Coating film, method for manufacturing same, and PVD apparatus

Abstract

Provided is a physical vapor deposition (PVD) method in which a thick, hard carbon film having excellent durability can be formed, and chipping resistance and wear resistance can bot be achieved while improving the low friction properties and peeling resistance of the formed hard carbon film. Provided is a coating film having a total film thickness of greater than 1 μm and less than or equal to 50 μm, wherein, when observed using a bright field TEM image, the cross section of the coating film is revealed to consist of relatively white hard carbon layers and relatively black hard carbon layers alternately stacked in the thickness direction, and the white hard carbon layers have a region having a columns-shape, which has grown in the thickness direction.

Claims

1. A coating film, coated on a substrate surface, wherein when a cross-section is observed through a bright-field TEM image, white hard carbon layers shown as relatively white and black hard carbon layers shown as black are alternately laminated in a thickness direction to have a total film thickness ranging from 1 μm to 50 μm, and the white hard carbon layers have regions that are grown in a columns-shape in the thickness direction, wherein the columns-shape have structures that (002) surfaces are in parallel with the substrate, and a c-axis grows perpendicular to the substrate.

2. The coating film according to claim 1, further comprising an adhesion layer comprising relatively-white hard carbon in between the white hard carbon layer shown as relatively white and the black hard carbon layer shown as black when the cross-section is observed through the bright-field TEM image.

3. The coating film according to claim 2, wherein a sp.sup.2/sp.sup.3 ratio of the adhesion layer comprising the white hard carbon is 0.4-0.9.

4. The coating film according to claim 1, wherein a sp.sup.2/sp.sup.3 ratio of the black hard carbon layer is 0.1-0.45.

5. The coating film according to claim 1, wherein a sp.sup.2/sp.sup.3 ratio of the white hard carbon layer is 0.45-0.85.

6. The coating film according to claim 1, wherein when electron beam diffraction is performed to the white hard carbon layers, diffraction spots are shown at positions with a lattice spacing of 0.3-0.4 nm, and the (002) surfaces are aligned so as to become a direction of lamination on the substrate.

7. The coating film according to claim 1, wherein an electrical resistance on the coating film surface of a member having the coating film is 0.1-1000 Ω.

8. The coating film according to claim 1, wherein a thickness of each layer of the white hard carbon layers is 20-2000 nm, and a thickness of each layer of the black hard carbon layers is 20-1000 nm.

9. The coating film according to claim 8, wherein a ratio of the thickness of the white hard carbon layer to the thickness of the black hard carbon layer changes in the thickness direction of the coating film, and increases from the substrate side toward a surface side.

10. The coating film according to claim 1, wherein a hydrogen content of the black and/or the white hard carbon layers is below 10 atom %.

11. The coating film according to claim 1, wherein at least one layer of the white hard carbon layers exists in a region within a depth of 1 μm from the surface, and the sp.sup.2/sp.sup.3 ratio of the white hard carbon layer is above 0.5.

12. The coating film according to claim 1, wherein an outermost surface is the white hard carbon layer.

13. The coating film according to claim 1, wherein a nano indentation hardness of the black hard carbon layers is 30-80 GPa.

14. The coating film according to claim 13, wherein a nano indentation hardness of the white hard carbon layers is 10-30 GPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional bright-filed TEM image of a coating film (hard carbon film) according to an implementation form of the present invention.

(2) FIG. 2 is an enlarged view of one part of FIG. 1.

(3) FIG. 3 is an electron beam diffraction result of columns-shaped hard carbon layers.

(4) FIG. 4 is a diagram schematically indicating a cross-section of a coating film (hard carbon film) according to another implementation form of the present invention.

(5) FIG. 5A and FIG. 5B are diagrams that schematically indicates main parts of a furnace for use in hard carbon film formation of an arc PVD apparatus according to an implementation form of the present invention, FIG. 5A is a situation is which a structure for cooling (cooling tower) is not disposed in the center, and FIG. 5B is a situation in which the structure is disposed.

(6) FIG. 6 is a diagram that conceptually indicates changes of the substrate temperature when forming a hard carbon film according to an implementation form of the present invention.

(7) FIG. 7 is a diagram that schematically indicates a friction-wear testing method.

(8) FIG. 8 is a microscope photo that indicates a friction-wear testing result of example 1.

(9) FIG. 9 is a microscope photo that indicates a friction-wear testing result of comparative example 1.

(10) FIG. 10 is a microscope photo that indicates chipping and peeling in the friction-wear testing result.

DESCRIPTION OF THE EMBODIMENTS

(11) The present invention is described below according to implementation forms and with reference to the drawings.

(12) 1. Substrate

(13) In the present invention, the substrate to form a hard carbon film which becomes a coating film is not particularly limited, and in addition to iron-based substrates, non-iron-based metal or ceramic, hard composite and other substrates can be used. Specifically, carbon steel, alloy steel, bearing steel, quenched steel, tool steel, cast iron, aluminum alloy, Mg alloy or super-hard alloy etc. can be listed, and if the film-forming temperature of the hard carbon film is considered, a substrate whose characteristics are not significantly degraded at a temperature above 250° C. is preferred.

(14) 2. Intermediate Layer

(15) When the hard carbon film is formed, an intermediate layer is preferably pre-set on the substrate. Thus, adhesion between the substrate and the hard carbon film can be increased, and in the case that the hard carbon film is worn, the exposed intermediate layer can be given play to the function of wear resistance.

(16) At least one of Cr, Ti, Si, W, B and other elements can be employed for such an intermediate layer. In addition, nitride, carbon nitride, carbide and the like of at least one of Cr, Ti, Si, Al, etc. can be used in a lower layer of the elements, and such compounds include, for example, CrN, TiN, CrAlN, TiC, TiCN, TiAlSiN and the like.

(17) 3. Coating Film

(18) The coating film of the present invention has two types of hard carbon layers which are shown as relatively black and white when observed in a cross-sectional bright-field TEM image, and the white hard carbon layers and the black hard carbon layers are alternately laminated to form a hard carbon film.

(19) FIG. 1 is a cross-sectional bright-field TEM image of a coating film (hard carbon film) according to an implementation form of the present invention. FIG. 2 is an enlarged view of one part of FIG. 1. In addition, FIG. 1 and FIG. 2 are bright-field TEM images obtained under the condition of an acceleration voltage of 300 kV.

(20) In FIG. 1, the symbol 1 is a coating film, and the symbol 2 is a substrate. As shown in FIG. 1, in this implementation form, on the coating film 1, black hard carbon layers 1a and white hard carbon layers 1b are alternately laminated toward the surface of the coating film 1. In addition, in FIG. 1, an intermediate layer 1c of Cr is arranged right above the substrate 2.

(21) Besides, according to FIG. 2, the white hard carbon layers 1b grow into a columns-shape in the thickness direction, and the growth direction is substantially perpendicular to the substrate. If the direction perpendicular to the substrate is set to 0°, the growth direction inclines at an angle within ±5°. Besides, it is observed that the white hard carbon layers 1b have a growth shape with a characteristic which can be described as column-like, fiber-like, comb-like, bar-like and so on, and in the thickness direction of the hard carbon film, the change from the black carbon layers to white carbon layers is abrupt and clear.

(22) Moreover, bright-field TEM images as shown in FIG. 1, FIG. 2 are obtained, the thickness of the black hard carbon layer 1a having a small sp.sup.2/sp.sup.3 ratio and the thickness of the white hard carbon layer 1b having a great sp.sup.2/sp.sup.3 ratio are measured, and calculation is performed on how the two ratios change in the thickness direction of the coating film, by which the ratio change in the thickness of the two layers, that is, the black hard carbon layer 1a having a small sp.sup.2/sp.sup.3 ratio and the white hard carbon layer 1b having a great sp.sup.2/sp.sup.3 ratio, in the thickness direction of the coating film can be measured.

(23) In the present invention, regarding the white hard carbon layers 1b having a high sp.sup.2/sp.sup.3 ratio, the sp.sup.2/sp.sup.3 ratio is preferably 0.45-0.85, and more preferably 0.5-0.8. Besides, preferably, the white hard carbon layers 1b have diffraction spots (scattering pattern of graphite) at positions with a lattice spacing of 0.3-0.4 nm in an electron beam diffraction, and (002) surfaces are aligned in a direction parallel to the substrate. In this way, most of the white hard carbon has a scattering pattern of graphite and shows a specific orientation; accordingly, for the white hard carbon layers 1b, low friction property is greatly improved because the slip surface of graphite with excellent low friction property becomes a horizontal direction relative to the substrate, and chipping resistance is greatly improved because the columns-shaped crystals exhibit high strength when stress repeatedly acts on the hard carbon film which is a coating film.

(24) On the other hand, the sp.sup.2/sp.sup.3 ratio of the black hard carbon layers 1a is preferably 0.1-0.45, and more preferably 0.15-0.4. Besides, the hydrogen content of the black hard carbon layers 1a is preferably below 10 atom %, more preferably below 5 atom %, and further preferably 0 atom %, and it is preferable if the remaining part substantially contains carbon only since hardness is increased and wear resistance is improved. In addition, the expression of “substantially contains carbon only” here means not containing impurity except N, B, Si and other inevitable impurity.

(25) When electron beam diffraction is performed to the white hard carbon layers, diffraction spots are shown at positions with a lattice spacing of 0.3-0.4 nm, and the (002) surfaces are aligned so as to be laminated on the substrate, which indicates the moment when diffraction spots as shown in FIG. 3 are obtained. In FIG. 3, the diffraction spots originated from the (002) surface of graphite appear in a vertical direction, and thus it can be determined that the (002) surfaces are aligned so as to be laminated on the substrate.

(26) It is also preferable that the hydrogen content of the white hard carbon layers 1b is below 10 atom %, and more preferably below 5 atom %, and the remaining part substantially contains carbon only, not containing impurity except N, B, Si and other inevitable impurity; however, even if these elements are contained in the white hard carbon layers 1b, chipping resistance can also be improved.

(27) Moreover, the nano indentation hardness of the black hard carbon layer 1a is preferably 30-80 GPa, by which wear resistance of the hard carbon film can be further improved. On the other hand, the nano indentation hardness of the white hard carbon layer 1b is preferably 10-30 GPa. By making each hard carbon layer have suitable hardness in this way, insufficiency of wear resistance of the hard carbon film can be inhibited, and chipping resistance can be effectively improved.

(28) 4. Manufacturing Method of Coating Film (Hard Carbon Film) and Arc PVD Apparatus

(29) (1) Manufacturing Method

(30) When the coating film 1 is formed, an arc PVD method, a sputtering PVD method and the like may be used, and particularly the arc PVD method is preferred.

(31) In the arc PVD method, a minus bias voltage is applied to the substrate. For this reason, when carbon ions flying out of a target collide with the substrate, the carbon ions are subject to the influence of the high-temperature substrate and a high bias voltage, and crystal growth easily occurs in a fixed direction, and thus the hard carbon layers easily grow in the form of columns-shaped hard carbon layers.

(32) In this implementation form, in the case that the hard carbon film is formed using the arc PVD method, a bias voltage or arc current is regulated, or the substrate is heated by a heater, or the substrate is cooled in a forced way by importing a cooling mechanism on a fixture (holder) provided with the substrate to control the substrate temperature and control the furnace pressure and the like, thereby forming a hard carbon film in which hard carbon layers with different sp.sup.2/sp.sup.3 ratios are alternately laminated.

(33) Besides, when forming the black hard carbon layers with a sp.sup.2/sp.sup.3 ratio of 0.1-0.45, it is formed in an existing way at a substrate temperature ranging from more than 50° C. to less than 250° C. Therefore, in order to alternately laminate the black hard carbon layers and the white hard carbon layers, the following method can be used which imports a cooling step after the formation of white hard carbon layers to decrease the substrate temperature, and forms the black hard carbon layers when the substrate temperature is less than 250° C.

(34) On the other hand, when forming the columns-shaped white hard carbon layers with a sp.sup.2/sp.sup.3 ratio of 0.45-0.85, it is controlled so that the substrate temperature ranges from above 250° C. to below 400° C., more preferably 275° C. to 380° C. In addition, such control of substrate temperature is preferably carried out by controlling the bias voltage to −275 to −400 V; however, the substrate temperature can also be controlled by methods such as change of the arc current, heating by a heater or cooling by a holder, applying a bias voltage intermittently such as discontinuously or pulse-like to change the voltage value, therefore the method is not particularly limited to bias voltage control only.

(35) In contrast with such an implementation form, in the existing hard carbon film manufacturing method, particularly in the case that arc PVD is used for film formation, in order to form a high-density hard carbon film, usually only the bias voltage or the arc current is controlled to form the film under the condition that the substrate temperature is more than 250° C. and does not increase, but the furnace temperature is not uniform due to thermal capacity of a workpiece, a mounting fixture or charge amount, and the substrate temperature cannot be sufficiently controlled.

(36) In this way, in the existing hard carbon film manufacturing method, a concept of strictly controlling the substrate temperature is lacking, and there is no understanding about the following effect from the existing hard carbon film manufacturing method: as in the present invention, the structure of the hard carbon layer can be controlled by controlling the substrate temperature, chipping resistance and wear resistance can be balanced by alternately laminating hard carbon layers with different sp.sup.2/sp.sup.3 ratios, and low friction properties and peeling resistance can also be improved simultaneously by controlling the structure growth shape of the hard carbon layer having a great sp.sup.2/sp.sup.3 ratio.

(37) In addition, during film-forming, the substrate is made to rotate and revolve, and preferably, the substrate rotates at 10-200 rpm, and revolves at 1-20 rpm.

(38) Under such a manufacturing condition, the white hard carbon layer having a great sp.sup.2/sp.sup.3 ratio can be formed, although the reason why the hard carbon layers grow into a columns-shape is uncertain, it may be considered as follows.

(39) That is, it is considered that if the film is formed in a range that the substrate temperature is above 250° C. and below 400° C. and the bias voltage is −275-400 V, when the carbon ions flying out of the target collide with the substrate, the ions are subject to the influence of the high-temperature substrate and a high minus bias voltage, and crystal growth easily occurs in a fixed direction, and thus the hard carbon layers easily grow in the form of columns-shaped hard carbon layers.

(40) In addition, hereinabove, the substrate temperature is preferably ranging from above 250° C. to below 400° C. when forming the white hard carbon layers having a high sp.sup.2/sp.sup.3 ratio, and the reason is as follows: when the substrate temperature is below 250° C., it is difficult for the columns-shaped white hard carbon layers to grow even if the carbon ions are incident into the substrate from the front; on the other hand, when the substrate temperature is above 400° C., although the white hard carbon layers are columns-shaped, hardness easily decreases and wear resistance easily decreases.

(41) Also, as mentioned above, in addition to adjusting the bias voltage, the substrate temperature can be adjusted by adjusting the arc current, the heater temperature, the furnace pressure and the like, but when the bias voltage is above −275 V, it is difficult to form columns-shaped hard carbon layers, and when the bias voltage is below −400 V, wear resistance easily decreases. With consideration of this situation, the bias voltage is preferably −275 to −400 V, and more preferably −275 to −380 V. Besides, regarding the furnace pressure, in the case of a vacuum environment set as 10.sup.−4 to 5×10.sup.−1 Pa, compared with the situation where hydrogen or nitrogen is imported, a low-friction and high-wear-resistance hard carbon film can be obtained, which is thus preferred.

(42) It is preferable that in the temperature increase initial step after the temperature decrease, the bias voltage is set to −400 V to −1500 V and the arc current is set to 10-200 A to carry out a bombard treatment using graphite target, and a purification treatment of the substrate surface exposed to furnace atmosphere during the temperature decrease and/or film-formation of the adhesion layer 1d including white hard carbon are carried out (see FIG. 4). The reason is that: if the bias voltage is greater than −400 V, it is difficult to carry out the purification treatment of the substrate surface, if the arc current is below 10 A, the purification treatment is hard to be effective, and if the arc current is above 200 A, the film-forming mode is stronger than the purification treatment, influence of droplet increases and surface roughness decreases, and thus it is preferably below 200 A.

(43) The hard carbon film in this implementation form can be manufactured using an arc PVD apparatus, and a specific film-forming device, for example, may be an arc PVD apparatus M720 manufactured by the Japanese ITF Company. In the following, manufacturing of a hard carbon film (coating film) using the arc PVD apparatus is specifically described.

(44) First, a metal raw material (surface roughness Ra: 0.2 μm) becoming a substrate is prepared, and the substrate is set in an arc PVD apparatus provided with a rotating and revolving fixture.

(45) Next, the arc current and the bias voltage are adjusted, in a way that the substrate temperature is more than 50° C. but less than 250° C. while the substrate is made to rotate and revolve, to form a black hard carbon layer having a small sp.sup.2/sp.sup.3 ratio. Then, control in a way that the substrate temperature is above 250° C. but below 400° C., and in a way of heating the substrate by a heater or adjusting the bias voltage or the arc current to make the substrate temperature increase continuously, and make the white hard carbon layer having a great sp.sup.2/sp.sup.3 ratio grow in a columns-shape. Then, a film-forming time of becoming non-bias and/or non-arc-current is imported to cool the substrate, and when the substrate temperature decreases to a predetermined temperature, form a black hard carbon layer again; by repeating the film-formation step of the black hard carbon layer in this way, the hard carbon film in which the black hard carbon layers and the white hard carbon layers are alternately laminated can be formed.

(46) As mentioned above, it is considered that, by changing the substrate temperature continuously in this way from a low-temperature environment to a high-temperature environment, the highly active hard carbon particles which can fly into the substrate with certain probability and have a great sp.sup.2/sp.sup.3 ratio become the starting points, the growth of the hard carbon layer is influenced by the lower layer, and the white hard carbon layer having a great sp.sup.2/sp.sup.3 ratio grows out of the black hard carbon layer having a small sp.sup.2/sp.sup.3 ratio in a columns-shape in the thickness direction as in a CVD growth.

(47) (2) Arc PVD Apparatus

(48) Then, the arc PVD apparatus of the implementation form is specifically described. FIG. 5A and FIG. 5B are diagrams that schematically indicates main parts of a furnace for use in formation of hard carbon film of the arc PVD apparatus according to the implementation form, FIG. 5A is a situation in which a structure for cooling (cooling tower) is not disposed in the center, and FIG. 5B is a situation in which the structure is disposed.

(49) As shown in FIG. 5A, the arc PVD apparatus includes a furnace 11 for use in film-forming and a control device (not shown). In the furnace 11, a vacuum chamber 12, a plasma generation device (not shown), a heater 13, a rotating and revolving fixture 14 serving as a substrate supporting device, a thermocouple (T.C.10 mm square bar) 15 serving as a temperature measuring device, a bias power source (not shown) and a pressure adjusting device (not shown) that adjusts the pressure in the furnace are arranged.

(50) Besides, a cooling and heating device that supplies cooling water and/or warm water or steam is provided on the substrate supporting device. In addition, the symbol T is a target (carbon target), and the symbol 21 is a substrate (iron substrate) with an intermediate layer formed thereon. Besides, actually there are five targets T, but for the sake of simplification, only one target is depicted in FIG. 5A.

(51) The plasma generation device includes an arc power source, a cathode and an anode, by discharge through a vacuum arc between the cathode and the anode, carbon is evaporated from the carbon target T as a cathode material, and plasma containing an ionized cathode material (carbon ion) is generated. The bias power source applies a predetermined bias voltage to the substrate 21 to make the carbon ions fly towards the substrate 21 with suitable kinetic energy.

(52) The rotating and revolving fixture 14 is disk-like, and freely rotates in the arrow direction with the center of the disk as a rotation center; on the upper surface, multiple rotary shafts concentrically perpendicular to the center of the disk are provided at an equal interval. Multiple substrates 21 are retained by the rotary shafts respectively, and freely rotate in the arrow direction. Thus, the substrate 21 is retained on the rotating and revolving fixture 14 to rotate and revolve freely. Besides, for the rotating and revolving fixture 14, a metal material with high thermal conductivity such as stainless steel is used in a manner of quickly transferring heat between the substrates 21 and the rotating and revolving fixture 14 and making temperatures of the substrates 21 and the rotating and revolving fixture 14 substantially equal.

(53) The heater 13 and the cooling device heat and cool the rotating and revolving fixture 14 respectively, thus indirectly heating and cooling the substrates 21. Here, the heater 13 is formed in a manner of regulating the temperature. On the other hand, the cooling device is formed in a manner of adjusting a supply speed of cooling water. Specifically, the cooling device is formed in a manner of supplying the cooling water for the rotating and revolving fixture 14 and/or the rotary shaft during implementation of cooling and stopping supplying the cooling water when the cooling stops, and is formed in a manner of supplying warm water or steam for the rotating and revolving fixture 14 and/or the rotary shaft during heating and stopping supplying the warm water or steam when the heating stops.

(54) Besides, the thermocouple 15 is installed near the substrate 21, and is formed in a manner of indirectly measuring the substrate temperature to make at least one of the arc current value, the bias voltage value, and the heater temperature change in film-forming, thus controlling the substrate temperature to be a target substrate temperature.

(55) Regarding the rotary speed of the rotating and revolving fixture 14, the control device controls various rotary speeds to be a predetermined rotary speed under a preselected combination of rotation and revolution in a manner of forming a columns-shaped hard carbon layer having a great sp.sup.2/sp.sup.3 ratio and forming a film without bias; in addition, according to the measurement results of the thermocouple 15 for the temperature of the substrate 21, the bias voltage, the arc current, the heater temperature, and the furnace pressure are optimized. Thus, the temperature of the substrate 21 during film-forming can be maintained within a temperature range of more than 50° C. but below 400° C. Besides, the work of the cooling device and the applied pattern of the bias voltage are controlled as required.

(56) For example, a feedback system is preferably added when the substrate is disposed in 3 segments, and the feedback system measures substrate temperature in upper, middle and lower segments, properly changes arc current values or bias voltage in various positions of the upper, middle and lower segments during film-forming according to measured values, and sets the substrate temperatures in various positions of the upper, middle and lower segments as a target temperature. Thus, stabilization of a film structure of hard carbon films formed on the substrate disposed on the upper, middle and lower segments can be achieved.

(57) In addition, in the film-forming of the existing hard carbon film, for film-forming parameters such as bias voltage, arc current and the like, in most cases, predetermined values are input into the control device before film-forming, film-forming is conducted under a pre-programmed film-forming condition, and the arc current or the heater temperature is not changed according to the substrate temperature measured in the middle of film-forming based. Therefore, in the existing hard carbon film formation, temperatures in the furnace or temperatures between batches are more non-uniform.

(58) Preferably, in the central part of the arc PVD apparatus, a cylindrical structure (cooling tower 16) as shown in FIG. 5B for cooling the substrate is arranged. By circulating and using cooling water in such a cylindrical structure, even if readily available water is used as a cooling medium, the cooling ability does not become too high, and the substrate can be easily heated to a target temperature, thus the white hard carbon layers are easily formed, and sufficient cooling ability during the cooling can be ensured, thus it is preferable.

(59) During the formation of the coating film 1 (see FIG. 1), the temperature control device makes the substrate 21 repeatedly alternates temperature increase and temperature decrease between a temperature set within a low temperature range of more than 50° C. but less than 250° C. and a temperature set within a high temperature range of above 250° C. and below 400° C. An example is shown in FIG. 6. In FIG. 6, the vertical axis is the substrate temperature (° C.), and the horizontal axis is the film-forming time of the hard carbon film, specifically, a ratio (%) of the film-forming time when the time required for formation of the total film thickness is set as 100%. The temperature in the low temperature range, the temperature in the high temperature range, speed and cycle numbers of temperature increase and temperature decrease are suitably set according to the thickness of each layer of the black hard carbon layers and the white hard carbon layers, total film thickness of the hard carbon film and the like.

(60) 5. Inspection Method of Hard Carbon Film (Coating Film)

(61) The hard carbon film (coating film) formed in the above is inspected according to the following items.

(62) (1) Observation of TEM Structure

(63) Through a TEM (Transmission Electron Microscope), a coating film thin-filmed using a Focused Ion Beam (FIB) is observed, for example, in a bright-field TEM image at an acceleration voltage of 300 kV.

(64) (2) Measurement of Hydrogen Content

(65) The hydrogen content in the coating film is measured through Hydrogen Forward Scattering (HFS) analysis.

(66) (3) Judgment Method of Crude Density of the Hard Carbon Layer

(67) The density of the hard carbon film may generally be measured using a Grazing Incidence X-ray Analysis (GIXA) method or a Grazing Incidence X-ray Reflectivity (GIXR) method. However, in a situation where small-density crude hard carbon and large-density dense hard carbon in the hard carbon layer are dispersed finely, it is difficult to utilize the method to measure density of various portions with high precision.

(68) For the crude density judgment of such a hard carbon layer, for example, a method of effectively utilizing brightness of a bright-field TEM image disclosed in Japanese Patent Gazette No. 4918656 can be used. Specifically, in the bright-field TEM image, the lower the density is, the more the penetration amount of the electron beam increases. Therefore, in the case of forming the same substance, the lower the density is, the whiter the image is. So, in order to judge the density of each layer in multiple hard carbon layers of the same composition, preferably, a cross-sectional bright-field TEM image of the structure of the hard carbon layer is used.

(69) In the cases of the bright-field TEM images in FIG. 1 and FIG. 2, it can be seen that the color of the hard carbon layers of the section 1b is whiter than the color of the hard carbon of the section 1a. Moreover, in the section 1b, the white hard carbon is a complicated state able to be described as column-like, fiber-like, comb-like, bar-like and the like extending in the thickness direction. In order to make a color difference between white and black evident, color correction can be made in a manner of highlighting the contrast.

(70) (4) Amorphous Judgment Method of the Coating Film

(71) The coating film formed by thin-filming the cross-section using FIB carries out electron beam diffraction under a condition of an acceleration voltage of 200 kV, a sample absorption current 10.sup.−9 A, and a beam spot size of 0.7 nmϕ, to obtain an image of a tiny beam diffraction pattern, if the image is a diffuse scattering pattern, it is judged as amorphous, and if a spot-like pattern is observed, intensity spacing L near the spot is measured, and lattice spacing λ (nm) is calculated according to a relation that 2Lλ=camera length.

(72) (5) Measuring Method of ID/IG Ratio Obtained by Raman Spectroscopy

(73) The hard carbon layer may be obtained by separating peaks of Raman spectrum obtained through Raman spectroscopy. Specifically, the peak position of the D band is fixed to 1350 cm.sup.−1 for selection, the area intensity of this peak is set as ID, the peak position of the G band is near 1560 cm.sup.−1 for free setting and peak separation, the area intensity of this peak is set as IG, and the ID/IG ratio is calculated.

(74) (6) Measuring Method of the Sp.sup.2/Sp.sup.3 Ratio

(75) Through Electron Energy-Loss Spectroscopy (EELS) analysis, 1s.fwdarw.π* intensity and 1s.fwdarw.σ* intensity is measured, the 1s.fwdarw.π* intensity is viewed as the sp.sup.2 intensity, the 1s.fwdarw.σ* intensity is viewed as the sp.sup.3 intensity, and the ratio, that is, a ratio of 1s.fwdarw.π* intensity to 1s.fwdarw.σ* intensity is calculated as the sp.sup.2/sp.sup.3 ratio. Accordingly, the sp.sup.2/sp.sup.3 ratio in the present invention is actually the ratio of π/σ intensity. Specifically, with a spectral imaging method in a STEM (scanning TEM) mode, under a condition of an acceleration voltage of 200 kV, a sample absorption current of 10.sup.−9 A, and a beam spot size of ϕ1 nm, EELS obtained at an interval of 1 nm is accumulated to extract a C-K absorption spectrum in the form of average information from a region of about 10 nm, and the sp.sup.2/sp.sup.3 ratio is calculated.

(76) If the measuring method is used, the sp.sup.2/sp.sup.3 ratio in a tiny portion can be measured; as the sp.sup.2/sp.sup.3 ratio of the high-density hard carbon is less than that of the low-density hard carbon, the judgment method of crude density of hard carbon can be substituted.

(77) (7) Measuring Method of Nano Indentation Hardness

(78) The nano indentation hardness is measured using a Nanoindenter ENT1100a manufactured by Elionix Company. When the hardness of each layer of the laminated hard carbon layers is measured, after the cross-section of the film is mirror-polished, an indentation load value is decreased to carry out measurement.

(79) (8) Measuring Method of Electrical Resistance of Columns-Shaped Hard Carbon Layers

(80) By the two-terminal method, a fixed current is applied between the terminals and a voltage decrease between two terminals is measured to calculate the electrical resistance value. Specifically, the electrical resistance is calculated by a method in which a tester (multimeter) is used and the electrical resistance (Ω) is obtained by setting a distance between two terminals to 1 cm.

(81) 6. Effect of the Implementation Form

(82) As stated above, in the hard carbon film (coating film) of the present invention, the hard carbon layer which has a small sp.sup.2/sp.sup.3 ratio and is black in the bright-field image of the TEM structure and the hard carbon layer which has a great sp.sup.2/sp.sup.3 ratio and is white in the bright-field image of the TEM structure are alternately laminated. Besides, the white hard carbon layers have parts that are grown in a columns-shape, and if the white hard carbon layers are specifically observed, the white hard carbon layers are a complicated structure which can be described as column-like, fiber-like, comb-like, bar-like and so on in the thickness direction.

(83) In addition, when the white hard carbon layers are formed, if the film-forming temperature is not increased to above 250° C., the structure does not become a columns-shape, and the film may be formed in a configuration that the white hard carbon layers having a complicated shape which can be described as mesh-like, scale-like, branch-like have grown in a fan shape in the thickness direction. In the present invention, there are also cases in which such white hard carbon layers are included.

(84) Moreover, the white hard carbon having a small sp.sup.2/sp.sup.3 ratio is soft and has resistance to impact and excellent low friction property, and thus stress applied externally can be very efficiently dispersed, and low friction property and chipping resistance are excellent.

(85) As a result, chipping resistance and wear resistance can be sufficiently balanced, and low friction properties and peeling resistance are improved. As a result, sliding characteristics can be significantly increased compared with the existing hard carbon film, and chipping resistance and peeling resistance can also be significantly increased compared with the existing hard carbon film. Besides, because black and white hard carbon layers can be repeatedly alternated and laminated to form thick film, durability is also excellent. It is particularly suitable for use in automobile parts such as a piston ring, a piston pin, a gear, a bearing, a valve lifter and common mechanical parts such as a vane and a bearing.

EXAMPLES

(86) Next, the present invention is more specifically described according to examples.

[1] Experiment 1

(87) 1. Manufacturing of Test Sample

(88) (1) Forming of Substrate and Intermediate Layer

(89) A substrate (in line with a material of SWOSC-V) was prepared, to form a piston ring shape with a diameter of 80 mm, a ring radial-direction width (a1) of 2.6 mm, a ring width-direction width (h1) of 1.2 mm, grinding was carried out after a CrN layer having a thickness of 10 μm coated the surface of the sliding plane using an arc PVD apparatus, and a CrN layer coated steel substrate having surface roughness Rz of 0.3 μm was prepared.

(90) (2) Forming of Coating Film

(a) Example 1

(91) In example 1, an arc PVD apparatus provided with the furnace 11 shown in FIG. 5A for film-forming is used to form a hard carbon film with a total film thickness of 7.6 μm on the surface of the substrate 21 by a method similar to the coating film manufacturing method of the above implementation form.

(92) Specifically, after the substrate on which a CrN layer is formed is disposed on the rotating and revolving fixture 14 which is also a substrate supporting device, set the substrate in the furnace 11 of the arc PVD apparatus and coat metal Cr layer with a thickness of 0.1 μm as an intermediate layer, then use a graphite cathode to start forming a hard carbon film.

(93) At this point, the substrate 21 is made to rotate at a speed of 39 rpm and revolve at a speed of 4 rpm. Besides, regarding the temperature condition during film-forming, after arc discharge is carried out at a bias voltage of −700 V and an arc current of 40 A for 10 minutes, bias voltage −170 V, arc discharge is carried out at a bias voltage of −170 V and an arc current of 40 A to increase the temperature to a temperature range of more than 50° C. and below 200° C. for 1200 seconds to form a black hard carbon layer with a film thickness of 0.2 mm. After that, arc discharge is carried out at a bias voltage of −350 V and an arc current of 40 A to form a black hard carbon layer with a film thickness of 0.15 μm in a temperature range of more than 200° C. and less than 250° C. while heater heating is carried out, and to form a white hard carbon layer with a film thickness of 0.15 μm in a temperature range of 250° C. to 290° C. while heater heating is carried out. The black hard carbon layers formed in this step is 0.35 μm, and the white hard carbon layer formed is 0.15 μm, making a total film thickness of 0.5 μm. After that, arc discharge is stopped at a bias voltage of 0 V and an arc current of 0 A to cool to 125° C. for 4800 seconds. After that, arc discharge is carried out at a bias voltage of −1000 V and an arc current of 40 A for 90 seconds to form an adhesion layer including white hard carbon, then arc discharge is carried out again at a bias voltage of −170 V and an arc current of 40 A to increase the temperature to a temperature range of more than 50° C. and less than 200° C. for 1200 seconds to form a black hard carbon layer with a film thickness of 0.2 μm. Then, arc discharge is carried out at a bias voltage of −350 V and an arc current of 40 A to form a black hard carbon layer with a film thickness of 0.15 μm in a temperature range of more than 200° C. and less than 250° C. while heater heating is carried out, and to form a white hard carbon layer with a film thickness of 0.15 μm in a temperature range of 250° C. to 290° C. while heater heating is carried out. Similar to the above step, the black hard carbon layer is 0.35 μm, the white hard carbon layer is 0.15 μm, and the hard carbon layer including the two layers has a total film thickness of 0.5 μm. The repeating cycle of temperature increase and cooling in which the hard carbon layer is coated is carried out 14 times to form a hard carbon film with a total film thickness of 7.6 μm.

(b) Comparative Example 1

(94) In the comparative example 1, the existing PVD method is used and arc discharge is carried out at a bias voltage of −75 V and an arc current of 40 A for 80 minutes to form a hard carbon film with a thickness of 1.0 μm on the surface of the substrate 21.

(c) Comparative Example 2

(95) In the comparative example 2, except that the film-forming time is changed from 80 minutes in the comparative example 1 to 96 minutes, and the film-forming thickness is set to 1.2 μm, a hard carbon film is formed similarly as the comparative example 1.

(d) Comparative Example 3

(96) In the comparative example 3, the existing CVD method is used and a hard carbon film with a thickness of 7.5 μm is formed on the surface of the substrate 21. In addition, the total film-forming time is set to 130 minutes.

(97) 2. Evaluation of Coating Film

(98) Observe the structure of the coating films obtained in the example and comparative example 1 to comparative example 3 and measure the film thickness of the coating film to evaluate wear resistance, chipping resistance, low friction, and peeling resistance respectively. In addition, except the comparative example 3 which uses methane (hydrocarbon gas) in raw material gas, the hydrogen content in other coating films are all below 10 atom %.

(99) (1) Structure and Properties of Coating Film

(100) Take an image of each formed coating film by a bright-field TEM with an acceleration voltage of 200-300 kV, observe the structure of each coating film and measures the film thickness of each coating film.

(101) Besides, the sp.sup.2/sp.sup.3 ratio of the black layers and the white layers, the electrical resistance of the uppermost layer, the crystal nature and the orientation of the (002) surfaces obtained by the electron beam diffraction, are measured. In addition, evaluation of the crystal nature and the orientation of the (002) surfaces obtained by the electron beam diffraction are performed for the white columns-shaped hard carbon layers. The measuring results of these measurements are shown in table 1.

(102) (2) Evaluation of Wear Resistance, Chipping Resistance, Low Friction, Peeling Resistance, and Durability

(103) Next, use each formed coating film to conduct a friction-wear testing by a SRV (Schwingungs Reihungund and Verschleiss) experiment machine commonly used in the evaluation of sliding members for automobile. Specifically, as shown in FIG. 7, in the state that the sliding surface of a friction-wear testing sample W contacts with SUJ2 material 24 which is a sliding object, use 5W-30 (Mo-DTC free) for the lubricant oil and apply a load of 100-1000 N (increment of 100 N), slide back and forth for 10 minutes under each load and observe the sliding surface of the friction-wear testing sample W by a microscope. Then, obtain from the observation result the load under which damage is present in each coating film. Besides, calculate the friction coefficient under the load. In addition, in FIG. 7, the symbol 21′ is CrN, the symbol 22 is the intermediate layer, and the symbol 23 is the coating film.

(104) The result of each evaluation is shown in table 1. Besides, the friction-wear testing results of the example 1 and the comparative example 1 are shown in FIG. 8 and FIG. 9 respectively. In addition, in the comparative example 2, during film-forming, the coating film is already self-destructed, thus the evaluation by SRV experiment machine is not conducted.

(105) TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example 1 example 1 example 2 example 3 Structure of the Black layers and Black layer only Black layer only White layer only coating film white layers are alternately laminated, and the outermost surface layer is a white layer Number of Black layer 15 Black layer 1 Black layer 1 White layer 1 laminated layers White layer 15 Total thickness of 7.6 μm 1.0 μm 1.2 μm 7.5 μm the coating film (self-destructed) (μm) White hard carbon Existing None None None layers grown in a columns-shape in the thickness direction sp.sup.2/sp.sup.3 ratio 0.3 for the black 0.2 for the black 0.2 for the black 0.5 for the white layer, layer layer layer 0.7 for the white layer Electron beam Diffraction spots are — — Diffraction spots diffraction detected at positions are detected at with a lattice spacing positions with a of 0.3-0.4 nm lattice spacing of 0.3-0.4 nm Orientation of Horizontal direction — — None (002) surfaces relative to the substrate Electrical 5-20 Ω .Math. cm 10 KΩ .Math. cm — 6 MΩ .Math. cm resistance Load under which Not generated even 300N — 200N peeling or under 1000N and is chipping is able to continue generated Low friction 0.07 0.08 — 0.09 properties (friction coefficient)

(106) According to table 1, it is confirmed that, in the example 1, a coating film with a film thickness of 7.6 μm and without internal destruction can be formed, and as shown in FIG. 8, normal surface shape is maintained even after 10 minutes of SRV test under a high load of 1000 N; therefore, by alternately laminating the black hard carbon layers and the white hard carbon layers and forming a coating film which has white hard carbon layers grown in a fan shape in the thickness direction, a thick coating film, which has a thickness above 1 μm and good wear resistance, chipping resistance, peeling resistance, durability and low friction properties, can be provided.

(107) In contrast, in the comparative example 1 which sets the film thickness to 1.0 μm, no peeling or chipping occurs under 100 N, 200 N, and evaluation can be conducted under normal wear, but as shown in FIG. 9, under a load of 300 N, the film is stripped or chipped and the substrate is exposed, the evaluation is ended under this load. According to the test result, it can be confirmed that, in a coating film with black hard carbon layers only, chipping resistance and peeling resistance is not good, and durability is also insufficient.

(108) Besides, in the comparative example 2 which sets the film thickness to 1.2 μm, internal destruction occurs during film-forming and the film is self-destructed, even without setting the film to the SRV experiment machine can it be confirmed that durability (service life) is low. Furthermore, in the comparative example 3 which sets the film thickness to 7.5 μm in the CVD method, no peeling or chipping occurs under 100N, and evaluation can be conducted under normal wear, but under a load of 200 N, the film is stripped or chipped and the substrate is exposed, the evaluation is ended under this load.

[2] Experiment 2

1. Example 2-Example 19

(109) According to the result of the experiment 1, it can be confirmed that when the black hard carbon layers and the white hard carbon layers are laminated to form a coating film, wear resistance, chipping resistance, low friction properties, peeling resistance and durability (service life) is good; therefore, in the experiment 2 below, various film-forming conditions are changed, and the sp.sup.2/sp.sup.3 ratio of the black hard carbon layer, the sp.sup.2/sp.sup.3 ratio of the white hard carbon layer, the thickness of the black hard carbon layer and the thickness of the white hard carbon layer are made to be different respectively to form coating films of examples 2-19 as shown in Table 2, so that hard carbon layers are formed that in the structure where the black layers and the white layers are alternately laminated as in the example 1, the outermost surface layer is the white layer, and the total film thickness is 4.8-5.8 μm.

(110) TABLE-US-00002 TABLE 2 Laminating sp.sup.2/sp.sup.3 ratio Thickness (nm) number of Black hard White hard Black hard White hard black and Total film carbon carbon carbon carbon white hard thickness layers layers layers layers carbon layers (μm) Example 2 0.07 0.7 300 300 8 5.0 Example 3 0.1 0.7 300 300 8 5.0 Example 4 0.25 0.7 300 300 8 5.0 Example 5 0.4 0.7 300 300 8 5.0 Example 6 0.45 0.7 300 300 8 5.0 Example 7 0.2 0.4 300 300 8 5.0 Example 8 0.2 0.45 300 300 8 5.0 Example 9 0.2 0.8 300 300 8 5.0 Example 10 0.2 0.85 300 300 8 5.0 Example 11 0.2 0.9 300 300 8 5.0 Example 12 0.3 0.7 5 300 16 5.0 example 13 0.3 0.7 20 300 16 5.1 Example 14 0.3 0.7 1000 300 4 5.4 Example 15 0.3 0.7 1100 300 4 5.8 Example 16 0.3 0.7 300 5 16 5.0 Example 17 0.3 0.7 300 20 16 5.1 Example 18 0.3 0.7 300 2000 2 4.8 Example 19 0.3 0.7 300 2500 2 5.8

2. Evaluation

(111) As for the coating films of example 2-example 19, the method similar to the experiment 1 is used, the films are slid back and forth by the SRV test device under a load of 1000 N for 60 minutes, and the sliding surface of the friction-wear testing sample W is observed by a microscope. Then, chipping resistance and peeling resistance of the coating film are evaluated according to the observation result. Wear resistance is evaluated from wear depth, and low friction property are evaluated by measuring the friction coefficient value. The evaluation result is shown in Table 3. A photo of a real coating film for which peeling and chipping occur during the SRV test is shown in FIG. 10.

(112) In addition, the evaluation references in each evaluation are as follows.

(113) (1) Wear Resistance

(114) It is evaluated as “excellent” when the total wear amount is within ¼ of the total film thickness, as “good” when over ¼ but within ½, as “qualified” when the base is not exposed and the wear amount is above ½ of the total film thickness, and as “unqualified” when the wear amount is above the total film thickness and the base is exposed.

(115) (2) Chipping Resistance

(116) It is evaluated as “excellent” when there is no chipping, as “good” when there are 1-4 points of tiny chipping, as “qualified” when there is more than 5 tiny chipping, and as “unqualified” when the chipping is above 0.05 mm.

(117) (3) Peeling Resistance

(118) It is evaluated as “excellent” when there is no peeling, as “good” when the total peeling amount is within ⅛ of the total sliding area, as “qualified” when within ¼, and as “unqualified” when the peeling is over ¼.

(119) TABLE-US-00003 TABLE 3 Wear Chipping Low friction Peeling resistance resistance property resistance Example 2 Excellent Qualified 0.07 Good Example 3 Excellent Good 0.07 Excellent Example 4 Excellent Excellent 0.07 Excellent Example 5 Excellent Excellent 0.07 Excellent Example 6 Qualified Excellent 0.07 Excellent Example 7 Excellent Qualified 0.08 Good Example 8 Excellent Excellent 0.07 Excellent Example 9 Excellent Excellent 0.06 Excellent Example 10 Good Excellent 0.06 Excellent Example 11 Qualified Excellent 0.06 Excellent Example 12 Qualified Excellent 0.07 Excellent Example 13 Good Excellent 0.07 Excellent Example 14 Excellent Good 0.07 Excellent Example 15 Excellent Qualified 0.07 Good Example 16 Excellent Qualified 0.07 Qualified Example 17 Excellent Good 0.07 Good Example 18 Good Excellent 0.07 Excellent Example 19 Qualified Excellent 0.07 Excellent

(120) According to table 3, when comparing the example 2-example 6 in which the sp.sup.2/sp.sup.3 ratios of the black hard carbon layer are made to be different respectively, in the example 2 with a sp.sup.2/sp.sup.3 ratio of the black hard carbon layer below 0.1, chipping resistance decreases slightly. Besides, in the example 6 with a sp.sup.2/sp.sup.3 ratio of the black hard carbon layer above 0.4, wear resistance decreases slightly. Accordingly, it can be confirmed that the sp.sup.2/sp.sup.3 ratio of the black hard carbon layer is preferably 0.1-0.4 as in the example 3-example 5.

(121) Besides, when comparing the example 7-example 11 in which the sp.sup.2/sp.sup.3 ratios of the white hard carbon layer are made to be different respectively, in the example 7 with a sp.sup.2/sp.sup.3 ratio of the white hard carbon layer below 0.45, chipping resistance decreases slightly, and in the example 11 with a sp.sup.2/sp.sup.3 ratio above 0.85, wear resistance decreases slightly. Accordingly, it can be confirmed that the sp.sup.2/sp.sup.3 ratio of the white hard carbon layer is preferably 0.45-0.85 as in the example 8-example 10.

(122) Next, when comparing the example 12-example 15 in which the thickness of the black hard carbon layer is made to be different respectively, it can be confirmed that as in the example 12, when the thickness of the black hard carbon layer is below 20 nm, wear resistance decreases, and it can be confirmed that when the thickness is above 1000 run, chipping resistance decreases. Accordingly, it can be confirmed that the thickness of the black hard carbon layer is preferably 20-1000 nm as in the example 13-example 14.

(123) Then, when comparing the example 16-example 19 in which the thickness of the white hard carbon layer is made to be different respectively, it can be confirmed that, when the white hard carbon layer is too thin, chipping resistance decreases, and when the white hard carbon layer is too thick, wear resistance decreases. Then, it can be confirmed that the thickness of the white hard carbon layer is preferably 20-2000 run as in the example 17-example 18.

[3] Experiment 3

1. Example 20-example 21

(124) In the experiment 3 below, in order that in the structure where the black layer and the white layer are alternately laminated as in the example 1, the outermost surface layer is the white layer and the total film thickness is 8 μm, the coating films of the examples 20-21 as shown in Table 4 are formed in the following manner: nine black layers and nine white layers are alternately laminated, various film-forming conditions are changed, and a ratio of the thickness of the white hard carbon layer to the thickness of the black hard carbon layer changes in the thickness direction of the coating film.

(125) TABLE-US-00004 TABLE 4 sp.sup.2/sp.sup.3 ratio Thickness (nm) Black White Black White hard hard Position in the hard hard carbon carbon film thickness carbon carbon layer layer direction layer layer Example 20 0.3 0.7 Film surface side 300 300 Film middle part 300 300 Film base side 300 300 Example 21 0.3 0.7 Film surface side 150 450 Film middle part 300 300 Film base side 550 50

2. Evaluation

(126) As for the coating films of the example 20-example 21, the method similar to the experiment 2 is used, the evaluation is conducted by the SRV test device under a load of 1000 N for an evaluation time prolonged for 30 minutes in each example, and wear resistance, low friction properties and durability are evaluated based on the average value in 3 tests. The evaluation result is shown in Table 5. In addition, regarding the durability, the duration time when no chipping or peeling occurs in the test piece is set as the evaluation time.

(127) TABLE-US-00005 TABLE 5 Wear Low friction resistance property Durability Example 20 Excellent 0.06 180 minutes Example 21 Excellent 0.06 No chipping and peeling damage in 360 minutes

(128) According to Table 5, in the example 21 for which the ratio of the thickness of the white hard carbon layer to the thickness of the black hard carbon layer changes in the thickness direction of the coating film and the value increases from the substrate side toward the surface side, compared with the example 20 in which the ratio of the thickness of the white hard carbon layer to the thickness of the black hard carbon layer does not change, durability increases significantly. Accordingly, it can be confirmed that, in the coating film for which the ratio of the thickness of the white hard carbon layer to the thickness of the black hard carbon layer changes in the thickness direction of the coating film and the value increases from the substrate side toward the surface side, excellent durability can be expected.

[4] Experiment 4

1. Example 22-Example 23

(129) In the experiment 4 below, the coating film of the example 22 is formed, wherein the coating film has a film structure similar to the example 21, and is a hard carbon layer film with a total film thickness of 8 μm which contains 15 atom % of hydrogen in the hard carbon by flowing methane gas in a step of form the hard carbon into a film in a manner that hydrogen is contained in the hard carbon.

2. Evaluation

(130) Then, use the method similar to the experiment 3 to evaluate wear resistance, low friction properties and durability with the coating films of the example 22 containing hydrogen and of the example 21 not containing hydrogen by the SRV test device under a load of 1000 N. However, the test is conducted under the condition that Mo-DTC is contained in the lubricant oil. The evaluation result is shown in Table 6.

(131) TABLE-US-00006 TABLE 6 Wear Low friction resistance property Durability Example 21 Excellent 0.06 No chipping and peeling damage in 360 minutes Example 22 Qualified 0.06 60 minutes

(132) According to Table 6, in the example 21 in which the hydrogen content of the black hard carbon layer and the white hard carbon layer is below 10 atom %, compared with the example 22 in which the hydrogen content of the black hard carbon layer and the white hard carbon layer is above 10 atom %, durability increases significantly. Accordingly, it can be confirmed that for the coating film in which the hydrogen content in the hard carbon is below 10 atom %, excellent wear resistance and durability can be expected.

(133) Then, the nano indentation hardness of each layer of the hard carbon layers of the example 21 exhibiting excellent sliding performance is evaluated, and the hardness can be confirmed to be the hardness as shown in Table 7.

(134) TABLE-US-00007 TABLE 2 Nano indentation sp.sup.2/sp.sup.3 ratio hardness Black White Black White hard hard hard hard carbon carbon carbon carbon layer layer layer layer Example 21 0.3 0.7 Film surface side 33 GPa 10 GPa Film middle part 50 GPa 17 GPa Film base side 64 GPa 25 GPa

[5] Experiment 5

1. Example 24

(135) In the experiment 5 below, a coating film of the example 24 is formed, which is a film of hard carbon layers with a total film thickness of 5.3 μm, and in the film-formation step of the example 21, the adhesion layer containing white hard carbon is not formed.

2. Evaluation

(136) Then, use the method similar to the experiment 3 to evaluate wear resistance, low friction properties and durability with the coating film of the example 24 not containing the adhesion layer by the SRV test device under a load of 1000 N.

(137) TABLE-US-00008 TABLE 8 Wear Low friction resistance property Durability Example 21 Excellent 0.06 No chipping and peeling damage in 360 minutes Example 24 Good 0.06 90 minutes

(138) According to Table 8, in the example 24 not containing the adhesion layer, compared with the example 21 containing the adhesion layer, wear resistance and durability decrease. Accordingly, for the coating film containing the adhesion layer, excellent wear resistance and durability can be expected.

(139) The above describes the present invention according to implementation forms, but the present invention is not limited to the implementation forms. Various changes can be made to the implementation forms within the same and equivalent scopes of the present invention.