Crn coating and sliding member

Abstract

The technical problem of the present invention is to provide a CrN coating film which is excellent in peeling resistance and in which peeling of the coating film starting from a crack does not easily occur even in a more severe lubrication environment. The present invention solves the technical problem by a CrN coating film, the preferential orientation based on XRD is 200, the X-ray diffraction intensity ratio (200) / (111) of the (200) plane to the (111) plane is 5.5 or more, and in the distribution of the grain size determined by EBSD analysis, the proportion of grains of 1 μm or less is 85% or more.

Description

Technical Field

[0001] The present invention relates to a CrN film and a sliding member coated with the CrN film. Background Technology

[0002] CrN coatings are applied to the sliding surfaces of sliding components used in harsh sliding environments, requiring good sliding properties and wear resistance. For example, in piston rings used in internal combustion engines, the interaction of factors such as increased in-cylinder pressure, direct injection, and decreased viscosity of the lubricating oil tends to increase the load on their surfaces. Therefore, the CrN coating covering the piston ring surface sometimes cracks due to sliding effects, or the CrN coating peels off.

[0003] To address this problem, a coating is proposed having a composition in which an element selected from the group consisting of carbon, phosphorus, nitrogen, boron, and silicon is dissolved in metallic chromium, and it exhibits high hardness, resistance to hydrogen embrittlement, high toughness, and fatigue resistance (see Patent Document 1).

[0004] In addition, a coating composed of CrN-type chromium nitride is disclosed, which improves sliding properties and peel resistance by using a coating with a specific range of crystal lattice constant and Cr content (see Patent Document 2).

[0005] Furthermore, it is disclosed that by forming a coating composed of a mixture of chromium metal with nitrogen in solid solution and Cr2N, a high-toughness coating with excellent wear resistance and especially crack / peel resistance can be provided (see Patent Document 3).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 58-144473

[0009] Patent Document 2: Japanese Patent Application Publication No. 2001-335878

[0010] Patent Document 3: International Publication No. 2013 / 136510 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] As described above, a CrN coating with excellent peel resistance has been proposed. However, when sliding in more demanding lubrication environments, the coating is prone to peeling starting from cracks. The technical problem of the present invention is to provide a CrN coating with excellent peel resistance, which is not prone to peeling starting from cracks even in such more demanding lubrication environments, and a sliding member covered with the CrN coating.

[0013] Solution for solving the problem

[0014] In order to solve the above-mentioned technical problems, the inventors conducted research and found that by reducing the size of the crystals forming the CrN film and setting the preferred orientation to a specific range, the above-mentioned technical problems could be solved, thereby completing the present invention.

[0015] This invention relates to a CrN coating having a preferred orientation of 200 based on XRD (X-ray Diffraction), an X-ray diffraction intensity ratio of (200) / (111) between the (200) and (111) planes of 5.5 or higher, and a grain size distribution determined by EBSD (Electron Backscatter Diffraction Pattern) analysis in which the proportion of grains smaller than 1 μm is 85% or higher. Furthermore, it is preferable that no particles with a grain size of 2.3 μm or larger are present, and more preferably, no particles with a grain size of 2.0 μm or larger are present.

[0016] Furthermore, the preferred option is a microVickers hardness of 800 HV or higher and 1300 HV or lower. By achieving density while suppressing the hardness of the coating, a non-brittle coating is created, resulting in improved peel resistance, which is preferable. When the microVickers hardness is less than 800 HV, wear resistance is sometimes insufficient; when the microVickers hardness is greater than 1300 HV, there is a tendency for defects and peeling to occur easily due to processing operations.

[0017] Furthermore, a preferred approach is to use a Vickers indenter to measure a plasticity power of 61% or higher and 69% or lower, according to the international standard for nanoindentation testing, as specified in ISO 14577-1. Plasticity power refers to the proportion of plastic deformation work to the total indentation work during the indentation test. In films with high plasticity power, the peel resistance of the film based on cracks is improved. When the plasticity power is less than 61%, there is a tendency for the hardness to be higher than 1300 HV; when the plasticity power is greater than 69%, there is a tendency for the hardness to be lower than 800 HV.

[0018] In addition, another aspect of the present invention is a sliding member, wherein the sliding surface is coated with the aforementioned CrN film.

[0019] Invention Effects

[0020] According to the present invention, a CrN coating with excellent peel resistance and a sliding member covered with the CrN coating can be provided, which is not prone to peeling of the coating starting from cracks even in more severe lubrication environments. Attached Figure Description

[0021] Figure 1This is a cross-sectional schematic diagram of a piston ring coated with a CrN film, which is one embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of an apparatus for depositing a CrN film onto piston rings using ion plating.

[0023] Figure 3 This is a magnified image of the grains of the CrN film obtained in the formation example (instead of a photograph in the accompanying drawings).

[0024] Figure 4 This is a graph showing the grain size distribution of the CrN film in Example 1.

[0025] Figure 5 This is a cross-sectional schematic diagram of a pin-disc testing apparatus used for peel resistance testing.

[0026] Figure 6 This is an image of the CrN film after the peel resistance test (a photograph used instead of the attached image). Detailed Implementation

[0027] One embodiment of the present invention is a CrN coating. The CrN coating is a coating with CrN as the main component, but may also contain Cr₂N, dissolved nitrogen in metallic chromium, unavoidable impurities, etc. The phase composition of the CrN coating can be evaluated by XRD (X-ray diffraction). The composition of the CrN coating can be analyzed using EPMA (Electron Probe Microanalyzer). In the CrN coating, Cr can be 45 at% or more, 50 at% or more, or less than 60 at% . Furthermore, the nitrogen content in the coating can be 40 at% or more, 50 at% or more, or less than 55 at% .

[0028] In this embodiment, regarding the CrN coating, the preferred orientation based on XRD is 200, the X-ray diffraction intensity ratio of the (200) plane to the (111) plane is 5.5 or more, and in the grain size distribution determined by EBSD analysis, the proportion of grains with a size of 1 μm or less is 85% or more.

[0029] Regarding the CrN coating, the preferred orientation based on XRD is 200, and the X-ray diffraction intensity ratio (200) / (111) between the (200) and (111) planes is 5.5 or more, preferably 6 or more, and more preferably 6.5 or more, thereby improving peel resistance. There is no upper limit to the X-ray diffraction intensity ratio (200) / (111), which is generally 20 or less, and can be 10 or less.

[0030] Regarding the CrN coating, in the grain size distribution determined by EBSD analysis, the proportion of grains smaller than 1 μm is 85% or more, preferably 86% or more, and more preferably 90% or more. This results in a dense CrN coating, which is less prone to crack bonding even if cracks occur, thus improving peel resistance. There is no upper limit to the proportion of grains smaller than 1 μm; it can be 100% or less, 99% or less, or 95% or less.

[0031] Regarding the CrN coating, according to the international standard for nanoindentation testing (ISO 14577-1), the plasticity power measured using a Vickers indenter is preferably 61% or more, more preferably 64% or more, and further preferably 69% or less. The CrN in this embodiment is a dense CrN coating with high plasticity power.

[0032] Furthermore, regarding the CrN coating, the microVickers hardness is preferably 800 HV or higher and 1300 HV or lower, more preferably 1100 HV or lower, and even more preferably 1000 HV or lower. The microVickers hardness of the coating is not too high, thus resulting in a non-brittle coating and improved peel resistance.

[0033] To obtain the CrN film of this embodiment, it is preferable to form the CrN film using the ion plating method described below. In particular, by changing the position and shape of the control magnet disposed around the cathode, the behavior of the arc point formed on the target surface during discharge can be changed, thereby controlling the physical properties of the CrN film.

[0034] Figure 1 This is a cross-sectional view of a piston ring as an example of this embodiment. The upper and lower surfaces and the sliding surface (left side in the figure) of the piston ring 10 have a CrN coating 12. In this embodiment, at least the sliding surface of the piston ring 10 has a CrN coating 12, but it may also have a CrN coating on other surfaces, such as the outer peripheral surfaces of the upper and lower surfaces. The thickness of the CrN coating on the sliding surface is not particularly limited, but is generally 3 μm or more, and can be 5 μm or more, and is also generally 50 μm or less, and can be 30 μm or less. It should be noted that the piston ring is one type of sliding member. Other sliding members include pistons, bearings, washers, and valve lifters.

[0035] In the case of piston rings, the base material 11 of the piston ring 10 can be any material that has been conventionally used as a piston ring base material, and the material is not particularly limited. For example, stainless steel or steel is preferred, and specifically, martensitic stainless steel or silicon-chromium steel is preferred.

[0036] Between the CrN coating and the piston ring substrate, a Cr-plated coating, a chromium nitride coating, a titanium nitride coating, etc., can be further formed; alternatively, a CrN coating can be formed directly on the piston ring substrate. Furthermore, when the substrate is stainless steel, a nitriding treatment can be applied to the substrate.

[0037] CrN films can be formed using physical vapor deposition methods such as ion plating and sputtering. An example of CrN film formation using ion plating is illustrated with accompanying figures.

[0038] Figure 2 This is a cross-sectional schematic diagram illustrating an example of an apparatus 20 for forming a CrN film using ion plating. A vacuum chamber 21 is connected to a gas inlet pipe 22 and a vacuum exhaust system piping 23. Furthermore, the temperature within the vacuum chamber 21 can be controlled by a heater (not shown). The apparatus 20 also includes a cathode 24 and an anode 25. A control magnet 26 is positioned at the top of the cathode 24 (the right end of the cathode in the figure), and plasma / ionization of the target material 27 is performed via arc discharge.

[0039] A piston ring is mounted on a rotating stage (not shown) inside the vacuum chamber 21. Nitrogen gas is introduced through the gas inlet pipe 22 while ionizing chromium, the target material, and depositing it onto the surface of the piston ring. The operating conditions of the device at this time can be as follows: the arc current is set to 100-200A, the bias voltage is set to 0-50V, the chamber pressure is set to 1-4Pa, and the heating temperature using the heater is set to 300-400℃.

[0040] The nitrogen content in CrN can be controlled by the internal pressure of the introduced gas and the nitrogen partial pressure.

[0041] Furthermore, the properties of the CrN film can also be controlled by changing the position / shape of the control magnets arranged around the cathode. For example, by arranging the magnets around the top of the cathode, the arc points are miniaturized, and the speed at which each arc point moves on the cathode surface is increased. The generated plasma extends to the vicinity of the piston rings, thus increasing the ionization rate and making it easier to form a denser CrN film.

[0042] Example

[0043] The present invention will be described in more detail below through embodiments, but the present invention is not limited to the following embodiments.

[0044] The physical properties of the film were measured using the following apparatus.

[0045] <X-ray Diffraction Measurement>

[0046] The preferred orientation of the coating based on XRD was determined using an XRD apparatus (Bruker AXS D8 DISCOVER). For the XRD tube and X-rays used, Cu and Kα rays were employed, and measurements were performed at a tube voltage of 40 kV and a tube current of 40 mA within the range of 2θ = 30°–90°. For the sample, a piston ring with a CrN coating on its outer peripheral surface was cut off, and X-rays were irradiated from its outer sliding surface side for measurement. Based on the obtained XRD pattern, the peak intensities of the (111) and (200) planes of CrN were determined, and their ratio was calculated.

[0047] <Crystal Size Determination (EBSD Analysis)>

[0048] The crystal grain size of the coating was determined using FE-SEM (JSM-7100F, NEC) and EBSD analysis software (TSL Digiview IV). Measurements were performed at an accelerating voltage of 15.0 kV, a measurement interval of 0.02 μm, and a measurement area of ​​20 × 20 μm. For the sample, a piston ring with a CrN coating on its outer peripheral surface was cut off for use. The outer peripheral sliding surface was ground with diamond slurry and then ultrasonically cleaned. Ar ion milling was performed to remove grinding marks, followed by electron beam irradiation from the outer peripheral side for measurement. For tilted samples, the electron beam was irradiated, and the reflected electron diffraction pattern (Kikuchi line) was measured based on the scattered electron beam. The Kikuchi line was analyzed, and an inverse pole figure was constructed along each crystal orientation. Based on the inverse pole figure, consecutive measurement points within an azimuth difference of less than 5° were defined as a single grain, and an inverse pole figure mapping was constructed within the measurement area. Based on the grain size measurement length of each grain using the inverse polar orientation diagram, the area ratio relative to the entire measurement area is calculated in 0.1 μm intervals. Based on the histogram of grain size distribution created in 0.1 μm intervals, the proportion (area ratio) of grains smaller than 1 μm relative to the entire measurement surface is calculated.

[0049] <Coating Components>

[0050] The coating composition was determined using EPMA. The EPMA determination was performed using Shimadzu EPMA-1720HT. Quantitative analysis was performed with an accelerating voltage of 15 kV, an irradiation current of 50 nA, an electron beam diameter of 100 μm, and pure Cr and BN as the standard samples. Samples were prepared in the same order as those used in EBSD. The intensity obtained from the standard sample was set as 100%, and the weight percentage of the sample was measured based on the ratio of the intensity to that of the unknown sample. For the elements being measured, the atomic percentages were calculated by normalizing the sum of the obtained weight percentages to 100%.

[0051] <Plastic Power>

[0052] The plastic power of the coating was determined using a FISCHER INSTRUMENTS nanoindentation tester, model HM-2000. Following the determination method of ISO 14577-1, a Vickers indenter was used, and the time until the indentation load reached 1000 mN (maximum indentation load) was set to 30 seconds. The specimen was obtained by cutting a piston ring with a CrN coating on its outer peripheral surface, embedding it in resin, and then grinding the outer peripheral surface, which served as the measurement surface, with sandpaper and diamond slurry. The plastic power was set as the plastic deformation power ηplast calculated from the load-indentation depth curve.

[0053] <Examples and Comparative Examples>

[0054] As the base material for the piston rings, steel equivalent to JIS G3651 SWOSC-V is prepared and machined into a piston ring shape (φ73.0mm × thickness 1.0mm). A simplified diagram is shown below. Figure 2 An apparatus for forming a CrN film using ion plating was used to form a CrN film on a piston ring substrate. The formation of the CrN film was carried out under the conditions shown in Table 1 below.

[0055] Next, the physical properties of the formed CrN films were measured. The results are shown in Table 2. It should be noted that all CrN films had a preferred orientation of 200. Furthermore, no grain sizes larger than 2.0 μm were found in the examples. The grain size of the CrN film from Example 1 is shown in Table 2. Figure 3 The grain size distribution of the CrN film in Example 1 is shown in... Figure 4 .

[0056] <Peel Resistance Test>

[0057] In the peel resistance test, the piston ring is pressed against the side of a disc rotating at a fixed speed, and the presence or absence of sliding surface damage (cracks, peeling) after a certain period of operation is used to evaluate the performance. For the determination of peel resistance, the case with no peeling on the sliding surface is designated as A, the case with peeling less than 100 μm of the maximum length is designated as B, and the case with peeling greater than 100 μm of the maximum length is designated as C. Figure 5 The diagram shows a cross-sectional schematic of a pin disc testing apparatus for peel resistance testing. In the pin disc testing apparatus 30, a pin (upper test piece) 32 is pressed against the side of a disc (lower test piece) 31 that rotates at a fixed speed. A piston ring is used as the pin (upper test piece) 32.

[0058] The test conditions were as follows: a load of 40 N, a speed of 5–10 m / s, a time of 5 minutes, and 0 W-20 lubricating oil. The disc was made of S45C material, and the surface roughness was 1.5 μm, calculated according to the ten-point average roughness Rzjis of JIS-B0601 (2001).

[0059] The determination method is as follows: images of the sliding marks are taken using a metallurgical microscope (Olympus GX71 inverted metallurgical microscope), and the maximum length of the peeling marks is determined using image analysis software (Olympus Stream industrial image analysis software).

[0060] [Table 1]

[0061] Arc current 100～200A bias voltage 0～50V Intracavitary pressure 1~4Pa Utilizing the heating temperature of the heater 300～400℃

[0062] [Table 2]

[0063]

[0064] Peel resistance tests were performed on the CrN films obtained in Examples 1-8 and Comparative Examples 1-4. The peel resistance tests were conducted as described above by observing the film surface after a pin-disc sliding test. A portion of the observation results and judgments are illustrated below. Figure 6 The results are shown in Table 2.

[0065] The results of the observations were that, although the CrN films of the examples showed localized cracks, these were CrN films that did not exhibit film peeling and CrN films with peeling sizes smaller than 100 μm in maximum length. On the other hand, the CrN films of the comparative examples showed cracks and peeling with a maximum length of 100 μm or more.

[0066] Explanation of reference numerals in the attached figures

[0067] 10: Piston ring; 11: Piston ring substrate; 12: CrN coating; 20: CrN coating forming apparatus; 21: Vacuum chamber; 22: Gas inlet pipe; 23: Vacuum exhaust system piping; 24: Cathode; 25: Anode; 26: Control magnet; 27: Target material; 30: Pin-disc test apparatus; 31: Disc (lower test piece); 32: Pin (upper test piece).

Claims

1. A sliding member, wherein, The sliding surface of the sliding member is coated with a CrN film. For the CrN coating, the preferred orientation based on XRD is 200, the X-ray diffraction intensity ratio of the (200) plane to the (111) plane is 5.5 or more, and in the grain size distribution determined by EBSD analysis, the proportion of grains with a diameter of less than 1 μm is 85% or more, and the plastic power of the CrN coating measured by Vickers indenter according to ISO14577-1 is 61% or more and 69% or less, where plastic power is the proportion of plastic deformation power in the total indentation work.

2. The sliding member according to claim 1, wherein, The sliding surface of the sliding member is covered by the CrN film. The micro Vickers hardness of the CrN coating is above 800 HV and below 1300 HV.

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