JPH0560241A - Piston ring and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a piston ring made of Ti alloy, which has the excellent abrasion resistance and scuffing resistance and the manufacture of which is facilitated. CONSTITUTION:A piston ring raw material is made of Ti alloy of Ti-6Al-4V, and gas nitriding is performed to the whole surface thereof. Next, a nitrogen compound layer of the surface is eliminated, and grinding processing is performed to the peripheral sliding surface so as to form a nitrogen diffused layer 3 at surface roughness of 0.8muRz or less, and the peripheral sliding surface is coated with a hard film 4 such as TiN film and CrN film or the like in a PVD processing furnace. When the nitriding is performed at a nitrogen compound generative temperature or less (about 730 deg.C or less), since a nitrogen compound layer is not generated on the surface, the grinding process for elimination can be omitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston ring for an internal combustion engine, and more particularly to a piston ring effective for a high speed and high power internal combustion engine and a method for manufacturing the piston ring.

[0002]

2. Description of the Related Art Recent gasoline engines for automobiles are aimed at high speed, high output and low friction.
Along with this, demands for the function and quality of piston rings are increasing. Along with this, there has been an urgent need to solve the problem that the blow-by amount increases rapidly when the engine speed exceeds a certain limit.

This blow-by rapid increase phenomenon is closely related to the flutter ring of the piston ring. Therefore, reducing the ring width dimension to reduce the inertial force of the piston ring, or the twist design of the top ring is considered to be an effective solution. Has been done.

However, since the reduction of the ring width causes another problem associated with the reduction of the rigidity of the piston ring, it has been considered to replace the material of the piston ring with a normal cast iron or steel and a Ti alloy having a small specific gravity.

On the other hand, as a surface treatment of a steel piston ring, attention has been paid to PVD treatment which exhibits wear resistance and scuffing resistance higher than that of Cr plating (Japanese Patent Laid-Open No. 57-578).
68, JP-A-57-65837, JP-A-58-35.
648, etc.). However, in reality, nothing related to the PVD treatment of the piston ring made of Ti alloy is found.

[0006]

The specific gravity of Ti alloy is about 1/2 of the specific gravity of iron, which is a preferable material for reducing the inertial force of the piston ring. However, it has a drawback that machinability is generally poor as compared with the conventional materials for piston rings, such as cast iron and steel. Moreover, since Ti alloy is inferior in wear resistance, not only the sliding surface but also the upper and lower surfaces need a hard wear resistant coating.

Further, when combined with a cylinder or cylinder liner made of cast iron or Al alloy, scuffing is likely to occur.

Therefore, in order to put the Ti alloy piston ring into practical use, it was necessary to study a surface treatment method and a processing method suitable for it.

An object of the present invention is to provide a piston ring made of a Ti alloy which is excellent in wear resistance and scuffing resistance and is easy to manufacture, and a method for manufacturing the piston ring.

[0010]

In order to solve the above problems, the piston ring of the present invention has a base material made of a Ti alloy, and a nitrogen diffusion layer of the Ti alloy forming the base material is provided on at least the outer periphery and the upper and lower surfaces. It is formed, and at least the outer peripheral sliding surface is characterized in that the nitrogen diffusion layer is coated with a hard film by PVD treatment.

Here, the Ti alloy may be a structural Ti alloy that is generally used commercially.

The thickness of the nitrogen diffusion layer is usually 10 μm to 12 μm.
The range of 0 μm is desirable.

Further, the hard film formed by PVD treatment has Ti
It may be a film made of one or more substances selected from the group consisting of N, Ti (C, N), CrN, and Cr (C, N). For example, in the case of TiN film or CrN film, in a nitrogen atmosphere. It can be coated by ion plating Ti or Cr. The PVD film may be a single-layer film of the above substances, or a multi-layer or mixed film of the above substances. The thickness of these hard coatings is usually 2 μm to 50 μm, although it depends on the usage conditions of the piston ring.

The piston ring manufacturing method of the present invention is
After nitriding at least the outer circumference and the upper and lower surfaces of a material made of i alloy, at least the outer peripheral sliding surface is pre-processed as a base, and then at least the outer peripheral sliding surface is coated with a hard film by PVD treatment. And

The surface roughness of the base of the hard coating is 0.8 μRz
The following is preferable.

The nitriding treatment includes gas nitriding, salt bath nitriding,
Ion nitriding or the like may be used as appropriate, but it is preferably performed at a temperature at which the nitrogen compound can be generated or lower (about 730 ° C. or lower).

[0017]

When the piston ring is made of Ti alloy, the weight can be reduced by about 40% as compared with the steel piston ring having the same size. Due to this weight reduction, the inertial force of the piston ring is reduced, fluttering is less likely to occur, and the number of revolutions when the blow-by amount sharply increases can be increased.

Further, by forming at least the outer peripheral sliding surface with a hard coating by PVD treatment, it is possible to impart extremely excellent scuffing resistance and wear resistance to the piston ring made of Ti alloy.

Further, by using the nitrogen diffusion layer as the base of the PVD-treated film, the machinability of the Ti alloy is improved,
The grinding cost can also be reduced. It also has the effect of improving fatigue resistance. Further, when the hard coating by PVD treatment is worn out, the nitrogen diffusion layer is exposed, but the wear is slower than when the Ti alloy without the nitrogen diffusion layer is exposed, and the occurrence of scuffing is also an important advantage. Become. Further, the upper and lower surfaces of the piston ring are worn by being hit against the ring groove of the piston, but the nitrogen diffusion layer is formed, so that the wear resistance is excellent.

The surface roughness of the base of the PVD-treated film is 0.8.
When it is not more than μRz, it is advantageous that the PVD-treated surface after PVD treatment does not need to be polished, and it is not necessary to coat a PVD film having an excessive thickness for polishing. Note that P
The surface roughness of the VD-treated film is preferably 1.0 μRz or less in relation to the wear of the cylinder, which is the mating material.

If the nitriding treatment is carried out at a temperature lower than the temperature at which the nitrogen compound can be formed, a nitrogen compound layer harmful to the PVD treatment cannot be formed on the surface, so that the post-processing for removing the nitrogen compound layer is not necessary and the processing step can be shortened.

[0022]

EXAMPLE An example of the present invention will be described below. Ti-6
Make a piston ring material with Al-4V Ti alloy,
The entire surface was subjected to gas nitriding treatment. The conditions of the nitriding treatment are a gas pressure of 3 × 10 ^-2 Torr, a temperature of 740 ° C., and a treatment time of 4 hours. The thickness of the nitrogen diffusion layer after nitriding is 95μ
It was m. The thickness of the surface nitrogen compound layer formed at this time was 2 μm. The nitrogen compound layer was removed by grinding, and further the surface roughness of the outer peripheral sliding surface was ground to 0.8 μRz or less. The polishing process of the nitrogen diffusion layer is easier than the polishing process of the Ti alloy base material. Then PV
In the D treatment furnace, the outer peripheral sliding surface was coated with a hard coating to obtain the piston ring of the present invention. PVD treatment is nitrogen partial pressure 8 ×
The TiN film was coated under the conditions of 10 ⁻⁴ Torr, temperature 460 ° C., and treatment time 45 minutes.

Next, another embodiment will be described. The above is the same as the above except that the nitriding condition and the PVD hard film are different. The nitriding treatment is performed in a mixed gas atmosphere of 95% nitrogen gas and 5% argon gas at a total gas pressure of 3 × 1.
It was carried out under the conditions of 0 ^-2 Torr, temperature 720 ° C, and treatment time 2 hours. In this case, a nitrogen compound layer harmful to the subsequent PVD treatment was not formed on the nitrided surface, and only a nitrogen diffusion layer was formed. Therefore, in this case, there is no step of removing the nitrogen compound layer by grinding, and the surface roughness of the outer peripheral sliding surface is 0.8 μRz.
The following polishing process may be performed. The polishing process for the nitrogen diffusion layer is T
The processing is easier than the polishing processing of the i alloy base material.
PVD treatment is performed with nitrogen partial pressure of 5 × 10 ⁻⁴ Torr and temperature of 500.
The CrN film was coated under conditions of a temperature of 120 ° C. and a treatment time of 120 minutes.

FIG. 1 shows the piston ring 1, 2 is a Ti alloy base material, 3 is a nitrogen diffusion layer formed on the entire outer peripheral surface, upper and lower surfaces, and inner peripheral surface of the piston ring 1, and 4 is nitrogen diffusion. It is a PVD-treated hard coating on the outer peripheral sliding surface coated on the layer 3.

[0025]

As described above, according to the present invention, since the piston ring is made of a Ti alloy, fluttering is less likely to occur, and the blowby rapid increase rotational speed can be increased. Further, the hard film formed by PVD treatment can impart extremely excellent scuffing resistance and abrasion resistance.
By using the nitrogen diffusion layer as the base of the PVD-treated film, the Ti alloy has improved machinability and fatigue resistance.
Further, it is possible to obtain effects such as good wear resistance and scuffing resistance when the PVD-treated film is worn. Also,
Since the nitrogen diffusion layers are formed on the upper and lower surfaces, the wear resistance is excellent. The surface roughness of the base of the PVD-treated film is 0.8 μRz
It is advantageous that the PVD-treated surface after the PVD treatment is not required to be polished, and it is not necessary to coat the PVD film having an excessive thickness for polishing. Further, if the nitriding treatment is performed at a temperature at which the nitrogen compound can be generated or less, a nitrogen compound layer cannot be formed on the surface, so that post-processing for removing the nitrogen compound layer is unnecessary, and the processing process can be shortened.

[Brief description of drawings]

FIG. 1 is a sectional view showing a part of a piston ring showing an embodiment of the present invention.

[Explanation of symbols]

 1 Piston ring 2 Ti alloy base material 3 Nitrogen diffusion layer 4 PVD treated hard coating

Claims (7)

[Claims] 1. A base material is made of a Ti alloy, and a nitrogen diffusion layer of a Ti alloy forming the base material is formed on at least the outer periphery and upper and lower surfaces, and at least the outer peripheral sliding surface is PVD-treated on the nitrogen diffusion layer. A piston ring characterized by being coated with a hard coating. 2. The surface roughness of the base of the hard coating is 0.8 μR.
The piston ring according to claim 1, wherein the piston ring is z or less. 3. The hard coating is TiN, Ti (C, N), C
The piston ring according to claim 1, wherein the piston ring is a film made of one or more substances selected from the group consisting of rN and Cr (C, N). 4. A nitriding treatment is applied to at least the outer periphery and upper and lower surfaces of a material made of a Ti alloy, at least the outer peripheral sliding surface is subjected to a pretreatment of a base, and then a PVD treatment is performed to form a hard coating on at least the outer peripheral sliding surface. A method for manufacturing a piston ring, which comprises coating. 5. The surface roughness of the base of the hard coating is 0.8 μR.
The method for manufacturing a piston ring according to claim 4, wherein z is set to z or less. 6. The hard coating is TiN, Ti (C, N), C
The method for producing a piston ring according to claim 4, wherein the film is a coating of one or two or more substances selected from the group of rN and Cr (C, N). 7. The method for producing a piston ring according to claim 4, wherein the nitriding treatment is performed at a temperature at which a nitrogen compound can be produced or less.