JP7115849B2 - sliding member - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sliding member, particularly to a sliding member such as an automobile part, which requires high reliability.

2. Description of the Related Art In recent years, in internal combustion engines mainly used in automobiles, there has been a demand for improved output, longer life, and improved fuel efficiency. Therefore, it is common practice to form a hard carbon film known to have a low coefficient of friction, so-called diamond-like carbon (DLC), on the sliding surface of a sliding member used in, for example, an internal combustion engine. ing. ^The bonds between carbon atoms that constitute DLC are a mixture of sp3 bonds that form diamond and ^sp2 bonds that form the hexagonal lattice of graphite, and DLC does not have a specific crystal structure. Therefore, DLC has hardness, wear resistance, and chemical stability similar to those of diamond, as well as solid lubricity similar to that of graphite. Therefore, it is suitable as a protective film for sliding members such as automobile parts that are used under harsh environments such as high temperatures and high loads.

Depending on the difference in the method of supplying the carbon constituting the hard carbon film and the method of film formation, there are those containing hydrogen (hereinafter referred to as "hydrogen-containing hard carbon") and those not containing hydrogen (hereinafter referred to as called "hydrogen-free hard carbon"). Hydrogen-containing hard carbon is formed mainly by plasma CVD (chemical vapor deposition) by introducing a hydrocarbon-based gas containing hydrogen as a constituent element such as methane or acetylene. On the other hand, hydrogen-free hard carbon uses PVD (physical vapor deposition) such as arc ion plating, which forms a film by evaporating and ionizing solid carbon such as graphite by arc discharge. formed by Therefore, the latter hydrogen-free hard carbon is formed without introducing any gas containing hydrogen as a constituent element from the outside, except for hydrogen that is inevitably mixed in the film from substances such as water that remain during film formation. , and the hydrogen content is 10 atomic % or less, preferably 5 atomic % or less.

Among hard carbon coatings formed by various methods, a hydrogen-free hard carbon coating formed by a filtered arc ion plating method, in which fewer fine carbon particles are incorporated into the coating, has attracted attention. In the arc ion plating method, a cathode composed of solid carbon such as graphite is vaporized by arc discharge, and the ionized carbon reaches the substrate surface to form a coating. At this time, fine particles of carbon are also emitted from the cathode with the arc discharge, and are incorporated into the coating. As a result, the surface roughness becomes rough, and fine particles fall off the sliding surface during use, which attacks the coating surface and causes defects such as wear and cracks, and increases friction loss. become. Furthermore, a boundary is formed in the film starting from the carbon microparticles incorporated in the film. This becomes a factor that reduces the mechanical strength of the hard carbon coating.

In contrast, the hard carbon coating formed by the filtered arc ion plating method has a small number of fine carbon particles incorporated into the coating. As a result, compared to the coating formed by the arc ion plating method without a filter, in addition to becoming a smoother coating, the frequency of carbon fine particles falling off the sliding surface during use is reduced, resulting in wear. and the frequency of occurrence of defects and friction loss are reduced. In addition, since defects are less likely to be formed in the coating, it is possible to form a coating with high mechanical strength.

Although the film has such excellent properties, it must be formed with sufficient adhesion to the substrate in order to exhibit this function. A method is proposed.

One of the well-known techniques in this technical field is the technique of forming a metal intermediate layer such as Cr or Ti. This technique is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2002-200012. According to Patent Document 1, such an element reacts with carbon to form a carbide, so that the element forming the intermediate layer and carbon are bonded at the interface between the intermediate layer and the carbon film, and high adhesion can be obtained. It is stated that it is possible.

Next, Japanese Patent Laid-Open No. 2002-200002 discloses a technique that defines the structure of a carbon coating for improving the adhesion of the carbon coating. One of the main causes of peeling of the carbon coating is the high internal stress of the carbon coating. Due to the internal stress, a force acts on the interface between the base material and the intermediate layer to peel off the carbon film, and as the film thickness increases, this force becomes stronger, making the film easier to peel off. On the other hand, in the technique disclosed in Patent Document 2, the internal stress is relieved by stacking a layer having a high internal stress and a layer having a low internal stress.

Techniques are known for defining the structure in the vicinity of the interface between the substrate or intermediate layer and the carbon coating. Patent Document 3 discloses a method of forming a new mixed layer of W or Ti and carbon on the substrate surface. Patent Document 4 discloses a method of diffusing carbon on the substrate surface to form a mixed layer with carbon. Disclosed is a method of forming a

Japanese Patent Application Laid-Open No. 2001-316800 JP-A-10-237627 JP-A-7-62541 JP-A-2000-87218

In recent years, internal combustion engines, such as downsized turbo engines that have improved fuel efficiency in response to environmental conservation, have higher combustion temperatures and higher surface pressures on sliding parts, and low engine oil. Boundary lubrication is likely to occur due to increased viscosity, and the load on the sliding surfaces of sliding members is increasing. Therefore, there is a demand for a sliding member having a hard carbon coating that can reduce friction loss, improve fuel efficiency, and prevent peeling even in extremely severe sliding environments.

However, in the prior art described above, the morphology of the hard carbon coating in the vicinity of the interface with the base material and the intermediate layer has not been sufficiently studied, and there is room for improvement from the viewpoint of high adhesion even under severe sliding conditions.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sliding member having a hard carbon coating that exhibits high adhesion even under severe sliding conditions.

In order to achieve the above object, the present inventors conducted extensive studies and found that the defect near the interface in contact with the intermediate layer of the hard carbon coating made of hydrogen-free hard carbon formed by filtered arc ion plating is a high surface. It was found that this is a factor that reduces the adhesion during sliding under pressure. This is because most of the neutral elements and particles are removed by the filter, and the proportion of ions that contribute to the formation of the film is large, so the unevenness of the base material and intermediate layer surfaces has a greater effect on the film formation. It is speculated that this is a problem specific to the filtered arc ion plating method that a linear low-density region is generated in the hard carbon coating in the vicinity.

In the filtered arc ion plating method, when the carbon cathode is vaporized and ionized by arc discharge, it is common to perform the discharge in a high vacuum environment where no gas is introduced from the outside in order to avoid a drop in transport efficiency in the filter section. target. Then, by passing through the filter, a plasma composed mostly of carbon ions and electrons is sent out from the outlet of the filter section. A sheath electric field is formed in the vicinity of the surface of the intermediate layer placed in this plasma. The ions are accelerated by the sheath electric field in addition to the acceleration by the bias voltage, so when they reach the film formation portion, they are incident on the surface of the intermediate layer from the normal direction. The surface of the intermediate layer forming the hard carbon film generally has irregularities formed by machining, and electric field concentration occurs on the convex portions. Since the ions are accelerated by the electric field and move, the ions also tend to concentrate on the convex portion where the electric field concentrates. Conversely, since the electric field is weak around the convex portion and the concave portion, less ions reach there. As a result, it is considered that unevenness occurs in the film formation at the initial stage of film formation, and linear low-density regions with low carbon density are generated from this as a starting point.

The present invention was completed based on the above knowledge by examining a method for suppressing the formation of a region with a low carbon density formed near the interface with the intermediate layer of the hard carbon coating and increasing the adhesion. The structure of the abstract is as follows.
(1) a substrate;
an intermediate layer having a thickness of 0.010 μm or more and 0.6 μm or less formed on the substrate;
a hard carbon film having a hydrogen content of 10 atomic % or less formed on the intermediate layer;
has
The hard carbon coating has an area ratio of 12% or less of concave portions and convex portions on the surface,
When the cross section of the hard carbon coating in the vicinity of the interface with the intermediate layer is observed with a transmission electron microscope, the number of linear low-density carbon parts observed in a region with a height of 300 nm and a width of 5000 nm from the interface is A sliding member used under oil lubrication, characterized by having 12 or less points.

^{( 2} ) ^{The above (} 1) The sliding member as described in 1).

(3) The sliding member according to (1) or (2) above, wherein the hard carbon coating has a hydrogen content of 5 atomic % or less.

(4) The sliding member according to any one of (1) to (3) above, wherein the hard carbon coating has a thickness of 5 μm or more.

(5) the intermediate layer is composed of at least one element selected from the group consisting of Cr, Ti, Co, V, Mo and W, carbides, nitrides and carbonitrides thereof, and SiC; The sliding member according to any one of (1) to (4) above.

The sliding member of the present invention has a hard carbon coating that exhibits high adhesion even under severe sliding conditions.

1 is a schematic cross-sectional view of a sliding member 100 according to one embodiment of the present invention; FIG. 1 is an image obtained by observing a cross section of a hard carbon coating in Example 1-1 with a transmission electron microscope. 1 is an image obtained by observing a cross section of a hard carbon coating in Comparative Example 1-1 with a transmission electron microscope. It is a figure which shows the method of evaluating each thickness of an intermediate layer and a hard carbon coating. 1 is a diagram showing a method for evaluating adhesion of a hard carbon coating in Example 1. FIG. FIG. 10 is a diagram showing a method of calculating the amount of wear of a hard carbon coating in Example 2; FIG. 10 is a diagram showing a reciprocating sliding test method in Example 2;

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention are described below. It should be noted that the present invention is not limited to the examples shown below.

FIG. 1 is a diagram schematically showing a cross section of a sliding member according to one embodiment of the present invention. Referring to FIG. 1, a sliding member 100 according to one embodiment of the present invention includes a base material 10, an intermediate layer 12 formed on this base material, and a surface formed on this intermediate layer and having at least a sliding surface. and a hard carbon coating 14 that serves as a moving surface.

(Base material)
In the present embodiment, the material of the base material 10 is not particularly limited as long as it has the strength required for the base material of the sliding member. A material having Furthermore, at least a part of the sliding surface of the base material 10 is coated with a hard coating such as a metal nitride such as chromium nitride or titanium nitride, a metal carbonitride, or a metal carbide. Hardening treatment such as nitriding treatment may be performed. As for the roughness of the substrate, at least the sliding surface preferably has an arithmetic mean roughness Ra of 0.01 μm or more and 0.1 μm or less according to JIS-B0601 (2001). When the arithmetic mean roughness Ra is less than 0.01 μm, the processing time and steps become long, resulting in an increase in cost. On the other hand, if Ra exceeds 0.1 μm, the surface roughness after forming the hard carbon film is not preferable as a sliding member. Even if the hard carbon coating is subjected to a polishing treatment, it is difficult to process due to its high wear resistance, resulting in high costs.

The surface roughness of the substrate can be evaluated with a stylus roughness tester before forming the hard carbon coating. If the surface roughness before film formation cannot be evaluated, a cross-sectional sample including the boundary between the hard carbon coating and the substrate is prepared by a method such as Focused Ion Beam (FIB) or Cross Section Polisher. The boundary between the hard carbon coating and the base material is obtained based on the image observed using a scanning electron microscope or the like. Then, the calculation formula for the arithmetic mean roughness Ra described in JIS-B0601 (2001) is applied to this boundary to calculate the arithmetic mean roughness Ra of the substrate.

(middle layer)
The intermediate layer 12 is formed between the base material 10 and the hard carbon coating 14 and has the function of relieving the stress at the interface with the base material 10 and increasing the adhesion of the hard carbon coating 14 . From the viewpoint of exhibiting this function, the intermediate layer 12 contains one or more elements selected from the group consisting of Cr, Ti, Co, V, Mo and W, their carbides, nitrides and carbonitrides, and It is preferably made of at least one type of SiC. The intermediate layer 12 may be made of one or more materials selected from the above group and may be a single layer, a multi-layer laminate, or a laminate in which two or more different layers are combined.

The thickness of the intermediate layer 12 is 0.010 μm or more and 0.6 μm or less, preferably 0.020 μm or more and 0.5 μm or less. If the thickness is less than 0.010 μm, it is difficult to form a uniform intermediate layer, and the function of enhancing the adhesion of the hard carbon coating 14 may not be obtained sufficiently. On the other hand, if the thickness exceeds 0.6 μm, the intermediate layer 12 tends to undergo plastic flow during sliding, and cracks tend to occur in the hard carbon coating 14 .

Examples of methods for forming the intermediate layer 12 include an arc ion plating method, a sputtering method, a plasma CVD method, and the like. For example, in the sputtering method, the substrate 10 after cleaning is placed in a vacuum chamber of a PVD film forming apparatus, a glow discharge plasma is excited in the vicinity of the target while Ar gas is introduced, and the generated Ar ions generate the target. The material is sputtered to deposit the intermediate layer 12 . Targets may be selected from Cr, Ti, Co, V, Mo, W and WC. The thickness of the intermediate layer 12 can be adjusted by adjusting the discharge time of the metal target, applied power, and the like. When SiC is formed as the intermediate layer, a hydrocarbon-based gas containing Si as a constituent element such as tetramethylsilane (TMS) and, if necessary, an inert gas such as Ar or a hydrocarbon-based gas such as methane are introduced. The intermediate layer 12 can be deposited by plasma CVD using high frequency plasma, electron beam excited plasma, or the like. Note that the thickness of the intermediate layer 12 can be adjusted by the discharge time.

As for the surface roughness of the intermediate layer 12, at least the sliding surface preferably has an arithmetic mean roughness Ra of 0.01 μm or more and 0.1 μm or less according to JIS-B0601 (2001). When the arithmetic mean roughness Ra is less than 0.01 μm, the processing time and steps become long, resulting in an increase in cost. On the other hand, if Ra exceeds 0.1 μm, the surface roughness after forming the hard carbon film is not preferable as a sliding member. Even if the hard carbon coating is subjected to a polishing treatment, it is difficult to process due to its high wear resistance, resulting in high costs.

The surface roughness of the intermediate layer on the sliding surface can be evaluated with a stylus roughness tester before forming the hard carbon film. If the surface roughness before film formation cannot be evaluated, a cross-sectional sample including the boundary between the hard carbon coating and the intermediate layer is prepared by a method such as Focused Ion Beam (FIB) or Cross Section Polisher. The boundary between the hard carbon coating and the intermediate layer is determined based on the image observed using a scanning electron microscope or the like. Then, the calculation formula for the arithmetic mean roughness Ra described in JIS-B0601 (2001) is applied to this boundary to calculate the arithmetic mean roughness Ra of the intermediate layer.

(hard carbon coating)
The hard carbon film 14 is an amorphous hard carbon film that does not substantially contain hydrogen, and preferably has a sp ³ bond ratio of more than 60% and less than 100% among sp ² bonds and sp ³ bonds. The hard carbon coating 14 may have an arbitrary distribution of the ratio of sp ³ bonds as long as the ratio is within the above range. For example, multiple layers with different ratios of sp ³ bonds may be stacked. In addition, the ratio of sp ³ bonds in the depth direction of the hard carbon coating may vary linearly from the substrate side toward the surface, and may have a minimum value or a maximum value of 1 or more in the coating, It may change stepwise instead of continuously.

The thickness of the hard carbon coating 14 as a whole is preferably 5 μm or more and 30 μm or less. If the thickness is less than 5 μm, the required durability cannot be secured in sliding with the mating material. This is because problems such as chipping and peeling may occur, concentrating on the carbon portion 16 .

Preferably, the hard carbon coating 14 consists only of amorphous hard carbon (DLC) that does not substantially contain hydrogen. Amorphous carbon can be confirmed by Raman spectrum measurement using a Raman spectrophotometer (Ar ion laser).

For example, the hard carbon coating 14 is formed by using arc discharge in a high vacuum or an atmosphere in which an inert gas such as Ar gas is introduced without introducing a gas containing hydrogen as a constituent element such as a hydrocarbon gas in a vacuum. It can be formed using a PVD method such as a filtered arc ion plating method equipped with a filter that removes carbon microparticles, such as a magnetic filter with curved magnetic lines of force. As a result, it is possible to form an amorphous carbon film that is smooth, contains little hydrogen, has high hardness, and is excellent in wear resistance. Introducing an inert gas makes it easier to maintain a stable arc discharge, but increases the probability of neutralizing carbon ions due to charge-exchange scattering, and the neutralized carbon passes through the filter. The amount of carbon ions that contribute to the film formation due to the inability to do so is reduced. For this reason, it is preferable to form the hard carbon film in a high-vacuum atmosphere in which no gas is introduced from the outside, except for the initial stage of forming the hard carbon film, which will be described later. In addition, in the actual film formation, it is unlikely that hydrogen will inevitably be mixed into the film due to atmospheric leaks due to the operation of the equipment or the release of water adsorbed on the walls of the film formation chamber during film formation. Unavoidable. Therefore, the hydrogen content of the hard carbon coating 14 is preferably 10 atomic % or less, more preferably 5 atomic % or less.

Here, the ratio of sp ³ bonds in the hard carbon coating 14 is determined by the bias voltage applied to the substrate 10 and the Ar gas introduced as the atmosphere gas when using the ion plating method by vacuum arc discharge using a carbon cathode. It can be adjusted by pressure. As the bias to be applied, an application method such as direct current, pulse, or floating potential can be used. A plurality of methods may be combined. In particular, since pulse bias and floating potential can reduce the bias current flowing through the film, they are preferred bias application methods for forming insulating hard carbon films with a high ^sp3 ratio. Specifically, when the bias voltage is increased, the kinetic energy of the carbon ions colliding with the substrate increases, and the conductivity is ensured in the coating, so that the ratio of ^sp2 bonds in the hard carbon coating increases. get higher For this reason, in order to form a hard carbon film having a ratio of sp ³ bonds exceeding 60%, it is preferable to form the film with the bias voltage set within a predetermined range. The bonding state of carbon (ratio of sp ² bonding and sp ³ bonding) in the hard carbon coating can be measured by Electron Energy Loss Spectroscopy (EELS).

(Area ratio of carbon microparticles and recesses and protrusions formed from these particles)
Carbon microparticles are emitted from the carbon cathode along with the arc discharge. Such carbon microparticles adhere to the surface of the film or are mixed in the film. In addition, the coating may grow locally starting from foreign matter mixed in the coating to form protrusions. Furthermore, there is a case where the convex portion falls off to form a concave portion. As a result, the surface roughness of the film becomes rough and unsuitable for a sliding member, and it becomes difficult to apply a smoothing process. As a method for reducing the unevenness formed on the coating surface, a filtered arc ion plating method equipped with a mechanism for removing carbon fine particles emitted from the cathode due to arc discharge, such as a magnetic filter equipped with curved magnetic lines of force. can be used. As a result, it is possible to reduce the carbon microparticles incorporated into the coating surface and its interior, and the protrusions and recesses formed on the coating surface starting from these particles.

The area ratio of such recesses and protrusions on the coating surface can be specified as follows. First, an image is acquired by observing with an optical microscope from a direction perpendicular to the coating surface. It is preferable to use a confocal laser microscope that can obtain images with high resolution. The obtained image is grayscaled as necessary, and then subjected to automatic binarization processing using the differential histogram method, and binary image fill-in processing. Then, the area ratio can be specified by calculating the area ratio of the dark portion to the entire image. If the area ratio of the recesses and protrusions on the surface of the film is 12% or less, the number of fine carbon particles and the like falling off during sliding can be reduced, the wear resistance can be improved, and the friction loss can be reduced. More preferably, the area ratio is 10% or less. As described above, the smaller the number of fine carbon particles incorporated into the hard carbon coating, the more preferable the hard carbon coating is for sliding member applications. However, if the removal rate of carbon microparticles emitted by arc discharge is increased, the amount of carbon ions required for film formation is also reduced. As a result, the use efficiency of the carbon cathode is lowered and the film formation speed is also lowered, resulting in a longer film formation time and an increase in the cost spent to form the hard carbon coating. Alternatively, if the frequency of occurrence of carbon microparticles emitted with arc discharge is reduced, the arc discharge current will be reduced, so the film formation rate will be reduced and the film formation time will be increased. Increases the cost spent. Therefore, it is preferable that the area ratio of the recesses and protrusions on the coating surface is 1% or more.

(Linear low-density carbon part)
The linear low-density carbon part is a defect inside the coating formed near the boundary between the hard carbon coating and the intermediate layer, and near the boundary between the hard carbon coating and the intermediate layer produced using FIB. When observing the cross section of a thin piece sample containing with a transmission electron microscope, it refers to a bright linear part with respect to the brightness of the entire hard carbon coating. The low-density carbon part is distributed on the surface in the hard carbon coating, but by preparing a cross-sectional sample, a part of it is cut out and appears as a line. FIG. 3 shows the linear low-density carbon portions observed in Comparative Example 1-1. In this example, a Ti intermediate layer is formed on the substrate surface and a hard carbon coating is formed.

In this embodiment, also referring to FIG. 1, when a cross section near the interface of the hard carbon coating 14 with the intermediate layer is observed with a transmission electron microscope, the It is essential that the number of linear low-density carbon portions 16 is 12 or less. As a result, the hard carbon coating has sufficiently high mechanical strength, and can exhibit high adhesion even under severe sliding conditions.

As a result of intensive research on the conditions under which linear low-density carbon portions are formed in the hard carbon coating, the present inventors found that the unevenness of the interface forming the hard carbon coating and the ionization rate as in the filtered arc ion plating method are different. It has been found that the application of a high film formation method, particularly the latter, is a factor strongly related to the formation of linear low-density carbon portions. From these facts, the following mechanism can be considered as one of the formation mechanisms of the linear low-density carbon part.

In the filtered arc ion plating method, a magnetic filter with curved magnetic lines of force is used to suppress the inclusion of fine carbon particles emitted from the carbon cathode during arc discharge into the film. Equipped with a mechanism to remove carbon microparticles with a small specific charge even if they have an electric charge due to charging or the like. Since this filter also removes carbon atoms, the hard carbon coating is formed mainly by carbon ions. A bias voltage is normally applied during film formation. Even when no bias is applied, a sheath electric field is formed near the surface of the intermediate layer, so the carbon ions are accelerated by this electric field and reach the film formation portion. On the surface of the intermediate layer, which is a mirror surface with no unevenness, the flow of ions is almost perpendicular to the intermediate layer and uniform. However, since the sliding member generally has unevenness formed by machining, an electric field is formed in the vicinity of the surface of the intermediate layer such that the electric field concentrates on the convex portion. This electric field affects the flow of ions, making them more likely to move toward the protrusions. As a result, the number of ions that reach near the convex portion decreases, and a boundary with low carbon density is formed due to the difference in film formation rate. It is believed that this boundary appears linear by observing a thinned cross-sectional sample of the coating.

Therefore, in order to prevent the formation of low-density carbon parts, it is important to have a situation in which a hard carbon film can be formed without being affected by the electric field, that is, to increase the contribution of uncharged carbon atoms to the film formation. I came to the idea that it is. And as one method to realize this, an inert gas that does not affect the elements that form the hard carbon film such as He and Ar is introduced at an appropriate pressure and transported by a magnetic filter by the filtered arc ion plating method. We devised a method to neutralize a part of the carbon ions formed by using charge-exchange scattering to enhance the contribution of carbon atoms to film formation. The flow rate of the inert gas is adjusted so that the film formation rate is 70% or more and 98% or less based on the film formation rate of the hard carbon layer when the inert gas is not introduced.

The filtered arc ion plating method removes neutral elements that do not have an electric charge, and charged carbon microparticles that do not have an electric charge or have a small specific charge, and is characterized by a high ratio of ions contributing to film formation. and On the other hand, as described above, the inert gas is introduced at a predetermined pressure to create a situation in which the ionization rate is temporarily low in the initial stage of film formation, thereby increasing the contribution of neutralized carbon to film formation. This suppresses the formation of low-density carbon portions. It is preferable that the inert gas is introduced for 1 minute or more and 20 minutes or less in the initial stage of hard carbon layer formation. In such a method, part of the ions are neutralized by charge exchange scattering even while the filter is being transported, resulting in a temporary drop in the film formation rate. However, since this method is used temporarily at the beginning of the formation of the hard carbon coating, the effect on the film formation time is small. The impact on time will be smaller and will not be a factor in increasing costs.

One or more elements selected from He, Ne, and Ar can be used as the inert gas to be introduced. If the atomic number is higher than that of an element such as Kr that constitutes the intermediate layer, the hard carbon coating and the intermediate layer may be damaged. It is more preferable to use He or Ne, which have a smaller atomic number than the elements forming the hard carbon coating and the intermediate layer.

In the sliding member of this embodiment described above, the adhesion of the hard carbon coating to the base material is good, and this can be recognized and maintained for a long period of time. Furthermore, foreign matter such as fine carbon particles that fall off the coating during sliding is suppressed from entering the sliding portion. These effects make it possible to stably maintain the low friction loss characteristics of the hard carbon coating over a long period of time. Therefore, for example, valve lifters and shims, which are valve train parts of internal combustion engines such as automobiles, piston pins and piston rings, which are parts of internal combustion engines, vanes for compressors and hydraulic pumps, etc., are used under high surface pressure and require durability. The present invention can be suitably applied to a sliding member that is to be used.

(Example 1-1)
As a test piece, a piston ring (top ring) made of spring steel with a nominal diameter of φ80, h1 = 1.2, and a1 = 2.5 was used, and the intermediate layer and hard carbon coating shown in Table 2 were applied to the outer peripheral surface. formed. Before film formation, the outer peripheral surface of the piston ring was polished to adjust the surface arithmetic mean roughness Ra to be in the range of 0.05 μm to 0.1 μm. Prior to film formation, cleaning was performed to remove stains such as antirust oil. Then, a film formation jig attached with a piston ring was installed on one axis of a rotation/revolution turntable installed in the film formation chamber of the film formation apparatus, and the pressure in the film formation chamber reached 5×10 ⁻³ Pa or less. Evacuation was performed.

After evacuation, the outer circumference of the piston ring was subjected to ion bombardment, and an intermediate layer made of Cr was formed on the outer circumference of the piston ring by a sputtering method. Next, using an arc evaporation source equipped with a magnetic filter, the formation of a hard carbon coating was started while evaporating the carbon cathode (98 atomic % or more) by arc discharge at a discharge current of 120A. At that time, He was introduced at a flow rate that gives the pressure shown in Table 2. Subsequently, after 3 minutes, without stopping the arc discharge, the flow rate of He was started to be decreased by a fixed amount, and 0 in 6 minutes from the start of formation of the hard carbon coating. In this state, a hard carbon film was formed, and the film forming conditions were adjusted so that the film thickness fell within the range of 5.0 to 5.3 μm. The pressure in the film formation chamber at this time is 0.008 Pa or less. The hard carbon film after film formation was polished to adjust the surface arithmetic mean roughness Ra to be in the range of 0.05 μm to 0.1 μm.

(Examples 1-2 to 1-6 and Comparative Examples 1-1 to 1-3)
In the same manner as in Example 1-1, the intermediate layer and the hard carbon coating were formed under the conditions of Examples 1-2 to 1-6 and Comparative Examples 1-1 to 1-3 shown in Table 2. membrane was performed. The intermediate layer in Comparative Example 1-2 was formed by plasma CVD by introducing tetramethylsilane (TMS).

[Evaluation of thickness of intermediate layer and hard carbon coating]
The surface of the piston ring, which is the base material, and the surfaces of the intermediate layer and the hard carbon coating formed on this surface are not flat but uneven due to polishing or the like. Therefore, the thicknesses of the intermediate layer and the hard carbon layer were measured by the following method.

A part of the piston ring on which the hard carbon coating is formed is cut out, and a focused ion beam (FIB) is applied to the thickness direction (h1 direction) of the piston ring perpendicular to the surface of the hard carbon coating as shown in FIG. A thin section with a uniform cross section was prepared. This cross section is observed with a transmission electron microscope to determine the coordinates of 10 different points P1, P2, . A quadratic curve BL representing In addition, when the intermediate layer is not formed, the boundary between the substrate 10 and the hard carbon film 14 is obtained.

D1 is the distance from 10 randomly selected positions on the curve BL to the boundary between the intermediate layer 12 and the hard carbon coating 14 in the direction perpendicular to the curve BL, and from this boundary to the surface of the hard carbon coating 14. The distance of D2 was measured respectively. Then, the average values of the distances D1 and D2 were obtained and used as the thickness of the intermediate layer 12 and the thickness of the hard carbon coating 14 . When the intermediate layer was not formed, the distance between the base material 10 and the surface of the hard carbon coating 14 was defined as D2, and the average value was obtained to obtain the thickness of the hard carbon coating 14 . Table 2 shows the thicknesses of the intermediate layer and the hard carbon coating evaluated in this manner.

[Evaluation of hydrogen content of hard carbon coating]
The hydrogen content of the hard carbon coating is evaluated by RBS (Rutherford Backscattering Spectrometry)/HFS (Hydrogen Forward Scattering Spectrometry) for the hard carbon coating formed on a flat surface or a surface with a sufficiently large curvature of the sliding part. can be evaluated. On the other hand, a hard carbon coating formed on an uneven sliding surface such as the outer peripheral surface of a piston ring is evaluated by combining RBS/HFS and SIMS (Secondary Ion Mass Spectrometry). Although RBS/HFS is a known method of coating composition analysis, it is not applicable to the analysis of uneven surfaces, so RBS/HFS and SIMS are combined as follows.

First, as a reference sample having a flat surface, a mirror-polished flat test piece (hardened SKH51 disk, φ25 × thickness 5 mm, hardness HRC 60 to 63) was applied to a hard surface to be measured as a reference value. Forms a carbon coating.

Film formation on the reference sample is performed by introducing C ₂ H ₂ , Ar, and H ₂ as atmosphere gases using a reactive sputtering method. Then, by changing the H ₂ flow rate and/or the C ₂ H ₂ flow rate to be introduced, the amount of hydrogen contained in the hard carbon layer is adjusted. In this way, hard carbon coatings composed of hydrogen and carbon with different hydrogen contents are formed, and these are evaluated for hydrogen content and carbon content by RBS/HFS.

Next, the above sample is analyzed by SIMS to measure the secondary ion intensities of hydrogen and carbon. Here, SIMS analysis can also be used to measure non-flat surfaces, such as coatings formed on the outer peripheral surface of piston rings. Therefore, the hydrogen content and carbon content (unit: atomic %) obtained by RBS/HFS and the secondary An empirical formula (metric line) showing the relationship with the ratio of ionic strength is obtained. By doing so, the hydrogen content and the carbon content can be calculated from the SIMS hydrogen and carbon secondary ion intensities measured on the outer peripheral surface of the actual piston ring. For the value of the secondary ion intensity by SIMS, the average value of the secondary ion intensity of each element observed in a range of 50 nm square and at a depth of at least 20 nm from the film surface is adopted. Table 2 shows the hydrogen content of the hard carbon coating calculated in this way.

[Observation near boundary of hard carbon film]
The vicinity of the boundary between the hard carbon coating formed on the sliding surface and the intermediate layer is observed using a transmission electron microscope (TEM). A FIB is used to make a section perpendicular to the surface of the hard carbon coating. Then, in the vicinity of the boundary between the intermediate layer and the hard carbon coating, the hard carbon coating having a thickness of 350 nm or more is within the field of view, and an approximately 1000 nm square is observed so that the boundary is not interrupted. For example, when H-9000NAR manufactured by Hitachi High-Technologies Corporation is used as a transmission electron microscope, observation can be performed at an acceleration voltage of 200 kV and a magnification of 205,000. In this way, the boundary region between the intermediate layer and the hard carbon coating is observed for the region where the carbon microparticles incorporated into the hard carbon coating are not observed in the field of view, and the image is continuous over the region with a width of 5 μm. to get At this time, it is desirable that the images of adjacent regions overlap each other by 10% or more of the field of view. Then, the number of linear low-density carbon portions observed in a region with a height of 300 nm and a width of 5000 nm from the interface is evaluated from these adjacent and consecutively acquired images. However, since a thin sample prepared by FIB has a thickness, the same low-density carbon portion may be observed as a plurality of linear low-density carbon portions when obliquely observed. In order to avoid this, a plurality of linear low-density carbon portions recognized within a distance of 60 nm are determined to be the same and counted as one location. In addition, since the brightness of the image becomes bright in the TEM observation at the low-density portion, the brightness of the image may be adjusted so that the linear low-density carbon portion can be easily distinguished. Table 2 shows the number of linear low-density carbon portions evaluated in this way. Further, representative TEM images obtained in Example 1-1 and Comparative Example 1-1 are shown in FIGS. 2 and 3, respectively.

[Evaluation of area ratio of recesses and protrusions on coating surface]
The area ratio of unevenness on the surface of the coating on the sliding surface is calculated from an image of the sliding surface after cleaning and removing polishing dust and abrasives from the coating on the surface of the coating, as well as adhering dust and dirt. First, the coating surface of the sliding surface is observed from the vertical direction using a confocal laser microscope to obtain an image. As a confocal laser microscope, LEXT OLS4000 manufactured by Olympus Co., Ltd. with a 100-fold objective lens can be used. When the sliding surface is a curved surface with a small radius of curvature, an image projected onto a plane perpendicular to the observation direction is obtained. Laser light is irregularly reflected or absorbed in convex or concave portions, resulting in low luminance of the obtained image, which is darker than the film surface. By doing so, the area ratio of the dark portion to the entire image is calculated. Then, the area ratio is calculated by the above-described procedure at any five points on the sliding surface, and the average value is obtained. Table 3 shows the area ratios of the concave portions and the convex portions thus obtained.

[Evaluation of sp ³ ratio of hard carbon coating]
The ^sp3 ratio of carbon constituting the hard carbon coating was evaluated using the hard carbon coating thin section sample used in the TEM observation described above. This is evaluated by electron energy loss spectroscopy (TEM-EELS) using a scanning transmission electron microscope. For example, JEM-ARM200F manufactured by JEOL Ltd. can be used for the scanning transmission electron microscope, and QuantumER manufactured by Gatan can be used for the detector.

Information on the bonding state between carbons can be obtained by analyzing the observed values near the CK loss edge of the electron energy loss spectrum obtained by EELS. Usually, this spectrum does not provide observed values as they are, but provides a spectrum corrected for effects such as multiple scattering and background signals. Based on this corrected spectrum, analysis is performed according to the following procedure to calculate the sp ³ ratio between carbons.

ここで、ｘは電子の損失エネルギー（単位：ｅＶ）であり、式（１）の右辺第一項は観測された電子数の減衰を、第二項は観測値全体の傾きを表す。
（Ｂ）得られた回帰曲線を基にして、式（２）に従って観測値を規格化する。

（Ｃ）上記（Ｂ）の規格化されたデータを用いて、２８０ｅＶ以上２９５ｅＶ以下の範囲において、２つのピークが存在するとみなし、Ｇａｕｓｓ関数を用いてピーク分離を行い、低エネルギー側のピーク（２８５ｅＶ付近のピーク）に相当するＧａｕｓｓ関数の面積を求める。これをＳ_πとする。
（Ｄ）上記（Ｂ）の規格化されたデータにおいて、２８０ｅＶ以上３１０ｅＶ以下の面積を算出する。これをＳ_{（σ＋π）}とする。
（Ｅ）同様に、ダイヤモンド及びグラファイトの薄片化された試料について、上記（Ａ）～（Ｄ）までの手順で観測し、２８５ｅＶ付近のピークに相当するＧａｕｓｓ関数の面積、及び規格化された電子エネルギー損失スペクトルの２８０ｅＶ以上３１０ｅＶ以下の面積をそれぞれ算出する。ダイヤモンドについて得られたそれぞれの面積を、Ｓ_ｄπ及びＳ_{ｄ（σ＋π）}、グラファイトについては、Ｓ_ｇπ及びＳ_{ｇ（σ＋π）}とする。
（Ｆ）式（３）に上記のそれぞれの面積を代入してｓｐ^３比率を算出する。

このようにして評価したｓｐ^３比率を表２に示す。 Here, the energy loss spectrum starts at least below 240 eV and acquires data at intervals of 0.25 eV or less in the energy region up to 550 eV or above.
(A) For data with an energy loss of 320 eV or more, an approximate curve is calculated using the function shown in Equation (1).

Here, x is electron loss energy (unit: eV), the first term on the right side of Equation (1) represents the attenuation of the number of observed electrons, and the second term represents the slope of the entire observed value.
(B) Based on the obtained regression curve, the observed values are normalized according to Equation (2).

(C) Using the normalized data of (B) above, it is assumed that there are two peaks in the range of 280 eV or more and 295 eV or less, peak separation is performed using the Gaussian function, and the low energy side peak (285 eV The area of the Gaussian function corresponding to the peak in the vicinity) is obtained. Let this be S _π .
(D) Calculate the area of 280 eV or more and 310 eV or less in the normalized data of (B) above. Let this be S _(σ+π) .
(E) Similarly, the diamond and graphite sliced specimens were observed by the above procedures (A) to (D), and the area of the Gaussian function corresponding to the peak near 285 eV and the normalized electron The area of the energy loss spectrum of 280 eV or more and 310 eV or less is calculated. Let the respective areas obtained for diamond be S _dπ and S _d(σ+π) and for graphite S _gπ and S _g(σ+π) .
(F) Calculate the sp ³ ratio by substituting each of the above areas into equation (3).

Table 2 shows the sp ³ ratios evaluated in this way.

[Adhesion evaluation test]
FIG. 5 shows an outline of the reciprocating motion test used to evaluate adhesion. For the test, a test piece 50 was obtained by cutting a portion at 170 to 190 degrees with respect to the gap of the piston ring on which the hard carbon film was formed. Then, it was fixed to a holder (not shown) and a constant load was applied from above. A SUJ-2 plate (length 80 mm in the sliding direction, length 30 mm in the direction perpendicular to the sliding direction, thickness 8 mm, HRC 58 to 63) was used as the mating member 52 that slides against the test piece 50 . The SUJ-2 plate was polished in random directions and adjusted to have a surface roughness Ra of 0.04 to 0.07 μm. These were arranged as shown in FIG.

Then, the sliding surface after the test was observed with an optical microscope to observe the state of remaining hard carbon coating. "○" indicates that no peeling of the hard carbon coating is observed, and "△" indicates that peeling occurs within the range of the cross section (sliding part) of the hard carbon coating formed by sliding, outside this range. In Table 2, "x" indicates the case where the film peeled off in the non-sliding area.

As is clear from Table 2, in Examples 1-1 to 1-6, the number of linear low-density carbon portions was 12 or less, and it was confirmed that they had good adhesion. In particular, in Examples 1-1 to 1-3 and Examples 1-5 and 1-6, in which the number of linear low-density carbon portions was 10 or less, the hard carbon coating peeled off at the sliding portion. is not observed and has better adhesion.

On the other hand, in Comparative Example 1-1, in which the number of linear low-density carbon portions exceeds 12, and in Comparative Example 1-2, in which the thickness of the intermediate layer is less than 0.010 μm, the peeling of the hard carbon film is smooth. It spreads further than the moving part and does not have sufficient adhesion. In Comparative Example 1-3, in which the thickness of the intermediate layer was more than 0.6 μm, no peeling of the hard carbon coating was observed. I confirmed that there was a crack. When this cracked portion was processed into a thin sample by FIB and observed with a scanning electron microscope, it was confirmed that a crack was formed in the hard carbon coating and the thickness of the intermediate layer located near the crack was different. From this, it is considered that the sliding load causes the intermediate layer to undergo plastic flow, and a shearing force acts on the film in the sliding direction.

(Example 2-1)
A piston ring (top ring) made of spring steel with a nominal diameter of φ80, h1 = 1.2, and a1 = 2.5 was used as a test piece, and an intermediate layer and a hard carbon coating were formed on the outer peripheral surface of the ring. Before film formation, the outer peripheral surface of the piston ring was polished to adjust the surface arithmetic mean roughness Ra to be in the range of 0.05 μm to 0.1 μm. Prior to film formation, cleaning was performed to remove stains such as antirust oil. Then, a film formation jig attached with a piston ring was installed on one axis of a rotation/revolution turntable installed in the film formation chamber of the film formation apparatus, and the pressure in the film formation chamber reached 5×10 ⁻³ Pa or less. Evacuation was performed.

After evacuation, the outer periphery of the piston ring was subjected to ion bombardment, and an intermediate layer made of Cr and having a thickness of 0.33 μm was formed by an arc ion plating method. Next, using an arc evaporation source equipped with a magnetic filter, a hard carbon coating was formed under the same conditions as in Example 1-1. The hard carbon film after film formation was polished to adjust the surface arithmetic mean roughness Ra to fall within the range of 0.05 μm to 0.08 μm.

(Examples 2-2 to 2-6)
A film was formed on the test piece under the same conditions as in Example 2-1. However, the hard carbon layer was formed under the discharge current conditions shown in Table 3.

(Example 2-7)
Under the same conditions as in Example 2-1, the heater in the film formation chamber was energized to control the temperature to 200±2° C., and film formation was performed.

(Comparative Example 2-1)
Under the same conditions as in Example 2-1, CH ₄ and H ₂ were introduced under predetermined conditions to form a hard carbon coating with a high hydrogen content.

(Comparative Example 2-2)
Using an arc-type evaporation source without a filter, Ar was introduced, and under the conditions of a discharge current of 40 A and a pressure of 0.03 Pa, a hard carbon coating was formed to the film thickness shown in Table 3.

[Evaluation of hard carbon coating]
Table 3 also shows the thickness of the hard carbon coating, the amount of hydrogen, the number of linear low-density carbon portions, the area ratio of concave portions and convex portions, and the sp ³ ratio obtained by the method described above.

[Evaluation of wear test and wear coefficient]
Each piston ring of each example and comparative example was produced, and a reciprocating wear test was used to evaluate the wear resistance and friction coefficient of the hard carbon coating. The sliding mating material is a test piece (flat plate) of FC250, which is equivalent to a cylinder, and its surface roughness is adjusted to a ten-point average roughness Rzjis according to JIS-B0601 (2001) of 0.9 μm to 1.3 μm. was used. Next, the piston ring of each example and comparative example was cut to a length of about 30 mm to prepare a piston ring piece, which was attached to a fixture (not shown) of a reciprocating sliding tester, and the piston ring was The hard carbon film formed on the outer peripheral surface was pressed against the surface of the test piece of the sliding mating material with a vertical load of 40N. In this state, the test was conducted by reciprocatingly sliding the piston ring piece in the thickness direction at a reciprocating width of 50 mm and an average sliding speed of 1.0 m/s. Lubricating oil (engine oil; 10W-30) was dripped onto the surface of the test piece at a rate of 0.1 ml/min, the temperature of the test piece during the test was set to 120°C, and the test time was set to 10 minutes. After the test, elliptical sliding marks were observed when the hard carbon coating was worn.

As shown in FIG. 6(a), the wear amount of the hard carbon film on the outer peripheral surface was calculated. First, the shape of the outer periphery including the sliding portion 80a of the piston ring piece 80 after the test was measured in the circumferential direction using a stylus type roughness measuring instrument (SURFCOM1400D manufactured by Tokyo Seimitsu Co., Ltd.). Then, from the curvature radius (known) of the outer circumference of the piston ring piece 80 before the test, the outer edge 80f of the piston ring piece 80 before the test is calculated, and the maximum value of the radial dimensional difference between the outer edge 80f and the sliding portion 80a. was taken as the amount of wear. In addition, as shown in FIG. 6(b), shape measurement was performed at a position L near the center of the sliding portion 80a along the axial direction of the piston ring piece 80. As shown in FIG. The coating wear amount shown in Table 3 is expressed as a relative value when the wear amount of Example 2-1 is set to 1.

The above wear test was performed using the reciprocating motion wear tester shown in FIG. The value obtained by dividing the maximum friction force in one reciprocating motion of the piston ring piece by the pressing load is the friction coefficient a, and the final average value of the friction coefficient a for 1 minute before the end of the test (9 to 10 minutes after the start of the test) was adopted as a reasonable friction coefficient. Table 3 shows relative values with the wear coefficient of Example 2-1 as the standard (1.00).

As is clear from Table 3, in Examples 2-1 to 2-7 in which the area ratio of concave portions and convex portions on the coating surface due to the carbon microparticles incorporated in the hard carbon coating was 12% or less, It has a low coefficient of friction and good wear resistance. In particular, Examples 2-1 and 2- in which the hydrogen content was 5 atomic % or less, the area ratio of unevenness on the film surface was 10% or less, and the ratio of sp ³ bonds between carbons was 60% or more. 2. In Examples 2-4 to 2-6, the coefficient of friction was particularly small, and the wear of the film was small, indicating good sliding properties. Examples 2-1 to 2-5, in which the area ratio of unevenness on the coating surface was 12% or less, confirmed that the film formation rate exceeded 3 times that of Example 2-6, and high production was achieved. It has properties that are preferable as a hard carbon coating that is applied to sliding members for use in industrial products, since it has good wear resistance while having a low coefficient of friction while having good properties.

On the other hand, in Comparative Example 2-1, in which the hydrogen content exceeded 10 atomic %, the wear amount of the film was large and the wear resistance was poor. In Comparative Example 2-2, in which the area ratio of the recesses and projections exceeded 12%, the coefficient of friction was high and the amount of coating wear was large. After the test, when the film sliding portion of the test piece was observed with an optical microscope, many scratches were present in the sliding direction. This is because the fine carbon particles taken into the coating during sliding and the coating growth portion resulting therefrom fall off due to the load of sliding, and when mixed with the lubricating oil, they stay in the sliding portion, resulting in the formation of the coating. This is thought to be due to accelerated wear.

The sliding member of the present invention is used under severe sliding conditions such as a downsized turbo engine aimed at improving fuel efficiency in response to environmental conservation, where the combustion temperature is higher and the surface pressure of the sliding part is higher. Since it has high wear resistance and low friction loss even when it is used under the environment, it can be suitably used especially for sliding members used in internal combustion engines.

REFERENCE SIGNS LIST 100 sliding member 10 substrate 12 intermediate layer 14 hard carbon coating 16 linear low-density carbon part

Claims (5)

a base material;
an intermediate layer having a thickness of 0.010 μm or more and 0.6 μm or less formed on the substrate;
a hard carbon film having a hydrogen content of 10 atomic % or less formed on the intermediate layer;
has
The hard carbon coating has an area ratio of 12% or less of concave portions and convex portions on the surface,
When a cross section of the hard carbon coating near the interface with the intermediate layer is observed with a transmission electron microscope at an acceleration voltage of 200 kV, a linear low density is observed in a region of 300 nm in height and 5000 nm in width from the interface. A sliding member used under oil lubrication, characterized in that the number of carbon portions is 12 or less. 2. The hard carbon coating according to claim 1, wherein the hard carbon film is made of carbon in which sp ² bonds and sp ³ bonds are mixed, and the ratio of sp ³ bonds among the sp ² bonds and sp ³ bonds is more than 60% and less than 100%. sliding member. 3. The sliding member according to claim 1, wherein the hard carbon coating has a hydrogen content of 5 atomic % or less. The sliding member according to any one of claims 1 to 3, wherein the hard carbon coating has a thickness of 5 µm or more. The intermediate layer comprises at least one element selected from the group consisting of Cr, Ti, Co, V, Mo and W, carbides, nitrides and carbonitrides thereof, and SiC. 5. The sliding member according to any one of 1 to 4.

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