Amorphous hard carbon film, method for manufacturing the same, apparatus for manufacturing the same, and sliding member

Abstract

The present invention provides an amorphous hard carbon film with low surface roughness and low hardness, a method for producing the same, a manufacturing apparatus therefor, and a sliding member. [Solution] An amorphous hard carbon film coated on the surface of a substrate, wherein the amorphous hard carbon film has raised portions on its surface from which a portion of an abnormal growth product, which has grown using macroparticles present in the amorphous hard carbon film as a starting point for growth, protrudes, and in a cross section perpendicular to the plane direction of the amorphous hard carbon film, the side surface of the abnormal growth product from the starting point of growth to each of the two intersections between the raised portion and the surface of the amorphous hard carbon film has a stepped shape.

Description

Technical Field

[0001] The present invention relates to an amorphous hard carbon film, a method for producing the same, an apparatus for producing the same, and a sliding member.

Background Art

[0002] Amorphous hard carbon films containing carbon as a main component, generally called DLC (diamond-like carbon) films, have attracted attention in recent years as materials excellent in low friction property and welding resistance. Such amorphous hard carbon films are broadly classified into hydrogen-containing amorphous hard carbon films formed using hydrocarbon gas as a carbon raw material, and hydrogen-free amorphous hard carbon films formed using solid carbon as a carbon raw material. Among these, hydrogen-free amorphous hard carbon films, in particular, have high hardness, high heat resistance, and a low coefficient of friction in oil, and thus are used as surface treatment films for base materials such as molds, automobile parts, and tools.

[0003] In particular, extensive studies have been conducted on coating the amorphous hard carbon film on surfaces of members requiring sliding properties, such as shafts and bearings, engine base materials and other mechanical base materials in the automobile field. When used in such members, when the hardness of the amorphous hard carbon film is within a relatively low hardness range, the aggressiveness to the counterpart sliding member can be reduced, and the sliding property in an initial sliding stage can be improved.

[0004] Hydrogen-free amorphous hard carbon films are generally formed using an arc ion plating method. As methods for forming a low-hardness amorphous hard carbon film on a surface of a base material by the method, a method of forming a film by applying a high bias voltage to the base material (for example, Non-Patent Document 1) and a method of forming a film at high temperature (for example, Patent Document 1) are known.

[0005] Non-Patent Document 1 describes that in DLC film formation using an arc ion plating method, hardness tends to decrease as the bias voltage is increased for both direct current bias and pulse bias.

[0006] Patent Document 1 describes the production of an amorphous hard carbon film with a low hardness of 10 to 35 GPa under film formation conditions in which a bias voltage of -275V to -400V is applied to the substrate and the substrate temperature is raised to a high temperature of 250°C to 400°C. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2018-123431 [Non-patent literature]

[0008] [Non-Patent Document 1] Shojiro Miyake, Takashi Saito, Ke-Ching Yu, Takashi Mikami, and Kiyoshi Ogata, Surface Technology, pp. 669-676, Vol. 55, No. 10, 2004. [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the conventional techniques described above have a problem in that the surface roughness of the amorphous hard carbon film increases due to abnormal growth of macroparticles as the substrate temperature rises, resulting in a deterioration of the sliding properties of the sliding member coated with the amorphous hard carbon film. In addition, there is the problem that the substrate softens as the substrate temperature rises, so it cannot be used for substrates that soften at high temperatures. On the other hand, if the film is formed in a low temperature range, there is a problem in that the hardness of the amorphous hard carbon film cannot be reduced.

[0010] One aspect of the present invention aims to provide an amorphous hard carbon film with low surface roughness and low hardness, a method for producing the same, a manufacturing apparatus therefor, and a sliding member. [Means for solving the problem]

[0011] To solve the aforementioned problems, the present invention includes the following embodiments.

[0012] [1] An amorphous hard carbon film coated on the surface of a substrate, The amorphous hard carbon film has raised portions on its surface, where some of the abnormally grown products, which have grown using macroparticles present in the amorphous hard carbon film as growth starting points, protrude. In a cross-section perpendicular to the plane direction of the amorphous hard carbon film, An amorphous hard carbon film in which the side surface of the abnormal growth, from the starting point of growth to each of the two intersections between the raised portion and the surface of the amorphous hard carbon film, has a stepped shape.

[0013] [2] The amorphous hard carbon film according to [1], wherein the side surface of the abnormally grown material has a stepped shape in which the growth angle changes alternately.

[0014] [3] The amorphous hard carbon film according to [1] or [2], wherein the side surface of the abnormally grown material has a stepped shape in which portions in which the macroparticles grew perpendicular to the film surface and portions in which they grew spreading out in a substantially conical shape are alternately formed.

[0015] [4] The amorphous hard carbon film according to any one of [1] to [3], wherein, in a cross section perpendicular to the plane direction of the amorphous hard carbon film, the angle between the two lines connecting each of the two intersection points of the raised portion and the film surface of the amorphous hard carbon film and the closer of the two points of maximum diameter in a direction parallel to the film surface of the macroparticle is greater than 0 and less than or equal to 16 degrees.

[0016] [5] An amorphous hard carbon film as described in any of [1] to [4], having a hardness of 10 GPa to 40 GPa.

[0017] [6] An amorphous hard carbon film according to any one of [1] to [5], wherein the surface roughness index Ra / d, obtained by dividing the surface roughness Ra (μm) of the film surface by the film thickness d (μm), is 0.035 or less.

[0018] [7] The amorphous hard carbon film according to any one of [1] to [6], wherein a hydrogen content is 10 atomic% or less.

[0019] [8] The amorphous hard carbon film according to any one of [1] to [7], wherein a film thickness is 0.1 μm to 20.0 μm.

[0020] [9] A sliding member comprising the amorphous hard carbon film according to any one of [1] to [8], and a base material.

[0021]

[10] A method for producing an amorphous hard carbon film, comprising: a film forming step of applying a pulse voltage as a negative bias voltage to a base material by an arc ion plating method to form an amorphous hard carbon film on the base material, the negative bias voltage applied to the base material is in a range of -100 V to -1000 V, and a frequency of the pulse voltage is less than 1.0 Hz.

[0022]

[11] An apparatus for producing an amorphous hard carbon film, comprising: a film forming mechanism that applies a pulse voltage as a negative bias voltage to a base material by an arc ion plating method to form an amorphous hard carbon film on the base material, wherein a bias power supply control unit included in the film forming mechanism controls the negative bias voltage applied to the base material to fall within a range of -100 V to -1000 V, and controls a frequency of the pulse voltage to be less than 1.0 Hz.

Effects of the Invention

[0023] According to one aspect of the present invention, there can be provided an amorphous hard carbon film having low surface roughness and low hardness, a method for producing the same, an apparatus for producing the same, and a sliding member.

Brief Description of Drawings

[0024] [Figure 1] FIG. 1 is a schematic diagram showing the structure of an amorphous hard carbon film according to an embodiment of the present invention. [Figure 2] This is a schematic diagram representing the structure of a conventional amorphous hard carbon film. [Figure 3] This figure shows an example of the pulse shape of a pulse voltage applied to a substrate as a negative bias voltage in a method for manufacturing an amorphous hard carbon film by arc ion plating according to one embodiment of the present invention. [Figure 4] This is a block diagram showing the schematic configuration of a manufacturing apparatus for amorphous hard carbon films according to one embodiment of the present invention. [Modes for carrying out the invention]

[0025] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more, B or less".

[0026] [1] Amorphous hard carbon film In order to solve the above problems, the inventors of the present invention investigated whether it would be possible to reduce the hardness of an amorphous hard carbon film by modifying the negative bias voltage applied to the substrate under deposition conditions where the substrate temperature is 200°C or lower when forming an amorphous hard carbon film using the arc ion plating method.

[0027] Conventionally, the negative bias voltage applied to the substrate was either a DC bias or, in the case of a pulse bias, a pulse voltage with a period of several Hz to several hundred Hz. In contrast, the inventors applied a negative bias voltage in the range of -100V to -1000V, and a pulse voltage with a frequency of less than 1.0 Hz, which is completely different from conventional methods. Surprisingly, they found that it was possible to reduce the hardness of an amorphous hard carbon film even under film formation conditions where the substrate temperature was 200°C or less.

[0028] Furthermore, the amorphous hard carbon film obtained in this way had low surface roughness. In film deposition using the arc ion plating method, fine particles (macroparticles) with diameters of several tens of nanometers to several micrometers are emitted from the cathode during arc discharge and incorporated into the amorphous hard carbon film during deposition, which can increase surface roughness. Figure 2 is a schematic diagram representing the structure of a conventional amorphous hard carbon film. As shown in Figure 2, macroparticles 4 incorporated into the amorphous hard carbon film 2 by the heat during deposition grow from these macroparticles 4 as a starting point for growth, becoming abnormal growths 5 that spread out in a roughly conical shape toward the film surface 3. A part of these abnormal growths 5 protrudes from the film surface 3, forming raised parts 6, which increases the surface roughness of the amorphous hard carbon film 2. When the inventors of the present invention observed a cross-section perpendicular to the plane direction of an amorphous hard carbon film whose hardness had been reduced by the method described above using a scanning electron microscope (SEM, hereinafter abbreviated as "SEM"), they found that the sides of the abnormal growths that spread out in a roughly conical shape toward the film surface had a stepped shape, and that this roughly conical spreading was significantly smaller than the roughly conical spreading of abnormal growths in conventional amorphous hard carbon films. Due to the shape of these abnormal growths, the diameter of the raised portion protruding from the film surface becomes smaller. Therefore, it is thought that the surface roughness of the obtained amorphous hard carbon film was reduced.

[0029] In other words, an amorphous hard carbon film according to one embodiment of the present invention is an amorphous hard carbon film coated on the surface of a substrate, wherein the amorphous hard carbon film has a raised portion on its surface from which a part of an abnormally grown product, which has grown using macroparticles present in the amorphous hard carbon film as a starting point for growth, protrudes, and in a cross section perpendicular to the plane direction of the amorphous hard carbon film, the side surface of the abnormally grown product from the starting point of growth to each of the two intersections between the raised portion and the surface of the amorphous hard carbon film has a stepped shape.

[0030] (Amorphous hard carbon film) In one embodiment of the present invention, the amorphous hard carbon film is a film of amorphous carbon mainly composed of carbon, commonly known as a DLC (diamond-like carbon) film. Preferably, the amorphous hard carbon film is a hydrogen-free amorphous hard carbon film formed using solid carbon as the carbon raw material. Furthermore, from the viewpoint of more effectively solving the problem of the present invention, which is to obtain an amorphous hard carbon film with low surface roughness and low hardness, it is even more preferable that the hydrogen-free amorphous hard carbon film is an amorphous hard carbon film formed using the arc ion plating method.

[0031] Figure 1 is a schematic diagram showing the structure of an amorphous hard carbon film according to one embodiment of the present invention. As shown in Figure 1, the amorphous hard carbon film 2 according to one embodiment of the present invention has raised portions 6 on the film surface 3 from which a part of an abnormally grown product 5, which has grown using macroparticles 4 present in the amorphous hard carbon film 2 as a starting point for growth, protrudes. In this specification, the "film surface" of the amorphous hard carbon film is the surface having the raised portions that is opposite to the substrate 1. When a substrate coated with an amorphous hard carbon film is used as a sliding member, the "film surface" constitutes the outermost surface of the sliding member. The outermost surface is the part that comes into contact with the mating member in the sliding portion formed by the sliding member.

[0032] In a cross-section perpendicular to the plane direction of the amorphous hard carbon film, the angle between the two lines connecting each of the two intersection points 7 between the raised portion 6 and the film surface 3 of the amorphous hard carbon film and the closer of the two points of maximum diameter in the direction parallel to the film surface of the macroparticle (the angle represented as "α" in Figure 1, hereinafter referred to as "angle α") is preferably greater than 0 and 16 degrees or less. Note that the angle between the two lines connecting each of the two intersection points 7 between the raised portion 6 and the film surface 3 of the amorphous hard carbon film and the closer of the two points of maximum diameter in the direction parallel to the film surface of the macroparticle refers to the angle enclosed by the two extensions of the two lines extended until they intersect. If the angle α is greater than 0 and 16 degrees or less, the diameter of the raised portion protruding from the film surface becomes smaller. Therefore, the surface roughness of the amorphous hard carbon film becomes smaller.

[0033] Here, in the amorphous hard carbon film according to one embodiment of the present invention, multiple or numerous abnormal growth products are observed. In this specification, the angle α means the average value of the angles α of five or more abnormal growth products arbitrarily selected from the abnormal growth products included in a cross section perpendicular to the plane direction of the amorphous hard carbon film. If the number of abnormal growth products included in the cross section is less than five, it means the average value of the angles α of all observed abnormal products. The method for measuring the angle α is not particularly limited, and for example, the following method can be given. First, an image is obtained by observing an arbitrary cross section obtained by cutting the amorphous hard carbon film in a direction perpendicular to the plane direction using a SEM. Within the image, select five or more abnormal growths, or if the number of abnormal growths in the cross-section is less than five, select all observed abnormal products. For each abnormal growth, draw a straight line connecting the closer of the two points with the maximum diameter in the direction parallel to the film surface of the macroparticle of the abnormal growth to each of the two intersection points between the raised portion of the abnormal growth and the film surface of the amorphous hard carbon film. Measure the angle between the two resulting straight lines. Calculate the average value of the measured angles.

[0034] In the amorphous hard carbon film according to this embodiment, in a cross-section perpendicular to the plane direction, the side surface of the abnormal growth product from the starting point of growth to two intersections between the raised portion and the film surface of the amorphous hard carbon film has a stepped shape. Here, it is thought that the stepped shape is due to the alternating changes in the growth angle of the macroparticles. In film deposition using the arc ion plating method, for example, by applying a negative bias voltage to the substrate in the range of -100V to -1000V and a pulse voltage with a frequency of less than 1.0Hz to the substrate, it is thought that portions in which macroparticles grew perpendicular to the film surface and portions in which they grew spreading out in a substantially conical shape were alternately formed. Here, the portion in which macroparticles grew perpendicular to the film direction is the portion to which a bias voltage was applied to the substrate, and the portion that spreads out in a substantially conical shape is the portion to which a bias voltage was not applied to the substrate. Because the abnormal growth product has this shape, the substantially conical spreading is reduced, and therefore the diameter of the raised portion protruding from the film surface is reduced. Therefore, the surface roughness of the amorphous hard carbon film is reduced. In the stepped shape, the length of each step, in which the growth angle changes alternately, is, for example, 2 nm or more. There is no particular upper limit to the length of each step, but for example, it is 50 nm or less.

[0035] Furthermore, in the amorphous hard carbon film according to this embodiment, the shape of the raised portion that protrudes from the surface of the amorphous hard carbon film, where a part of the abnormal growth is located, is preferably rounded, or in other words, not angular. If the raised portion is not angular, when the substrate coated with the amorphous hard carbon film is slid as a sliding member, the aggressiveness towards the mating member it slides against can be reduced, and the sliding performance in the initial stages of sliding, i.e., the initial break-in period, can be improved.

[0036] The shape of the side surface and the shape of the raised portion can be confirmed by observing any cross-section obtained by cutting the amorphous hard carbon film in a direction perpendicular to the surface direction using a scanning electron microscope (SEM) or optical microscope.

[0037] In one embodiment of the present invention, the hardness of the amorphous hard carbon film is preferably 10 GPa to 40 GPa. If the hardness of the amorphous hard carbon film is within the above range, when the substrate coated with the amorphous hard carbon film is slid as a sliding member, the aggressiveness towards the mating member it slides against can be reduced, and the initial sliding performance, i.e., the initial break-in, can be improved. The lower limit of the hardness of the amorphous hard carbon film is more preferably 15 GPa or more, and even more preferably 20 GPa or more. The upper limit of the hardness is more preferably 35 GPa or less, and even more preferably 30 GPa or less.

[0038] Here, the hardness refers to the indentation hardness that can be measured when a diamond indenter is pressed into an object, and can be measured, for example, by the nanoindentation method.

[0039] In one embodiment of the present invention, the surface roughness Ra of the amorphous hard carbon film is preferably 0.001 μm to 0.700 μm. If the surface roughness Ra of the amorphous hard carbon film is within the above range, when the substrate coated with the amorphous hard carbon film is slid as a sliding member, the aggressiveness towards the mating member being slid can be reduced, and the initial sliding performance, i.e., the initial break-in, can be improved. The lower limit of the surface roughness Ra of the amorphous hard carbon film is more preferably 0.002 μm or more, and even more preferably 0.003 μm or more. The upper limit of the surface roughness Ra is more preferably 0.600 μm or less, and even more preferably 0.500 μm or less. Here, the surface roughness Ra is a value measured by a method conforming to ANSI B46.1, and can be measured, for example, by the method described in the examples.

[0040] In one embodiment of the present invention, the thickness d of the amorphous hard carbon film is preferably 0.1 μm to 20.0 μm. A thickness d of 0.1 μm or more is preferable because it effectively reduces the aggressiveness towards the mating member when the substrate coated with the amorphous hard carbon film is slid as a sliding member. A thickness d of 20.0 μm or less is preferable because it prevents the sliding member from becoming excessively large and difficult to incorporate into machinery or other devices. The lower limit of the thickness d of the amorphous hard carbon film is more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. The upper limit of the thickness d is more preferably 15.0 μm or less, and even more preferably 10.0 μm or less. Here, the thickness d can be measured by observing an arbitrary cross-section obtained by cutting the amorphous hard carbon film in a direction perpendicular to the surface direction using a scanning electron microscope (SEM). Furthermore, the film thickness d can be adjusted by the deposition time required to form the amorphous hard carbon film.

[0041] In one embodiment of the present invention, the surface roughness index Ra / d, obtained by dividing the surface roughness Ra (μm) of the amorphous hard carbon film surface by the film thickness d (μm), is preferably 0.035 or less. If the surface roughness index Ra / d of the amorphous hard carbon film is within the above range, when the substrate coated with the amorphous hard carbon film is slid as a sliding member, the aggressiveness towards the mating member it slides against can be reduced, and the sliding performance in the initial stages of sliding, i.e., the initial break-in, can be improved. The upper limit of the surface roughness index Ra / d of the amorphous hard carbon film is more preferably 0.030 or less, and even more preferably 0.025 or less.

[0042] In one embodiment of the present invention, the hydrogen content of the amorphous hard carbon film is preferably 10 atomic percent or less. The hydrogen content of an amorphous hard carbon film formed using the arc ion plating method is usually 10 atomic percent or less. A hydrogen content of 10 atomic percent or less is preferable because it provides higher hardness and better heat resistance than a higher hydrogen content. The lower limit of the hydrogen content is 0, the upper limit is more preferably 5 atomic percent or less, and most preferably 0. The hydrogen content can be measured by HFS (Hydrogen Forward Scattering) analysis.

[0043] In one embodiment of the present invention, in addition to the amorphous hard carbon film described above, one or more other amorphous hard carbon layers different from the amorphous hard carbon film may be formed on the side opposite to the surface of the film. The other amorphous hard carbon layers are formed between the amorphous hard carbon film and the substrate. The thickness of the other amorphous hard carbon layers is not particularly limited as long as it does not impair the effects of the present invention.

[0044] (base material) An amorphous hard carbon film according to one embodiment of the present invention is an amorphous hard carbon film that is coated on the surface of a substrate. Here, "coated on the surface of the substrate" means that it covers the surface of the substrate, whether it is directly coated on the surface of the substrate or indirectly coated with other layers in between.

[0045] The substrate material may be selected according to the application. The substrate material may, for example, be used in a sliding member whose sliding surface is a surface coated with an amorphous hard carbon film according to one embodiment of the present invention. When the sliding member is used in the manufacture of a piston ring, piston pin, or compressor, the substrate material for the vibrating member can be any of the substrate materials commonly used for piston rings, piston pins, and compressors, such as various types of steel, stainless steel, cast iron, and cast steel.

[0046] An amorphous hard carbon film according to one embodiment of the present invention can be formed even under film formation conditions where the substrate temperature is 200°C or lower, and is therefore particularly suitable for use with substrates that tend to soften when the substrate temperature rises. Examples of such substrates include chromium-molybdenum steel (SCM) and alloy tool steel (SKS, SKD, SKT).

[0047] The substrate may be pre-treated as necessary before being coated with an amorphous hard carbon film. Examples of such pre-treatment include adjusting the surface roughness by surface polishing and cleaning the surface using a cleaning agent and plasma.

[0048] [2] Sliding member A sliding member according to one aspect of the present invention includes the amorphous hard carbon film and the substrate. Because the amorphous hard carbon film has a low surface roughness and low hardness, such a sliding member can reduce the aggressiveness towards the mating member that slides against it in the sliding part, and can also improve the sliding performance in the initial stages of sliding.

[0049] (Other layers) In one embodiment of the present invention, the sliding member may include an intermediate layer between the substrate and the amorphous hard carbon film (or amorphous hard carbon layer if another amorphous hard carbon layer is formed thereon; hereinafter, the amorphous hard carbon film and the amorphous hard carbon layer may be collectively referred to as "amorphous hard carbon film, etc."). The intermediate layer may be a layer for improving the adhesion between the substrate and the amorphous hard carbon film, etc., and is composed of a metal element or its metal carbide that has lattice compatibility with the metal constituting the substrate and is more likely to form carbides with the carbon of the first amorphous carbon layer than the metal. Specifically, the metal element is at least one metal element selected from the group consisting of titanium (Ti), chromium (Cr), silicon (Si), cobalt (Co), vanadium (V), molybdenum (Mo), and tungsten (W).

[0050] The thickness of the intermediate layer is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.03 μm or more, even more preferably 0.05 μm or more, and particularly preferably 0.1 μm or more. If the thickness of the intermediate layer is equal to or greater than the above values, it is preferable in that the intermediate layer can suitably improve the adhesion between the substrate and the amorphous hard carbon film, etc. On the other hand, if the intermediate layer is excessively thick, deformation of the intermediate layer may adversely affect the adhesion between the substrate and the amorphous hard carbon film, etc. Therefore, from the viewpoint of preventing the aforementioned adverse effects, the thickness of the intermediate layer is preferably 5 μm or less, more preferably 0.4 μm or less, even more preferably 0.3 μm or less, and particularly preferably 0.2 μm or less.

[0051] [3] Method for producing amorphous hard carbon film A method for manufacturing an amorphous hard carbon film according to one embodiment of the present invention is a method for manufacturing an amorphous hard carbon film according to one embodiment of the present invention, comprising a film formation step of forming an amorphous hard carbon film on a substrate by an arc ion plating method, wherein the negative bias voltage applied to the substrate is in the range of -100V to -1000V, and the frequency of the pulse voltage is less than 1.0Hz.

[0052] (Film forming process) Arc ion plating is a method of forming an amorphous hard carbon film by depositing carbon ions onto a substrate by evaporating and ionizing a carbon material using an arc discharge and then blowing the carbon ions onto the substrate. Arc ion plating is also called arc PVD and is performed under vacuum.

[0053] The arc ion plating method is not particularly limited and may be, for example, a filtered arc ion plating method that filters out macroparticles emitted from the cathode, or a filterless arc ion plating method. A filtered arc ion plating method is more preferable because it can reduce macroparticles.

[0054] In the film formation process, an amorphous hard carbon film is formed on the substrate by applying a pulsed voltage as a negative bias voltage using the arc ion plating method. The negative bias voltage applied to the substrate is preferably in the range of -100V to -1000V, more preferably in the range of -200V to -1000V, and even more preferably in the range of -500V to -1000V.

[0055] Furthermore, the frequency of the pulse voltage is preferably less than 1.0 Hz, more preferably 0.5 Hz or less, and even more preferably 0.1 Hz or less.

[0056] If the negative bias voltage applied to the substrate is within the range and the frequency of the pulse voltage is within the range, it is preferable that the hardness of the amorphous hard carbon film can be reduced even under film formation conditions where the substrate temperature is 200°C or less.

[0057] Furthermore, by applying a pulse voltage in the range of -100V to -1000V at the aforementioned frequency, a portion of the abnormal growth material will grow straight upward when bias is applied, thereby reducing the conical spread of the abnormal growth material. Consequently, the diameter of the raised portion protruding from the film surface becomes smaller, thereby reducing the surface roughness of the amorphous hard carbon film.

[0058] Figure 3 shows an example of the pulse shape of the pulse voltage applied to the substrate in the film-forming process according to one embodiment of the present invention. In the example in Figure 3, the negative bias voltage applied to the substrate is -1000V, and the frequency of the pulse voltage is 0.1Hz. In other words, in the example in Figure 3, during film formation at 0V, a bias voltage of -1000V is periodically applied to the substrate at a rate of once every 10 seconds, and the period is 1 second / period = 1 second / 10 seconds = 0.1Hz.

[0059] In the example shown in Figure 3, a bias voltage of -1000V is applied to the substrate with a pulse width of 1 second at a rate of once every 10 seconds. The duty cycle, which is the ratio of the pulse width to the period, i.e., (pulse width (seconds) / period (seconds)) × 100 (%), is (1 second / 10 seconds) × 100 = 10% in the example shown in Figure 3. In this film-forming process, the duty cycle is preferably less than 45%, preferably less than 42%, and more preferably less than 40%. If the duty cycle is within the above range, it is more preferable from the viewpoint of adjusting the substrate temperature to 200°C or less.

[0060] The substrate temperature during the film formation process is preferably 200°C or lower. A substrate temperature of 200°C or lower suppresses the abnormal growth of macroparticles, thereby reducing the surface roughness of the amorphous hard carbon film. Furthermore, substrates that soften easily at high temperatures can be used. The lower limit of the substrate temperature is not limited to this, but is, for example, 50°C. Here, the substrate temperature can be monitored, for example, by a thermocouple thermometer installed inside the film formation apparatus.

[0061] In one embodiment of the present invention, the temperature of the substrate can be lowered by applying the aforementioned predetermined pulse bias to the substrate. However, the substrate temperature is determined by the total amount of ion energy applied to the substrate, and the total amount of ion energy can also be increased by increasing the substrate bias voltage, increasing the number of evaporation sources in the arc ion plating method, and increasing the arc current. If the total amount of ion energy becomes large and the substrate temperature exceeds 200°C, the formation of the amorphous hard carbon film may be interrupted as appropriate in the film formation process, and the substrate may be cooled once or multiple times.

[0062] Furthermore, the method for manufacturing an amorphous hard carbon film according to one embodiment of the present invention may optionally include other steps in addition to the film formation step. Examples of such other steps include a step of forming the intermediate layer on the substrate, and a step of forming the other amorphous hard carbon layer between the amorphous hard carbon film and the substrate. Known methods for forming the intermediate layer and the other amorphous hard carbon layer can be employed in these other steps.

[0063] [4] Apparatus for manufacturing amorphous hard carbon film The amorphous hard carbon film according to one embodiment of the present invention is manufactured using an arc ion plating apparatus. The structure of the apparatus is not limited in any way other than being able to apply the predetermined pulse voltage as a negative bias voltage to the substrate, and can include conventionally known structures.

[0064] Figure 4 is a block diagram showing the schematic configuration of an amorphous hard carbon film manufacturing apparatus according to one embodiment of the present invention. The manufacturing apparatus 8 according to one embodiment of the present invention is an amorphous hard carbon film manufacturing apparatus and includes a film deposition mechanism 9 that applies a pulse voltage as a negative bias voltage to a substrate by arc ion plating and deposits an amorphous hard carbon film on the substrate. The bias power supply control unit 10 of the film deposition mechanism controls the negative bias voltage applied to the substrate to be in the range of -100V to -1000V and controls the frequency of the pulse voltage to less than 1.0Hz.

[0065] An apparatus for manufacturing an amorphous hard carbon film according to one embodiment of the present invention comprises, for example, a film deposition chamber, a vacuum exhaust pump for evacuating the film deposition chamber to a vacuum, a substrate holder installed in the film deposition chamber for holding a substrate to be processed, a target (carbon material) constituting the cathode, an anode, an arc power supply connected between the target and the anode, a bias power supply for applying a pulse voltage as a negative bias voltage to the substrate, and a bias power supply control unit for controlling the supply of the bias power supply.

[0066] The bias power supply control unit controls the negative bias voltage applied to the substrate within the range of -100V to -1000V, and controls the frequency of the pulse voltage to less than 1.0Hz. This makes it possible to reduce the hardness of the amorphous hard carbon film even under film deposition conditions where the substrate temperature is 200°C or lower. Furthermore, it is possible to manufacture an amorphous hard carbon film with low surface roughness and low hardness. [Examples]

[0067] The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited by these examples.

[0068] [Measurement Methods and Evaluation Methods] The measurement and evaluation methods for various items used in the examples and comparative examples are described below.

[0069] (film thickness) The steel substrates coated with amorphous hard carbon films obtained in the examples and comparative examples were cut in a direction perpendicular to the plane direction of the amorphous hard carbon film. The resulting cross-sections were then chemically polished by ion milling (CP processing), and the thickness of the amorphous hard carbon film was measured by observing the cross-sections using a scanning electron microscope (SEM).

[0070] (Evaluation of the shape of abnormally grown organisms) The steel substrates coated with amorphous hard carbon films obtained in the examples and comparative examples were subjected to CP processing using the method described in the (film thickness) section above. Cross-sections were observed using an optical microscope and a scanning electron microscope, and the following (1) and (2) were evaluated.

[0071] (1) The shape of the side surface of the abnormal growth from the starting point of the abnormal growth to two intersection points between the raised portion where a part of the abnormal growth protrudes from the surface of the amorphous hard carbon film and the surface of the amorphous hard carbon film.

[0072] (2) The shape of the raised portion of the abnormally grown product.

[0073] (Angle α) Images were obtained by observing the cross-sections of the steel substrates coated with amorphous hard carbon films, obtained in the examples and comparative examples, using a scanning electron microscope (SEM), after CP processing using the method described in the (film thickness) section above. Within the images, five or more abnormal growths were arbitrarily selected, or if the number of abnormal growths in the image was less than five, all observed abnormal products were selected. For each abnormal growth, a straight line was drawn connecting the closer of the two points of maximum diameter in the direction parallel to the film surface of the macroparticle that is the starting point of the growth of the abnormal growth, and each of the two intersection points between the raised portion of the abnormal growth and the film surface of the amorphous hard carbon film. The angle between the two resulting straight lines was measured. The average value of the measured angles was calculated.

[0074] (film thickness) The steel substrates coated with amorphous hard carbon films obtained in the examples and comparative examples were subjected to a Calotest test, and the film thickness was measured. The Calotest was performed using a steel ball with a diameter of 30 mm and a diamond slurry with a particle size greater than 0 μm and less than or equal to 2 μm, so that the diameter of the Calotest marks on the Cr substrate (described later) was 25% or less of the diameter of the Calotest marks on the obtained amorphous hard carbon film.

[0075] (hardness) Hardness was measured using the nanoindentation method, with a triangular pyramidal indenter (Berkovich indenter) and a load of 300 mgf. Specifically, the hardness of the amorphous hard carbon film was measured using an ultra-micro indentation hardness tester (ENT-1100a, manufactured by Elionix Co., Ltd.) with a load of 300 mgf, 500 load divisions, and a load application time of 1 second.

[0076] (Surface roughness of the film surface, and surface roughness index) For the steel substrates coated with amorphous hard carbon films obtained in the examples and comparative examples, the surface roughness Ra of the amorphous hard carbon film was measured using a tactile roughness meter (Dektak 150, ULVAC, Inc.) in accordance with ANSI B46.1. Subsequently, the measured surface roughness Ra (unit: μm) value was divided by the film thickness d (unit: μm) of the amorphous hard carbon film to calculate the surface roughness index (Ra / d), which is the surface roughness per unit film thickness.

[0077] (Evaluation of sliding properties) The steel substrates coated with amorphous hard carbon films obtained in the examples and comparative examples were used as sliding members and tested in a ball-on-disk type sliding tester under unlubricated conditions to evaluate mating force and initial break-in properties.

[0078] Specifically, a flat plate-shaped test specimen with a diameter of 31 mm was cut from a steel substrate coated with an amorphous hard carbon film, as obtained in the examples and comparative examples, and used as a sliding test specimen. The thickness of the sliding test specimen was 3 mm. A spherical test specimen with a diameter of 10 mm (material: A5052) was used as the mating test specimen.

[0079] Using a ball-on-disc type sliding test machine, specifically a reciprocating sliding test device (manufactured by OPTIMOL, product name SRV5), sliding tests were conducted under the following conditions without lubrication. • Frequency: 5Hz • Test temperature: 30°C • Load: 20N • Exam time: 10 minutes Initial break-in was determined by the time it took for the coefficient of friction to become constant after the start of the sliding test. Tests where the coefficient of friction became constant quickly (within 1 minute of the start of the sliding test) were marked with ○, and those where it took a long time (more than 1 minute of the start of the sliding test) were marked with ×.

[0080] The aggressiveness towards the mating part was determined by observing the mating test piece under a microscope after the sliding test was completed, and measuring the size of the worn area. A small worn area (0.1 mm) indicates aggressiveness. 2 Items with a wear area of ​​less than 0.1 mm are marked with a circle (〇), and items with a large wear area (0.1 mm) are marked with a circle (〇). 2 The above items were marked with an "X".

[0081] [Example 1] As the base material, a steel material made of chromium-molybdenum steel (product name: SCM415, Rockwell hardness (HRC): approximately 58) was used, and an amorphous hard carbon film was coated onto the base material.

[0082] Using a filtered vacuum arc PVD apparatus (hereinafter referred to as FVA apparatus) that filters macroparticles generated from the target, the steel substrate was placed in a substrate holder that rotates 2R inside a vacuum chamber. Subsequently, the vacuum chamber was evacuated. Then, argon (Ar) gas was introduced into the evacuated vacuum chamber, and Ar plasma was generated by glow discharge, followed by the generation of Ar plasma using secondary electron emission to clean the surface of the substrate.

[0083] Inside the vacuum chamber, a chromium (Cr) intermediate layer (Cr base) was coated onto the cleaned substrate by sputtering using a chromium (Cr) target. Then, while evacuating the inside of the vacuum chamber, the substrate was left to cool until its temperature fell below 100°C.

[0084] After the substrate temperature had decreased, the substrate was coated by depositing an amorphous hard carbon film on it in the vacuum chamber under the following conditions: Ar gas 3 sccm, arc current 150 A, substrate temperature 150°C, substrate pulse bias frequency 0.1 Hz, duty cycle 10%, and voltage 0V-1000V. The pulse bias had the pulse shape shown in Figure 3.

[0085] In the examples and comparative examples, since the temperature tends to rise when the total ion energy is large, a cooling step was included to control the substrate temperature so that it did not exceed the set temperature during coating.

[0086] For steel substrates coated with the obtained amorphous hard carbon film, the film thickness d, morphology of abnormal growths, angle α, hardness, surface roughness Ra, and surface roughness index were measured and evaluated. Furthermore, the sliding properties of the steel substrates coated with the amorphous hard carbon film were evaluated when used as sliding members.

[0087] [Example 2] Except for changing the substrate temperature to 190°C, the substrate pulse bias frequency to 0.4 Hz, the duty cycle (i.e., pulse width / period of a -100V pulse voltage) to 40%, and the voltage to 0V-100V, the same procedure as in Example 1 was performed to deposit an amorphous hard carbon film on the substrate, and the sliding properties of the amorphous hard carbon film were evaluated.

[0088] [Comparative Example 1] An amorphous hard carbon film was formed on the substrate using the same procedure as in Example 1, except that the substrate temperature was 150°C and no bias voltage was applied. The sliding properties of the amorphous hard carbon film were then evaluated.

[0089] [Comparative Example 2] Except for the substrate temperature being 300°C and the application of a -50V DC bias to the substrate, the same procedure as in Example 1 was performed to deposit an amorphous hard carbon film on the substrate, and the sliding properties of the amorphous hard carbon film were evaluated.

[0090] [Comparative Example 3] Except for the substrate temperature being 210°C, and the substrate pulse bias frequency being changed to 0.5 Hz, the duty cycle (i.e., pulse width / period of the -100V pulse voltage) to 50%, and the voltage to 0V-100V, the same procedure as in Example 1 was performed to deposit an amorphous hard carbon film on the substrate, and the sliding properties of the amorphous hard carbon film were evaluated.

[0091] [Comparative Example 4] Except for the substrate temperature being 180°C, and the substrate pulse bias frequency being changed to 0.5 Hz, the duty cycle (i.e., pulse width / period of the -100V pulse voltage) to 50%, and the voltage to 0V-100V, the same procedure as in Example 1 was performed to deposit an amorphous hard carbon film on the substrate, and the sliding properties of the amorphous hard carbon film were evaluated.

[0092] [Comparative Example 5] Except for the substrate temperature being 170°C, and the substrate pulse bias frequency being changed to 10.0 Hz, the duty cycle (i.e., pulse width / period of the -100V pulse voltage) to 5%, and the voltage to 0V-100V, the same procedure as in Example 1 was performed to deposit an amorphous hard carbon film on the substrate, and the sliding properties of the amorphous hard carbon film were evaluated.

[0093] [Table 1]

[0094] [Evaluation Results] Table 1 shows the film formation conditions for amorphous hard carbon films in the examples and comparative examples, as well as the evaluation results of the amorphous hard carbon films and their sliding properties.

[0095] As shown in Table 1, in Example 1, where the substrate was coated under the conditions of a substrate pulse bias frequency of 0.1 Hz, duty cycle of 10%, voltage of 0V-1000V, and substrate temperature of 150°C, and in Example 2, where the substrate was coated under the conditions of a substrate pulse bias frequency of 0.4 Hz, duty cycle of 40%, voltage of 0V-100V, and substrate temperature of 190°C, amorphous hard carbon films with low hardness and a small surface roughness index were obtained. Furthermore, the sides of the abnormal products had a stepped shape. Substrates coated with such amorphous hard carbon films exhibited excellent properties as sliding members, with reduced mating aggressiveness and good initial conformability.

[0096] On the other hand, the amorphous hard carbon film obtained in Comparative Example 1, where no bias voltage was applied and the substrate temperature was 150°C, had high film hardness, and the sliding properties of the coated substrate were characterized by high mating aggression and poor initial conformability. Furthermore, no stepped shape was observed on the side surface of the abnormal product.

[0097] Furthermore, in Comparative Example 2, where a DC bias of -50V was applied to the substrate and the substrate temperature was 300°C, and in Comparative Example 3, where the substrate pulse bias frequency was 0.5Hz, the duty cycle was 50%, the voltage was 0V-100V, and the substrate temperature was 210°C, the substrate temperature was high, and although the resulting amorphous hard carbon film had low hardness, the surface roughness index was large. Also, no stepped shape was observed on the side surface of the abnormal product. When the sliding properties of the coated substrates in Comparative Examples 2 and 3 were evaluated, the initial break-in was poor.

[0098] In Comparative Example 3, the substrate temperature exceeded 200°C, and it is thought that the abnormal growth due to high temperature was dominant over the effect of applying a pulse bias voltage to the substrate, resulting in the abnormal product having a conical shape without a stepped form on its sides.

[0099] In Comparative Example 4, where the substrate pulse bias frequency was 0.5 Hz, the duty cycle was 50%, the voltage was 0V-100V, and the substrate temperature was 180°C, and in Comparative Example 5, where the substrate pulse bias frequency was 10.0 Hz, the duty cycle was 5%, the voltage was 0V-100V, and the substrate temperature was 170°C, the resulting amorphous hard carbon film had low hardness despite the substrate temperature being below 200°C. The surface roughness index was also low. However, in Comparative Examples 4 and 5, the abnormal growths were not conical, but rather nearly straight, growing slightly inward and upward, and the sides did not have a stepped shape. Furthermore, the raised portions where parts of the abnormal growths protruded from the surface of the amorphous hard carbon film had angular tips. Therefore, the sliding properties of the coated substrates in Comparative Examples 4 and 5 were highly aggressive towards the mating surface and had poor initial conformation.

[0100] In Comparative Example 4, the duty cycle exceeded 50%, resulting in a dominant bias effect. Therefore, the abnormally grown plants grew almost straight upwards, and their sides did not have a stepped shape. Similarly, in Comparative Example 5, the frequency was 10.0 Hz, which also resulted in a dominant bias effect. Therefore, the abnormally grown plants grew almost straight upwards, and their sides did not have a stepped shape. [Explanation of Symbols]

[0101] 1 Base material 2. Amorphous hard carbon film 3 Membrane surface 4 Macroparticles 5 Abnormal growth 6 ridges 7. Intersection of the raised portion and the surface of the amorphous hard carbon film.

Claims

1. An amorphous hard carbon film coated on the surface of a substrate, The amorphous hard carbon film has raised portions on its surface, where some of the abnormally grown products, which have grown using macroparticles present in the amorphous hard carbon film as growth starting points, protrude. In a cross-section perpendicular to the plane direction of the amorphous hard carbon film, An amorphous hard carbon film in which the side surface of the abnormal growth product, from the starting point of growth to each of the two intersections between the raised portion and the surface of the amorphous hard carbon film, has a stepped shape.

2. The amorphous hard carbon film according to claim 1, wherein the side surface of the abnormally grown material has a stepped shape in which the growth angle changes alternately.

3. The amorphous hard carbon film according to claim 1, wherein the side surface of the abnormally grown material has a stepped shape in which portions in which the macroparticles grew perpendicular to the film surface and portions in which they grew spreading out in a substantially conical shape are alternately formed.

4. The amorphous hard carbon film according to claim 1, wherein, in a cross-section perpendicular to the plane direction of the amorphous hard carbon film, the angle between the two lines connecting each of the two intersection points of the raised portion and the film surface of the amorphous hard carbon film and the closer of the two points of maximum diameter in a direction parallel to the film surface of the macroparticle is greater than 0 and less than or equal to 16 degrees.

5. The amorphous hard carbon film according to claim 1, wherein the hardness is 10 GPa to 40 GPa.

6. The amorphous hard carbon film according to claim 1, wherein the surface roughness index Ra / d, obtained by dividing the surface roughness Ra (μm) of the film surface by the film thickness d (μm), is 0.035 or less.

7. The amorphous hard carbon film according to claim 1, wherein the hydrogen content is 10 atomic percent or less.

8. The amorphous hard carbon film according to claim 1, wherein the film thickness is 0.1 μm to 20.0 μm.

9. A sliding member comprising an amorphous hard carbon film according to any one of claims 1 to 8 and a substrate.

10. A method for producing an amorphous hard carbon film, The process includes a film deposition step in which a pulsed voltage is applied to a substrate as a negative bias voltage by arc ion plating to form an amorphous hard carbon film on the substrate. The negative bias voltage applied to the substrate is in the range of -100V to -1000V. A method wherein the frequency of the pulse voltage is less than 1.0 Hz.

11. Apparatus for manufacturing amorphous hard carbon films, The device features a film deposition mechanism that applies a pulsed voltage as a negative bias voltage to a substrate using the arc ion plating method, thereby forming an amorphous hard carbon film on the substrate. The bias power supply control unit included in the aforementioned film deposition mechanism The negative bias voltage applied to the substrate is controlled to be within the range of -100V to -1000V, A manufacturing apparatus that controls the frequency of the pulse voltage to less than 1.0 Hz.

Images