KR100299401B1 - Sliding material and its manufacturing method - Google Patents

Abstract

The present invention forms a chromium nitride-based film containing at least CrN on a base material by contacting the base material with a gaseous phase mixed with Cr and N by the PVD method, and the fracture surface crystals of the film are formed on the surface of the base material. Sliding with a chromium nitride-based coating formed in a columnar shape toward the surface and having a hollow hole ratio of 1.5 to 20% and preferentially oriented to a (111) plane parallel to the sliding surface in a single phase. It is a material and its manufacturing method.

This invention is excellent in peeling resistance, abrasion resistance, and plasticity resistance of a film compared with the film conventionally used.

Description

Sliding material and its manufacturing method

1 is an explanatory diagram of an abrasion test by a super pressure abrasion test apparatus.

2 is a sectional view taken along line A-A of FIG.

3 is a schematic diagram of a rolling fatigue tester.

4 is a micrograph of a chromium nitride (CrN) layer metal structure formed on the outer circumferential surface of a piston ring for use in the present invention.

5 is a micrograph of a columnar chromium nitride layer structure, not a columnar shape, formed on the outer circumferential surface of the piston ring used in Comparative Example 3. FIG.

<Description of the symbols for the main parts of the drawings>

1: Stator holder 2: Disc (relative material)

3: oil filling hole 4: rotor

5: test piece 6: stainless steel rod

7: Load Cell 8: Dynamic Distortion System

9: Recorder 10: Pin-shaped protrusion of test piece (5mm angle)

11: test roller 12: load roller

13: test piece

[Industrial use]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding member excellent in abrasion resistance and baking resistance having a chromium nitride coating containing CrN as a main component and containing Cr ₂ N, and a method for producing the same.

[Prior art]

Background Art Conventionally, sliding parts having a film having excellent sliding characteristics by surface treatment have been used for sliding parts of, for example, automobile engine parts and various mechanical parts. Conventionally, the surface treatment method is a method such as nitriding treatment, chromium plating treatment, molybdenum spray treatment (Mo flame spraying treatment).

However, in recent years, as the use conditions of sliding parts are high speed and high loads, the sliding characteristics required for the parts become more severe, and it is not possible to cope with conventional surface treatment, so that a film having better wear resistance and plastic resistance is desired. ought.

In response to such a request, it has recently been proposed to coat a film of metal nitride, metal carbide or the like on the sliding surface of the sliding member by PVD (Physical Vapor Deposition) method.

PVD coatings such as TiN, TiC, CrN, and the like have excellent wear resistance and plasticity resistance, and are particularly noticeable as practical coatings such as titanium nitride and chromium nitride, and are used in some mechanical parts and engine parts.

However, at present, the use conditions become more severe and there is a situation that cannot be said that the sliding characteristics are sufficient even if these titanium nitrides or chromium nitrides are used. In particular, in addition to the sliding motion, the vibrational motion in the normal direction acts synergistically on the sliding surface, and the contact surface is peeled off, or when the load in the normal direction fluctuates in the sliding motion. In hard coatings, including chromium nitride coatings by ion plating, flaking occurs and the life of the sliding material can be shortened. In addition, the same flaw-like peeling of the hard film is observed even under conditions of strict lubrication, such as when a lubricating oil film is hardly formed on a sliding portion having a high use temperature or a large contact load. Therefore, there is a demand for a sliding material coated with a ceramic coating film that is superior in peeling resistance than the current surface treatment.

[Problems to Solve Invention]

Accordingly, it is an object of the present invention to provide a sliding material coated with a film excellent in wear resistance and plastic resistance without causing flaw-like peeling even under stringent use conditions, and a method for manufacturing the same.

[Means and Their Actions to Solve Problems]

As a result of careful research in view of the above problems, the present inventors have contacted a gas phase mixture of chromium and nitrogen to the substrate by PVD method, CrN as the main component on the surface of the substrate, and Cr ₂ A chromium nitride-based film containing N was formed, at which time the fracture surface crystals of the film were in a columnar shape from the surface of the base material toward the surface of the film, and the porosity of the film was 1.5-20%. The present invention was completed by finding out that a sliding material having a flaw-like peeling hardly generated and excellent in wear resistance and plastic resistance was obtained.

That is, the sliding material of the present invention at least a CrN as a main component and the sliding material made by coating the formed chromium nitride-based compound on the basis recyclable by containing Cr ₂ N and the cutting plane determined in said film is toward the film surface from the base material surface It is characterized by having a columnar shape and having a limited film porosity.

The base material which coats a film is suitably selected from an iron (Fe) material, an aluminum material, and a titanium material according to a use. The PVD method described in detail below is similar to the low temperature treatment compared to the CVD (chemical vapor deposition) method, but heat input due to the deposition phenomenon cannot be avoided. It is preferable to use it.

The coating in the sliding material of the present invention is a chromium nitride compound composed of at least CrN and containing Cr ₂ N, and crystals of the fracture surface of the coating have a columnar shape from the surface of the base material toward the coating surface. Have As for the film whose fracture surface is columnar crystal | crystallization, flaw-like peeling considered to be due to pitching hardly arises.

In addition, as the chromium nitride-based coating becomes more dense, the coating will be brittle and flaw-like peeling will likely occur. The theoretical density of CrN is 6.14 g / cm ³ , and in order to prevent peeling, it is necessary to make the film void ratio 1.5% or more. On the other hand, when the film porosity is too high, the hardness decreases and the wear resistance deteriorates. Therefore, it is necessary to set the upper limit of the film void porosity to 20%. The porosity can be easily calculated as a ratio to the theoretical density by measuring the density of the obtained film.

Film hardness is affected by the crystal form of the film, the film porosity (porosity in the film formed in the material yarn), and the crystal orientation. The hardness of the film of the present invention is about 600 to 1000 in HmV (Vickers Micro Hardness) measured on the surface.

Further, in order to further improve the peeling resistance in the chromium nitride-based coating, it is also possible to further preferentially align the (111) plane in parallel with the sliding motion surface.

The thickness of the film is 1 to 80 µm, particularly preferably 35 to 50 µm. When the thickness of the film is less than 1 m, the life of the film is short due to abrasion. On the other hand, when the thickness of a film exceeds 50 micrometers, a film may peel or a crack may arise, and adhesive force with a base material falls. In addition, it is not economically desirable to thicken the film more than necessary.

In the present invention, the base material is brought into contact with the gas phase in which chromium and nitrogen are mixed by the PVD method. The PVD method is a kind of technology for forming a film, and can be basically classified into three methods of deposition, sputtering, and ion plating.

In particular, in the present invention, a reactive ion plating method in which a chromium nitride film is deposited on a base material by reacting a vapor material of chromium with nitrogen is most preferable.

The vapor of chromium is obtained by irradiating and evaporating chromium on a high energy beam such as an HCD gun or an electron beam. Further, chromium vapor may be obtained by allowing chromium particles to be released from the cathode, such as cathode arc plasma ion plating and sputtering.

When plasma is generated in a gaseous state in which nitrogen is mixed with the chromium vapor, chromium is ionized and combined with nitrogen ions to form a chromium nitride compound. As a result, a chromium nitride film is formed on the surface of the base material.

Although the ion plating method is described below as an example, this invention is not limited to this.

First, the base material is washed, the dirt adhering to the surface is removed, sufficiently cleaned and inserted into the vacuum chamber of the ion plating apparatus. The vacuum is maintained until the pressure in the chamber is 1.3 x 10 ^-3 to 5 x 10 ^-3 Pa, and then heated by a heater built in the ion plating apparatus to release the internal gas of the substrate. The heating temperature is preferably 300 to 500 ° C. After that, cool down to 100 ~ 400 ℃.

When the pressure in the chamber becomes 4x10 ^-3 Pa or less, the target chromium is used as the cathode, and an arc discharge is generated at the surface thereof to release chromium ions. At this time, the base material is subjected to a bias voltage and the metal ions emitted from the cathode are bombarded with high energy on the substrate surface, so-called bombardment cleaning, to perform oxide removal and activation on the surface of the base material. The bias voltage at that time is preferably set to -700 to -900V.

The nitrogen gas is then introduced into the chamber and passed through the plasma while lowering the bias voltage and depositing chromium ions on the base material surface. It ionizes nitrogen, nitrogen partial pressure is about 1.3x10 <^-1> ~ 13.3 Pa, and bias voltage is applied from 0 to -100V, and an ion plating film is formed in the base material surface. After the film is formed, it is cooled down to 200 ° C or less in the vacuum chamber and then the sliding material is taken out of the chamber. The void ratio of the film can be controlled by adjusting the pressure to be used.

In the above manner, a chromium nitride-based coating having a columnar shape in which the film fracture surface crystals have a columnar shape and excellent wear resistance and plasticity can be formed on the sliding surface of the sliding material.

Although the above method is to form a chromium nitride-based coating on the base material in a form in which crystals of the film fracture surface become columnar, in the present invention, a metal bottom layer may be interposed between the film and the base material. In the above-described film forming process, when ion plating is performed before the introduction of nitrogen gas, a bottom layer of chromium metal is formed on the substrate. The bottom layer of this chromium metal has good adhesion and well-deforming because the coefficient of thermal expansion is close to that of the base material and is less affected by thermal stress. It is preferable to form the bottom layer of chromium metal in the thickness of 0.1-2 micrometers. If it is less than 0.1 micrometer, the effect of adhesive improvement is small and it shows sufficient effect in the thickness of 0.1-2 micrometers. Moreover, even if it exceeds 2 micrometers, the further effect cannot be acquired and it is also unpreferable economically.

Thus, forming a bottom layer with sufficient adhesion and flexibility between the film and the base material is effective in preventing peeling of the film.

EXAMPLE

The present invention will be described in more detail with reference to specific examples below.

Example 1

In this embodiment, a base material of SUS440 material was used.

PVD treatment used a cathode arc plasma type ion plating apparatus. The base was washed with Freon and inserted into the vacuum chamber of the ion plating apparatus.

After vacuuming until the pressure in the chamber is 1.3 x 10 ^-3 Pa, it is heated to 300 to 500 ° C by a heater built in the ion plating apparatus to release the internal gas of the base material, and then Cooled to 200 ° C.

When the pressure in the chamber becomes 4 x 10 ^-3 Pa or less, a bias voltage is applied at -700 to 900 V to generate an arc discharge to release chromium ions. Thereafter, the partial pressure of nitrogen gas introduced into the chamber was changed to a range of about 1.3 x 10 ^-1 to 13.3 Pa, and a bias voltage of 0 to -100 V was applied to form an ion plating film having a thickness of 5 µm on the surface of the base material. After the film was formed, it was cooled down to 200 ° C. or less in a vacuum chamber to obtain a sliding material.

The fracture surface form, composition, porosity, and surface microhardness of the obtained film were examined.

The tension fracture surface of the film was observed by a scanning electron microscope with a second electronic figure. A columnar crystal was confirmed from the base material toward the coating surface. As a result of analyzing the composition by X-ray diffraction, it was also confirmed that the (111) plane, which is a single phase of CrN and parallel to the sliding surface, is oriented. The porosity was 3.9% and the surface hardness was HmV 770.

[Examples 2 and 3 and Comparative Example 1]

The baking resistance of the inventive material is evaluated.

5mm square (5mm) using a test piece (5) made of SKD61 material and having three pin-shaped protrusions (10; FIGS. 1 and 2) arranged at equal intervals on a concentric circle. The test piece which formed the film of this invention in thickness of 10 micrometers in the square cross section of () was created, and the fire resistance test was done by the ultra-high pressure abrasion tester. The coating of the test piece was formed by the method described in Example 1, and the crystal of the fracture surface had a columnar shape from the surface of the base material toward the surface of the coating, and preferentially oriented to the (111) plane parallel to the sliding surface of CrN. It is. A film having an empty porosity of 3.9% (Example 2), and a crystal having a fractured surface having a columnar shape from the surface of the base material toward the surface of the film (Example 3). . The surface microhardness of the film was HmV 770 in Example 2 and HmV 845 in Example 3.

As a comparative example, the same test was done using the test piece which provided the 100-micrometer-thick chromium plating film (comparative example 1) in the 5 mm square cross section of a test piece.

The equipment and test conditions of the ultra high pressure wear tester used in this test are as follows.

The test apparatus schematically shows the main part in FIG. 1 and FIG. 2 aa a sectional view of FIG. 1 aa, and is detachably attached to the stator holder 1 and has a polishing finish of 80 mm diameter x 10 mm thickness. Lubricating oil is lubricated through the lubrication port 3 from the rear side in the center of the mating material). The pressing force P acts on the stator holder 1 at a predetermined pressure toward the right side in the drawing by a hydraulic device (not shown). The rotor 2 is opposed to the disk 2 and is rotated at a predetermined speed by a drive device not shown. The rotor 4 is freely attached to the disk 2 by sliding the cross section of a 5 mm square square on which the test piece 5 has formed a surface treatment layer.

In such an apparatus, a predetermined pressing force (P) is applied to the stator holder (1), and the disk 2 and the pin-shaped protrusions 10 of the test piece 5 are brought into contact with the sliding surface from the oil filling port 3 at a predetermined surface pressure. The rotor 4 is rotated while refueling at a predetermined oil supply speed. The pressure acting on the stator holder 1 gradually increases at a predetermined time and is generated in the stator holder 1 by friction between the test piece 5 and the disk 2 facing each other by the rotation of the rotor 4. The torque T is applied to the load cell 7 through the stainless rod 6 and the change is a signal suitable for the recorder by dynamically varying the amount of torsion in the load cell between the distortion meter, the load cell and the recorder. Is converted into an electrical signal and amplified until it is measured to measure the amount of twist) and recorded in the recorder 9. Baking occurs when the torque T rises sharply, and the contact surface pressure at this time determines whether the plastic resistance characteristics are good or bad. Iron-based FC 25 ash was used as a mating material. The test conditions are as follows.

Friction Speed: 8 m / s

Relative Material: FC 25

Contact surface pressure: 20 kg / cm ² evenly, increase pressure by 10 kg / cm ² until firing, hold for 3 minutes at each surface pressure

Lubricant: Motor Oil # 30

Oil Temperature 80 ° C, Supply 250cc / min

Table 1 shows the test results.

As a counterpart of Fc 25, the present invention fired at contact surface pressures of 280 and 283 kg / cm ₂ . Comparative product higher than that in the firing surface pressure 253 kg / cm ² of chrome plating is excellent in plastic.

Example 4, Comparative Example 2

The corrosion abrasion test of the material of the present invention was conducted by a Kakenshiki test apparatus. Substrate material is SKD-61 material, and the formation is 5mm x 5mm x 20mm in height, and the test piece with one end in the longitudinal direction of R 6mm is used to dig at the tip of the test piece by the method described in Example 1. The crystal of the cross section has a columnar shape from the surface of the base material to the film surface, and is preferentially oriented to the (111) plane parallel to the sliding surface in the CrN single phase. A film (Example 4) having a film porosity of 3.9% was coated with a thickness of 10 m. The surface microhardness of the film was HmV 770.

As a comparative example, the same test was done using the chromium plating test piece of thickness of 100 micrometers in test piece tip R part.

In the test, the front end portion R of the test piece subjected to the surface treatment was matched with the curved surfaces in line with the outer peripheral part of the counterpart material processed in a drum shape, and a predetermined load was applied.

To rotate at a predetermined speed. Lubrication was carried out by dropping a sulfuric acid aqueous solution adjusted to PH = 2 by a certain amount to the acid position.

The test conditions are as follows.

Sliding relative material: FC 25 ash

Friction Speed: 0.25 m / s

Friction time: 6 hours

Contact load: 4 kg

Atmosphere: The sulfuric acid aqueous solution adjusted to PH = 2.0 in a sliding part is dropped per 1.5 cc / min.

The measured value of the film wear amount is shown in Table 2. The results are shown in relative values where the wear amount of the chromium plated film is 100.

Compared with the chromium plated product as a comparative product, the wear amount of the present invention is greatly reduced to about 1/30.

[Examples 5 and 6 and Comparative Example 3]

Peeling resistance of the film coated on the material of the present invention was evaluated by a rolling fatigue tester (roller pitching tester) with sliding. The board | substrate material of a test piece is the material which carburized SCM 420 material, the shape is a roller shape of 26 mm x 28 mm, and the film of this invention was treated with the thickness of 45 micrometers on the outer peripheral surface. The film of the test piece was formed by the method described in Example 1, and the crystal of the fracture surface had a columnar shape from the surface of the base material toward the film surface, and was oriented in the (111) plane parallel to the sliding surface of CrN single phase. A film having a vacant porosity of 3.9% (Example 5) and a crystal having a fracture surface have a columnar shape from the surface of the base material toward the surface of the film, and a film having a porosity of 2.3% (Example 6) It was. In addition, the surface microhardness of the film was HmV 770 for the film of Example 5 and HmV 845 for the film of Example 6. FIG.

As a comparative example, the same materials as in Examples 5 and 6 were coated on the outer circumference of the test piece body with 42 μm of CrN film having a very low fracture surface having a columnar shape and a 0.2% void area. Peeling resistance was measured.

The apparatus and test conditions of the pitching tester used in this test are as follows.

3 shows a diagrammatic view of the main part and a load roller 12 is opposed to a test roller 11 to which a test piece 13 having a Ф 26 mm x 28 mm is attached and a pressing force is applied at a predetermined pressure. I'm letting you. The test roller 11 is rotated at a predetermined speed by a simultaneous driving device, and forms a surface treated phase on the outer circumference of the test piece 13. The load roller 12 has a size of 130 x 18, and the outer circumference has a shape of R 300 mm, and is microscopically contacted with the test piece 13, and a large pressing force is applied. In addition, the load roller 12 is driven and rotated relative to the test roller 11 through a gear wheel (not shown). The sliding rate is represented by (U ₁₃ -U ₁₂ ) / U ₁₃ by the test piece circumferential speed U ₁₃ and the load roller circumferential speed U ₁₂ , and is arbitrarily selected. Lubricant is injected into the contact portion between the test piece 11 and the load roller 12 through a filling hole not shown.

In such an apparatus, a predetermined pressing force is applied to the test piece 13, the test piece 13 and the load roller 12 are brought into contact with each other at a predetermined surface pressure, and the test roller is rotated at a predetermined speed while lubricating the contact portion at a predetermined oiling speed. At the same time, the load roller 12 is rotated at a predetermined sliding rate.

Carefully observe the surface of the specimen regularly during the test, and judge the good and bad peeling resistance by cumulative rotation until flaw peeling occurs on the surface of the specimen. The material of the load roller, which is a relative material, is made of FC 25. The test conditions are as follows.

Test conditions Transformer (Hertz pressure): 160 kgf / mm ₂

Test piece peripheral speed: 82m / s

Slip rate: 20%

Oil Used: # 30 (Base Oil)

Oil flow rate: 1200 cc / min

Oil temperature: 80 ° C

Table 3 shows the test results.

This invention is very excellent in peeling resistance with respect to a comparative example.

[Effects of the Invention]

As has been found to have been described above, the present invention has conventionally been carried out by crystallizing the fracture surface of the chromium nitride coating coated on the surface of the base material from the surface of the base material toward the surface of the film and limiting the film porosity. In addition to providing a sliding material excellent in peeling resistance compared to the film used, a method of manufacturing the sliding material can be provided.

The material of the present invention is suitable for sliding parts, cutting tools, and the like, such as piston parts, engine parts such as cam followers, and compressor parts such as shoe discs.

Claims (6)

A sliding material formed by coating a chromium nitride-based coating containing at least CrN on a substrate, wherein the fracture crystal of the coating has a columnar shape from the surface of the substrate to the surface of the coating. A sliding material characterized by the above-mentioned. The sliding material according to claim 1, wherein the porosity of the chromium nitride coating is 1.5 to 20%. The sliding material according to claim 1 or 2, wherein the coating is preferentially oriented in a (111) plane which is CrN composition and parallel to the sliding plane. 4. The sliding material of claim 3, wherein the microhardness of the film has a value of 600 to 1000 HmV measured from the surface. A sliding material according to claim 3, wherein a foundation layer made of chromium is interposed between the coating and the base material. The sliding material film of any one of Claims 1-5 is formed by contacting a base material and a gas phase mixture which mixed chromium and nitrogen by the PVD method. Method of preparation.