Method for producing thin film carbon material

Abstract

To achieve a long life thin film carbon material that is excellent in wear resistance due to ultralow friction and excellent even in peel resistance.SOLUTION: A thin film carbon material is obtained by laminating a DLC film having a film thickness of 100 nm-2 μm and a density of 2.8 g / cm3 or more containing substantially no hydrogen and oxygen and formed by carbon vapor deposition under argon gas cluster ion irradiation with a nitrogen containing DLC film having a film thickness of 10-100 nm and a nitrogen content of 1-20 at% by carbon vapor deposition under nitrogen gas cluster ion irradiation on the surface. The peak intensity ratio of a D band to a G band by the Raman spectroscopic analysis of the nitrogen containing DLC film is ID / IG<0.9, and the DLC film has a hardness of 30-50 GPa and an average surface roughness of 0.5-5 nm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a thin film carbon material having superlubricity due to ultra-low friction and excellent wear resistance, peel resistance, and hydrophobicity. of The manufacturing method thereof can be applied to mechanical parts and sliding members that do not use lubricating oil, etc., and can also be used for biological members and electronic members other than wear-resistant members.

Background Art

[0002] Among carbon-based thin films used for sliding members and wear-resistant members, DLC (Diamond-Like Carbon) having excellent smoothness and a low friction coefficient is often adopted. The low friction coefficient of DLC is due to the generation of minute carbonaceous wear debris formed at the sliding part. On the other hand, the generation of carbonaceous wear debris appears as the progress of wear due to long-time sliding and leads to the end of the life. In particular, it is known that peeling larger than minute carbonaceous wear debris sometimes occurs due to strong residual stress possessed by a high-hardness DLC film, leading to the end of the life of the DLC-coated member.

[0003] According to ISO20523, DLC is classified into four types: ta-C, a-C, ta-C:H, and a-C:H. Ta-C:H and a-C:H are carbon materials containing a large amount (10 - 40%) of hydrogen in their composition and have a low hardness of 30 GPa or less. On the other hand, ta-C and a-C are basically carbon materials that do not contain hydrogen. Further, the C-C bond in the carbon material is classified according to the ratio of the SP 3 hybrid orbital bond of diamond and the SP 2 hybrid orbital bond of graphite. When SP 3 / (SP 2 +SP 3 ) > 50%, it is called ta-C or ta-C:H, and when the ratio is 50% or less, it is called a-C or a-C:H. All DLCs have a structure in which SP 3 bonds and SP 2 bonds coexist. In particular, ta-C and a-C that do not contain hydrogen have many unbonded carbons called dangling bonds in atomic bonds, strongly affecting the wear characteristics of sliding members and wear-resistant members.

[0004] Oxygen or water present in the DLC film or adsorbed on the film surface reacts with the unbonded carbon to form a compound, and minute carbonaceous wear debris is generated on the friction surface due to the friction during sliding. This is considered to be a factor for the low coefficient of friction, but on the other hand, it is thought to cause larger film breakage and progress of local wear on the friction surface.

[0005] In Patent Document 1, a method for forming a hydrogen-free DLC film that is highly hard and excellent in wear resistance, thermal stability, and adhesion to a substrate is shown by heating a crucible containing a carbon source to evaporate it and simultaneously irradiating it with argon gas cluster ions while depositing carbon on the substrate surface.

[0006] In Patent Document 2, DLC was formed by a filtered arc ion plating method using a graphite target. Nitrogen gas was introduced at the initial stage of DLC film formation in the portion close to the substrate, and then the nitrogen gas was gradually decreased to form a DLC film that does not contain nitrogen in the surface layer portion of the film. It is stated that the adhesion strength of DLC was improved by reducing the film hardness and residual stress by incorporating nitrogen in the film close to the substrate.

[0007] In Patent Document 3, a hydrocarbon gas was used as a carbon source, and DLC was coated on the container of a non-aqueous electrolyte battery by a CVD method using high-frequency plasma for the purpose of suppressing the penetration of moisture into the container. The examples show that the water permeability resistance deteriorates as the number of dangling bonds increases, and the hydrocarbon gas type and coating conditions were studied to reduce the dangling bonds and improve the water permeability resistance.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention aims to provide a long-life DLC (Diamond-Like Carbon) thin film material that is used for wear-resistant members such as sliding members and tools, and has excellent wear resistance and excellent peel resistance. In wear-resistant members, the DLC film is worn out and reaches the end of its life due to the progress of wear caused by the accumulation of minute wear, or due to destruction such as minute chipping or peeling. There is an idea that the hardness of the film should be increased to improve the wear resistance of the DLC film. However, in order to increase the hardness of DLC, it is common to form the film by high-energy ion bombardment that is 10 to 100 times the diamond C-C bond energy. For this reason, strong residual compressive stress remains, and film peeling and chipping are likely to occur, resulting in problems such as a short film life or a failure to reduce the frictional resistance. In addition, high-energy ion bombardment is also an attempt to increase the ratio of diamond SP 3 hybrid orbital bonding, but at the same time, many dangling bonds, which are unbonded hands of carbon atoms, remain, and chemical bonds are formed with metal atoms of the friction mating material, etc., resulting in a problem that wear progresses.

[0010] Since the wear of the DLC film is the chemical wear of unbonded carbon atoms at the atomic level, it is necessary to stabilize the bonds of carbon that make up the DLC film in order to improve wear resistance and achieve an ultra-low coefficient of friction. However, in the current manufacturing method, the DLC film formation method by high-energy ion bombardment is common. Even if densification progresses, a large amount of unbonded hands of carbon atoms remain, and the problem of residual stress due to strong ion bombardment is not solved.

[0011] The present invention has been made in view of such points, and an object thereof is to realize a long-life thin-film carbon material that has ultra-low friction, excellent wear resistance, and excellent peel resistance by stabilizing the bonds of carbon that make up the DLC film.

Means for Solving the Problems

[0012] The invention according to claim 1 is a thin-film carbon material characterized in that a DLC film with a film thickness of 100 nm to 2 μm and a density of 2.8 g / cm 3 or more with a hardness of 30 to 50 GPa is formed by carbon deposition under argon gas cluster ion-assisted irradiation, and a nitrogen-containing DLC film with a film thickness of 10 nm to 100 nm and a nitrogen content of 1 to 20 at% is laminated on the surface thereof by carbon deposition under nitrogen gas cluster ion-assisted irradiation to do manufacturing method

[0013] The invention according to claim 2 is the thin-film carbon material according to claim 1 manufacturing method wherein the peak intensity ratio of the D band to the G band in the Raman spectroscopic analysis of the nitrogen-containing DLC film is I D / I G <0.9 to be The invention according to claim 3 is the thin-film carbon material according to claim 1 or 2 manufacturing method characterized in that the average surface roughness is 0.5 nm to 5 nm

[0014] The invention according to claim 4 is a method for manufacturing a thin-film carbon material, comprising the steps of forming an intermediate layer film made of one or more of silicon, chromium, tungsten, titanium and their carbides on the surface of a substrate, forming a DLC film with a film thickness of 100 nm to 2 μm and a density of 2.8 g / cm 3 or more with a hardness of 30 to 50 GPa by carbon deposition under argon gas cluster ion-assisted irradiation on the surface of the intermediate layer film, and laminating a nitrogen-containing DLC film with a film thickness of 10 nm to 100 nm and a nitrogen content of 1 to 20 at% by carbon deposition under nitrogen gas cluster ion-assisted irradiation on the surface of the DLC film

Advantages of the Invention

[0015] The thin-film carbon material according to claim 1 by the manufacturing method can stabilize the bonding of carbon on the film surface by reducing the unbonded carbon atoms on the film surface, and the film is not easily broken, so it has excellent peel resistance

[0016] According to claim​​​1 According to the invention, it is possible to suppress the residual stress in the film to a low level despite the high film density, and since the film is difficult to peel off, there is an effect of obtaining a long-life thin-film carbon material.

[0017] In claim 3 by the manufacturing method Since the thin-film carbon material has an extremely flat surface, it is difficult for oxygen and water to be adsorbed on the film surface, and it is possible to prevent the progress of film breakage and local wear on the friction surface due to the reaction of these with unbonded carbon, and there is an effect of being able to extend the life as a sliding member and wear-resistant member.

[0018] According to the invention of claim 4, since the bonding strength of the carbon film can be increased by the intermediate layer film, there is an effect of being able to further enhance the peel resistance. Also, if the formation of the intermediate layer film is also carried out under gas cluster ion beam-assisted irradiation, it is possible to further flatten the surface of the intermediate layer film compared to the surface of the substrate, and thereby further flatten the surface of the DLC film. As a result, the sliding resistance is further reduced, the peel resistance and wear resistance are improved, and there is an effect of obtaining a longer-life thin-film carbon material.

Embodiments for Carrying Out the Invention

[0019] The reason why the friction coefficient of DLC (Diamond-Like Carbon) is small and excellent is said to be that due to the friction of the sliding part, minute carbonaceous wear powder formed by the reaction of dangling bonds from the DLC surface with oxygen and moisture detaches, lubricating the sliding interface. Dangling bonds exist not only on the DLC film surface but also in the film interior. Also, oxygen and moisture not only adsorb on the surface but also remain in the film interior, promoting the generation of minute carbonaceous wear powder. For further improvement of the wear and friction coefficient of the sliding part, it is effective to stabilize, that is, inactivate, the dangling bonds and suppress the generation of fine carbonaceous wear powder. It is considered that by making the detachment size of the fine carbonaceous wear powder from the surface smaller by inactivation, ultra-low friction can be realized.

[0020] As a method of eliminating or reducing carbon dangling bonds, it is conceivable to completely diamondize the carbon film. However, since diamond films are crystalline, have a rough surface, and are highly hard, when applied to a sliding surface, they will strongly abrade the mating material, and due to the generation of rough wear powder of the mating material, the friction coefficient will rapidly deteriorate. Also, carbon films mainly composed of graphite are not suitable as sliding members because of their low hardness.

[0021] On the other hand, as a means of stabilizing carbon dangling bonds and improving the low friction and high wear resistance of DLC, it is considered effective to bond nitrogen to the carbon dangling bonds. Oxygen, water, and hydrogen easily bond to carbon dangling bonds, forming compounds of carbon, oxygen, and hydrogen, which are the main causes of wear and the formation of fine wear powder. On the other hand, nitrogen is known to form a stable bond with carbon, for example, by using ultra-high pressure technology to synthesize C3N4 carbon nitride crystals with a triple bond similar to that of diamond. In the present invention, the aim is not to form a diamond bond of carbon-nitrogen, but to bond active carbon dangling bonds with nitrogen for the purpose of stabilizing them, and by further refining and suppressing carbonaceous wear powder, the coexistence of an ultra-low friction coefficient and wear resistance is realized.

[0022] In the present invention, a carbon vapor deposition method under irradiation assisted by argon gas clusters is used as the method for forming the carbonaceous film. Argon gas clusters are ionized and accelerated by the potential difference between the electrodes to impact the carbon deposited on the substrate surface with ions. The energy of the ion impact is set to an ion impact energy that is approximately 20 - 30% greater than the carbon bond energy of diamond, which is about 7.2 eV per argon atom, and close to diamond at 2.8 g / cm 3A DLC film with a film thickness of 100 nm to 2 μm and the above density is formed. Subsequently, carbon vapor deposition in which argon gas clusters are changed to nitrogen gas clusters is performed, and a nitrogen-containing DLC film with a film thickness of 10 nm to 100 nm and containing 1 to 20 at% of nitrogen is laminated. By this method, although a triple bond of carbon-nitrogen in the form of C3N4 nitride carbon cannot be obtained, unbonded carbon hands are stabilized with nitrogen, it is oxygen and hydrogen free, has a density close to diamond, and can produce a carbonaceous film with ultra-low friction and high wear resistance with little residual stress.

[0023] As a method for obtaining a DLC film with a density close to diamond, generally, carbon is ionized and a voltage of -100 V to -1000 V is applied to the substrate to impact the substrate with high-energy ions for production. In this method, the ion impact energy is one to two orders of magnitude larger than that of the gas cluster ion assisted irradiation method. The DLC film has high hardness and high density, but strong compressive residual stress remains in the film, and there are also many unbonded carbon hands. When this film is applied to a sliding member, minute flaws and film peeling of the DLC film are likely to occur, the friction coefficient also increases, and the life is reached quickly.

[0024] The gas cluster ion assisted irradiation method impacts a carbon film with an appropriate amount of ions and ion energy, so that a density of 2.8 g / cm 3 or higher and a high density close to diamond can be obtained, and the amount of unbonded carbon hands can also be reduced. The Raman spectroscopy value was used as a method for estimating unbonded carbon hands. In the Raman spectrum of the carbon film, for the D band around 1330 cm -1 due to the disorder and defects of the graphite structure, the ratio of the intensity to the G band around 1550 cm -1 corresponding to crystallinity, I D / I G <0.9 was set as the limitation of the present invention. The D band spectrum may also include bonds in which unbonded carbon hands are stabilized with nitrogen. Also, since it is considered that the instability of the carbon film increases when the nitrogen content in the carbonaceous film is too high, the nitrogen content in the film is preferably 1 to 20 at%, and further I D / I G <0.9 is preferred.

[0025] In the gas cluster ion assisted irradiation method, the film surface is flattened by irradiating with appropriate energy. Although a large number of carbon dangling bonds also exist inside the film, there are even more on the film surface. The amount is considered to increase as the surface roughness increases, and thus flattening of the film is also necessary. Further, the surface roughness is also related to the amount of surface-adsorbed oxygen and water, and is important for reducing the adsorption amount of oxygen and water that destabilize the carbon dangling bonds. For this reason, the surface roughness of the film is preferably as flat as possible, but an average surface roughness (arithmetic mean roughness Ra of JIS B 0601) of 0.5 nm to 5 nm is preferred.

[0026] Before forming the DLC film, it is preferable to form an intermediate layer film composed of one or more of silicon, chromium, tungsten, titanium, and their carbides on the substrate surface. By optimizing the ion impact energy of the DLC film to match the carbon-carbon bond energy of diamond, the residual stress can be reduced to less than half that of general high-density DLC, but the adhesion strength between the DLC film with high hardness and excellent slidability and the substrate can be improved by inserting an intermediate layer. The film thickness of the intermediate layer may be as thin as 5 nm to 30 nm. Note that the substrate may be a Si substrate, a ferrous or non-ferrous metal, or a non-metal such as ceramic.

[0027] The DLC film thickness of the present invention was set to 100 nm to 2 μm. If the film thickness becomes too thick, the film is likely to peel off, and if it is too thin, the wear resistance is inferior, so it was set to 100 nm to 2 μm. Further, the film thickness of the nitrogen-containing DLC film is preferably 10 nm to 100 nm. The nitrogen-containing DLC film has a lower density and a lower hardness than DLC that does not contain nitrogen. When the film thickness exceeds 100 nm, the wear resistance tends to decrease when applied to a sliding member where particularly strong abrasion occurs, and when the film thickness is less than 10 nm, sufficient chemical stability of the carbon dangling bonds cannot be obtained.

[0028] The DLC film and nitrogen-containing DLC film of the present invention substantially do not contain hydrogen and oxygen. Hydrogen or oxygen easily binds to unbonded carbon, easily forms hydrocarbon compounds during the friction process of the sliding material, and desorbs as a gas, etc., which becomes a factor inhibiting the stabilization of carbon. In the present invention, the stabilization of unbonded carbon is to be realized by bonding with nitrogen, and hydrogen and oxygen are not preferable. Further, since the film formation according to the present invention is carried out under ultra-high vacuum, it is in an environment where hydrogen and oxygen are easily excluded. However, since the working environment after film formation and the usage environment as sliding parts are mainly in the atmosphere, etc., it is inevitable that moisture and oxygen adsorb on the film surface to the surface roughness and the surface film thickness corresponding thereto.

[0029] Hereinafter, based on the test results of the present invention, examples of the present invention will be shown and described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various embodiments can be taken more specifically.

Example

[0030] The carbonaceous film of the present invention was produced under the following conditions. In the process of producing the first DLC film, a DLC film with a thickness of 200 nm was formed by carbon vapor deposition while irradiating with argon gas cluster ions. The acceleration voltage of the argon gas cluster ions was 10 eV per argon atom. In the second step, argon was changed to nitrogen, and carbon vapor deposition was performed while accelerating and irradiating with the same energy as argon, and a nitrogen-containing DLC film with a thickness of 20 nm containing 10.5 at% of nitrogen was laminated. As comparative samples, a comparative sample 1 consisting of a DLC film with a thickness of 200 nm by only the process of producing the first DLC film and a comparative sample 2 of a DLC film (ta-C) containing no nitrogen and hydrogen produced by the filtered cathode method were prepared. For each sample, the hardness was measured with a push-in type hardness tester (nanoindenter), the film density was measured by X-ray total reflection method, and the intensity ratio I of the spectra of the D band and the G band was measured by Raman spectroscopic analysis. D / I G The measurement results are shown in Table 1.

[0031]

Table 1

[0032] As shown in Table 1, for the sample of Comparison 2, both the hardness and density showed values larger than those of the sample of the present invention. This is considered to be because the DLC film produced by the filtered cathode method has an ion impact energy 5 to 10 times larger than that of the sample of the present invention, so that a large amount of impact energy is accumulated in the film. In particular, the hardness measurement by the nanoindenter also shows that the residual stress of the film is large at the same time. Also, in the sample of the present invention, the reason why I D / I G is more than that of the comparative sample is judged to be due to the formation of carbon-nitrogen bonds in the film, resulting in an increase in the I D spectral value.

[0033] For each sample in Table 1, the coefficient of friction was measured using a reciprocating sliding friction and wear tester. The friction and wear test was carried out in an environment controlled at a temperature of 25°C and a humidity of 50%. The test conditions were a load of 200 gf, a friction speed of 16 mm / sec, a reciprocating stroke of 8 mm, and a friction counter material of SUJ-2 with a ball diameter of 3 / 8 inch. The values of the coefficient of friction at 500 reciprocations and 1000 reciprocations are shown in Table 2.

[0034]

Table 2

[0035] The sample of the present invention showed a stable ultra-low coefficient of friction. On the other hand, the sample of Comparison 1 showed stable characteristics although the coefficient of friction was low. Also, in the sample of Comparison 2, the coefficient of friction deteriorated significantly at 1000 reciprocations. This is considered to be related to the fact that the residual stress of the DLC film of Comparison 2 is large, and wear accompanied by relatively large peeling tends to progress.

[0036] The carbonaceous film produced under irradiation assisted by cluster ion beams of argon gas and nitrogen gas according to the present invention stabilizes unbonded carbon with nitrogen and exhibits an ultra-low coefficient of friction. This is because an appropriate ion impact enabled the production of a carbonaceous film with high density, low residual stress, and low susceptibility to film peeling and breakage. This film can be utilized for mechanical parts and electronic components where low friction, low residual stress, and high wear resistance are desired.

Claims

1. By carbon deposition under irradiation assisted by argon gas cluster ions, a DLC film with a film thickness of 100 nm to 2 μm and a density of 2.8 g / cm 3 or more and a hardness of 30 to 50 GPa is formed. On the surface thereof, a nitrogen-containing DLC film with a film thickness of 10 nm to 100 nm and a nitrogen content of 1 to 20 at% is laminated by carbon deposition under irradiation assisted by nitrogen gas cluster ions. A method for producing a thin film carbon material, characterized by this.

2. The manufacturing method of the thin film carbon material according to claim 1, characterized in that the peak intensity ratio of the D band to the G band by Raman spectroscopic analysis of the nitrogen-containing DLC film is I D / I G < 0.9

3. A method for manufacturing a thin-film carbon material according to Claim 1 or 2, characterized in that the average surface roughness is 0.5 nm to 5 nm.

4. A step of forming an intermediate layer film composed of one or more of silicon, chromium, tungsten, titanium and their carbides on the surface of a substrate, and by carbon vapor deposition under argon gas cluster ion assisted irradiation on the surface of the intermediate layer film, the film thickness is 100 nm to 2 μm, and the density is 2.8 g / cm 3 A step of forming a DLC film with a hardness of 30 to 50 GPa or more, and a step of laminating a nitrogen-containing DLC film with a film thickness of 10 nm to 100 nm and a nitrogen content of 1 to 20 at% by carbon vapor deposition under nitrogen gas cluster ion assisted irradiation on the surface of the DLC film. A method for producing a thin film carbon material, characterized by comprising the steps.

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