JPH06322515A - Wear resistant coating film - Google Patents

Abstract

PURPOSE:To form a coating film excellent in wear resistance, initial fitness and workability on the surface of the sliding substrate of each of sliding parts by continuously increasing the concn. of Cr in a coating film of chromium nitride formed on the surface of the substrate from the surface of the substrate toward the surface of the coating film in a direction perpendicular to the surface of the substrate. CONSTITUTION:When a coating film consisting of chromium and nitrogen is formed on the surface of the sliding substrate of each of sliding parts, the structure of the coating film brought into contact with the surface of the substrate is made of chromium nitride and the concn. of chromium in the coating film is continuously increased from the surface of the substrate toward the surface of the coating film in a direction perpendicular to the surface of the substrate. The objective coating film hardly wearing its opposite material and excellent in wear resistance is obtd. The interior of this coating film is made of hard nitride.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating formed on the surface of a sliding base material of a sliding part such as a piston ring, which has excellent wear resistance, initial conformability and workability.

[0002]

2. Description of the Related Art A hard chrome plating treatment is a typical example of a surface coating treatment which is performed to obtain the abrasion resistance required of a sliding member such as a piston ring for an internal combustion engine. However, as the output of internal combustion engines has become higher, performance has improved, and exhaust gas regulation measures have advanced, the requirements for piston rings have become more and more severe, and the conventional chromium plating has heat, wear, and seizure resistance. It is becoming difficult to obtain satisfactory performance in.

In order to improve these, composite plating, thermal spraying,
Surface treatments such as nitriding have been proposed, ion plating films have recently been announced, and they are beginning to be used on outer peripheral sliding surfaces such as piston rings. In particular, a piston ring formed by reacting with nitrogen while evaporating Cr and forming chromium nitride as a film has been used as an industrially very advantageous technique in terms of cost, wear resistance, and seizure resistance.
However, since these coatings are ceramic coatings and have a large hardness difference from the mating cylinder material, there is a phenomenon in which blow-by becomes large by damaging the cylinder in the familiar running operation at the initial stage of operation. Although self-abrasion has been reduced by the surface treatment as described above, it may be said that a ring having a satisfactory function has not yet been provided because the mating material may be abraded. Tin plating, composite dispersion plating, etc. on ceramic coatings such as Cr-N and Ti-N
A soft-meal film coated on the outermost layer is also used, but there are problems in terms of cost and adhesion.

[0004]

The above-mentioned problems of the conventional coating applied to the surface of the sliding base material are solved, and the severe load of the internal combustion engine in which the heat load is increased due to high output, measures against exhaust gas, etc. To provide a coating formed on the surface of a sliding base material that is used as a sliding surface of a sliding component such as a piston ring used under various conditions and has sufficient wear resistance and initial conformability. The present invention is aimed at.

[0005]

In order to achieve the above object, the present invention provides a coating formed on a surface of a sliding base material such as a piston ring, the coating being made of chromium and nitrogen. By continuously increasing the chromium concentration in the direction perpendicular to the base material surface, from the base material surface or in the middle of the coating, to the surface of the coating, the initial conformability and workability are excellent and wear resistance is improved. Providing a coating provided.

The coating according to the present invention has a soft chrome nitride or chrome on the outer periphery and is excellent in initial conformability, and in addition, in the direction of the base material after conforming, there is a high hardness chromium nitride exhibiting abrasion resistance. Therefore, when used for a piston ring or the like, the performance of ceramic chromium nitride can be exhibited without damaging the mating material. Further, in the case of metal-ceramic bonding between the metal of the base material and the coating, there may be a problem in adhesion. In that case, wear-resistant nitrogen chromium is not formed from the base metal boundary, but from the base metal surface, in the direction perpendicular to the base metal surface, starts to be formed from metal chromium having a nitrogen content of zero, and then continuously forms nitrogen. The concentration is increased to form the desired wear resistant chromium nitride, followed by the coating of the present invention. Since this chrome film has a coefficient of thermal expansion close to that of the base material, it is not easily affected by thermal stress and adheres well to the base material, and is also highly flexible, which is very advantageous for the sliding surface of harsh sliding parts. It is a film.

The present invention will be specifically described below with reference to examples. The outline of the ion plating device used is shown in FIG. The base material 1 held by the base material holder 2 is heated by the heater 3, and the base material 1 is heated and held at a predetermined temperature by a temperature controller (not shown). Below the base material 1, a water-cooled steel crucible 6 containing a metal 5 as an evaporation source is installed.
These are housed in a container 9. An inlet pipe 11 for introducing nitrogen gas into the container 9 and an electron gun 8 for evaporating the metal 5 are attached to the side wall of the container 9. A focusing coil 7 is installed around the crucible 6 so that the evaporated metal 5 is irradiated with the electrons emitted from the electron gun 8. The inside of the container 9 is decompressed by a vacuum pump (not shown). A shutter 10 is provided between the crucible 6 and the holder 2. Using such a device, SUS
440C stainless steel 50 × 50 × 10 mm plate material is used, the inside of the container 9 is evacuated, and then argon gas is introduced from the introduction pipe 11 to adjust the pressure inside the container 9 to 1 × 10 ^−1.
_{Torr was used} , and the base material 1 was discharged using the cathode as a cathode to clean the surface of the base material 1. Next, while heating the base material to 400 ° C., the inside of the container 9 was depressurized to 5 × 10 ⁻⁵ _Torr , and then the metal chromium 5 housed in the crucible 6 was irradiated with an electron beam from the electron gun 8 to make the metal chromium 5 Was evaporated. Then, nitrogen gas is blown out from the introduction pipe 11 to adjust the nitrogen partial pressure in the container 9 to 2 × 10 ^−3.
_After setting to _Torr , the shutter 10 was opened and vapor deposition was started. The state was maintained for 2 minutes, Yuki reduce the 3 × 10 ^-4 _{the To} continuously nitrogen gas to _rr nitrogen partial pressure is zero over 20 minutes followed, the shutter 2 minute hold at its partial pressure 10 Closed. Then, after the base material 1 was cooled, the base material 1 having the vapor-deposited coating formed on its surface was taken out from the easy base 9. The following tests were performed on the vapor-deposited coating film thus formed.

(1) Analysis of Changes in Nitrogen Concentration and Chromium Concentration by X-ray Microanalyzer To examine the change in average concentration of chromium and nitrogen in the coating, a sample was cut in the direction perpendicular to the surface, and the inside was cut from the surface by an X-ray microanalyzer. The line analysis was performed toward. (Fig. 2
And Fig. 3) From the figure, the chromium concentration in the coating is low in the innermost layer in contact with the base material and increases as it approaches the surface, and the nitrogen concentration in the coating is highest in the innermost layer in contact with the base material and You can see that it gets lower as you get closer.

(2) Analysis of the outermost surface structure by X-ray diffraction The result of the analysis of the outermost surface structure of the vapor-deposited coating by X-ray diffraction and the ASTM card reveals that Cr + Cr ₂ N.

(3) Analysis of cross-sectional structure by X-ray diffraction As described above, the chemical composition of the coating film according to the present invention continuously changes from the inside to the surface, and the types of phases constituting the coating film are naturally from the inside. It is envisioned that they vary across the surface, but they cannot be directly investigated by X-ray diffraction. Therefore, in order to investigate the phases that compose the coating, 0.3-
The film formed with a constant nitrogen partial pressure within the range of 2.0 × 10 ⁻³ _Torr was analyzed for the texture by X-ray diffraction.
(The conditions other than the nitrogen partial pressure are the same as those in the above test.) The analysis results are shown in Table 1.

[0011]

[Table 1]

The coating film according to the present invention is formed by decreasing the nitrogen partial pressure to 2 × 10 ^-3 _{Torr first} and then continuously, but on the vapor-deposited layer consisting only of chromium nitride, A vapor-deposited layer consisting of chromium nitride and chromium is formed, and a layer consisting of only chromium is further formed on it, and the chromium concentration continuously increases from the inside to the surface. , Which is in good agreement with the above-mentioned line analysis by an X-ray microanalyzer.

(4) Cross-sectional hardness analysis in coating film Table 2 shows the cross-sectional hardness distribution of the coating film of the present invention. Table 2 shows the cross-sectional hardness of the A to E coatings of the above-mentioned samples. From these, it can be seen that the hardness gradually decreases from the vicinity of the base material toward the surface layer, and since it is almost the same as the hardness of each structural component of Samples A to E in Table 1, the base material hardness is From the inside to the surface, it becomes lower continuously, and it can be seen that the coating itself gradually becomes soft.

[0014]

[Table 2]

(5) Abrasion test With respect to abrasion resistance, the sample subjected to the X-ray diffraction analysis by a Kaken type abrasion tester was used as a pin, and the mating drum was FC.
-25 material is used, load 2kg, friction speed 0.2m / sec,
As a lubricating liquid, a sulfuric acid aqueous solution having a pH of -2.5 was used. For comparison, a similar test was conducted on pins plated with hard chrome. The test results are shown in FIG. 4, which shows that the coating of the present invention has superior wear resistance to the hard chromium plating layer at any depth position from the surface in the coating. See. Further, it can be seen that when the nitrogen partial pressure is low as in sample E, self-abrasion is higher than in A and C, but the amount of wear of the mating cylinder is reduced. Further, although A and C have less self-abrasion, the counterpart material is abraded as compared with E. This means that when the present invention is used with a piston ring or other sliding member, it does not damage the mating material during the initial operation and is allowed to adapt to it, and then wears with a film of A or C with less self-wear. It can be said to be a film that can secure the property. However, this is because the structural component does not change continuously, and an extreme change, for example, when a film of E is suddenly formed, the hardness of the film suddenly changes and wear of the mating material increases.

[0016]

According to the present invention, the coating film made of chromium and nitrogen formed on the surface of the sliding base material of the sliding component has the chromium concentration continuously increasing in the vertical direction from the surface of the base material, and the coating surface has chromium. Therefore, the mating material is less likely to be worn, and the inside of the coating is a hard nitride, so that the coating itself has excellent wear resistance. Therefore, when it is used for sliding parts that are required to have high performance, such as piston rings, the film has excellent wear resistance and initial conformability.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an ion plating apparatus used in the present invention.

2 is a cross-sectional view of a coating obtained according to the present invention used for line analysis.

3 shows a line analysis result of the coating according to FIG.

FIG. 4 is a diagram showing the results of wear tests of coatings obtained by ion plating under various nitrogen partial pressures.

[Explanation of symbols]

 1 sliding base material 2 base material holder 3 heater 5 evaporation source metal 6 water cooling crucible 7 focusing coil 8 electron gun and Ar inlet 9 vacuum container 10 shutter 11 nitrogen gas inlet

Claims (3)

[Claims] 1. A coating made of chromium and nitrogen formed on the surface of a sliding base material of a sliding part, wherein the coating structure in contact with the surface of the base material is chromium nitride, and the chromium concentration in the coating is A wear-resistant coating film characterized in that it continuously increases from the surface of the base material to the surface of the coating film in a direction perpendicular to the surface of the base material. 2. A coating made of chromium and nitrogen formed on the surface of a sliding base material of a sliding part, wherein the coating structure in contact with the surface of the base material is chromium nitride, and the chromium concentration in the coating is A wear-resistant coating characterized in that it is constant in the direction perpendicular to the base material surface up to the middle of the coating and then increases continuously to the surface of the coating. 3. The wear resistant coating according to claim 1, wherein the sliding component is a piston ring.