JP4761374B2 - Piston ring for internal combustion engine - Google Patents

Description

  The present invention relates to a piston ring that is used by being attached to a ring groove provided in a piston of an internal combustion engine, and particularly relates to a piston ring that has high breakage resistance and excellent wear resistance.

  A piston ring used in an internal combustion engine is incorporated into a piston ring groove disposed in a reciprocating manner in a cylinder liner of the engine so that the outer peripheral surface thereof and the inner peripheral surface of the cylinder liner are in a sliding contact relationship. The piston ring mainly serves to seal the combustion chamber, control the thickness of the lubricating oil film formed on the cylinder surface, and cool the piston by transferring the combustion heat from the piston to the cylinder liner during engine operation. . Therefore, the piston ring is required to have high characteristics such as wear resistance, seizure resistance, heat resistance, and oil retention.

  Conventionally, the outer peripheral sliding surface of a piston ring for an internal combustion engine has been subjected to surface treatment for the purpose of improving wear resistance such as hard chrome plating treatment or nitriding treatment in order to improve its durability. . However, in recent years, internal combustion engines have become increasingly lighter and more powerful, and the sliding environment of the piston ring has become extremely harsh. Surface treatment such as that described above has sufficient wear resistance and other functions. Can no longer be satisfied. Recently, for the purpose of further extending the life of the piston ring, a piston ring having a hard coating (chromium nitride, titanium nitride, etc.) formed by an ion plating method on the outer peripheral sliding surface is used. In addition, in order to improve the breakage resistance of the piston ring, an ion plating film is formed only on the outer peripheral sliding surface, and a nitride layer is formed only on the upper and lower surfaces and the inner peripheral surface, thereby nitriding the base of the ion plating film. A piston ring of a type that suppresses the propagation of cracks without any treatment is used.

  Since the piston ring as described above forms a hard film on the outer peripheral sliding surface by ion plating, and then performs nitriding treatment on the upper and lower surfaces and the inner peripheral surface, the hard film is emptied during nitriding. Nitrogen penetrates from the hole to the outer peripheral surface of the base material, and the base material is nitrided, so that a hard nitrided layer enters between the base material and the hard coating, and the breakage resistance of the part decreases. There is a case. In particular, at both end portions of the outer peripheral sliding surface, the thickness of the hard coating is thinner than that of the central portion of the outer peripheral sliding surface, so that nitrogen easily enters and the breakage resistance is reduced.

  Therefore, in Patent Document 1, a nitriding prevention layer is formed on the outer peripheral sliding surface, and then the piston ring is subjected to nitriding treatment. After the nitriding treatment, the nitriding preventing layer is removed, and the outer peripheral sliding surface is hardened by an ion plating method. By forming the film, nitriding of the outer peripheral sliding surface is prevented. However, the above method requires the formation and removal of the nitriding prevention layer, which leads to an increase in manufacturing steps and an increase in production cost, and cannot be said to be a practical method.

  In Patent Document 2, after forming a hard film by ion plating on the outer peripheral sliding surface, the upper and lower surfaces and the inner peripheral surface are subjected to nitriding treatment, and the upper and lower surfaces of the piston ring are polished, whereby the hard film and the Vickers There is a disclosure of a piston ring characterized in that nitride layers having a hardness (Hv) of 700 or more are separated from each other to improve fatigue strength. In this forming method, when a hard coating is formed on the outer peripheral sliding surface in a state where a plurality of piston rings are stacked in the axial direction, the ends of the outer peripheral sliding surface (upper and lower surfaces and outer peripheral sliding surface) Since the piston ring has a curved shape, a recessed space is formed at a location where the piston rings are adjacent to each other. When a hard coating is formed on the outer peripheral sliding surface of the piston ring in such a state, a hard coating is also formed on the recessed portion, and the hard coating 6 is formed on the upper and lower surfaces of the piston ring 1 as shown in FIG. A fogging portion 70 is generated. Since the formed cover part 70 varies for each piston ring 1, when the base material 2 having such a cover part 70 is subjected to nitriding, the formed nitride layer 7 also varies for each piston ring 1. Even if the upper and lower surfaces of the piston ring 1 are polished thereafter, the separation distance between the hard coating 6 and the nitride layer 7 of Hv 700 or more varies, which is not preferable in manufacturing.

JP-A-5-172248 JP 2000-291800 A

  The present invention has been made in view of the above problems, and a main object of the present invention is to provide a piston ring having high breakage resistance and excellent wear resistance.

  In order to achieve the above object, the present invention provides a piston ring for an internal combustion engine that is mounted in a ring groove of a piston and slides with a cylinder liner or a cylinder bore. The piston ring includes an outer peripheral sliding surface, an upper and lower surface, and an inner peripheral surface. In a piston ring having a surface, a nitride layer is formed only on the upper and lower surfaces, or only on the upper and lower surfaces and the inner peripheral surface, and a hard film is formed on the outer peripheral sliding surface by an ion plating method. The hard coating is composed of a dense layer made of metal formed on the outer peripheral surface of the piston ring base material and a porous layer formed on the dense layer. The maximum height roughness Rz is in the range of 1.0 to 4.0 μm, the thickness of the dense layer is in the range of 1 to 5 μm, and the porosity of the porous layer is 0.5 to 20 .0% range Provided is a piston ring characterized in that

  The hard coating by ion plating (hereinafter sometimes referred to simply as a hard coating) provided on the outer peripheral sliding surface of the piston ring of the present invention is a dense material that inhibits the penetration of nitrogen into the outer peripheral surface of the base material. And a porous layer having excellent breakage resistance formed on the dense layer. The piston ring having such a configuration has high breakage resistance because the outer peripheral surface of the base material is prevented from nitriding, and the surface of the base material other than the outer peripheral surface is nitrided, and thus has excellent resistance to resistance. It has wear properties. In addition, since such a piston ring can be obtained only by nitriding the entire piston ring after forming the hard coating on the outer peripheral surface of the base material, it has excellent characteristics by making the piston ring in the above configuration. A piston ring can be manufactured efficiently.

  In the above invention, the dense layer is preferably made of Cr, Cr-based alloy, Ti, or Ti-based alloy. This is because these metals have a thermal expansion coefficient close to that of the base material of the piston ring and are not easily affected by thermal stress, so that a dense layer having good adhesion to the base material can be formed.

  Moreover, in the said invention, it is preferable that the said porous layer consists of Cr-N type | system | group, a Cr-B-N type | system | group, a Cr-B-Si-N type | system | group, or a Ti-N type material. By forming the porous layer from the nitride of the material forming the nitride layer, it is possible to form a porous layer having good adhesion to the dense layer and having a thermal expansion coefficient close to that of the dense layer. It is.

  The present invention has an effect that a piston ring having high breakage resistance and excellent wear resistance can be obtained.

  The piston ring of the present invention is a piston ring for an internal combustion engine that is mounted in a ring groove of a piston and slides with a cylinder liner or a cylinder bore, and the piston ring has an outer peripheral sliding surface, an upper and lower surface, and an inner peripheral surface, In the piston ring in which a nitride layer is formed only on the upper and lower surfaces, or only on the upper and lower surfaces and the inner peripheral surface, and a hard coating is formed on the outer peripheral sliding surface by an ion plating method, the hard coating is a piston It is composed of a dense layer made of metal formed on the outer peripheral surface of the ring base material and a porous layer formed on the dense layer, and the maximum height roughness of the outer peripheral surface of the piston ring base material Rz is in the range of 1.0 to 4.0 μm, the thickness of the dense layer is in the range of 1 to 5 μm, and the porosity of the porous layer is in the range of 0.5 to 20.0%. This is inside It is characterized by.

  Hereinafter, the piston ring of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of a piston ring of the present invention. As illustrated in FIG. 1, a hard coating 6 composed of a dense layer 4 and a porous layer 5 formed on the dense layer 4 on the outer peripheral surface of the base material 2 of the piston ring 1 of the present invention. Is formed. A nitride layer 7 is formed on the upper and lower surfaces and the inner peripheral surface of the base material 2 of the piston ring other than the outer peripheral sliding surface 3 portion.

  The outer peripheral sliding surface of the piston ring of the present invention is formed with a hard film composed of a dense layer that inhibits intrusion of nitrogen and a porous layer that is formed on the dense layer and has excellent breakage resistance. Yes. Therefore, even when the entire piston ring after the hard coating is formed on the outer peripheral surface of the base material is subjected to nitriding, the outer peripheral surface of the base material is not nitrided, and a base material like a conventional piston ring is used. It is possible to prevent a decrease in breakage resistance due to nitriding of the material.

Conventionally, much time and cost are spent to prevent nitriding of the outer peripheral surface of the base material. However, in the present invention, it is possible to prevent nitriding of the outer peripheral surface of the base material only by forming the dense layer before forming the porous layer, and it is not necessary to remove the dense layer. And economical. Furthermore, since the dense layer is a layer having intermediate properties between the base material which is the lower layer and the porous layer which is the upper layer, there is an advantage that the adhesion between the two can be improved.
Hereafter, each structure and manufacturing method of such a piston ring of this invention are each demonstrated in detail.

1. Dense layer In the present invention, on the surface of the outer peripheral surface of the base material of the piston ring, a dense layer, which is a dense layer made of metal, formed by an ion plating method is within a range of 1 to 5 μm, preferably 2 to 2 μm. The film thickness is in the range of 4 μm. If the film thickness of the dense layer is less than the above range, the nitrogen intrusion prevention function is insufficient, and a nitride layer may be formed under the dense layer. On the other hand, an unnecessarily thick dense layer whose film thickness exceeds the above range is not desirable in terms of production efficiency because it takes time to form, and is not desirable from the viewpoint of material cost.

  The metal used for forming the dense layer is not particularly limited as long as it can form a dense layer capable of preventing intrusion of nitrogen, and is usually a single metal or a plurality of metals. An alloy containing is used. In the present invention, from the viewpoint of adhesion with the base material of the piston ring, thermal expansion coefficient, flexibility, etc., Cr, Cr-based alloy, Ti, Ti-based alloy, etc., among others, Cr, Cr-based alloy (Cr-B alloy, Cr-V-B alloy, Cr-B-Si alloy, etc.) are preferably used. By forming a dense layer using such a metal having intermediate properties between the base material and the porous layer, the adhesion between them can be improved, and the base material, the porous layer, It is possible to prevent peeling due to a difference in thermal expansion coefficient between the two.

  The degree of denseness of the dense layer is not particularly limited as long as it can inhibit the penetration of nitrogen into the base material under the dense layer and prevent nitridation of the base material during nitriding. Is not to be done. In the present invention, the porosity of the dense layer is preferably in the range of 0 to 0.4% in order to effectively inhibit nitrogen intrusion.

2. Porous layer In the present invention, a porous layer is formed on the dense layer described above by an ion plating method. Since the porous layer is a layer having pores that absorb stress, by forming such a porous layer on the outer peripheral sliding surface of the piston ring, the fracture resistance of the outer peripheral sliding surface is improved. be able to.

  The porosity of the porous layer used in the present invention is formed in the range of 0.5 to 20.0%, preferably in the range of 1.0 to 10.0%. When the porosity of the porous layer is less than the above range, the amount of pores that absorb stress is not sufficient, and preferable breakage resistance may not be obtained. On the other hand, when the porosity exceeds the above range, there is a possibility that the strength of the porous layer is lowered due to too many pores.

The material for forming the porous layer is not particularly limited as long as it can form a layer having a porosity as described above. In general, an inorganic material such as a metal nitride is used. Among them, a metal nitride forming the dense layer, for example, a Cr-N-based material, a Cr-B-N-based material, a Cr-B-Si-N-based material, or a Ti-N-based material is preferably used. In particular, CrN, Cr ₂ N, a mixture of CrN and Cr ₂ N, a mixture of Cr and CrN, a mixture of Cr and Cr ₂ N, a mixture of Cr, CrN and Cr ₂ N, or TiN are preferably used. It is done. By forming a porous layer using such a material, a porous layer having characteristics close to that of the dense layer can be formed, so that adhesion to the dense layer can be improved, and the dense layer and It is possible to prevent the peeling due to the difference in the thermal expansion coefficient.

  The film thickness of the porous layer is not particularly limited as long as desired fracture resistance can be obtained, and is usually in the range of 5 to 80 μm, preferably in the range of 10 to 50 μm. It is formed.

3. Base material The base material used for the piston ring of the present invention has a maximum height roughness Rz on the outer peripheral surface in the range of 1.0 to 4.0 μm, preferably in the range of 1.5 to 2.5 μm. It is done. If the maximum height roughness Rz of the outer peripheral surface of the base material is less than the above range, the surface area of the base material may be too small, and the adhesion with the dense layer formed thereon may deteriorate. On the other hand, if the maximum height roughness Rz exceeds the above range, it becomes difficult to form the dense layer with a uniform thickness when forming the dense layer by the ion plating method. The film thickness may be thin or not formed. In such a case, during the nitriding process, the dense layer has a thin film thickness, or nitrogen enters from a portion where the dense layer is not formed, and a nitride layer is formed on the base material under the dense layer, thereby forming the dense layer. This is not preferable because the obtained effect cannot be obtained sufficiently.

  Here, the maximum height roughness Rz is the sum of the maximum value of the peak height Zp and the maximum value of the valley depth Zv of the contour curve (roughness curve) at the reference length based on JIS B 0601: 2001. This value is expressed in micrometers (μm).

  The material of the base material is not particularly limited as long as it has the maximum height roughness Rz as described above, and a material generally used for piston rings can be used. For example, martensitic stainless steel represented by SUS440B or DINX90, SUS410 material, SUS440 material, 10Cr steel (Cr: 9 to 11% by mass), austenitic stainless steel, or the like can be used.

  The shape and dimensions of the base material are not particularly limited, and can be appropriately adjusted according to the use of the piston ring.

4). Nitride Layer In the piston ring of the present invention, a nitride layer is formed only on the upper and lower surfaces of the base material or on the upper and lower surfaces and the inner peripheral surface. This is because, by forming the nitride layer, it is possible to improve the wear resistance against the tapping of the upper and lower surfaces of the piston ring with the upper and lower surfaces of the piston ring groove. Such a nitride layer is not particularly limited as long as the desired wear resistance can be obtained, and a nitride layer formed by invading and diffusing nitrogen into a base material by a general method can be used. it can.

  The form of diffusion into the base material of the nitride layer is not particularly limited, and can be formed in any form. For example, as illustrated in FIG. 1, the nitride layer and the dense layer may be in contact with each other in the entire thickness direction of the nitride layer. Further, as illustrated in FIG. 2, the nitride layer and the dense layer may not be in contact with each other in the entire thickness direction of the nitride layer, and may be in contact only with the outermost periphery of the upper and lower surfaces of the base material. The film thickness of such a nitride layer is not particularly limited, and is usually formed with a film thickness in the range of 10 to 100 μm, preferably in the range of 10 to 70 μm.

5. Manufacturing Method The manufacturing method of the piston ring of the present invention is not particularly limited as long as the piston ring having the above-described configuration can be obtained. For example, an ion plating method is applied to the outer peripheral surface of the base material of the piston ring. Thus, a hard film composed of the dense layer and the porous layer is formed, and the upper and lower surfaces of the piston ring are polished and subjected to nitriding treatment. Hereinafter, each process of the manufacturing method of such a piston ring is demonstrated.

a) Formation of Hard Film by Ion Plating Method In this step, a hard film composed of the dense layer and the porous layer can be formed on the outer peripheral surface of the base material of the piston ring by the following method.
First, prior to the formation of the dense layer, the base material is heated within a range of 300 to 660 ° C. with a furnace heater of an arc ion plating apparatus set to a vacuum degree of 8 × 10 ⁻⁵ Torr or less. The gas adsorbed on the base material is released. Thereafter, a bias voltage in the range of −1000 to −600 V is applied to the base material, and arc discharge is generated between the cathode metal target and the anode to vaporize and ionize the metal of the target. Alternatively, the surface of the base material was cleaned by introducing argon gas and performing ion bombardment. In this case, a metal target forming a dense layer is used as the cathode target.

Argon gas is introduced into the furnace in which arc discharge is generated after the cleaning is performed until it falls within the range of 4 × 10 ⁻³ to 4 × 10 ⁻² Torr, and the range of −10 to 50V A dense layer is formed on the outer peripheral surface of the base material by applying the internal bias voltage. Further, a porous layer is formed on the dense layer by introducing a nitrogen gas until it falls within a range of 4 × 10 ⁻³ to 4 × 10 ⁻² Torr and applying a bias voltage within a range of −10 to −50 V. Can be formed.

b) Polishing In the present invention, the hard coating is formed on the outer peripheral surface of the base material of the piston ring. However, when the hard coating is formed, the hard coating is also applied to locations other than the outer peripheral surface such as the upper surface and the lower surface of the base material. A hard film may be formed. When a hard coating is formed on the upper and lower surfaces of the base material, the hard coating prevents nitrogen from entering the base material, and a nitride layer is uniformly formed on the upper and lower surfaces of the base material during the subsequent nitriding treatment. Therefore, it is preferable to polish the upper surface and the lower surface of the base material within the range of 10 to 20 μm, particularly within the range of 10 to 15 μm after the hard coating is formed. By performing such a polishing process and removing the cover portions of the hard film formed on the upper and lower surfaces, a nitride layer can be uniformly and stably formed on the upper and lower surfaces of the base material.

c) Nitriding treatment In the present invention, by nitriding the piston ring having the hard film formed on the outer peripheral surface of the base material, a nitride layer is formed on the upper and lower surfaces, or the upper and lower surfaces and the inner peripheral surface of the piston ring. Form. The method of the nitriding treatment is not particularly limited, and known methods such as a gas nitriding method (60 to 180 minutes at 550 to 600 ° C.) and a salt bath nitriding (tuftride) method (10 to 300 minutes at 570 to 590 ° C.). It can be done by a method.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Examples 1 to 6]
The maximum height roughness Rz shown in Table 1 below, the diameter Φ is 90 mm, the radial width (a1 shown in FIG. 1) is 2.7 mm, and the axial height (h1 shown in FIG. 1) is 1.0 mm. Piston ring base material (equivalent to SUS410 material, C: 0.65 mass%, Si: 0.40 mass%, Mn: 0.35 mass%, P: 0.03 mass% or less, S: 0.03 mass% or less , Cr: 13.5% by mass, Mo: 0.3% by mass, balance: Fe), and performing hard film formation, polishing, and nitriding by the method described in “5. Production method” above. Thus, a piston ring having a dense layer and a porous layer formed on the outer peripheral surface of the base material and a nitride layer formed on the upper and lower surfaces and the inner peripheral surface was manufactured. At that time, a Cr target was used as the cathode of the arc ion plating apparatus. The formed dense layer was made of Cr, the film thickness was as shown in Table 1 below, and the porosity was 0 to 0.2%. The formed porous layer was composed of a mixture of Cr, CrN, and Cr ₂ N, and had a film thickness of 20 μm and a porosity of 1 to 7%. Further, after the formation of the porous layer, the upper and lower surfaces of the piston ring were each polished by 15 μm and subjected to nitriding treatment by gas nitriding (nitriding time: 60 minutes, temperature 550 ° C.).

[Comparative Examples 1-15]
A piston ring having the maximum height roughness Rz of the outer peripheral surface of the base material shown in Table 1 below and the thickness of the dense layer was produced by the same method as in the above example.

[Comparative Examples 16-17]
Having the maximum height roughness Rz of the outer peripheral surface of the base material shown in Table 1 below, not forming the dense layer, and without polishing the upper and lower surfaces of the piston ring after forming the porous layer A piston ring was manufactured by the same method as in the above example except that the nitride layer was formed.

[Comparative Examples 18-19]
After forming a nitride layer on the entire surface (outer peripheral surface, inner peripheral surface and upper and lower surfaces) of the base material by performing nitriding treatment on the base material having the maximum height roughness Rz of the outer peripheral surface shown in Table 1 below, the porosity A piston ring was produced by the same method as in the above example, except that the quality layer was formed and the dense layer was not formed.

[Fracture resistance test]
A breakage resistance test was performed on the piston rings manufactured in the above examples and comparative examples. For the breakage resistance test, the piston ring performance evaluation apparatus according to the first embodiment disclosed in FIG. 1 of Japanese Patent Application Laid-Open No. 2001-208650, which has a pressing jig that contacts and deforms the piston ring, is used. It was. At this time, the pressing portion of the performance evaluation device uses a taper-shaped taper surface (taper angle: 7.5 °), and the reciprocating motion of the pressing jig until the piston ring breaks. Was measured. The test was performed by reciprocating the push jig so that the displacement of the load applied by the push jig of the performance evaluation device was a sine wave of 30 Hz. The piston ring breakage was detected by flowing 9.8 MPa of air through the part sealed by the piston ring, recording the air pressure change in the sealed part on the recorder, and stopping the test machine when the pressure change occurred. .

  Table 1 below shows the results of the breakage resistance test. In addition, the fracture resistance index in the following Table 1 indicates the respective pistons when the fatigue strength of the piston ring of Comparative Example 16 (which does not have a dense layer and was subjected to nitriding after formation of a hard coating) is 100. The fatigue strength of the ring was indexed to give a value indicating breakage resistance.

[Twist test]
A twist test was performed on the piston rings manufactured in the above examples and comparative examples using the test apparatus shown in FIGS. 3 (a) and 3 (b). In the twist test, as shown in FIG. 3A, the opposite ends 31a and 31b of the joint of the piston ring 1 are fixed to the grippers 32a and 32b, respectively, and the gripper 32a is fixed. In this state, the gripping tool 32b is rotated with the straight line Y as the rotation axis so that the abutment end 31b in FIG. 3 (a) comes to the position of the abutment end 31b in FIG. This was done by adding a twist of a predetermined angle. The twisted piston ring 1 is cut at the center point 33 which is the center position of the joint end portion 31a and the joint end portion 31b, and the hard coating on the cut surface (fracture surface) is peeled off from the piston ring base material. The presence or absence was visually observed.

[Shock test]
An impact test was further performed on the piston ring in which peeling was not confirmed in the twist test using the test apparatus shown in FIGS. 4 (a) and 4 (b). In the impact test, as shown in FIG. 4A, the sample 41 is placed on the abutment 42, the indenter 44 biased by the spring 43 is moved in the direction indicated by the arrow in FIG. 44 was made to collide with the coating surface (outer peripheral sliding surface) 45 of the sample 41. An impact energy of 43.1 mJ (4.4 kgfmm) was applied per collision, and the number of times until peeling occurred on the coating surface 45 was measured. The presence or absence of peeling was determined by observing the coating surface 45 with a magnifier 15 times magnified.

[Evaluation]
Table 1 below shows the maximum height roughness Rz, dense layer thickness, fracture resistance index, adhesion, productivity, and specifications of the piston ring base material manufactured in the above examples and comparative examples. Show. As for adhesion, x indicates that peeling was confirmed in the twist test, Δ indicates that peeling was not confirmed in the twist test, and peeling was confirmed in subsequent 30 impact tests, and the 30th time. The case where peeling was not confirmed even after the impact test was rated as ◯. Further, regarding productivity, “Good” indicates that the productivity is good, and “Poor” indicates that the productivity is not good, such as a long time for manufacturing. Here, productivity refers to the time required for film formation.

  From Table 1 above, it can be seen that the piston rings of Examples 1 to 6 have high breakage resistance and excellent adhesion and productivity. The piston rings of Comparative Examples 1 to 15 in which the maximum height roughness Rz and / or the dense layer thickness of the outer peripheral surface of the base material are outside the above numerical range are the above in terms of breakage resistance, adhesion, or productivity. It was inferior to the Example. Moreover, the piston rings of Comparative Examples 16 to 19 in which a dense layer was not formed had a low breakage resistance index and poor adhesion.

  5 and 6 show optical micrographs of the cross section of the outer peripheral sliding surface of the piston ring. FIG. 5 is a photograph of the outer peripheral sliding surface of the piston ring of the above-described Example 6 and FIG. 6 is a photograph of the outer peripheral sliding surface of the piston ring (4% of nighttal corrosion). The upper part of the photograph is the outer peripheral sliding surface of the piston ring, and the left and right side surfaces are the upper and lower surfaces of the piston ring. The black layer and the gray layer on the upper and lower surfaces of the piston ring are both nitride layers, the black layer is a layer having a Vickers hardness of 700 Hv0.1 or more, and the gray layer is a layer having a Vickers hardness of less than 700 Hv0.1. is there. In FIG. 5, a dense layer and a porous layer are formed on the outer peripheral surface of the base material, and it can be confirmed that the nitride layer does not enter the base material on the outer peripheral surface. On the other hand, in FIG. 6, it can be confirmed that the nitride layer partially penetrates the outer peripheral surface of the base material (a black layer and a gray layer can be confirmed).

  As described above, by forming a dense layer having a film thickness within the above range on the outer peripheral surface of the base material and forming a porous layer thereon, nitridation of the outer peripheral surface of the base material is prevented, and fracture resistance It can be seen that a piston ring excellent in adhesion and productivity can be obtained.

It is a schematic sectional drawing which shows an example of the piston ring of this invention. It is a schematic sectional drawing which shows the other example of the piston ring of this invention. In this invention, it is the schematic which shows the apparatus used for the twist test of a piston ring. In this invention, it is the schematic which shows the apparatus used for the impact test of a piston ring. It is an optical microscope photograph of the outer periphery sliding surface cross section of the piston ring of Example 6. 16 is an optical micrograph of a cross section of the outer peripheral sliding surface of the piston ring of Comparative Example 16. It is a schematic sectional drawing which shows the edge part of the outer peripheral sliding surface of the piston ring manufactured by the conventional manufacturing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piston ring 2 ... Base material 3 ... Outer peripheral sliding surface 4 ... Dense layer 5 ... Porous layer 6 ... Hard film 7 ... Nitride layer

Claims (3)

In a manufacturing method of a piston ring for an internal combustion engine having an outer peripheral sliding surface, an upper and lower surface, an inner peripheral surface , mounted in a ring groove of a piston, and sliding with a cylinder liner or a cylinder bore,
On the outer peripheral sliding surface of the base material of the piston ring, Ri consists of metal, and a dense layer that inhibits penetration of nitrogen, the hard film is composed of a porous layer formed on the dense layer, ion plating A step of forming by a ting method;
Polishing the upper and lower surfaces of the piston ring after the hard coating is formed;
Method of manufacturing a piston ring, characterized in that and a step of nitriding the piston ring the hard film on the outer circumferential sliding surface is formed of the base material. 2. The method of manufacturing a piston ring according to claim 1, wherein the dense layer is made of Cr, a Cr-based alloy, Ti, or a Ti-based alloy. The porous layer is made of a Cr-N-based material, a Cr-BN-based material, a Cr-B-Si-N-based material, or a Ti-N-based material. Manufacturing method for piston rings.

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