JP2010100878A - Substantially hydrogen-free low chromium-containing dlc film and sliding component - Google Patents

Abstract

Sliding with a low chromium-containing DLC (diamond-like carbon) film substantially free of hydrogen and a low chromium-containing DLC film substantially free of hydrogen that can withstand a high load even under high-speed sliding Provide parts.
When the Cr content in the DLC film is X (at%) and the surface hardness of the DLC film is Y (Hv) in terms of Vickers hardness, the formulas 0.5 ≦ X ≦ 0.7, 300 ≦ A low-chromium-containing DLC film that does not substantially contain hydrogen and is in the range of the region satisfying the equations of Y <500 and Y <−869X + 1043. Also, a sliding component is formed in which a first layer made of only Cr and a second layer made of Cr and C are formed between the DLC film and the base material.
[Selection] Figure 3

Description

  The present invention relates to a DLC (diamond-like carbon) film containing substantially no hydrogen and containing a small amount of chromium, and a sliding component on which the DLC film is formed.

  In the trend of protecting the global environment, it is important to save energy in transportation equipment such as automobiles and trains, home appliances and industrial machinery. For this reason, development that raises the efficiency of energy engines and development that reduces friction loss at sliding parts in engines and drive systems are being addressed as important issues. As a measure to reduce friction loss, the friction of the sliding surface has been reduced and the durability has been improved. For example, the formation of a diamond-like carbon (hereinafter referred to as DLC) film has been studied. It is already used in some industrial fields.

  As a specific use of the DLC film, for example, in Patent Document 1, a DLC film containing 100 ppm to 1% of Cr (chromium) has high hardness and excellent wear resistance, so that scratches generated on the recording medium of the magnetic disk, etc. It is disclosed that the present invention can be applied as a protective film for protecting from the above.

  In Patent Document 2, a soft carbon film having a surface hardness of Vickers hardness of 500 to 2000 Hv and not containing hydrogen and a hard carbon film having a surface hardness of 2000 to 4000 Hv and not containing hydrogen are alternately formed on the base material. In addition, it is possible to prevent cracking with low friction by forming a DLC film containing hydrogen with a surface hardness of 500 to 2000 Hv as the uppermost layer on top of four or more layers. It is disclosed that a DLC film can be applied as a wear-resistant tool such as a metal mold.

Japanese Examined Patent Publication No. 4-9870 JP 2008-1951 A

  However, the DLC film disclosed in Patent Document 1 has a high hardness, so it is easily broken and has a problem in use under a high load environment.

  In addition, the DLC film disclosed in Patent Document 2 describes that cracking can be prevented even under a high load environment. For example, the DLC film can be used under high-speed sliding such as a high-speed rotating part in an automobile engine. There is no suggestion or disclosure as to whether or not it can withstand high loads. Here, “high-speed sliding” means a state of sliding at a speed of 90 m / min (1500 mm / s) or more, and “high load” means a state of applying a force of 8.0 kN (816 kgf) or more. Shall.

  In view of the above-described problems, an object of the present invention is to provide a DLC film that can withstand a high load even under high-speed sliding, and a sliding component on which the DLC film is formed.

  In order to solve the above-described problem, the present applicant forms a DLC film under various film formation conditions within a range of Cr content in the DLC film of 0 to 2.0 at%, and then forms Cr in the DLC film. The relationship between the surface hardness and seizure property due to the change in the content was investigated.

  As a result, as shown in FIG. 3 to be described later, the surface hardness decreases as the Cr content in the DLC film increases. In particular, the Cr content in the DLC film is 0.5 to 0.7 at% in atomic%. In the above range (formula (1) described later), it has been found that the seizure property of the DLC film greatly changes with the surface hardness being 500 Hv as a boundary.

  Specifically, the seizure of a DLC film having a surface hardness of the DLC film in the range of 300 Hv or more and less than 500 Hv (formula (2) described later) It was found to be superior to the membrane.

  Further, in order to strictly define the range of the Cr content and the surface hardness of the DLC film according to the present invention, the seizure start load was less than 8.5 kN (867 kgf) based on the Falex test result described later. By excluding the region of the test result, the following formula (3) was derived.

Therefore, in the present invention, when the Cr content in the DLC film is X (at%) and the surface hardness is Y (Hv) in terms of Vickers hardness, the formula 0.5 ≦ X ≦ 0.7. (1)
300 ≦ Y <500 (2)
Y <−869X + 1043 (3)
The above-mentioned problem was solved by using a low-chromium-containing DLC film that is in the range of a region that satisfies the above formulas and that does not substantially contain hydrogen.

  That is, the low chromium-containing DLC film according to the present invention is a DLC film that can secure toughness that can withstand a high load even under high-speed sliding while reducing surface hardness and suppressing adhesion during sliding. It became. Here, the adhesion property refers to the property that solids adhere to each other by the bonding force with the surface atoms of the mating material. For this reason, if the adhesiveness at the time of sliding becomes strong, the DLC film adheres strongly to the sliding counterpart material, and as a result, it causes peeling of the DLC film.

  Regarding the Cr content in the DLC film, the surface hardness of the DLC film is reduced by limiting the range of the above-described formula (1), that is, the content to a range of 0.5 to 0.7 at%. Reduces adhesion during movement. The reason for limiting the Cr content in the DLC film is the result of the Falex test, which will be described later, as shown in FIG. 3. However, when the Cr content is less than 0.5 at%, the hardness of the DLC film and the internal stress are increased. It is considered that the DLC film breakage occurs under a high load environment due to the decrease in the toughness of the DLC film due to the increase in the thickness, making it difficult to withstand use. On the other hand, when the Cr content exceeds 0.7 at%, the amorphous structure unique to the DLC film may be destroyed, and the adhesion during sliding is considered to be strong.

  Moreover, about the surface hardness of a DLC film, the DLC film can be made tough by limiting the hardness to the range of the above formula (2), that is, the Vickers hardness within a range of 300 Hv or more and less than 500 Hv. . The reason for limiting the surface hardness of the DLC film is also based on the Falex test result described later as shown in FIG. 3, but it is considered that the wear resistance due to low hardness is insufficient when it is less than 300 Hv. Moreover, when it is 500 Hv or more, it is considered that the risk that the DLC film is brittlely broken increases.

  In the invention according to claim 2, the first layer made of only Cr, the second layer made of Cr and C on the base material made of an iron-base alloy, and substantially hydrogen according to the invention of claim 1 are used. The sliding component was formed in the order of the low-chromium-containing DLC film not containing. This improves the adhesion between the base material, the first and second layers, and the low chromium-containing DLC film that does not substantially contain hydrogen.

  Note that the low chromium-containing DLC film according to the present invention was a DLC film substantially free of hydrogen. “Substantially no hydrogen” means that the hydrogen content in the gas introduced from the outside is positively excluded, and it is attached to the target and the base material for film formation, etc. Below, 3 atomic% or less of hydrogen present from the beginning is assumed to be “substantially free of hydrogen”. The “substantially hydrogen-free” DLC film has a detailed mechanism unknown compared to the “substantially hydrogen-containing” DLC film formed using a hydrocarbon-based gas. It is said to have excellent heat resistance.

  The “iron-based alloy” according to the present invention refers to an alloy containing iron as a main component. Specifically, carbon steel (JIS G4052) and alloy steels (JIS G4053) such as manganese steel, manganese chrome steel, chrome steel, nickel chrome steel, nickel chrome molybdenum steel, and chrome molybdenum steel. Further, tool steels such as carbon tool steel (JIS G4401) and high speed tool steel (JIS G4403), and cast materials such as stainless steel and cast iron and cast steel are also included in the “iron-based alloy” according to the present invention.

As described above, in the present invention, when the Cr content in the DLC film is X (at%) and the surface hardness of the DLC film is Vickers hardness as Y (Hv), the formula 0.5 ≦ X ≦ 0.7 (1)
300 ≦ Y <500 (2)
Y <−869X + 1043 (3)
By using a low-chromium-containing DLC film that does not substantially contain hydrogen within a range that satisfies the above formulas, the surface hardness of the DLC film is reduced and adhesion during sliding is suppressed. However, it is possible to ensure toughness that can withstand high loads even under high-speed sliding. As a result, the seizure resistance of the DLC film is improved, and it can be applied as a coating (thin film) of a sliding part that can withstand long-term use.

  In addition, a low-chromium-containing DLC film that does not substantially contain hydrogen is formed on a base material made of an iron-based alloy in the order of a first layer made of only Cr and a second layer made of Cr and C. Adhesion between the base material, the first and second layers, and the DLC film is improved by using the sliding component formed as the outermost layer. Thereby, a sliding component having excellent peeling resistance can also be provided.

  An example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a magnetron sputtering apparatus used for forming a first layer, a second layer, and a DLC film according to the present invention. This magnetron sputtering apparatus includes a vacuum vessel 1 that is evacuated through an exhaust port 3 connected to a vacuum exhaust pump (not shown), and a workpiece (hereinafter referred to as a workpiece) provided in the center of the vacuum vessel 1. And a rotating jig 8 attached to the lower side of the mounting jig 9. In addition, targets 6 and 6 ′ for generating sputtered particles 7 toward one end of the work held by the mounting jig 9 are provided on the side surface in the vacuum vessel 1. Further, a sputtering power supply 11 connected to the targets 6 and 6 ′ and a work bias power supply 10 for applying a negative bias voltage to the work held by the mounting jig 9 are provided outside the vacuum vessel 1. . In addition, 2 is a reactive gas inlet, 4 is a magnet, and 5 is a booster coil.

  The generation process of the first layer, the second layer, and the DLC film is divided into an ion bombardment process and a film formation process. First, the ion bombardment process will be described. Argon which is an inert gas filled in the vacuum vessel 1 from the reaction gas inlet 2 shown in FIG. 1 is positive in the plasma generated by glow discharge generated by applying a negative voltage to the sputtering power source 11. It becomes an argon ion charged to the electric charge. These argon ions are electrically attracted to the workpiece applied with a negative voltage, collide with the surface, and the surface layer is physically removed by the etching action. As a result, the adhesion between the workpiece and the first layer is improved in the film forming step described below.

  Next, the film forming process will be described. After introducing argon as a sputtering gas into the vacuum vessel 1 from the reaction gas inlet 2, each target 6, 6 ′ is negatively charged by a sputtering power source 11 individually attached to the plurality of targets 6, 6 ′. By applying, plasma is generated and argon is ionized. As a result, argon ions are present in the plasma, and each target 6, 6 ′ material is made to collide with each target 6, 6 ′ applied with a negative potential by utilizing the sputtering phenomenon. Scatter. The scattered target constituent particles are further activated in the plasma by the magnet 4 and the booster coil 5. Finally, a negative bias voltage is applied to the work using a work bias power source 10 to positively take in the ionized constituent particles in the plasma to form a film on the work surface.

  In the present invention, after the work surface is cleaned by the above-described ion bombardment process, a Cr layer is formed to a thickness of 0.1 μm as a first layer using a Cr target 6. Next, the target 6 'made of C is simultaneously operated to continuously reduce the Cr amount and continuously increase the C amount to form the second layer having a thickness of 0.20 μm. The Cr content in the surface layer of the second layer is the same as the Cr content in the DLC film described later.

  Finally, while the power output of the target 6 ′ made of C is fixed at 7.0 kW, the power output of the target 6 made of Cr is changed in the range of 0.2 to 0.3 kW, so that Cr is contained in the DLC film. The amount is controlled within a certain range of 0.5 to 0.7 at% (atomic%). Moreover, the work bias electric power comprised by the bias voltage and electric current to a workpiece | work is set to 1500W, and the booster coil electric current which controls the magnetic field which contributes to a plasma state is set to the range of 50-100A. In this state, the surface hardness of the DLC film is controlled within a certain range of 300 Vv or more and less than 500 Hv in terms of Vickers hardness.

  The Cr content of the formed DLC film can be measured using a measuring device such as an EPMA (electron beam microanalysis) or an Auger electron spectroscopic analyzer. The surface hardness can be measured using a micro Vickers hardness meter or the like.

After the first layer and the second layer were formed on the surface of the rod-shaped test piece (work) using the apparatus shown in FIG. 1 under the conditions described above, a DLC film was formed under the following conditions.
・ Work bias power: 1500W
-Booster coil current: 20-160A
-Power output of target 6 'consisting of C: 7.0 kW
-Power output of the target 6 made of Cr: 0 to 1.0 kW

After the film formation under the above-mentioned conditions, there is a practical problem with a rod-shaped test piece having a surface hardness of the DLC film of less than 200 Hv due to insufficient wear resistance due to low hardness. It was decided not to perform sex evaluation. That is, in this example, only a DLC film having a surface hardness of 200 Hv or higher was subjected to a Falex test under the following conditions in order to evaluate the seizure property. It explains using.
・ Test atmosphere: in oil ・ Oil type used: Automale fluid for automobiles (manufactured by Nippon Oil Corporation: ENEOS AT fluid)
Test piece rotation speed: 1750 rpm (98.91 m / min)
-Specimen material (base material): SCr420H material (carbonitrided product)
・ Pressing jig material: SNCM220 material ・ Pressing jig surface treatment: carbonitriding process ・ Test time (pressing time): 1 minute

  FIG. 2 is an enlarged view showing a rotating portion of the Falex test apparatus. Here, the Falex test is a load that starts sticking of a bar-shaped test piece by pressing a V-shaped pressing jig from both sides against a rotating bar-shaped test piece as shown in FIG. This is a test for evaluating the seizure resistance of the film by measuring (load).

  FIG. 3 shows the relationship between the Cr content (at%) in the DLC film and the surface hardness (HV) in the above-described rod-shaped test piece, the seizure start load is (1) less than 8.5 kN (867 kgf), (2 ) It is a diagram showing the variation in three cases of 8.5 kN (867 kgf) or more and less than 10.0 kN (1020 kgf) and (3) 10.0 kN (1020 kgf) or more.

  As shown in FIG. 3, the surface hardness decreased as the Cr content in the DLC film increased regardless of the seizure start load of the bar-shaped test piece. Further, there was a correlation between the Cr content in the DLC film and its surface hardness.

  Among them, when the Cr content was in the range of 0.5 to 0.7 at%, the results of seizure start load of the Falex test were largely divided with the surface hardness being 500 Hv as a boundary. That is, when the surface hardness is in the range of 300 Hv to less than 500 Hv, the seizure start load is concentrated in the range of (2) 8.5 kN or more and less than 10.0 kN, and (3) 10.0 kN or more. The attached starting load was only (1) less than 8.5 kN.

From the above, in the present invention, when the Cr content in the DLC film is X (at%) and the surface hardness of the DLC film is Y (Hv) in terms of Vickers hardness, the formula 0.5 ≦ X ≦ 0.7 (1)
300 ≦ Y <500 (2)
Y <−869X + 1043 (3)
By using a low-chromium-containing DLC film that does not substantially contain hydrogen within a range that satisfies the above formulas, a DLC film that can withstand a high load even under high-speed sliding could be provided.

  In this example, when a load is applied at 8.0 kN, 8.5 kN, and 10.0 kN, the surface pressure (compressive stress) applied to the rod-shaped test piece is 1731 MPa, respectively, using Hertz's maximum contact stress equation. 1785 MPa and 1936 MPa.

It is a longitudinal cross-sectional view of the magnetron sputtering apparatus used in order to form the 1st layer, 2nd layer, and DLC film which concern on this invention. It is an enlarged view which shows the rotation part of the Falex testing apparatus for measuring the seizure start load of the rod-shaped test piece used in the Example which concerns on this invention. The relationship between the Cr content (at%) in the DLC film and the surface hardness (Hv) in the rod-shaped test pieces used in the examples according to the present invention is as follows. The seizure start load is less than (1) 8.5 kN (867 kgf). (2) It is a figure showing the variation divided into three cases of 8.5 kN (867 kgf) or more and less than 10.0 kN (1020 kgf) and (3) 10.0 kN (1020 kgf) or more.

Claims (2)

When the Cr (chromium) content in the DLC (diamond-like carbon) film is X (at%) and the surface hardness of the DLC film is Vickers hardness, Y (Hv), the following formulas (1) to (3 A low-chromium-containing DLC film that does not substantially contain hydrogen, and is in a range of a region that satisfies each of the following formulas:
0.5 ≦ X ≦ 0.7 (1)
300 ≦ Y <500 (2)
Y <−869X + 1043 (3) 2. The low hydrogen-free material according to claim 1, wherein a first layer made only of Cr and a second layer made of Cr and C are formed in this order on a base material made of an iron-based alloy, A sliding component characterized in that a chromium-containing DLC film is formed as an outermost layer.

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