Method for manufacturing sliding member, sliding member, and piston ring

Abstract

Provided is a method for manufacturing a sliding member provided with a base material and a coating film that is provided so as to cover at least part of a surface of the base material, the method comprising (A) a step for obtaining an intermetallic compound that contains Cr and a metal element containing at least Si, and (B) a step for forming a coating film by arc ion plating using the intermetallic compound, and the method being such that, in step (B), a bias voltage within the range of −2 to −25 V is set under a nitrogen atmosphere. Also provided is a sliding member comprising a base material and a coating film that is provided so as to cover at least part of a surface of the base material, the coating film containing Cr, N, and a metal element containing at least Si, the coating film having a base part and dispersed particle parts scattered within the base part, and the hardness of the coating film being 1900 HV0.1 or less.

Description

Method for manufacturing a sliding member, sliding member, and piston ring

[0001] The present invention relates to a method for manufacturing a sliding member, a sliding member, and a piston ring.

[0002] A sliding member such as a piston ring is used in an engine of an automobile or the like. The piston ring is mounted in a groove provided on the outer peripheral surface of the piston. The piston ring is required to contribute to improving the performance of the engine and reducing the fuel consumption, for example, by its wear resistance and seizure resistance characteristics. Conventionally, various efforts have been made to improve the wear resistance of the piston ring.

[0003] For example, the invention described in Patent Document 1 was made to provide a sliding member having excellent wear resistance even under severe conditions in an engine to which direct fuel injection or exhaust gas recirculation (EGR) is applied. This sliding member has a film composed of a mixed structure of a crystalline phase and an amorphous phase made of a metal nitride or a metal carbide or a metal carbonitride covering the base material.

[0004] The invention described in Patent Document 2 was made to provide a piston ring for an internal combustion engine having both wear resistance and crack resistance / peel resistance. This piston ring is composed of Cr, N, and Si as constituent elements, has the same crystal structure as CrN, and is composed of a crystal phase in which Si atoms are dissolved at a ratio of 1% or more and 9.5% or less in the crystal lattice. A hard film is formed at least on the outer peripheral sliding surface.

[0005] JP-A-2002-266697 JP-A-2008-14228

[0006] Sliding components are required not only to have excellent wear resistance on their own but also to have low aggressiveness towards the mating material. Therefore, a high degree of balance is required so that neither the sliding component nor the mating material wears down. Furthermore, in recent years, in order to meet the demands of higher engine output and exhaust gas regulations, for example, combustion temperatures have been increased, low viscosity lubricants have been adopted, and oil volume has been reduced. In addition, FFVs (Flex Fuel Vehicles) that use a wide range of gasoline and biofuel mixtures are available on the market. Consequently, the operating environment for sliding components is becoming increasingly harsh and border lubrication environments, resulting in not only increased wear on the sliding component coating but also coating peeling due to increased sliding resistance.

[0007] Therefore, the present invention provides a method for manufacturing a sliding member, a sliding member, and a piston ring that have excellent peel resistance even in harsh environments, a good balance between wear resistance and mating resistance, and can be achieved at a sufficiently high level.

[0008] The present invention includes, for example, the following: [1] A method for manufacturing a sliding member comprising a substrate and a film provided to cover at least a portion of the surface of the substrate, comprising: (A) a step of obtaining an intermetallic compound containing Cr and a metal element containing at least Si; (B) a step of forming the film using the intermetallic compound by an arc ion plating method, wherein in step (B), a bias voltage in the range of -2 to -25 V is set under a nitrogen atmosphere. [2] A sliding member comprising a substrate and a film provided to cover at least a portion of the surface of the substrate, wherein the film contains Cr and N and a metal element containing at least Si, the film has a base portion and dispersed particle portions scattered within the base portion, and the hardness of the film is 1900 HV 0.1 or less. [3] The sliding member according to [2], wherein the metal element comprises at least one selected from the group consisting of Ti, Al, Mo, V, W, Nb, Mn, Zn, Cu, and Zr. [4] The sliding member according to [2] or [3], wherein the content of the metal element in the base portion is 1 to 25 at%. [5] The sliding member according to any one of [2] to [4], wherein the content of the metal element in the dispersed particle portion is greater than the content of the metal element in the base portion. [6] The sliding member according to any one of [2] to [5], wherein the hardness of the film is 800 HV 0.1 to 1500 HV 0.1. [7] A piston ring comprising the sliding member according to any one of [2] to [6].

[0009] According to the present invention, a method for manufacturing a sliding member, a sliding member, and a piston ring are provided that exhibit excellent peel resistance even in harsh environments, have a good balance of wear resistance and mating resistance, and can be achieved at a sufficiently high level.

[0010] Figure 1 is a schematic cross-sectional view of a sliding member according to one embodiment of the present invention. Figure 2 is a schematic diagram of the surface of a coating on a sliding member according to one embodiment of the present invention. Figure 3 is the result of EPMA analysis of the surface of the piston ring of Example 1. Figure 4 is a binarized image of the surface of the piston ring of Example 1. Figure 5 is a schematic diagram showing the configuration of a sliding fatigue testing machine.

[0011] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.

[0012] (Sliding Member) Figure 1 is a schematic cross-sectional view of a sliding member according to one embodiment of the present invention. The sliding member 10 shown in Figure 1 comprises a base material 1 and a coating 5 provided so as to cover at least a part of the surface of the base material 1. The coating 5 may be provided on the outer circumferential surface of the base material 1 (the surface corresponding to the sliding surface 10F). The sliding member 10 is, for example, a pressure ring (piston ring) for an internal combustion engine (for example, an automobile engine). The pressure ring is fitted, for example, into a ring groove formed on the side surface of a piston. The pressure ring is a ring that is exposed to the environment of a particularly high thermal load in the engine.

[0013] When the sliding member is a piston ring, the piston ring is annular, for example, with an outer diameter of 40 to 300 mm. Here, "annular" may be a closed circle or a substantially circular shape with an opening. Also, the piston ring may be perfectly circular or elliptical in plan view. The piston ring may be substantially rectangular in cross-section, and the sliding surface may be rounded with an outward bulge.

[0014] The base material is made of a heat-resistant alloy. Specific examples of alloys include spring steel and martensitic stainless steel. The base material may also have a nitrided layer formed on its surface.

[0015] The coating consists of a Cr-Me-N system material (where Me represents a metallic element). The metallic element Me contains at least Si, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and anti-aggression properties. In addition to Si, the metallic element Me may further contain at least one selected from the group consisting of, for example, Ti, Al, Mo, V, W, Nb, Mn, Zn, Cu, and Zr.

[0016] The thickness of the coating may be, for example, 5 to 70 μm, or 10 to 50 μm. A coating thickness of 5 μm or more tends to increase the durability of the sliding member, while a thickness of 70 μm or less ensures high production efficiency of the coating.

[0017] As shown in Figure 2, the coating 5 has a base portion 5A and dispersed particle portions 5B scattered within the base portion 5A. The presence of a base portion and dispersed particle portions can be confirmed by observing the coating with a scanning electron microscope (SEM or FE-SEM) and obtaining the backscattered electron image.

[0018] The base portion and the dispersed particle portion are each made of Cr-Me-N based materials, but with different amounts of each element. The amount of metal elements in the dispersed particle portion may be greater than that in the base portion, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and anti-aggression properties. The dispersed particle portion containing metal elements such as Si is also called the alloy dispersed particle portion.

[0019] The equivalent circle diameter of the dispersed particles is, for example, 0.1 to 10 μm. The equivalent circle diameter of the dispersed particles can be measured based on the backscattered electron image obtained by observing the surface of the coating with a SEM or the like.

[0020] The elemental composition of the base and dispersed particle portions of the sliding member is measured by the following method. First, the surface of the coating formed on the outer circumferential surface of the sliding member is polished using a polishing machine (for example, IS-POLISHER manufactured by Ikegami Seiki Co., Ltd.). Specifically, the sample is obtained by polishing with a diamond film with a particle size of 0.5 μm, gradually increasing the grit size from #600. Next, an elemental concentration map is obtained from the obtained sample using an EPMA (for example, JXA-8100 manufactured by JEOL Ltd.). The measurement conditions are an acceleration voltage of 15 kV and an irradiation current of 5.0 × 10⁻¹⁰. －８A. The beam diameter is set to 0 μm (minimum setting), the scan interval is 0.30 μm in the vertical direction and 0.30 μm in the horizontal direction, the scan time is 30 ms / point, and the number of scan points is 200 points in the vertical direction and 200 points in the horizontal direction, to obtain a concentration map (60 μm x 60 μm) for each element to be analyzed. Note that even if the measurement beam diameter is set to the minimum setting of the EPMA, the actual beam diameter will not be 0 μm, but will be on the order of nm. For the elemental amounts in the base and dispersed particle parts, the largest dispersed particle part (dispersed particle part with an equivalent circle diameter of at least 2 μm) is selected in the concentration map, and a line scan is performed to pass through that dispersed particle part, and the concentration of each element relative to the scan position is determined by profile. When small dispersed particles are scanned, the base part surrounding the dispersed particles is also analyzed, so the elemental concentration in the dispersed particle part is not the true value and is shifted towards the elemental concentration of the base part, which is undesirable. In the line scan concentration profile obtained in this way, the baseline of the profile is taken as the average concentration of the base portion, and the concentration of the portion corresponding to the dispersed particles is taken as the maximum concentration of the dispersed particles, allowing for a comparison between the concentration of the base portion and the concentration of the dispersed particles portion.

[0021] A sliding member according to one embodiment of the present invention has a coating that contains Cr and N and a metal element including at least Si, and has a base portion and dispersed particle portions scattered within the base portion, and the hardness of the coating is 1900 HV 0.1 or less, resulting in an excellent balance of wear resistance, peel resistance and mating aggressiveness. The inventors surmise the following reasons for this: <1> Because the dispersed particles scattered within the base portion of the coating of the sliding member contain not only Cr but also metal elements such as Si, the dispersed particle portion (alloy dispersed particle portion) is strongly bound to the base portion, increasing the toughness of the entire coating and making it less likely to become the starting point for peeling due to sliding resistance, thus improving peel resistance. <2> Because the dispersed particle portion contains not only Cr but also other metal elements, a lubricating film called a tribofilm is formed by reaction with lubricating oil during sliding between the coating and the mating material, and the lubricating film functions as a protective film, improving wear resistance and reducing mating aggressiveness. <3> If the hardness of the coating is too high, the coating will have low flexibility, stress will concentrate easily, cracks will easily occur, the coating will peel off easily, and the mating material will wear down easily. However, if the hardness of the coating is low to a certain extent, peel resistance will be improved and the aggressiveness towards the mating material will be reduced. In addition, generally, if the hardness of the coating is low, the wear resistance tends to be insufficient, but by including metal elements such as Si in the dispersed particle portion, the wear resistance of the dispersed particle portion itself will be improved. Through the above mechanism, compared with dispersed particle portion of Cr alone that does not contain metal elements such as Si, the wear resistance of the entire coating can be ensured even if the overall hardness of the coating is low, and the toughness of the entire coating is increased, making peeling of the coating less likely and improving peel resistance. However, the mechanism of the present invention is not limited to the above.

[0022] The Cr content in the base portion may be 30 at% or more, 35 at% or more, or 40 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. Similarly, from the same viewpoint, it may be 60 at% or less, 55 at% or less, or 50 at% or less. From these viewpoints, the Cr content in the base portion may be 30 to 60 at%.

[0023] The total content of metal elements in the base portion may be 1 at% or more, 3 at% or more, or 5 at% or more, from the viewpoint of achieving a better balance of wear resistance, peeling resistance, and mating resistance. Similarly, from the same viewpoint, it may be 25 at% or less, 22 at% or less, 20 at% or less, 15 at% or less, 12 at% or less, 10 at% or less, 8 at% or less, 7 at% or less, 6 at% or less, 5 at% or less, 4 at% or less, 3.5 at% or less, or 3 at% or less. From these viewpoints, the total content of metal elements in the base portion may be 1 to 25 at%, 1 to 20 at%, 1 to 12 at%, 1 to 8 at%, 1 to 5 at%, or 1 to 3 at%.

[0024] The Si content in the base portion may be 1 at% or more, 2 at% or more, or 3 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. Similarly, from the same viewpoint, it may be 8 at% or less, 7 at% or less, 6 at% or less, 5 at% or less, 4 at% or less, 3.5 at% or less, or 3 at% or less. From these viewpoints, the Si content in the base portion may be 1 to 8 at%, 1 to 5 at%, or 1 to 3.5 at%.

[0025] The Ti content in the base portion may be 0 at% or more, 4 at% or more, or 7 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. Similarly, from the same viewpoint, it may be 25 at% or less, 20 at% or less, or 17 at% or less. From these viewpoints, the Ti content in the base portion may be 0 to 25 at%.

[0026] The total content of Si and Ti in the base portion may be 1 at% or more, 6 at% or more, or 10 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. Similarly, from the same viewpoint, it may be 30 at% or less, 24 at% or less, or 20 at% or less. From these viewpoints, the total content of Si and Ti in the base portion may be 1 to 30 at%.

[0027] The N content in the base portion may be 35 at% or more, 40 at% or more, or 45 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. Similarly, from the same viewpoint, it may be 65 at% or less, 60 at% or less, or 55 at% or less. From these viewpoints, the N content in the base portion may be 35 to 65 at%.

[0028] The Cr content in the dispersed particles may be 40 at% or more, 45 at% or more, or 50 at% or more, from the viewpoint of achieving a better balance of abrasion resistance, peeling resistance, and anti-aggression properties. Similarly, it may be 80 at% or less, 75 at% or less, or 70 at% or less. From these viewpoints, the Cr content in the dispersed particles may be 40 to 80 at%.

[0029] The total content of metal elements in the dispersed particles may be 1 at% or more, 3 at% or more, or 5 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and anti-aggression properties. Similarly, from the same viewpoint, it may be 30 at% or less, 26 at% or less, 24 at% or less, 22 at% or less, 20 at% or less, 15 at% or less, or 10 at% or less. The total content of metal elements in the dispersed particles may be 1 to 30 at%, 1 to 24 at%, 1 to 20 at%, 1 to 15 at%, or 1 to 10 at%.

[0030] The Si content in the dispersed particles may be 2 at% or more, 3 at% or more, 4 at% or more, or 5 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. Similarly, from the same viewpoint, it may be 15 at% or less, 13 at% or less, 10 at% or less, 8 at% or less, or 6 at% or less. From these viewpoints, the Si content in the dispersed particles may be 2 to 15 at% or 3 to 10 at%.

[0031] The Ti content in the dispersed particles may be 0 at% or more, 6 at% or more, or 9 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. Similarly, from the same viewpoint, it may be 30 at% or less, 22 at% or less, or 19 at% or less. From these viewpoints, the Ti content in the dispersed particles may be 0 to 30 at%.

[0032] The total content of Si and Ti in the dispersed particles may be 3 at% or more, 10 at% or more, or 14 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and anti-aggression properties. Similarly, from the same viewpoint, it may be 40 at% or less, 30 at% or less, or 25 at% or less. From these viewpoints, the total content of Si and Ti in the dispersed particles may be 3 to 40 at%.

[0033] The N content in the dispersed particles may be 10 at% or more, 15 at% or more, or 20 at% or more, from the viewpoint of achieving a better balance of abrasion resistance, peeling resistance, and anti-aggression properties. Similarly, it may be 50 at% or less, 45 at% or less, or 40 at% or less. From these viewpoints, the N content in the dispersed particles may be 10 to 50 at%.

[0034] The difference between the total content of metal elements in the dispersed particle portion and the total content of metal elements in the base portion (dispersed particle portion - base portion) may be 0.5 at% or more, 1 at% or more, or 1.5 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance, and may also be 3 at% or less, 2.5 at% or less, or 2 at% or less, from the same viewpoint.

[0035] The difference in Si content between the dispersed particle portion and the base portion (dispersed particle portion - base portion) may be 1 at% or more, 2 at% or more, or 2.5 at% or more, from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance, and may also be 5 at% or less, 4 at% or less, or 3 at% or less, from the same viewpoint.

[0036] The area ratio of dispersed particles with an equivalent circular diameter of 0.1 μm or more on the surface of the coating may be 0.5 to 5% from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance. When the area ratio of dispersed particles with an equivalent circular diameter of 0.1 μm or more is 0.5% or more, an appropriate gap can be created between the sliding member and the mating material, which tends to result in a better balance of wear resistance, peel resistance, and mating resistance. When the area ratio of dispersed particles with an equivalent circular diameter of 0.1 μm or more is 5% or less, the shedding of dispersed particles can be suppressed, which tends to result in a better balance of wear resistance, peel resistance, and mating resistance. The area ratio of dispersed particles with an equivalent circular diameter of 0.1 μm or more on the surface of the coating may be greater than 1.0%, 4.5% or less, or 4% or less from the viewpoint of achieving a better balance of wear resistance, peel resistance, and mating resistance.

[0037] The area ratio of dispersed particles with an equivalent circular diameter of 0.1 μm or more on the surface of the coating can be measured by the following method. Specifically, the surface of the coating on the sliding member is polished using a polishing machine (for example, IS-POLISHER manufactured by Ikegami Seiki Co., Ltd.). More precisely, the sample is obtained by polishing with a diamond film with a particle size of 0.5 μm, gradually increasing the grit size from #600. Next, the obtained sample is observed with an FE-SEM (for example, JSM-7100F manufactured by JEOL Ltd.) and a backscattered electron image is obtained at a magnification of 2000x. A region of 45 μm × 62.5 μm is extracted from the obtained backscattered electron image and binarized using image analysis software (for example, A-Image-kun manufactured by Asahi Kasei Engineering Co., Ltd.). The total area of ​​dispersed particles with an equivalent circular diameter of 0.1 μm or more is measured from the binarized image. The area ratio can be calculated by dividing the total area of ​​the dispersed particles with an equivalent circular diameter of 0.1 μm or more by the measurement area (45 μm × 62.5 μm).

[0038] The hardness of the coating is 1900 HV 0.1 or less. A hardness of 1900 HV 0.1 or less provides an excellent balance between peel resistance and mating resistance. The hardness of the coating may also be 800-1800 HV 0.1, 800-1500 HV 0.1, 900-1500 HV 0.1, or 1000-1300 HV 0.1, from the viewpoint of allowing moderate elastic deformation, reducing Hertz stress caused by sliding, and easily achieving excellent peel resistance. The hardness of the coating can be measured using a Vickers hardness tester (e.g., model name: HM-220, manufactured by Mitutoyo) based on the method specified in ISO 6507.

[0039] (Method for manufacturing sliding member) Next, a method for manufacturing a sliding member will be described. The manufacturing method of this embodiment includes the following steps: (a) A step of obtaining an intermetallic compound containing Cr and a metal element containing at least Si. (b) A step of forming a film using the intermetallic compound by arc ion plating.

[0040] (a) The process involves mixing a powder containing Cr and a metal element, cold forming it, and sintering it by hot isostatic pressing (HIP) or hot pressing to obtain an intermetallic compound of a predetermined shape.

[0041] (a) The process involves first mixing a predetermined amount of metal powder containing Cr and metal powder containing Si, with Cr as the main constituent element and at least one metal element containing Si as a secondary constituent element. In addition to the metal powder containing Cr and metal powder containing Si, the metal powder may also contain at least one element selected from the group consisting of Ti, Al, Mo, V, W, Nb, Mn, Zn, Cu, and Zr. The metal powder may contain multiple metal elements. The method for producing the metal powder is not particularly limited. The metal powder may be a powder composed substantially of only one element, or it may be a powder produced by melting and pulverizing multiple components. It may also be a powder alloyed in a solid state, such as a mechanical alloy.

[0042] Next, the mixed metal powder is cold-formed into a predetermined shape using a press or the like, and sintered by a hot isostatic pressing method (HIP method) or a hot pressing method to obtain a target material containing an intermetallic compound of a predetermined shape.

[0043] The temperature at the time of sintering by the hot isostatic pressing method (HIP method) or the hot pressing method may be, for example, 900 to 1300 °C, or 900 to 1100 °C.

[0044] The pressure at the time of sintering by the hot isostatic pressing method (HIP method) or the hot pressing method may be, for example, 100 to 140 MPa.

[0045] By adjusting the types, mixing ratios, and sintering conditions of the material components for obtaining the intermetallic compound, while dispersing and arranging dispersed particles in the film, it is possible to adjust the amount of scattered dispersed particles and the size of the dispersed particle portion during film formation. For example, by reducing the pressure of sintering when obtaining the intermetallic compound, the formation of intermetallic compounds of metal elements such as Cr and Si in the dispersed particle portion in the film can be suppressed.

[0046] The manufacturing method of the sliding member may include a step for cleaning the surface of the base material before the step (b). For example, it may include a step of performing a cleaning treatment such as degreasing or shot blasting. In addition to this, the manufacturing method of the sliding member may include a step of performing bombardment cleaning in the chamber.

[0047] (b) The film formation in the process can be carried out by the arc ion plating method. Specifically, the inside of the chamber is set to a nitrogen atmosphere, and the bias voltage is set in the range of -2 to -25 V. When forming a film by the arc ion plating method using an intermetallic compound, the bias voltage being -2 to -25 V can suppress the film from becoming too dense and relieve the residual stress inside the film. Thereby, even in a harsh environment, a sliding member excellent in peel resistance, having a good balance between wear resistance and counter-attack property, and capable of achieving a sufficiently high level can be manufactured. The bias voltage may be -3 to -15 V or -4 to -10 V from the viewpoint of better balance of wear resistance, peel resistance, and counter-attack property of the sliding member.

[0048] The nitrogen pressure inside the chamber may be 1 to 10 Pa, 2 to 8 Pa, or 4 to 6.5 Pa from the viewpoint of better balance of wear resistance, peel resistance, and counter-attack property of the sliding member. The film formation temperature may be, for example, 300 to 500 °C. The arc current may be 100 to 200 A.

[0049] The constituent elements ionized from the target material containing an intermetallic compound by arc discharge are deposited on the substrate applied to the cathode, and at the same time, the droplets generated at the arc spots on the surface of the intermetallic compound are also released simultaneously and are dispersed and arranged in the base part as the dispersed particle part.

[0050] Hereinafter, the present invention will be described in more detail based on invention examples and comparative examples. The present invention is not limited to the following invention examples.

[0051] (Examples 1-14 of Inventions and Comparative Examples 1-9) <Formation of the coating> JIS SWOSC-V (silicon-chromium steel oil-tempered wire) was used as the base material for the sliding member (piston ring) and processed into a ring shape. Next, as preparation for film formation, the base material was degreased and washed, and then the ring base material was placed in an ion plating apparatus. Then, in the chamber, the chamber atmosphere was set to nitrogen, and a target material (including a metal compound or intermetallic compound) with the nitrogen pressure shown in Table 1, the bias voltage shown in Table 1, a film formation temperature of 400°C, and the composition shown in Table 1 was ionized to form a coating with a thickness of approximately 20 μm on the surface of the base material. At this time, the arc current was 150 A for Examples 1-14 of Inventions and Comparative Examples 1, 2, 4-6, 8, and 9, the arc current was 100 A for Comparative Example 3, and the arc current was 350 A for Comparative Example 7. The intermetallic compounds were prepared by mixing predetermined amounts of Cr-containing metal powder and metal powder containing an arbitrary metal element to achieve the target composition shown in Table 1, cold forming using a press, and then sintering by hot isostatic pressing (HIP) at a temperature of 900 to 1300°C and a pressure of 100 to 140 MPa.

[0052] The elemental composition of the base and dispersed particle portions of the fabricated piston rings was measured by the following method. First, the surface of the film formed on the outer circumferential surface of the piston ring was polished using a polishing machine (IS-POLISHER, manufactured by Ikegami Seiki Co., Ltd.). Specifically, the sample was obtained by polishing with a diamond film with a particle size of 0.5 μm, gradually increasing the grit size from #600. Next, an elemental concentration map was obtained from the obtained sample using an EPMA (device name: JXA-8100, manufactured by JEOL). The measurement conditions were an acceleration voltage of 15 kV and an irradiation current of 5.0 × 10⁻¹⁰. －８A. The beam diameter was set to 0 μm (minimum setting), the scan interval was 0.30 μm in the vertical direction and 0.30 μm in the horizontal direction, the scan time was 30 ms / point, and the number of scan points was 200 points in the vertical direction and 200 points in the horizontal direction, and a concentration map (60 μm × 60 μm) of each element to be analyzed was obtained. For the elemental amounts in the base and dispersed particle sections, the dispersed particle section with the largest concentration was selected in the concentration map, and a line scan was performed to pass through that dispersed particle section, and the concentration of each element relative to the scan position was determined by profile. In the concentration profile of the line scan obtained in this way, the baseline of the profile was taken as the average concentration of the base section, and the concentration of the part corresponding to the dispersed particle section was taken as the maximum concentration of the dispersed particles, and the concentration of the base section and the concentration of the dispersed particle section were compared. Figure 3 shows the results of EPMA analysis of the surface of the piston ring of Example 1. In Figure 3, the darker the black area, the higher the Si concentration.

[0053]

[0054] <Coating Characteristics> Table 1 shows the characteristics of the piston ring coatings for the examples and comparative examples. Each characteristic was measured by the following method. (Area ratio of dispersed particles) The surface of the coating on the fabricated piston ring was polished using a polishing machine (IS-POLISHER manufactured by Ikegami Seiki Co., Ltd.). Specifically, the grit size was gradually increased from #600, and finally polished with a diamond film with a grit size of 0.5 μm to obtain a sample. Next, the obtained sample was observed with an FE-SEM (JSM-7100F manufactured by JEOL Ltd.), and a backscattered electron image was obtained at a magnification of 2000x. A region of 45 μm × 62.5 μm was extracted from the obtained backscattered electron image and binarized using image analysis software (for example, A-Image-kun manufactured by Asahi Kasei Engineering Co., Ltd.). Figure 4 shows the binarized image of the surface of the piston ring of Example 1. In Figure 4, the black area is the base area, and the white area is the dispersed particle area. The total area of ​​dispersed particles with an equivalent circle diameter of 0.1 μm or larger was measured from the binarized image. The area ratio of the dispersed particles was calculated by dividing the total area of ​​dispersed particles with an equivalent circle diameter of 0.1 μm or larger by the measured area (45 μm × 62.5 μm). The evaluation criteria for the area ratio of dispersed particles are as follows: A: Area ratio is 1% or less. B: Area ratio is greater than 1% and 4% or less. C: Area ratio is greater than 4%.

[0055] (Hardness) The hardness HV of the coating was obtained by performing a hardness test using a Vickers hardness tester (device name: HM-220, manufactured by Mitutoyo) in accordance with the method specified in ISO 6507, with a test load of 0.98 N.

[0056] <Sliding Fatigue Test> As an accelerated wear test, a sliding fatigue test was conducted using a testing machine configured as shown in Figure 5. The testing machine 50 shown in Figure 5 includes a rotating drum 51, a mechanism for bringing a test piece S (a cut piece of piston ring) into contact with the surface of the drum 51, a mechanism for repeatedly applying a load to the test piece S, and a mechanism for supplying lubricating oil to the sliding parts. This allows the test piece to be worn down in a relatively short time. The test conditions were as follows: ・Test load: 20-80 N, sine curve (50 Hz) ・Matching material (drum): SUJ2 heat-treated material (80 mm diameter) ・Driving speed: Forward and reverse trapezoidal pattern operation ・Lubricating oil: Base oil (0.1 cc drop every 30 seconds) ・Drum surface temperature: 80°C ・Test time: 5 cycles of 2-3 minutes per cycle

[0057] <Evaluation> Table 1 shows the evaluation results of the piston ring coatings for the examples and comparative examples. For each evaluation result, 20 piston rings for the examples and comparative examples were prepared and subjected to 20 sliding fatigue tests. The peel resistance of the coating was evaluated by visually observing the coating after the sliding fatigue test. In addition, wear resistance and mating aggressiveness were evaluated by using the amount of wear of the coating of Comparative Example 1 as the amount of wear of a conventional CrN coating. The evaluation criteria were as follows: (Peeling Resistance) A: The peeling rate among the 20 samples is 40% or less. B: The peeling rate among the 20 samples is more than 40% but less than 80%. C: The peeling rate among the 20 samples is 80% or more.

[0058] (Abrasion Resistance) Abrasion amount compared to the abrasion amount of a conventional CrN coating, which is set to 1.0. A: Abrasion amount is 0.7 or less. B: Abrasion amount is greater than 0.7 but less than 0.9. C: Abrasion amount is 0.9 or more.

[0059] (Attack on the mating material) Wear amount when the wear amount of the mating material (SUJ2 heat-treated material) with a conventional CrN coating is set to 1.0 A: Wear amount is 1.0 or less. B: Wear amount is greater than 1.0 but less than 1.2. C: Wear amount is 1.2 or more.

[0060] The present invention provides a piston ring and a method for manufacturing the same, which is provided that has a coating containing Cr and N and at least one metallic element selected from the group consisting of Si, Ti, Al, Mo, V, and W, and which can achieve a good balance and sufficiently high level of wear resistance, peel resistance, and mating resistance.

[0061] 1...Substrate, 5...Coating, 5A...Base part, 5B...Dispersed particle part, 10...Sliding member, 10F...Sliding surface.

Claims

1. A method for manufacturing a sliding member comprising a base material and a coating provided so as to cover at least a portion of the surface of the base material, comprising: (A) a step of obtaining an intermetallic compound containing Cr and a metal element containing at least Si; (B) a step of forming the coating using the intermetallic compound by an arc ion plating method, wherein in step (B), a bias voltage in the range of -2 to -25V is set under a nitrogen atmosphere.

2. A sliding member comprising: a base material; and a coating provided so as to cover at least a portion of the surface of the base material, wherein the coating contains Cr and N and a metal element including at least Si, the coating has a base portion and dispersed particle portions scattered within the base portion, and the hardness of the coating is 1900 HV 0.1 or less.

3. The sliding member according to claim 2, wherein the metal element includes at least one selected from the group consisting of Ti, Al, Mo, V, W, Nb, Mn, Zn, Cu, and Zr.

4. The sliding member according to claim 2 or 3, wherein the content of the metal element in the base portion is 1 to 25 at%.

5. The sliding member according to claim 2 or 3, wherein the content of the metal element in the dispersed particle portion is greater than the content of the metal element in the base portion.

6. The sliding member according to claim 2 or 3, wherein the hardness of the coating is 800 to 1500 HV 0.

1.

7. A piston ring comprising the sliding member according to claim 2 or 3.

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