JPH0931628A - Sliding member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sliding member excellent in wear and seizing resistances by specifying the size of a metal Cr structure existing in a coating film in a dotty state when the top of a substrate is coated with the coating film having a composite structure based on metal Cr and chromium nitride. SOLUTION: The top of a substrate is coated with a coating film having a composite structure based on metal Cr and chromium nitride by a reactive ion plating method to produce a sliding member. At this time, the size of a metal Cr structure scattered in the coating film is regulated to 0.2-5μm and the Cr structure is allowed to account for 1-20% of the total area of the coating film. A chromium nitride structure in the coating film is made of CrN, Cr2 N or a mixture of them. The substrate is properly selected from among Fe-, Al- and Ti-base materials. The objective sliding member not causing chipping or peeling even under severe service conditions is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to CrN and Cr ₂
The present invention relates to a sliding member having a chromium nitride-based coating containing N as a main component and having excellent wear resistance and seizure resistance, and a method for producing the same.

[0002]

2. Description of the Related Art For example, sliding parts having a film having excellent sliding properties formed by surface treatment are used for sliding parts of automobile engine parts, various mechanical parts and the like. Conventional surface treatment methods include a nitriding treatment, a chromium plating treatment, and a molybdenum spraying treatment. However, as the use conditions of sliding parts have become severer in recent years, parts have become required to have higher sliding characteristics, and in some cases conventional surface treatments may not be able to cope with them. There has been a demand for a film having properties and seizure resistance. In response to such a request, recently, PVD (Physical Vap
It has been proposed to coat the sliding surface of the sliding member with a film of metal nitride, metal carbide, or the like by the (or deposition) method. PVD coatings such as TiN, TiC, and CrN have excellent wear resistance and seizure resistance. Particularly, titanium nitride, chromium nitride, and the like are attracting attention as coatings that can be put to practical use. Used in parts. But,
At present, use conditions have become more severe, and even with the use of titanium nitride or chromium nitride, there has been a situation in which the sliding characteristics cannot be said to be sufficient. Strict use of sliding conditions, especially when the contact surface separates due to the vibration motion in the normal direction acting on the sliding surface in addition to the sliding motion, or when the load in the normal direction fluctuates in the sliding motion. Under the conditions, chipping peeling may occur in a hard film such as a chromium nitride film by ion plating, which may shorten the life of the sliding member. Further, similar chipping of the hard film is observed even under severe lubricating conditions such as when the operating temperature is high or the lubricating oil film is hardly formed on the sliding portion due to a large contact load. Therefore, a sliding member coated with a ceramic coating film that is more excellent in chipping resistance and peeling resistance than the current surface treatment film is desired.

[0003]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above-mentioned viewpoints, and has a chromium nitride which is free from chipping and peeling even under severe use conditions and has sufficient seizure resistance and abrasion resistance. An object of the present invention is to provide a sliding member coated with an object film and a method for manufacturing the same.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have brought a gaseous phase containing a mixture of chromium and nitrogen into contact with a substrate by a PVD method, and deposited CrN on the surface of the substrate. And Cr ₂ N as main components to form a composite film in which a metallic chromium structure is scattered in the film, and the size of the scattered metallic chromium structure is 0.2 to 5 μm; By adjusting the area ratio to 1 to 20%, it was found that a sliding member excellent in abrasion resistance and seizure resistance and less likely to cause chipping-off was obtained, and the present invention was completed. That is, the sliding member according to the present invention forms a chromium nitride composite film having CrN and Cr ₂ N as main components and a chromium metal structure scattered in the film. And the area ratio of the metallic chromium structure is limited. The coating in the sliding member of the present invention is excellent in toughness as compared with a coating composed of only chromium nitride having high hardness, since the soft metallic chromium structure is uniformly scattered in the chromium nitride coating. Therefore, the member is less likely to be chipped or peeled.

In order to form a film in which the chromium metal structure is scattered in the chromium nitride structure, an ion plating method provided with a plurality of chromium metal evaporation sources is used. By adjusting the partial pressure of the reaction gas and the distance between each metal chromium evaporation source and the object to be treated, the reaction rate between the chromium evaporation and the reaction gas is controlled to form a target film.
By adjusting the reaction nitrogen gas partial pressure, the distance between the metal chromium evaporation source and the object to be treated, and the arc current ratio, the amount and size of the metal chromium structure in the film and the composition of chromium nitride can be appropriately adjusted. is there. The size of the metallic chromium structure is limited to the range of 0.2 to 5 μm, and the area ratio is limited to the range of 1 to 20%. If the size of the metallic chromium structure is 0.2 μm or less or the area ratio is 1% or less, the effect of the metallic chromium structure is not remarkable, and no improvement in chipping resistance and peeling resistance is observed. If the size of the metallic chromium structure is 5 μm or more, the metallic chromium structure is locally exposed on the surface, and the scuff resistance is lower than that of a single chromium nitride structure. On the other hand, when the area ratio is 20% or more, the film hardness decreases, and both the scuff resistance and the abrasion resistance deteriorate as compared with the chromium nitride single structure. The total thickness of the coating is preferably 1 to 80 μm. Particularly preferably 2
0 to 60 μm. If the film thickness is less than 1μm,
The life of the film is short due to abrasion. On the other hand, if the total thickness of the coating exceeds 60 μm, the coating peels off or cracks occur in the coating, and the adhesion to the substrate is reduced. It is not economically preferable to make the film thicker than necessary. The substrate to be coated with the film is appropriately selected from iron-based materials, aluminum-based materials, and titanium-based materials according to the application. The PVD method described in detail below is based on CVD (Chemical Vapor).
Although it is similar to low-temperature treatment as compared with the Deposition method or the like, since heat input due to the evaporation phenomenon is inevitable, it is preferable to use a heat-resistant iron-based material and a titanium material as a base material if possible.

The above is a method for forming a chromium nitride film on which a chromium metal structure is scattered on a substrate. In the present invention, a metal underlayer may be interposed between the film and the substrate. If ion plating is performed before the introduction of nitrogen gas during the above-described film formation process, an underlayer of chromium metal is formed on the substrate. The chromium metal base layer has a coefficient of thermal expansion close to that of the base material and is less susceptible to thermal stress, so that it has good adhesion and high flexibility. The underlayer of chromium metal is 0.1 ~
Preferably, it is formed to a thickness of 2 μm. If the thickness is less than 0.1 μm, the effect of improving the adhesion is small, and if it exceeds 2 μm, no further effect can be obtained, and it is not economically preferable. Forming an underlayer with high adhesion and flexibility between the film and the substrate in this manner is effective in preventing the film from peeling.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described below in more detail by way of specific examples. In the present invention, a gas phase in which chromium and nitrogen are mixed is brought into contact with a substrate by a PVD method. P
The VD method is a kind of technology for forming a film, and can be basically classified into three methods of vapor deposition, sputtering, and ion plating. In particular, in the present invention, the reactive ion plating method of depositing a chromium nitride film on a substrate by reacting chromium vapor with nitrogen is most preferable. Chromium vapor is obtained by irradiating chromium with a high energy beam such as an HCD gun or an electron beam and evaporating it. Alternatively, chromium vapor may be obtained by ejecting chromium particles from the cathode, as in a cathodic arc plasma ion plating method and a sputtering method. When plasma is generated in the gas phase in which nitrogen is mixed with the chromium vapor, chromium is ionized and combines with nitride ions to generate chromium nitride. As a result, a chromium nitride film is formed on the substrate surface. Hereinafter, the ion plating method will be described as an example, but the present invention is not limited to this.

FIG. 1 shows an example of an ion plating apparatus used in the present invention. The apparatus includes a vacuum vessel 24 having a reaction nitrogen gas inlet 22 and an exhaust port 23, and a first target 26 connected to a cathode of an arc power supply 25 and a second target 26 connected to a cathode of an arc power supply 27 in the vacuum vessel 24. Two targets 28 are arranged. Metal chromium is set on the first and second targets. The first target and the second target are installed at different distances from the object. Further, a rotary table 30 connected to a bias power supply 29 is disposed in the vacuum vessel 24, and an object 31 to be processed is set on the table. Next, a method for forming the film of the present invention on the object 31 using the ion plating apparatus will be described. First, the object 31 is washed, dirt adhering to the surface is removed, sufficiently cleaned, inserted into the vacuum vessel 24 of the ion plating apparatus, and then exhausted from the exhaust port 23. After evacuation is performed until the pressure in the container becomes 1.3 × 10 ^{−3 to} 5 × 10 ⁻³ Pa, heating is performed by a heater built in the ion plating apparatus to release gas contained in the base material. . The heating temperature is preferably from 300 to 500C. When the pressure in the chamber becomes 4 × 10 ⁻³ Pa or less, chromium as a target is used as a cathode, and arc discharge is generated on the surface to cause chromium to fly out. At this time, a bias voltage is applied to the object to be processed 31, and the metal ions ejected from the cathode are caused to collide with the substrate surface with high energy, that is, the oxide removal and the activation treatment of the substrate surface are performed by so-called bombard cleaning. Do. It is preferable that the bias voltage at that time be -700 to -900V. Thereafter, the bias voltage is lowered, and nitrogen gas is introduced into the container while chromium ions are deposited on the surface of the base material, and the nitrogen gas is passed through the plasma to ionize nitrogen. At this time, the nitrogen partial pressure is set to about 1.3 × 10 ^{−1 to} 13.3 Pa, and a bias voltage of 0 to −100 V is applied to form an ion plating film on the substrate surface. At the time of this film formation, the chromium particles evaporated from the first target have a low probability of colliding with the nitrogen molecules of the reaction gas because the distance to the object to be processed is short, and the chromium particles are ionized because they pass through the plasma for a short time. However, depending on the selection of the gas partial pressure and the distance, the metal can be deposited on the workpiece as it is. Further, since the distance between the chromium particles evaporated from the second target and the object to be processed is longer than that of the first target, Cr ₂ N, Cr ₂ N + Cr can be selected by selecting the gas partial pressure and the work distance.
A mixed film of N and CrN can be deposited. That is, by appropriately selecting the partial pressure of the gas and arranging the first target at a distance at which chromium metal is deposited and the second target at a distance at which chromium nitride is deposited, a coating of a composite composition comprising metal chromium and chromium nitride is formed. Can be formed.
Further, by appropriately setting the arc current value flowing through each target and the distance between the target and the object to be processed, the composite ratio of the metal chromium structure and the chromium nitride structure can be changed, and the size and The area ratio can be controlled. The operation and effect will be described below with reference to specific examples. The material is SU
Various chromium nitride composite coatings having a metallic chromium structure scattered on the test piece surface of the S440 material were prepared. The distance between the first target and the object to be processed is about 50 mm, which has been confirmed by preliminary experiments that metallic chromium is deposited.
It was also confirmed that the size of the metallic chromium structure was proportional to the arc current. The area ratio of the metal chromium structure can be adjusted by the ratio of the two arc currents. Further, the distance between the second target and the object was set to about 200 mm. The composition varies depending on the nitrogen partial pressure, and as the nitrogen partial pressure increases, Cr ₂ N, C
r ₂ N + CrN mixed film, changed to CrN. The composition of the coating was measured by X-ray diffraction using EPMA for the size and area ratio of the metal chromium structure, and the coating hardness was measured using a micro-Vickers hardness tester. Table 1 shows preparation conditions and measurement results of the member of the present invention.

[0009]

[Table 1]

As a comparative example, a conventionally known chromium nitride film was prepared and its properties were measured similarly (Comparative Examples 1 to 3). Furthermore, comparison was also made on examples in which the chromium metal structure was scattered in the chromium nitride film, but the size and area ratio of the chromium metal structure were inappropriate (Comparative Examples 4 to 6). Table 2 shows their preparation conditions and measurement results.

[0011]

[Table 2]

[Seizure Resistance] The seizure resistance of the material of the present invention is evaluated. Made of SKD61 material, length 5mm x width 5mm x height 5
Using a test piece 5 in which three mm-shaped pin-shaped protrusions 10 (see FIGS. 2 and 3) are arranged at equal intervals on a concentric circle, a film according to the present invention was formed on a 5 mm square end face in a thickness of 20 to 30 μm. A test piece was prepared, and a seizure resistance test was performed using an ultra-high pressure wear tester. Tests were performed on the example film and the comparative example film formed by the method described above. Further, as a comparative example, a similar test was added using a test piece in which a 100 μm-thick chromium plating film (Comparative Example 7) was formed on a 5 mm square end face of the test piece. The equipment and test conditions of the ultra-high pressure wear tester used in this test are as follows. The test apparatus is schematically illustrated in FIG. 2 and FIG. 3 which is a cross-sectional view taken along the line AA of FIG. 2, and has a diameter of 80 mm × a thickness of 10 mm removably attached to the stator holder 1. In the center of the polished disk 2 (counterpart), lubrication port 3
The lubricating oil is supplied through. A pressing force P is applied to the stator holder 1 with a predetermined pressure toward the right in the figure by a hydraulic device (not shown). A rotor 4 is opposed to the disk 2, and is rotated at a predetermined speed by a driving device (not shown). A test piece 5 is slidably attached to the disk 2 on the rotor 4 with a 5 mm square end face having a surface treatment layer formed thereon as a sliding surface. In such an apparatus, a predetermined pressing force P is applied to the stator holder 1 so that the disk 2 and the pin-shaped projections 10 of the test piece 5 come into contact with each other at a predetermined surface pressure, and slide from the lubrication port 3. The rotor 4 is rotated while refueling the surface at a predetermined refueling speed. The pressure acting on the stator holder 1 is gradually increased at regular intervals, and the rotation of the rotor 4 causes the test piece 5 to rotate.
The torque T generated in the stator holder 1 by the friction between the disk and the counterpart disk 2 is applied to the load cell 7 via the stainless steel fiber 6, and the change is read by the dynamic strain meter 8 and recorded on the recorder 9. Assuming that the seizure occurred when the torque T sharply increased, the quality of the seizure resistance is judged based on the contact surface pressure at this time. As the partner material, iron-based FC
250 materials were used. The test conditions are as follows. Friction Speed: 8m / sec mating member: FC250 member contact surface pressure: After leveling at 20 kgf / cm ^2, until the seizure occurred by 10 kgf / cm ² pressure increase. Hold at each contact pressure for 3 minutes. Lubricating oil: motor oil # 30 Oil temperature 80 ° C., supply rate 250 cc / min The test results are shown in Table 3.

[0013]

[Table 3]

The product of the present invention has a contact surface pressure of 281
At 290 kgf / cm ² . The surface pressure of seizure of the chrome plating of the comparative product is 253 kgf / cm ² or more, which is equivalent to that of the CrN single film (Comparative Example 3) having excellent seizure resistance. Even if the metallic chromium structure is scattered in the chromium nitride film, the effect is small if the metallic chromium structure is large and its area ratio is large (Comparative Example 6).

[Abrasion Resistance] A corrosion abrasion test of the material of the present invention was carried out using a Kaken abrasion tester. Substrate material is SKD-
Using 61 specimens, the shape of the specimen was 5 mm long × 5 mm wide × 20 mm long, and one end in the longitudinal direction was a curved surface of R6 mm.
Coated with a thickness of μm. Further, as a comparative example, a similar test was performed using a chromium-plated test piece having a thickness of 100 μm at the tip R of the test piece. (Comparative Example 7) In the test, the tip R of the surface-treated test piece was processed into a drum shape so that the curved surfaces were in line contact with the outer peripheral portion of the mating material, a predetermined load was applied, and the test piece was rotated at a predetermined speed. I do. The lubrication was performed by dropping a fixed amount of a sulfuric acid aqueous solution adjusted to PH = 2 to the contact portion to make an acidic atmosphere. The test conditions are as follows. Sliding partner material: FC250 material Friction speed: 0.25 m / sec Friction time: 6 hours Contact load: 4 kg Atmosphere: 1.5 cc / min of sulfuric acid aqueous solution adjusted to PH = 2.0 is dropped on the sliding part Are shown in Table 4.

[0016]

[Table 4]

The result is that the wear amount of the chromium plating film is 100
The relative values are shown as follows. Compared with the chrome-plated product of the comparative example, the product of the present invention has a greatly reduced abrasion amount of 1/20 to 1/25, and is equivalent to a CrN single film (comparative example 3) having particularly excellent wear resistance. is there. Even if the metallic chromium structure is scattered in the chromium nitride film, the effect is small if the metallic chromium structure is large and its area ratio is large (Comparative Example 6).

[Peeling Resistance] The peeling resistance of the film coated on the member of the present invention was evaluated by a rolling fatigue tester with roller (roller pitting tester). The substrate material of the test piece is a material obtained by carburizing SCM420 material, and the shape is φ26mm.
The film of the present invention and the film of the comparative example were treated to a thickness of about 50 μm on the outer surface of a roller having a size of × 28 mm. The thicknesses of the various coatings were adjusted by adjusting the coating time. The equipment and test conditions of the pitching tester used in this test are as follows. FIG. 4 schematically shows a main part of the test apparatus.
A load roller 12 is provided opposite to the test roller 11 to which a test piece 13 of 26 mm × 28 mm is attached, and a pressing force is applied at a predetermined pressure. Test roller 1
Reference numeral 1 denotes a rotating device at a predetermined speed by a driving device (not shown), and a surface treatment layer is formed on the outer periphery of the test piece 13. The load roller 12 has a size of φ130 × 18, an outer circumference of R300 mm, and microscopically makes point contact with the test piece 13 to apply a large pressing force. The load roller 12 is a test roller 11
, Driven by a gear (not shown), and rotates while sliding relatively. The slip rate is determined by the test piece peripheral speed (U
13) and the load roller peripheral speed (U12), (U13
−U12) / U13 and can be arbitrarily selected. Lubricating oil is poured into a contact portion between the test piece 11 and the load roller 12 through a lubrication port (not shown). In such an apparatus, a predetermined pressing force is applied to the test piece 13 so that the test piece 13 and the load roller 12 come into contact with each other at a predetermined surface pressure, and the test is performed while lubricating the contact portion at a predetermined lubrication rate. The roller is rotated at a predetermined speed, and the load roller 12 is rotated at a predetermined slip ratio. During the test, the surface of the test specimen is carefully observed periodically, and the quality of the peel resistance is determined from the total number of rotations until the chipped peel occurs on the surface of the test specimen.
The material of the load roller as the mating material was FC250. The test conditions are as follows. Surface pressure (Hertz stress): 160 kgf / mm ² Specimen peripheral speed: 82 m / s Slip ratio: 20% Oil used: # 30 (base oil) Oil flow rate: 1200 cc / min Oil temperature: 80 ° C. Test results are shown in Table 5. Was.

[0019]

[Table 5]

The product of the present invention is very excellent in peel resistance as compared with the comparative example of high hardness chromium nitride. Even when the chromium metal structure is scattered in the chromium nitride film as in Comparative Examples 4 and 5, peeling is likely to occur when the size is small or the area ratio is low.

[0021]

As is apparent from the above description,
The present invention uses a PVD method to deposit CrN and C on the surface of a substrate.
Excellent wear and seizure resistance compared to conventional hard coatings by forming a composite coating with r ₂ N as the main component and a metallic chromium structure scattered throughout the coating. Further, a sliding member in which chipped peeling is unlikely to occur, and
A method for manufacturing the sliding member is provided. The member of the present invention is suitable for sliding parts and cutting tools including engine parts such as piston rings and cam followers, and compressor parts such as shoe disks.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an ion plating apparatus.

FIG. 2 is an explanatory view of partially crushing an ultra-high pressure wear tester.

FIG. 3 is a cross-sectional view taken along the line AA of FIG. 1;

FIG. 4 is a schematic explanatory view of a rolling fatigue tester.

[Explanation of Signs] 1 Stator holder 2 Disk (counterpart material) 3 Lubrication port 4 Rotor 5 Test piece 6 Stainless steel fiber 7 Load cell 8 Dynamic strain gauge 9 Recorder 10 Pin-like projection of test piece (5 mm square) 11 Test roller 12 Load Roller 13 Test piece 22 Reaction gas inlet 23 Exhaust port 24 Vacuum container 25, 27 Arc power supply 26 First target 28 Second target 29 Bias power supply 30 Rotary table 31 Workpiece

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[Procedure amendment]

[Submission date] September 5, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

[0011]

[Table 2]

Claims (6)

[Claims] 1. A sliding member comprising a base material coated with a film having a composite structure mainly composed of chromium metal and chromium nitride, wherein the size of the chromium metal structure scattered in the film is large. A sliding member having a size of 0.2 μm to 5 μm. 2. A sliding member coated with a composite film of chromium nitride in which a chromium metal structure is scattered, wherein an area ratio of the chromium metal structure scattered to the entire film is 1 to 20%.
A sliding member characterized by the following. 3. The sliding member according to claim 1, wherein the chromium nitride structure in the coating is CrN.
A sliding member comprising a chemical composition of Cr ₂ N and a mixture thereof. 4. The sliding member according to claim 1, wherein a base layer made of chromium is interposed between said coating and said base material. 5. The sliding member according to claim 1, wherein the sliding member is a piston ring. 6. A sliding member according to claim 1, wherein the sliding member is formed by bringing a base material into contact with a gas phase in which chromium and nitrogen are mixed by the coating PVD method. A method for manufacturing a sliding member.