JP2968907B2 - Wear resistant coating - Google Patents

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 is excellent in wear resistance, initial conformability and workability.

[0002]

2. Description of the Related Art Hard chromium plating is a typical surface coating treatment performed to obtain the required wear resistance of a sliding member such as a piston ring for an internal combustion engine. However, as the output and performance of internal combustion engines increase and exhaust gas regulations are advanced, the conditions required for piston rings become more and more severe, and conventional chrome plating requires heat resistance, wear resistance, and seizure resistance. It is becoming difficult to obtain satisfactory performance.

In order to improve these, composite plating, thermal spraying,
A surface treatment such as nitriding has been proposed, and an ion plating film has recently been announced, and has begun to be used for outer peripheral sliding surfaces such as piston rings. In particular, a piston ring in which chromium nitride is formed as a film by reacting with nitrogen while evaporating Cr has been used as an industrially very advantageous technique in terms of cost, wear resistance, and seizure resistance.
However, since these films are ceramic films and have a large difference in hardness from the mating cylinder material, a phenomenon in which blow-by becomes large due to damage to the cylinder in the running-in operation at the beginning of operation appears. As described above, although the self-wear is reduced by the surface treatment, the mating material may be worn, and it can be said that a ring having a satisfactory function has not yet been provided. Such as tin plating and composite dispersion plating on ceramic films such as Cr-N and Ti-N
An outermost layer coated with a soft film is also used, but has problems in cost, adhesion, and the like.

[0004]

SUMMARY OF THE INVENTION The problem of the conventional coating applied to the surface of the sliding base material is solved and the severe load of the internal combustion engine is increased due to high output and measures against exhaust gas. Provide a coating formed on the surface of a sliding base material to be used as a sliding surface of a sliding component such as a piston ring used under various conditions, and to have sufficient wear resistance and initial conformability. It is an object of the present invention.

[0005]

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

The coating according to the present invention is made of chromium nitride or chromium having a soft outer periphery, and has excellent initial conformability. In addition, high hardness chromium nitride showing wear resistance exists in the direction of the base material after conformation. Therefore, when used for a piston ring or the like, the performance of ceramic chromium nitride can be exhibited without damaging the mating material. In addition, when metal-to-ceramic bonding is performed between the metal of the base material and the coating, a problem may occur in adhesion. In this case, instead of forming wear-resistant nitrogen chromium from the base material boundary, the wear-resistant nitrogen chromium starts to be formed from metal chromium having a zero nitrogen amount in a direction perpendicular to the base material surface, 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. This chromium film has a coefficient of thermal expansion close to that of the base material, so it is hardly affected by thermal stress and adheres closely to the base material, and because it is rich in flexibility, it is very advantageous for the sliding surface of severe sliding parts. It is a coating.

Hereinafter, the present invention will be described specifically with reference to examples. FIG. 1 shows an outline of the ion plating apparatus used. 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 accommodated in the container 9. An introduction 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 provided around the crucible 6 so as to irradiate the evaporating metal 5 with electrons emitted from the electron gun 8. The pressure inside the container 9 is reduced by a vacuum pump (not shown). A shutter 10 is provided between the crucible 6 and the holder 2. SUS using such a device
Using a 440C stainless steel plate material of 50 × 50 × 10 mm, the inside of the container 9 was evacuated, and argon gas was introduced from the inlet tube 11 to reduce the pressure in the container 9 to 1 × 10 ^−1.
_{At Torr} , the surface of the base material 1 was cleaned by discharging using the base material 1 as a cathode. Next, the inside of the container 9 is depressurized to 5 × 10 ⁻⁵ _Torr while heating the base material to 400 ° C., and then the electron beam is irradiated from the electron gun 8 onto the metal chromium 5 accommodated in the crucible 6 so that the metal chromium 5 Was evaporated. Next, nitrogen gas is blown out from the introduction pipe 11 to reduce the nitrogen partial pressure in the container 9 to 2 × 10 ^−3.
_Torr was set, the shutter 10 was opened, and vapor deposition was started. The state is maintained for 2 minutes, and then the nitrogen gas is continuously reduced to 3 × 10 ^-4 _{To rr} over 20 minutes until the nitrogen partial pressure becomes zero. Closed. Thereafter, after the base material 1 was cooled, the base material 1 on which the vapor-deposited film was formed on the surface was easily taken out from the base material 9. The following test was performed on the deposited film thus formed.

(1) Analysis of changes in nitrogen concentration and chromium concentration using an X-ray microanalyzer To examine changes in the average concentration of chromium and nitrogen in a coating film, a sample is cut in a direction perpendicular to the surface, and an X-ray microanalyzer is used. Line analysis was performed toward. (Figure 2
And FIG. 3) From the same figure, the chromium concentration in the coating is lower in the innermost layer in contact with the base material, and increases as approaching the surface. The nitrogen concentration in the coating is highest in the innermost layer in contact with the base material, and It can be seen that it gets lower as you get closer.

(2) Analysis of the outermost surface structure by X-ray diffraction As a result of analyzing the outermost surface structure of the deposited film by X-ray diffraction, it is found that it is Cr + Cr ₂ N by an ASTM card.

(3) Analysis of cross-sectional structure by X-ray diffraction As described above, the chemical composition of the coating according to the present invention is continuously changed from the inside to the surface. It is conceivable that it has changed over the surface, but these cannot be directly investigated by X-ray diffraction. Therefore, in order to examine the phases that constitute the coating,
The structure of the coating formed at a constant nitrogen partial pressure in the range of 2.0 × 10 ⁻³ _Torr was analyzed by X-ray diffraction.
(The conditions other than the partial pressure of nitrogen are the same as those in the above test.) The analysis results are shown in Table 1.

[0011]

[Table 1]

The coating according to the present invention is formed by reducing the partial pressure of nitrogen to 2 × 10 ⁻³ _{Torr at first} and then continuously decreasing it. As shown in the table, a vapor deposition layer consisting of chromium nitride and chromium was formed, and a layer consisting of only chromium was formed thereon, and the chromium concentration continuously increased from the inside to the surface. This is in good agreement with the line analysis by an X-ray microanalyzer.

(4) Analysis of Cross-sectional Hardness in Coating Table 2 shows the cross-sectional hardness distribution of the coating of the present invention. Table 2 shows the cross-sectional hardnesses of the AE coatings of the above 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 the hardness of each of the tissue components of Samples A to E in Table 1 substantially matches, the base material hardness is It can be seen that the coating becomes lower continuously from the inside to the surface, and the coating itself gradually becomes softer.

[0014]

[Table 2]

(5) Wear test Regarding the wear resistance, the sample subjected to the X-ray diffraction analysis by a Kaken abrasion tester was used as a pin,
Using -25 material, load 2kg, friction speed 0.2m / sec,
The test was performed using a sulfuric acid aqueous solution having a pH of 2.5 as a lubricating liquid. For comparison, a similar test was performed on a pin subjected to hard chrome plating. The test results are as shown in FIG. 4. From the figure, it is understood that the coating of the present invention has better wear resistance than the hard chromium plating layer at any depth from the surface in the coating. Like. Also, when the nitrogen partial pressure is reduced as in the sample E, the self-wear is larger than that of the samples A and C, but the wear amount of the mating cylinder is reduced. A and C have less self-wear, but wear the mating material more than E. In other words, when the present invention is used with a piston ring or other sliding member, the mating material is not damaged in the initial operation, and is allowed to adapt, and thereafter, wear resistance is reduced by the film of A or C which has less self-wear. It can be said that this is a film that can ensure the properties. However, in this case, when the composition of the tissue does not change continuously, but an extreme change occurs, for example, when the film of E is suddenly formed from the film of A, the change in hardness becomes rather large and the wear of the mating material increases.

[0016]

According to the present invention, the coating made of chromium and nitrogen formed on the surface of the sliding base material of the sliding component according to the present invention has a chromium concentration which continuously increases in the vertical direction from the surface of the base material, and the surface of the coating is made of chromium. Therefore, the coating material itself is excellent in wear resistance because the mating material is hardly worn and the inside of the coating is hard nitride. Therefore, when used for a sliding part requiring high performance, for example, a piston ring, a film having excellent wear resistance and initial conformability can be obtained.

[Brief description of the drawings]

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

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

3 shows the results of a line analysis of the coating according to FIG. 2;

FIG. 4 is a view showing a wear test result of a coating film obtained by ion plating at various nitrogen partial pressures.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sliding base material 2 Base material holder 3 Heater 5 Evaporation source metal 6 Water-cooled crucible 7 Focusing coil 8 Electron gun and Ar inlet 9 Vacuum container 10 Shutter 11 Nitrogen gas inlet

Claims (3)

(57) [Claims] 1. A coating comprising chromium and nitrogen formed on a sliding base material surface of a sliding component, wherein a coating structure in contact with the base material surface is chromium nitride, and a chromium concentration in the coating is: A wear-resistant coating characterized by a continuous increase from the base material surface to the coating surface in a direction perpendicular to the base material surface. 2. A coating made of chromium and nitrogen formed on a sliding base material surface of a sliding component, wherein a coating structure in contact with the base material surface is chromium nitride, and a chromium concentration in the coating is: A wear-resistant coating characterized by being constant in a direction perpendicular to the surface of the base material up to the middle of the coating and then continuously increasing to the coating surface. 3. The wear-resistant coating according to claim 1, wherein the sliding component is a piston ring.