JP2020003022A - piston ring - Google Patents

Abstract

To provide a piston ring coated with a DLC coating having wear resistance and a low attacking property to a cylinder bore sliding surface.SOLUTION: A piston ring has a sliding surface coated with a DLC coating. The DLC coating has the number of pits of 15 or less per 3 μm×10 μm when being observed in the thickness direction cross-sectional SEM image (×10,000) thereof and hardness of 1,000 HV or more and 2,000 HV or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a piston ring that can be used for an internal combustion engine.

  The sliding surface of the piston ring is coated with a hard carbon coating in order to improve low friction and wear resistance. The hard carbon coating is also called a DLC (diamond-like carbon) coating, and various developments have been made.

  Patent Document 1 discloses that in a piston ring in which a sliding surface is coated with a DLC coating, the DLC coating is a laminated coating in which two or more layers of two different hardnesses are laminated, and the hardness difference between the two types of layers is different. Is 500 to 1700 HV.

Patent Literature 2 discloses a hard carbon coating formed on at least an outer peripheral sliding surface of a piston ring base material, and has a sp ² component ratio of 40 to 80% measured by a TEM-EELS spectrum, A hard carbon coating having a macroparticle area ratio of 0.1% to 10% on the coating surface is disclosed.

JP 2012-202522 A International Publication No. 2014/133095

Various developments have been made on the DLC coating. In addition to the wear resistance that suppresses the wear of the DLC coating against sliding, it does not wear the sliding surface of the cylinder bore, that is, the cylinder bore sliding surface has low aggressiveness. Is also required.
It is an object of the present invention to provide a piston ring coated with a DLC coating having low abrasion resistance on a cylinder bore sliding surface in addition to wear resistance.

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and have come to the conclusion that the DLC coating with reduced defects in the internal structure is a coating having excellent wear resistance and low aggressiveness on the cylinder bore sliding surface. Completed the invention.

The present invention relates to a piston ring having a sliding surface covered with a DLC coating,
The DLC coating includes a piston ring whose number of pits observed in a cross-sectional SEM image (× 10,000) in the thickness direction is 15 or less per 3 μm × 10 μm and whose hardness is 1000 HV or more and 2000 HV or less. .

In addition, the DLC film preferably has a refractive index measured by a spectroscopic ellipsometer of 2.3 or more at a wavelength of 550 nm, which tends to have no pits in the internal structure, which is preferable.
The DLC coating preferably has a hardness of 1,000 HV or more and 1700 HV or less, a friction coefficient of the sliding surface surface of preferably 0.10 or less, and, from the viewpoint of cylinder bore sliding surface aggression, reciprocation. In a wear amount measurement test using a dynamic friction tester, the wear amount of the mating member is preferably 0.6 μm or less.

  According to the present invention, it is possible to provide a piston ring covered with a DLC film having low abrasion resistance on a cylinder bore sliding surface in addition to wear resistance.

It is a schematic diagram which shows the structure of a reciprocating friction tester. 3 shows a cross-sectional SEM image of the DLC film produced in Example 1 (a photograph as a substitute for a drawing). 5 shows a cross-sectional SEM image of the DLC film produced in Example 2 (a photograph as a substitute for a drawing). 6 shows a cross-sectional SEM image of the DLC film produced in Comparative Example 1 (a photograph as a substitute for a drawing). 5 shows a cross-sectional SEM image of the DLC film produced in Comparative Example 2 (a photograph as a substitute for a drawing).

  One embodiment of the present invention is a piston ring in which a sliding surface is covered with a DLC film, and the DLC film has a number of pits observed in a cross-sectional SEM image (× 10,000) in a thickness direction of the piston ring. The number is 15 or less per 3 μm × 10 μm, and the hardness is 1000 HV or more and 2000 HV or less.

In the present embodiment, the DLC film has reduced defects in its internal structure. The internal defect of the DLC film can be confirmed by observing a cross-sectional SEM image of the DLC film in the thickness direction. In the present embodiment, the internal defect of the DLC film is confirmed by the number of pits observed when the cross-sectional SEM image has a low magnification because the defect may not be observed when the magnification is small. .
The DLC film has a number of pits of 15 or less, 10 or less, 5 or less, or 3 or less in a 3 μm × 10 μm region in a cross-sectional SEM image (× 10,000). , 2 or less, and 1 or less. By reducing the number of pits in the cross section observation of the DLC film, the DLC film becomes a film having excellent wear resistance and low aggressiveness on the cylinder bore sliding surface.

  In the present embodiment, a pit refers to a V-shaped defect existing at a location surrounded by a circle in the SEM images shown in FIGS. The presence of a large number of such pits inside the DLC coating causes irregularities to remain on the surface of the DLC coating when the sliding surface is formed, so that the aggressiveness to the mating material, specifically, the aggressiveness to the cylinder bore sliding surface The present inventors presume that the cylinder bore material wear amount is increased. In the DLC film of the present embodiment, the number of pits present inside the DLC film is reduced, so that it is possible to form a sliding surface without unevenness, and it is possible to reduce the aggressiveness to a partner material.

The number of pits is measured at 3 μm × 10 μm. In consideration of the thickness of the DLC film usually formed on the piston ring, a width of 3 μm is set in the thickness direction of the DLC film and a width of 10 μm is set in the circumferential direction of the piston ring. It is typical to do so. However, the measurement width may be set conversely, or the measurement width may be set diagonally.
In the present embodiment, at least a part of the DLC film may have a region having 15 or less pits per 3 μm × 10 μm, but the number of pits per 3 μm × 10 μm is 50% or more of the DLC film. It is preferably 15 or less, more preferably 80% or more, even more preferably 90% or more.

  The DLC film having the reduced number of pits is manufactured by using a filtered arc ion plating method (FCVA) in the manufacturing process, by increasing the pulse bias voltage, and by not excessively increasing the hardness of the DLC film. Can be formed.

  In the present embodiment, the hardness of the DLC film is 1000 HV or more and 2000 HV or less, 1700 HV or less, or 1500 HV or less. Generally, considering the wear resistance, it is preferable that the hardness of the coating is high. However, if the hardness of the coating is too high, the aggressiveness of the cylinder bore sliding surface tends to increase. In the present embodiment, it is preferable that the thickness is not excessively hard because the coating formed on the surface causes the coating to be broken when the piston is deformed at the time of assembling the piston.

  The DLC coating preferably has a refractive index measured by a spectroscopic ellipsometer of 2.3 or more at a wavelength of 550 nm. When the refractive index is above this range, pits in the DLC coating tend to be reduced. The refractive index may be 2.35 or higher, and may be 2.40 or higher. As the spectral ellipsometer for measuring the refractive index, for example, a spectral ellipsometer UVISEL (manufactured by Horiba, Ltd.) can be used.

  Since the DLC coating according to this embodiment has low aggressiveness to the mating material, it is preferable that the friction coefficient of the sliding surface of the DLC coating has a relatively low value. Specifically, the friction coefficient μ of the sliding surface of the DLC coating covering the piston ring is preferably 0.10 or less. The coefficient of friction μ may be less than 0.10, may be 0.095 or less, and may be 0.090 or less.

The DLC film according to the present embodiment is a film mainly composed of amorphous carbon, but may contain hydrogen or may contain other unavoidable impurities. The hydrogen contained in the DLC coating is typically at most 5 at%, at most 3 at%, at most 2 at%, at most 1 at%, or at most 0.5 at%. .
The DLC coating has a sp ² component ratio of usually 40% or more, 50% or more, 60% or more, and usually 80% or less as measured by electron energy loss spectroscopy (EELS). It is.

The method for producing a DLC film according to the present embodiment is not particularly limited as long as a DLC film having the above physical properties can be produced. As an example, a method of forming a coating film by using a filtered arc ion plating method (FCVA) can be cited. In the FCVA method, the entire DLC film may be formed in a single step, or the DLC film may be formed by changing the pulse bias to be applied or by performing film formation a plurality of times without changing the pulse bias. Good.
The pulse bias to be applied is not particularly limited, but may be -500 V or lower, -800 V or lower, -1000 V or lower, -1500 V or lower, -2000 V or lower, Further, the voltage may be −3000 V or more.

  The thickness of the DLC film to be manufactured is not particularly limited. However, when a film is formed on the sliding surface of the piston ring, the thickness is usually 1 μm or more, 3 μm or more, 5 μm or more, and 20 μm or more. And may be 15 μm or less.

  The manufactured DLC coating has a significantly reduced aggressiveness on the mating material. The opponent material aggressiveness can be evaluated by a wear amount measurement test using a reciprocating friction tester. In the test, when sliding for 60 minutes, the wear amount of the cast iron cylinder bore material as the mating material is preferably 0.6 μm or less, may be 0.5 μm or less, and may be 0.4 μm or less. It may be smaller than 0.3 μm.

The wear amount measurement test by the reciprocating friction tester is as follows.
The test is performed using a pin-on-plate type reciprocating friction tester shown in FIG. The upper test piece used in the reciprocating friction test is a piston ring or a member simulated on the outer peripheral portion of the piston ring.The material of the pin is a piston ring base material, and the piston ring is A nitriding treatment is performed in the same manner as the base material to form a nitrided layer. Then, various DLC films are formed on the surface of the nitride layer.
The pin used for producing the upper test piece had a diameter of 8 mm, and the tip (sliding surface) of the pin used had a mirror-finished surface with a radius of curvature of 18 mm. As the lower test piece, a plate (a material equivalent to FC250: HRB100, A type graphite 75%, carbide precipitation 0.5% or less, Rz 1.0 μm, polishing finish using # 600 emery paper) with a cylinder bore made of cast iron is used.

In the reciprocating friction test, lubricating oil was supplied to the sliding interface between the upper and lower test pieces using a tubing pump or an air dispenser. The test conditions at this time are shown below.
<Test conditions>
・ Stroke: 50mm
・ Load: 50N
・ Speed: 300 cycle / min
・ Temperature of lower test piece: 80 ° C
・ Lubricant: 0W-20 (150μl)
・ Test time: 60min

A DLC coating was produced by the following method.
(Example 1)
With the piston ring substrate set in a filtered arc ion plating apparatus, the inside of the apparatus was evacuated to reduce the pressure, and then the substrate was heated. Thereafter, ion bombardment was performed with argon ions while a pulse bias voltage was applied to the substrate in a range of -500 to -1500 V.
Next, after setting a bias voltage in a range of −50 to −300 V with respect to the piston ring substrate by using a sputtering method, a Ti film was formed on the piston ring substrate as an adhesive layer.
Next, a first amorphous carbon layer and a second amorphous carbon layer were alternately formed and laminated on the Ti film. Here, the first amorphous carbon layer is formed using a sputtering method, a bias voltage is applied to the piston ring substrate within a range of -50 to -300 V, and an argon gas atmosphere is formed using a carbon target. Filmed. The second amorphous carbon layer was formed by using a filtered arc method and using a carbon target while applying a pulse bias voltage to the substrate within a range of -500 to -1500 V.
Note that the first amorphous carbon layer and the second amorphous carbon layer were formed without introducing a gas containing hydrogen into the film formation chamber so that hydrogen was not taken into the films. The thickness of the first amorphous carbon layer was 2 to 8 nm, and the thickness of the second amorphous carbon layer was 350 to 400 nm. Then, one layer of the first amorphous carbon layer and one layer of the second amorphous carbon layer were made into one set and two layers, and this set was repeatedly laminated in units of two layers to obtain a DLC film having a thickness of 5.0 μm. .

(Example 2)
With the piston ring substrate set in a filtered arc ion plating apparatus, the inside of the apparatus was evacuated to reduce the pressure, and then the substrate was heated. Thereafter, ion bombardment was performed with argon ions while a pulse bias voltage was applied to the substrate in a range of -500 to -1500 V.
Next, using a sputtering method, a bias voltage was set in the range of −50 to −300 V with respect to the piston ring substrate, and then a Ti film was formed as an adhesive layer on the piston ring substrate.
Next, an amorphous carbon layer was formed on the Ti film. The amorphous carbon layer was formed using a carbon target while applying a pulse bias voltage to the substrate within a range of -2000 to -3000 V. Note that the amorphous carbon layer was formed without introducing a gas containing hydrogen into the film formation chamber so that hydrogen was not taken in the film. The thickness of one amorphous carbon layer was set to 350 to 400 nm, and repeated 13 times to obtain a 5.0 μm thick DLC film.

(Comparative Example 1)
A piston ring substrate was prepared, and a 10 μm thick CrN layer was coated using an arc-type PVD apparatus. Thereafter, a Cr intermediate layer having a thickness of 0.2 μm was coated. After performing arc discharge at a bias voltage of -700 V and an arc current of 40 A for 10 minutes while heating the heater to 245 ° C., arc discharge was performed at a bias voltage of -170 V and an arc current of 40 A to form a black film having a total film thickness of 0.5 μm. After forming the hard layer and the white hard layer, the film was once cooled to 125 ° C.
Thereafter, an arc discharge was performed at a bias voltage of −1000 V and an arc current of 40 A for 90 seconds to form an adhesion layer made of white hard carbon, and then an arc discharge was performed again at a bias voltage of −170 V and an arc current of 40 A to perform 245 arc discharge. The heating and cooling were repeated eight times to form a black hard layer and a white hard layer having a total film thickness of 0.5 μm eight times, and a DLC film having a total film thickness of 5.0 μm was formed. A film was formed.

(Comparative Example 2)
With the piston ring base set in the arc ion plating apparatus, the inside of the apparatus was evacuated to reduce the pressure, and then the base was heated. Thereafter, with a bias voltage applied to the substrate in the range of -500 to -1000 V, the substrate was discharged with an arc current of 50 to 100 A using a Cr target to perform Cr ion bombardment.
Next, in arc ion plating, with a bias voltage applied to the piston ring substrate in the range of -10 to -100 V, using a Cr target, discharging at an arc current of 50 to 100 A, and forming an adhesive layer A Cr coating was formed on the piston ring substrate.
Next, an amorphous carbon layer was formed on the Cr film. The amorphous carbon layer is discharged by an arc current of 50 to 100 A using a carbon target in a state where a bias voltage is applied to the substrate within a range of 0 to -100 V, and the amorphous carbon layer thickness is reduced. A 5.0 μm DLC coating was obtained.

For the DLC films obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the number of pits (number of pieces / 3 × 10 μm ² ) by cross-sectional SEM, refractive index by spectroscopic ellipsometer, hardness (Hv), sp ² component ratio ( %), A friction coefficient (μ) by a reciprocating friction test, a DLC film wear amount (μm), and a mating material wear amount (μm). The friction coefficient one minute after the start of the reciprocating friction test was taken as the friction coefficient. Table 1 shows the results.

100 upper test piece 110 lower test piece 120 movable block 122 heater

Claims (5)

A piston ring having a sliding surface covered with a DLC coating,
The piston ring, wherein the number of pits observed in a cross-sectional SEM image (× 10,000) in the thickness direction of the DLC film is 15 or less per 3 μm × 10 μm, and the hardness is 1000 HV or more and 2000 HV or less.   The piston ring according to claim 1, wherein the DLC coating has a refractive index measured by a spectroscopic ellipsometer of 2.3 or more at a wavelength of 550 nm.   The piston ring according to claim 1, wherein the hardness of the DLC coating is 1000 HV or more and 1700 HV or less.   The piston ring according to any one of claims 1 to 3, wherein the DLC coating has a friction coefficient of a surface of a sliding surface of 0.10 or less.   The DLC film according to any one of claims 1 to 4, wherein, in a wear amount measurement test using a reciprocating friction tester, a wear amount of a test piece corresponding to a cast iron cylinder bore as a mating material is 0.6 µm or less. The described piston ring.