JP2711962B2 - Piston ring and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston ring having a molybdenum-nitrogen coating excellent in abrasion resistance and seizure resistance and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a coating having excellent sliding characteristics is formed on a sliding portion of a piston ring by surface treatment. Conventional surface treatment methods include nitriding, chrome plating,
There is a method such as molybdenum spraying. However, in recent years, as the use conditions of piston rings have become faster and higher in load, there have been cases where conventional surface treatments cannot be used.
Further, a film having excellent wear resistance and seizure resistance has been desired.

In order to meet such a demand, P
VD (Physical Vapor Deposit)
It has been proposed to coat a sliding surface of a sliding material such as a piston ring with a film such as a metal nitride or a metal carbide by an ion) method. PVD coatings such as TiN, TiC, and CrN exhibit excellent wear resistance and seizure resistance. In particular, titanium nitride, chromium nitride, and the like have attracted attention as coatings that can be put to practical use, and are used for machine parts and engine parts. However, the use conditions of piston rings have become more severe at present, 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.

[0004] Accordingly, an object of the present invention is to provide a piston ring coated with a molybdenum-nitrogen based coating having excellent wear resistance and seizure resistance, and a method for producing the same.

[0005]

Means for Solving the Problems As a result of intensive studies in view of the above-mentioned object, the present inventor has found that a gaseous mixture of molybdenum vapor and nitrogen is brought into contact with a substrate by a cathodic arc plasma type ion plating, and A piston excellent in wear resistance and seizure resistance by forming a film containing at least molybdenum nitride on the surface and setting the atomic ratio of molybdenum / nitrogen in the film to 1 / 0.05 to 1/1. They discovered that a ring could be obtained and arrived at the present invention.

That is, in the piston ring of the present invention, a film containing at least molybdenum nitride is formed on a substrate by a cathodic arc plasma ion plating method, and the molybdenum / nitrogen atomic ratio in the film is 1%. /
0.05 to 1/1.

Further, the method of the present invention for producing a piston ring having a coating containing at least molybdenum nitride includes contacting a base material with a gas phase in which molybdenum vapor and nitrogen are mixed by a cathodic arc plasma ion plating method. Features.

[0008] The present invention will be described in detail below. Regarding the coating composition of the piston ring of the present invention, the atomic ratio of molybdenum / nitrogen is set to 1 / 0.05 to 1/1. If the atomic ratio of nitrogen to molybdenum is less than 0.05, the formation of molybdenum nitride is reduced, so that the hardness of the film is reduced and the wear resistance is also reduced. The preferred atomic ratio of molybdenum / nitrogen is from 1 / 0.1 to 1/1.

Within the above range of the molybdenum / nitrogen atomic ratio, the film consists of (a) only molybdenum nitride;
(B) It may be composed of a mixed phase of molybdenum nitride and molybdenum metal. Since the film is formed by the cathodic arc plasma ion plating method, the ratio between molybdenum nitride and molybdenum metal can be set arbitrarily.

The thickness of the coating is preferably 1 to 50 μm. When the thickness of the film is less than 1 μm, the life of the film is short due to abrasion. On the other hand, when the thickness of the film exceeds 50 μm, the film is chipped or the film is cracked, so that the adhesion to the substrate is reduced. It is not economically preferable to make the film thicker than necessary.

The substrate on which the film is formed is preferably made of an iron-based material. Cathodic arc plasma ion plating, which is one type of PVD, is based on CVD (Chemica).
Although it is similar to low-temperature treatment as compared with the 1Vapor Deposition method or the like, since heat input due to the vapor deposition phenomenon cannot be avoided, it is preferable to use a heat-resistant iron-based material as the piston ring base material.

In the present invention, a molybdenum / nitrogen hard coating is formed by a cathodic arc plasma ion plating method. In the cathodic arc plasma ion plating method, molybdenum vapor is obtained by projecting molybdenum particles from a cathode made of molybdenum. And nitrogen ions to form molybdenum nitride. As a result, a film of molybdenum nitride is formed on the substrate surface.

More specifically, first, the base material is washed to remove dirt attached to the surface, sufficiently cleaned, and placed in a vacuum chamber of an ion plating apparatus. After evacuation is performed until the pressure in the chamber becomes 1.3 × 10 ^{−3 to} 5 × 10 ⁻³ Pa, the internal pressure gas of the base material is released by heating with a heater built in the ion plating apparatus. Let it. The heating temperature is preferably from 300 to 500C. Then, it cools to 100-400 degreeC.

When the pressure in the chamber becomes 4 × 10 ⁻³ Pa or less, molybdenum as a target is used as a cathode, an arc discharge is generated on the surface, and molybdenum ions are ejected. At this time, a bias voltage is applied to the base material, and a metal ion protruding from the cathode is caused to collide with the base material surface with high energy, that is, oxide removal and activation treatment of the base material surface are performed by a so-called bombard cleaning method. . The bias voltage at that time is -700 V to -90
Preferably, it is 0V.

After that, while lowering the bias voltage and depositing molybdenum ions on the surface of the base material, nitrogen gas is introduced into the chamber and is passed through the plasma. Thereby, nitrogen is ionized and the nitrogen partial pressure is set to 1.3 × 10 ⁻¹ to
At about 1.6 Pa, a bias voltage of -10 V to -100 V is applied to form an ion plating film on the surface of the base material. If the arc discharge is not stable due to a low nitrogen partial pressure, an appropriate amount of argon gas is adjusted, and nitrogen gas is further introduced. After film formation, 2 in vacuum chamber
After cooling to below 00 ° C., the piston ring is removed from the chamber.

The piston ring obtained by the cathodic arc plasma ion plating method has a high surface hardness, a good adhesion between the film and the substrate, and an excellent abrasion resistance. It also has good corrosion resistance and excellent corrosion and wear resistance.

In the present invention, a metal underlayer may be interposed between the substrate and the film. If ion plating is performed before the introduction of nitrogen gas when forming the film, a molybdenum metal base layer is formed on the substrate. The molybdenum metal base layer has a coefficient of thermal expansion close to that of the base material and is not easily affected by thermal stress. Therefore, the adhesion of the film to the base material is improved, and a film having high flexibility is obtained. The underlayer of molybdenum metal is preferably formed to a thickness of 0.1 to 2 μm.
If the thickness is less than 0.1 μm, the effect is weak, and if it exceeds 2 μm, no further effect can be expected, which is uneconomical.

Alternatively, the ion plating may be started by reducing the amount of nitrogen gas introduced, and thereafter, the amount of nitrogen gas introduced may be gradually increased. When ion plating is continued by gradually introducing nitrogen gas without forming the underlayer or when the thickness of the underlayer reaches a predetermined value, the evaporated molybdenum is converted into molybdenum nitride. The conversion is low when the nitrogen gas partial pressure is low, and the conversion increases as the nitrogen gas partial pressure gradually increases. Thus, on the surface of the base material, with or without a molybdenum metal base layer,
When a hard film is formed such that the ratio of nitrogen / molybdenum increases toward the film surface, the film is more effective in preventing peeling of the film.

[0019]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Examples 1 to 3 A substrate made of SKD61 was washed with Freon and placed in a vacuum chamber of a cathode arc plasma type ion plating apparatus. After evacuation is performed until the pressure in the chamber becomes 1.3 × 10 ⁻³ Pa or less, 300 to 50 is applied by a heater built in the ion plating apparatus.
Heat to 0 ° C. to release the gas inside the substrate, and then
Cooled to 00 ° C.

When the pressure in the chamber became 4 × 10 ⁻³ Pa or less, a bias voltage of −700 V to −900 V was applied to generate an arc discharge to eject molybdenum ions. Thereafter, the partial pressure of nitrogen introduced into the chamber was changed in the range of 0.27 to 1.60 Pa, and -10
By applying a bias voltage of V to -100 V, a film having a thickness of 5 m was formed on the substrate surface. After the film was formed, it was cooled in a vacuum chamber to 200 ° C. or lower to obtain a piston ring.

As a result of analyzing the composition of the film by X-ray diffraction, it was confirmed that molybdenum nitride was present in the film. When the nitrogen gas partial pressure was low, it was also confirmed that unreacted molybdenum was present in the film.

The atomic ratio of the constituent elements of the film was analyzed by XPS (X-ray photoelectron spectroscopy). Molybdenum 3
Each spectrum of D3 electron, 3D5 electron and nitrogen 1S electron was used. Table 1 shows the measurement results of the atomic ratios of the constituent elements of the film.

The microhardness of the film obtained in each example was measured using a micro Vickers hardness tester under the conditions of a load of 25 g and a holding time of 15 seconds. Table 1 shows the measurement results.

[0025]

[0026] As is clear from Table 1, the hard film according to the present invention, since the microhardness is very hard sufficiently higher than 1200H _Mv, has excellent wear resistance.

Examples 4 and 5 and Comparative Examples 1 and 2 Using the test apparatus shown in FIGS. 1 and 2, the test pieces were tested for seizure resistance. A disk 2 (diameter: 80 mm, thickness: 10 mm) having a honed sliding surface as a mating member is detachably attached to a stator holder 1 of the test apparatus. The lubricating oil is supplied through the through hole. Here, a hydraulic device (not shown) attaches the stator holder 1 to FIG.
In the above, a predetermined pressing force (P) is applied to the right direction. The test piece holder 5 mounted on the rotor 4 facing the disk 2 is provided with three holes at equal intervals on a circumference concentric with the rotation axis.

A test piece 10 having a length of 5 mm, a width of 5 mm and a height of 5 mm was attached to each hole. The 5 mm square tip surface of each test piece 10 was 5 μm thick in the same manner as in Examples 1 to 3.
Was formed. The atomic ratio of molybdenum / nitrogen in each coating was 1: 0.42 in Example 4 and 1: 0.85 in Example 5. With the tip end surface of the test piece 10 having the film formed thereon being in contact with the disk 2, the rotor 4 is driven by a driving device (not shown) while supplying lubricating oil at a constant temperature to the sliding surface from the lubrication port 3 on the stator side. ) At a predetermined speed. As a result, a torque T (T in FIG. 2) is generated in the stator holder 1 due to friction between the test piece 10 and the disk 2, and the torque T is detected by the load cell 7 through the stainless steel fiber 6 and pushed. The change in the torque T due to the change in the pressure P was read by the dynamic strain meter 8 and recorded by the recorder 9. When the seizure occurs, the torque T sharply increases. Therefore, the pressing force P at that time is defined as the seizure occurrence value. The test conditions are shown in Table 2 and the measurement results are shown in Table 3. The seizure occurrence value corresponds to the seizure resistance of each test piece.

[0029]

As a comparative example, a 100 mm thick chromium plating film was formed on a 5 mm square tip surface of a test piece 10 (Comparative Example 1), and a 5 μm thick titanium nitride film was formed by an ion plating method. (Comparative Example 2)
It was used. A seizure resistance test was conducted in the same manner as described above. The results are shown in Table 3.

[0031]

As is evident from Table 3, the test piece of the present invention was compared with the chromium-plated test piece (Comparative Example 1) and the titanium nitride film-formed (Comparative Example 2). The seizure occurrence value is high and the seizure resistance is excellent for both iron-based materials and aluminum-based materials.

Example 6, Comparative Example 3, 4 A base made of SKD61 having a length of 5 mm × width 5 mm × length 20 mm and one end in the longitudinal direction having a curved surface of R6 mm was used. A hard coating having a thickness of 10 μm was formed on the curved surface portion in the same manner as in Examples 1 to 3 to obtain a test piece (Example 6). The molybdenum / nitrogen atomic ratio in the hard coating was 1: 0.85.

As a comparative example, a chrome plating having a thickness of 100 μm was applied to the tip R portion of the base material (Comparative Example 3), and a 10 μm thick film was formed by an ion plating method.
(Comparative Example 4) on which a chromium nitride film was formed was used as a test piece.

Using a Kaken-type abrasion tester, the tip R of each test piece having the film formed thereon is aligned with the outer peripheral part of a counterpart material processed into a drum shape so that the curved surfaces are in line contact with each other, and a predetermined load is applied. By rotating at a predetermined speed, a corrosion wear test of each piston ring was performed under the test conditions shown in Table 4 below. The lubrication was performed by dropping a fixed amount of a sulfuric acid aqueous solution whose pH was adjusted to 2.0 to the contact portion to form an acid atmosphere.

[0036]

Table 5 shows the measurement results of the film wear amount. The measurement results are shown as relative values when the amount of abrasion of the coating of Comparative Example 3 is 100.

As is evident from Table 5, the piston ring according to the present invention is more resistant to corrosion than the piston ring coated with chromium (Comparative Example 3) and the one formed with a chromium nitride film (Comparative Example 4). Excellent wear properties.

[0039]

As described in detail above, the piston ring of the present invention is formed by forming a film of molybdenum nitride or a film of molybdenum nitride and molybdenum on the surface of a base material by a cathodic arc plasma ion plating method. Has superior wear resistance and seizure resistance as compared to piston rings used conventionally.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an ultra-high pressure wear tester.

FIG. 2 is a sectional view taken along line AA of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Stator holder 2 ... Disk (partner material) 3 ... Lubrication port 4 ... Rotor 5 ... Test piece holder 6 ... Stainless steel fiber 7 ... Load cell 8 ... Moving Strain gauge 9 ・ ・ ・ Recorder 10 ・ ・ ・ Test piece

Claims (4)

(57) [Claims] 1. A piston ring formed by forming a film containing at least molybdenum nitride on a substrate by a cathodic arc plasma ion plating method, wherein the atomic ratio of molybdenum / nitrogen in the film is 1/0. .05 / 1 /
A piston ring, which is 1. 2. The piston ring according to claim 1, wherein the coating is made of molybdenum nitride or molybdenum nitride and molybdenum, and the ratio of nitrogen to molybdenum increases from the substrate surface side toward the coating surface. A piston ring. 3. The piston ring according to claim 1, wherein an underlayer made of molybdenum is interposed between said coating and said base material. 4. A method of manufacturing a piston ring having a coating containing at least molybdenum nitride, comprising contacting a base material with a gas phase in which molybdenum vapor and nitrogen are mixed by a cathodic arc plasma ion plating method. Of manufacturing piston rings.