DLC layer forming method and mold manufacturing method

Abstract

To provide a method for depositing a DLC layer, capable of suppressing increase in friction coefficient with a mating member contacting the surface of the DLC layer in wet environment.SOLUTION: A method for depositing a DLC layer 5, capable of depositing the DLC layer 5 on the surface of a base material 2 by an unbalanced magnetron sputtering method using a carbon target comprises: controlling the flow rates of argon gas supplied in a chamber subjected to film deposition and hydrocarbon gas so that the flow ratio (the argon gas flow rate / the hydrocarbon gas flow rate) of the argon gas to the hydrocarbon gas is 20-60; and applying a bias voltage of 175-400 V to the base material 2 in a pulse shape to deposit the DLC layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for forming a DLC (Diamond-Like Carbon) layer on a substrate surface. [Background technology]

[0002] Conventionally, a hard layer has been formed on the surface of a die used in press working or forging to improve the durability of the die or to reduce wear of the workpiece due to friction between the die surface and the die. DLC layers, known for their high hardness, excellent durability, and low coefficient of friction, are increasingly being used as hard layers to be formed on die surfaces. Known methods for forming a DLC layer on a die surface include those using a plasma CVD method, as described in Patent Document 1, and those using unbalanced magnetron sputtering (hereinafter referred to as UBM sputtering), as described in Patent Document 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-178670 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-079445 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, in an effort to reduce the weight of automobiles, the material used for automobile parts has been replaced from steel to aluminum materials such as pure aluminum and aluminum alloys. The forming process of the workpiece is carried out in an environment where lubricant oil is present between the workpiece and the mold surface (a so-called wet environment). However, with molds on which a DLC layer has been formed using conventional methods, the coefficient of friction between the workpiece and the DLC layer tends to increase even in a wet environment. When the workpiece is aluminum, the increased coefficient of friction tends to generate wear particles from the workpiece, which can stick to the surface of the mold. If the forming process is carried out under such conditions, there is a concern that scratches may occur on the workpiece.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a method for forming a DLC layer that can suppress an increase in the coefficient of friction between the surface of the DLC layer and a counter member that comes into contact with the surface of the DLC layer in a wet environment. [Means for solving the problem]

[0006] The inventors of the present invention conceived the idea that forming recesses on the surface of a DLC layer would provide oil reservoirs that would hold and supply lubricating oil, thereby suppressing an increase in the coefficient of friction between the surface of the DLC layer and a mating member that comes into contact with the surface of the DLC layer. They then conducted extensive research, focusing on the UBM sputtering method as a DLC layer deposition method that would enable the formation of recesses on the surface of the DLC layer.

[0007] As a result, they discovered that it is possible to utilize the so-called reverse sputtering phenomenon, in which the deposited DLC layer is sputtered by the collision of argon ions. Furthermore, since the collision energy of argon ions with the DLC layer becomes too strong when only argon gas is supplied as the deposition gas, they discovered that the above-mentioned object can be achieved by supplying a hydrocarbon gas and controlling the flow rate ratio, which led to the completion of the present invention.

[0008] One aspect of the present invention that solves the above-mentioned problems is a method for forming a DLC layer on the surface of a substrate by unbalanced magnetron sputtering using a carbon target, wherein the flow rate ratio of argon gas to hydrocarbon gas (flow rate of argon gas / flow rate of hydrocarbon gas) supplied into a chamber where the film formation process is performed is 35 The flow rates of the argon gas and the hydrocarbon gas were adjusted so that the substrate was heated to about 60°C. 190 ~ 275 It is characterized by applying a bias voltage V in pulses.

[0009] According to another aspect of the present invention, a mold is manufactured by using the above-described method for forming a DLC layer on the surface of the substrate. [Effects of the Invention]

[0010] It is possible to form a DLC layer that can suppress an increase in the coefficient of friction with a counter member that contacts the surface of the DLC layer in a wet environment. Note that in this specification, the coefficient of friction with a counter member that contacts the surface of the DLC layer in a wet environment refers to the coefficient of friction measured by a ball-on-disk test, with polyalphaolefin interposed between the sample and the ball. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing an outline of a layered structure of a DLC coating material according to one embodiment of the present invention. [Figure 2] 1 is a diagram showing a schematic configuration of a film forming apparatus as a UBM sputtering apparatus according to one embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the substrate shape of a test piece. [Figure 4] FIG. 1 is a schematic diagram of a ball-on-disk test. [Figure 5] 1 shows the results of a ball-on-disk test (wet environment) for Example 1 and Comparative Example 1. [Figure 6]Results of the ball-on-disk test (wet environment) of Example 2. [Figure 7] Results of the ball-on-disk test (wet environment) of Example 3. [Figure 8] Results of the ball-on-disk test (wet environment) of Example 4. [Figure 9] Results of the ball-on-disk test (wet environment) of Example 5. [Figure 10] Results of the ball-on-disk test (dry environment) of Example 1. [Figure 11] Results of the ball-on-disk test (dry environment) of Example 2. [Figure 12] Results of the ball-on-disk test (dry environment) of Example 3. [Figure 13] Results of the ball-on-disk test (dry environment) of Example 4. [Figure 14] Results of the ball-on-disk test (dry environment) of Example 5. [Figure 15] SEM image of the surface of the DLC layer of Example 1. [Figure 16] SEM image of the surface of the DLC layer of Comparative Example 1.

Mode for Carrying Out the Invention

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0013] <Layer Structure of DLC Coating Material> FIG. 1 is a diagram showing an example of the laminated structure of a DLC coating material in which a DLC layer is formed on the surface of a substrate obtained by the manufacturing method of the present invention. The DLC coating material 1 of the present embodiment shown in FIG. 1 has a substrate 2, an intermediate layer 3 formed on the substrate 2, a DLC intermediate layer 4 formed on the intermediate layer 3, and a DLC layer 5 formed on the DLC intermediate layer 4.

[0014] The base material 2 is made of a steel material such as alloy tool steel or high-speed tool steel for die applications like SKD11, but the base material 2 is not limited to these steel materials.

[0015] The intermediate layer 3 is a layer formed as needed to improve the adhesion between the base material 2 and the DLC layer 5. The intermediate layer 3 has a hardness intermediate between that of the base material 2 and the DLC layer 5. The intermediate layer 3 preferably contains an element in the chemical composition of the base material 2 in order to improve the compatibility with the base material 2 and the adhesion therewith. For example, the intermediate layer 3 preferably contains one or more elements selected from the group consisting of Cr, W, Ti, V, and Mo that can be contained in the chemical composition of the steel material. Further, when the base material 2 is a steel material such as alloy tool steel or high-speed tool steel for die applications, the intermediate layer 3 preferably contains chromium, which is contained in such steel materials in large amounts. Also, the intermediate layer 3 is preferably a layer whose hardness increases from the base material 2 side toward the DLC layer 5 side. Note that the intermediate layer 3 may have a multilayer structure.

[0016] The DLC intermediate layer 4 is a carbon layer formed as needed to improve the adhesion between the intermediate layer 3 and the DLC layer 5, and has a hardness intermediate between that of the intermediate layer 3 and the DLC layer 5. Also, the DLC intermediate layer 4 is preferably a layer whose hardness increases from the base material 2 side toward the DLC layer 5 side.

[0017] The DLC intermediate layer 4 of the present embodiment has a two-layer structure including a first DLC intermediate layer 4a formed on the intermediate layer 3 and a second DLC intermediate layer 4b formed on the first DLC intermediate layer 4a and being denser than the first DLC intermediate layer 4a. The second DLC intermediate layer 4b is preferably harder than the first DLC intermediate layer 4a. Note that the DLC intermediate layer 4 is not limited to a two-layer structure and may not have a multilayer structure.

[0018] <Method for manufacturing DLC coating material> A method for manufacturing the DLC coated material 1 in which the DLC layer 5 is formed on the surface of the substrate 2 will be described. The DLC coated material 1 is formed by UBM sputtering.

[0019] (Film forming equipment) The deposition equipment used to manufacture DLC coating materials includes a sputtering pulse power supply that supplies power to the target, multiple magnetic poles positioned behind the target, a bias pulse power supply that applies a negative bias voltage to the substrate in pulses, and gas inlets that supply argon gas and hydrocarbon gas. The UBM sputtering method is a deposition method that uses such equipment to increase the plasma density near the substrate by imbalancing the magnetic poles and extending some of the magnetic field lines to the vicinity of the substrate, and utilizes the ion-assisted effect, which can increase the collision energy of argon ions with the substrate by applying a bias voltage to the substrate.

[0020] FIG. 2 is a diagram illustrating an example of a film formation apparatus as a UBM sputtering apparatus. The film formation apparatus 10 shown in FIG. 2 includes a chamber 11 in which a substrate 2 is accommodated and a film formation process is performed, a stage 12 on which the substrate 2 is placed, and a bias pulse power supply 13 connected to the stage 12 and applying a bias voltage to the substrate 2 via the stage 12. A gas inlet 14 is provided on the side wall of the chamber 11 to supply film formation gases used in forming the intermediate layer 3, DLC intermediate layer 4, and DLC layer 5. The gas inlet 14 is connected to a gas supply source 15 equipped with a control unit for adjusting the flow rate of the film formation gas. A gas exhaust pipe 16 is provided on the bottom wall of the chamber 11 to exhaust the atmospheric gas from the chamber 11, and the gas exhaust pipe 16 is connected to a vacuum pump (not shown). During the film formation process, the pressure within the chamber 11 is controlled by appropriate exhaust through the gas exhaust pipe 16. Various targets 17 used in forming the intermediate layer 3, DLC intermediate layer 4, and DLC layer 5 are arranged above the stage 12. The target 17 is connected to a pulsed power supply 18 for sputtering that is arranged outside the chamber 11. A magnetic pole 19 is provided on the rear side of the target 17, and when the magnetic pole 19 is unbalanced, the generated plasma 20 reaches the vicinity of the substrate 2 placed on the stage 12.

[0021] The method for producing the DLC coating material 1 will be described below in order of steps.

[0022] (Base material cleaning process) Before forming the intermediate layer 3, the DLC intermediate layer 4, and the DLC layer 5 on the substrate 2, an argon bombardment process is performed as necessary to clean the surface of the substrate 2.

[0023] (Intermediate layer film formation process) To improve adhesion between the substrate 2 and the DLC layer 5, an intermediate layer 3 may be formed as needed. The film formation conditions are not particularly limited as long as an intermediate layer 3 having a hardness intermediate between that of the substrate 2 and that of the DLC layer 5 can be formed. To improve adhesion to the substrate 2, the intermediate layer 3 may be formed by appropriately adjusting the power supplied to the target 17 so that the intermediate layer 3 contains one or more elements selected from the group consisting of Cr, W, Ti, V, Mo, and C, which may be contained in the chemical composition of the substrate 2. For example, when the steel material of the substrate 2 is SKD11, it is preferable to form an intermediate layer containing Cr, W, and C to a thickness of 1 μm or more by UBM sputtering. To improve adhesion between the substrate 2 and the DLC layer 5, the voltage of the sputtering pulse power supply may be changed continuously or stepwise to form the intermediate layer 3 so that its hardness increases from the substrate 2 side to the DLC layer 5 side. The film formation process may also be performed so that the intermediate layer 3 has a multi-layer structure, as needed.

[0024] (DLC intermediate layer deposition process) In order to improve the adhesion between the intermediate layer 3 and the DLC layer 5, a film-forming step of the DLC intermediate layer 4 is carried out as necessary.

[0025] The film formation conditions are not particularly limited as long as they allow the formation of a DLC intermediate layer 4 having a hardness intermediate between the hardness of the intermediate layer 3 and the hardness of the DLC layer 5. Furthermore, from the viewpoint of improving the adhesion between the intermediate layer 3 and the DLC layer 5, for example, the power supplied to the carbon target during the formation of the DLC intermediate layer 4 is set to be lower than the power supplied to the carbon target during the formation of the DLC layer 5. Furthermore, from the viewpoint of improving the adhesion between the intermediate layer 3 and the DLC layer 5, the bias voltage during the film formation is increased continuously or stepwise to change the density of the film, thereby increasing the hardness from the substrate 2 side toward the DLC layer 5 side.

[0026] Furthermore, if necessary, the DLC intermediate layer 4 is formed to have a multi-layer structure. For example, after forming a first DLC intermediate layer 4a, a second DLC intermediate layer 4b, which is a layer denser than the first DLC intermediate layer 4a, is formed. When forming such a DLC intermediate layer 4, for example, the bias voltage is kept constant during the formation of the first DLC intermediate layer 4a, and the bias voltage is gradually increased during the formation of the second DLC intermediate layer 4b.

[0027] (DLC layer deposition process) Argon gas and hydrocarbon gas are supplied to the chamber 11 as deposition gases for the DLC layer 5. Examples of hydrocarbon gases include methane (CH), acetylene (C2H2), ethylene (C2H4), ethane (C2H6), benzene (C6H6), and toluene (C7H8). From the standpoints of handling and cost, it is preferable to use methane gas or acetylene gas. When supplying deposition gases to the chamber 11, a single type of hydrocarbon gas may be supplied, or multiple types of hydrocarbon gases may be mixed and supplied.

[0028] A negative bias voltage is applied to the substrate 2. In this specification, when comparing bias voltages, the bias voltage with a smaller absolute value is referred to as a "lower bias voltage." In other words, the higher the bias voltage, the more argon ions generated by the plasma are attracted toward the substrate 2, and the stronger the energy with which they collide with the substrate 2. In the DLC layer 5 deposition process, the bias voltage is set to 175 to 400 V. Applying a bias voltage to the substrate 2 within this range facilitates the formation of recesses on the surface of the DLC layer 5. If the bias voltage is less than 175 V, the argon ions are attracted toward the substrate 2, and the energy with which they collide with the substrate 2 is weak, resulting in the formation of recesses on the surface of the DLC layer 5. If the bias voltage exceeds 400 V, the argon ions are attracted toward the substrate 2, and the energy with which they collide with the substrate 2 is too strong, preventing the formation of a DLC layer 5. The bias voltage may vary during the deposition of the DLC layer 5 as long as it is within the range of 175 to 400 V. Moreover, the bias voltage is preferably 300V or less.

[0029] The DLC layer 5 is formed by argon ions colliding with the carbon target, causing the sputtered carbon to deposit on the substrate 2. Meanwhile, while a bias voltage is being applied to the substrate 2, argon ions are attracted to the substrate 2 and collide with the formed DLC layer 5. In other words, while a bias voltage is being applied to the substrate 2, the formation of the DLC layer 5 and the collision of the argon ions with the DLC layer 5 occur simultaneously. Note that while the application of the bias voltage to the substrate 2 is stopped, the argon ions mainly collide with the carbon target, and the sputtered carbon is deposited on the substrate 2, thereby progressing the formation of the DLC layer 5.

[0030] It is believed that the time for which the bias voltage is applied to the substrate 2 affects the number of recesses formed on the surface of the DLC layer 5. The voltage application time of the bias pulse power supply 13 can be controlled by adjusting the duty ratio, which is the voltage application time per cycle. The duty ratio is calculated as follows: Duty ratio [%] = 100 x application time (ON time) / {application time (ON time) + application stop time (OFF time)}

[0031] The duty ratio is preferably set to 30 to 80%. When the duty ratio is 30% or more, recesses are more easily formed on the surface of the DLC layer 5 than when the duty ratio is less than 30%, and the number of recesses can be increased. When the duty ratio is 80% or less, the DLC layer 5 is more easily formed than when the duty ratio exceeds 80%. Therefore, in order to achieve a high level of both the formation of the DLC layer 5 and the formation of recesses, the duty ratio is preferably set to 30 to 80%. For example, when the bias voltage is 175 to 300 V, the duty ratio is preferably 60 to 80%.

[0032] In the process of forming the DLC layer 5, simply setting the bias voltage to 175 to 400 V may result in the energy of argon ions colliding with the substrate 2 being too strong, preventing the formation of the DLC layer 5. Therefore, in the process of forming the DLC layer 5, the flow rates of the argon gas and hydrocarbon gas supplied into the chamber 11 are adjusted so that the flow rate ratio (argon gas flow rate / hydrocarbon gas flow rate) is maintained within a range of 20 to 60. Because the argon gas and hydrocarbon gas are supplied while the chamber 11 is being evacuated, the flow rate ratio (argon gas flow rate / hydrocarbon gas flow rate) within the chamber 11 is also 20 to 60. For example, when the bias voltage is 175 to 300 V, the flow rate ratio (argon gas flow rate / hydrocarbon gas flow rate) of the argon gas and hydrocarbon gas is preferably 30 or greater. Furthermore, the flow rate ratio is preferably 50 or less. The flow rates of the gases are "mass flow rates" and are controlled by mass flow controllers. In this specification, the "mass flow rate" is a "flow rate converted to standard conditions" that is independent of the temperature and pressure of the actual gas used, and the "standard conditions" are 101.3 kPa (1 atm) and 0°C.

[0033] By setting the flow rate ratio of argon gas to hydrocarbon gas (argon gas flow rate / hydrocarbon gas flow rate) to 20 to 60, ionization of the argon gas is suppressed, and the number of argon ions attracted to the substrate 2 is reduced. In other words, the energy of the argon ions colliding with the DLC layer 5 can be prevented from becoming too strong, making it possible to form recesses on the surface of the DLC layer 5 while depositing the DLC layer 5. The flow rate of the argon gas supplied to the chamber 11 is preferably 100 to 450 ml / min, and the flow rate of the hydrocarbon gas is preferably 5 to 15 ml / min. Note that experiments by the present inventors have confirmed that the DLC layer 5 cannot be formed if hydrocarbon gas is not supplied.

[0034] The sputtering power in the film formation step of the DLC layer 5 is preferably 2.5 to 12 kW. "Sputtering power" refers to the power supplied to the target 17. The sputtering power is more preferably 3 to 10 kW, and even more preferably 5 to 6 kW.

[0035] The sputtering power density in the film formation process of the DLC layer 5 is 2.5 to 10 W / cm 2 The "sputtering power density" is the ratio of the sputtering power (W) to the target 17 to the area (cm) of the surface 17a of the target facing the substrate 2. 2 ) is the value divided by the sputtering power density of 2.5W / cm 2 If the sputtering power density is 10 W / cm or more, the sputtering of the carbon target is promoted, the speed of forming the DLC layer 5 is increased, and the production efficiency is improved. 2 If the temperature is below this, cracking of the target due to a rise in the temperature of the target can be suppressed, which is desirable.

[0036] The DLC-coated material 1 is manufactured through the above steps. In the DLC-coated material 1 of this embodiment, recesses are formed on the surface of the DLC layer 5 during the DLC layer 5 deposition process. These recesses function as oil reservoirs. When the DLC-coated material 1 is, for example, a mold, they can stably supply lubricant to the workpiece and the mold surface even after repeated use. This makes it possible to suppress an increase in the coefficient of friction between the workpiece and the mold surface in a wet environment. In particular, when the workpiece is aluminum, an increase in the coefficient of friction tends to generate wear particles from the aluminum material. However, a mold having a DLC layer 5 with recesses can suppress an increase in the coefficient of friction, thereby significantly suppressing scratches on the workpiece caused by wear particles. The DLC-coated material 1 can be used not only for molds but also for components that slide against other components.

[0037] From the viewpoint of suppressing wear and ensuring high durability, the Vickers hardness of the DLC layer 5 is preferably 1800 HV or more. From the viewpoint of suppressing film stress and improving adhesion, the Vickers hardness of the DLC layer 5 is preferably 4000 HV or less.

[0038] The above explanation has been about DLC layers with a low coefficient of friction in a wet environment using lubricating oil, but from the perspective of reducing costs and improving the working environment, it is desirable for molding processing of workpieces to be carried out in an environment where no lubricating oil exists between the workpiece and the mold surface (a so-called dry environment). However, molding processing in a dry environment results in greater friction between the workpiece and the DLC layer than processing in a wet environment, making processing a harsh environment for workpieces such as aluminum.

[0039] To form a DLC layer with a low coefficient of friction even in such a dry environment, it is preferable to set the flow rate ratio of argon gas to hydrocarbon gas (argon gas flow rate / hydrocarbon gas flow rate) to 35 to 60 and the bias voltage to 190 to 275 V in the DLC layer formation process. A DLC layer 5 formed to satisfy these conditions exhibits a low coefficient of friction with respect to the workpiece not only in wet environments but also in dry environments. To obtain a DLC layer with a low coefficient of friction even in dry environments, the flow rate ratio of argon gas to hydrocarbon gas is more preferably 50 or less, and even more preferably 40 or less. To obtain a DLC layer with a low coefficient of friction even in dry environments, it is more preferable to set the bias voltage to 200 V or more. From the same perspective, it is even more preferable to set the bias voltage to 250 V or less. Note that, in this specification, the coefficient of friction between the DLC layer surface and a mating member in contact with the surface in a dry environment refers to the coefficient of friction measured by a ball-on-disk test.

[0040] Although one embodiment of the present invention has been described above, the present invention is not limited to this example. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the technical idea described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Example]

[0041] A test piece was prepared in which a DLC layer was formed on the surface of the substrate, and its properties were evaluated.

[0042] SKD11, a type of alloy tool steel, was prepared and processed to a diameter of 22 mm and a thickness of 7 mm as shown in Figure 3. The deposition system used to deposit the intermediate layer and DLC layer was the UBMS707 UBM sputtering system manufactured by Kobe Steel, Ltd., which has the configuration shown in Figure 2 above.

[0043] The substrate was vacuum hardened and tempered. The substrate's coating surface (Figure 3) was then polished until the 10-point average roughness (Rzjis) specified in JIS B 0601:2013 was 0.5 μm or less. The substrate was then immersed in acetone (special grade) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and ultrasonically cleaned for 10 minutes. After ultrasonic cleaning, the substrate was dried with nitrogen blown over it and then loaded into the chamber of the UBM sputtering system.

[0044] Next, the chamber was filled with 2.6 × 10 -3 The substrate was evacuated to 100 Pa and heated for 120 minutes using a heater until the substrate reached 180°C. After heating, the surface of the substrate was cleaned using Ar bombardment. After cleaning, a chromium target, a tungsten carbide target, and a carbon target were sputtered using the UBM sputtering method to form an intermediate layer (1.7 μm thick) containing Cr, W, and C as elements.

[0045] (DLC intermediate layer film formation process) Next, a first DLC intermediate layer and a second DLC intermediate layer were deposited on the intermediate layer composed of chromium, tungsten, and carbon using unbalanced magnetron sputtering. The deposition conditions for the DLC intermediate layer are shown in Table 1 below. In the following explanation, "sputtering power" refers to the power supplied to the target. "Sputtering power density" is the value obtained by dividing the power (W) supplied to the carbon target by the area (cm2) of the surface of the carbon target facing the substrate.

[0046] [Table 1]

[0047] (First DLC intermediate layer deposition process) Argon gas was supplied into the chamber at a flow rate of 300 ml / min, and methane gas at a flow rate of 8 ml / min. The negative bias voltage applied to the substrate was set to 100 V, the carbon target sputtering power to 6 kW, and the bias voltage duty ratio to 75%. The carbon target was sputtered for 7.4 minutes.

[0048] (Second DLC intermediate layer deposition process) Subsequently, the bias voltage was gradually increased from 100 V to 200 V over a period of 36.6 minutes, while sputtering the carbon target.

[0049] (DLC layer deposition process) Next, a DLC layer was formed on the second DLC intermediate layer by unbalanced magnetron sputtering. The conditions for forming the DLC layer are shown in Table 2 below.

[0050] [Table 2]

[0051] Example 1 In this example, the argon gas flow rate and methane gas flow rate during the DLC layer deposition process were 300 ml / min and 8 ml / min, respectively. The flow rate ratio of the argon gas to the hydrocarbon gas (argon gas flow rate / hydrocarbon gas flow rate) supplied into the chamber was 37.5, within the aforementioned range (20-60). While adjusting the flow rates of the argon gas and hydrocarbon gas in this manner, the pulsed bias voltage applied to the substrate was set to 200 V, with a bias voltage duty ratio of 75%, and sputtering of the carbon target was performed for 264 minutes. This resulted in the deposition of a 1.0 μm DLC layer on the second DLC intermediate layer. Through the above steps, a test piece having a DLC layer deposited on the surface of the substrate was prepared as Example 1 of the present invention.

[0052] Example 2 A test piece on which a DLC layer of 1.0 μm was formed was prepared under the same conditions as in Example 1, except that the pulsed bias voltage applied to the substrate in the DLC layer forming step was set to 250 V.

[0053] Example 3 A test piece on which a DLC layer of 1.0 μm was formed was prepared under the same conditions as in Example 1, except that the pulsed bias voltage applied to the substrate in the DLC layer forming step was set to 300 V.

[0054] Example 4 A test piece on which a 1.0 μm DLC layer was formed was prepared under the same conditions as in Example 1, except that the pulsed bias voltage applied to the substrate in the DLC layer forming step was set to 175 V.

[0055] Example 5 A test piece on which a 1.0 μm DLC layer was formed was produced under the same conditions as in Example 1, except that the flow rate of methane gas was changed to 10 ml / min in the DLC layer formation process and the flow rate ratio of argon gas to hydrocarbon gas (flow rate of argon gas / flow rate of hydrocarbon gas) was set to 30.

[0056] (Comparative Example 1) Test pieces were prepared under the same conditions as in Example 1, except that the DLC intermediate layer deposition process was omitted and a DLC layer was deposited by plasma CVD on the surface of an intermediate layer made of chromium, tungsten, and carbon. The DLC layer in Comparative Example 1 was deposited under conditions in which only acetylene gas was supplied to the chamber at a flow rate of 1000 ml / min. In the DLC layer deposition process in Comparative Example 1, the pulsed bias voltage applied to the substrate was set to 800 V, with a bias voltage duty ratio of 30%, and the deposition process was carried out for 130 minutes, resulting in the deposition of a 1.5 μm DLC layer.

[0057] The test pieces of Examples 1 to 5 and Comparative Example 1 were subjected to a ball-on-disk test to evaluate their adhesion resistance to aluminum materials. Furthermore, a hardness measurement test was conducted to evaluate the hardness of the DLC layer. Furthermore, the test pieces of Example 1 and Comparative Example 1 were subjected to FE-SEM observation to observe the surfaces of the DLC layers.

[0058] (Ball-on-disk test) The test machine is CSM A Tribometer manufactured by Instruments was used. The disk was a test specimen from any of Examples 1 to 5 and Comparative Example 1. A pure aluminum ball with a diameter of 6 mm was used as the ball to be in contact with the disk. Under a wet environment with a temperature of 23 to 24°C, a humidity of 21%, and one drop of polyalphaolefin as a lubricant applied to the disk, the aluminum ball was brought into contact with the disk as shown in Figure 4. A load of 13 N was applied to the aluminum ball, and the disk was rotated at a sliding speed of 0.05 m / s. The contact point between the aluminum ball and the disk was a point 5 mm in radius from the center of the disk. The friction force between the disk and the aluminum ball was measured at 0.2-second intervals until the sliding distance between the disk and the aluminum ball reached 100 m, and the friction coefficient was measured using TRIBOX, the software provided with the testing machine. The test was stopped when the friction coefficient reached 0.5 or greater. The ball-on-disk test was also conducted in a dry environment without applying lubricant to the disk. The method for the ball-on-disk test in a dry environment is similar to the method for the ball-on-disk test in a wet environment, except that no lubricant is applied to the disk.

[0059] The results of the ball-on-disk test are shown in Figures 5 to 14 and the above-mentioned Table 2. Figures 5 to 9 show the test results in a wet environment, and Figures 10 to 14 show the test results in a dry environment. The lines in the graphs in each figure connect the measured values of the friction coefficient measured at 0.2 second intervals.

[0060] <Wet environment> As shown in Figure 5 and Table 2, the friction coefficient of the test piece of Example 1 varied between 0.003 and 0.093 until the sliding distance reached 100 m, but no significant increase in the friction coefficient was observed, demonstrating excellent adhesion resistance to the aluminum material. Figure 5 also shows the results of Comparative Example 1. The friction coefficient of the test piece of Comparative Example 1 rose to 0.5 or more immediately after the start of sliding, and the test was stopped. As shown in FIG. 6 and Table 2, the friction coefficient of the test piece of Example 2 changed between 0.027 and 0.122 until the sliding distance reached 100 m, but no significant increase in the friction coefficient was observed, and the test piece had excellent adhesion resistance to the aluminum material. As shown in FIG. 7 and Table 2, the friction coefficient of the test piece of Example 3 changed between 0.033 and 0.155 until the sliding distance reached 100 m, but no significant increase in the friction coefficient was observed, and the test piece had excellent adhesion resistance to aluminum materials. As shown in FIG. 8 and Table 2, the friction coefficient of the test piece of Example 4 changed between 0.007 and 0.093 until the sliding distance reached 100 m, but no significant increase in the friction coefficient was observed, and the test piece had excellent adhesion resistance to the aluminum material. As shown in FIG. 9 and Table 2, the friction coefficient of the test piece of Example 5 changed between 0.089 and 0.147 until the sliding distance reached 100 m, but no significant increase in the friction coefficient was observed, and the test piece had excellent adhesion resistance to aluminum materials.

[0061] The above results show that in Examples 1 to 5, the coefficient of friction with the aluminum material in a wet environment was very low, at 0.2 or less, and a DLC layer was formed in which an increase in the coefficient of friction was suppressed. Furthermore, in Examples 1 to 5, the DLC layer was formed at a high deposition rate of 0.2 μm / hr or more. In other words, the DLC layer deposition method according to the present invention can produce a DLC layer with a low coefficient of friction in a wet environment in a short time.

[0062] <Dry environment> As shown in FIG. 10 and Table 2, the friction coefficient of the test piece of Example 1 changed between 0.135 and 0.296 until the sliding distance reached 100 m, but no significant increase in the friction coefficient was observed, and the test piece had excellent adhesion resistance to the aluminum material. As shown in FIG. 11 and Table 2, the friction coefficient of the test piece of Example 2 changed between 0.099 and 0.269 until the sliding distance reached 100 m, but no significant increase in the friction coefficient was observed, and the test piece had excellent adhesion resistance to the aluminum material. As shown in FIG. 12 and Table 2, the friction coefficient of the test piece of Example 3 rose to 0.5 or more immediately after the start of sliding, and the test was stopped. As shown in FIG. 13 and Table 2, the friction coefficient of the test piece of Example 4 rose to 0.5 or more immediately after the start of sliding, and the test was stopped. As shown in FIG. 14 and Table 2, the friction coefficient of the test piece of Example 5 rose to 0.5 or more immediately after the start of sliding, and the test was stopped. As shown in Table 2, the friction coefficient of the test piece of Comparative Example 1 rose to 0.5 or more immediately after the start of sliding, and the test was stopped.

[0063] The above results show that in Examples 1 and 2, a DLC layer with a low coefficient of friction was formed not only in a wet environment but also in a dry environment.

[0064] (hardness measurement) Hardness measurements were performed using the nanoindentation method with a Fischer Instruments PICODENTOR® Hm500. Specifically, a Berkovich indenter was pressed into the test specimen with a maximum indentation load of 5 mN, and the indentation depth was continuously measured. Using the obtained indentation depth measurement data, Martens hardness and Vickers hardness converted from Martens hardness were calculated using Fischer Instruments' software, "WIN-HCU®." The calculated Vickers hardness was displayed on the screen of the measuring device, and this value was used as the hardness of the film at the measurement point. In this example, the Vickers hardness was measured at 20 random points on the surface of each test specimen, and the average of the obtained hardness values was recorded as the hardness of the film. Note that when pressing the indenter into the test specimen, the indentation load may propagate up to approximately 10 times the maximum indentation depth of the indenter. Therefore, if the indentation load propagates and reaches the substrate of the test specimen, the influence of the substrate may be included in the hardness measurement results. Therefore, in order to measure the hardness of a pure hard film, the following condition must be satisfied: "thickness of hard film > maximum indentation depth of indenter × 10".

[0065] As shown in Table 2, the test piece of Example 1 had a sufficient hardness of 2629 HV in Vickers hardness. The test piece of Example 2 had a sufficient hardness of 2535 HV in Vickers hardness. The test piece of Example 3 had a sufficient hardness of 2682 HV in Vickers hardness. The test piece of Example 4 had a sufficient hardness of 2404 HV in Vickers hardness. The test piece of Example 5 had a sufficient hardness of 2215 HV in Vickers hardness. The test piece of Comparative Example 1 had a sufficient hardness of 2052 HV in Vickers hardness.

[0066] (FE-SEM surface observation) Next, the surface of each test piece, i.e., the surface of the DLC layer of each test piece, was observed using an FE-SEM. Fig. 15 is an observation image of the DLC layer surface of Example 1. The DLC layer of Example 1 had recesses formed in places. Fig. 16 is an observation image of the DLC layer surface of Comparative Example 1. The DLC layer of Comparative Example 1 had minute protrusions formed on its surface, but unlike Example 1, no recesses were formed.

[0067] The above results show that the reason why the test piece of Example 1 has a lower coefficient of friction with the aluminum material than the test piece of Comparative Example 1 is because recesses are formed on the surface of the DLC layer. Such a DLC layer is formed by setting the bias voltage to a high value and regulating the flow rate ratio of argon gas to hydrocarbon gas (flow rate of argon gas / flow rate of hydrocarbon gas) within a specific range in the DLC film formation process. [Industrial Applicability]

[0068] The present invention can be used, for example, when forming a hard film on the surface of a mold used to mold aluminum material. [Explanation of symbols]

[0069] 1 DLC coating material 2 Base material 3. Middle class 4 DLC middle tier 4a First DLC Intermediate Layer 4b Second DLC Intermediate Layer 5 DLC tier 10 Film deposition equipment 11 Chambers 12 units 13 Bias pulse power supply 14 Gas inlet 15 Gas supply source 16 Gas exhaust pipe 17 Target 17a: Surface facing the substrate 18 Pulse power supply for sputtering 19 magnetic pole 20. Plasma

Claims

1. A method for forming a DLC layer on a surface of a substrate by unbalanced magnetron sputtering using a carbon target, comprising: adjusting the flow rates of the argon gas and the hydrocarbon gas so that the flow rate ratio (flow rate of the argon gas / flow rate of the hydrocarbon gas) of the argon gas and the hydrocarbon gas supplied into the chamber where the film formation process is performed is 35 to 60; A method for forming a DLC layer, comprising applying a bias voltage of 190 to 275 V in pulses to the substrate.

2. The method for forming a DLC layer according to claim 1 , wherein the flow rate ratio is 50 or less.

3. 3. The method for forming a DLC layer according to claim 1, wherein the duty ratio of the bias voltage is set to 30 to 80%.

4. 4. The method for forming a DLC layer according to claim 1, wherein the hydrocarbon gas is methane gas.

5. A method for manufacturing a mold, comprising: manufacturing a mold having a DLC layer formed on a surface of a substrate by using the method for forming a DLC layer according to any one of claims 1 to 4.

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