Low friction wear film and method for producing the same

Abstract

The low friction and wear film (10) comprises: a chromium layer (11) formed on the surface of a metal substrate (1); a tungsten carbide inclined layer (14) formed on the surface of the chromium layer (11); and a diamond-like carbon layer (15) as a top layer formed on the surface of the tungsten carbide inclined layer (14). The tungsten carbide inclined layer (14) comprises a chromium-tungsten carbide inclined layer (12) and a tungsten carbide uniform layer (13). The chromium-tungsten carbide inclined layer (14) does not form a tungsten concentrated layer containing a single substance of tungsten at the boundary between the chromium-tungsten carbide inclined layer (12) and the tungsten carbide uniform layer (13).

Description

Technical Field

[0001] The present invention relates to a low friction and wear film and a method for producing the same, and more particularly to a low friction and wear film having a DLC layer on a top layer and having improved alkali resistance and a method for producing the same. Background Art

[0002] DLC (diamond-like carbon) has high hardness, low friction coefficient, and wear resistance. Therefore, it is expected that a film having a DLC layer formed on the top layer (the outermost layer) can be used as a low-friction and low-wear film, i.e., a low-friction and wear film, in various fields. For example, by forming a low-friction and wear film with a DLC layer as the top layer on the surface of a die-casting mold, the life of the mold can be extended.

[0003] When a low-friction, low-wear film having a DLC layer as the top layer (hereinafter referred to as a low-friction, low-wear film) is formed on the surface of a metal substrate, a chromium layer (Cr layer) and a layer (WC layer) containing tungsten carbide (WC) are sometimes formed on the low-friction, low-wear film in order to improve its adhesion. In this case, a Cr layer is formed on the surface of the metal substrate, a WC layer is formed on the surface of the Cr layer, and a DLC layer is formed on the surface of the WC layer. The adhesion to the substrate is improved by the Cr layer, and the adhesion of the DLC layer is improved by the WC layer.

[0004] Japanese Patent Publication No. 2001-225412 discloses a low friction wear film having a Cr layer, a Cr-WC inclined layer, and a DLC layer formed in sequence on the surface of a metal substrate. The chromium content of the interface between the Cr-WC inclined layer and the Cr layer is 100wt%, and the chromium content of the interface with the DLC layer is 0wt%, and the composition ratio of Cr decreases and the composition ratio of WC increases from the Cr layer toward the DLC layer. According to the low friction wear film disclosed in Japanese Patent Publication No. 2001-225412, the adhesion can be further improved. Summary of the invention

[0005] The low friction and wear film having a DLC layer as the top layer is required to be further improved from the viewpoint of alkali resistance. Therefore, the present invention provides a low friction and wear film having improved alkali resistance and a method for producing the same.

[0006] The first aspect of the present invention is a low friction and wear film. The low friction and wear film includes: a chromium layer formed on the surface of a metal substrate; a tungsten carbide layer formed on the surface of the chromium layer; and a diamond-like carbon layer as a top layer formed on the surface of the tungsten carbide layer. The tungsten carbide layer includes a chromium-tungsten carbide inclined layer and a tungsten carbide uniform layer. The chromium-tungsten carbide inclined layer includes chromium and tungsten carbide, and has an inclined composition in which the composition ratio of the chromium decreases and the composition ratio of the tungsten carbide increases as it moves away from the chromium layer in the thickness direction. The tungsten carbide uniform layer is formed on the surface of the chromium-tungsten carbide inclined layer and is composed of tungsten carbide. The tungsten carbide layer does not form a tungsten concentrated layer containing tungsten alone at the boundary between the chromium-tungsten carbide inclined layer and the tungsten carbide uniform layer.

[0007] The low friction and wear film comprises a Cr layer formed on the surface of a metal substrate, a WC layer having a Cr-WC inclined layer formed on the surface of the Cr layer and a WC uniform layer formed on the surface of the Cr-WC inclined layer, and a DLC layer formed on the surface of the WC layer, wherein a W concentrated layer containing a single substance of tungsten (W) is formed at the boundary between the Cr-WC inclined layer and the WC uniform layer. The presence of such a W concentrated layer leads to a decrease in alkali resistance. In contrast, according to the above-mentioned configuration, since a tungsten concentrated layer is not formed at the boundary between the chromium-tungsten carbide inclined layer and the tungsten carbide uniform layer, the alkali resistance is high. Therefore, according to the above-mentioned configuration, a low friction and wear film having improved alkali resistance can be provided.

[0008] In the low friction and wear film, the ratio of the atomic concentration of the tungsten to the sum of the atomic concentration of tungsten and the atomic concentration of carbon in the tungsten carbide layer may be 50% or less. According to the above configuration, by adjusting the above ratio to 50% or less, the formation of a tungsten concentrated layer can be prevented. In addition, when there is an excess of carbon component in the tungsten carbide layer, the carbon component and the tungsten carbide component are used to form a tungsten carbide-carbon layer in the tungsten carbide layer.

[0009] The second aspect of the present invention is a method for manufacturing a low-friction wear film. The low-friction wear film comprises: a chromium layer formed on the surface of a metal substrate; a tungsten carbide layer formed on the surface of the chromium layer, the tungsten carbide layer comprising chromium and tungsten carbide, the tungsten carbide layer comprising a chromium-tungsten carbide inclined layer and a tungsten carbide uniform layer, the chromium-tungsten carbide inclined layer having an inclined composition in which the composition ratio of the chromium decreases and the composition ratio of the tungsten carbide increases as it moves away from the chromium layer in the thickness direction, the tungsten carbide uniform layer is formed on the surface of the chromium-tungsten carbide inclined layer and is composed of tungsten carbide; and a diamond-like carbon layer as a top layer formed on the surface of the tungsten carbide layer. The manufacturing method comprises: as a chromium layer film forming step, the chromium layer is formed by causing inert gas ions to collide with a chromium target composed of chromium and arranged in a vacuum chamber, so that chromium atoms knocked out from the chromium target are attached to the surface of the metal substrate; as a chromium-tungsten carbide inclined layer film forming step, the chromium layer is formed by causing inert gas ions to collide with the chromium target and a tungsten carbide target composed of tungsten carbide and causing chromium atoms knocked out from the chromium target and tungsten carbide components knocked out from the tungsten carbide target to attach to the surface of the chromium layer. The present invention relates to a tungsten carbide inclined layer; as a tungsten carbide uniform layer film forming process, the tungsten carbide uniform layer is formed by causing the inert gas ions to collide with the tungsten carbide target set in the vacuum tank and causing the tungsten carbide component knocked out from the tungsten carbide target to adhere to the surface of the chromium-tungsten carbide inclined layer; as a hydrocarbon ionization process, a hydrocarbon gas is introduced into the vacuum tank and the introduced hydrocarbon gas is ionized; and the diamond-like carbon layer is formed by causing the hydrocarbon ionized by the hydrocarbon ionization process to adhere to the surface of the tungsten carbide uniform layer. The hydrocarbon ionization process is started before the tungsten carbide uniform layer film forming process is performed.

[0010] According to the above configuration, the hydrocarbon ionization step is performed before the tungsten carbide uniform layer film forming step is performed. Therefore, ionized hydrocarbons are already present in the vacuum chamber at the start of the tungsten carbide uniform layer film forming step. Therefore, the excess tungsten generated in the tungsten carbide uniform layer film forming step combines with the ionized hydrocarbons to form tungsten carbide, which is consumed, thereby preventing the formation of a tungsten concentrated layer at the boundary portion of the chromium-tungsten carbide inclined layer and the tungsten carbide uniform layer. Therefore, a low friction wear film can be manufactured in which a tungsten concentrated layer is not formed at the boundary between the chromium-tungsten carbide inclined layer and the tungsten carbide uniform layer.

[0011] In the above-mentioned method for manufacturing the low-friction and wear film, the hydrocarbon ionization step can be started simultaneously with the chromium-tungsten carbide inclined layer film forming step. According to the above-mentioned structure, the ionized hydrocarbon can be sufficiently present in the vacuum chamber in advance at the beginning of the tungsten carbide uniform layer film forming step, so that almost all of the excess tungsten generated in the WC uniform layer film forming step can be bonded with the ionized hydrocarbon, thereby preventing the formation of a tungsten concentrated layer due to the excess tungsten generated at the beginning of the film forming of the tungsten carbide uniform layer film forming step. In addition, the excess tungsten generated at the end of the film forming of the chromium-tungsten carbide inclined layer film forming step is bonded with the ionized hydrocarbon to form tungsten carbide, thereby preventing the formation of a tungsten concentrated layer due to the excess tungsten generated at the end of the film forming of the chromium-tungsten carbide inclined layer film forming step. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0013] Figure 1 A schematic diagram showing a cross section of a portion of the low-friction and wear film according to the present embodiment.

[0014] Figure 2 A schematic diagram showing a cross section of a portion of a low friction wear film of the related art.

[0015] Figure 3 This is a TEM image showing a cross section of a portion where peeling of a low-friction wear film according to the related art remains.

[0016] Figure 4A Indicates that Figure 3 TEM image mapped to the mapping image of Cr component.

[0017] Figure 4B Indicates that Figure 3 TEM image mapped to the mapping image of the C component.

[0018] Figure 4C Indicates that Figure 3 TEM image mapped to the mapping image of the W component.

[0019] Figure 5 The cross-sectional view schematically shows a sputtering device for producing the low-friction and wear film according to the present embodiment, as viewed from the plane direction (upward direction).

[0020] Figure 6 It is a schematic diagram of an image showing a process for producing the low-friction and wear film according to the present embodiment.

[0021] Figure 7 : is a schematic diagram showing an image of a manufacturing process of a low friction wear film of the related art.

[0022] Fig. 8A This is a TEM image showing a cross section from the Cr layer to the WC layer in the low friction and wear film formed by the sample prepared in Example 1.

[0023] Figure 8B Yes Fig. 8A TEM image mapped to the mapping image of Cr component.

[0024] Figure 8C Yes Fig. 8A TEM image mapped to the mapping image of the W component.

[0025] Fig.8D Yes Fig. 8A TEM image mapped to the mapping image of the C component.

[0026] Fig.9A TEM image showing a cross section from the Cr layer to the WC layer in the low friction and wear film formed of the sample prepared in Comparative Example 1.

[0027] Fig. 9B Yes Fig.9A TEM image mapped to the mapping image of Cr component.

[0028] Fig. 9C Yes Fig.9A TEM image mapped to the mapping image of the W component.

[0029] Fig.9D Yes Fig.9A TEM image mapped to the mapping image of the C component. DETAILED DESCRIPTION

[0030] Figure 1 A schematic diagram of a cross section of a portion of the low friction and wear film of this embodiment is shown in FIG. Figure 1 As shown, the low friction and wear film 10 of this embodiment includes a Cr layer 11 , a WC layer 14 including a Cr—WC gradient layer 12 and a WC uniform layer 13 , and a DLC layer 15 as a top layer, which are sequentially formed on the surface of a metal substrate 1 .

[0031] The Cr layer 11 is a layer composed of chromium (Cr). The Cr layer 11 is formed on the surface of the metal substrate 1. As the metal substrate 1, an iron substrate is preferably used, especially from the viewpoint of adhesion with the Cr layer. As the iron substrate, for example, alloy tool steel (SKD, SKS, etc.) used in molds and tools can be exemplified, but it is not limited thereto. In addition, the Cr layer 11 is typically formed on the surface of the metal substrate 1 by sputtering.

[0032] The Cr-WC inclined layer 12 is formed on the surface of the Cr layer 11. The Cr-WC inclined layer 12 is configured to have an inclined composition in which the composition ratio of Cr and tungsten carbide (WC) is inclined in the thickness direction. Specifically, the Cr-WC inclined layer 12 is formed so that the composition ratio of Cr decreases and the composition ratio of WC increases as it moves away from the Cr layer 11 in the film thickness direction (the thickness direction of the low friction and wear film). The way the composition ratio of Cr and WC changes is not particularly limited, and it can be a primary change, a secondary change, or a change other than that.

[0033] Typically, the Cr—WC gradient layer 12 is formed by sputtering on the surface of the Cr layer 11. The Cr—WC gradient layer 12 can be formed by adjusting the voltage ratio between the voltage applied to the chromium (Cr) target and the voltage applied to the tungsten carbide (WC) target used in sputtering.

[0034] The WC uniform layer 13 is formed on the surface of the Cr—WC gradient layer 12. The WC uniform layer 13 is a layer composed of WC. Typically, the WC uniform layer 13 is formed on the surface of the Cr—WC gradient layer 12 by sputtering.

[0035] The WC layer 14 includes the above-mentioned Cr-WC gradient layer 12 and the WC uniform layer 13. In addition, the WC layer 14 may include a WC-C layer in which a trace amount of carbon (C) atoms are mixed into WC. Such a WC-C layer is sometimes formed on the surface of the WC uniform layer 13, that is, between the WC uniform layer 13 and the DLC layer 15.

[0036] In addition, a W concentrated layer containing a single substance of tungsten (W) is not formed at the boundary between the Cr-WC inclined layer 12 and the WC uniform layer 13. That is, the WC layer 14 is configured to have the Cr-WC inclined layer 12 and the WC uniform layer 13, and a W concentrated layer is not formed at the boundary between these layers. The effect of not forming a W concentrated layer and the manufacturing method thereof will be described later.

[0037] The DLC layer 15 (diamond-like carbon layer) is formed on the surface of the WC layer 14. The DLC layer 15 constitutes the top layer of the low friction and wear film 10 of this embodiment. 3 Bond and sp of graphite 2 The amorphous carbon film has a skeleton structure of carbon atoms. Therefore, it has both diamond-like properties and graphite-like properties. Therefore, by providing the DLC layer 15 on the top layer, a film with high hardness, low friction and low wear can be formed. The DLC layer 15 is formed on the surface of the WC layer 14 by, for example, a plasma CVD method.

[0038] Thus, the low friction and wear film 10 of the present embodiment includes the Cr layer 11, the WC layer 14 including the Cr-WC inclined layer 12 and the WC uniform layer 13, and the DLC layer 15. Moreover, as described above, no W concentrated layer is formed at the boundary between the Cr-WC inclined layer 12 and the WC uniform layer 13. On the other hand, in the low friction and wear film of the related art, a W concentrated layer is formed at the boundary between the Cr-WC inclined layer and the WC uniform layer. This is described below.

[0039] Figure 2 Schematic diagram showing a cross section of a portion of a low friction wear film 50 of the related art. Figure 2 As shown, the low friction and wear film 50 of the related art is provided with a Cr layer 51 formed on the surface of the metal substrate 1, a WC layer 54 having a Cr-WC inclined layer 52 formed on the surface of the Cr layer 51 and a WC uniform layer 53 formed on the surface of the Cr-WC inclined layer 52, and a DLC layer 55 formed on the surface of the WC layer 54, similarly to the low friction and wear film 10 of the present embodiment. In addition, a W concentrated layer 56 is formed in the low friction and wear film 50 of the related art. The W concentrated layer 56 is formed at the boundary between the Cr-WC inclined layer 52 and the WC uniform layer 53.

[0040] The reason for forming such a W concentrated layer 56 is as follows. The WC component in the Cr-WC inclined layer and the WC component constituting the WC uniform layer are generally supplied to each layer by sputtering of a WC target, and it is determined that the amount of W component (tungsten component) in the WC component knocked out from the WC target is greater than the amount of C component (carbon component). That is, the sputtering rate of W is higher than the sputtering rate of C. Therefore, at the end of the film formation of the Cr-WC inclined layer 52 and the beginning of the film formation of the WC uniform layer 53, a layer containing a simple substance of W is formed due to the excessive W component. The layer containing a simple substance of W formed in this way is formed as a W concentrated layer at the boundary between the Cr-WC inclined layer 52 and the WC uniform layer 53. In addition, at the beginning of the film formation of the Cr-WC inclined layer 52, the composition ratio of WC is small, so it is believed that the W concentrated layer is not formed. In addition, at the end of the film formation of the WC uniform layer 53, the W component and the C component knocked out from the WC target are equal in amount, so it is believed that the W concentrated layer is not formed.

[0041] When a W-concentrated layer is formed at the boundary between the Cr-WC gradient layer and the WC uniform layer, there is a concern that the film may peel off starting from the W-concentrated layer. The reasons are explained below. Figure 1 The low friction wear film 10 of the present embodiment shown and Figure 2In the case of the low friction and wear film 50 of the related art shown in the figure, cracks may be generated on the film surface. In addition, defects such as pinholes may be generated in the film during film formation, and the defects may be exposed to the surface. Moreover, when the W concentrated layer 56 is formed as in the low friction and wear film 50 of the related art, the above-mentioned cracks or defects may also reach the W concentrated layer 56.

[0042] If the low friction wear film 50 of the related art is continuously used in a state where cracks or defects reach the W concentrated layer 56, oxygen in the atmosphere (e.g., air) enters the W concentrated layer 56 through the cracks or defects, and the oxygen that enters contacts the W in the W concentrated layer 56, and the following oxidation reaction occurs. 2W+3O2→2WO3 Furthermore, if the tungsten oxide generated by the above reaction contacts an alkali solution (sodium hydroxide), the following reaction occurs. WO3+2NaOH→Na2WO4+H2O

[0043] The sodium tungstate produced by the above reaction dissolves in the alkali solution. That is, tungstic acid is soluble in the alkali solution. Therefore, the W concentrated layer 56 is dissolved. If the W concentrated layer 56 is dissolved, the portion formed thereon (the WC uniform layer 53 and the DLC layer 55) is peeled off.

[0044] Figure 3 This is a TEM image of a cross section of a portion of a low friction wear film of the related art where peeling occurs. Figure 3 As shown, compared with the Cr-WC gradient layer, the upper layers (WC uniform layer and DLC layer) have been peeled off, and only the Cr layer and the Cr-WC gradient layer remain on the surface of the metal substrate (Fe). Figure 4A to Figure 4C Yes Figure 3 TEM image distribution is mapped to the mapping images of Cr component, C component and W component. Figure 4A is the mapping image of Cr, Figure 4B is the mapping image of C, Figure 4C is the mapping image of W. Figure 4C As shown in detail, W component was detected on the surface of the part remaining in the peeling site, and C component was not detected in the part where the W component was detected. Therefore, it was confirmed that a W concentrated layer was formed at the boundary between the Cr-WC gradient layer and the WC uniform layer, and peeling occurred starting from the part where the W concentrated layer was formed.

[0045] Such a peeling phenomenon occurs significantly, for example, when the low-friction wear film 50 of the related art is applied to the surface of the die-casting mold. The die-casting mold is used in a harsh environment, so cracks sometimes occur in the DLC layer 55 of the top coating layer. When it is used continuously in this state, the cracks reach the W concentrated layer 56. In this way, as described above, the W in the W concentrated layer 56 is oxidized. In addition, in order to remove aluminum and the like attached to the die-casting mold, the die-casting mold is immersed in an alkaline cleaning solution. In this way, sodium tungstate is generated as described above, and the W concentrated layer 56 is dissolved into the alkaline cleaning solution. As a result, the DLC layer 55 and the WC uniform layer 53 are peeled off.

[0046] Therefore, according to the low friction and wear film 50 of the related art, since the W concentrated layer 56 is formed at the boundary between the Cr-WC inclined layer 52 and the WC uniform layer 53, the alkali resistance is low and the corrosion resistance is insufficient. In contrast, according to the low friction and wear film 10 of the present embodiment, the WC layer 14 is configured so that the W concentrated layer is not formed at the boundary between the Cr-WC inclined layer 12 and the WC uniform layer 13. Therefore, even if defects such as cracks are formed in the film, tungsten oxide is not formed in the WC layer 14, so that even when immersed in an alkaline solution, it is possible to prevent the DLC layer 15 and the WC uniform layer 13 from peeling off.

[0047] Next, a method for producing the low-friction and wear film 10 according to the present embodiment will be described. Figure 5 2 is a cross-sectional view schematically showing a sputtering device 100 for manufacturing the low friction and wear film 10 of the present embodiment, viewed from the plane direction (upward direction). Figure 5 As shown in FIG. 1 , the sputtering device 100 includes a vacuum chamber 101 having an internal space. A rotary table 102 is disposed in the vacuum chamber 101 .

[0048] The plane shape of the rotating worktable 102 is as follows: Figure 5 As shown, it is formed into a circle. On the upper surface of the rotating workbench 102, multiple ( Figure 5 The disc-shaped substrate holders 103 (eight in the embodiment) are arranged at regular intervals in the circumferential direction of the rotary table 102. The central axis of each substrate holder 103 is parallel to the central axis of the rotary table 102. In addition, a plurality of substrates (iron substrates in this embodiment) are placed and held on the plurality of substrate holders 103, respectively.

[0049] The rotary table 102 is configured to rotate in a predetermined direction (eg, Figure 5 In addition, the plurality of substrate holders 103 provided on the rotary table 102 are configured to rotate in a predetermined rotation direction (for example, as shown in the clockwise rotation direction indicated by the arrow A) around their central axis by a driving means not shown in the figure. Figure 5The rotating table 102 rotates (rotates) in the clockwise direction (in the direction indicated by the arrow B). Therefore, by rotating the rotating table 102 and the substrate holder 103, the iron substrate on the substrate holder 103 rotates while revolving. In addition, a bias power supply 104 is connected to the rotating table 102. The bias power supply 104 is configured to apply a negative bias voltage to the rotating table 102, the substrate holder 103, and the iron substrate held by the substrate holder 103.

[0050] In addition, the vacuum chamber 101 is provided with an exhaust port 105, an Ar gas inlet 106, and a hydrocarbon gas inlet 107. The exhaust port 105 is connected to a vacuum pump, the Ar gas inlet 106 is connected to an Ar gas source, and the hydrocarbon gas inlet 107 is connected to a hydrocarbon gas source. Examples of the hydrocarbon gas source include an acetylene gas source and a methane gas source.

[0051] In addition, a pair of Cr targets 111, 111 and a pair of WC targets 112, 112 are provided in the vacuum chamber 101. The pair of Cr targets 111, 111 are respectively made of chromium, such as Figure 5 As shown in FIG. 1 , when viewed from the plane direction, the rotating table 102 is clamped and arranged to face each other in the radial direction of the rotating table 102. A pair of WC targets 112, 112 are respectively made of tungsten carbide, such as Figure 5 As shown, when viewed from the plane direction, the rotating table 102 is clamped and arranged to face each other in the radial direction of the rotating table 102. The opposing direction of the pair of Cr targets 111, 111 is approximately orthogonal to the opposing direction of the pair of WC targets 112, 112. Therefore, the targets are arranged at intervals of 90 degrees in the circumferential direction of the rotating table 102. The pair of Cr targets 111, 111 are respectively connected to Cr sputtering power supplies 113, 113 arranged outside the vacuum chamber 101. The pair of WC targets 112, 112 are respectively connected to WC sputtering power supplies 114, 114 arranged outside the vacuum chamber 101. Negative voltage (sputtering voltage) is applied to these targets by each sputtering power supply.

[0052] When the low-friction and wear film 10 of the present embodiment is manufactured using the sputtering device 100 having the above-mentioned structure, first, the iron substrate is held in the substrate holder 103. Next, the vacuum chamber 101 is closed, and the vacuum pump connected to the exhaust port 105 is operated to reduce the pressure inside the vacuum chamber 101 to a predetermined low pressure. In addition, the rotary table 102 and each substrate holder 103 are rotated to rotate and revolve the iron substrate held in the substrate holder 103. By causing the iron substrate to revolve in the vacuum chamber 101, the low-friction and wear film 10 can be uniformly formed on the surface of the iron substrate.

[0053] Next, a Cr layer film forming process is performed. In the Cr layer film forming process, while the internal pressure of the vacuum chamber 101 is maintained at a predetermined low pressure, Ar gas as an inert gas is introduced into the vacuum chamber 101 from the Ar gas inlet 106 connected to the Ar gas source, and the Cr sputtering power supply 113 is controlled in such a way as to apply a predetermined negative high voltage to the Cr target 111. As a result, discharge is induced from the Cr target 111, and plasma 121 is generated in front of the Cr target 111 (facing the surface of the rotary table 102). The Ar gas is ionized in the plasma 121, and the ionized Ar gas (Ar + ) is negatively charged and collides with the Cr target 111, so that Cr is knocked out from the Cr target 111. The knocked-out Cr atoms adhere to the surface of the iron substrate held by the substrate holder 103, thereby forming (filming) a Cr layer 11 on the surface of the iron substrate.

[0054] After a predetermined time has passed or the film thickness of the Cr layer 11 reaches a predetermined film thickness, the Cr layer film forming process is terminated, and then the Cr-WC inclined layer film forming process is implemented. In the Cr-WC inclined layer film forming process, while a negative voltage is applied to the Cr target 111, a negative voltage is also applied to the WC target 112 using the WC sputtering power supply 114, and a plasma 122 is also generated in front of the WC target 112. In addition, at the same time as the Cr-WC inclined layer film forming process starts, a hydrocarbon gas such as acetylene is introduced into the vacuum chamber 101 from a hydrocarbon gas inlet 107 connected to a hydrocarbon gas source. The hydrocarbon gas introduced into the vacuum chamber 101 is ionized in the plasma 121 and the plasma 122 (hydrocarbon ionization process). That is, the hydrocarbon ionization process starts simultaneously with the Cr-WC inclined layer film forming process. It should be noted that in the related art, the introduction of the hydrocarbon gas in the hydrocarbon gas ionization process starts simultaneously with the WC uniform layer film forming process described later.

[0055] When the Cr—WC gradient layer film forming step is performed, the Ar in the plasma 121 formed in front of the Cr target 111 + The WC target 112 collides with the Cr target 111, Cr atoms are knocked out of the Cr target 111, and Ar atoms are formed in the plasma 122 in front of the WC target 112. + The WC components are knocked out from the WC target 112 by colliding with the WC target 112. Here, the WC components knocked out from the WC target 112 include WC particles, W atoms, and C atoms. The Cr atoms knocked out from the Cr target 111 and the WC components knocked out from the WC target 112 are respectively attached to the surface of the Cr layer 11 formed on the surface of the iron substrate.

[0056] In addition, in the Cr-WC inclined layer film forming process, the Cr sputtering power source 113 and the WC sputtering power source 114 are controlled so that the negative voltage applied to the Cr target 111 gradually decreases in the negative direction over time, and the negative voltage applied to the WC target 112 gradually increases in the negative direction over time. Therefore, the amount of Cr atoms knocked out from the Cr target 111 gradually decreases, and the amount of WC components knocked out from the WC target 112 gradually increases. As a result, in the Cr-WC inclined layer film forming process, a film having an inclined composition ratio of Cr and WC, i.e., a Cr-WC inclined layer 12, is formed (filmed) on the surface of the Cr layer 11. The Cr-WC inclined layer 12 has an inclined composition in which the composition ratio of Cr decreases and the composition ratio of WC increases as it moves away from the Cr layer 11 in the film thickness direction.

[0057] Here, in the sputtering of the WC target 112, as described above, the amount of W atoms in the WC component knocked out from the WC target 112 is greater than the amount of C atoms, and therefore, there is a concern that a W concentration layer may be formed due to the excessive W atoms. In particular, at the end of the Cr-WC inclined layer film forming process, the WC component knocked out from the WC targets 112, 112 increases, and therefore, excessive W atoms are generated at the end of the film forming process. Therefore, in the related art, a W concentration layer is formed at the end of the film forming of the Cr-WC inclined layer 12. In contrast, according to the present embodiment, the hydrocarbon ionization process is started at the beginning stage of the formation of the Cr-WC inclined layer 12, and hydrocarbon gas is introduced from the hydrocarbon gas inlet 107, and the introduced hydrocarbon gas is ionized in each plasma 121, 122 as described above. However, the ionized hydrocarbons are bonded to the excessive W component to form WC. In this way, the excessive W is consumed by the formation of WC, thereby preventing the formation of a W concentration layer at the end of the film forming of the Cr-WC inclined layer 12.

[0058] The Cr-WC inclined layer film forming process is completed when the negative voltage applied to the Cr target 111 drops to a predetermined voltage. Thereafter, the WC uniform layer film forming process is implemented. In the WC uniform layer film forming process, the negative voltage applied to the Cr target 111 is stopped, and the negative voltage applied to the WC target 112 is maintained at a predetermined voltage. Thus, only the WC component can be knocked out from the WC target 112. The WC component knocked out in this way adheres to the surface of the Cr-WC inclined layer 12 formed on the iron substrate. Thus, a WC uniform layer 13 composed of WC is formed (filmed) on the surface of the Cr-WC inclined layer 12.

[0059] In addition, in the WC uniform layer film forming process, the hydrocarbon ionization process is performed after the Cr-WC gradient layer film forming process, and the introduction of hydrocarbon gas from the hydrocarbon gas inlet 107 is continued. Here, as described above, the amount of W atoms in the WC component knocked out from the WC target 112 is greater than the amount of C atoms. Therefore, in the related art, the W concentrated layer is formed by using the excess W component generated at the initial stage of the film forming of the WC uniform layer 13. In contrast, in the present embodiment, the hydrocarbon ionization process is started before the WC uniform layer film forming process is performed, and the plasma 122 is fully contained in the ionized hydrocarbons at the start of the WC uniform layer film forming process. Therefore, the excess W generated at the initial stage of the WC uniform layer film forming process is bonded with the ionized hydrocarbons to form WC. That is, the excess W generated at the initial stage of the film forming of the WC uniform layer is consumed by bonding with the hydrocarbon ions generated in the hydrocarbon ionization process to form WC. Therefore, the formation of the W concentrated layer at the initial stage of the film forming of the WC uniform layer 13 is prevented. Thus, the formation of the W concentrated layer is prevented at the end of the formation of the Cr—WC gradient layer 12 and the beginning of the formation of the WC uniform layer 13 , so that no W concentrated layer is formed at the boundary between the Cr—WC gradient layer 12 and the WC uniform layer 13 .

[0060] After a predetermined time has passed or after the film thickness of the WC uniform layer 13 reaches a predetermined film thickness, the WC uniform layer film forming process is terminated, and then the DLC layer film forming process is performed. In the DLC layer film forming process, the negative voltage applied to the WC target 112 is stopped. In addition, hydrocarbon gas is introduced into the vacuum chamber 101 from the hydrocarbon gas inlet 107 at a predetermined flow rate, and a predetermined negative voltage is applied to the substrate holder 103 and the iron substrate held by the substrate holder 103 by the bias power supply 104 connected to the rotary table 102. As a result, plasma is generated around the iron substrate, and the hydrocarbon gas introduced into the vacuum chamber 101 is ionized by the plasma. That is, the hydrocarbon ionization process is also continued in the DLC layer film forming process. In this way, the ionized hydrocarbon radicals are attached to the surface of the WC uniform layer 13 formed on the iron substrate as DLC. In this way, the DLC layer 15 is formed on the surface of the WC uniform layer 13 (that is, on the surface of the WC layer 14) by the plasma CVD method.

[0061] The low friction and wear film 10 of this embodiment is manufactured through the above steps. It should be noted that the above steps only show the steps required for the description of the present invention, and other steps may be added in actual manufacturing. For example, before the Cr layer forming step, a negative voltage may be applied to the iron substrate using the bias power supply 104 to make the Ar + The cleaning process is performed by colliding with the iron substrate. In addition, the film quality can be improved by applying a predetermined voltage to the iron substrate using the bias power supply 104 in each film forming process. Figure 5The sputtering device 100 shown schematically shows only the configuration necessary for explaining the present invention, and an actual manufacturing device may have other configurations. For example, the sputtering device 100 may be used as a magnetron sputtering device to increase the film formation speed.

[0062] Figure 6 Schematic diagram of an image showing a process for producing the low-friction and wear film of the present embodiment produced as described above. Figure 6 The horizontal axis of the graph is time. Figure 6 The graph represented by the two-dot chain line shows an image of the temporal change of the voltage applied to the Cr target 111. Figure 6 The graph represented by the dashed line shows an image of the temporal change of the voltage applied to the WC target 112. Figure 6 The graph indicated by the solid line shows an image of the change over time in the amount of hydrocarbon gas introduced.

[0063] like Figure 6 As shown in the figure, as time goes by, the Cr layer, Cr-WC layer, WC uniform layer, and DLC layer are formed in sequence. Figure 6 In the graph, a Cr layer is formed from the start of film formation to time t1, a Cr-WC gradient layer is formed from time t1 to time t2, a WC uniform layer is formed from time t2 to time t3, and a DLC layer is formed from time t3 to time t4.

[0064] In addition, during the formation of the Cr layer, that is, during the period from the start of the film formation to time t1, only a negative voltage is applied to the Cr target 111. Therefore, the Cr layer is formed by Cr atoms knocked out from the Cr target 111.

[0065] During the film formation of the Cr-WC inclined layer, that is, from time t1 to time t2, a negative voltage is applied to both the Cr target 111 and the WC target 112. In addition, as time passes, the applied voltage of the Cr target 111 decreases, and the applied voltage of the WC target 112 increases. Therefore, the Cr-WC inclined layer is formed into an inclined composition in which the composition ratio of Cr decreases and the composition ratio of WC increases as it moves away from the Cr layer in the film thickness direction. In addition, the hydrocarbon ionization process is started simultaneously with the start of the film formation of the Cr-WC inclined layer, and hydrocarbon gas is introduced into the vacuum chamber 101. The introduced hydrocarbon gas is ionized in the vacuum chamber 101, and the ionized hydrocarbon combines with the excess W knocked out from the WC target to form WC, thereby preventing the formation of a W concentrated layer at the end of the film formation of the Cr-WC inclined layer.

[0066] In addition, during the film formation of the WC uniform layer, that is, during the period from time t2 to time t3, the application of voltage to the Cr target 111 is stopped, and only a negative voltage is applied to the WC target 112. Therefore, the WC uniform layer is formed by using the WC component knocked out from the WC target 112. In addition, since the hydrocarbon gas is continuously introduced during the film formation of the WC uniform layer, the excess W knocked out from the WC target 112 combines with the ionized hydrocarbon to form WC. As a result, the formation of the W concentrated layer at the initial stage of the film formation of the WC uniform layer is prevented. Moreover, as described above, since the formation of the W concentrated layer at the end of the film formation of the Cr-WC inclined layer and the initial stage of the film formation of the WC uniform layer is prevented, the W concentrated layer is not formed at the boundary between the Cr-WC inclined layer and the WC uniform layer.

[0067] In addition, when the WC uniform layer is formed, the amount of W atoms knocked out from the WC target and the amount of C atoms are approximately equal, and the excess W atoms are reduced, so that the C layer is sometimes formed by the ionized hydrocarbons. In this case, the WC component knocked out from the WC target 112 and the carbon in the ionized hydrocarbons are sometimes formed into a WC-C layer. That is, there is sometimes a case where the WC layer contains a WC-C layer. In this case, the WC-C layer is formed between the Cr-WC inclined layer and the WC uniform layer and the DLC layer.

[0068] Then, when the DLC layer is formed, that is, during the period from time t3 to time t4, the voltage application to both the Cr target and the WC target is stopped, and the amount of hydrocarbon gas introduced is increased to a predetermined amount. In addition, a predetermined bias voltage is applied to the iron substrate. As a result, the hydrocarbon gas is ionized, and the DLC layer is formed by the ionized hydrocarbon.

[0069] Figure 7 Schematic diagram of an image showing a process for manufacturing a low friction wear film of the related art. Figure 7 The horizontal axis of the graph is time. Figure 7 The graph represented by the two-dot chain line, the graph represented by the one-dot chain line, the graph represented by the solid line and Figure 6 Similarly, an image showing the temporal change of the voltage applied to the Cr target, an image showing the temporal change of the voltage applied to the WC target, and an image showing the temporal change of the amount of hydrocarbon gas introduced are respectively shown.

[0070] Figure 6 The chart and Figure 7 The difference between the graphs is only in the timing of hydrocarbon gas introduction, that is, the timing of starting the hydrocarbon ionization process. Figure 7In the case shown, the introduction of hydrocarbon gas (hydrocarbon ionization process) and the WC uniform layer film forming process are started simultaneously. Therefore, since hydrocarbon gas is not introduced when the Cr-WC inclined layer is formed, the excess W generated when the Cr-WC inclined layer is formed is used to form a W concentrated layer at the end of the Cr-WC inclined layer film forming. In addition, although hydrocarbon gas is introduced at the initial stage of the WC uniform layer film forming, the amount introduced is small, and there is insufficient C to fully combine with the excess W generated at the initial stage of the WC uniform layer film forming. Therefore, a W concentrated layer is also formed at the initial stage of the WC uniform layer film forming. Therefore, the W concentrated layer is formed at the boundary between the Cr-WC inclined layer and the WC uniform layer. The W in the W concentrated layer thus formed is oxidized as described above, and the tungsten oxide reacts with the alkali solution to cause a peeling phenomenon.

[0071] In contrast, Figure 6 In the case of the present embodiment shown, the introduction of hydrocarbon gas (hydrocarbon ionization process) starts before the WC uniform layer film forming process is implemented. Specifically, the introduction of hydrocarbon gas (hydrocarbon ionization process) starts simultaneously with the Cr-WC inclined layer film forming process. Therefore, in the low friction and wear film of the present embodiment, the W concentrated layer is not formed at the boundary portion of the Cr-WC inclined layer and the WC uniform layer. Therefore, even if cracks are generated on the film surface and the cracks reach the boundary between the Cr-WC inclined layer and the WC uniform layer, since there is no W concentrated layer at the boundary, tungsten oxide will not be formed, and the peeling phenomenon caused by the reaction of tungsten oxide and alkali solution will not occur. Therefore, the low friction and wear film of the present embodiment has high alkali resistance.

[0072] (Example) Use Figure 1 The sputtering device 100 shown in the figure forms a Cr layer, a Cr-WC inclined layer, a WC uniform layer, and a DLC layer on the surface of a cylindrical iron substrate in sequence by the above-mentioned manufacturing method. At this time, the sputtering voltage applied to the WC target 112 and the amount and timing of introduction of hydrocarbon gas are controlled in such a manner that the ratio of the atomic concentration W [at%] of W to the sum (W+C) of the atomic concentration W [at%] of W in the WC layer (Cr-WC layer and WC uniform layer) and the atomic concentration C [at%] of C is controlled to be the ratio shown in Examples 1 to 4 and Comparative Example 1 in Table 1. Thus, samples of each Example and Comparative Example 1 in which a low friction and wear film is formed on the surface of the iron substrate are prepared. It should be noted that in the preparation of the samples of Examples 1 to 4, the introduction of hydrocarbon gas (hydrocarbon ionization process) is started simultaneously with the Cr-WC inclined layer film forming process, and in the preparation of the sample of Comparative Example 1, the introduction of hydrocarbon gas (hydrocarbon ionization process) is started simultaneously with the WC uniform layer film forming process.

[0073] Next, each sample was immersed in a 6% alkaline aqueous solution (a mixed solution of NaOH and KOH) and placed in a thermostatic bath at an ambient temperature of 40°C for 48 hours. Afterwards, each sample was taken out of the thermostatic bath, and the presence or absence of peeling of the low friction and wear film formed on the surface of the iron substrate was confirmed visually and by SEM. The confirmation results of the peeling state are shown in Table 1.

[0074] [Table 1]

[0075]

[0076] As shown in Examples 1 to 4 of Table 1, when the ratio W / (W+C) was 50% or less, no peeling of the film was confirmed. This is considered to be because if the ratio W / (w+C) in the WC layer (Cr-WC gradient layer and WC uniform layer) is 50% or less, there is no excess W in the WC layer, and therefore, a W concentrated layer containing a single substance of W is not formed. On the other hand, as shown in Comparative Example 1, when the ratio W / (W+C) in the WC layer was 77%, peeling of the film was confirmed. This is considered to be because the ratio of W in the WC layer is high, and therefore, a W concentrated layer is formed in the WC layer, and peeling occurs with the W concentrated layer as the starting point. Based on this result, it was confirmed that the ratio W / (W+C) in the WC layer can be 50% or less.

[0077] Figures 8A to 8D TEM images showing the cross section from the Cr layer to the WC uniform layer in the low friction and wear film formed by the sample produced in Example 1 and mapping images obtained by mapping the TEM image to the Cr component, the W component, and the C component, respectively. Fig. 8A For TEM images, Figure 8B is the mapping image of Cr, Figure 8C is the mapping image of W, Fig.8D is the mapping image of C. Fig. 8A As shown in FIG. 1 , it can be seen that a Cr layer, a Cr-WC gradient layer, and a WC uniform layer are formed from the surface of the iron substrate. Figure 8C It is found that no W-concentrated portion is found at the boundary between the Cr—WC gradient layer and the WC uniform layer. Therefore, it is found that the WC layer of Example 1 is configured to include a Cr—WC layer and a WC uniform layer, and no W-concentrated layer is formed at the boundary between them.

[0078] FIG. 9A to FIG. 9D 1 and 2 show a TEM image of a cross section from a Cr layer to a WC uniform layer in a low-friction and wear film formed of a sample prepared in Comparative Example 1 and a mapping image obtained by mapping the TEM image to Cr component, W component, and C component, respectively. Fig.9A For TEM images, Fig. 9B is the mapping image of Cr, Fig. 9C is the mapping image of W, Fig.9D is the mapping image of C. In particular, Fig. 9CAs shown in FIG. 1 , a layer with a high W composition ratio was detected at the boundary between the Cr-WC inclined layer and the WC uniform layer. Since almost no C component was detected in this layer, it is considered that this layer is a W concentrated layer. Therefore, it is considered that in Comparative Example 1, a W concentrated layer was formed at the boundary between the Cr-WC inclined layer and the WC uniform layer, and peeling occurred with this W concentrated layer as the starting point.

[0079] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. For example, the application of the low friction and wear film of the present invention can be used as a coating film on the surface of the above-mentioned die casting mold, but it is not limited to this. For example, it can also be used as a coating film on the surface of a urea injector using urea water, a brake linear valve for a brake using brake fluid, etc., which are parts used in an alkaline environment among automobile parts. In addition, the manufacturing device for manufacturing the low friction and wear film of the present invention is not limited to the structure of the sputtering device 100 shown in the above embodiment. The present invention can be deformed as long as it does not deviate from its main purpose.

Claims

1. A low friction and wear film (10), comprising: A chromium layer (11) is formed on the surface of the metal substrate (1); A tungsten carbide layer (14) is formed on the surface of the chromium layer (11), the tungsten carbide layer (14) comprising a chromium-tungsten carbide inclined layer (12) and a tungsten carbide uniform layer (13), the chromium-tungsten carbide inclined layer (12) comprising chromium and tungsten carbide and having an inclined composition in which the composition ratio of chromium decreases and the composition ratio of tungsten carbide increases as the chromium layer (11) moves away from the chromium layer (11) in the thickness direction, the tungsten carbide uniform layer (13) is formed on the surface of the chromium-tungsten carbide inclined layer (12) and is composed of tungsten carbide, and the tungsten carbide layer (14) does not form a tungsten concentrated layer containing a single substance of tungsten at a boundary between the chromium-tungsten carbide inclined layer (12) and the tungsten carbide uniform layer (13); and A diamond-like carbon layer (15) as a top layer is formed on the surface of the tungsten carbide layer (14).

2. The low friction and wear film (10) according to claim 1, wherein: The ratio of the atomic concentration of tungsten to the sum of the atomic concentration of tungsten and the atomic concentration of carbon in the tungsten carbide layer (14) is 50% or less.

3. A method for manufacturing a low friction and wear film (10), the low friction and wear film (10) comprising: a chromium layer (11) formed on the surface of a metal substrate (1); a tungsten carbide layer (14) formed on the surface of the chromium layer (11), the tungsten carbide layer (14) comprising a chromium-tungsten carbide inclined layer (12) and a tungsten carbide uniform layer (13), the chromium-tungsten carbide inclined layer (12) comprising chromium and tungsten carbide, and having an inclined composition in which the composition ratio of the chromium decreases and the composition ratio of the tungsten carbide increases as it moves away from the chromium layer (11) in the thickness direction, the tungsten carbide uniform layer (13) being formed on the surface of the chromium-tungsten carbide inclined layer (12) and being composed of tungsten carbide; and a diamond-like carbon layer (15) as a top layer, formed on the surface of the tungsten carbide layer (14); The manufacturing method comprises: As a chromium layer film forming step, the chromium layer (11) is formed by causing inert gas ions to collide with a chromium target (111) composed of chromium disposed in a vacuum chamber (101) and causing chromium atoms ejected from the chromium target (111) to adhere to the surface of the metal substrate (1); As a chromium-tungsten carbide inclined layer film forming step, the chromium-tungsten carbide inclined layer (12) is formed by causing an inert gas to collide with the chromium target and a tungsten carbide target (112) composed of tungsten carbide disposed in the vacuum chamber (101) and causing chromium atoms knocked out from the chromium target (111) and tungsten carbide components knocked out from the tungsten carbide target to adhere to the surface of the chromium layer; As a tungsten carbide uniform layer film forming step, the tungsten carbide uniform layer (13) is formed by causing an inert gas to collide with the tungsten carbide target (112) disposed in the vacuum chamber (101) and causing the tungsten carbide component knocked out from the tungsten carbide target (112) to adhere to the surface of the chromium-tungsten carbide inclined layer (12); As a hydrocarbon ionization step, introducing hydrocarbon gas into the vacuum chamber (101) and ionizing the introduced hydrocarbon gas; and The diamond-like carbon layer (15) is formed by attaching the hydrocarbon ionized by the hydrocarbon ionization step to the surface of the tungsten carbide uniform layer (13), The hydrocarbon ionization step and the chromium-tungsten carbide gradient layer formation step are started simultaneously.

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