JPH10130891A - Composite cr plating film, and sliding member having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite Cr plating film in which hard grains are contained in the network cracks formed in a hard Cr plating film and which is excellent in wear resistance and seizure resistance and reduced in attacks on a mating material at sliding. SOLUTION: A nitrided layer 2 is formed in the whole surface of a piston ring 1, and a composite Cr plating film 3 is formed on the nitrided layer 2, on the outside peripheral side. The composite Cr plating film 3 has network cracks 4 in its surface and inner part, and Si3 N4 grains 5 are contained and fixed in the cracks 4. The average grain size of the Si3 N4 grains 5 is 0.8-3μm, and the compounding ratio of the Si3 N4 grains is 3-15% by volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite Cr plating film in which hard particles are contained in network-like cracks formed in a hard Cr plating film, and a piston ring or a compression ring for an internal combustion engine coated with this film. The present invention relates to a sliding member such as a machine vane.

[0002]

2. Description of the Related Art There is an attempt to improve the wear resistance of a Cr plating film by dispersing hard particles in the hard Cr plating film. The following methods have been proposed for dispersing hard particles in a hard Cr plating film. A relatively low current density for eutectoid fixation of hard particles;
A pulse electrolysis method (Japanese Patent Publication No. 59-028) in which electrolysis is repeatedly performed using a current density at which r plating is electrodeposited at a normal speed.
No. 640). A method of adding a rare earth element or a compound thereof to a Cr plating bath (see JP-A-61-003895). A method of adding hard particles and self-lubricating particles to a trivalent Cr plating bath (see JP-A-62-120498).

However, none of these methods has been put to practical use, and even in our additional tests, reproducibility is poor,
There are problems such as an extremely low composite ratio or an extremely low plating rate.

The above-described composite Cr plating is intended to uniformly disperse the hard particles in the hard Cr plating film, but enlarges and forms a network-like crack formed in the hard Cr plating film. Some of them contain hard particles (see JP-A-62-56600). The composite Cr plating by this method can satisfy reproducibility, controllability of composite ratio, plating speed, and the like.

[0005] The matters disclosed in the above-mentioned publications are: ・ Thickness of the composite Cr plating film: 10 to 1000 μm ・ Width of mesh cracks: 0.5 μm or more, especially 1 μm or more ・ Particle size of hard particles: 0.5 to 15 μm In the example, 0.5 to 5 μm. Hard particles: WC, Al ₂ O ₃ , SiC, Si ₃ N ₄ , BC, diamond.

The above-mentioned composite Cr plating film has been put to practical use in Europe for some piston rings for low-load diesel engines. The specifications of the composite Cr plating film are as follows.・ Film thickness: 100-200 μm ・ Film hardness: HV850-HV1000 ・ Hard particles: Al ₂ O ₃ pulverized powder ・ Average particle size of hard particles: 4.5 μm ・ Composite ratio of hard particles: 5% by volume ratio

[0007]

However, this composite C
The piston ring coated with the r-plated film has the characteristic of being excellent in its own wear resistance and seizure resistance, but has a large aggressiveness to a mating material and has a disadvantage that the wear amount of the cylinder bore is significantly increased. Therefore, a piston ring having the composite Cr plating film formed thereon cannot be used for a high-load diesel engine or gasoline engine.

[0008] The aggressiveness of the composite Cr plating to the mating material is as follows:
It is thought that the type and content of the hard particles may affect the above, but the above publication does not describe these at all. And this composite Cr plating is a conventional Ni-based or Ni-
Unlike the Co-P-based composite plating, the distribution state of the hard particles and the matrix metal are different, so that it is not possible to reduce the aggressiveness of the opponent using the knowledge of the conventional composite plating.

An object of the present invention is to provide a composite Cr plating film in which hard particles are contained in a network-like crack formed in the hard Cr plating film, which is excellent in wear resistance and seizure resistance, and which is a sliding partner. An object of the present invention is to provide a composite Cr plating film having low aggressiveness to a material. A further object of the present invention is to provide a sliding member such as a piston ring having the above-described composite Cr plating film.

[0010]

According to the present invention, there is provided a composite Cr plating film in which hard particles are contained in a network-like crack formed in the hard Cr plating film, wherein the hard particles are Si ₃ N ₄ particles. The hard particles have an average particle size of 0.8 to 3 μm, and the composite ratio of the hard particles is 3 to 15% by volume.

The composite Cr plating film is coated on a sliding surface of a sliding member such as a piston ring for an internal combustion engine or a vane for a compressor.

The composite Cr plating film of the present invention has a predetermined S
It can be formed by repeatedly performing a composite Cr plating step and an etching step using a Cr plating bath containing i ₃ N ₄ particles dispersed therein.

The density of mesh-like cracks formed in the composite Cr plating step and the etching step can be simply represented by the number of cracks intersecting with a line segment (length 1 mm) parallel to the plating surface. Crackless) ~ 200 / mm
(Micro crack plating). If the crack density is high, the strength of the plating film is reduced. Conversely, if the crack density is low, the composite ratio of the hard particles cannot be increased. A desirable range of the crack density in the present invention is 40 to 90 cracks / mm.

The crack has a substantially V-shaped cross section.
The opening width must be larger than the particle size of the hard particles. If the opening width is small, the composite ratio of the hard particles cannot be increased, and if it is too large, the film strength decreases. Generally, a desirable range of the opening width is a range of 4 to 10 μm.

In the composite Cr plating film, the tip surface of the Si ₃ N ₄ particles forms a primary sliding surface, and the Cr plating surface forms a secondary sliding surface.

It is considered that the aggressiveness of the composite Cr plating film on the sliding partner differs depending on the material of the particles. By comparing Al ₂ O ₃ composite Cr plating and Si ₃ N ₄ composite Cr plating having the same particle diameter, shape, and composite ratio,
It was confirmed that the latter was superior.

When the composite ratio of the Si ₃ N ₄ particles increases, the aggressiveness of the partner decreases. Incidentally, in the case of Al ₂ O ₃ particles, when the composite ratio increases, the opponent aggressiveness increases. In order to improve abrasion resistance and seizure resistance, the composite ratio of the hard particles is preferably higher. A Cr plating film in which Si ₃ N ₄ particles are compounded in a volume ratio of 3% or more is a conventional Al ₂ O ₃
The opponent aggression is extremely low as compared with the Cr plating film in which particles are combined.

In order to increase the composite ratio, cracks must be increased. However, since this has a certain limit, it is not possible to composite in a volume ratio exceeding 15%.

On the other hand, when the particle size of the Si ₃ N ₄ particles is large, the aggressiveness of the partner increases, and when the particle size is small, the wear of the Si ₃ N ₄ particles increases.
The desirable range of the average particle size (powder particle size) of the hard particles is
0.8 to 3 μm.

[0020]

FIG. 1 is a longitudinal sectional view showing a part of a piston ring according to an embodiment of the present invention. A nitride layer 2 is formed on the entire surface of the piston ring 1, and a composite Cr plating film 3 is formed on the nitride layer 2 on the outer peripheral surface. The composite Cr plating film 3 has a network-like crack 4 on its surface and inside when viewed from a direction perpendicular to the plating surface, and the crack 4 contains and fixes Si ₃ N ₄ particles 5. . The average particle size of the Si ₃ N ₄ particles 5 is 0.8
And the composite ratio of the Si ₃ N ₄ particles 5 is ₃ to 15% by volume.

Next, the plating of the composite Cr plating film 3 of the piston ring 1 will be described.

(Composite Cr plating) → (Composite Cr plating step-Repeating of etching step) is performed on the outer peripheral surface of the piston ring.

An example of the plating bath composition of the composite Cr plating and each condition of the composite Cr plating step and the etching step are shown below. The first composite Cr plating is strike plating, usually for 3 to 10 minutes, and the other conditions are the same as those described below.

Plating bath composition CrO ₃ 250 g / l H ₂ SO ₄ 1.0 g / l H ₂ SiF ₆ 5 g / l Hard particles (Si ₃ N ₄ ) 20 g / l The average particle size of the hard particles is 1.2 μm. . According to the plating bath containing fluoride, the adhesion between the Cr plating layers in the cycle of (composite Cr plating step-etching step) is excellent. Composite Cr plating Current density 60A / dm ² Plating bath temperature 55 ° C Plating time 10 minutes Etching Current density 50A / dm ² Plating bath temperature 55 ° C Etching time 1 minute

Under the above conditions, when one cycle of the composite Cr plating step → the etching step is performed, as shown in FIG. 2A, the composite Cr plating layer 3A becomes the nitrided layer on the outer peripheral surface of the piston ring 1. 2 is formed. In the composite Cr plating layer 3A, cracks 4 extending in a mesh shape are formed on the surface, and Si ₃ N ₄ particles 5 are fixed to the cracks 4.

Further, when the composite Cr plating step → etching step is repeatedly performed, as shown in FIG. 2 (b), the composite Cr formed in the first one cycle step is formed.
The composite Cr plating layer 3B is further laminated on the plating layer 3A. Therefore, the Si ₃ N ₄ particles 5 in the cracks 4 of the first composite Cr plating layer 3A are confined and fixed in the layer. And the second layer composite Cr plating layer 3B
Has cracks 4 extending in a mesh on the surface, and Si ₃ N ₄ particles 5 are fixed to the cracks 4.

Thereafter, when the composite Cr plating step → etching step is repeatedly performed a predetermined number of times, a composite Cr plating film 3 having a predetermined thickness is formed on the nitride layer 2 on the outer peripheral surface of the piston ring 1.

When one cycle of the composite Cr plating step → etching step is performed under the above conditions, a plating thickness of about 10 μm can be obtained. For example, in order to obtain a completed thickness of the composite Cr plating film 3 of 100 μm. Is required to have a plating thickness of 120 μm in addition to the polishing allowance.
Repeat cycle.

Next, the results of a wear test performed using a reciprocating friction tester will be described.

FIG. 3 shows an outline of the reciprocating friction tester used for the test. Pin-shaped upper test piece 10 is fixed block 1
1, a downward load is applied from above by a hydraulic cylinder 12 and pressed against a lower test piece 13.
On the other hand, the flat plate-shaped lower test piece 13 is held by a movable block 14 and reciprocated by a crank mechanism 15. Reference numeral 16 denotes a load cell.

The test conditions are as follows. Load: 98N Speed: 600 cpm Stroke: 50 mm Time: 1 hour Lubricating oil: Bearing oil with viscosity equivalent to light oil

(1) Wear Test 1 The effect of the type and content of hard particles on the wear of the mating material was tested using the reciprocating friction tester described above.

Test piece Upper test piece: cast iron material for cylinder liner Lower test piece: Composite Cr plating was applied to the surface of a lower test piece made of steel for a piston ring. According to the above-mentioned vertical relationship of the test pieces, the wear of the upper test piece is promoted, so that it is convenient to evaluate the wear of the mating material due to the composite Cr plating film.

Composite Cr Plating Same as the composite Cr plating process for the piston ring 1 described in the embodiment of the present invention. However, the hard particles in the plating bath are as shown in Table 1.

[0035]

Test Method Using the reciprocating friction tester described above, a wear test was carried out while changing the composite ratio (volume ratio) of the hard particles.

Results FIG. 4 shows the results of the wear amount of the upper test piece (partner material) with respect to the composite ratio of the hard particles. The test was also performed when the lower test piece was coated with a normal hard Cr plating film. The wear ratio in FIG. 4 is the wear amount of the upper test piece when the lower test piece was coated with the hard Cr plating film. Is set to 1. FIG.
As can be seen from the graph, when the content of the composite Cr plating film containing Al ₂ O ₃ particles increases, the wear amount of the upper test piece (partner material) rapidly increases. On the other hand, in the case of the composite Cr plating film containing Si ₃ N ₄ particles, as the content increases, the wear amount of the upper test piece (partner material) decreases. It can be seen that the wear amount is extremely small as compared with the composite Cr plating film containing Al ₂ O ₃ particles.

(2) Wear Test 2 The influence of the particle size of the Si ₃ N ₄ particles on the wear of the mating material was tested using the reciprocating friction tester described above.

Specimen Both the upper and lower specimens are the same as those described in the above (1) Wear test 1.

Composite Cr Plating Same as the composite Cr plating process for the piston ring 1 described in the embodiment of the present invention. However, the hard particles in the plating bath are as shown in Table 2.

[0041]

Test Method A wear test was performed using the above reciprocating friction tester while changing the average particle size of Si ₃ N ₄ particles.

Results Upper test piece (counterpart material) with respect to the average particle size of Si ₃ N ₄ particles
FIG. 5 shows the results of the abrasion loss. The test was also performed when the lower test piece was coated with a normal hard Cr plating film. The wear ratio in FIG. 5 is the wear amount of the upper test piece when the lower test piece was coated with the hard Cr plating film. Is set to 1. As shown in FIG. 5, when the composite Cr plating film containing Si ₃ N ₄ particles has a large average particle size,
The wear amount of the upper test piece (part material) has increased,
It can be seen that in the range of μm, the wear amount of the upper test piece (the counterpart material) is small.

(3) Wear Test 3 The effect of the type and particle size of the hard particles on their own wear was tested using the reciprocating friction tester described above.

Specimen Upper specimen: Composite Cr plating was applied to the surface of an upper specimen made of steel for a piston ring. Lower specimen: Cast iron material for cylinder liner

Composite Cr Plating Same as the composite Cr plating process for the piston ring 1 described in the embodiment of the present invention. However, the hard particles in the plating bath are as shown in Table 3.

[0047]

Test Method A wear test was performed using the reciprocating friction tester described above.

Results FIG. 6 shows the results of the wear amount of the upper test piece. Note that the test was also performed on a case where the upper test piece was coated with a normal hard Cr plating film, and the wear ratio in FIG.
The amount of abrasion of the upper test piece when coating with the r-plated film is set to 1. As shown in FIG. 6, the wear amount of the wear amount i.e. its upper test piece, Si ₃ N ₄ Al ₂ particle composite Cr plating film containing an average particle size 0.8μm or more
The wear amount is almost the same as that of the composite Cr plating film containing O ₃ particles, and it can be seen that the wear resistance is much better than that of the hard Cr plating film. The composite Cr plating film containing Si ₃ N ₄ particles has an average particle size of 0.4
It can be seen that the wear amount is slightly increased at μm.

[0050]

As described above, the composite Cr plating film of the present invention has an effect of being excellent in abrasion resistance and seizure resistance and of being less aggressive to a sliding partner material.
Therefore, if this composite Cr plating film is applied to a sliding member such as a piston ring of a high-load diesel engine or a gasoline engine or a vane of a compressor, a sliding member having excellent sliding characteristics can be provided.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, in which (a) is a longitudinal sectional view showing a part of a piston ring, and (b) shows a part of a composite Cr plating film on the piston ring in a direction perpendicular to a plating surface. It is the enlarged view seen from.

FIG. 2 is a perspective view for explaining a manufacturing process of a composite Cr plating film on the piston ring, and FIG.
r shows one cycle after the plating process → the etching process,
(B) shows two cycles after the same step.

FIG. 3 is an explanatory view of a reciprocating friction tester.

FIG. 4 is a graph showing test results of wear test 1.

FIG. 5 is a graph showing test results of wear test 2.

FIG. 6 is a graph showing test results of wear test 3.

[Explanation of symbols]

Reference Signs List 1 piston ring 2 nitride layer 3 composite Cr plating film 4 crack 5 Si ₃ N ₄ particle 10 upper test piece 11 fixed block 12 hydraulic cylinder 13 lower test piece 14 movable block 15 crank mechanism 16 load cell

Claims (4)

[Claims] 1. A composite Cr plating film containing hard particles in a network-like crack formed in the hard Cr plating film, wherein the hard particles are Si ₃ N ₄ particles, and the average particle size of the hard particles is A composite Cr plating film having a diameter of 0.8 to 3 μm and a composite ratio of the hard particles of 3 to 15% by volume. 2. A sliding member, wherein the composite Cr plating film according to claim 1 is formed on a sliding surface. 3. The sliding member is a piston ring,
3. The sliding member according to claim 2, wherein the composite Cr plating film is formed on an outer peripheral surface that is a sliding surface of the piston ring. 4. The sliding member according to claim 3, wherein said piston ring has a nitrided layer formed on upper and lower surfaces.