JP6499949B2 - piston ring - Google Patents

Description

  The present invention relates to a piston ring for an internal combustion engine.

  Piston rings for internal combustion engines are required to have high sliding performance on their sliding surfaces. Therefore, a hard coating is provided on the outer peripheral surface of the piston ring base material. As a piston ring having such a hard coating, a piston ring having a CrN-based hard coating is known. For example, Patent Document 1 proposes a piston ring that is provided with a high-toughness CrN-based hard coating that is excellent in wear resistance and particularly has crack resistance and peel resistance.

WO2013 / 136510

  On the other hand, in recent years, fuels that contain a large amount of alcohol such as sulfur and ethanol are sometimes used as fuels for automobile internal combustion engines. However, when such a fuel is used, even with a conventional piston ring having a CrN-based hard coating, the wear resistance, crack resistance, and peel resistance may be insufficient.

  The present invention has been made in view of the above circumstances, and wear resistance, crack resistance, and peel resistance are also achieved in an internal combustion engine using a fuel containing a large amount of sulfur, alcohol, or both of these components. It is an object to provide an excellent piston ring.

The above-mentioned subject is achieved by the following present invention. That is,
The piston ring of the present invention includes a piston ring base material and a hard coating provided so as to cover at least the outer peripheral surface of the piston ring base material, and the micro Vickers hardness (H) of the hard coating and the hard coating The ratio (H / EIT ′) to the indentation elastic modulus (EIT ′) including the Poisson's ratio is 0.050 or more, and the hard coating contains at least Cr, Al and Ti as metal elements, and as a nonmetal element It has a NaCl-type crystal structure containing at least N, and the content ratio of each constituent element contained in the hard coating satisfies the following formulas (1) to (5).
Formula (1) 15 ≦ b ≦ 65
Formula (2) 0 <c ≦ 40
Formula (3) 0 <(e + f) ≦ 40
Formula (4) 0 <e ≦ 40
Formula (5) 0 <f ≦ 20
[However, in each formula, b represents the Al content ratio (atomic%) with respect to the total amount of all metal elements contained in the hard coating, and c represents the Ti content with respect to the total amount of all metal elements contained in the hard coating. Represents an amount ratio (atomic%), e represents an O content ratio (atomic%) with respect to the total amount of all nonmetallic elements contained in the hard coating, and f represents the total amount of all nonmetallic elements contained in the hard coating. The content ratio (atomic%) of C with respect to is represented . ]

In another embodiment of the piston ring of the present invention, the indentation elastic modulus (EIT ′) including the Poisson's ratio is preferably 245 GPa or more.

In another embodiment of the piston ring of the present invention, the surface roughness Ra in the circumferential direction of the hard coating coated on the outer peripheral surface of the piston ring base material is preferably 0.30 μm or less.

In another embodiment of the piston ring of the present invention, it is preferable that the hard coating is formed by an arc ion plating method.

  According to the present invention, a piston ring excellent in wear resistance, crack resistance and peeling resistance is provided even in an internal combustion engine using a fuel containing a large amount of sulfur, alcohol, or both of these components. Can do.

It is a schematic cross section which shows an example of the piston ring of this invention. It is a schematic diagram which shows an example of the arc ion plating apparatus used for manufacture of the piston ring of this invention. It is a schematic diagram of a ring-on-plate type reciprocating wear tester. It is a schematic diagram of a ring-on-disk tester.

  The piston ring of the present embodiment includes a piston ring base material and a hard coating provided so as to cover at least the outer peripheral surface of the piston ring base material. The hard coating has a micro Vickers hardness (H) and a hard coating. The ratio (H / EIT ′) to the indentation elastic modulus (EIT ′) including the Poisson's ratio of the coating is 0.050 or more, and the hard coating contains at least Cr, Al and Ti as metal elements, and is a nonmetallic element And having a NaCl-type crystal structure containing at least N, and the content ratio of each constituent element contained in the hard coating satisfies the following formulas (1) to (5).

Formula (1) 15 ≦ b ≦ 65
Formula (2) 0 <c ≦ 40
Formula (3) 0 ≦ (e + f) ≦ 40
Formula (4) 0 ≦ e ≦ 40
Formula (5) 0 ≦ f ≦ 20

  In each formula, b represents the Al content ratio (atomic%) with respect to the total amount of all metal elements contained in the hard coating, and c represents the Ti content with respect to the total amount of all metal elements contained in the hard coating. Represents the ratio (atomic%), e represents the content ratio (atomic%) of O to the total amount of all nonmetallic elements contained in the hard coating, and f represents the total amount of all nonmetallic elements contained in the hard coating. The content ratio (atomic%) of C is represented.

In the piston ring of this embodiment, the indentation elastic modulus (EIT ′) including the Poisson's ratio of the hard coating is not particularly limited, but is preferably 245 GPa or more. By setting the indentation elastic modulus (EIT ′) including the Poisson's ratio to 245 GPa or more, it becomes easier to ensure the rigidity required as a hard coating for the piston ring. The upper limit of the indentation elastic modulus (EIT ′) including the Poisson's ratio is not particularly limited, but is preferably 370 GPa or less for practical use. The indentation elastic modulus (EIT ′) including the Poisson's ratio is a value represented by EIT / (1- (νs) ² ), where EIT is the indentation elastic modulus of the hard coating and νs is the hard coating. Poisson's ratio.

  Further, the ratio of the micro Vickers hardness (H) [GPa] of the hard coating to the indentation elastic modulus (EIT ′) [GPa] including the Poisson ratio (indentation elastic modulus including the micro Vickers hardness (H) / Poisson ratio) (EIT ′) is 0.050 or more, preferably 0.055 or more, and more preferably 0.060 or more.By setting H / EIT ′ to 0.050 or more, it is used in a conventional piston ring. As compared with the general CrN hard coating, it is possible to obtain an excellent wear resistance equivalent to or higher than that of the general CrN hard coating, although the upper limit value of H / EIT ′ is not particularly limited. 0.1 or less is preferable.

  Further, the hard coating has a NaCl-type crystal structure containing Cr, Al, and Ti as metal elements and N as a nonmetal element. Note that Cr, Al, Ti, and N are essential elements constituting the hard coating. Here, the hard coating may further contain other metal elements other than Cr, Al, and Ti as necessary.

  As a nonmetallic element, in addition to N, one or more other nonmetallic elements may be further contained. As such other nonmetallic elements, O or C is preferable.

  That is, the composition of the hard coating of the present embodiment can be broadly divided into non-metallic elements in which N and e are 0 atom%, e is more than 0 atom% and not more than 40 atom%, and f NO system with 0 atomic%, e system with 0 atomic%, NC system with f exceeding 0 atomic% and 20 atomic% or less, and e exceeding 0 atomic% and 40 atomic% or less In addition, there is a NOC system in which f is more than 0 atomic% and 20 atomic% or less. In addition, as a hard coating composed of a suitable combination of various metal elements (Cr, Al, Ti) listed above and non-metallic elements (N, C, O), a CrAlTiN-based coating, a CrAlTiNO-based coating, a CrAlTiNC-based coating Examples of the coating include a CrAlTiNOC-based coating.

  In addition, since Cr can form a passive state, a hard coating containing Cr is considered to be basically excellent in corrosion resistance. However, as a result of investigations by the present inventors, a piston ring having a hard coating composed of a simple CrN composition is compared with a fuel containing a large amount of sulfur and alcohol, that is, a low sulfur, non-alcohol type general fuel. Even when used in an internal combustion engine using highly corrosive fuel, the wear resistance, crack resistance and peel resistance could not be sufficiently ensured. However, if it is a nitride-based hard coating containing Cr, Al and Ti as essential elements used in the piston ring of this embodiment, sufficient wear resistance even in an internal combustion engine using a fuel containing a large amount of sulfur or alcohol It becomes easy to ensure crack resistance and peel resistance. Although details of this reason are unknown, the present inventors presume as follows. That is, in addition to the fact that Al is suitable for solid solution strengthening of Cr, Al and Ti can also form a passive state and have corrosion resistance characteristics different from those of Cr. For this reason, the nitride hard film containing Cr and Al as essential metal elements (for example, a nitride hard film having a metal component composition of CrAl, CrAlZr, or CrAlV) is described in detail in this specification. In the nitride-based hard coating containing Cr, Al, and Ti as essential metal elements used in the piston ring of this embodiment, it is more excellent in the use environment of an internal combustion engine using a fuel containing a large amount of sulfur or alcohol. It is considered that it exhibits high corrosion resistance, and as a result, improves wear resistance, crack resistance and peel resistance.

  The Cr content ratio a to the total amount of all metal elements in the hard coating may be a residual amount obtained by subtracting the content ratio of other metal elements constituting the hard coating other than Cr from the total amount of all metal elements. Usually, it is in the range of 35 to 85 atomic%. Further, the Al content ratio b with respect to the total amount of all metal elements in the hard coating is in the range of 15 to 65 atomic% as shown in the formula (1). When b is less than 15 atomic%, the effect of solid solution strengthening is hardly exhibited, and sufficient crack resistance and peel resistance cannot be obtained. On the other hand, if b exceeds 65 atomic%, hexagonal AlN crystallizes in the hard coating and coexists with NaCl-type crystals, so that wear resistance is reduced and crack resistance and peel resistance are also reduced. In addition, b is preferably within the range of 20 to 65 atomic%, and more preferably within the range of 30 to 65 atomic%.

  Further, the Ti content ratio c with respect to the total amount of all metal elements in the hard coating is in the range of more than 0 and not more than 40 atomic% as shown in Formula (2). In some cases, it is easier to improve crack resistance and peel resistance as compared with the case where only Cr and Al are contained as metal elements (when c is 0 atomic%). Moreover, if c is 40 atomic% or less, it can also suppress that wear resistance falls remarkably, maintaining the outstanding crack resistance and peeling resistance. From the viewpoint of improving the wear resistance, crack resistance and peel resistance in a well-balanced manner, c is more preferably in the range of more than 0 and not more than 25 atomic%, and more preferably in the range of 5 to 25 atomic%. preferable.

  In addition, the hard coating contains other metal elements other than Cr, Al, and Ti as necessary as long as they do not significantly affect the wear resistance, crack resistance, and peel resistance. It may be. In this case, the content ratio of other metal elements to the total amount of all metal elements is preferably 5 atomic% or less, and more preferably 3 atomic% or less. However, it is usually most preferable that other metal elements are not substantially contained except in the case where a trace amount is contained as an impurity in the hard coating.

  In addition, the hard coating contains at least N as a nonmetallic element, but may further contain O and C as necessary. By adding an appropriate amount of O and / or C to the hard coating in a form that replaces part of N, solid solution strengthening can be achieved by forming an interstitial solid solution, and the crystal of the hard coating is refined, and the inside of the crystal grains It becomes easy to strengthen. In this case, it becomes easy to improve crack resistance and peel resistance.

  The content ratio d of N to the total amount of all nonmetallic elements in the hard coating should be the remaining amount obtained by subtracting the content ratio of other nonmetallic elements constituting the hard coating other than N from the total amount of all nonmetallic elements. Usually, it is in the range of 60 to 100 atomic%. Further, the content ratio of nonmetallic elements O and C other than N to the total amount of all nonmetallic elements; (e + f) is 0 to 40 atomic% as shown in the formula (3). When (e + f) exceeds 40 atomic%, when the content ratio of O as a non-metallic element other than N is large, Cr is oxidized to chromium oxide, leading to a decrease in crack resistance and peel resistance. When the content ratio of C as a non-metallic element other than the above is large, the hardness decreases, the wear amount increases, and the crack resistance and the peel resistance decrease.

  In addition, from the viewpoint of preventing a decrease in crack resistance and peel resistance due to a large content ratio of O, the content ratio of O with respect to the total amount of all nonmetallic elements; As shown, it is in the range of 0 to 40 atomic%. Here, e is preferably in the range of 15 to 40 atomic%, and more preferably in the range of 20 to 30 atomic%, from the viewpoint of further improving crack resistance and peel resistance. Further, from the viewpoint of preventing a decrease in wear resistance, crack resistance and peel resistance due to a large C content ratio, the C content ratio relative to the total amount of all nonmetallic elements; As shown in (5), it is in the range of 0 to 20 atomic%. Further, f is preferably in the range of 5 to 20 atomic%, more preferably in the range of 5 to 10 atomic%, from the viewpoint that it is easier to improve the wear resistance, crack resistance and peel resistance in a balanced manner. More preferred.

  In addition, when both O and C are included as non-metallic elements at the same time, it is easier to improve the wear resistance, crack resistance and peel resistance in a balanced manner than when no O and C are included. (E + f) is more preferably in the range of 15 to 40 atomic%, and still more preferably in the range of 15 to 30 atomic%. The atomic ratio of O and C is not particularly limited, but about 3: 1 to 3: 2 is appropriate.

Further, the ratio of all nonmetallic elements to all metal elements in the hard coating is 0.50 stoichiometrically, but is not particularly limited, and is practically 0.48 to 0.58. If it is about the range of this. In addition, the value (atom%) of af was calculated | required based on this, calculating | requiring the mass of each metallic element and each nonmetallic element contained in a hard film by EPMA (Electron Probe MicroAnalyser) measurement. Here, EPMA-8705 manufactured by Shimadzu Corporation was used for EPMA measurement. Specifically, the EPMA measurement was performed according to the following procedure. First, a measurement sample such as a piston ring piece on which a hard coating was formed was ultrasonically cleaned with an organic solvent such as IPA (isopropyl alcohol) for about 10 minutes, and then placed in an analysis chamber. Next, after evacuating the analysis chamber, the measurement sample was irradiated with an electron beam to quantitatively analyze the component composition of the metal coating. The observation conditions were an acceleration voltage of 15 kV, a sample current of 50 to 100 nA, and an electron beam beam diameter of 30 to 100 μm. The quantitative value of each element is the characteristic X-ray measured from the standard material and the characteristic X-ray measured from the hard coating after analyzing the standard material corresponding to each element constituting the hard coating by the quantitative analysis program. It was calculated by comparing with. Note that the ZAF method was used to calculate the quantitative value. As a standard substance used for quantitative analysis, when the target of quantitative analysis is a metal element such as Cr, a pure metal corresponding to each metal element is used, and when the target of quantitative analysis is N, O, or C, BN, Al ₂ O ₃ and graphite were used for each.

  As a material constituting the piston ring base material, known materials for piston ring base materials such as carbon steel, low alloy steel, high alloy steel, cast iron, and stainless steel can be used without limitation. In addition, when using the piston ring base material which consists of stainless steel, you may use the piston ring base material which performed the nitriding process previously and removed the surface porous layer formed by the nitriding process. Moreover, in order to improve the adhesiveness of a piston ring base material and a hard film, you may provide an undercoat layer between a piston ring base material and a hard film as needed. As this undercoat layer, for example, a thin film mainly composed of Ti, Cr, Cr—Al alloy or the like can be used.

  Although the film thickness of a hard film is not specifically limited, From a viewpoint of ensuring durability, it is preferable that it is 5 micrometers or more. The upper limit value of the film thickness is not particularly limited, but is preferably 50 μm or less from the practical viewpoint such as productivity. Moreover, after forming a hard film, it is preferable to perform lapping and a grinding | polishing process, and to make surface roughness Ra of a hard film into 0.30 micrometer or less. By reducing the surface roughness Ra of the hard coating, it is easier to suppress the damage of the hard coating by reducing the frictional resistance while suppressing the wear of the counterpart material. The layer structure of the hard coating may be a single layer structure or a multilayer structure. However, in the case of a multilayer structure, at least one of the layers must satisfy the above-described film composition and mechanical property values, and in particular, the outermost surface layer must satisfy the above-described film composition and mechanical property values. Is preferred.

  FIG. 1 is a schematic cross-sectional view showing an example of a piston ring according to the present embodiment. Specifically, the piston ring includes a surface including the axial direction (not shown in the drawing) of the piston ring extending in the vertical direction in FIG. It is a figure which shows an example of the cross-sectional structure at the time of cut | disconnecting a ring. A piston ring 10 shown in FIG. 1 includes a ring-shaped piston ring base material 12 provided with a gap and a hard coating 16 provided to cover at least the outer peripheral surface 14 of the piston ring base material 12. Yes. In the example shown in FIG. 1, the hard coating 16 has a single-layer structure and covers only the outer peripheral surface 14 of the piston ring base material 12. When the piston ring 10 is used in an internal combustion engine, the piston ring 10 is mounted in a groove formed along the outer peripheral direction of the outer peripheral surface of the cylindrical piston. When the piston moves up and down in the cylinder bore, the outer peripheral sliding surface 18 (the surface of the hard coating 16) of the piston ring 10 and the inner peripheral surface of the cylinder bore slide. In this case, since the outer peripheral sliding surface 18 of the piston ring 10 is composed of the hard coating 16, wear of the outer peripheral sliding surface 18 can be prevented.

  Normally, the top ring groove, the second ring groove, and the oil ring groove are formed on the outer peripheral surface of the piston along the outer peripheral direction, and the top ring, the second ring, and the oil ring are attached to each groove. Is done. The piston ring of this embodiment can be applied to any of a top ring, a second ring, and an oil ring.

  As described above, the piston ring of the present embodiment can be suitably used for an internal combustion engine that uses a fuel containing a large amount of components of sulfur, alcohol, or both. Examples of such fuels include fuels having a sulfur content of about 50 to about 1000 ppm and / or an alcohol content of more than 5% by mass and less than 100% by mass on the market level. As the internal combustion engine using the piston ring of the present embodiment, an internal combustion engine in which the use of the above-described fuel is permitted or recommended by the manufacturer of the internal combustion engine can be mentioned. However, the piston ring of this embodiment has a low sulfur concentration and is generally widely used fuel that does not substantially contain alcohol (sulfur content: 5 ppm or less, alcohol content: 5 mass% or less). Of course, it can also be used, and it can also be used for an internal combustion engine in which use of only such fuel is permitted or recommended. It is also known that such a fuel contains, for example, water as an impurity, and the piston ring of this embodiment can also be used in this fuel mixed with water.

  The manufacturing method of the piston ring of this embodiment is not particularly limited, and a method of forming a hard film on at least the outer peripheral surface of the piston ring base material using a known film forming method can be employed. However, the arc ion plating method is suitable as the method for forming the hard coating. Hereinafter, the case where the piston ring is manufactured using the arc ion plating apparatus shown in FIG. 2 will be described more specifically.

  Here, the arc ion plating apparatus 30 shown in FIG. 2 includes a vacuum chamber 40, a metal target 42 that functions as a cathode disposed in the vacuum chamber 40, a support base 44 that can rotate in the horizontal direction, and a vacuum chamber 40. The gas supply port 46 and the exhaust port 48 provided in the vacuum chamber 40, the arc supply source 50 arranged outside the vacuum chamber 40 and connected to the metal target 42, and arranged outside the vacuum chamber 40 and connected to the support base 44. The bias power supply source 52 is provided. The arc supply source 50 is also connected to an anode (not shown in the figure).

In film formation, first, the piston ring base 12 is placed on the support base 44, and then the inside of the vacuum chamber 40 is depressurized until the pressure becomes about 1.3 × 10 ⁻³ Pa. Next, the piston ring base 12 is heated to about 573K to 673K. Then, ion bombardment is performed by applying a bias voltage of about −600 to −800 V to the piston ring base material 12 from the bias power supply source 52 via the support base 44. Thereafter, the bias voltage is lowered to about -5 to -50V. Thereby, arc discharge is performed and the metal target 42 becomes the metal ion 60. On the other hand, the process gas introduced into the vacuum chamber 40 from the gas inlet 46 becomes reaction gas molecules 62. The hard film 16 is formed by depositing the metal ions 60 and the reactive gas molecules 62 on the outer peripheral surface 14 of the piston ring base material 12 to which a bias voltage is applied.

  Here, the composition of the metal target 42 is appropriately selected according to the composition of the hard coating 16 to be formed. For example, a CrAlTi alloy target can be used as the metal target 42. The ratio of Cr, Al and Ti constituting this CrAlTi alloy target is appropriately selected according to the composition of the hard coating 16 to be formed.

  Further, b of the hard coating 16 can be adjusted by combining metal targets 42 having different compositions, or is adjusted by the arc current value of each metal target 42 when forming a film using them. It is possible. For example, when the first metal target 42 made of Cr and the second metal target 42 made of a Ti—Al alloy and having an atomic ratio of Ti and Al of 1: 1 are formed one by one, If the evaporation rate of the target material of each metal target 42 is substantially the same, b of the hard coating 16 is 25 atomic% [= 100 × {0 + 1 / (1 + 1)} / 2], and c is 25 atomic% [= 100. × {0 + 1 / (1 + 1)} / 2]. In addition, when the evaporation rates of the target materials of the respective metal targets are different, b and c of the hard coating 16 can be easily obtained based on a value obtained by integrating the composition ratio and the evaporation rate of each metal target. .

  Further, since the evaporation amount of the metal target 42 changes by raising and lowering the arc current value of each metal target 42, the hard coating 16 can be obtained by increasing the arc current value of the metal target 42 containing a large amount of components to be increased. The composition of can be controlled. In general, when the metal target 42 is consumed, the film forming efficiency is lowered. Therefore, in order to manage the composition of the hard coating 16 with high accuracy, it is preferable to use the metal target 42 having the same amount of consumption.

  Moreover, when using in combination of 2 or more types of metal targets 42, as a combination other than having illustrated above, the combination of a Cr-Al alloy target and a Ti target etc. can be mentioned, for example. Further, when two or more kinds of metal targets 42 are used in combination, each metal target 42 may be provided at the same position in the vacuum chamber 40 or may be provided at different positions. For example, when two types of metal targets 42 are used in the arc ion plating apparatus 30 shown in FIG. 2, each of them is located at a position that is substantially point symmetric with respect to the support base 44, such as the left and right positions in FIG. 2. In this case where the metal target 42 may be disposed, it is possible to produce a hard coating having a multilayer structure in which hard coatings made of two types of target materials are alternately laminated. Each lamination period can be controlled by the arc current of each metal target 42 and the rotation speed of the support base 44. In addition, when two types of targets are installed in close proximity, an inclined structure in which the composition change of the boundary portion between the hard coatings made of the respective target materials gradually changes can be formed.

Further, the process gas can be appropriately selected according to the composition of the hard coating 16, but is usually N ₂ gas or a gas containing at least one nonmetallic element selected from N ₂ gas and C and O. A mixed gas mixed at a predetermined ratio can be used. As the gas containing C are mentioned hydrocarbon gas such as CH ₄ gas, as the gas containing O include O ₂ gas.

  Further, the values of the micro Vickers hardness (H) and the indentation elastic modulus (EIT ′) including the Poisson's ratio can be adjusted by controlling the composition of the hard coating by appropriately selecting the film forming conditions. Furthermore, the value of the indentation elastic modulus (EIT ′) including the micro Vickers hardness (H) / Poisson ratio can also be adjusted by the bias voltage and the internal pressure during film formation. By appropriately increasing the bias voltage or decreasing the internal pressure, The value tends to increase.

When the hard coating 16 is formed by the arc ion plating method, unreacted particles called droplets are mixed in the hard coating 16. The unreacted particles are particles that are taken into the hard coating 16 without sufficiently reacting with a gas component such as N ₂ gas because a large amount of film forming raw material is released at once from the arc spot on the metal target 42. Refers to a substance in the form of a solid. In the arc ion plating method, it is difficult to make the droplets completely zero. Further, voids are formed in the periphery of the unreacted particles and in the traces of the unreacted particles dropping out in the hard coating 16. And the unreacted particle which exists in such a hard film 16 and the space | gap formed resulting from this unreacted particle reduce the mechanical characteristic of the hard film 16. FIG. For this reason, when forming the hard coating 16, it is necessary to reduce the number and size of the unreacted particles generated and to reduce the proportion of voids formed due to the unreacted particles.

  Therefore, in the hard coating 16 (hard coating containing unreacted particles and having voids) formed by the arc ion plating method, the area ratio (voids) due to the voids in the hard coating 16 in the cross section of the hard coating 16 The area ratio is preferably 2.2% or less. The cross-sectional area ratio of the unreacted particles contained in the hard coating 16 is preferably about 1.5% or less. By setting the void area ratio to 2.2% or less, local strength reduction of the hard coating 16 can be suppressed, and as a result, when a high load is applied to the hard coating 16, the hard coating 16 is cracked and peeled off. It becomes easier to suppress. In addition, by making the cross-sectional area ratio of the unreacted particles about 1.5% or less, it is possible to suppress the occurrence of microscuffing in the portion where the unreacted particles are formed in the hard coating 16, and as a result, It becomes easy to suppress damage to the hard coating 16. The void area ratio is more preferably 1.8% or less, and the closer to 0%, the better. Further, the cross-sectional area ratio of unreacted particles is preferably as close to 0%. In addition, since the coarser the unreacted particles, the more easily microscuffing occurs. Therefore, the particle size of the unreacted particles is preferably 7 μm or less, more preferably 5 μm or less, and the smaller the particle size, the better. .

  The method for reducing the number and size of the voids is not particularly limited. For example, there is a method for increasing the bias voltage by increasing the distance between the metal target 42 and the piston ring substrate 12 that is the film formation target. It is valid. In order to reduce the number and size of unreacted particles, for example, it is effective to arrange an adhesion preventing plate or the like in the vicinity of the metal target 42. In addition, since the number and size of voids and unreacted particles increase when the metal target 42 is consumed by film formation, increasing the frequency of replacement of the metal target 42 also suppresses the number and size of voids and unreacted particles. The above is effective. In addition, a technique for reducing the number of unreacted particles by increasing the magnetic field of the evaporation source can be employed.

  Examples of the present invention will be described below, but the present invention is not limited only to the following examples.

<Preparation of sample for evaluation>
Samples for evaluation were prepared according to the following procedure in both the examples, comparative examples, and reference examples. First, after setting the piston ring base material 12 in the arc ion plating apparatus 30, the inside of the vacuum chamber 40 was evacuated and decompressed, and the piston ring base material 12 was heated. Thereafter, ion bombardment was performed by applying a predetermined bias voltage to the piston ring substrate 12. Next, after setting the bias voltage to a predetermined value, a process gas is introduced into the vacuum chamber 40, thereby forming the hard coating 16 having a thickness of 20 μm to 30 μm on at least the outer peripheral surface 14 of the piston ring substrate 12. did. Finally, a piston ring sample was obtained by lapping the surface of the hard coating. In each of the piston ring samples of each example, comparative example, and reference example, the surface roughness Ra in the circumferential direction of the hard coating was 0.30 μm or less.

Tables 1 to 6 show the compositions and mechanical properties of the hard coating 16 of the piston ring samples of the examples, comparative examples, and reference examples. Note that the piston ring samples of Comparative Example 1 and Reference Example 1 using the same CrN film as a hard coating were used in a commercially available automobile engine using a general fuel not containing alcohol and having a sulfur content of 5 ppm or less. It is substantially equivalent to a widely used piston ring. In addition, the piston ring samples of Comparative Example 2 and Reference Example 2 using the same TiN film as the hard coating were compared with Comparative Examples 1 and 2 in terms of indentation elastic modulus (EIT ′) including micro Vickers hardness (H) and Poisson's ratio. A TiN film having a high strength with respect to the hard film (CrN film) of the piston ring sample of Reference Example 1 is used as the hard film. Moreover, when the crystal structure of the hard film 16 of Example 1-3 and Reference Example 3-20 was examined by X-ray diffraction measurement, both were NaCl type.

<Abrasion resistance test>
The abrasion resistance test of the hard coating was performed by the following method using a piston ring sample. For the wear resistance test, a ring-on-plate reciprocating friction tester 100 shown in FIG. 3 was used. The ring-on-plate reciprocating friction tester 100 is configured such that a test piece 102 is pressed against the plate 104 by applying a load P by a spring load, and the plate 104 reciprocates to slide both.

  Here, a cut piece obtained by cutting a piston ring sample into a length of 1 to 2 cm in the circumferential direction was used as the test piece 102, and a cast iron plate made of the same material as the cylinder bore material for an automobile engine was used as the plate 104. In sliding, the surface of the test piece 102 on which the hard coating 16 was formed was brought into contact with the surface of the plate 104, and lubricating oil was supplied using a tubing pump or an air dispenser.

Here, the piston ring samples of Example 1-3, Reference Example 3-20, and Comparative Example 1-9 are assumed to be used in an automobile engine using a fuel containing a large amount of ethanol and sulfur and after a long period of operation. Degraded oil was used to perform the evaluation. This deteriorated oil is obtained by conducting a bench test for several hundred hours using a commercially available SN class 5W-30 engine oil with a fuel containing about 25 mass% ethanol and about 300 ppm sulfur ( Deteriorated oil A). The deteriorated oil A thus obtained had a base number of almost 0, and the amount of insoluble oil extracted in high-speed centrifugation at 40,000 G × 30 minutes (G: gravitational acceleration) was about 2%. . The test conditions for the wear resistance test are shown below.

Moreover, about the piston ring sample of Reference Example 1-2 , in order to perform the evaluation which assumed use with the engine for motor vehicles using the general fuel which does not contain alcohol and whose sulfur content is 5 ppm or less, it is SN class. The oil (deteriorated oil B) in a state after a bench test of several hundred hours using 5W-30 engine oil was used.

-Test conditions-
Load P: 30N
Average speed of reciprocation of plate 104: 0.5 m / s
Stroke of reciprocation of plate 104: 50mm
Test time: 120 min
Lubricating oil: Degraded oil A
(Example 1-3, Reference Example 3-20 and Comparative Example 1-9 )
Deteriorated oil B (Reference Example 1-2 )
Lubricating oil drop rate: 1 ml / hr
Material of plate 104: FC (gray cast iron)

  The evaluation results of the abrasion resistance test are shown in Tables 1 to 6. The ratio of the relative wear amount, which is the evaluation result shown in Tables 1 to 6, is the relative wear amount when the wear amount of Comparative Example 1 is set as the reference value (1.00). Reference Example 1 is a condition simulating a combination of a non-alcohol / low sulfur concentration general fuel and a piston ring widely used in commercial vehicles. 30 means a sufficiently practical level. Here, as is clear from the difference in the relative amount of wear between Comparative Example 1 and Reference Example 1, compared with the automobile engine using a general fuel, the automobile uses a high alcohol / high sulfur concentration type fuel. In engines, the wear of CrN films used in commercial vehicle piston rings has increased about three times. That is, it can be understood that when a piston ring is used in an automobile engine that uses a high alcohol / high sulfur concentration type fuel instead of a normal fuel, it is a severe condition in which the wear of the hard coating is extremely accelerated.

In addition, the judgment criteria of the judgment results shown in Tables 1 to 6 are as follows.
A: Relative wear amount is 1.00 or less B: Relative wear amount exceeds 1.00 and is 1.15 or less C: Relative wear amount exceeds 1.15

<Measurement of indentation elastic modulus including micro Vickers hardness and Poisson's ratio>
The measurement of indentation elastic modulus (EIT ′) including micro Vickers hardness (H) and Poisson's ratio of the hard coating was carried out using an indentation tester HM-2000 manufactured by Fisher Instruments. The indenter was made of the same diamond as the Vickers hardness measurement, and the measurement load was 1000 mN. In the measurement, the load was increased to the maximum load over 30 seconds, then the maximum load was maintained for 5 seconds, and then unloaded for another 30 seconds. Here, the micro Vickers hardness was calculated based on these measured values because the diagonal length of the indentation can be measured from the shape of the indenter and the indentation depth.

  The indentation elastic modulus including the Poisson's ratio was calculated from the relationship between the test force and the indenter indentation depth in the above measurement. Specifically, using the analysis software attached to the indentation tester HM-2000 (setting: linear extrapolation mode, specifying 65% -95% section of maximum load), the minimum unloading-indentation depth curve The slope of the straight line obtained from the square fit and the intersection with the indentation depth axis when this straight line passes through the maximum load were obtained, and the calculation was performed according to ISO 14577-1 (A.5). In the calculation, the indenter elastic modulus was 1200 GPa and the indenter Poisson ratio was 0.07.

<Crack resistance and peel resistance test>
The crack resistance and peel resistance tests of the hard coating were performed by the following method using a piston ring sample. A ring-on-disk tester 110 shown in FIG. 4 was used for the crack resistance and peel resistance tests. The ring-on-disk tester 110 rotates the disk 114 in the direction of arrow R under predetermined conditions while pressing a test piece 112 to which a constant load Q is applied against a disk-shaped disk 114 as a counterpart material. This is a testing machine for evaluating the crack resistance and peel resistance of the hard coating provided on the test piece 112.

  Here, as the test piece 112, a cut piece obtained by cutting a piston ring sample into a length of 1 to 2 cm in the circumferential direction is used in the same manner as that used in the wear resistance test, and the disk 114 is an S45C steel material of JIS G4051. A disc consisting of The test conditions for the crack resistance and peel resistance tests are shown below. The sliding speed shown in the following test conditions means the peripheral speed of the disk 114 at a position where the test piece 112 is in contact with the surface of the disk 114.

-Test conditions-
Load Q: 30N
Sliding speed: 10m / s
(Example 1-3, Reference Example 3-20 and Comparative Example 1-9 )
5 m / s (Reference Example 1-2 )
Test time: 600 min
(Example 1-3, Reference Example 3-20 and Comparative Example 1-9 )
60 min (Reference Example 1-2 )
Lubricating oil: 5W-30
Material of disk 114: Steel (S45C)

In addition, the test conditions of Example 1-3, Reference Example 3-20, and Comparative Example 1-9 are based on the premise that the sliding distance is increased under a sliding condition where the sliding surface is scuffed. The purpose is to evaluate crack resistance and peel resistance.

Evaluation of crack resistance and peel resistance was performed by observing the sliding surface of the hard coating film after a predetermined test time with an electron microscope. In addition, the evaluation criteria of the evaluation results shown in Tables 1 to 6 are as follows. Here, A and B are practically acceptable levels, and C and D are practically unacceptable levels.
A: No cracks and peeling were confirmed B: Cracks and peeling were not observed, but a scuffy trace of sliding was confirmed C: Only cracks were confirmed D: Crack and peeling The occurrence of both was confirmed

<Surface roughness measurement>
The surface roughness of the hard coating of the piston ring sample was measured with a laser microscope VK-9700 manufactured by Keyence Corporation. The photographing conditions were an objective lens magnification of 50 times, height smoothing 2, automatic tilt correction, and measurement was performed by specifying the circumferential direction of the piston ring in the measurement field of view. The surface roughness Ra was measured according to JISB0601-2001. Note that JISB0601-2001 is compliant with ISO4287-1997.

<Evaluation results>
The evaluation results are shown in Tables 1 to 6 together with the composition and physical properties of the hard coating of the piston ring samples of each Example, Comparative Example, and Reference Example.

DESCRIPTION OF SYMBOLS 10: Piston ring 12: Piston ring base material 14: Outer peripheral surface 16: Hard film 18: Outer peripheral sliding surface 30: Arc ion plating apparatus 40: Vacuum chamber 42: Metal target 44: Support stand 46: Gas introduction port 48: Exhaust port 50: Arc supply source 52: Bias power supply source 60: Metal ion 62: Reaction gas molecule 100: Ring-on-plate reciprocating friction tester 102: Test piece 104: Plate 110: Ring-on-disk tester 112: Test piece 114: disc

Claims (4)

A piston ring base material;
A hard coating provided to cover at least the outer peripheral surface of the piston ring base material,
The ratio (H / EIT ′) between the micro Vickers hardness (H) of the hard coating and the indentation elastic modulus (EIT ′) including the Poisson's ratio of the hard coating is 0.050 or more,
The hard coating has a NaCl-type crystal structure including at least Cr, Al, and Ti as metal elements, and at least N as a nonmetal element,
The piston ring, wherein the content ratio of each constituent element contained in the hard coating satisfies the following formulas (1) to (5).
Formula (1) 15 ≦ b ≦ 65
Formula (2) 0 <c ≦ 40
Formula (3) 0 <(e + f) ≦ 40
Formula (4) 0 <e ≦ 40
Formula (5) 0 <f ≦ 20
[In the above formulas, b represents the Al content ratio (atomic%) to the total amount of all metal elements contained in the hard coating, and c represents the total amount of all metal elements contained in the hard coating. Ti represents a content ratio (atomic%), e represents an O content ratio (atomic%) with respect to the total amount of all nonmetallic elements contained in the hard coating, and f represents a total content contained in the hard coating. The content ratio (atomic%) of C with respect to the total amount of nonmetallic elements is represented. ] 2. The piston ring according to claim 1, wherein an indentation elastic modulus (EIT ′) including the Poisson's ratio is 245 GPa or more. 3. The piston ring according to claim 1, wherein a surface roughness Ra in a circumferential direction of the hard coating coated on an outer peripheral surface of the piston ring base material is 0.30 μm or less. The hard coating is characterized by being formed by an arc ion plating method, the piston ring according to any one of claims 1-3.