HARD CARBON FILM, MANUFACTURING METHOD FOR SAME, AND SLIDING MEMBER

Abstract

A hard carbon film that forms a sliding surface of a sliding member, wherein the hard carbon film includes terminal atoms that bond to carbon atoms and has a plurality of protruding shaped parts, part of which protrude from the surface thereof, with the periphery of each of the plurality of protruding shaped parts being terminated by a terminal atom. A manufacturing method for the hard carbon film for producing the hard carbon film on a sliding surface of the sliding member using arc vapor deposition having graphite as the vaporization source, wherein a gas containing the terminal atoms that bond to carbon atoms is introduced, and the plurality of protruding shaped parts is grown on the surface of the hard carbon film while terminating the periphery of the plurality of protruding shaped parts by bonding of the terminal atoms to carbon atoms.

Claims

1. A hard carbon film forming a sliding surface of a sliding member, the hard carbon film comprising: terminal atoms that bond to carbon atoms; and a plurality of protruding shaped parts each of which has a part projecting from a surface of the hard carbon film, wherein the periphery of each of the plurality of protruding shaped parts is terminated by the terminal atoms.

2. The hard carbon film according to claim 1, formed in a way that a hard carbon layer containing a larger amount of terminal atoms bonding to carbon atoms and a hard carbon layer containing a smaller amount of terminal atoms bonding to carbon atoms are alternately layered at a nano level.

3. The hard carbon film according to claim 1, wherein a distribution density of the protruding shaped parts increases toward the surface.

4. The hard carbon film according to claim 1, wherein among the plurality of protruding shaped parts, the number of protruding shaped parts growing from a position shallower than a depth of 1.5 μm from the surface is 90% or more of the entire plurality of protruding shaped parts.

5. The hard carbon film according to claim 1, wherein the terminal atoms are any one of hydrogen atoms, oxygen atoms, and fluorine atoms.

6. The hard carbon film according to claim 1, wherein a content of the terminal atoms in a region to a thickness of 0.3 μm at the beginning of deposition of the hard carbon film is lower than a content of the terminal atoms in a shallower region than the aforementioned region.

7. The hard carbon film according to claim 1, wherein a carbon layer having a higher content of terminal atoms than other parts is formed in a periphery of the protruding shaped parts.

8. The hard carbon film according to claim 5, wherein the terminal atoms are hydrogen atoms, and a content of hydrogen is 5 to 15 atom %.

9. The hard carbon film according to claim 1, wherein a nanoindentation hardness is 35 GPa or greater.

10. The hard carbon film according to claim 1, wherein a peak position of a G-peak in a Raman spectrum is higher in an inside than the surface.

11. The hard carbon film according to claim 1, wherein a carbon film with a lower hardness is further coated as an upper layer.

12. The hard carbon film according to claim 11, wherein the carbon film with a lower hardness is a carbon film having a content of hydrogen of 20 atom % or higher and less than 50 atom %.

13. The hard carbon film according to claim 11, wherein the carbon film with a lower hardness has an ID/IG ratio in a Raman spectrum of 0.7 or higher.

14. The hard carbon film according to claim 11, wherein the carbon film with a lower hardness contains any one of a metal element, silicon, nitrogen, and boron.

15. The hard carbon film according to claim 11, wherein a thickness of the carbon film with a lower hardness is 0.1 to 1.0 μm.

16. A sliding member to be used for sliding in an oil containing sulfurized molybdenum dialkyldithiocarbamate, wherein the hard carbon film according to claim 1 is formed on a sliding surface.

17. A manufacturing method for a hard carbon film for depositing a hard carbon film on a sliding surface of a sliding member using arc vapor deposition having graphite as a vaporization source, the method comprising: introducing a gas containing terminal atoms that bond to carbon atoms, causing a plurality of protruding shaped parts to grow on a surface of the hard carbon films while terminating a periphery of the plurality of protruding shaped parts by bonding the terminal atoms to the carbon atoms.

18. The manufacturing method for a hard carbon film according to claim 17, wherein, in the arc vapor deposition, the hard carbon film is deposited in a state in which the film is not irradiated with carbon ions coming from the graphite vaporization source at a regular time interval.

19. The manufacturing method for a hard carbon film according to claim 17, wherein a gas containing any one of hydrogen atoms, oxygen atoms, fluorine atoms is used as a gas containing terminal atoms that bond to carbon atoms, and wherein the hard carbon film is deposited while an amount of the gas introduced is caused to change over time.

20. The manufacturing method for a hard carbon film according to claim 17, wherein, in a region of a hard carbon film to a thickness of 0.3 μm at the beginning of deposition, the hard carbon film is deposited by reducing an amount of the gas introduced at the beginning of deposition compared with an amount of the gas introduced for other regions.

21. The manufacturing method for a hard carbon film according to claim 17, wherein the hard carbon film is deposited while introducing Ar gas together with the gas containing terminal atoms that bond to carbon atoms.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0077] FIG. 1 is a schematic diagram illustrating a cross-section of a hard carbon film according to an embodiment of the present disclosure.

[0078] FIG. 2 is a schematic diagram illustrating a surface of the hard carbon film according to an embodiment of the present disclosure.

[0079] FIG. 3 is a TEM image (bright field image) of a cross-section of a hard carbon film according to an embodiment of the present disclosure.

[0080] FIG. 4 is an enlarged view of the vicinity of the interface between the hard carbon film shown in FIG. 3 and a protruding shaped part.

[0081] FIG. 5 is an enlarged view of the vicinity of the interface between the hard carbon film shown in FIG. 3 and a protruding shaped part.

[0082] FIG. 6 is a schematic diagram illustrating a cross-section of a hard carbon film covered by a carbon film having low hardness.

[0083] FIG. 7 is a graph showing a distribution of hydrogen atoms in a hard carbon film part of Example 1-1 obtained from TOFU-SIMS in the depth direction.

[0084] FIG. 8 is a graph showing a distribution of hydrogen atoms in a protruding shaped part of Example 1-1 obtained from TOF-SIMS in the depth direction.

[0085] FIG. 9 shows cross-sectional SEM images from Example 1-1 and Comparative example 1-1.

[0086] FIG. 10 shows enlarged photos showing states of surfaces before and after a lapping process.

[0087] FIG. 11 shows views of three-dimensional shapes of surfaces after a lapping process obtained through SPM measurement.

[0088] FIG. 12 is an explanatory diagram of a sliding test.

[0089] FIG. 13 shows SEM images of a sliding surface of each specimen after two hours of an SRV test.

[0090] FIG. 14 is a graph showing change of a friction coefficient over time in a sliding test.

DESCRIPTION OF EMBODIMENTS

[0091] The present disclosure will be described based on embodiments using the appended drawings below. Furthermore, although a vacuum arc vapor deposition will be exemplified as an arc vapor deposition below, there is no limitation to arc vapor deposition. In addition, although hydrogen atoms are used as terminal atoms that bond to carbon atoms, the terminal atoms may be oxygen atoms or fluorine atoms.

[1] Configuration of Hard Carbon Film

[0092] FIG. 1 is a schematic diagram illustrating a cross-section of a hard carbon film according to the present embodiment, and FIG. 2 is a schematic diagram illustrating a surface of the hard carbon film according to the present embodiment. Furthermore, in FIGS. 1 and 2, 2 denotes the hard carbon film, 3 denotes an protruding shaped part, 5 denotes a base material, 2a denotes an outermost surface part of the hard carbon film 2, 3a denotes a part of the protruding shaped part 3 protruding from a surface of the hard carbon film 2, 3b denotes a part of the protruding shaped part 3 below the surface of the hard carbon film 2, 3c denotes a side outer circumferential part of 3b, 2b denotes a surface part of the hard carbon film 2 facing 3c, and 3d denotes an outermost surface part of the protruding shaped part 3. In addition, 4 denotes a bottom of the protruding shaped part 3 that is a part of a periphery at the 3b below the surface of the hard carbon film 2, 2c denotes a surface part of the hard carbon film 2 facing 4, and 7 denotes a boundary between the protruding shaped part 3 and the hard carbon film 2 on a film surface. Furthermore, D denotes a depth of the protruding shaped part 3 from the surface of the hard carbon film 2.

[0093] As illustrated in FIGS. 1 and 2, the hard carbon film 2 according to the present embodiment is formed on the base material 5 and has a plurality of protruding shaped parts 3 each of which is a part protruding from the surface of the hard carbon film.

[0094] In the present embodiment, the hard carbon film 2 is deposited using a vacuum arc vapor deposition, and thus the protruding shaped parts 3 are formed toward the surface of the hard carbon film 2. However, since a gas containing hydrogen atoms, such as a hydrocarbon gas or hydrogen gas is introduced during deposition in the present embodiment, the surface parts 2b and 2c of the hard carbon film 2 and the outer circumferential part 3c and the bottom 4 of the protruding shaped part 3 are covered by a hydrogen-containing carbon film terminated by hydrogen atoms bonding to carbon atoms.

[0095] Since the protruding shaped parts 3 whose periphery is covered by the hydrogen-containing carbon film as described above are inhibited from bonding to the deposited hard carbon film 2, cracking may be caused to easily occur at the interface between the hard carbon film and the protruding shaped parts, and thus the protruding shaped parts can fall off and be removed even in a weak lapping process, the hard carbon film can be easily smoothed, and aggressiveness to counterpart materials can be significantly reduced.

[0096] In addition, the recess formed after the protruding shaped part falls off functions as an oil reservoir during sliding in an oil, and thus a friction coefficient of the hard carbon film can be drastically reduced.

[0097] Accordingly, the hard carbon film according to the present embodiment can exhibit not only excellent wear resistance which is a characteristic of hard carbon films deposited in the vacuum arc vapor deposition but also excellent low abrasiveness.

[0098] However, when a hard carbon film produced in an arc vapor deposition is deposited in a state in which the film is continuously irradiated with a graphite vaporization source and thus carbon ions are generated as described above, even if a hydrocarbon gas is introduced during the deposition, the supply of hydrogen atoms serving for bonds is insufficient for the generated carbon ions, and thus it is difficult to sufficiently terminate dangling bonds on the surface of the hard carbon film.

[0099] Thus, in the present embodiment, it is desirable to set a state in which a film is periodically irradiated with carbon ions coming from the graphite vaporization source at the time of deposition as described above. Accordingly, a hard carbon layer containing a larger amount of hydrogen and a hard carbon layer containing a smaller amount of hydrogen are alternately layered at a nano level, and dangling bonds in the hard carbon layer formed on the surface can be sufficiently terminated.

[0100] FIG. 3 is a transmission electron microscope (TEM) image (bright field image) of a cross-section of a hard carbon film deposited as described above. In addition, FIG. 4 and FIG. 5 are enlarged views of the vicinity of the interface between the hard carbon film shown in FIG. 3 and a protruding shaped part. Further, in FIG. 3 to FIG. 5, a carbon film 6 having low hardness, which will be described below, is layered.

[0101] As shown in FIG. 3, there is a region brighter than other parts around the hard carbon film 2 and the protruding shaped part 3, particularly, between the bottom 4 of the protruding shaped part 3 and the hard carbon film 2, and the presence of a low density layer with a high content of hydrogen and a void caused by cracking in the region is indicated.

[0102] Furthermore, it is found from FIG. 4 and FIG. 5 that a super-multilayer structure in which thick bright layers and dark layers are alternately layered at a nano level is formed in the hard carbon film 2.

[0103] Further, the protruding shaped part 3 is not likely to fall off from the hard carbon film 2 when the protruding shaped part 3 is formed at a deep position close to the substrate side, and therefore, if a film thickness of the hard carbon film 2 is thick, it is preferable to reduce the protruding shaped parts 3 formed at deep positions by using a deposition technique and deposition conditions that are likely to generate less protruding shaped parts 3 at the beginning of deposition, for example, deposition using simple filtering with a shielding plate, using a low arc current, or the like, and returning to a predetermined deposition technique or deposition conditions toward the surface of the hard carbon film 2.

[0104] Specifically, it is preferable for D to be 90% or more of the entire protruding shaped part 3 that is formed at a depth of 1.5 μm or less.

[0105] In addition, considering the protruding shaped part 3 easily falling off from the hard carbon film 2, although a higher content of terminal atoms is better, a higher overall content of terminal atoms inside the hard carbon film 2 leads to a decrease in hardness thereof, which may cause deterioration in wear resistance. For this reason, it is preferable for a content of terminal atoms in the periphery 3c and the bottom 4 of the protruding shaped part 3 and the surface 2b and 2c of the hard carbon film 2 facing 3c and 4 to be higher than a content of terminal atoms in other parts of the hard carbon film 2.

[0106] When Ar gas is introduced together with a gas containing terminal atoms during the deposition of the hard carbon film 2, some of terminal atoms in the surface 2a of the hard carbon film 2 and the surface 3d of the protruding shaped product 3 are removed due to the effect of physical etching using Ar ions. Meanwhile, since an electric field is concentrated on the protruding protrusion product 3 on the boundary part 7 between the hard carbon film 2 and the protruding shaped part 3, the electric field becomes weak, physical etching using Ar ions becomes weak, and thus it becomes difficult for the terminal atoms to be removed. Therefore, the situation causes a state in which the surface 2b and the surface 3c having a higher content of terminal atoms than other parts are easily formed.

[0107] Furthermore, in order to make the protruding shaped part 3 more easily fall off, it is preferable for a content of hydrogen in the hard carbon film 2 to be 5 to 15 atom %, and at this time, it is preferable for a nanoindentation hardness to be 35 GPa or greater.

[0108] In addition, it is preferable for the peak position of the G-peak of the hard carbon film 2 in a Raman spectrum to be higher in the inside of the hard carbon film than the surface thereof, thus a hard carbon film having a high content of hydrogen in the surface and a low content of hydrogen in the inside is deposited, and therefore, a hard carbon film formed with the supply of hydrogen atoms that are terminal atoms in a sufficient amount to the surface can be provided.

[2] Manufacturing Method for Hard Carbon Film

[0109] A hard carbon film according to the above-described embodiment can be manufactured through the following steps.

[0110] 1. Preparation of Base Material

[0111] First, a base material for forming a hard carbon film is prepared and set in a deposition tank. At that time, a noble gas such as Ar gas or hydrogen gas is introduced into the film to a deposition tank to generate plasma, a bias voltage is applied to the base material, and thereby dirt and an oxide layer on the surface of the base material on which a hard carbon film is to be formed are desirably removed.

[0112] Then, if a metal film as an intermediate layer is formed in advance on the surface on which a hard carbon film is formed from which dirt and the oxide layer have been removed, adhesion with the hard carbon film can be desirably enhanced. Further, the intermediate layer (metal film) can be formed using the vacuum arc vapor deposition which uses a metal raw material such as Cr or W as an arc vaporization source.

[0113] 2. Formation of Hard Carbon Film

[0114] A hard carbon film is formed on the base material using the vacuum arc vapor deposition which uses a Graphite cathode as an arc vaporization source. At that time, a gas containing hydrogen atoms as terminal atoms like a hydrocarbon gas such as methane gas or acetylene gas or hydrogen gas is introduced into the deposition tank. Accordingly, the carbon around the protruding shaped products that grow having, as the nuclei, graphite fine particles scattering from the graphite vaporization source can be terminated by the hydrogen, and the carbon on the surface of the hard carbon film being deposited can be terminated by hydrogen. As a result, bonding of the protruding shaped products to the hard carbon film can be suppressed, and thus the protruding shaped products can be caused to easily fall off from the hard carbon film.

[0115] In that case, it is preferable to control the introduction of the gas so that a content of hydrogen in the deposited hard carbon film is 5 to 15 atom %, and a hard carbon film containing a high content of hydrogen can be formed by increasing the amount of gas introduced. By controlling the introduction of the gas so that a content of hydrogen in the hard carbon film is 5 to 15 atom %, the hard carbon film from which protruding shaped products can be easily removed while maintaining high hardness can be obtained.

[0116] In addition, it is preferable to deposit the hard carbon film by setting the amount of the gas introduced into the region of the hard carbon film to a thickness of 0.3 μm at the beginning of deposition smaller than that introduced into the deeper region so that a content of terminal atoms in the region to the thickness of 0.3 μm at the beginning of deposition is lower than that of terminal atoms in the region deposited thereafter. Accordingly, by reducing the supply of hydrogen atoms serving as terminal atoms in the region with a smaller number of protruding shaped products, durability can be increase in the entire film while facilitating removal of the protruding shaped products.

[0117] Further, when carbon ions are continuously generated from the graphite vaporization source and the base material is irradiated with the carbon ions during the deposition, the supply of hydrogen atoms serving as terminal atoms is insufficient for the generated carbon ions even if a gas is introduced, and thus it is not possible to sufficiently terminate the bond of the hydrogen to the carbon on the surface of the hard carbon film, and it is difficult to sufficiently suppress the bonding of the protruding shaped products to the hard carbon film unless a larger amount of gas is introduced.

[0118] Therefore, it is preferable for the hard carbon film not to be periodically irradiated with carbon ions coming from the graphite vaporization source. While the film is not irradiated with carbon ions coming from the graphite vaporization source, the supply of hydrogen atoms increase, thus the surface of the hard carbon film can be subjected to sufficient termination even if a small amount of gas is introduced, and therefore the bonding of the protruding shaped products to the hard carbon film can be sufficiently suppressed.

[3] Coating of Low-Hardness Carbon Film

[0119] In the present embodiment, a carbon film with a lower hardness than the above-described hard carbon film may be coated as an upper layer of the hard carbon film. FIG. 6 is a schematic view of a cross-section of the hard carbon film whose upper layer has been coated with a low-hardness carbon film.

[0120] With respect to the hard carbon film formed as described above, since the protruding shaped parts 3 can easily fall off from the hard carbon film 2 as described above, in a case where a lapping treatment is performed after a low-hardness carbon film 6 is coated, the protruding shaped parts 3 can be easily removed even in a weak lapping treatment that is not likely to affect the low-hardness carbon film 6. In addition, since the low-hardness carbon film 6 is coated on the hard carbon film 2 even after the lapping treatment, a more excellent abrasion reduction effect can be obtained in comparison to a case of the hard carbon film 2 alone.

[0121] In addition, since the high-hardness hard carbon film 2 exists on the base material 5 even if the low-hardness carbon film 6 is abraded, seizure does not occur between sliding counterpart materials. Furthermore, even when the low-hardness carbon film 6 undergoes wear, the sliding surface is smoothed due to the wear of the low-hardness carbon film 6, a low friction coefficient can be maintained as before.

[0122] A content of hydrogen in the low-hardness carbon film 6 is preferably 20 atom % or higher. In addition, an ID/IG value of a Raman spectrum is preferably 0.7 or more.

[0123] Accordingly, a dramatic effect attributable to the coating of the above-described low-hardness carbon film 6 can be exhibited.

[0124] In addition, the low-hardness carbon film 6 may contain metal elements of Cr, Fe, W, Ti, and the like, silicon, nitrogen, and boron, thus generation of a tribofilm is promoted or occurrence of abnormal wear is suppressed, and therefore low abrasiveness can be exhibited.

[0125] Further, in the present embodiment, a thickness of the low-hardness carbon film 6 is preferably 0.1 to 1.0 μm in order to sufficiently exhibit the above-described effects.

[0126] Although the low-hardness carbon film may be coated as described above using a deposition apparatus different from that for the hard carbon film, there is concern of the adhesion of the low-hardness carbon film to the hard carbon film deteriorating since the surface of the hard carbon film deposited first is exposed to the air and dirt in that case, and therefore, it is preferable to deposit the hard carbon film and then consecutively deposit and coat the low-hardness carbon film thereon in the same apparatus.

[0127] In the present embodiment, the hard carbon film is deposited on the base material in the vacuum arc vapor deposition apparatus, a rare gas such as Ar gas and a hydrocarbon gas are introduced, a bias voltage is applied to the base material to cause self-discharge CVD discharge, and thereby the low-hardness carbon film is deposited and coated on the hard carbon film.

[0128] Specifically, the present inventor has ascertained that the friction coefficient greatly dropped in comparison to the case of a hard carbon film alone when the gas containing hydrogen atoms was introduced to deposit the hard carbon film having a thickness of 1 μm on the base material, a hydrocarbon gas was introduced thereto, and the low-hardness carbon film was deposited and coated thereon using a self-discharge plasma CVD method in which a DC voltage is applied to the base material.

[0129] Further, as another deposition method of depositing and coating a low-hardness carbon film, a CVD method of using CVD discharge with an external plasma source, a reactive sputtering method of having a graphite cathode as a sputtering source, introducing a rare gas such as Ar gas and a hydrocarbon gas, and depositing a film, or the like can be used.

[0130] In addition, a hard carbon film having a high content of hydrogen can also be deposited and coated as a low-hardness carbon film using vacuum arc vapor deposition which is the same as the deposition method of the hard carbon film. However, when this method is employed, an amount of gas introduced needs to be increased to increase a content of hydrogen. As a result, gas pressure in the deposition tank rises, and arc discharge (arcing) easily occurs on the base material on which the hard carbon film has been deposited. In addition, an amount of ions radiated onto the base material (an amount of current flowing to the base material) on which the hard carbon film has been deposited increases, which leads to an abrupt temperature increase, and thus there is concern of the hard carbon film being carbonized. Considering the above description, the above-described CVD method or reactive sputtering method is preferably employed as a deposition method of depositing and coating the low-hardness carbon film.

[4] Application of Hard Carbon Film to Sliding Member

[0131] A sliding member whose sliding surface has a hard carbon film according to the above-described embodiment can exhibit sufficient wear resistance by suppressing abrasive wear caused by falling protruding shaped part even when the sliding member slides in an oil, and can bring a dramatic reduction in a friction coefficient since recesses generated after the protruding shaped parts fall off function as oil reservoirs. In addition, in a case where the oil is oil containing MoDTC, abnormal wear does not occur in the hard carbon film, and since a low-hardness carbon film is further coated as an upper layer of the hard carbon film, the low-hardness carbon film is removed in an early stage due to abnormal wear, a surface suitable for sliding is formed in a shorter period of time, and therefore, a lower friction coefficient can be expected.

[0132] Further, examples of the sliding member that slides in oil containing MoDTC may include, for example, engine parts such as valve lifters, piston pins, piston rings, bearings, pistons, pulp, fuel injection plungers, and the like.

[0133] Further, when the sliding member is produced, the hard carbon film according to the present embodiment can allow most protruding shaped parts to be removed in an initial stage of sliding even if the lapping treatment is not performed thereon after the deposition since bonding of the hard carbon film to the protruding shaped parts is very weak and the protruding shaped parts can be caused to easily fall off therefrom, and the lapping treatment is unnecessary in an environment in which running-in can be performed. In addition, even in a case where the lapping treatment is to be performed, the protruding shaped parts can be easily removed in a weaker lapping treatment than for a conventional hard carbon film that is produced in vacuum arc vapor deposition, for example, aero-lapping, or the like.

EXAMPLE

[1] Evaluation on Characteristics of Hard Carbon Film

[0134] First, an evaluation test for characteristics of a hard carbon film was conducted.

[0135] 1. Production of Specimen

(1) Example 1-1

[0136] A hard carbon film having a thickness of 1.0 μm was deposited by using a carburized disc (31 mm in diameter (φ)×3 mm in thickness (t), HRC 60, and surface roughness Ra<0.01 μm) formed of SCM 415 as a base material, and introducing a gas containing hydrogen atoms onto the base material using arc vapor deposition.

[0137] Specifically, first, the base material with the surface from which dirt and an oxide layer had been removed beforehand was set in a jig inside a deposition apparatus, and a Cr film having a thickness of 50 nm was formed as an intermediate layer on the deposition target surface using an arc ion plating method using Cr as an arc vaporization source.

[0138] Next, while vaporizing a graphite cathode through arc discharge, Ar gas and methane gas were introduced from outside, and a hard carbon film having a thickness of 1.0 μm was deposited on the base material. Further, at this time, by rotating the jig on which the base material was set, deposition is performed while a time in which carbon ions are not periodically radiated from the graphite vaporization source is set, and the content of hydrogen in the hard carbon film was controlled at 5 to 15 atom %.

(2) Example 1-2

[0139] A hard carbon film having a thickness of 1.0 μm was first deposited on a base material on which an intermediate layer had been formed likewise similarly to Example 1-1. Then, Ar gas and acetylene gas were introduced into the same deposition apparatus, self-discharge CVD discharge was generated by applying a bias voltage of 600 V thereto at a gas pressure of 3.0 Pa, and thereby a low-hardness carbon film having a thickness of 0.3 μm was deposited and coated on the hard carbon film.

(3) Comparative Example 1-1

[0140] A hard carbon film having a thickness of 1.0 μm was deposited on the same base material using conventional vacuum arc vapor deposition in which no gas is introduced. Specifically, the hard carbon film was deposited on the base material on which an intermediate layer had been formed as in Example 1-1 and Example 1-2 by introducing only Ar gas from outside while vaporizing a graphite cathode through arc discharge.

[0141] 2. Evaluation of Film Characteristics

[0142] Each of the hard carbon films obtained in Example 1-1, Example 1-2, and Comparative example 1-1 was evaluated for the following items.

[0143] (1) Content of Hydrogen

[0144] A content of hydrogen in each of the hard carbon films was measured using Rutherford Backscattering Spectrometry (RBS).

[0145] As a result, it was ascertained that the content was 11 atom % in Example 1-1, and 11 atom % in the hard carbon film and 23 atom % in the low-hardness carbon film in Example 1-2. In addition, the content was equal to or lower than the measurement limit in Comparative example 1-1.

[0146] In addition, in Example 1-1, when an amount of hydrogen in the hard carbon film part in the depth direction was measured using Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), it was ascertained that the amount of hydrogen increased and decreased for every 2 to 4 nm as shown in FIG. 7. Furthermore, in measurement of the protruding shaped parts in the depth direction, it was ascertained that there were portions having a particularly large amount of hydrogen in the film and that there were portions a particularly large amount of hydrogen in regions at a depth of 0.55 to 0.63 μm between the protruding shaped parts and the hard carbon film as shown in FIG. 8. In FIGS. 7 and 8, the vertical axis represents intensity and the horizontal axis represents depth from the surface.

[0147] (2) sp.sup.3/(sp.sup.3+sp.sup.2) Ratio

[0148] The hard carbon films have a mixture of a sp.sup.2 structure and a sp.sup.3 structure, a hardness of the hard carbon film changes according to a ratio thereof (sp.sup.3/(sp.sup.3+sp.sup.2) ratio), and specifically, a hardness becomes higher as a ratio of sp.sup.3 become higher.

[0149] In addition, since the sp.sup.3/(sp.sup.3+sp.sup.2) ratio is correlated with the (ID/IG) ratio based on a Raman spectrum, the value can be estimated from a result of Raman spectroscopy by using a calibration curve.

[0150] Specifically, Raman spectroscopy was performed by radiating laser light having a wavelength of 532 nm using NRS-5100 manufactured by JASCO Corporation. The obtained Raman spectrum was separated into two waveforms of the D-peak and G-peak that are often used for analysis of hard carbon films and interpreted. Specifically, a straight base line was drawn between 900 cm.sup.−1 and 1800 cm.sup.−1, the base line was processed to be zero, the D-peak centered around 1350 cm.sup.−1 and the G-peak centered around 1550 cm.sup.−1 were fitted to a Gaussian function and separated, and the area ID of the D-peak and the area IG of the G-peak were quantified.

[0151] A sp.sup.3/(sp.sup.3+sp.sup.2) ratio was obtained using the following empirical formula (Formula 1) based on the ID/IG area ratio obtained in Raman spectroscopy. This empirical formula can be used as a formula for estimating the sp.sup.3/(sp.sup.3+sp.sup.2) ratio since a good correlation was found by taking the correlation between the Raman spectroscopy result of various hard carbon films and the analysis result of the sp.sup.3/(sp.sup.3+sp.sup.2) ratio using nuclear magnetic resonance (NMR).

sp.sup.3/(sp.sup.3+sp.sup.2)ratio=55.5X.sup.2−163.9X+142.0  (Formula 1)

[0152] ※ X: ID/IG area ratio

[0153] As a result, it was ascertained that the ratio was 0.76 (ID/IG of 0.46) in Example 1-1, and the ratio of the hard carbon film was 0.76 (ID/IG of 0.46) and the ratio of the low-hardness carbon film was 0.43 (ID/IG of 0.85) in Example 1-2. In addition, the ratio was 0.90 (ID/IG of 0.36) in Comparative example 1-1.

[0154] (3) Film Hardness (Nanoindentation Hardness)

[0155] A nanoindentation hardness was measured as film hardness of each of the hard carbon films. Specifically, a nanoindentation hardness was measured at a load of 300 mgf using ENT-1100a that is an indentation hardness meter manufactured by Elionix Inc.

[0156] As a result, it was ascertained that the hardness was 38 GPa in Example 1-1, and the hardness of the hard carbon film was 38 GPa and the hardness of the low-hardness carbon film was 23 GPa in Example 1-2. In addition, it was ascertained that the hardness was 55 GPa in Comparative example 1-1.

[0157] (4) SEM Image

[0158] FIG. 9 shows cross-sectional SEM images from Example 1-1 and Comparative example 1-1. According to FIG. 9, there are no spots having a significantly different contrast other than below the protruding shaped products indicated by the dotted lines in Comparative example 1-1. This indicates that the hard carbon films and the protruding shaped products were combined and continuous, which caused the protruding shaped products not to easily fall off. Meanwhile, in Example 1-1, contrasts around the protruding shaped products are significantly different as indicated by the dotted lines, and thus it is ascertained that the bonding of the hard carbon film to the protruding shaped products was weak and the protruding shaped products could easily fall off.

[0159] (5) Surface Roughness Measurement

[0160] Surface roughness of each of the hard carbon films was measured under the following measurement conditions using SPM-9700 manufactured by Shimadzu Corporation.

[0161] Scanner: 30 μm

[0162] Observation mode: Dynamic

[0163] X-Y scanning range: 30 μm

[0164] Scanning speed: 0.6 Hz

[0165] Number of pixels [0166] X: 256 pixels [0167] Y: 256 pixels

[0168] Scanning mode: Same height

[0169] As a result, it was ascertained that Rz in Example 1-1 was 0.949 μm, Rz in Example 1-2 was 0.999 μm, and Rz in Comparative example 1-1 was 0.839 μm.

[0170] (6) Lapping Test

[0171] In order to investigate ease of removal of the protruding shaped parts, a lapping process was performed on the hard carbon films produced in Example 1-1 and Comparative example 1-1 using AERO LAP YT-300 manufactured by Yamashita Works Co., Ltd., under the following conditions, and then surface roughness was measured.

[0172] Speed of conveyer: 50

[0173] Lapping time: 3 minutes

[0174] As a result, the surface roughness Rz in Example 1-1 was 0.323 μm, the surface roughness Rz in Comparative example 1-1 was 0.696 μm, and therefore it was found that the surface roughness was substantially halved even with the lapping process for a short period of time.

[0175] In addition, FIG. 10 shows enlarged photos of the surface states before and after the lapping process, and FIG. 11 shows views of the three-dimensional shapes of the surfaces after the lapping process measured through SPM. It was ascertained from FIG. 11 that, while most of the surface of the hard carbon film of Comparative example 1-1 had a convex structure including many remainder of the protruding shaped parts, the surface of the hard carbon film of Example 1-1 had less convex structure due to many removed protruding shaped parts and was sufficiently smoothed.

[2] Evaluation of Sliding Property of Sliding Member

[0176] Next, a test for evaluating a sliding property of a sliding member having the hard carbon film was performed.

[0177] 1. Production of Specimen

[0178] A specimen of Example 2-1 was produced by deposition a hard carbon film in a similar manner as in Example 1-1 using a carburized material cylinder SCM 415 as a base material (15 mm in diameter (φ)×22 mm in length (L), HRC 60). Then, the specimen of Example 2-2 was produced by depositing the hard carbon film on which the low-hardness carbon film was coated in the similar manner as in Example 1-2, and the specimen of Comparative example 2-1 was produced by depositing the hard carbon film in the similar manner as in Comparative example 1-1. In addition, the specimen of Comparative example 2-2 was produced by depositing the hard carbon film on the base material using a CVD method.

[0179] 2. Sliding Test Method

[0180] A sliding test was performed on each of the produced specimen by using a steel disk (100CR6 (DIN standard)) as a sliding object.

[0181] Specifically, the sliding test (SRV test) was performed to evaluate sliding characteristics by causing a cylinder 41 on which the hard carbon film was formed to reciprocally slide against the steel disk 42 using a Schwingungs Reihungund and Verschleiss (SRV) tester manufactured by Optimol Instruments as illustrated in FIG. 12.

[0182] Further the test conditions in that case were as follows. [0183] Load: 100 N (50 N only at the time of prior running-in) [0184] Frequency: 33 Hz [0185] Amplitude: 1.5 mm [0186] Time: 120 minutes (5 minutes for prior running-in) [0187] Temperature: 80° C. [0188] Oil: MoDTC-added OW-16

[0189] 3. Test Result

[0190] (a) Surface State and Cross-Section State

[0191] The SEM images of the sliding surfaces of the specimen after two hours of the SRV test are shown in FIG. 13.

[0192] While abnormal wear did not occur in Comparative example 2-1 as is known from the past, the holes were formed in the parts indicated by the arrows after the protruding shaped parts had fallen off, scratches were visible in the reciprocating movement directions around the holes, and therefore it is ascertained from FIG. 13 that abrasive wear attributable to the falling protruding shaped part had occurred. In addition, it is ascertained from Comparative example 2-2 that wear had progressed to the base material due to abnormal wear.

[0193] On the other hand, since abnormal wear did not occur and the protruding shaped parts were removed before sliding in Example 2-1, it is ascertained that abrasive wear resulting from falling of the protruding shaped parts did not occur. In addition, it is ascertained that, although the hard carbon film was partly exposed due to abnormal wear of the low-hardness carbon film in Example 2-2, no further wear progressed. Accordingly, it was ascertained that the abrasive wear of the hard carbon films of Example 2-1 and Example 2-2 caused by the falling of the protruding shaped parts was suppressed.

[0194] (b) Friction Coefficient

[0195] The change of the friction coefficient of each specimen over time during the sliding test is shown in FIG. 14.

[0196] It is ascertained from FIG. 14 that, in Comparative example 2-1, the friction coefficient increases over time and the protruding shaped parts that had fallen off were caught in sliding and thus stable sliding was not possible. Meanwhile, it is ascertained that, while a comparatively high friction coefficient was shown in Example 2-1 as in Comparative example 2-1, the behavior of the friction coefficient was stable.

[0197] In addition, it is ascertained that, while a low friction coefficient was shown in the beginning of sliding in Comparative example 2-2, an increase of the friction coefficient is shown from halfway, and then a low friction coefficient is shown again and reduced to a substantially half of that of Comparative example 2-1.

[0198] The reason for the cause of the changes of the friction coefficients can be considered as follows. That is, it is known that, in a case where a hard carbon film containing a high content of hydrogen is caused to slide in oil containing MoDTC, a low friction coefficient is shown due to a reaction of MoDTC, abnormal wear occurs at the same time, and thus the hard carbon film wears soon. Also in Comparative example 2-2, while a low friction coefficient was shown since the low-hardness carbon film (CVD-hard carbon film) containing a high content of hydrogen existed in the beginning of sliding, the CVD-hard carbon film wore out due to abnormal wear. Then, the friction coefficient became unstable when the steel serving as a base material began to be exposed. However, since the MoDTC-derived tribofilm was gradually formed on the steel thereafter, it is considered that the friction coefficient began to decrease with the formation of the tribofilm.

[0199] Meanwhile, in Example 2-2, the lower friction coefficient than in Comparative example 2-2 was shown consistently from the beginning of sliding. The decrease in the friction coefficient in the beginning of sliding is considered as the effect of the coated low-hardness carbon film (CVD-hard carbon film). The abnormal wear of the CVD-hard carbon film caused by MoDTC was mild wear while the speed of wear was high, and no abrasive wear occurred in the sliding part since the protruding shaped parts of the hard carbon film fell off, and thus, the hard carbon film and the sliding surface of the counterpart material were nicely flattened, and thus a surface suitable for sliding was formed. For this reason, the CVD-hard carbon film worn out, and even if the hard carbon film was exposed, the surface suitable for sliding was already formed, and therefore, it is considered that the low friction coefficient could be maintained.

[0200] Although the present disclosure has been described above based on the embodiments, the present disclosure is not limited thereto. Various modifications can be made on the above-described embodiments within a scope equal or equivalent to the present disclosure.

REFERENCE SIGNS LIST

[0201] 2 Hard carbon film [0202] 2a Outermost surface part of hard carbon film [0203] 2b Surface part of hard carbon film facing side outer circumferential part of protruding shaped part [0204] 2c Surface part of hard carbon film facing bottom of protruding shaped part [0205] 3 Protruding shaped part [0206] 3a Part of protruding shaped part protruding from surface of hard carbon film [0207] 3b Part of protruding shaped part below surface of hard carbon film [0208] 3c Side outer circumferential part of protruding shaped part below surface of hard carbon film [0209] 3d Outermost surface part of protruding shaped part [0210] 4 Bottom of protruding shaped part below surface of hard carbon film [0211] 5 Base material [0212] 6 Low-hardness carbon film [0213] 7 Boundary between protruding shaped part and hard carbon film on film surface [0214] 41 Cylinder [0215] 42 Steel disk [0216] D Depth of protruding shaped part from surface of hard carbon film