Sliding member and piston ring

Abstract

Provided are a sliding member and a piston ring having a DLC coating film that has excellent wear resistance even when used in a boundary lubrication environment. This sliding member has a base material and a DLC film that is formed on the surface of the base material and does not substantially contain hydrogen, and is characterized in that: the center wave number of the G band in the Raman spectrum of the DLC film obtained by Raman spectroscopy using laser light in the visible region as excitation light is 1585 cm-1 or more; the DLC coating film obtained by a nanoindentation method has a hardness (HIT) of 15 GPa or more and 35 GPa or less in a gigapascal unit.

Description

Technical Field

[0001] This invention relates to sliding components and piston rings. Background Technology

[0002] Piston rings are a type of sliding component installed on the piston in an internal combustion engine to maintain a gas-tight seal between the piston and the cylinder. Two or three piston rings are installed near the piston head to create a seal, preventing combustion gases generated in the cylinder from leaking to the crankshaft side. Furthermore, piston rings control the thickness of the oil film that forms on the inner wall of the cylinder. Finally, piston rings also help to expel combustion heat from the piston into the cylinder.

[0003] In addition to these basic functions, piston rings also require durability. In particular, the outer circumferential surface of the piston ring rubs against the inner wall of the cylinder during the reciprocating motion of the piston, thus requiring wear resistance. To reduce the sliding friction between the piston ring and the inner wall of the cylinder, the formation of a hard carbon film on the surface of the piston ring substrate is being investigated.

[0004] For example, Patent Document 1 describes an invention of a component in which a hard carbon layer composed of diamond-like carbon (hereinafter sometimes referred to as "DLC") is formed on the surface of a substrate. When the hard carbon layer is measured by Raman spectroscopy, the area intensity ratio (ID / IG) of the D band to the G band peaks in the Raman spectrum is 1 to 6. Furthermore, Patent Document 2 describes an invention of a component in which hard carbon layers composed of two different types of DLC with different properties are alternately stacked on the surface of a substrate. These prior art hard carbon layers are formed by applying a bias voltage to the substrate while heating the substrate with a heater during film formation.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-123431;

[0008] Patent Document 2: International Publication No. 2017 / 104822. Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In existing technologies, a method to improve piston ring durability involves forming a high-hardness DLC film on the surface of the piston ring substrate. By having a high-hardness DLC film on its surface, the piston ring can effectively prevent wear on the DLC film on its outer circumferential surface, which rubs against the cylinder wall. This extends the piston ring's lifespan and thus reduces the replacement frequency.

[0011] In recent automotive engines, to meet the demands for higher output and stricter exhaust regulations, there is a trend towards increasing the combustion temperature of gasoline in the cylinder, using engine oil with lower viscosity than before, and reducing the amount of engine oil used. Along with these new technological trends, the lubrication between the outer circumference of the piston rings and the inner wall of the cylinder is shifting from a fluid lubrication environment where an oil film continuously forms to a boundary lubrication environment where a thin oil film locally creates direct metal-to-metal contact.

[0012] According to the inventors' research, when piston rings with a high-hardness DLC film on their surface are used in boundary lubrication environments, the wear of the DLC film on the outer circumferential surface of the piston ring is more accelerated than in fluid lubrication environments. This indicates that for piston rings used in boundary lubrication environments, simply increasing the hardness of the DLC film, as has been done previously, is insufficient to ensure the required wear resistance of the piston ring.

[0013] Furthermore, in existing technologies, when using high-hardness DLC films to improve piston ring durability, the DLC film thickness must be substantial. In this case, the time required for DLC film formation increases the manufacturing cost of the piston rings.

[0014] The present invention was made in view of the above-mentioned problems, and aims to provide a sliding member and piston ring having a DLC film with excellent wear resistance even when used in a boundary lubrication environment.

[0015] Solution for solving the problem

[0016] The main contents of this invention are as follows.

[0017] [1] A sliding member, characterized in that it has a substrate and a substantially hydrogen-free DLC film formed on the surface of the substrate.

[0018] The central wavenumber of the G band in the Raman spectrum of the aforementioned DLC film, obtained by Raman spectroscopy using a laser in the visible range as excitation light, is 1585 cm⁻¹. -1 above,

[0019] The hardness H of the DLC film obtained by nanoindentation, expressed in gigapascals. IT The range is between 15 GPa and 35 GPa.

[0020] [2] According to the sliding member described in [1], wherein the elastic modulus of the DLC film obtained by nanoindentation, expressed in gigapascals, is set as E. IT When, hardness H ITRelative to elastic modulus E IT The ratio of H IT / E IT It is above 0.095.

[0021] [3] According to the sliding member of [1] or [2], there is an intermediate layer between the substrate and the DLC film, which is composed of one or more elements selected from Cr, Ti, Co, V, Mo, Si and W or their carbides, nitrides or carbonitrides.

[0022] [4] A piston ring, which is made of any one of the sliding members described in [1] to [3].

[0023] Invention Effects

[0024] According to the present invention, compared with the prior art, the sliding wear of the DLC film during sliding between the sliding member and the mating part is suppressed. As a result, the wear resistance of the sliding member is improved. Furthermore, the film thickness of the DLC film can be made thinner than before. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating an example of the cross-sectional shape of a sliding member.

[0026] Figure 2 This is a schematic diagram showing an example of the cross-sectional shape of a piston ring substrate.

[0027] Figure 3 This is a schematic diagram showing the structure of the sliding wear testing machine.

[0028] Figure 4 This is a graph showing the relationship between the central wavenumber of the G band and the sliding friction ratio in the Raman spectrum of the DLC film obtained by Raman spectroscopy.

[0029] Figure 5 This is a graph showing the relationship between the hardness and sliding friction ratio of DLC films obtained by nanoindentation.

[0030] Figure 6 This is a graph showing the relationship between the ratio of hardness to elastic modulus and the ratio of sliding friction of the DLC film.

[0031] Figure 7 This is a graph showing the relationship between the area intensity ratio (ID / IG) of the D band and the G band peaks in the Raman spectrum of the DLC film obtained by Raman spectroscopy and the sliding friction ratio. Detailed Implementation

[0032] The following is a detailed description of the methods for carrying out the present invention.

[0033] [Sliding component]

[0034] In one embodiment, the present invention is an invention of a sliding member. Figure 1 This is a schematic diagram showing an example of the cross-sectional shape of the sliding member of the present invention. The sliding member 100 has a substrate 10 and a hydrogen-free DLC film 12 formed on the surface of the substrate 10. Due to its excellent wear resistance, the sliding member 100 of the present invention can be applied to various products, such as piston rings, pistons, piston pins, tappets, valve tappets, gaskets, rocker arms, cams, camshafts, timing gears, timing chains, etc. used in the sliding parts of internal combustion engines that contain lubricating oil such as engine oil, or blades, injectors, plungers, cylinders, etc. used in fuel supply systems.

[0035] [Substrate]

[0036] The sliding member of the present invention has a substrate and a substantially hydrogen-free DLC film formed on the surface of the substrate. The substrate is the main component of the sliding member. The material and shape of the substrate constituting the sliding member of the present invention can be any material and shape, as long as they are materials and shapes capable of forming a DLC film on the surface.

[0037] [DLC film]

[0038] The sliding member of the present invention has a DLC film formed on the surface of a substrate. The DLC film is a film composed of amorphous carbon, i.e., diamond-like carbon, exhibiting properties close to diamond. The DLC film of the sliding member of the present invention can be formed directly on the surface of the substrate, or it can be formed on the surface of one or more intermediate layers formed on the surface of the substrate.

[0039] The sliding member of the present invention has a DLC film that is substantially hydrogen-free. In this specification, "substantially hydrogen-free DLC film" means that the amount of hydrogen contained in the diamond-like carbon constituting the DLC film is 2.0% or less on an atomic percentage basis. DLC films tend to soften due to the presence of hydrogen. In the present invention, by making the DLC film of the sliding member substantially hydrogen-free, the hardness required for the DLC film as specified in the present invention (described later) can be ensured. The amount of hydrogen contained in the DLC film is preferably 1.0% or less on an atomic percentage basis, more preferably 0.5% or less.

[0040] [Method for determining the amount of hydrogen contained in DLC film]

[0041] The hydrogen content in a DLC film can be determined by using RBS (Rutherford Backscattering Spectrometry) / HFS (Hydrogen Forward Scattering Spectrometry) on a DLC film formed on a flat surface with sufficient curvature in the sliding part. RBS / HFS is a well-known analytical method for film composition, but it is not suitable for analyzing uneven surfaces. Therefore, for DLC films formed on uneven sliding surfaces such as the outer circumferential surface of the piston ring, the hydrogen content can be determined by combining RBS / HFS with SIMS (Secondary Ion Mass Spectrometry). The procedure is described below.

[0042] First, a DLC film, serving as the reference value, was formed on a mirror-polished, flat test piece (a quenched SKH51 disk, φ25 × 5 mm thick, hardness HRC60–63). C2H2, Ar, and H2 were introduced as ambient gases into the film formation of the reference sample using reactive sputtering. The hydrogen content in the DLC film was then adjusted by varying the flow rates of the introduced H2 and / or C2H2. DLC films composed of hydrogen and carbon with varying hydrogen contents were formed in this way, and their hydrogen and carbon contents were evaluated using RBS / HFS.

[0043] Next, the above-mentioned sample was analyzed using SIMS to determine the secondary ion strength of hydrogen and carbon. SIMS analysis can also measure uneven surfaces, such as the DLC film formed on the outer circumferential surface of a piston ring. Therefore, for the same film on a reference sample with a DLC film applied, an experimental formula (econometric curve) was derived representing the relationship between the hydrogen and carbon content (in atomic percent) obtained by RBS / HFS and the secondary ion strength of hydrogen and carbon obtained by SIMS. In this way, the hydrogen and carbon content can be calculated from the secondary ion strength of hydrogen and carbon measured by SIMS on the outer circumferential surface of an actual piston ring. Furthermore, the secondary ion strength values ​​based on SIMS are the average values ​​of the secondary ion strengths of each element observed at least 20 nm above the surface of the DLC film and within a 50 nm square region.

[0044] [Film formation method of DLC film]

[0045] In this invention, to form a substantially hydrogen-free DLC film on the surface of the substrate of the sliding member, a PVD method such as ion plating can be used to form the DLC film. The ion plating method utilizes a vacuum arc discharge using a carbon target. The PVD method can form a DLC film with high hardness and excellent wear resistance that is virtually hydrogen-free. Furthermore, a filter-type cathode vacuum arc discharge (FCVA) method with a filter for removing fine carbon particles is preferred. However, the method for forming a substantially hydrogen-free DLC film is not limited to these methods.

[0046] The DLC film can be formed on at least a portion of the surface of the substrate, or it can be formed on the entire surface of the substrate. When the DLC film is formed on a portion of the substrate surface, it is preferable to form the DLC film on a portion of the surface of the sliding member where wear resistance is particularly important. In this case, the surface of the formed DLC film constitutes the sliding surface of the sliding member.

[0047] [Center wavenumber of G band]

[0048] The DLC film of the sliding member of the present invention has a Raman spectrum obtained by Raman spectroscopy using a laser in the visible region as excitation light, in which the center wavenumber of the G band is 1585 cm⁻¹. -1 The Raman spectrum of the DLC film can be obtained by measuring the surface of a sliding component with a DLC film formed thereon using Raman spectroscopy. A visible laser is used as the excitation light for measuring the Raman spectrum. When it is desired to measure the Raman spectrum of different parts of the sliding component, a micro-Raman spectroscopy apparatus can be used.

[0049] The G band in the Raman spectrum of the DLC film can be considered to be related to the sp bonds of the carbon atoms contained in the DLC film. 2 The bond composition is related and varies with the crystal structure of graphite. The center wavenumber of the G band in this invention is determined by the following steps. First, the obtained Raman spectrum is analyzed in the range of 900–1900 cm⁻¹. -1 After removing the background within the range, assume a height of 1350cm. -1 The nearby peak is in zone D, at 1550 cm. -1 The nearby peaks are identified as G-band, and two Gaussian functions are used for fitting. Next, the wavenumbers of the peak positions in the separated G-band spectra are calculated, and this wavenumber is taken as the center wavenumber of the G-band.

[0050] In this invention, the center wavenumber of the G band in the Raman spectrum of the DLC film is 1585 cm⁻¹. -1 The above. When the DLC film of the sliding member meets this condition, the wear amount during sliding friction between the sliding member and the mating part is reduced compared with the sliding member having the DLC film of the prior art as a comparison benchmark.

[0051] Although the wear of the DLC film of the sliding component during sliding friction with the mating parts is 1585 cm⁻¹ in the central wavenumber of the G band in the Raman spectrum of the DLC film. -1 The reasons for the decrease in the above values ​​are not entirely clear, but it is likely due to the following: As mentioned above, the center wavenumber of the G-band can be assumed to vary with the crystal structure of the graphite contained in the DLC film. It is speculated that the load and heat generated by sliding easily form a protective film called a tribofilm on the surface of the DLC film, or that it suppresses the abrasive wear phenomenon caused by foreign matter scraping the surface between the friction surfaces.

[0052] The center wavenumber of the G-band is 1585 cm⁻¹. -1 The above is sufficient; there is no specific upper limit. However, it can be considered that the shift of the G-band with changes in the crystal structure of graphite is finite. Therefore, the value of the center wavenumber of the G-band is essentially limited to 1610 cm⁻¹. -1 the following.

[0053] [Hardness of DLC film]

[0054] The sliding component of this invention has a DLC film with a hardness (H) expressed in gigapascals (GPascals) obtained by nanoindentation. IT The hardness is between 15 GPa and 35 GPa. In this specification, "nanoindentation method" refers to the determination method based on the nanoindentation hardness test method specified in the international standard ISO 14577. In this method, a tiny diamond indenter with a tip shaped like a regular triangular pyramid (Berkovich type) is pressed into the sample surface, and the load-displacement curve is measured, thereby determining the hardness and elastic modulus of a small area. Furthermore, to avoid the influence of the substrate, which serves as the base for the DLC film, the indentation load is set to a maximum indentation depth of less than 1 / 10 of the film thickness. In addition, as a pretreatment, the test area is mirror-polished to suppress deviations in the test values.

[0055] The hardness H of the DLC film, as determined by nanoindentation, is known. IT The hardness varies greatly depending on the film-forming conditions of the DLC film. For example, the hardness of graphite is approximately 4 GPa, while the hardness of diamond is 90-100 GPa. The sliding member of the present invention has a DLC film with a hardness H... IT It lies between these values.

[0056] When the hardness of the DLC film is H IT When the hardness is less than 15 GPa, the wear of the DLC film increases during sliding friction with the sliding component. When the hardness H of the DLC film...IT At pressures greater than 35 GPa, the abrasive wear caused by the generation of abrasive particles increases, leading to greater wear on the DLC film. Therefore, the hardness H of the DLC film... IT Whether the size is too small or too large, the wear of the DLC film will increase. The hardness H of the DLC film... IT Within the range of 15 GPa or higher and 35 GPa or lower as specified in this invention, the wear of the DLC film is reduced to less than half compared to the prior art DLC film used as a comparison benchmark.

[0057] [DLC film thickness]

[0058] In a preferred embodiment, the thickness of the DLC film in the sliding member of the present invention is not particularly limited, but is preferably 1.0 μm or more and 30 μm or less. This is because if it is 1.0 μm or more, the durability of the DLC film will not be insufficient, and if it is 30 μm or less, there will be no insufficient adhesion to the base material, thus preventing peeling. More preferably, the thickness of the DLC film is 5.0 μm or more and 20.0 μm or less. The thickness of the DLC film can be measured by using a ball milling film thickness tester (Calotest) or by observing the cross-section of the film after resin embedding.

[0059] [The ratio of the hardness of the DLC film to its elastic modulus]

[0060] In a preferred embodiment, the elastic modulus of the DLC film obtained by nanoindentation, expressed in gigapascals, is set as E. IT When, hardness H IT Relative to elastic modulus E IT The ratio of H IT / E IT The elastic modulus E of the DLC film is above 0.095. IT The elastic modulus E of a DLC film is an indicator of how easily it undergoes elastic deformation when subjected to load. IT The smaller the value, the more flexibly the DLC film will deform when the sliding member with the DLC film is pressed against the mating part. Therefore, it can be considered that when the hardness H is... IT When comparing under the same conditions, H IT / E IT The larger the value, the more pliable the DLC film becomes, thus inhibiting the progression of abrasive wear on the DLC film.

[0061] In a preferred embodiment, the ratio of the hardness of the DLC film to its elastic modulus H IT / E ITA value of 0.095 or higher is acceptable; there is no specific upper limit. Generally, there is a certain correlation between the elastic modulus and hardness of a material. Therefore, for DLC films that are essentially hydrogen-free, the ratio of hardness to elastic modulus (H, expressed in the same units) is... IT / E IT It is essentially limited to below 0.120.

[0062] [Middle Layer]

[0063] In a preferred embodiment, the sliding member of the present invention further comprises an intermediate layer between the substrate and the DLC film, consisting of one or more elements selected from Cr, Ti, Co, V, Mo, Si, and W, or their carbides, nitrides, or carbonitrides. The intermediate layer is disposed on at least a portion of the surface of the substrate. The presence of the intermediate layer on the surface of the substrate alleviates the stress between the substrate and the DLC film, thereby improving the adhesion of the DLC film.

[0064] The intermediate layer can cover at least a portion or all of the surface of the substrate. When a piston ring is chosen as the substrate for the sliding member, for example, the outer circumferential surface of the piston ring can be covered. This improves the adhesion of the DLC film on the outer circumferential surface, and is therefore preferred. When the entire surface of the substrate is covered, the covered intermediate layer can remain on the entire surface of the substrate, or the unwanted portion of the intermediate layer can be removed after molding by polishing or other processes, thus exposing the substrate.

[0065] The thickness of the interlayer is preferably 0.1 μm or more and 0.6 μm or less, more preferably 0.2 μm or more and 0.5 μm or less. This is because if it is 0.1 μm or more, the adhesion of the DLC film can be improved, and if it is 0.6 μm or less, the interlayer is less likely to cause plastic flow during sliding, making the DLC film difficult to peel off. The interlayer can be formed on the substrate, for example, by appropriately using a known PVD (physical vapor deposition) method.

[0066] Piston rings

[0067] In other embodiments, the present invention relates to a piston ring. The piston ring of the present invention is a piston ring constructed from the sliding member of the present invention. The base material of the piston ring of the present invention is made of steel having a ring shape. The steel used for the base material is not particularly limited as long as it possesses the strength, elastic modulus, thermal conductivity, and other properties required for a piston ring. Carbon steel, spring steel, and martensitic stainless steel are preferred as the steel. The piston ring of the present invention has a ring shape, with a gap provided in a portion of the ring shape. The piston ring is installed in a groove provided on the outer circumferential surface of the piston in a closed-gap, reduced-diameter state. Inside the cylinder, the outer circumferential surface of the piston ring slides while being pressed against the inner wall of the cylinder under tension.

[0068] Figure 2 This is a schematic diagram illustrating an example of the cross-sectional shape of the substrate of the piston ring of the present invention. Figure 2 In this context, the DLC membrane, described later, is omitted. For example... Figure 2 As shown, the piston ring 200 includes a base material 20 with an approximately rectangular cross-section. However, the shape of the cross-section of the base material 20 constituting the piston ring can vary greatly and may not necessarily be rectangular.

[0069] The outer peripheral surface 22 is located further outward than the outer peripheral surface of the piston when the piston ring 200 is installed in the groove of a piston (not shown), and slides while contacting the inner wall of the cylinder. The shape of the outer peripheral surface 22 can be as follows: Figure 2 The flat shape shown can also be a cylindrical shape that expands outward from the center, or a conical shape whose diameter continuously varies depending on the position. As mentioned above, the outer peripheral surface 22 is required to have wear resistance that makes it difficult to wear due to sliding with the inner wall of the cylinder. In the piston ring of the present invention, a DLC film (not shown) is formed on the outer peripheral surface 22.

[0070] Sides 24a and 24b are the surfaces where the piston ring 200 contacts the groove of a piston (not shown). Figure 2 The upper side surface 24a and the lower side surface 24b are shown. An inner peripheral surface 28 exists on the opposite side of the outer peripheral surface 22. Outer peripheral edges 26a and 26b exist at the boundaries between the outer peripheral surface 22 and the sides 24a and 24b. Typically, chamfers (not shown) are provided at the outer peripheral edges 26a and 26b to prevent defects in the substrate 20.

[0071] [Sliding Fatigue Test]

[0072] A method for evaluating the wear amount of the DLC film of the sliding member when sliding friction occurs between the sliding member and the mating part of the present invention will be described. Figure 3This is a schematic diagram illustrating a general method for conducting the sliding fatigue test for this evaluation. The sliding fatigue testing machine 300 used for the sliding fatigue test has a rotating drum 30. The sliding fatigue testing machine 300 applies repeated loads while pressing the surface of the test piece 32 against the outer peripheral surface of the drum 30 via a drive mechanism (not shown). By measuring the dimensional changes of the test piece 32 before and after the test, the wear amount of the DLC film formed on the surface of the test piece 32 is determined. This wear amount is divided by the wear amount of a standard specimen tested under the same conditions to obtain the sliding wear ratio.

[0073] The following describes the test conditions for performing a sliding fatigue test. The roller 30, which serves as the sliding mating part of the test piece 32, is a cylindrical component with a diameter of 80 mm. The material constituting the roller 30 is preferably a steel with high wear resistance, such as bearing steel of grade SUJ2 specified in Japanese Industrial Standard JIS G 4805 "High Carbon Chromium Bearing Steel". The circumferential speed of the roller 30 rotating relative to the stationary test piece 32 is set to 10.0 m / s. The rotation of the roller 30 is accelerated to a speed of 10.0 m / s over 30 seconds from a stationary state, maintained at 10.0 m / s for 20 seconds, and then decelerated to zero speed over 30 seconds. Next, the rotation direction is reversed, and the acceleration, holding, and deceleration are repeated as one cycle, repeated 10 times.

[0074] The test piece 32 is repeatedly loaded by a drive mechanism (not shown), pressing it vertically against the outer circumferential surface of the roller 30. The load is set to a maximum of 50 N and a minimum of 20 N, and is varied over time between the maximum and minimum loads in a sinusoidal wave pattern with a vibration frequency of 50 Hz. The surface temperature of the roller 30 is maintained at 80 °C by a heater (not shown). Oil is supplied from the tip of the oil supply pipe 34 at a rate of 0.1 cm / min. 3 Unadded oil is supplied to the surface of roller 30 at a rate that is insufficient for fluid lubrication, thus creating a boundary lubrication environment.

[0075] Example

[0076] The present invention will now be described with reference to embodiments, but the present invention is not limited thereto.

[0077] As the substrate for the piston ring, a ring-shaped substrate with an approximately rectangular cross-section, made of silicon-chromium steel, was prepared. The substrate dimensions are: nominal diameter 78 mm, thickness 2.5 mm, and width 1.2 mm. The outer peripheral surface is a slightly bulging cylindrical surface in the center. A C-face chamfer with a width of 0.15 mm is applied to the outer peripheral edge of the substrate. Using a cathodic arc ion plating apparatus (manufactured by ITF Co., Ltd., Japan, M720), the outer peripheral surface of the substrate is coated with a 0.5 μm thick intermediate layer made of chromium.

[0078] Next, after degreasing and cleaning the substrate, it was placed in a cathode arc ion plating apparatus with its sides in contact with each other. After surface cleaning by ion bombardment, the outer peripheral surface of the substrate was coated with a DLC film using an ion plating method based on vacuum arc discharge. After the DLC film was formed, the DLC film wrapped around the sides was removed using a honing and lapping apparatus, resulting in multiple piston rings of Examples 1-5 and Comparative Examples 1-9 as shown in Table 1. The film formation conditions of the DLC film are shown in Table 1.

[0079] [Table 1]

[0080]

[0081] The set bias voltage shown in Table 1 refers to the bias voltage of the substrate set on the device during film formation. Regardless of the set bias voltage value, the bias voltage holding circuit of the device functions to maintain the bias voltage at the set bias voltage value. The measured bias voltage shown in Table 1 refers to the actual bias voltage of the substrate monitored during film formation. Even when the set bias voltage is set to zero, the substrate will become charged due to the charge of carbon ions, resulting in a non-zero bias voltage. This is sometimes referred to as the self-bias voltage. By generating a self-bias voltage, carbon ions accelerate and energy increases, and the substrate temperature easily rises even without heating by a heater.

[0082] As shown in Examples 1-4, when the absolute value of the self-bias voltage is greater than the absolute value of the set bias voltage, the measured bias voltage is dominated by the self-bias voltage and is not affected by the set bias voltage. Furthermore, when the set bias voltage is the same, the measured bias voltage varies according to the magnitude of the arc current.

[0083] In Example 5, "floating potentialization" refers to disconnecting the bias voltage holding circuit of the device and not controlling the bias voltage. In this case, the substrate is also charged due to the charge carried by the carbon ions.

[0084] Regarding the film formation rates shown in Table 1, "fast" indicates a faster film formation rate compared to the conditions of Comparative Example 1, which serves as the baseline; "equal" indicates that the film formation rates are equal; and "slow" indicates a slower film formation rate.

[0085] The piston ring samples obtained in this way were evaluated as follows. First, the Raman spectrum of the DLC film on the outer circumferential surface of the piston ring was measured using a Raman spectrometer (Renishaw, inViaReflex). The measurement was performed under the conditions of Ar ion excitation laser wavelength of 532.0 nm, laser output power of 50 mW, objective lens of 100x, and beam attenuation. Based on the obtained Raman spectrum data, the center wavenumber of the G band and the area intensity ratio of the D band to the G band, ID / IG, were determined.

[0086] Next, the hardness H of the DLC film was determined according to the nanoindentation method of international standard ISO 14577 using an Elionix nanoindentation instrument (model ENT-1100a). IT and elastic modulus E IT The ratio H of hardness to elastic modulus is calculated from the obtained measured values. IT / E IT .

[0087] Next, use Figure 3 The sliding fatigue testing machine shown was used to measure the sliding wear of the DLC film on the piston ring under the above test conditions. A test piece with a length of approximately 20 mm, including the outer circumferential surface, was cut from a piston ring sample. In the sliding wear test, the wear was measured when the 1-hour test was repeated 10 times. The ratio of this wear to the wear of Comparative Example 1, which served as a benchmark, was calculated as the sliding wear ratio. These evaluation results are shown in Table 2. Furthermore, Table 2 shows the center wave number and hardness H of the G-band. IT H IT / E IT The relationship between the ratio of ID / IG and the sliding wear ratio is shown in the figure. Figures 4 to 7 middle.

[0088] [Table 2]

[0089]

[0090] According to Table 2 and Figure 4 The center wavenumber of the G band is 1585 cm⁻¹. -1 Of the piston rings described above, the piston rings of Examples 1 to 5 show a significant reduction in sliding wear compared to Comparative Example 1, which has a prior art DLC film as a comparison benchmark. The center wave number of the G-belt does not exceed 1585 cm. -1 The sliding wear of the piston rings in Comparative Examples 2 to 7 was greater than that in Comparative Example 1, or even if it was slightly less, there was no significant improvement. In addition, in Comparative Examples 8 and 9, the hardness of the DLC film (described later) was insufficient, and the sliding wear was increased compared to Comparative Example 1.

[0091] According to Table 2 and Figure 5 The hardness H of the DLC film IT For piston rings with a pressure of 15 GPa or higher and 35 GPa or lower, the piston rings of Examples 1 to 5 showed a significant reduction in sliding wear compared to Comparative Example 1. Comparative Examples 3, 4, and 6, as described above, had a center wave number of less than 1585 cm⁻¹ for the G-belt. -1 Therefore, compared to Comparative Example 1, the sliding wear was not significantly reduced. From the above results, it can be seen that the sliding component of the present invention exhibits superior wear resistance compared to the prior art, and the film-forming speed can also be accelerated by appropriately adjusting the film-forming conditions.

[0092] Secondly, according to Figure 6 Except for Comparative Example 5, which has extremely high hardness, the ratio of hardness to elastic modulus H... IT / E IT A good correlation can be observed between H and the ratio of sliding wear. IT / E IT In the range of 0.095 and above, it shows less sliding wear compared to Comparative Example 1. This indicates that, when compared with a DLC film of the same hardness, the elastic modulus E... IT The smaller the value, the more flexible the DLC film is to repeated loads, thereby reducing sliding wear.

[0093] On the other hand, according to Table 2 and Figure 7 No significant correlation was found between the area intensity ratio of the peaks of the D and G bands, i.e., ID / IG, and the sliding wear ratio, as described in Patent Document 1.

[0094] Furthermore, as mentioned above, the DLC films of Examples 1 to 5, which exhibited good wear resistance, were all formed without heating the substrate using a heater, under conditions where the bias voltage was set to 0V or a floating potential and the self-bias voltage was approximately 0V to -35V. In contrast, in the DLC film of Comparative Example 4, where the bias voltage was set to a non-zero value under the same conventional film formation conditions, the center wavenumber of the G-band was not 1585cm. -1 The sliding wear ratio was not improved. This can be attributed to the fact that in DLC films formed with a non-zero bias voltage, the hard sp 3 Clusters tend to increase.

[0095] Furthermore, regarding heater heating, it is preferable not to use heater heating, but to regulate the substrate temperature solely through heating caused by the electric arc. This is because if heater heating is used, during film formation, the adhesion of foreign matter such as macroscopic particles from the film formed outside the substrate tends to increase, leading to increased wear. Thus, in the sliding member of the present invention, the film formation conditions of DLC film formation shown in Table 1 are adjusted to achieve the following: the center wave number and hardness H of the G-band... ITWhen these properties are within the specified range, excellent sliding friction characteristics can be obtained.

[0096] Explanation of reference numerals in the attached figures

[0097] 100: Sliding component;

[0098] 10: Substrate;

[0099] 12: DLC film;

[0100] 200: Piston ring;

[0101] 20: Substrate;

[0102] 22: Outer perimeter;

[0103] 24a, 24b: Side view;

[0104] 26a, 26b: outer perimeter;

[0105] 28: Inner circumferential surface;

[0106] 300: Sliding fatigue testing machine;

[0107] 30: Roller;

[0108] 32: Test piece;

[0109] 34: Oil supply pipe.

Claims

1. A sliding member, characterized in that, It has a substrate and a substantially hydrogen-free DLC film formed on the surface of the substrate. The center wavenumber of the G band in the Raman spectrum of the DLC film, obtained by Raman spectroscopy using a visible laser as excitation light, is 1585 cm⁻¹. -1 above, The hardness H of the DLC film, expressed in gigapascals, obtained by nanoindentation, is as follows: IT The range is between 15 GPa and 35 GPa.

2. The sliding member according to claim 1, wherein, The elastic modulus of the DLC film obtained by nanoindentation, expressed in gigapascals, is set as E. IT When, hardness H IT Relative to elastic modulus E IT The ratio of H IT / E IT It is above 0.

095.

3. The sliding member according to claim 1, wherein, An intermediate layer composed of one or more elements selected from Cr, Ti, Co, V, Mo, Si and W, or their carbides, nitrides and carbonitrides, is further provided between the substrate and the DLC film.

4. A piston ring comprising a sliding member according to any one of claims 1 to 3.

Images