DLC/Me-C composite film and preparation method thereof
Technical Field
The invention discloses a DLC/Me-C composite film and a preparation method thereof, belonging to the technical field of preparation of diamond-like carbon film materials.
Background
The diamond-like carbon film has excellent mechanics, friction resistance and corrosion resistance, can be deposited at low temperature, and has great application potential in the fields of tribology, biomedicine and the like. However, the diamond-like thin film has a characteristic of high internal stress, which makes the film base binding force very weak and the thickness of the diamond-like thin film is very limited. For this purpose, transition layers or dopings have to be added to the diamond-like film. Doping can weaken certain aspects of the diamond-like film. Finding a suitable transition layer is therefore key to facilitating diamond-like thin film applications. The transition layer not only affects the binding force of the diamond-like carbon film, but also greatly affects the corrosion resistance, so that the bonding strength with the substrate and the diamond-like carbon film is high, the self corrosion resistance is high, and the corrosion of the film or the substrate is not accelerated.
At present, diamond-like carbon films mainly comprise three preparation methods of cathodic arc deposition, Plasma Enhanced CVD (PECVD) and magnetron sputtering.
Cathodic arc was the first method used to deposit diamond-like thin films by depositing carbon atoms on a substrate under the action of a strong electric field, with the main drawbacks: 1, the prepared diamond-like carbon film has extremely high internal stress, so that the thickness of the diamond-like carbon film is limited to be nano-scale, and a transition layer is difficult to add or dope; 2, a large amount of graphite particles are bombarded out by the strong electric field and finally deposited on the substrate, a high-quality diamond-like carbon film cannot be obtained, the graphite particles are reduced by adding the magnetic filtering device, a large part of carbon ions or atoms are filtered at the same time, the deposition efficiency is reduced, and the filtering device is complex and has high cost. Although the magnetic filtration cathode arc can prepare the diamond-like carbon film with high sp3C content, the diamond-like carbon film cannot be applied industrially and is not favored by enterprises.
The PECVD method for preparing the diamond-like carbon film has high deposition efficiency, the diamond-like carbon film has high sp3C content and relatively low internal stress, and the comprehensive performance is excellent, however, the doping elements of the diamond-like carbon film must be input in an atmosphere form, which greatly hinders the preparation of the metal doped diamond-like carbon film.
The magnetron sputtering mainly comprises ion source auxiliary magnetron sputtering and direct-current bias magnetron sputtering; the diamond-like carbon film prepared by ion source assisted magnetron sputtering has high bonding strength and a plurality of varieties, but has poor comprehensive performance and high ion source and maintenance cost. When the diamond-like carbon film is prepared by the direct current bias magnetron sputtering, the metal target is insulated because the carbide and the like are generated and accumulated on the surface of the target during sputtering, positive ions bombarding the target surface are accumulated on the target surface, the target potential is increased, the electric field between the electrodes is gradually reduced until the glow discharge is extinguished and the sputtering is stopped, and meanwhile, because the conductivity of the DLC film is poor, the direct current bias effect is weakened or even does not work any more, and the deposition thickness of the film is limited. In the three different preparation methods, substrate bias is necessary, but because the conductivity of the diamond-like carbon film is extremely low, the prior art generally adopts direct current bias, so that the influence of the substrate bias on the structure of the diamond-like carbon film is weakened along with the increase of the deposition thickness, and the diamond-like carbon film completely fails when the thickness reaches 4 mu m.
In addition, due to the defects of the DLC film, the electrolyte diffuses to the substrate along the defects, forming microcell corrosion, with a very fast corrosion rate even exceeding that of substrates without film protection, resulting in poor long-term corrosion resistance of the DLC film protected substrate. Although the prior art has a structure adopting a transition layer, the prior art does not solve the potential problem among a film layer, the transition layer and a substrate, and the corrosion resistance of the prior art is unsatisfactory.
In conclusion, the prior art has the defects of non-ideal film-substrate binding force, large film internal stress, non-ideal corrosion resistance, high preparation cost and the like, so an effective solution is urgently needed.
Disclosure of Invention
The invention aims to provide a method for preparing a diamond-like carbon film with excellent comprehensive performance at low cost and high efficiency.
The invention relates to a DLC/Me-C composite film, which is characterized in that a Me-C film and a DLC film are sequentially prepared on the surface of a metal or alloy substrate by adopting a magnetron sputtering technology.
According to the DLC/Me-C composite film, after an amorphous metal or alloy modified layer is prepared on the surface of a metal or alloy substrate, a magnetron sputtering technology is adopted to prepare the Me-C film and the DLC film in sequence; the thickness of the amorphous metal or alloy modified layer is 5-100 nm.
The invention relates to a DLC/Me-C composite film, wherein a metal or alloy matrix is selected from metal magnesium, aluminum, titanium, copper, iron and alloys thereof.
According to the DLC/Me-C composite film, the Me-C film is of a gradient structure, the content of Me in the Me-C film is sequentially decreased, the content of C in the Me-C film is sequentially increased, and Me in the Me-C film is selected from elements capable of forming strong carbides; specifically, the metal is one selected from Cr, Ti, Si, W and Mo.
The invention relates to a preparation method of a DLC/Me-C composite film, which is characterized in that a metal or alloy matrix is placed in magnetron sputtering equipment, and the Me-C film and the DLC film are prepared on the surface of the metal or alloy matrix in situ.
The invention relates to a preparation method of a DLC/Me-C composite film, wherein the Me-C film is prepared by adopting reactive magnetron sputtering, Me is used as a sputtering target material, and the sputtering atmosphere is Ar and C2H2、CH4Mixed atmosphere of at least one of (1), sputteringThe radiation source is selected from one of radio frequency, intermediate frequency or direct current power supply, in the preparation process, the content of Me is controlled to be linearly reduced, the flow of carbon-containing atmosphere is linearly increased, and the gradient Me-C film is prepared; the rate of linear decrease of the content of Me is the same as the rate of linear increase of the flow rate of the carbon-containing atmosphere;
the magnetron sputtering process parameters are as follows:
ar and C in mixed atmosphere2H2Or Ar and CH4The flow ratio of (A) is 1-8, and the target power density is 3.5-18.5 W.cm-2The working pressure is 0.5-10Pa, and the deposition time is 5-60 min.
In the preparation process, the content of Me is gradually reduced to 0, and the content of carbon-containing atmosphere is gradually increased to 100 percent from 0;
when the DLC film is prepared, a graphite target or metal is used as a sputtering target material, when the graphite is used as the target material, the sputtering atmosphere is argon, and a sputtering source is a radio frequency, intermediate frequency or direct current power supply; the magnetron sputtering process parameters are as follows:
the target power density is 3.5-18.5W cm-2The working pressure is 0.25-5Pa, the deposition time is 5-60min, and the bias voltage is 20V-300V.
When the metal target is adopted for sputtering, the sputtering atmosphere is Ar and C2H2Or Ar and CH4The sputtering source is a radio frequency or medium frequency power supply; the metal target is selected from one of W, Mo, Ti, Cr, Si and Al or alloy thereof; the magnetron sputtering process parameters are as follows:
ar and C in mixed atmosphere2H2Or Ar and CH4The flow ratio of (A) is 0.5-6, and the target power density is 3.5-18.5W cm-2The working pressure is 0.5-10Pa, the deposition time is 5-60min, and the bias voltage is 20V-300V.
The invention relates to a preparation method of a DLC/Me-C composite film, which is characterized in that when the DLC film is prepared, the initial bias voltage is 20-25V, in the magnetron sputtering process, the bias voltage is increased every 5-10 minutes, the amplitude of the increase of the bias voltage is 5-30V, and when the bias voltage reaches 300V, the increase of the bias voltage is stopped, so that the film has the gradient hardness which is continuously enhanced from inside to outside, the residual stress in the film is reduced, and the abrasion resistance of the film is improved.
The invention relates to a preparation method of a DLC/Me-C composite film, which comprises the steps of placing a metal or alloy matrix on a sample base station of a magnetron sputtering device, insulating the sample base station from a grounded vacuum chamber and connecting the sample base station with a jet bias power supply, applying bias voltage to a pure metal or alloy matrix, bombarding the surface of the metal or alloy matrix by adopting plasma, carrying out ion etching and ion implantation on the surface of the metal or alloy matrix to obtain a surface modification layer, and preparing the Me-C film and the DLC film on the surface modification layer of the metal or alloy matrix by adopting magnetron sputtering.
The invention relates to a preparation method of a DLC/Me-C composite film, which comprises the following process parameters of plasma bombardment treatment:
applying a bias voltage of 500-1000V, Ar plasma or Ar and N plasma for 10-60 min; the thickness of the surface modification layer is 5-100 nm, and the surface modification layer is an amorphous layer.
According to various defects of the prior art, the invention provides the radio frequency bias auxiliary magnetron sputtering deposition DLC, and radio frequency biases of different sizes can be applied to the substrate, so that the diamond-like carbon film with high bonding strength of the film base and excellent mechanical property, friction resistance and corrosion resistance can be efficiently prepared. By changing the radio frequency bias voltage, 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 regulated in a large range. The invention can dope DLC or prepare transition layer by introducing gas doping source or using metal target. The invention selects the Me-C transition layer as a buffer layer between the DLC film and the substrate, solves the problem of overhigh stress in the DLC film, further improves the DLC performance, uses Ar and N plasmas to bombard the substrate under the condition of high radio frequency bias pressure before the Me-C transition layer is prepared, prepares the amorphous modified layer on the substrate, and has the advantages of improving the surface state of the substrate to enable the surface to be more compact, improving the bonding performance between the substrate and the transition layer, reducing the corrosion potential between the substrate and a second phase and the like.
The invention has the following advantages due to the adoption of the process method and the film layer structure:
1. the preparation method has the advantage of preparing the diamond-like carbon film with excellent comprehensive performance at low cost and high efficiency by adopting a radio frequency bias auxiliary magnetron sputtering preparation technology. The technology can use radio frequency bias to carry out ion cleaning on the substrate so as to improve the bonding force, can also use the radio frequency bias to improve the ionization rate of the carbon-containing atmosphere and simultaneously apply the substrate bias to improve the mechanical property, and the magnetron target can deposit a transition layer and provide doping elements or use a graphite target to prepare the intrinsic diamond-like carbon film.
The rf substrate bias also has the advantage that the bias effect does not decrease significantly with increasing film thickness. Because the radio frequency power supply is alternating current and acts on the target periodically and alternately, when the sputtering target is in a positive half cycle, electrons flow to the target surface to neutralize positive charges accumulated on the surface of the target and accumulate the electrons to enable the surface of the target to present negative bias, and positive ions are attracted to bombard the target material in a negative half cycle of the radio frequency voltage, so that the sputtering process is continuously carried out, and the target poisoning phenomenon is reduced or prevented; in addition, the rf voltage can pass through any kind of impedance, so when the DLC film is deposited thick, the bias can be continued without being affected by the thickness because the DLC film itself has a weak shielding effect against the rf power source.
2. Preparing amorphous transition layer to improve film-substrate binding force
1) The amorphous modified layer improves the surface state of the matrix and enables the surface to be more compact;
because the amorphous layer has the characteristics of uniform single phase, more uniform composition and structure, less fluctuation of the composition, no obvious crystal boundary, no second-phase particles or dislocation and the like, the preparation of the amorphous modified layer on the surface of the matrix can greatly improve the uneven state of the metal or alloy surface of the matrix and eliminate the defects of holes or pores, cracks, pinholes and the like existing on the surface of the matrix, thereby greatly reducing the number of corrosion core defects on the surface of the matrix 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 in the process of preparing the amorphous layer can lead the substrate or impurity elements in the substrate and the same ions to be chemically combined to generate a new phase with a similar structure, thereby increasing the chemical uniformity of the surface of the substrate and reducing the corrosion potential between the original substrate and the second phase. In addition, the amorphous layer can suppress diffusion of an impurity element in the base body to the surface of the base body, and avoid a case where the impurity diffuses to the surface of the base body to become a core of pitting corrosion.
3) The corrosion-resistant new phase of the matrix is generated in the preparation process of the amorphous modified layer:
the ions will combine with the atoms of the matrix to form a new phase during ion bombardment or ion implantation. For example, the new Mg3N2 phase which generates the corrosion-resistant phase when N plasma bombards or N ions are implanted into the surface of the magnesium alloy substrate is the corrosion-resistant phase, thereby improving the corrosion resistance of the surface of the substrate.
4) Due to the disorder of the structural atoms of the amorphous layer, the amorphous layer has better corrosion resistance, and meanwhile, impurity ions or ions in electrolyte are difficult to move in the amorphous layer, so that the occurrence of matrix corrosion is hindered.
The invention adopts plasma to bombard the surface of metal or alloy, because of using several hundred volts or even kilovolt bias voltage, the plasma bombardment is completed under the condition of larger bias voltage, which makes the surface temperature of the substrate rise rapidly, the surface component of the substrate and the plasma component will generate certain metallurgical bonding under higher temperature, or the surface component of the substrate will dissolve again, after the plasma bombardment is finished, the bias voltage is reduced to a very low value or the deposition transition layer is directly closed, because the whole process of the plasma bombardment of the surface of the substrate only needs about 10-20 minutes, the temperature of the substrate rises rapidly to high temperature and the temperature of the surrounding environment will not rise obviously, after the bombardment of high temperature, the surface is in the surrounding environment with lower temperature, and the substrate is cooled rapidly, so the plasma bombardment is similar to a rapid melting and rapid solidification process, the fast cooling condition required for forming the amorphous layer is satisfied. In addition, when plasma bombardment is carried out under the action of high bias voltage, energetic particles impact the surface of the substrate to generate a large number of vacancies or interstitial atoms, and the point defects continuously migrate and form dislocations under the action of thermal activation. Higher dislocation densities are caused by the bombardment with high energy for longer periods of time, and because of the inherent limit of dislocation density that can be maintained on the surface of each metal or alloy, when the density of dislocations caused by the bombardment of the substrate surface with plasma exceeds this inherent limit, the internal crystal lattice of the substrate surface is broken down to cause a disordered state, and finally an amorphous layer is formed on the substrate surface.
3. Effectively improves the film base potential through the amorphous transition layer
The invention takes the plasma immersion ion implantation technology as the pretreatment mode of the deposited film, and is very suitable for implanting N ions because the needed energy is low, the efficiency is high, and the invention is easy to realize the composition with other vacuum preparation technologies. Besides the change, the corrosion resistance can be improved by changing the structure of the metal or the alloy; so that the metal or the alloy has long-term stable corrosion resistance.
4. The invention adopts the in-situ continuous preparation of the Me-C/DLC film, the Me-C film and DLC have no obvious boundary, the films are combined very tightly and basically have no defects or holes, the penetration of electrolyte is effectively blocked, and the corrosion resistance is greatly improved; in addition, in the Me-C/DLC film, Me and C are in gradient change, namely the content of the C element is gradually increased from the Me-C layer to the DLC film, and the content of the metal element Me is gradually reduced to 0; particularly, the DLC film is prepared under the condition of variable bias voltage, the DLC film structure is continuously changed, the sp3 proportion in the DLC film is gradually increased, the residual stress of the film is effectively reduced, and the quality and the performance of the film are improved.
In sum, the radio frequency bias auxiliary magnetron sputtering technology of the invention solves various defects in the prior art and has obvious advantages.
Drawings
FIG. 1 is a cross-sectional view of a film prepared in example 3 of the present invention;
FIG. 2 is a diagram showing a spectrum distribution of the element lines corresponding to the positions of the horizontal white lines in FIG. 1.
As can be seen from the attached figure 1, the gradient composition DLC H prepared by the invention has the thickness of about 4 mu m, and no new interface exists between the prepared film layers.
As can be seen from the element distribution diagram of fig. 2: the film prepared by the invention has the C content gradually increased from 0 to 100 percent, the Cr content gradually decreased to 0, and almost all C in the range of 1 μm of the outermost layer.
Detailed Description
The present invention will be described in further detail with reference to examples and comparative examples.
Example 1: preparation of DLC/Me-C composite film containing amorphous layer (ex-situ deposition)
(1) Preparation of Ar, N plasma modified layer
The method comprises the steps of taking stainless steel as a matrix, putting a cleaned stainless steel substrate into a sputtering chamber, enabling the substrate to face a graphite target, connecting the substrate with a radio frequency power supply, introducing argon and nitrogen, enabling the flow ratio to be 4:1, enabling the sputtering power supply to be a direct current power supply, enabling the power supply power to be 37W, enabling the working pressure to be 1.1pa, applying matrix bias voltage to be 700V, and enabling bombardment time to be 15min, so that an amorphous modified layer is obtained on the surface of the matrix.
(2) Preparation of gradient Cr-doped CrC transition layer
The stainless steel substrate is opposite to the metal chromium target, the substrate is connected with a radio frequency power supply, argon and acetylene are simultaneously introduced, the flow rate of the argon is fixed at 16sccm in the deposition process, the flow rate ratio of the acetylene is slowly increased by 6sccm from 0(sccm), and the bias voltage is gradually increased to 110V from 40V. The sputtering power supply is a direct current power supply, the power supply power is 200W, the working air pressure is 0.8pa, and the deposition time is 15 min; because of the adoption of the direct current sputtering source, the metal target is insulated due to the generation and accumulation of covered carbide on the surface of the target during sputtering, the number of chromium ions in the metal chromium target is gradually reduced to zero along with the extension of the sputtering time, and the gradient distribution of Cr and C in the film layer is realized.
(3) Preparation of DLC film
The substrate is opposite to the graphite target, the substrate is connected with a radio frequency power supply, bias voltage of 130V is applied, argon and acetylene are simultaneously introduced, the flow ratio is 8:3, the sputtering power supply is the radio frequency power supply, the power supply power is 200W, the working pressure is 7.0pa, and the deposition time is 15 min.
Example 2: DLC/Me-C composite film prepared by in-situ deposition (amorphous layer-free)
(1) And in-situ deposition of the DLC film containing the transition layer with gradient bias voltage and components enables a stainless steel substrate to face a metal chromium target, the substrate is connected with a radio frequency power supply, argon and acetylene are simultaneously introduced, in the deposition process, the flow rate of the argon is fixed to be 16sccm, the flow rate of the acetylene is increased by 1sccm from 0(sccm) every 2 minutes until the flow rate is increased to 8(sccm), and simultaneously, the substrate bias voltage is linearly increased by 5V from 25V per minute until the flow rate is increased to 140V. The sputtering power supply is a direct current power supply, the power supply power is 150W, the working air pressure is 0.75Pa, and the deposition time is 30 min.
EXAMPLE 3 preparation of DLC/Me-C composite film by in-situ deposition of amorphous-containing layer
(1) Preparation of Ar, N plasma modified layer
The method comprises the steps of taking stainless steel as a matrix, putting a cleaned stainless steel substrate into a sputtering chamber, enabling the substrate to face a graphite target, connecting the substrate with a radio frequency power supply, introducing argon and nitrogen, enabling the flow ratio to be 4:1, enabling the sputtering power supply to be a direct current power supply, enabling the power supply power to be 37W, enabling the working pressure to be 1.1pa, applying matrix bias voltage to be 700V, and enabling bombardment time to be 15min, so that an amorphous modified layer is obtained on the surface of the matrix.
(2) In-situ deposition of graded bias and composition DLC films containing transition layers
The method comprises the following steps of enabling a stainless steel substrate to face a metal chromium target, connecting the substrate with a radio frequency power supply, introducing argon and acetylene simultaneously, fixing the flow of the argon at 16sccm in the deposition process, increasing the flow of the acetylene from 0(sccm) to 8(sccm) every 2 minutes, and linearly increasing the substrate bias voltage from 25V to 140V every minute by increasing 5V. The sputtering power supply is a direct current power supply, the power supply power is 150W, the working air pressure is 0.75Pa, and the deposition time is 30 min; because of the adoption of the direct current sputtering source, the metal target is insulated due to the generation and accumulation of covered carbide on the surface of the target during sputtering, the number of chromium ions in the metal chromium target is gradually reduced to zero along with the extension of the sputtering time, and the gradient distribution of Cr and C in the film layer is realized.
Example 4:
DLC/Me-C composite membrane prepared by adopting radio-frequency sputtering source to realize Me-C gradient adjustment
(1) Preparation of Ar, N plasma modified layer
The method comprises the steps of taking stainless steel as a matrix, putting a cleaned stainless steel substrate into a sputtering chamber, enabling the substrate to face a graphite target, connecting the substrate with a radio frequency power supply, introducing argon and nitrogen, enabling the flow ratio to be 4:1, enabling the sputtering power supply to be a direct current power supply, enabling the power supply power to be 37W, enabling the working pressure to be 1.1pa, applying matrix bias voltage to be 700V, and enabling bombardment time to be 15min, so that an amorphous modified layer is obtained on the surface of the matrix.
(2) In-situ deposition of graded bias and composition DLC films containing transition layers
The method comprises the following steps of enabling a stainless steel substrate to face a metal chromium target, connecting the substrate with a radio frequency power supply, introducing argon and acetylene simultaneously, fixing the flow of the argon at 16sccm in the deposition process, increasing the flow of the acetylene from 0(sccm) to 8(sccm) every 2 minutes, and linearly increasing the substrate bias voltage from 25V to 140V every minute by increasing 5V. The sputtering power source is a radio frequency source, the power source power is 150W, the radio frequency power is adjusted and reduced by 20W every 2 minutes until the radio frequency power is zero, the gradient distribution of Cr and C in the film layer is realized, the working air pressure is 0.75Pa, and the deposition time is 30 min;
comparative example 1: DLC/Me-C composite film without amorphous layer and deposited in-situ
(1) Preparation of gradient Cr-doped CrC transition layer
The stainless steel substrate is opposite to the metal chromium target, the substrate is connected with a radio frequency power supply, argon and acetylene are simultaneously introduced, the flow rate of the argon is fixed at 16sccm in the deposition process, the flow rate ratio of the acetylene is slowly increased by 6sccm from 0(sccm), and the bias voltage is gradually increased to 110V from 40V. The sputtering power supply is a direct current power supply, the power supply power is 200W, the working air pressure is 0.8pa, and the deposition time is 15 min.
(2) Preparation of DLC film
The substrate is opposite to the graphite target, the substrate is connected with a radio frequency power supply, bias voltage of 130V is applied, argon and acetylene are simultaneously introduced, the flow ratio is 8:3, the sputtering power supply is the radio frequency power supply, the power supply power is 200W, the working pressure is 7.0pa, and the deposition time is 15 min.
Comparative example 2: DLC/Me-C film without change in gradient composition
(1) Preparation of CrC transition layer
The substrate is opposite to the chromium target, the substrate is connected with a radio frequency power supply, a bias voltage of 50V is applied, argon and acetylene are simultaneously introduced, the flow ratio is 16:3, the sputtering power supply is a direct current power supply, the power supply power is 200W, the working pressure is 0.8pa, and the deposition time is 15 min.
(2) Preparation of DLC film
The substrate is opposite to the graphite target, the substrate is connected with a radio frequency power supply, bias voltage of 130V is applied, argon and acetylene are simultaneously introduced, the flow ratio is 8:3, the sputtering power supply is the radio frequency power supply, the power supply power is 200W, the working pressure is 7.0pa, and the deposition time is 15 min.
And (3) performance detection results:
the various properties of the obtained diamond-like composite film were measured and the results are shown in table 1. And (3) measuring the nano hardness of the film by using a nano indentation technology, and using a constant load mode to ensure that the indentation depth does not exceed one tenth of the integral thickness of the film when the nano hardness is measured. The wear resistance was characterized using a frictional wear test using a mating part of silicon nitride spheres (diameter 4.2mm), a sliding distance of 8mm, a load of 8N and a frequency of 8 Hz. The electrochemical test was carried out (test conditions: three-electrode system, reference electrode is a saturated Ag/AgCl electrode, counter electrode is a Pt sheet (15 mm. times.15 mm. times.0.1 mm), sample is a working electrode (exposed area 0.25 cm)2) Electrolyte 3.5 wt.% NaCl solution) was known for its corrosion resistance, and its corrosion current was obtained by tafel polarization curve.
TABLE 1
And (3) comprehensive performance comparison:
nano hardness:
example 3 > example 4 > example 2 > example 1 > comparative example 2 > comparative example 1
Coefficient of friction:
example 4 < example 3 < example 2 < example 1 < comparative 2;
corrosion current density:
example 3 < example 4 < example 2 < example 1 < comparative example 2.