtering process parameters are: In the mixed atmosphere, the flow ratio of Ar and C ₂ H ₂ or Ar and CH ₄ is 0.5-6, the target power density is 3.5-18.5 W·cm ^-2 , the working pressure is 0.5-10Pa, the deposition time is 5-60min, and the initial The bias voltage is 20-25V. During the magnetron sputtering process, the bias voltage is increased every 5-10 minutes, and the bias voltage adjustment increment is 5-30V. When the bias voltage reaches 300V, the bias voltage adjustment is stopped.