JP7284700B2 - sliding mechanism - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sliding mechanism in which a first member having an iron-based thermal spray coating and a second member having a hard carbon coating are combined. It relates to a combination of a cylinder with a piston ring and a piston ring.

2. Description of the Related Art In recent years, there has been a strong demand for improved fuel efficiency in internal combustion engines, mainly automobile engines. Therefore, research and development aimed at miniaturization, weight reduction, reduction of friction loss, etc. are being widely carried out. For example, attempts have been made to use an aluminum alloy with a low specific gravity for the cylinder and to coat the outer peripheral sliding surface of the piston ring with a hard carbon coating having a low coefficient of friction.

An example of this hard carbon film is amorphous carbon called diamond-like carbon (DLC). The structural essence of DLC is a mixture of diamond bonds (sp ³ bonds) and graphite bonds (sp ² bonds) as carbon bonds. Therefore, DLC has hardness, wear resistance, thermal conductivity, and chemical stability similar to diamond, while having solid lubricity similar to graphite, so it is suitable as a protective film for piston rings.

On the other hand, the aluminum alloy cylinder has a cast iron liner cast on the inner peripheral surface that directly slides on the piston ring, or has an iron-based thermal spray coating formed by thermally spraying iron-based alloy powder on the inner peripheral surface. There is In particular, cylinder bore thermal spraying technology is attracting attention, which is expected to reduce the overall bore temperature and improve uniformity by improving heat transfer performance, and to improve wear resistance and scuff resistance of piston rings.

In Patent Document 1, "Using a cylinder bore thermal spraying technology that can use aluminum alloy castings by ordinary die casting, it has excellent scuff resistance and wear resistance even if the engine is subjected to high load and severe sliding conditions. The objective is to provide a combination of a cylinder bore and a piston ring with low friction loss. The piston ring forms a hard carbon coating on the outer peripheral sliding surface, and the Rpk value (JIS B 0671-2: 2002) in the roughness curve of the surface of the iron-based thermal spray coating is less than 0.20 μm, and the hard carbon A cylinder bore and piston ring combination characterized in that the coating has an Rpk value of less than 0.15 μm.

JP 2015-59544 A

The gas generated after combustion of fuel contains corrosive substances such as sulfides, and as the number of combustion times increases, corrosion may occur on the inner peripheral surface of the cylinder. Therefore, in order to suppress the occurrence of this corrosion, it has been proposed to form a highly corrosion-resistant iron-based thermal spray coating containing high chromium on the inner peripheral surface of the cylinder. However, in this case, compared with the case where the inner peripheral surface is formed of a cast iron liner or a general iron-based thermal spray coating, the piston ring with the hard carbon coating has a large wear amount of the coating. Such a problem is not limited to the combination of a cylinder and a piston ring, but is common to all sliding mechanisms that combine a first member on which a high chromium-containing iron-based thermal spray coating is formed and a second member on which a hard carbon coating is formed. It applies.

Therefore, in view of the above problems, the present invention provides a combination of a first member having a high chromium-containing iron-based thermal spray coating and a second member having a hard carbon coating to reduce the amount of wear of the hard carbon coating. In particular, even if the inner peripheral surface of the cylinder is formed of a highly corrosion-resistant, high-chromium-containing iron-based thermal spray coating, the hard carbon forming the outer peripheral surface of the piston ring An object of the present invention is to provide a combination of a cylinder and a piston ring that can reduce the amount of wear of the coating.

In order to solve the above problems, the present inventors have made intensive studies and found that a cylinder having a highly corrosion-resistant iron-based thermal spray coating containing 8% or more of Cr on the bore surface does not substantially contain hydrogen and has a Vickers hardness 1100 HV or more and 2100 HV or less, and a ratio Wp/We of plastic deformation energy Wp to elastic deformation energy We of 0.60 or more. It has been found that the amount of wear of the DLC film can be significantly reduced by this.

The gist and configuration of the present invention completed based on the above findings are as follows.
(1) A sliding mechanism combining a first member and a second member that slides on the first member,
The sliding surface of the first member is formed of an iron-based thermal spray coating containing Fe as a main component and containing 8% or more by mass of Cr,
The second member has a sliding surface with a sliding surface of the first member formed of an amorphous carbon film that does not substantially contain hydrogen,
The amorphous carbon film has a Vickers hardness of 1100 HV or more and 2100 HV or less, and the ratio Wp/We of the plastic deformation energy Wp to the elastic deformation energy We of the amorphous carbon film is 0.60 or more. Characterized sliding mechanism.

(2) The sliding mechanism according to (1) above, wherein the first member is a cylinder of an internal combustion engine, and the second member is a piston ring having an outer peripheral surface that slides on an inner peripheral surface of the cylinder.

The sliding mechanism of the present invention is a combination of a first member on which a high chromium-containing iron-based thermal spray coating is formed and a second member on which a hard carbon coating is formed. It is possible. In particular, if the sliding mechanism of the present invention is a combination of a cylinder and a piston ring, even if the inner peripheral surface of the cylinder is formed of a highly corrosion-resistant iron-based thermal spray coating containing high chromium, the piston ring It is possible to reduce the amount of wear of the hard carbon film forming the outer peripheral surface of the.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the combination of the cylinder and piston ring by one Embodiment of this invention, (A) is sectional drawing of the cylinder 10, (B) is a sectional perspective view of the piston ring 20. Fig. 3 is a graph showing a typical load-indentation depth curve obtained in nanoindentation testing; 4 is a graph showing test results of Experimental Example 1. FIG. 7 is a graph showing test results of Experimental Example 2. FIG. 7 is a graph showing test results of Experimental Example 3. FIG. 9 is a graph showing test results of Experimental Example 4. FIG.

The present invention is a sliding mechanism that combines a first member and a second member that slides on the first member. Hereinafter, as one embodiment of the present invention, a combination of a cylinder and a piston ring, in which the first member is a cylinder of an internal combustion engine and the second member is a piston ring, will be described. A combination of a cylinder and a piston ring according to one embodiment of the present invention is shown in FIGS. a ring 20; The piston ring 20 is fitted over a known piston (not shown), and the outer peripheral surface 22 of the piston ring 20 slides on the inner peripheral surface 12 of the cylinder 10 when the piston reciprocates within the cylinder 10 . The inner peripheral surface 12 of the cylinder 10 is formed with a high chromium-containing iron-based thermal spray coating 14 . The piston ring 20 is composed of a substrate 20A and an amorphous carbon film (DLC film) 28 that does not substantially contain hydrogen, and is formed into a ring shape by four surfaces, an outer peripheral surface 22, an inner peripheral surface 24, and upper and lower surfaces 26A and 26B. , and the outer peripheral surface 22 is formed of the DLC coating 28 .

(Cylinder)
Although the base material for forming the high chromium-containing iron-based thermal spray coating 14 in the cylinder 10 is not particularly limited, for example, a general aluminum alloy can be used. The cylinder 10 is a linerless cylinder in which an iron-based spray coating 14 with a high chromium content is formed by directly spraying iron-based alloy powder with a high chromium content on the inner peripheral surface of the base material made of the aluminum alloy. . Thermal spraying is not particularly limited and may be plasma spraying, arc spraying, high-velocity flame spraying (HVOF, HVAF) or the like, but wire arc spraying using iron-based alloy wire is economically superior and preferable.

In the present embodiment, the high chromium-containing iron-based thermal spray coating 14 contains Fe as a main component and contains 8% or more of Cr in terms of mass %. As shown in Experimental Example 1 (FIG. 3) described later, by setting the Cr content of the iron-based thermal spray coating to 8% or more, the corrosion amount of the cylinder inner peripheral surface 12 (that is, the high chromium-containing iron-based thermal spray coating 14) can be reduced. can be significantly reduced. In addition, it is more preferable to use a coating that is thermally sprayed with a thermal spraying material having a component ratio equivalent to that of SUS410.

For example, among the high chromium-containing iron-based thermal spray coating 14 as described above, in particular, the component containing, in mass%, C: 1.2% or less and Cr: 10.5% or more, and the balance being Fe and unavoidable impurities It is preferable to adopt a stainless thermal spray coating having a composition. Moreover, the amount of C is more preferably 0.3% or less. Sulfides, nitrides, and the like are generated when the fuel is burned. In recent years, in particular, corrosive gas may be contained in intake gas due to hydrogen sulfide gas and the like present in exhaust gas from an exhaust gas recirculation (EGR) device or the like. Therefore, the inner peripheral surface of the cylinder may be exposed to corrosive gas with a higher concentration than before. Therefore, corrosion of the inner peripheral surface of the cylinder tends to progress easily. Therefore, in order to improve the corrosion resistance of the inner peripheral surface of the cylinder, it is preferable to coat the inner peripheral surface of the cylinder with a thermally sprayed stainless steel coating that is resistant to corrosion. The composition of the stainless steel sprayed coating is, in mass %, C: 0.15% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.04% or less, S: 0.04% or less. 03 or less, Ni: 0.6% or less, Cr: 11.5 to 13.5%, Mo: 0.3 to 0.6%, and the balance is Fe and unavoidable impurities. preferable.

In the present embodiment, the Vickers hardness of the high chromium-containing iron-based thermal spray coating 14, that is, the Vickers hardness of the inner peripheral surface 12 of the cylinder 10 is 300HV or more and 800HV or less.

The surface porosity of the high chromium-containing iron-based thermal spray coating 14 is preferably 0.3% or more and 2.5% or less. "Porosity" is obtained by the following method. The surface of the thermal spray coating was observed with a scanning electron microscope at a magnification of 200 times, the minute pits that looked like pits and the other matrix were binarized, and the area ratio of the minute pits was determined by image analysis. The "porosity" in the present invention was obtained by averaging the area ratios of the three fields of view.

Although the thickness of the high chromium-containing iron-based thermal spray coating 14 is not particularly limited, it is preferably 50 μm or more and 300 μm or less. According to conventional knowledge, if the film thickness is about 50 μm, the base material is not exposed. If the film thickness exceeds 300 μm, only the film formation time is spent, and on the other hand there is no particular effect in terms of performance.

(piston ring)
The base material 20A of the piston ring is not particularly limited, and for example, known or arbitrary materials such as silicon chromium steel (JIS SEOSC-V) and martensitic stainless steel (JIS SUS440B) for compression rings can be used.

In this embodiment, the amorphous carbon film 28 is made only of DLC that does not substantially contain hydrogen. In recent years, MoDTC-containing low-viscosity oil is frequently used as oil for internal combustion engines. It is known that when this oil is used in a high-temperature and sliding environment, a tribofilm containing molybdenum disulfide as its main component is formed. When the tribofilm is formed, the frictional force between the piston ring 20 and the inner peripheral surface 12 of the cylinder is reduced. However, when a DLC film containing hydrogen is used, there is a problem that the MoDTC component attacks the DLC film containing hydrogen, increasing wear. Therefore, in this embodiment, a DLC film containing no hydrogen is used. Amorphous carbon can be confirmed by Raman spectrum measurement using a Raman spectrophotometer (Ar laser). Here, the term "substantially free of hydrogen" as used herein means that the hydrogen content in the amorphous carbon film is 2 atomic % or less, and the remainder consists essentially of carbon. .

[Method for measuring hydrogen content of amorphous carbon film]
For the evaluation of the hydrogen content of the amorphous carbon film, RBS (Rutherford Backscattering Spectrometry)/HFS (Hydrogen Forward) is used for the amorphous carbon film formed on a flat surface or a surface with a sufficiently large curvature. can be evaluated by Scattering Spectrometry). On the other hand, an amorphous carbon film 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 well-known method of analyzing film composition, 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 coated with carbon Forms a film.

Film formation on the reference sample is performed by introducing a hydrocarbon-based gas such as methane, Ar, and H ₂ as atmosphere gases using a reactive sputtering method. Then, the amount of hydrogen contained in the carbon film is adjusted by changing the flow rate of H ₂ and/or the flow rate of the hydrocarbon-based gas to be introduced. In this way, carbon films composed of hydrogen and carbon and having 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, the SIMS analysis can also be used to measure a film formed on an uneven surface, such as the outer peripheral surface of a piston ring. Therefore, the hydrogen content and carbon content (unit: atomic %) obtained by RBS/HFS and the secondary ions of hydrogen and carbon obtained by SIMS for the same coating of the reference sample with carbon coating. Find an empirical formula (metric line) that shows the relationship between intensity and ratio. By doing so, the hydrogen content rate and the carbon content rate can be calculated from the SIMS secondary ion intensities of hydrogen and carbon 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 surface of the carbon film is adopted.

[Characteristic structure of amorphous carbon film]
In the present embodiment, the DLC film 28 has (A) a Vickers hardness of 1100 HV or more and 2100 HV or less, and (B) a ratio Wp/We of the plastic deformation energy Wp to the elastic deformation energy We of 0.60 or more. It is important to satisfy both Satisfying these (A) and (B) makes it possible to reduce the amount of wear of the DLC coating 28 when the inner peripheral surface 12 of the cylinder is formed of the high chromium-containing iron-based thermal spray coating 14. be. A more detailed description will be given below.

[Vickers hardness of amorphous carbon film]
In this embodiment, firstly, it is important that the DLC film 28 has a Vickers hardness of 1100 HV or more and 2100 HV or less. As is clear from Experimental Example 2 (FIG. 4) described later, when the Vickers hardness of the DLC film exceeds 2100 HV, the amount of wear of the DLC film increases. On the other hand, when the Vickers hardness of the DLC film 28 is 2100 HV or less, the wear amount of the DLC film 28 can be reduced. Since the area of the DLC coating that forms the outer peripheral surface of the piston ring is sufficiently small relative to the area of the sliding range of the cylinder bore, conventionally, the higher the hardness of the DLC coating that forms the outer peripheral surface of the piston ring, the better the wear resistance. It was thought that the abrasion resistance of the DLC film would be reduced. However, in the present invention, based on the technical idea that there is an appropriate hardness magnitude relationship between the piston ring and the cylinder bore, the hardness of the DLC film is applied on the low hardness side, which is contrary to the conventional idea. It was found that the wear amount of the DLC film was reduced.

Further, as is clear from FIG. 4, when the Vickers hardness of the DLC film is in the range of 1100 HV or more and 2100 HV or less, the change in the amount of wear is small with respect to the change in the hardness of the film, and the amount of wear is stably low. can be realized. Conventionally, the amount of wear was controlled by the hardness of the DLC film, which required strict control of the hardness. It leads to improvement of non-defective product rate, and has great merits in terms of manufacturing such as improvement of yield.

Also, from FIG. 4, it can be understood that it is possible to maintain a low wear loss regardless of the magnitude relationship of the surface porosity of the thermal spray coating. That is, when the inner peripheral surface of the cylinder is formed of a high-chromium-containing iron-based thermal spray coating, fine abrasion powder generated on the inner peripheral surface during sliding bites into the sliding surface, attacks the DLC coating, and causes wear. promote it. At this time, the presence of pores (recesses) on the surface of the iron-based thermal spray coating with a high chromium content traps abrasion powder, thereby suppressing wear of the DLC coating. However, if the porosity of the high chromium-containing iron-based thermal spray coating varies due to manufacturing factors, there is a problem that the trapping effect cannot be obtained and the wear of the DLC coating also varies. Here, by reducing the Vickers hardness of the DLC film, the DLC film becomes more likely to deform following the shape of the abrasion powder when it is bitten by the abrasion powder. Wear amount can be reduced. It is believed that such an effect can reduce wear, and that even if the porosity of the bore fluctuates, the variation in wear will be reduced.

Moreover, as is clear from Experimental Example 3 (FIG. 5) described later, when the Vickers hardness of the DLC film exceeds 2100 HV, the wear amount of the DLC film fluctuates depending on the temperature of the cylinder. On the other hand, when the Vickers hardness of the DLC film 28 is 2100 HV or less, the wear amount of the DLC film 28 can be reduced without depending on the temperature of the cylinder. That is, the amount of wear of the DLC film 28 can be reduced even when the engine is not sufficiently warmed up.

When the Vickers hardness of the DLC film is less than 1100 HV, it is considered that scuff resistance and other mechanical properties are inferior. Therefore, the DLC film 28 should have a Vickers hardness of 1100 HV or more. More preferably, the DLC film 28 has a Vickers hardness of 1100 HV or more and 2050 HV or less.

The Vickers hardness of the DLC film can be measured with a Vickers hardness tester (eg, FLC-50VX manufactured by Futuretech Co., Ltd.). The indenter is pressed into the film surface and judged by the size of the indentation formed. The load value for indentation was set so that the depth of indentation was 1/5 or less of the film thickness of the film in order to reduce the influence of the hardness of the substrate. In the case of a thin film of several μm, it is difficult to measure it with the above Vickers hardness tester without being affected by the substrate. Then, the indentation hardness (HIT) is measured with a load of several mN to several tens of mN so that the indentation depth is 1/5 or less of the film thickness, and the conversion formula HV = HIT (N/mm ² )×0.0945 may be used as the Vickers hardness. If the surface to be measured is not smooth, the surface to be measured is polished with a diamond film or the like before the measurement is performed, because the hardness is affected by the roughness and an accurate hardness cannot be obtained.

[Ratio Wp/We of the plastic deformation energy Wp of the amorphous carbon film to the elastic deformation energy We]
Secondly, in this embodiment, it is important that the ratio Wp/We of the plastic deformation energy Wp to the elastic deformation energy We of the DLC film 28 is 0.60 or more. The plastic deformation energy Wp is the work (energy) that the indenter pushed from the coating surface in the nanoindentation test spends on the deformation of the coating. Energy. The elastic deformation energy We is the energy released when the indenter is removed and the coating returns to its original state. Therefore, Wp/We is an index indicating the easiness of plastic deformation when a foreign substance is pushed into the film surface.

As is clear from Experimental Example 5 (Table 1) described later, in the present embodiment, by setting Wp/We to 0.60 or more, that is, by making the DLC coating 28 a coating that is easily plastically deformed, the inner diameter of the cylinder is reduced. It was found that the amount of wear of the DLC coating 28 can be reduced when the peripheral surface 12 is formed of the high chromium-containing iron-based thermal spray coating 14 . This is because if the DLC coating is prone to plastic deformation when sliding against a high-chromium-containing iron-based thermal spray coating, foreign matter (such as fine abrasion powder from the thermal spray coating and the DLC coating, carbon sludge generated during combustion, etc.) may occur during sliding. It is presumed that this is because the DLC film is plastically deformed to promote the discharge of foreign matter when it is bitten, and the lubricity is improved by creating an appropriate escape route for the lubricating oil.

In this embodiment, Wp/We is 0.60 or more and the Vickers hardness is 1100 HV or more and 2100 HV or less. It is considered that the amount of wear is reduced by reducing the amount of wear.

When Wp/We exceeds 0.80, the DLC film tends to be excessively plastically deformed, resulting in many scratches on the sliding surface, resulting in deterioration of sealability and peeling of the film. Therefore, Wp/We is preferably 0.80 or less. Wp/We is more preferably 0.60 or more and 0.73 or less.

The plastic deformation energy Wp and the elastic deformation energy We of the DLC film are calculated using the load-indentation depth curve obtained in the nanoindentation test. FIG. 2 shows an example of the calculation method. When the indenter is pushed into the DLC film surface, the indentation depth increases as the load increases (curve OC). Then, when the maximum load is reached, it is held for a certain period of time (straight line CD). In general, even while the load is being held, the area around the indenter contact portion of the DLC film may be deformed and the indentation depth may increase. Next, when the load is unloaded, the indentation depth becomes shallower due to the release of the elastic deformation of the DLC film, but due to the plastic deformation of the DLC film, the indentation depth becomes deeper than before contact with the indenter (curve DA). . In the load-indentation depth curve obtained in this manner, the area of the region OADC is the plastic deformation energy Wp consumed for plastic deformation of the DLC film by the indentation of the indenter. The area of the region ABD is the elastic deformation energy We used for the elastic deformation of the DLC film by the pressing of the indenter. In the present invention, as the values of Wp and We, the DLC film surface is measured at 14 points, and the average value of 10 measured values obtained by removing the maximum value of 2 points and the minimum value of 2 points is used. do.

Although the thickness of the DLC film 28 is not particularly limited, it is preferably 1 μm or more and 30 μm or less. If the thickness is less than 1 μm, the film thickness is excessively thin and the film is worn out. If the thickness exceeds 30 μm, the internal stress of the film increases, and chipping tends to occur. In addition, in the present invention, the thickness of the DLC film shall be measured by the following method. That is, the piston ring on which the DLC film is formed is cut perpendicularly to its circumferential direction, the cut cross section is polished with a diamond film to smooth it, and the polished surface is observed with a microscope to measure the DLC film thickness.

In this embodiment, the DLC film 28 can be formed, for example, using a PVD method such as ion plating by vacuum arc discharge using a carbon target. The PVD method can form a DLC film that contains little hydrogen and has excellent wear resistance. In addition, without introducing a gas containing hydrogen as a constituent element such as a hydrocarbon gas in a vacuum, an arc discharge is used in an atmosphere in which an inert gas such as a high vacuum or Ar gas is introduced. A filtered arc ion plating method equipped with a filter that removes carbon microparticles, such as a filter, may also be used.

Here, the Vickers hardness of the DLC film 28 can be controlled by adjusting the bias voltage applied to the base material of the piston ring during film formation. It can be controlled by adjusting the temperature of the material.

Specifically, when the bias voltage is increased, the kinetic energy of carbon ions colliding with the base material of the piston ring increases, so carbon is sputtered off from the base material surface without depositing on the base material surface. For this reason, the DLC film formed has a rough structure, and the hardness is reduced.

When the temperature of the base material during film formation is increased, the heat reduces three-dimensional carbon bonds, making it easier to form a stable two-dimensional structure, reducing the connection of the bond network, and increasing Wp/We. It is considered to be.

From the above, it is easy to form a DLC film that satisfies the conditions of the present invention by setting the bias voltage to a relatively high value while appropriately raising the temperature of the base material by heating with a heater or the like. The bias to be applied can be applied by direct current, pulse, floating potential, or the like, and a plurality of methods may be combined. In particular, pulse bias and floating potential are suitable bias application methods for preventing the temperature of the substrate from rising excessively.

(middle layer)
In addition, although the piston ring according to the above-described embodiment has been exemplified by forming the DLC film directly on the base material of the piston ring, the present invention is not limited to this. For example, a metallic intermediate layer having a thickness of 0.1 to 1.0 μm may be formed between the base material of the piston ring and the DLC coating to enhance adhesion. Materials for the metallic intermediate layer include one or more elements selected from the group consisting of chromium, titanium, and tungsten, or carbides thereof. Furthermore, even if the DLC film wears out due to the usage environment, a hard metal nitride with excellent scuff resistance is placed between the piston ring base material and the DLC film, or between the base material and the metal intermediate, so that scuffing does not occur. It may be formed with a thickness of 1 to 30 μm between layers. The hard metal nitride may be chromium nitride, titanium nitride, or carbides thereof.

(Experimental example 1)
The inner wall of the cylinder block made of ADC12 aluminum alloy is provided with unevenness by machining, and then, by the arc-type thermal spraying method using nitrogen gas as a carrier, the amount of Cr is various levels, and the balance is Fe. Thickness of about 250 μm was deposited. The surface of the thermal spray coating was ground to finish the surface roughness to about Ra 0.05 μm, and a test piece of 20 mm×20 mm was cut out for evaluation. The side surface and aluminum alloy rear surface of the cut test piece were coated with a resin to prevent acid corrosion, and the weight of the test piece was measured. After that, it was immersed in a 1% nitric acid aqueous solution at 25° C. for 1 hour. After the immersion, the test piece was sufficiently dried, and the weight of the test piece was measured again. FIG. 3 shows the relationship between the amount of Cr in the thermal spray coating and the amount of corrosion.

In the thermal spray coating containing no Cr, the nitric acid eluted metal components on the surface and the weight decreased by 294 mg. The thermal spray coating containing 10% Cr had a weight loss of 3.2 mg. Corrosion products such as oxides were not observed, and it was confirmed that the amount of corrosion itself was reduced. The amount of corrosion decreased to about 1/100 when the amount of Cr was changed from 3% to 8%, and almost no corrosion was observed when the amount of Cr was 8% or more.

(Experimental example 2)
Various levels of DLC films having a Vickers hardness in the range of 1100 to 2400 HV and Wp/We of 0.60 or more were formed on the outer peripheral surface of the piston ring. The film formation of the DLC film was carried out by using a vacuum arc type film formation apparatus and setting various bias voltages. When the hydrogen content of each level of DLC film was measured by the method described above, it was found to be 2 atomic % or less.

A cylinder having the following two levels of stainless steel thermal spray coating formed on the inner peripheral surface was produced, and this was cut into a size of 15×10 mm to obtain a bore test piece. The porosity of the stainless thermal spray coating is a value measured by the measurement method described above.
Level 1: SUS410 steel (porosity 1.4%)
Level 2: SUS410 steel (porosity 0.9%)

[Sliding test]
A reciprocating motion test was performed in a state where the outer peripheral surface of the piston ring and the bore test piece were in line contact by a vibration friction wear test (Optimol Co., Ltd.: SRV4 testing machine). Lubricating oil (engine oil base oil) at 100° C. was dripped onto the surface of the bore test piece at a rate of 0.25 mL/h. The test conditions are as follows.
Load: 450N
Frequency during reciprocating sliding: 25Hz
Amplitude during reciprocating sliding: 3 mm
Test time: 12 hours

The wear amount of the DLC film was obtained by the following method. That is, the outer peripheral shape of the piston ring before and after the sliding test was measured in the axial direction using a stylus type roughness measuring machine (SURFCOM1400D manufactured by Tokyo Seimitsu Co., Ltd.). Then, the wear depth of the film was obtained by superimposing the shapes before and after the test.

The results are shown in FIG. As is clear from FIG. 4, by setting Wp/We to 0.6 or more and the Vickers hardness of the DLC film to be 2100 HV or less, the wear amount of the DLC film can be significantly reduced. Further, by setting the Vickers hardness of the DLC coating to 2100 HV or less, the wear amount of the DLC coating could be reduced without depending on the porosity of the thermal spray coating.

(Experimental example 3)
As a test piece corresponding to the piston ring, a φ6 mm × 12 mm long SUJ2 cylinder was used as a base material, and DLC films with a Vickers hardness level of 1800 HV and a Vickers hardness level of 2300 HV were formed on the curved surface. Wp/We is 0.60 or more at any level. The film formation of the DLC film was carried out by using a vacuum arc type film formation apparatus and setting various bias voltages. When the hydrogen content of each level of DLC film was measured by the method described above, it was found to be 2 atomic % or less.

A flat plate (plate) of 20×20×3.5 mm made of stainless steel (SUS410 steel) was prepared as a test piece corresponding to a cylinder having a stainless thermal spray coating on the bore surface.

A sliding test was conducted under the following conditions to determine the wear amount of the DLC film. However, in Experimental Example 3, the temperature of the flat plate (plate) was previously heated to two levels of 80°C and 120°C.
Load: 360N
Frequency during reciprocating sliding: 25Hz
Amplitude during reciprocating sliding: 3 mm
Exam time: 2 hours

The results are shown in FIG. As is clear from FIG. 5, the influence of the flat plate temperature on the wear amount of the DLC film is smaller when the Vickers hardness of the DLC film is 1800 HV than when the Vickers hardness is 2300 HV.

(Experimental example 4)
As a test piece corresponding to the piston ring, a φ6 mm × 12 mm long SUJ2 cylinder was used as a base material, and DLC films with a Vickers hardness level of 1800 HV and a Vickers hardness level of 2300 HV were formed on the curved surface. Wp/We is 0.60 or more at any level. The film formation of the DLC film was carried out by using a vacuum arc type film formation apparatus and setting various bias voltages. When the hydrogen content of each level of DLC film was measured by the method described above, it was found to be 2 atomic % or less.

A flat plate made of stainless steel (SUS410 steel) with a size of 20×20×3.5 mm was prepared as a test piece corresponding to a cylinder having a stainless thermal spray coating on the bore surface.

A sliding test was performed in the same manner as in Experimental Example 3 to determine the amount of wear of the DLC film and the amount of wear of the stainless steel flat plate. However, in Experimental Example 4, assuming foreign matter such as abrasion powder generated from the SUS thermal spray coating, the test was conducted with SUS powder sprinkled between the curved surface of the cylinder and the surface of the stainless steel flat plate.

The results are shown in FIG. As is clear from FIG. 6, the amount of wear caused by the SUS thermal spray material can be reduced when the DLC coating has a Vickers hardness of 1800 HV compared to when it has a Vickers hardness of 2300 HV.

(Experimental example 5)
Various levels of DLC coatings shown in Table 1 were formed on the outer peripheral surface of the piston ring. The DLC film was formed using a vacuum arc type film forming apparatus with various bias voltages and substrate temperatures set.

As for the bore material, a cylinder having a stainless thermal spray coating of SUS410 steel (porosity 0.9%) formed on the inner peripheral surface was prepared, and cut into a size of 15×10 mm to obtain a bore test piece. The porosity of the stainless thermal spray coating is a value measured by the measurement method described above.

[Sliding test]
A reciprocating motion test was performed in a state where the outer peripheral surface of the piston ring and the bore test piece were in line contact by a vibration friction wear test (Optimol Co., Ltd.: SRV4 testing machine). Lubricating oil (engine oil base oil) at 100° C. was dripped onto the surface of the bore test piece at a rate of 0.25 mL/h. The test conditions are as follows.
Load: 450N
Frequency during reciprocating sliding: 25Hz
Amplitude during reciprocating sliding: 3mm
Test time: 12 hours

The wear amount of the DLC film was obtained by the following method. That is, the outer peripheral shape of the piston ring before and after the sliding test was measured in the axial direction using a stylus type roughness measuring machine (SURFCOM1400D manufactured by Tokyo Seimitsu Co., Ltd.). Then, the wear depth of the film was obtained by superimposing the shapes before and after the test.

As is clear from Table 1, in the invention examples using the DLC film having a Vickers hardness of 1100 HV or more and 2100 HV or less and a Wp/We of 0.60 or more, the inner peripheral surface of the cylinder is a high chromium iron-based The amount of wear of the DLC coating was able to be reduced when it was formed by thermal spray coating.

The sliding mechanism of the present invention is a combination of a first member on which a high chromium-containing iron-based thermal spray coating is formed and a second member on which a hard carbon coating is formed. It is possible. In particular, if the sliding mechanism of the present invention is a combination of a cylinder and a piston ring, even if the inner peripheral surface of the cylinder is formed of a highly corrosion-resistant iron-based thermal spray coating containing high chromium, the piston ring It is possible to reduce the amount of wear of the hard carbon film forming the outer peripheral surface of the.

10 Cylinder 12 Cylinder inner peripheral surface (bore surface)
14 High chromium content iron-based thermal spray coating (or stainless steel thermal spray coating)
20 Piston ring 20A Base material of piston ring 22 Outer peripheral surface of piston ring 24 Inner peripheral surface of piston ring 26A Upper surface (upper surface) of piston ring
26B Lower surface of piston ring (lower surface)
28 amorphous carbon film

Claims (2)

A sliding mechanism combining a first member and a second member that slides on the first member,
The sliding surface of the first member is formed of an iron-based thermal spray coating containing Fe as a main component and containing 8% or more by mass of Cr,
The second member has a sliding surface with a sliding surface of the first member formed of an amorphous carbon film that does not substantially contain hydrogen,
The amorphous carbon film has a Vickers hardness of 1100 HV or more and 2100 HV or less, and the ratio Wp/We of the plastic deformation energy Wp to the elastic deformation energy We of the amorphous carbon film is 0.60 or more. Characterized sliding mechanism. 2. The sliding mechanism according to claim 1, wherein said first member is a cylinder of an internal combustion engine, and said second member is a piston ring having an outer peripheral surface that slides on an inner peripheral surface of said cylinder.

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