JP7094739B2 - piston ring - Google Patents

Description

The present invention relates to a piston ring provided with a hard carbon film having excellent wear resistance.

Piston rings used in internal combustion engines have been used in harsh environments of high temperature and high pressure in recent years, and further improvement in wear resistance, initial familiarity, low friction and the like is required. In response to such demands, for example, Patent Document 1 proposes a piston ring provided with a carbon-based film having low friction and wear resistance. Specifically, it is a laminated film in which two or more layers having different hardness are laminated, and the hardness difference between the two types is 580 to 1700 HV, and the high hardness layer is the thickness of the low hardness layer. A piston ring having a thickness equal to or greater than that of the above and having a thickness of 5.0 μm or more as a whole film has been proposed. At this time, the low hardness layer is formed by sputtering, and the high hardness layer is formed by ion plating.

Further, Patent Document 2 proposes a piston ring having an amorphous hard carbon film having excellent adhesion to a piston ring base material, high hardness and excellent wear resistance. Specifically, on the surface of the first amorphous hard carbon layer, which is formed on the surface of the piston ring base material and contains almost no hydrogen and is substantially composed of carbon, and the surface of the first amorphous hard carbon layer. It is composed of a second amorphous hard carbon layer formed and substantially composed of carbon only, and when viewed from a cross section, a transmission electron microscope image of the first amorphous hard carbon layer is a second amorphous. A piston ring that is brighter than the transmission electron microscope image of the quality hard carbon layer has been proposed.

Further, Patent Document 3 proposes a piston ring having excellent initial compatibility with the inner peripheral surface of a cylinder liner, scuff resistance and wear resistance. Specifically, it is a piston ring in which a hard carbon laminated film is formed at least on the outer peripheral sliding surface, and the hard carbon laminated film is formed at a ratio of 58 to 70 wt% formed on the surface of the outer peripheral sliding surface. It contains Si, the balance is C, and W is contained in the ratio of 55 to 85 wt% formed under the first hard carbon film and the first hard carbon film which is an unavoidable impurity, and the ratio is 3 to 10 wt%. It is configured so that it contains Ni, the balance is C, and a second hard carbon film, which is an unavoidable impurity, is laminated. The film forming method is a mixture of a plasma CVD method and a sputtering method, and since a hydrocarbon gas is used, the film is formed as a hard carbon film containing hydrogen.

Further, in Patent Document 4, a cylinder or a cylinder liner made of an aluminum alloy is used as a mating material, and in a combination of the mating material and a piston ring having a single layer hard carbon film formed on an outer peripheral surface, the piston ring is used. The hard carbon film contains W, which is in the form of both a charcoal and a metal, in an amount of 0.5 atomic% or more and less than 5 atomic%, and the maltens hardness of the hard carbon film is 5.5 to 15 GPa. It has been proposed that the bond ratio of the carbon crystal structure be sp2 bond: sp3 bond = 4: 6 to 8: 2. The film forming method is a plasma CVD method, and since a hydrocarbon-based gas is used, the film is formed as a hard carbon film containing hydrogen.

Japanese Unexamined Patent Publication No. 2012-202522 Japanese Unexamined Patent Publication No. 2007-169698 Japanese Patent Application Laid-Open No. 2003-14121 WO2015 / 045745

The piston ring proposed in Patent Document 3 has a hard carbon film containing W in the range of 55 to 85 wt%, and the piston ring proposed in Patent Document 4 contains W in an amount of 0.5 atomic% or more. Although it has a hard carbon film containing less than 5 atomic%, all of the hard carbon films contain hydrogen and have not been evaluated in a state where hydrogen is substantially not contained.

The present invention has been made to solve the above problems, and an object thereof is a piston having a hard carbon film having easy film formation, low friction (mechanical friction loss), and excellent wear resistance. To provide the ring.

The piston ring according to the present invention has a hard carbon film formed on at least the outer peripheral sliding surface of the piston ring base material, and the hard carbon film is a laminated film or a single layer film, and tungsten is 0.05. It is contained in the range of atomic% or more and 0.4 atomic% or less, and the sp2 component ratio measured by the TEM ^- EELS spectrum obtained by combining electron energy loss spectroscopy (EELS) with a transmission electron microscope (TEM). Is in the range of 40% or more and 80% or less.

In the piston ring according to the present invention, the hard carbon film has a hydrogen content of less than 5 atomic%.

In the piston ring according to the present invention, the laminated film may include a white layer having a large ^sp2 component ratio.

In the piston ring according to the present invention, the total thickness of the hard carbon film can be configured to be within the range of 0.5 μm or more and 20 μm or less.

In the piston ring according to the present invention, the hard carbon film can be configured to be formed on a hard carbon base film having a thickness of 0.05 μm or more and 0.5 μm or less.

According to the piston ring according to the present invention, it is possible to easily form a film, have low friction, and have excellent wear resistance.

It is a schematic cross-sectional view which shows the example of the piston ring which concerns on this invention. It is a schematic sectional drawing which shows an example of the sliding surface of the piston ring which concerns on this invention. It is a schematic sectional drawing which shows another example of the sliding surface of the piston ring which concerns on this invention. It is a schematic cross-sectional view which shows still another example of the sliding surface of the piston ring which concerns on this invention. It is a surface photograph of the hard carbon film of Example 1 which shows macroparticles. It is a cross-sectional TEM image of a hard carbon film made of a laminated film. It is a structural principle diagram of the friction wear test using a disc type test piece. It is a photograph which shows the SRV test result.

The piston ring according to the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments as long as it has the technical features thereof.

As shown in FIGS. 1 to 4, the piston ring 10 according to the present invention has a hard carbon film 4 formed on at least the outer peripheral sliding surface 11 of the piston ring base material 1. The hard carbon film 4 is a laminated film or a single-layer film, and contains tungsten in the range of 0.05 atomic% or more and 0.4 atomic% or less. Further, in this hard carbon film 4, the sp2 component ratio measured by the TEM ^- EELS spectrum obtained by combining the transmission electron microscope (TEM) and the electron energy loss spectroscopy (EELS) is in the range of 40% or more and 80% or less. Within. Such a hard carbon film 4 has low friction and high wear resistance. The hard carbon film 4 is a hydrogen-free film having a hydrogen content of less than 5 atomic%.

Hereinafter, the components of the piston ring will be described in detail.

(Piston ring base material)
Examples of the piston ring base material 1 include various types used as the base material of the piston ring 10, and are not particularly limited. For example, various steel materials, stainless steel materials, casting materials, cast steel materials and the like can be applied. Among these, martensitic stainless steel, chromium manganese steel (SUP9 material), chromium vanadium steel (SUP10 material), silicon chromium steel (SWOSC-V material) and the like can be mentioned.

The piston ring base material 1 may be subjected to a nitriding treatment in advance to form a nitrided layer (not shown). Alternatively, a wear-resistant film (not shown) such as Cr—N system, Cr—BN system, Cr—B—VN system, Cr—BV—Ti—N system, Ti—N system is previously applied. It may be formed. Above all, it is preferable to form a wear-resistant film such as Cr—N system, Cr—BN system, Cr—B—V—N system, Ti—N system and the like. Since the piston ring 10 according to the present invention exhibits excellent wear resistance without such a nitriding treatment or a Cr-based or Ti-based wear-resistant film, the nitriding treatment or the Cr-based or Ti-based wear resistance. The sex film is not an essential structure and can be provided as needed.

The piston ring base material 1 may be pretreated if necessary. As the pretreatment, it is preferable to polish the surface to adjust the surface roughness. The surface roughness is preferably adjusted by, for example, a method of lapping the surface of the piston ring base material 1 with diamond abrasive grains to polish the surface. By adjusting the surface roughness in this way, the surface roughness of the piston ring base material 1 is kept within a preferable range of 0.02 μm or more and 0.07 μm or less in arithmetic average roughness Ra in JIS B 0601 (2001) and ISO 4287: 1997. Can be adjusted. The piston ring base material 1 adjusted in this way is used as a pretreatment before forming the hard carbon base film 3 described later, or as a pretreatment of the base film 2 provided in advance before forming the hard carbon base film 3. It can be preferably applied.

(Underground film)
As shown in FIG. 4, the piston ring base material 1 may be provided with a base film 2 such as titanium or chromium. The base film 2 does not necessarily have to be provided, and its formation is arbitrary. The undercoat film 2 such as titanium or chromium can be formed by various film forming means. For example, a film forming means such as a vacuum vapor deposition method, a sputtering method, or an ion plating method can be applied to the undercoat film 2 made of titanium or chromium. The thickness of the base film 2 is not particularly limited, but is preferably in the range of 0.05 μm or more and 2 μm or less. It is preferable that the base film 2 is formed at least on the outer peripheral sliding surface 11 on which the piston ring 10 slides in contact with the cylinder liner (not shown). However, it may be formed on other surfaces, for example, the upper surface 12, the lower surface 13, and the inner peripheral surface 14 of the piston ring 10.

For the formation of the undercoat film 2, for example, the piston ring base material 1 is set in the chamber, the inside of the chamber is evacuated, and then the inert gas is introduced by preheating and ion cleaning, and the vacuum deposition method or ion play is performed. This can be done by means such as the Ting method.

As shown in FIG. 4, the base film 2 may be directly formed on the piston ring base material 1. It is desirable that a hard carbon base film 3, which will be described later, is formed on the base film 2. The base film 2 improves the adhesion between the piston ring base material 1 and the hard carbon base film 3 and the hard carbon film 4, and forms the hard carbon base film 3 on the base film 2 to form the hard carbon thereof. It is possible to further suppress nucleation and nucleation when the undercoat film 3 is formed at a low speed. As a result, the hard carbon film 4 formed on the hard carbon base film 3 can be formed as a smooth film having small surface irregularities.

(Hard carbon base film)
The hard carbon base film 3 is preferably provided on the piston ring base material 1. Specifically, it is preferable that the hard carbon base film 3 is formed at least on the outer peripheral sliding surface 11 on which the piston ring 10 slides in contact with the cylinder liner (not shown). It can also be arbitrarily formed on other surfaces, for example, the upper surface 12, the lower surface 13, and the inner peripheral surface 14 of the piston ring 10.

As shown in FIGS. 1 to 3, the hard carbon undercoat 3 may be provided directly on the piston ring base material 1, or may be provided on the surface after the nitriding treatment or the wear-resistant film described above. Alternatively, as shown in FIGS. 4A and 4B, it may be provided on the above-mentioned base film 2 such as titanium or chromium. It is preferable that the hard carbon film 4 described later is directly provided on the hard carbon base film 3 without interposing another film.

The hard carbon base film 3 may be the same hard carbon film as the component of the hard carbon film 4 described later containing tungsten, or may be a hard carbon film having a lower tungsten content than the hard carbon film 4. , A hard carbon film containing no tungsten may be used. Since the hard carbon base film 3 is formed in the step before forming the hard carbon film 4, it is easy to manufacture that the hard carbon base film 3 has the same components as the hard carbon film 4 described later containing tungsten. It is advantageous from the viewpoint of improving wear resistance, but is not limited to this.

The hard carbon base film 3 can usually be formed by a film forming means such as an ion plating method by vacuum arc discharge using a carbon target. For example, when the hard carbon base film 3 is formed by the ion plating method by vacuum arc discharge (hereinafter referred to as “arc ion plating method”), specifically, the piston ring base material 1 or the wear resistance in advance. A piston ring base material 1 provided with a film, an undercoat film 2, or the like is set in a chamber, the inside of the chamber is evacuated, and then carbon plasma is discharged from a carbon target to form a film. The tungsten-containing hard carbon base film 3 can be obtained by forming a film using a tungsten-containing carbon target. The content of tungsten in the carbon target is set so that the content of tungsten contained in the hard carbon base film 3 after film formation is within a desired range. For example, similar to the hard carbon film 4 described later, tungsten is difficult to be contained in the hard carbon film, and the content of the target is about 1/10 to 1/15, so that the content of tungsten is 0.05 atomic%. As mentioned above, when it is intended to be contained within the range of 0.4 atomic% or less, the carbon target may contain a predetermined amount of tungsten so as to be approximately 1 atomic% or more and 6 atomic% or less.

The hard carbon base film 3 may be formed by controlling the film forming speed of the hard carbon film 4 described later to be reduced. That is, the film may be formed under low-speed film formation conditions. As a method for lowering the film forming conditions, a means for lowering the arc current can be mentioned in the arc ion plating method. Above all, it is preferable to form a film by the arc ion plating method in which the arc current is in the range of 40 A to 100 A and the pulse bias voltage is in the range of −2000 V to −100 V.

The above-mentioned arc current when the hard carbon base film 3 is formed by lowering the film forming speed is smaller than the arc current when the hard carbon film 4 described later is formed. Therefore, there is an advantage that poor adhesion due to a sudden increase in arc current, which tends to occur when the hard carbon film 4 is formed without forming the hard carbon base film 3 on the piston ring base material 1, can be suppressed. .. Further, the film formation of the hard carbon base film 3 with a small arc current has an advantage that nucleation can be suppressed, nucleation can be suppressed, and the increase of macroparticles can be suppressed. To suppress the increase of macroparticles, the hard carbon film 4 described later can be formed as a smooth film having small surface irregularities that is not affected by the hard carbon base film 3.

When reducing the arc current, it is preferable to set the arc current value to 80% or less of the arc current value at the time of forming the hard carbon film 4. When formed with an arc current value of 80% or less, the function as the hard carbon base film 3 can be effectively exhibited. That is, in the hard carbon undercoat 3 formed under the low-speed film formation condition, nucleation is suppressed and nucleation is also suppressed. Therefore, the hard carbon film 4 formed on the hard carbon base film 3 can suppress poor adhesion due to a rapid increase in arc current, and can further suppress the increase of macro particles in the hard carbon film 4. .. To suppress the increase of macroparticles, the hard carbon film 4 can be formed as a smooth film having small surface irregularities that is not affected by the hard carbon base film 3. As a result, the wear resistance of the hard carbon film 4 can be improved. The arc current value at this time is preferably 58% of the arc current value at the time of forming the hard carbon film 4 as the lower limit in order to preferably act as the hard carbon base film 3.

The above-mentioned action of the hard carbon base film 3 formed under the low-speed film forming conditions can be effectively realized within the range of the hard carbon base film 3 having a thickness of 0.05 μm or more and 0.5 μm or less. If the thickness of the hard carbon base film 3 is too thin, such as less than 0.05 μm, there is a problem that the effect of suppressing macroparticles in the hard carbon film 4 cannot be obtained. On the other hand, if the thickness of the hard carbon base film 3 is too thick to exceed 0.5 μm, there is a problem that the film formation of the hard carbon base film 3 is delayed and the cost is high.

The hardness of the hard carbon base film 3 thus formed is in the range of 2000 HV0.05 to 4000 HV0.05 in terms of Vickers hardness. Since the hard carbon undercoat 3 in the thickness range described above is too thin and it is difficult to measure the Vickers hardness itself, the Vickers hardness (JIS B 7725, ISO) when formed as thick as about 5 μm under the same film forming conditions. It was evaluated in 6587). The measurement can be performed using a Vickers hardness tester (manufactured by Future Tech Co., Ltd.) or the like, and "HV0.05" means that the Vickers hardness at a load of 58 gf is indicated. Further, when the hardness of the hard carbon base film 3 is measured by the nanoindentation method, the indentation hardness _HIT (15 mN load) is within the range of 20 GPa or more and 45 GPa or less. The measurement by the nanoindentation method can be performed by using, for example, nanoindentation manufactured by Elionix Inc.

(Hard carbon film)
As shown in FIGS. 1, 2 and 4 (A), the hard carbon film 4 is formed at least on the outer peripheral sliding surface 11 on which the piston ring 10 slides in contact with the cylinder liner (not shown). The hard carbon film 4 may be arbitrarily formed on other surfaces other than the outer peripheral sliding surface 11, for example, the upper surface 12, the lower surface 13, and the inner peripheral surface 14 of the piston ring 10.

The hard carbon film 4 may be a laminated film or a single-layer film. In the case of a laminated film, it is composed of a plurality of layers (also referred to as a nano-laminated film), and may be a film in which layers having the same thickness or layers having different thicknesses are laminated, or the film gradually becomes thicker. Alternatively, it may be a slanted film laminated so as to be thin, a film in which thick layers and thin layers are alternately or periodically laminated, or it is composed of various other laminated modes. It may be a laminated film. The thickness of each layer constituting the laminated film is not particularly limited, but is preferably in the range of 1 nm or more and 20 nm or less per layer, and more preferably in the range of 3 nm or more and 10 nm or less. The hard carbon film 4, which is a laminated film in which such thin layers are laminated, has excellent wear resistance.

The total thickness of the hard carbon film 4 made of a laminated film or a single-layer film is preferably in the range of 0.5 μm or more and 20 μm or less. The total thickness of the hard carbon film 4 may be a relatively thin range within a range of 0.5 μm or more and less than 2 μm, or a relatively thick range within a range of 2 μm or more and 20 μm or less. Even if the total thickness of the hard carbon film 4 is thin, the initial familiarity can be improved and the wear resistance can be improved, but when the total thickness is thick, there is an advantage that the effect is further sustained. ..

The hard carbon film 4 made of a laminated film has an arc current in the range of 80 A (however, larger than the arc current of the hard carbon base film 3) to 120 A, and an arc with a pulse bias voltage in the range of −2000 V to −100 V. It is preferable to form a film by the ion plating method. FIG. 6 is a cross-sectional TEM image of a hard carbon film 4 made of a laminated film. Such a laminated film can be formed, for example, by repeatedly changing the film forming conditions such as an arc current and a bias voltage over time.

A thin white layer is periodically present in the laminated film shown in FIG. This white layer has more sp ² components than sp ³ components and is rich in sp ² component ratio (sp ² / (sp ² + sp ³ )). Specifically, this layer has sp ² components. The layer has a ratio (sp ² / (sp ² + sp ³ )) of 58% or more and 75% or less. This white layer has a richer graphite structure than the diamond structure and has the property of relaxing the film stress, so that it has the effect of improving the film toughness of the hard carbon film 4 made of a laminated film. It is believed that there is.

The hard carbon film 4 made of a laminated film can be formed by alternately applying two or more different bias voltages in a pulse shape, and can be in a laminated form as shown in FIG. Examples thereof include 1) a predetermined low bias voltage and a predetermined high bias voltage can be alternately applied in a pulse shape. For example, a low bias voltage of -140 V and a high bias voltage of -220 V can be pulsed. May be added alternately to form a film. 2) A predetermined low bias voltage and a gradually increasing bias voltage can be applied as pulse voltages alternately, for example, a low bias voltage of -140V and a high bias voltage gradually increasing from -220V to -160V. May be alternately added in a pulse shape to form a film. 3) A predetermined low bias voltage and a predetermined high bias voltage can be applied alternately in a pulse shape, for example, a low bias voltage of -140V, a high bias voltage of -220V, and a low bias voltage of -158V. A high bias voltage of 1800 V may be applied in a pulse shape in the cycle order to form a film. The example of forming a film by alternately applying two or more different bias voltages in a pulse shape is not limited to the above 1) to 3), and other examples may be applied. The thickness of the laminated film is set to the number of repetitions of the pulse bias voltage so as to be within the above range.

The thin white layer appearing in the laminated film shown in FIG. 6 is a layer having a richer graphite structure than the diamond structure, as described above. Such a white layer can be formed, for example, by increasing the bias voltage, or by extending the application time of the high bias voltage when the high bias voltage and the low bias voltage are alternately applied. As shown in FIG. 6, it is preferable to form the film at regular intervals at regular intervals, but it may be present irregularly, or the film toughness may be maintained even if there is no regular or irregular white layer. The white layer may not be formed if it can be guaranteed to some extent.

The hard carbon film 4 made of a single-layer film has an arc current in the range of 80 A (however, larger than the arc current of the hard carbon base film 3) to 120 A, and a pulse bias voltage in the range of -2000 V to -100 V. The film can be formed by the arc ion plating method. The single-layer film can be formed by, for example, keeping the film forming conditions such as an arc current and a pulse bias voltage constant over time. The term "single-layer film" is used to mean that a gradient film such as a laminated film whose clear laminated form cannot be observed in a TEM image or the like is also used. For example, the film forming conditions such as arc current and bias voltage are gradually changed. Changed inclined membranes are also included.

In the present invention, since the hard carbon film 4 contains tungsten, friction (mechanical friction loss) can be reduced and wear resistance can be significantly improved. Tungsten in the hard carbon film 4 is preferably contained in a small range of 0.05 atomic% or more and 0.4 atomic% or less. If the tungsten content was less than 0.05 atomic%, the wear resistance could not be significantly improved. Moreover, it was difficult in itself to contain the tungsten so as to exceed 0.4 atomic%. The more preferable tungsten content can be in the range of 0.05 atomic% or more and 0.2 atomic% or less due to the manufacturing reason that the film forming rate decreases as the content increases. The content of tungsten in the hard carbon film 4 is represented by the result measured by a quantitative analysis method using an electron probe microanalyzer (EPMA).

The tungsten-containing hard carbon film 4 can be obtained by forming a film using a tungsten-containing carbon target. The content of tungsten in the carbon target is set so that the content of tungsten contained in the hard carbon film 4 after film formation is within the above range, and as described above, the content is 1 atomic% or more. A predetermined amount of tungsten is contained in the carbon target so as to be within the range of 6 atomic% or less.

The hard carbon film 4 does not substantially contain hydrogen and is, for example, less than 5 atomic%, and is usually 2 atomic% or less in the film forming method of the present invention. The lower limit of the hydrogen content is not particularly limited, but is not included (0 atomic%) or about 0.1 atomic%. In the present invention, in the formation of the hard carbon film 4 and the formation of the above-mentioned hard carbon base film 3, the film is formed under the condition that the hydrogen component is not contained. The formation of the hard carbon base film 3 and the hard carbon film 4 can be preferably formed by an arc ion plating method using a carbon target containing tungsten. As a result, since hydrogen and hydrides are not contained in the film forming process, the hard carbon base film 3 and the hard carbon film 4 do not substantially contain hydrogen components or are inevitably contained in them. Only. The degree of "substantially free" or "unavoidably contained" means that the hydrogen content in the hard carbon base film 3 and the hard carbon film 4 is less than 5 atomic%. There is. The hydrogen content means the content of the hard carbon film 4 as a whole. The hydrogen content in the hard carbon film 4 is represented by the result measured by the RBS / HFS analysis method. RBS is an abbreviation for Rutherford Backscattering Spectrometry, and HFS is an abbreviation for Hydrogen Forward Scattering.

The hard carbon film 4 does not substantially contain oxygen due to the manufacturing method, for example, oxygen is less than 5 atomic%, and in the film forming method of the present invention, it is usually 2 atomic% or less. The reason why oxygen is substantially not contained is that oxygen and oxides are not contained in the film forming process of the hard carbon film 4. That is, the hard carbon film 4 contains only unavoidable impurities inevitably contained in the process other than carbon and tungsten, and substantially does not contain hydrogen or oxygen. The oxygen content means the content of the hard carbon film 4 as a whole, and if any one point is analyzed, there may be a portion where oxygen inevitably mixed is 5 atomic% or more. The oxygen content in the hard carbon film 4 is represented by the result measured by the TEM-EDX semi-quantitative method. EDX is an abbreviation for Energy Dispersive X-ray Spectroscopy.

When the hard carbon film 4 is a laminated film, a tungsten-free carbon film may be present between a plurality of layers constituting the laminated film. The carbon film containing no tungsten can be formed by adjusting the film forming conditions, and has an effect of relaxing the stress of each hard carbon film containing tungsten. The thickness of this carbon film is not particularly limited, but can be, for example, in the range of 2 nm or more and 10 nm or less.

Since the hard carbon film 4 is formed directly on the hard carbon base film 3 which is formed under low-speed film formation conditions to suppress nucleation and nucleation and suppress the increase of macroparticles, the hard carbon film 4 is smooth with small surface irregularities. Can be formed as a thin film. The amount of macroparticles appearing on the surface of the hard carbon film 4 is in the range of 0.1% or more and 10% or less in terms of area ratio. As a result, wear resistance and initial familiarity can be improved. If the amount of macroparticles exceeds 10% in terms of area ratio, the unevenness of the surface becomes large, and excellent wear resistance may not be realized. On the other hand, when the amount of macroparticles is less than 0.1% in terms of area ratio, excellent wear resistance can be realized, but the film formation itself may be difficult, and there are some difficulties in terms of manufacturing control and cost. .. FIG. 5 is a surface photograph of the hard carbon film (tungsten-containing hard carbon film) of Example 1 showing macro particles.

The area ratio of the amount of macroparticles can be obtained by performing image analysis using a confocal microscope (OPTELICS H1200) manufactured by Lasertec Co., Ltd. Specifically, the outer circumference of the piston ring was photographed (objective lens 100 times, monochrome confocal image), and automatic binarization was performed. The threshold value determination method was performed by a discriminant analysis method, and the area ratio was extracted from the binarized image after making adjustments so as to exclude polishing scratches and the like. The area ratio of the macro particles was measured at 5 points at any point on the film and used as the average value.

The present invention has an advantage that the film peeling can be further suppressed by providing the hard carbon film 4 made of a laminated film or a single-layer film on the hard carbon base film 3. The reason is that in the case of a laminated film, a film formed with a lower bias voltage among two or more different bias voltages functions as a stress relaxation film, so that the piston ring substrate 1 and the hard carbon substrate film 3 are used. It acts to reduce the load applied to the interface of. Further, when the base film 2 is formed, it acts to reduce the load applied to the interface between the base film 2 and the hard carbon base film 3. Further, in the case of a single-layer film (including a gradient film), since the film is formed with a relatively low bias voltage, it functions as a stress relaxation film and is added to the interface between the piston ring base material 1 and the hard carbon base film 3. It works to reduce the load.

The piston ring 10 provided with such a hard carbon film 4 is particularly preferable in that it can be preferably applied to a joint portion where a temperature is applied and the contact becomes strong, and it is possible to eliminate film peeling of the hard carbon film 4 at the joint portion. ..

The hardness of the hard carbon film 4 is in the range of about 1000 HV0.05 to 2000 HV 0.05 in terms of Vickers hardness. The hardness of the hard carbon film 4 is in the range of 10 GPa or more and 25 GPa or less in the indentation hardness _HIT (15 mN load) measured by the nanoindentation method. The measurement of Vickers hardness and the measurement by the nanoindentation method are the same as in the case of the above-mentioned hard carbon undercoat.

The hard carbon film is a film in which a carbon bond sp ² bond typified by graphite and a carbon bond sp ³ bond typified by diamond are mixed. The sp ² component ratio indicates the component ratio (sp ² / (sp ² + sp ³ )) of the graphite component (sp ² ) to the graphite component (sp ² ) and the diamond component (sp ³ ) of the hard carbon film. .. In the observation with a transmission electron microscope (TEM), the layer rich in the sp ² component looks relatively white as compared with the layer rich in the sp ³ component.

The hard carbon film 4 has a sp2 component ratio of 40% or more and 80% or less as measured by TEM ^- EELS, which is a combination of a transmission electron microscope (TEM) and electron energy loss spectroscopy (EELS). preferable. When the sp ² component ratio is less than 40%, the diamond component (sp ³ ) is the main component, so that the film quality is dense but low toughness, which is not preferable for forming a hard carbon film. If the sp ² component ratio exceeds 80%, the graphite component (sp ² ) becomes the main component, which makes it difficult to form a hard carbon film, which is not preferable. As a preferable sp2 component ratio, as shown in Table ¹ below, the range of 58% or more and 75% or less can be mentioned. Such a covalent bond ratio can be measured by an EELS analyzer (Model 863GIF Tridiem, manufactured by Gatan). This measurement can be performed by the following procedure.

(1) The EELS spectrum is measured by an EELS analyzer. The peak intensity is normalized by fitting the measured EELS spectrum with a linear function before the peak and with a cubic function after the peak. (2) After that, the energy calibration is performed by comparing the diamond data with the graphite data and aligning the start positions of the peaks. (3) Obtain an area within the range of 280 eV to 310 eV for the calibrated data. (4) Separate into two peaks in the range of 280 eV to 295 eV (one is the peak of sp ² and the other is the peak of CH or amorphous), and the peak area near 285 eV is obtained. (5) The area in the range of 280 eV to 310 eV in (3) above and the peak area in the vicinity of 285 eV in (4) above are taken. Regarding this area ratio, graphite is 100, diamond is ⁰ , and the sp2 component ratio is obtained from the relative value. The value thus obtained is defined as the ^sp2 component ratio.

^The sp2 component ratio of the hard carbon film is evaluated by obtaining a plurality of points as measurement points at equal intervals in the thickness direction of the film. The number of measurement points is not particularly limited, but may be 10 as shown in Examples described later. ^In the present application, the "sp2 component ratio" obtained at a plurality of measurement points is represented by the average value of the film.

(Outermost film)
In the present invention, the outermost surface film 5 may be further provided on the hard carbon film 4 if necessary. Similar to the above-mentioned hard carbon film 4, the outermost surface film 5 may be a laminated thin hard carbon film (nano thin film) as shown in FIGS. 3 and 4 (B), or may be a single-layer film. May be. The outermost surface film 5 can be made to act so as to further enhance the initial familiarity.

When the outermost surface film 5 is a laminated film, the film is formed by repeating the high bias voltage treatment and the low bias voltage treatment by the arc ion plating method a plurality of times at predetermined intervals as in the case of the above-mentioned hard carbon film 4. can do. For example, while maintaining the arc current at 100A to 158A, which is the same as the film forming conditions of the hard carbon film 4, the pulse bias voltage is treated with a high bias voltage within the range of -2000V to -800V, and the pulse bias voltage is set to -200V. The film formation may be repeated a plurality of times with a low bias voltage treatment in the range of ~ -100V at predetermined intervals. The predetermined interval is an interval of about 1 second or more and 10 seconds or less. The outermost surface film 5 thus formed has high hardness, toughness is increased to prevent cracks and chips, and initial compatibility is improved.

Even when the outermost surface film 5 is a single-layer film, the film can be formed by constantly or gradually changing the bias voltage in the arc ion plating method, as in the case of the above-mentioned hard carbon film 4. Also in this outermost surface film 5, the monolayer film means that the inclined film is included.

The total thickness of the outermost surface film 5 is formed in the range of 0.05 μm or more and 1 μm or less. If the thickness of the outermost surface film 5 is too thin, there is a drawback that the effect of initial familiarity cannot be obtained. On the other hand, even if the outermost surface film 5 is too thick, the effect of initial familiarity does not change. When the outermost surface film 5 is a laminated film, the thickness of each layer is within the range of 0.01 μm or more and 0.02 μm or less, and a plurality of layers having a thickness within the range are laminated. ing. The thickness of the outermost surface film 5 can be measured with a transmission electron microscope (TEM). It is preferable that the hardness of the outermost surface of the outermost surface film 5 after the process treatment is formed to be about 2000 HV 0.05 in terms of Vickers hardness.

As described above, in the piston ring 10 according to the present invention, since the hard carbon film 4 which is a laminated film or a single layer film contains tungsten within the above range, friction is low and wear resistance is further enhanced. Can be done.

Hereinafter, the piston ring according to the present invention will be described in more detail with reference to Examples, Comparative Examples, and Conventional Examples.

[Example 1]
C: 0.55 atom%, Si: 1.35 atom%, Mn: 0.65 atom%, Cr: 0.70 atom%, Cu: 0.03 atom%, P: 0.02 atom%, S: A piston ring base material 1 equivalent to SWOSC-V material was used according to the JIS standard consisting of 0.02 atomic%, balance: iron and unavoidable impurities. A 30 μm Cr—N film (wear resistant film) was formed on the piston ring base material 1 by an ion plating method. The surface roughness was adjusted by lapping polishing, and then a titanium film having a thickness of 0.08 μm was formed as the undercoat film 2 by introducing an inert gas (Ar) by the ion plating method.

A hard carbon base film 3 made of an amorphous carbon film was formed on the base film 2. For film formation, an arc ion plating device is used, a carbon target containing 2 atomic% of tungsten is used, and an arc current of 90 A and a pulse bias voltage of -130 V are formed in a high vacuum chamber of 1.0 × 10 ^-3 Pa or less. It was formed so as to have a thickness of 0.3 μm under the condition of 40 minutes.

A tungsten-containing hard carbon film 4 made of a laminated film was formed on the hard carbon base film 3 by using the same arc ion plating apparatus. This film formation was performed by setting an arc current of 120 A and alternately applying a predetermined low bias voltage and a predetermined high bias voltage in a pulse shape. Specifically, a low bias voltage of -158V and a high bias voltage of -1800V were applied in pulse form for 1 second each (480 minutes in total) to form a film.

The total thickness of the hard carbon film 4 was 3.5 μm, and the thickness per layer was about 2 nm. Tungsten in the hard carbon film 4 was measured by EPMA quantitative analysis and had a content of 0.2 atomic% (corresponding to 2.9% by mass). The hydrogen content of the hard carbon film 4 was 1.3 atomic% as measured by the RBS / HFS method. The oxygen content of the hard carbon film 4 was 0.3 atomic% as a result of measurement by EDX semi-quantitative measurement. Other than that, it is an unavoidable impurity. The balance was carbon, which was about 98.2 atomic% (equivalent to about 96% by mass).

^The sp2 component ratio was measured at 10 points at equal intervals in the film thickness direction. The results are shown in Table 1. As shown in Table ¹ , the sp2 component ratio was in the range of 58% to 75%, and the average was 68%. In Table 1, the peak area (near 285 eV), the peak area (280 to 310 eV), and the sp ² peak area ratio are also shown.

In the hard carbon film 4 made of the laminated film shown in FIG. 6, a thin white layer (thickness of about 5 nm) is slightly present on a regular basis, and this white layer has an sp ² component ratio (sp ² /). (Sp ² + sp ³ )) was 58% or more and 75% or less of the sp ² component rich layer. This white layer has a richer graphite structure than the diamond structure, and is considered to have an effect of improving the film toughness of the hard carbon film 4. As described above, this white layer is periodically-in the process of forming a laminated film by applying a low bias voltage of -158V and a high bias voltage of -1800V in a pulse shape to the hard carbon film 4. It is formed by lengthening the application time of a bias voltage of 1800 V.

The area ratio of macroparticles appearing on the surface of the hard carbon film 4 was 0.7%. FIG. 5 is a surface photograph showing macroparticles of the hard carbon film 4. The Vickers hardness of the obtained hard carbon film 4 was 1242HV0.05. The measurement was performed using a Vickers hardness tester (manufactured by Future Tech Co., Ltd.). The indentation hardness HIT (15 mN load), which is the surface hardness of the hard carbon film 4 as measured using nanoindentation manufactured by _Elionix Inc., was 13 GPa.

[Example 2]
In Example 1, a carbon target containing 5 atomic% of tungsten was used. Other than that, the piston ring of Example 2 was obtained in the same manner as in Example 1.

The total thickness of the hard carbon film 4 was 3.0 μm, and the thickness per layer was about 5 nm. Tungsten in the hard carbon film 4 was measured by EPMA quantitative analysis and had a content of 0.5 atomic%. The hydrogen content of the hard carbon film 4 was 1.1 atomic% as measured by the RBS / HFS method. The oxygen content of the hard carbon film 4 was 1.0 atomic% as a result of measurement by EDX semi-quantitative measurement. Other than that, it is an unavoidable impurity. As shown in FIG. 6, in the hard carbon film 4 made of a laminated film, a thin white layer (thickness of about 5 nm) was slightly present on a regular basis as shown in FIG. 6, but this white layer also was present. The sp ² component rich layer had an sp ² component ratio (sp ² / (sp ² + sp ³ )) of 58% or more and 75% or less. The area ratio of macroparticles appearing on the surface of the hard carbon film 4 was 0.3%. The Vickers hardness of the obtained hard carbon film 4 was 1352 HV0.05. The indentation hardness _HIT (15 mN load) of the hard carbon film 4 was evaluated in the same manner as in Example 1 and was 14 GPa.

[Example 3]
In Example 1, instead of forming a laminated film, the film forming conditions were changed to form a single-layer film. Other than that, the piston ring of Example 3 was obtained in the same manner as in Example 1.

Specifically, a tungsten-containing hard carbon film 4 made of a single-layer film was formed on the hard carbon base film 3 by using the same arc ion plating apparatus. This film formation was performed with an arc current of 120 A and a predetermined bias voltage (-1800 V) applied. The thickness of the hard carbon film 4 made of the single-layer film was 3.0 μm. Tungsten in the hard carbon film 4 was measured by EPMA quantitative analysis and had a content of 0.2 atomic%. The hydrogen content of the hard carbon film 4 was 1.4 atomic% as measured by the RBS / HFS method. The oxygen content of the hard carbon film 4 was 1.5 atomic% as a result of measurement by EDX semi-quantitative measurement. Other than that, it is an unavoidable impurity. Since the hard carbon film 4 is a single-layer film, the white layer as shown in FIG. 6 does not exist. The area ratio of macroparticles appearing on the surface of the hard carbon film 4 was 0.4%. The Vickers hardness of the obtained hard carbon film 4 was 1180 HV0.05. The indentation hardness _HIT (15 mN load) of the hard carbon film 4 was evaluated in the same manner as in Example 1 and was 12 GPa.

[Reference Example 1]
In Example 1, a hard carbon base film 3 and a hard carbon film 4 were formed using a carbon target containing no tungsten. Other than that, the piston ring of Reference Example 1 was obtained in the same manner as in Example 1.

The total thickness of the hard carbon film 4 was 4.7 μm, and the thickness per layer was about 0.2 nm. The hard carbon film 4 did not contain tungsten. The hydrogen content of the hard carbon film 4 was 0.3 atomic% as measured by the RBS / HFS method. The oxygen content of the hard carbon film 4 was 0 atomic% as a result of measurement by EDX semi-quantitative measurement. Other than that, it is an unavoidable impurity. The sp2 component ratio was measured at ² points and was 52% at the analysis point on the surface side. The area ratio of macroparticles appearing on the surface of the hard carbon film 4 was 3.1%. The Vickers hardness of the obtained hard carbon film 4 was 1710 HV0.05. The indentation hardness _HIT (15 mN load) of the hard carbon film 4 was evaluated in the same manner as in Example 1 and was 18.5 GPa.

[Measurement of ^sp2 component ratio]
^The sp2 component ratio was calculated by the following procedures (1) to (5). (1) The EELS spectrum is measured by an EELS analyzer (Made by Gatan, Model863GIF Tridiem). The peak intensity is normalized by fitting the measured EELS spectrum with a linear function before the peak and with a cubic function after the peak. (2) After that, the energy calibration is performed by comparing the diamond data with the graphite data and aligning the start positions of the peaks. (3) Obtain an area within the range of 280 eV to 310 eV for the calibrated data. (4) Separate into two peaks in the range of 280 eV to 295 eV (one is the peak of sp ² and the other is the peak of CH or amorphous), and the peak area near 285 eV is obtained. (5) The area ratio between the area in the range of 280 eV to 310 eV in (3) above and the peak area in the vicinity of 285 eV in (4) above is taken. Regarding this area ratio, graphite is 100, diamond is ⁰ , and the sp2 component ratio is obtained from the relative value. The value thus obtained was taken as the ^sp2 component ratio. Analysis was performed at 10 points at equal intervals in the thickness direction of the hard carbon film 4.

[Friction wear test (SRV test)]
On the surface (outer peripheral sliding surface 11) of the piston ring base material 1 (JIS standard SWOSC-V material equivalent material, Example 1 material) having a ring diameter of φ80 mm, in the same manner as in Example 1 and Reference Example 1, Cr- An N film (wear resistant film), a titanium film (undercoat film 2), a hard carbon undercoat film 3, and a hard carbon film 4 were formed in this order. The obtained sample was subjected to a frictional wear test (SRV test / Schwingungs Reihungund und Verschleiss) in the manner shown in FIG. 7, and the presence or absence of wear was observed. At the same time, μ (coefficient of friction between the object and the slip surface) was measured.

The test conditions are as follows. The piston ring was cut out to a length of 20 mm and used as a sliding side test piece (pin type test piece) 20. As the mating test piece (disc type test piece) 21, a test piece having a diameter of 24 mm and a length of 7.9 mm (hardness HRC62 or more) is cut out from SUJ2 steel specified as a high carbon chrome bearing steel material in JIS G4805. The SRV test was carried out under the following conditions. The reference numeral Y in FIG. 7 indicates a sliding direction, and the sliding width in the sliding direction is 3 mm.

-Test equipment: SRV test equipment (see Fig. 7)
-Load: 580N, 1000N
・ Frequency: 58Hz
-Test temperature: 80 ° C
・ Sliding width: 3 mm
-Lubricating oil: 5W-30, 125mL / hr
・ Test time: 10 minutes, 60 minutes, 120 minutes

The obtained friction coefficient μ is shown in Table 2. The friction coefficient μ was evaluated at a test time of 60 minutes. From the results in Table 2, it can be seen that the friction coefficient μ decreases when tungsten is contained.

FIG. 8 is a photograph showing the SRV test results. FIG. 8A shows the test results for 10 minutes at 1000 N using the sample of Example 1. FIG. 8B shows the test results for 60 minutes at 1000 N using the sample of Example 1. FIG. 8C shows the test results for 120 minutes at 1000 N using the sample of Example 1. In the sample of Example 1, although the thickness is as thin as 2.7 μm, the wear does not proceed even in the test at 1000 N for 120 minutes, the friction (mechanical friction loss) is low, and the wear resistance is remarkably excellent. showed that. As a result of conducting a 10-minute test at 1000 N for the sample of Reference Example 1, wear occurred.

The Vickers hardness of the hard carbon film 4 in Example 1 was 1242 HV0.05, whereas the Vickers hardness of the hard carbon film 4 in Reference Example 1 was 1710 HV0.05. It is considered that the hard carbon film 4 in Example 1 contained tungsten to reduce the hardness, but the friction (mechanical friction loss) was low and the wear resistance was excellent, so that the toughness was improved. It is thought that it is.

1 Piston ring base material 2 Undercoat film 3 Hard carbon undercoat film 4 Hard carbon film 5 Outermost surface film 10,10A, 10B, 10C, 10D Piston ring 11 Sliding surface (outer peripheral sliding surface)
12 Top surface 13 Bottom surface 14 Inner peripheral surface 20 Sliding side test piece (pin type test piece)
21 Opponent test piece (disc type test piece)
P load

Claims (2)

It has a hard carbon film formed on at least the outer peripheral sliding surface of the piston ring base material, and has.
The hard carbon film is a laminated film or a single-layer film having a total thickness of 0.5 μm or more and 20 μm or less, which is continuously formed immediately above the hard carbon base film by the same film forming means, and has a tungsten of 0.05. It is contained in the range of atomic% or more and 0.4 atomic% or less, and the sp2 component ratio measured by the TEM ^- EELS spectrum obtained by combining electron energy loss spectroscopy (EELS) with a transmission electron microscope (TEM). Is in the range of 40% or more and 80% or less, and the hydrogen content is less than 5 atomic%.
The hard carbon base film is characterized in that it is a film having a thickness of 0.05 μm or more and 0.5 μm or less, which contains tungsten in the range of 0.05 atomic% or more and 0.4 atomic% or less. piston ring. The piston ring according to claim 1, wherein the hard carbon film is a laminated film.

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