Crn coating film

Description

1 / 13 “CRN COATING FILM” FIELD OF TECHNIQUE

[0001] The present invention relates to: a CrN film; and a sliding member coated with the CrN film. BACKGROUND OF THE TECHNIQUE

[0002] It is necessary that a CrN coating film, which is disposed on a sliding surface of a sliding member used in a severe sliding environment, has satisfactory sliding properties and wear resistance. For example, in a piston ring used in an internal combustion engine, the load applied to the piston ring surface tends to be increased in association with an increase in cylindrical internal pressure, direct fuel injection, reduction in the viscosity of a lubricating oil that is used, and the like. As a result, there are cases where a CrN coating film covering the piston ring surface is cracked and / or flaked due to the sliding effect.

[0003] In order to solve this problem, a coating film having a composition in which an element selected from the group consisting of carbon, phosphorus, nitrogen, boron and silicon is dissolved in solid solution in metallic chromium, wherein the coating film exhibits high hardness, resistance to hydrogen embrittlement, toughness and fatigue resistance has been proposed (see Patent Document 1).

[0004] Furthermore, it was revealed that the slip characteristics and resistance to peeling are enhanced by a coating film that is formed by CrN-type chromium nitride and in which the crystal lattice constant and Cr content are in specific ranges (see Patent Document 2).

[0005] Furthermore, it was revealed that a high-tenacity coating film with excellent wear resistance, particularly crack resistance and peel resistance, is provided by allowing a coating film with a composition that includes a mixture of Cr2N and metallic chromium with nitrogen dissolved in solid solution to have a specific diffraction peak. Petition 870260037396, dated 04 / 22 / 2026, page 9 / 38 2 / 13 (see Patent Document 3). RELATED TECHNICAL DOCUMENTS PATENT DOCUMENTS

[0006] [Patent Document 1] Publication of Patent Application not submitted for examination No. JP S58-144473

[0007] [Patent Document 2] Publication of Patent Application not submitted for examination no. JP 2001-335878

[0008] [Patent Document 3] document no. WO 2013 / 136510 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] As described above, CrN coating films that have excellent resistance to peeling have been proposed. However, during sliding in a more severe lubrication environment, these coating films are prone to peeling, starting at a crack. An object of the present invention is to provide: a CrN coating film that has excellent resistance to peeling such that peeling of the same starting at a crack is unlikely to occur even in such a more severe lubrication environment; and a sliding member coated with the same. MEANS TO SOLVE THE PROBLEMS

[0010] The present inventors conducted studies to solve the problem described above and consequently found that the problem can be solved by reducing the size of crystals that form a CrN coating film and controlling the preferred orientation within a specific range, thus completing the present invention.

[0011] The present invention is a CrN coating film having a preferred orientation along a vertical direction to the (200) plane as determined by XRD (X-ray diffraction), and in which the X-ray diffraction intensity ratio of the (200) plane to the (111) plane, (200) / (111) is 5.5 or greater, and the grain size ratio of 1 μm or less is 85% or greater in a crystal grain size distribution measured by EBSD (external beam diffraction) analysis. Petition 870260037396, dated 04 / 22 / 2026, page 10 / 38 3 / 13 of electrons backscattered) It is preferable that there are no grains that have a size of 2.3 μm or more, and it is more preferable that there are no grains that have a size of 2.0 μm or more.

[0012] Furthermore, in a preferred mode, the CrN coating film has a micro-Vickers hardness of 800 HV to 1300 HV. By controlling the coating film to have a lower hardness while remaining a dense film, the coating film becomes less brittle and has improved resistance to peeling, which is preferable. When the micro-Vickers hardness is less than 800 HV, the wear resistance may be insufficient, while when the micro-Vickers hardness is greater than 1300 HV, the coating film tends to crack or be lost due to handling during processing.

[0013] Furthermore, in a preferred mode, the CrN coating film has a plastic work rate of 61% to 69% as measured using a Vickers indenter according to the international standard for nanoindentation testing, ISO14577-1. The “plastic work rate” refers to a ratio of plastic deformation work to total indentation work in an indentation test. In a coating film that has a high plastic work rate, the resistance to peeling that begins at a crack is enhanced. When the plastic work rate is less than 61%, the hardness tends to be greater than 1300 HV, while when the plastic work rate is more than 69%, the hardness tends to be less than 800 HV.

[0014] Another embodiment of the present invention is a sliding member that includes a sliding surface coated with the CrN coating film described above. EFFECT OF THE INVENTION

[0015] According to the present invention, the following can be provided: a CrN coating film that has excellent resistance to peeling such that peeling of the same that begins at a crack is unlikely to occur even in the most severe lubrication environment; and a sliding member coated with the same. Petition 870260037396, dated 04 / 22 / 2026, page 11 / 38 4 / 13 BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1, Figure 1 is a schematic cross-sectional view of a piston ring coated with a CrN film, which is an embodiment of the present invention.

[0017] Figure 2, Figure 2 is a schematic drawing of an apparatus used for depositing a CrN coating film onto a piston ring by an ion deposition method.

[0018] Figure 3, Figure 3 is an enlarged image (substitute drawing) of grains forming a CrN film obtained in an Example.

[0019] Figure 4, Figure 4 is a graph showing the grain size distribution of the CrN coating film from Example 1.

[0020] Figure 5, Figure 5 is a schematic cross-sectional view of a pin-on-disc test used for a peel resistance test.

[0021] Figure 6, Figure 6 shows images (substitute drawings) of CrN films after a peel resistance test. METHODS FOR CARRYING OUT THE INVENTION

[0022] One embodiment of the present invention is a CrN coating film. This CrN coating film contains CrN as a major component and may also contain Cr2N, metallic chromium in which nitrogen is dissolved in solid solution, unavoidable impurities, and the like. The type of phase constituting the CrN coating film can be evaluated by XRD (X-ray Diffraction). The composition of the CrN coating film can be analyzed using an EPMA (Electron Microprobe Microanalysis). In the CrN coating film, the Cr content can be 45% per atom or more, 50% per atom or more, but 60% per atom or less. Furthermore, the nitrogen content in the coating film can be 40% per atom or more, 50% per atom or more, but 55% per atom or less.

[0023] In the present invention, the CrN coating film has a preferred orientation along a vertical direction to the (200) plane as determined by XRD, the X-ray diffraction intensity ratio of the (200) plane to the (111) plane, (200) / (111) is 5.5 or greater, and the grain size ratio of 1 μm or less is 85% or greater in a grain size distribution measured by an EBSD analysis. Petition 870260037396, dated 04 / 22 / 2026, page 12 / 38 5 / 13

[0024] The CrN coating film exhibits enhanced peel resistance having a preferred orientation along a vertical direction to the (200) plane as determined by XRD, and an X-ray diffraction intensity ratio of the (200) plane to the (111) plane, (200) / (111), of 5.5 or greater, preferably 6 or greater, more preferably 6.5 or greater. An upper limit of the X-ray diffraction intensity ratio is not limited and is generally 20 or less and may be 10 or less.

[0025] The CrN coating film becomes dense by controlling the grain ratio of 1 μm or less in a grain size distribution measured by an EBSD analysis to be 85% or greater, preferably 86% or greater, more preferably 90% or greater, and the CrN coating film exhibits enhanced flaking resistance since cracks, even if generated, are unlikely to be connected to each other. An upper limit of this ratio is not limited and may be 100% or less, 99% or less, or 95% or less.

[0026] In the CrN coating film, the plastic work rate is preferably 61% or higher, more preferably 64% or higher, but preferably 69% or lower, as measured using a Vickers indenter according to the international standard for nanoindentation testing, ISO14577-1. The CrN coating film of the present embodiment is dense and has a high plastic work rate.

[0027] In addition, the CrN coating film has a microVickers hardness of preferably 800 HV to 1300 HV, more preferably 1100 HV or less, even more preferably 1000 HV or less. By preventing the microVickers hardness of the coating film from being excessively high, the coating film becomes less brittle, and its resistance to peeling is improved.

[0028] In order to obtain the CrN coating film of the present embodiment, it is preferable to form a CrN coating film by the ion deposition method described below. In particular, by modifying the position and shape of a control magnet arranged around a cathode, the behavior of arc points formed on the surface of a target material during unloading can be Petition 870260037396, dated 04 / 22 / 2026, page 13 / 38 6 / 13 modified to control the physical properties of the resulting CrN coating film.

[0029] Figure 1 is a cross-sectional view of a portion of a piston ring that is an example of the present embodiment. A piston ring 10 has a CrN 12 coating film on its upper and lower surfaces and a sliding surface (the surface on the left side in the drawing). In the present embodiment, the piston ring 10 has the CrN 12 coating film at least on the sliding surface; however, the CrN coating film may also be provided on other surfaces, for example the upper and lower surfaces and the outer circumferential surface. The thickness of the CrN coating film on the sliding surface is not particularly limited, and it may generally be 3 μm or more, or 5 μm or more, but generally 50 μm or less, or 30 μm or less.It should be noted here that the piston ring is a type of sliding member, and examples of sliding members include pistons, bearings, washers, and valve lifters, in addition to piston rings.

[0030] In the case of a piston ring, a piston ring substrate 11 is not particularly limited in terms of its material as long as the material is conventionally used as a piston ring substrate. For example, a stainless steel material or a steel material may preferably be used and, specifically, martensitic stainless steel, silicon-chromium steel, or similar is preferably used.

[0031] Between the CrN coating film and the piston ring substrate, for example, a Cr-plated coating film, a chromium nitride coating film, or a titanium nitride coating film may be additionally provided, or the CrN coating film may be formed directly onto the piston ring substrate. When the substrate is made of stainless steel, a nitriding treatment may be performed on the substrate.

[0032] The CrN coating film can be formed by a physical vapor deposition process, such as an ion deposition method or a crackling method. An example where the CrN coating film is formed by a Petition 870260037396, dated 04 / 22 / 2026, page 14 / 38 The 7 / 13 ion deposition method will now be described with reference to a drawing.

[0033] Figure 2 is a schematic cross-sectional view illustrating an example of an apparatus 20 used for forming a CrN coating film by an ion deposition method. A gas introduction tube 22 and a vacuum exhaust tube 23 are connected to a vacuum chamber 21, and the temperature inside the vacuum chamber 21 can be controlled using a heater (not shown). The apparatus 20 also includes a cathode 24 and an anode 25, a control magnet 26 is disposed at the tip of the cathode 24 (the right end of the cathode in the drawing), and a target material 27 is ionized by plasma arc discharge.

[0034] Inside vacuum chamber 21, a piston ring is set on a rotating table (not shown), and the target material, which is chromium, is ionized and deposited on the surface of the piston ring while introducing nitrogen gas from the gas introduction tube 22. The operating conditions of the apparatus in this process can be defined as follows: arc current = 100 to 200 A, bias voltage = 0 to 50 V, internal chamber pressure = 1 to 4 Pa, heating temperature by the heater = 300 to 400 °C.

[0035] The nitrogen content in the resulting CrN can be controlled by adjusting the internal pressure and the partial pressure of nitrogen in the introduced gas.

[0036] The properties of the resulting CrN coating film can also be controlled by modifying the position and shape of the control magnet arranged around the cathode. For example, by arranging the magnet so that it rotates around the tip of the cathode, arc points are reduced in size, so that the speed of each arc point moving on the cathode surface is increased and the generated plasma reaches the surroundings of the piston ring; therefore, the ionization rate is enhanced, making a denser CrN coating film more likely to be formed. EXAMPLES

[0037] The present invention will now be described in more detail by way of Examples; however, the present invention is not limited to the Examples described below. Petition 870260037396, dated 04 / 22 / 2026, page 15 / 38 8 / 13

[0038] The physical property values ​​of a coating film were measured using the following equipment. X-RAY DIFFRACTION MEASUREMENT

[0039] The preferred orientation of a coating film was determined by XRD using an XRD apparatus (D8 DISCOVER, manufactured by Bruker AXS GmbH). Using an XRD tube and CuKa radiation as X-ray, the measurement was performed at a tube voltage of 40 kV and a tube current of 40 mA in a range of 2Θ = 30 to 90°. A piston ring coated with a CrN coating film on the outer circumferential surface was cut and used as a sample, and this sample was X-ray irradiated on the outer circumferential sliding surface side to perform the measurement. From the XRD pattern obtained in this way, the peak intensities of the (111) plane and the (200) plane of CrN were determined, and the ratio thereof was calculated. Grain Size Measurement (EBSD Analysis)

[0040] The grain size of a coating film was measured using a FE SEM (JSM-7100F, manufactured by JEOL Ltd.) and EBSD analysis software (DigiView IV, manufactured by TSL Solutions, Ltd.). The measurement was performed with an acceleration voltage of 15.0 kV at measurement intervals of 0.02 μm for a measurement area of ​​20 μm ≈ 20 μm. A piston ring coated with a CrN coating film on the outer circumferential surface was cut and used as a sample, and the outer circumferential sliding surface of this sample was polished with a diamond paste and then ultrasonically cleaned, after which the sample was subjected to Ar ion polishing to remove polishing marks, and subsequently irradiated with an electron beam from the outer circumferential surface side to perform the measurement.The electron beam was irradiated onto the tilted sample, and the reflected electron diffraction pattern (Kikuchi lines) was measured from the scattered electron beam. The Kikuchi lines were analyzed to prepare reverse pole figures for the respective crystal orientations. From the reverse pole figures obtained in this way, continuous measurement points within a misorientation of 5° or less were collectively defined. Petition 870260037396, dated 04 / 22 / 2026, page 16 / 38 9 / 13 as a single grain, and an inverse pole figure map of the measurement area was prepared. From the inverse pole figures, the grain size of each grain was measured, and the area ratio of the grains to the total measurement area was calculated at 0.1 μm intervals. From the histogram prepared in this way of the grain size distribution at 0.1 μm intervals, the ratio of grains having a size of 1 μm or smaller to the total measurement area (area ratio) was calculated. COATING FILM COMPONENTS

[0041] The components of a coating film were measured by EPMA. For the EPMA measurement, EPMA-1720HT manufactured by Shimadzu Corporation was employed. A quantitative analysis was performed using pure Cr and BN as standard Cr and N samples, respectively, at an accelerating voltage of 15 kV, an irradiation current of 50 nA, and an electron beam diameter of 100 pm. A sample was prepared using the same procedure as the sample used in the EBSD analysis. Taking the measured intensity for the respective standard samples as 100%, the quantity (% by weight) of the sample prepared in this way was determined from the ratio of the intensity of the respective standard samples to the intensity of an unknown sample. For the elements to be measured, the total quantity obtained in this way (% by weight) was normalized to 100%, and the quantity of each element was calculated as % per atom. PLASTIC LABOR RATE

[0042] To measure the plastic work rate of a coating film, a nanohardness tester (model HM-2000, manufactured by Fischer Instruments KK) was employed. Using the method according to ISO14577-1, the plastic work rate was measured with a Vickers indenter at an indentation load of 1000 mN, with the time before reaching a maximum indentation load being set at 30 s (seconds). As a sample, a piece obtained by cutting a piston ring coated with a CrN coating film on the outer circumferential surface, embedding the result in a resin, and then polishing the outer circumferential surface as a measuring surface using sandpaper and a diamond paste, was used. The plastic work rate was defined as Petition 870260037396, dated 04 / 22 / 2026, page 17 / 38 10 / 13 plastic deformation work nplast determined from a load indentation depth curve. EXAMPLES AND COMPARATIVE EXAMPLES

[0043] As a piston ring substrate, a steel material equivalent to the JIS G3651 SWOSC-V standard was prepared and processed into a piston ring shape (φ73.0 mm χ 1.0 mm thick). On this piston ring substrate, a CrN coating film was formed using the apparatus for forming a CrN coating film by an ion deposition method, the apparatus of which is schematically illustrated in Figure 2. The formation of the CrN coating film was carried out under the conditions shown in Table 1 below.

[0044] Next, the physical properties of the CrN coating film formed in this way were measured. The results are shown in Table 2. Note that all CrN coating films had a preferential orientation along a direction vertical to the (200) plane. Furthermore, in the Examples, no grains with a size of 2.0 μm or more were observed. The grains and grain size distribution of the CrN coating film from Example 1 are shown in Figures 3 and 4, respectively. PEELING RESISTANCE TEST

[0045] In a peel resistance test, a piston ring piece was pressed against the side surface of a disc rotating at a constant speed, and the relative peel resistance was evaluated based on the presence or absence of damage (cracking and peeling) to the sliding surface after a given period of operation. Peel resistance was rated as “A” when the sliding surface was not peeled, “B” when the size of a peeled portion had a maximum length of less than 100 µm, or “C” when the size of a peeled portion had a maximum length of 100 µm or more. Figure 5 shows a schematic cross-sectional view of a pin-on-disc test used for peel resistance testing. In a pin-on-disc test 30, a pin (upper specimen) 32 is pressed against the side surface of a disc (lower specimen) 31 that rotates at Petition 870260037396, dated 04 / 22 / 2026, p. 18 / 38 11 / 13 at a constant speed. A piston ring piece was used as the pin (upper test specimen) 32.

[0046] As with the test conditions, the test was conducted at a load of 40 N and a speed of 5 to 10 m / s for a period of 5 minutes using a 0W-20 lubricating oil. The disc was made of S45C steel, and had a surface roughness of 1.5 μm in terms of the 10-point average roughness Rzjis according to JIS-B0601 (2001).

[0047] As for the evaluation method, an image of slip marks was photographed under an optical microscope (GX71 inverted optical microscope, manufactured by Olympus Corporation), and the maximum length of the slough mark was measured using image analysis software (OLYMPUS Stream industrial image analysis software, manufactured by Olympus Corporation). TABLE 1 Arc current 100-200 A. Bias voltage (0 - 50 V). Internal chamber pressure 1 - 4 Pa. Heating temperature by heater 300 - 400 °C. TABLE 2 X-ray diffraction intensity ratio (200) / (111) Grain ratio of 1pm or less (%) Coating film hardness (HV) Plastic work rate (%) Peel resistance rating Example 1 6.0 95 1000 65 A Example 2 7.0 90 950 67 A Example 3 6.5 90 1050 63 A Example 4 9.5 85 800 69 A Example 5 5.5 85 1280 61 A Example 6 6.0 95 790 70 A Petition 870260037396, dated 04 / 22 / 2026, page 19 / 38 12 / 13 Example 7 5.5 90 1340 57 B Example 8 6.0 85 1300 59 B Comparative Example 1 5.0 95 1000 65 C Comparative Example 2 5.5 80 860 69 C Comparative Example 3 4.0 85 1120 62 C Comparative Example 4 5.0 80 1190 60 C

[0048] The peel resistance test was conducted for each of the CrN coating films obtained in Examples 1 to 8 and Comparative Examples 1 to 4. The peel resistance test was performed based on observation of the coating film surface after a pin-on-disc sliding test as described above. Figure 6 shows a portion of the observation results and evaluation examples. The results are shown in Table 2.

[0049] According to observational results, the CrN coating films of Examples were partially cracked; however, they were not flaked at all or were flaked only to a maximum length of less than 100 μm. On the other hand, the CrN coating films of Comparative Examples were not only cracked but also flaked to a maximum length of 100 μm or more. DESCRIPTION OF SYMBOLS

[0050] 10: piston ring

[0051] 11: piston ring substrate

[0052] 12: CrN coating film

[0053] 20: CrN coating film forming apparatus

[0054] 21: vacuum chamber

[0055] 22: gas introduction tube

[0056] 23: vacuum exhaust pipe

[0057] 24: cathode Petition 870260037396, dated 04 / 22 / 2026, p. 20 / 38 13 / 13

[0058] 25: anode

[0059] 26: control magnet

[0060] 27: target material

[0061] 30: pin-on-disc test

[0062] 31: disc (lower specimen)

[0063] 32: pin (upper specimen) Petition 870260037396, dated 04 / 22 / 2026, p. 21 / 38

Claims

1 / 1 CLAIMS 1. CrN coating film having a preferred orientation along a vertical direction to the (200) plane as determined by XRD, characterized in that the X-ray diffraction intensity ratio of the (200) plane to the (111) plane, (200) / (111), is 5.5 or greater, and the grain size ratio of 1 μm or less is 85% or greater in a grain size distribution measured by an EBSD analysis, and a plastic work rate of 61% to 69%, wherein the plastic work rate is measured using a Vickers indenter according to ISO14577-1.

2. CrN coating film, according to claim 1, characterized in that it has a micro-Vickers hardness of 800 HV to 1300 HV. Petition 870260037396, dated 04 / 22 / 2026, p. 22 / 38

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