JP4839120B2 - Piston ring with laminated coating - Google Patents

Description

The present invention relates to a piston ring for an internal combustion engine in which a sliding surface is coated with a hard film having excellent tribological characteristics. More specifically, the hard coating is composed of an ion plating laminated coating.

The piston ring functions as a gas seal function that seals the combustion chamber of the internal combustion engine, an oil control function that controls the thickness of the lubricating oil film formed on the cylinder liner surface, and a piston that is heated by the combustion of fuel. There is a heat conduction function that transfers the heat to the cylinder liner and cools it. In order to perform such a function, the piston ring must always stick to the cylinder liner with its own tension. As a result, the high-pressure combustion gas generated in the combustion process of the engine is sealed, so a large surface pressure is inevitably generated on the sliding surface of the Top ring, and wear and seizure are likely to occur accordingly. Have been exposed.

In recent years, the usage environment of piston rings has become increasingly severe due to stricter exhaust gas regulations for automobile engines, such as increased combustion temperature, increased surface pressure load, and the use of low-viscosity lubricants, improving wear resistance and seizure resistance. Expected. In addition, it is known that combustion products with a Vickers hardness of Hv1500 or more generated during the combustion process reach the sliding surface between the piston ring and the cylinder liner and cause abrasive wear (Hideo Yamamoto, 2 others) ; Research on hardness of soot in diesel engine oil, Machine lecture No.03-1 Vol. 3, (2003), 137).

For this reason, hard coatings such as nitrides and carbides by ion plating have been used on the outer peripheral sliding surface of the piston ring from the conventional nitriding treatment of hard Cr plating or martensitic stainless steel.

Japanese Unexamined Patent Publication No. 57-57868 discloses a piston ring in which a hard film such as TiC, TiN, CrN or the like is formed on a sliding surface by a PVD method, and TiC, TiN or reactivity formed by a reactive ion plating method. Piston rings coated with CrN by sputtering are said to be excellent in wear resistance and heat resistance. However, TiC and TiN films formed by reactive ion plating and CrN films coated by reactive sputtering have poor adhesion and peeling occurs when they are made thick. It was never served.

JP-A-61-87950 is an improvement of JP-A-57-57868, and a film made of an ultrafine mixed structure of metallic Cr and Cr nitride is applied to the sliding surface by reactive ion plating. A coated piston ring is disclosed. The coating film on the sliding surface is made of an ultra-fine mixed structure composed of metallic Cr and Cr nitride by the reactive ion plating method, which improves the adhesion of the film and enables use in thick films. Disclose. As a result, since the durability of the piston ring was improved, a piston ring coated with Cr nitride by the reactive ion plating method has been widely used. However, in a diesel engine, the environment in which the piston ring is used becomes more severe due to demands for exhaust gas purification and fuel efficiency improvement. In the top ring of the diesel engine, the Cr nitride film becomes chipped and peeled off. Countermeasures were sought.

Japanese Patent Laid-Open No. 6-248425 has been proposed for the problem that the Cr nitride film formed by the ion plating method tends to cause chipping or peeling of the film during use in a diesel engine. The piston ring that has a coating with a porosity of 1.5 to 20% on the outer peripheral sliding surface in the Cr nitride film formed by A is excellent in wear resistance and scuff resistance, and even in more severe use, It is disclosed that it is a piston ring that hardly causes chipping or peeling of the film. Since the Cr nitride film of the present invention has low residual stress and excellent adhesion, it can be easily formed into a thick film, and will be frequently used for piston rings for diesel engines that require durability thereafter. Became. However, since this film has a large number of pores in the film, the film hardness is lower than the original hardness of Cr nitride, and in an engine in which hard particles are generated in recent years, abrasive wear tends to occur. There is a problem, and improvement has come to be demanded.

As described above, a piston ring film having excellent wear resistance and excellent chipping resistance has not been developed. Under such circumstances, the oxidation resistance and crack resistance of the surface coatings of cutting tools and wear-resistant tools have been reviewed, and multilayering of carbide coatings and nitride coatings has been performed.

Japanese Patent Application Laid-Open No. 2001-329360 discloses that a multi-layered film of a soft nitride thin film and a hard nitride thin film becomes a film having more excellent mechanical properties such as wear resistance and peel resistance. However, the disclosed method for forming a film is to repeatedly form a soft nitride film with a relatively low bias voltage and then to form a hard nitride with a high bias voltage. A method of manufacturing a piston ring in which a large number of piston rings are stacked to form a cylinder and the film is formed while rotating it with a self-revolving jig cannot be applied because a film is not always formed. In addition, the wear resistance of the soft nitride film is expected to be low, and it is considered that there is a problem in the durability of the piston ring.

In JP-A-11-335813, a film such as a CrN, TiN, or TiCN layer having a lattice constant of 0.997 to 1.005 times the lattice constant described in JCPDS has a low internal stress, so that the propagation of microcracks generated in the film hardly occurs. It is disclosed that cracks can be prevented from occurring in the entire film, so that the film is hardly chipped and wear resistance and the like are improved. Furthermore, it is also disclosed that a film having high hardness and more excellent wear resistance can be obtained by repeatedly laminating at least two kinds of hard films. However, in the case of a CrN film, a thin CrN film is coated and then ion implantation of argon ions is performed, and this is repeated, and since an ion implantation apparatus is used, the cost must be high. In the case of other coatings, it is a composite nitride coating by the arc ion plating method or a laminated film thereof, and the inventor's experience is not sufficient in chipping resistance as a piston ring outer peripheral sliding surface coating.

JP-A-62-142768 relates to a cutting tool having a hard ceramic film, and a film in which a large number of films of TiC, TiN, Ti (CN) Ti (C, O), etc. are laminated with a limited film thickness. However, it is disclosed that cracking is difficult to occur and peeling and chipping are unlikely to occur. However, the film formation method in this method is a CVD method and cannot be applied to a piston ring in which deformation due to heat is a problem.

Japanese Patent Application Laid-Open No. 7-97679 has a high hardness and oxidation resistance in which a Ti-rich film composed of Ti, Al, and nitrogen and an Al-rich film are alternately laminated to provide a cutting tool, It is disclosed that it is suitable as a surface coating for wear-resistant tools. However, the coating film has high coating hardness due to the inclusion of Al, which is advantageous in terms of wear resistance. However, since the nitride of Al is inferior in toughness, the coating film is not used when used on the piston ring sliding surface. There is a problem that it is easily chipped.

Japanese Patent Laid-Open No. 8-302461 describes the surface of a base material made of cemented carbide, ceramics, cermet, or steel, or the interface of a multilayer coating made of nitride and carbonitride, with each of oxynitride and carbonitride. It is disclosed that the adhesiveness of the layer interface can be improved and the wear resistance of the film can be remarkably enhanced by using the product. However, the adhesion between the coatings may be improved, but the bonding layer itself is an oxide composite ceramic layer, and the crack resistance of the oxide is low, so there is a problem that the crack resistance of the interface is low. It seems that it cannot be used for the piston ring outer peripheral surface coating.

“Study on hardness of soot in diesel engine oil,” Machine Lecture No.03-1 Vol. 3, (2003), P137. JP-A-57-57868 JP 61-87590 JP-A-6-248425 JP2001-329360 JP 11-335813 A JP-A 62-142768 JP-A-7-97679 JP-A-8-302461

The present invention has been made in view of the above-mentioned problems of the conventional film, and has high hardness and excellent wear resistance and excellent crack resistance, and the film is not chipped or peeled even in a harsh sliding environment. It is to provide a piston ring that does not occur.

As a result of earnest research in view of the above object, the present inventor made a film formed on the outer peripheral sliding surface of the piston ring as a laminated film by an ion plating method, and the laminated film is TiCN composed of Ti, carbon, and nitrogen. Even if it is used on the outer peripheral sliding surface of the top ring of a diesel engine, which is currently the most severe, by forming the layers and CrCN layers composed of Cr, carbon, and nitrogen alternately, the film is lacking. It has been found that a piston ring that does not cause peeling and has excellent wear resistance can be obtained. Furthermore, it is desirable that the thickness of the TiCN layer and the CrCN layer of the laminated film be 3 to 9 nm, respectively, and it is more desirable that the carbon concentration of the TiCN layer and the CrCN layer be 4 to 8% by weight.
The TiCN layer and the CrCN layer mentioned here do not mean a stoichiometric composition.

Forming a hard ceramic film on the outer peripheral sliding surface of the piston ring is a commonly used technique today. The high hardness and excellent corrosion resistance of the hard ceramic coating has produced a large amount of hard combustion products, and has shown excellent durability in diesel engines, which are corrosive environments due to the formation of sulfur oxides. However, in a diesel engine, the combustion pressure is high, and the piston ring is pressed against the piston ring groove with a strong force due to combustion, causing deformation in the shape of a dish. High frictional force is repeatedly generated between the cylinder wall and the cylinder wall. For this reason, the hard ceramic film formed on the outer peripheral sliding surface of the piston ring is cracked due to fatigue, leading to chipping of the film. As a preventive measure for this chipping, it has been made to change the film type to a stronger film, but it is difficult to avoid scratches and fine cracks that occur during film processing, Progress occurred, and the chipping and peeling of the film could not be prevented. For this reason, it is thought that cracking and peeling caused by these can be prevented by making the coating less prone to crack growth than preventing cracking, and the fracture toughness values described below As a result, the present invention has been achieved.

で皮膜の欠けが発生した。空孔率が2％以上のものは破壊靭性値が2．63 ＭＰａ・

以上あり、皮膜の欠けは認められなかったが、皮膜硬度がＨｖ1008〜1530と比較的低硬度なためか摩耗量が空孔率ほぼ0％のものに比べ1．3〜2倍、と大きかった。このことから、本発明者等は破壊靭性値が約3 ＭＰａ・

以上あり、皮膜硬度がＨｖ1700以上あれば、現在のディーゼルエンジンのＴｏｐリングに使用しても欠けを生じず、且つ、耐摩耗性にも優れた皮膜になるとの確信を得た。 That is, the present inventors have proposed that the fracture toughness value of ceramic can be used as a scale for evaluating the difficulty of the crack development of the ceramic film, and that the chipping is not likely to occur. In order to verify the CrN-coated piston ring described in US Pat. No. 6-248425, a CrN film having a porosity of approximately 0%, approximately 1%, approximately 2%, approximately 4%, approximately 8% based on the description of the invention specification. Was formed on a top ring for a diesel engine, and the fracture toughness value of the coating was measured and an engine test was conducted. The engine test was performed for 100 hours with a 4/4 load using a high-load diesel engine with a cylinder bore of 135mm x 6 cylinders. The results are shown in Table 1. Those with a porosity of approximately 0% have a toughness value of 0.75 MPa ·

The film chipped. Those with a porosity of 2% or more have a fracture toughness value of 2.63 MPa ·

There was no crack in the film, but the film hardness was as high as 1.3 to 2 times compared to the one with a porosity of almost 0% due to the relatively low hardness of Hv1008-1530. . From this, the present inventors have a fracture toughness value of about 3 MPa ·

As described above, if the film hardness is Hv1700 or more, it was confirmed that the film would not be chipped even when used for the top ring of the current diesel engine and the film had excellent wear resistance.

＊皮膜の空孔率は画像解析による。 Table 1: Engine experiment results

* The porosity of the film is based on image analysis.

The fracture toughness value here was determined by the Vickers indentation method. The Vickers indentation method is a fracture toughness test method for fine ceramics standardized in JIS R 1607. JIS is a method for fracture toughness test at room temperature for fine ceramics used as high-strength materials such as machine parts and structural materials. Among them, the crack introduction fracture test method and the indenter press-in method are defined in advance. Specifically, the indentation and crack length generated by pushing the Vickers indenter into the test surface are measured, and the fracture toughness value can be obtained from the indentation load, the diagonal length of the indentation, and the crack length. However, JIS states that the thickness of the test piece is preferably 3 mm or more, and the film as in the present invention cannot be measured. Therefore, in the present invention, although different from the above JIS standard, the fracture toughness value was obtained from the indentation and crack length generated by pushing the Vickers indenter into the film cross section. At this time, since a crack is generated in parallel with the surface of the film due to the residual stress in the film, the length of the crack perpendicular to the surface of the film was defined as the distance from the center of the indentation to the corner. The formula for calculating the fracture toughness value is shown below.

Therefore, as a result of measuring the fracture toughness value and the Vickers hardness of various types of metal carbides, metal nitrides, metal carbonitride single layer films and laminated films prepared by the ion plating method of the present inventor, the present invention was achieved. It was.

以上とすることができるので、現在最も過酷であるディーゼルエンジンのTopリングに使用しても皮膜の欠けが生じない耐久性に優れたピストンリングを得ることが出来る。 That is, the present invention uses an ion plating method to form a TiCN layer having a carbon concentration of 4 to 8% by weight and a CrCN layer on the sliding surface of the outer periphery of the piston ring by forming a laminated film having a thickness of 3 to 9 nm. By providing a thickness of 50 μm, the coating hardness is HV1700 or more, the wear resistance is excellent, and the fracture toughness value is 3 MPa ·

As a result, it is possible to obtain a piston ring with excellent durability that does not cause chipping even when used in the top ring of the most severe diesel engine at present.

First, the reason why Ti and Cr were selected as the evaporated metal was that, as a result, satisfactory fracture toughness value and film hardness were obtained with this combination, but (1) it was relatively inexpensive with readily available metals. (2) Nitride or carbonitride film is used as the film of the sliding member (3) Cr is relatively difficult to generate droplets peculiar to arc ion plating (4) Film formation rate This is because it is relatively quick.

以下となることが解った。従って、炭素濃度は4〜8重量％で有ることが必要である。 Also, the carbonitride film is made of TiN and CrN films, when an intrusion-type solid solution element such as carbon is introduced, in addition to the mechanism that strengthens the inside of the crystal grains compared to before introduction, This is because it was thought that the fracture toughness value increased as a result of strengthening many interfaces in the film. From the experimental results, the effect is small when the carbon concentration is less than 4% by weight, and the residual stress is high when the carbon concentration is greater than 8%, and the fracture toughness value that is the index of the present application is 3 MPa ·

I found out that Therefore, the carbon concentration needs to be 4 to 8% by weight.

The thickness of each layer affects the hardness of the coating. This is because in the laminated film, dislocations cause plastic deformation by moving within the layer and at the boundary between layers. For this reason, dislocation deposition (Hall-Petch type strengthening mechanism) by reducing the layer spacing (that is, reducing the thickness of each layer) and increasing lattice strain at the layer interface by introducing many interfaces. This is because the hardness of the laminated film is considered to increase. However, if the layer spacing is too small, boundary slipping between layers occurs, resulting in a rapid decrease in hardness. Further, if the thickness of each layer is too large, the above effect cannot be obtained, and it is considered that the original hardness of the film is obtained. From the film hardness measurement, the thickness of each layer of the laminated film is optimally 3 to 9 nm.

In addition, it goes without saying that such a coating can be used for a piston ring for a gasoline engine. Also, since the ion plating method is used for forming the coating, the temperature increase of the piston ring during the coating is reduced. As in the prior art, it is possible to suppress the deterioration of the piston ring gas seal function and other functions such as oil amount adjustment due to the deformation of the piston ring and the strength reduction.

In the present invention, since the arc ion plating method is used, the vaporized metal droplets are included in the film, but the degree of influence on the object of the present invention cannot be measured, and is treated as an unavoidable impurity.

(1) Piston ring FIG. 1 is a longitudinal sectional view of a steel piston ring according to an embodiment of the present invention. A nitride layer 2 having no white layer with a Vickers hardness of 700 or more is formed on the entire peripheral surface of the piston ring 1, and chromium nitride or its gradient coating 3 and laminated coating 4 are formed on the nitride layer 2 by arc ions. Coatings with different components are alternately coated by plating. Note that the nitride layer 2 may have the nitride layer 2 only on the side surface and the inner periphery or may not have the nitride layer 2 as shown in the longitudinal sectional views of the piston ring in FIGS. Chromium nitride or its gradient coating 3 is a stress relaxation layer made of CrN or the like in which carbon is not dissolved. If no problem occurs in the adhesion of the film, chromium nitride or its gradient film 3 may be omitted. In addition to steel, cast iron can also be used as the piston ring material.

(2) Method for Forming Film Next, the arc ion plating apparatus used in the present invention and the method for forming a film by the arc ion plating method will be described in detail.

FIG. 4 shows an example of an ion plating apparatus for coating used in the present invention. The apparatus includes a vacuum vessel 14 having a gas inlet 12 and an exhaust port 13, and a first target 16 connected to the anode of the arc power source 15 and a second target connected to the anode of the arc power source 17 in the vacuum vessel 14. A target 18 is arranged. Metal Ti is set on the first target, and metal Cr is set on the second target. The first target and the second target are installed so that the distance from the piston ring surface is equal. Further, a rotary table 20 connected to a bias power source 19 is disposed in the vacuum vessel 14, and the piston ring 11 is installed on the rotary table 20. A method for forming the coating of the present invention on the piston ring 11 using this ion plating apparatus will be described. As described above, after the first target, the second target, and the piston ring 11 are arranged, the exhaust is exhausted from the exhaust port 13, the vacuum container 14 is decompressed to 0.04 Pa or less, and is adsorbed on the inner wall of the chamber or the piston ring. In order to promote the release of the gas, the heater 21 is used for heating and degassing treatment. When the heating temperature is low, sufficient degassing cannot be obtained, and when it is too high, the piston ring undergoes creep deformation. After completion of preheating, the table is rotated, argon gas is introduced from 12, and a bias voltage of −800 to −1000 V is applied to cause arc discharge between the cathode and anode to perform bombard cleaning. When the bias voltage is higher than −800, a sufficient bombard cleaning effect cannot be obtained, and when it is lower than −1000 V, the piston ring is heated and softened. Thereafter, while introducing the reactive gas from 12, the total pressure is controlled to 0.2 to 8 Pa, and a bias voltage of 0 to -100 V is applied to coat the laminated films 3 and 4 in FIG.

The composition of the TiCN layer and the CrCN layer forming the multilayer coating 4 in FIG. 1 can be controlled by controlling the partial pressure of each gas. For example, the carbon concentration in the TiCN layer increases when the partial pressure of the hydrocarbon gas is increased.
The thicknesses of the TiCN layer and the CrCN layer can be controlled by the arc current and the table rotation speed. When the deposition rate is T (μm / min) and the table rotation speed is R (rpm), the thickness H (nm / rotation) of each layer is expressed by H∝T / R. Here, the film formation speed T is a film formation speed when a single compound for forming a laminated film is ion-plated by this arc ion plating apparatus, and is proportional to the magnitude of the arc current during film formation. Therefore, the thickness of each layer decreases when the arc current is decreased or the table rotation speed is increased. Therefore, in order to control the thickness of each layer of the multilayer coating, the relationship between the arc current value of the compound itself that forms the multilayer coating as shown in FIG. However, even if the same ion plating apparatus is used, this relationship varies depending on the furnace structure, the shape of the target used, the distance between the target and the object to be processed, and the like.

以上破壊靭性値が必要であるから、炭素濃度を先に決定しなければならない。尚、高いバイアス電圧はピストンリングの熱変形を招くことから0〜-100Vとすることが必要である。
以下に実施例を示して具体的に本発明を説明する。 The film hardness of the laminated film can be controlled by bias voltage, total gas pressure, nitrogen gas partial pressure, hydrocarbon gas partial pressure, arc current value, and table rotation speed. The film hardness increases when the bias voltage is increased, the total gas pressure is decreased, the nitrogen gas partial pressure is decreased, or the hydrocarbon-based gas partial pressure is increased. Further, when the arc current is decreased or the table rotation speed is increased, the thickness of each layer is decreased, so that the film hardness is increased. However, 3 MPa ·

Since the fracture toughness value is necessary, the carbon concentration must be determined first. In addition, since a high bias voltage causes the thermal deformation of a piston ring, it is necessary to set it as 0--100V.
Hereinafter, the present invention will be specifically described with reference to examples.

First, the following experiment was performed to obtain the carbon concentration at which the fracture toughness value was 3 or more.
A 17Cr stainless steel piston ring wire with a rectangular cross section of 2.5 x 4.3 mm was bent into a ring shape of φ135 mm, then subjected to strain relief annealing, and a gap was removed, side polishing and outer peripheral surface polishing were performed. Thereafter, the outer peripheral surface of the piston ring was subjected to nitriding treatment and degreased by ultrasonic cleaning. In order to improve the adhesion between the piston ring base material and the coating, the surface of the base material was sandblasted to finish the surface roughness to 1.0 to 4.5 μm Rzjis, and dust on the surface was removed by air blow. The test piece for pin-on-disk wear test is a 17Cr stainless steel piston ring wire with a cross section of 5 x 5mm and a height of 20mm, polished to the tip 20R, and after forming an ion plating film, the surface roughness is Rzjis What was finished to 0.4 μm or less and degreased by ultrasonic cleaning was used, and the disc material used was a SUJ2 steel of φ120 × 12 mm finished with a surface roughness Rzjis = 0.8 to 1.6 μm.

Using an ion plating apparatus (AIP-3012) manufactured by Kobe Steel, after placing the metal Ti on the first target and the metal Cr on the second target, the work piece main body is placed on the turntable, and then the work piece. The vacuum vessel was depressurized to 0.04 Pa or less, and the object to be treated was heated to 873K with a heater to perform pre-heat treatment. In the bombard cleaning, argon gas was introduced, and a bias voltage of −700 V was applied to cause arc discharge between the cathode and the anode, the arc current value of the second target was set to 100 A, and the treatment was performed for 2 minutes. After that, for the formation of a stress relaxation layer made of CrN without solid solution of carbon, the pressure was set to 1.2 Pa, the bias voltage was set to -10 V, and the arc current value of the second target was set to 200 A while introducing nitrogen gas. For 30 minutes. Methane gas was introduced as a hydrocarbon-based gas in order to dissolve carbon in the nitride, and the methane partial pressure of 1 Pa to 9 Pa determined by the preliminary coating so that the carbon concentration in the laminated film was about 2 to 10 wt%. Was changed. The amount of nitrogen gas introduced was adjusted so that the total gas pressure at this time was about 2.7 Pa. Film formation was performed with the bias voltage set to -10V.
Next, about the obtained film | membrane, the film | membrane investigation was conducted by the following method using the piston ring, and the abrasion test was implemented using the abrasion test piece.

(1) Measurement of thickness of each layer The thickness of each layer of each sample was measured using CuKα rays using a powder X-ray diffractometer (RINT2100 manufactured by Rigaku Corporation), scanning range 2θ = 35-50 °, applied voltage 40 kV, The X-ray diffraction pattern was measured under the conditions of applied current 30mA, scan step 0.02 °, scan speed 2 ° / min, diverging slit 1deg, and receiving slit 0.3mm, and the satellite reflection angle of the satellite peak appearing near the (111) diffraction peak From these, the thickness of each layer was calculated using the following equation (FIG. 6).

(2) Measurement of carbon concentration The carbon concentration in the film was quantitatively analyzed with an electron beam microanalyzer, EPMA (JEOL JXA-8600S) manufactured by JEOL under the conditions of an acceleration voltage of 15 kV and a probe current of 5 × 10 ^-8 A. .
(3) Measurement of film hardness The film hardness was measured using a micro Vickers hardness tester manufactured by Akashi Co., Ltd. under conditions of a load of 50 gf and a time of 15 sec.

(3) Measurement of fracture toughness value As described above, the indentation and crack length generated by pushing the Vickers indenter into the center of the cross section of the laminated film are measured, and the fracture toughness is determined from the indentation load, the diagonal length of the indentation, and the crack length. The value was determined. Here, the test load was 200 gf and the time was 15 sec. The elastic modulus used for calculation of the fracture toughness value was 240263 MPa.

(4) Wear test The wear resistance was evaluated by a wear test using sooted oil. The test conditions for wear tests using sooted oil and the evaluation methods for wear characteristics are shown below. The wear test is a pin-on-disk test as shown in FIG.
Test conditions Test load 130.2N Sliding speed 0.5m / sec
Oil used: Oil containing soot (Mitsubishi Chemical Corporation Dia Contaminant WEAR)
Supply amount: 0.5cc / min
Test time: 4 hours Evaluation method After the test was completed, an image of the pin sliding surface was taken, and the wear weight was calculated from the width of the wear scar obtained from the image by the following formula. The film density was 7.75 × 103 Kg / m3.

1. Table 2 shows the film forming conditions of Example 1, the results of the investigation, and the results of the wear test.

以上有る皮膜は試料NO. 1-3〜NO.1-7で、炭素濃度が約4重量％〜約8重量％であった。皮膜硬さは何れの試料もＨv1800以上有り、比較例であるＣｒＮ単層膜に比べ耐摩耗性も同等以上であった。ＣｒＮ皮膜に炭素のような浸入型の固溶元素を導入されると結晶粒内を強化すると共に、積層皮膜各界面が強化されると考えら、その結果として、破壊靭性値が上昇すると考えられる。しかし、その量が一定量を超えると、皮膜の内部応力が強くなりすぎるため、脆くなり破壊靭性値が再び低下したものと思われる。実施例１の結果から、炭素濃度が4〜8重量％の皮膜は破壊靭性値が３ＭＰａ・

以上有り耐欠け性に優れると共に耐摩耗性も従来のＣｒＮ単層膜以上であることが認められた。 As is clear from Table 2, the fracture toughness value is 3 MPa ·

The above coatings were Samples No. 1-3 to No. 1-7, and the carbon concentration was about 4 wt% to about 8 wt%. The film hardness was Hv1800 or more in any sample, and the wear resistance was equal or higher than that of the CrN single layer film as a comparative example. It is considered that when an intrusion-type solid solution element such as carbon is introduced into the CrN film, the inside of the crystal grains is strengthened and each interface of the laminated film is strengthened, and as a result, the fracture toughness value is increased. . However, if the amount exceeds a certain amount, the internal stress of the film becomes too strong, and it becomes brittle and the fracture toughness value seems to have decreased again. From the results of Example 1, the film having a carbon concentration of 4 to 8% by weight has a fracture toughness value of 3 MPa ·

As described above, it was confirmed that the chip was superior in chipping resistance and also had wear resistance higher than that of the conventional CrN single layer film.

Next, in the laminated film, dislocations cause plastic deformation by moving in and between the layers. Therefore, by reducing the thickness of each layer, it is considered that dislocation accumulation and lattice strain at the layer interface increase and the hardness of the laminated film increases. In order to obtain the optimum value, after determining the relationship between the film formation rate and the arc current value as shown in FIG. 5 in advance so that the thickness of each layer is 3 to 10 nm, the arc current value of the target is changed. Each film was prepared. The methane partial pressure was 5 Pa, the table rotation speed was fixed at 10 rpm, and the process up to the film formation was the same as in Example 1. The film investigation method and wear test were also carried out in the same manner as in Example 1.

比較例２：空孔率約１．５％のＣｒN皮膜 Table 3 shows the film formation conditions, the investigation results, and the wear test results of the experiment in which the thickness of each layer was changed.

Comparative example 2: CrN film having a porosity of about 1.5%

以上あり目標を達成していた。しかしながら、各層の厚さが２．７ｎｍ以下の皮膜及び各層の厚さが約１０．２ｎｍ以上の皮膜は従来の皮膜である比較例１のＣｒＮ単層膜に比べ硬度が低く且つ耐摩耗性が同等以下であった。以上のことから、ＴｉＣＮ層層とＣｒＣＮ層層とからなる積層皮膜における一層あたりの膜厚は3〜9nmが最適であることが確認できた。しかしながら、一層あたりの膜厚は２．７ｎｍ以下或いは約１０．２ｎｍ以上であっても、従来の空孔のあるＣｒN皮膜（比較例２）よりも皮膜硬度が高いことや空孔がないことから耐摩耗性で優れており、ディーゼルエンジンのＴopリングに使用できるものと思える。尚、積層皮膜に於いて転位は層内と層と層の境界に於いて運動することにより塑性変形を起こす。そのため、各層の厚さを小さくすることは、この転位の堆積(ホールペッチ型強化機構)や層の界面における格子ひずみを増大し、積層皮膜の硬さは上昇させる効果が有り、耐摩耗性を向上させる。しかしながら、層間隔を小さくしすぎると層間における境界すべりが生じてしまい急激な硬度低下をまねく結果耐摩耗性も劣化する物と考えられる。 As a result, the fracture toughness value is 3.7 MPa ·

The above was achieved. However, a film having a thickness of each layer of 2.7 nm or less and a film having a thickness of each layer of about 10.2 nm or more have lower hardness and wear resistance than the conventional CrN single-layer film of Comparative Example 1. It was below equivalent. From the above, it was confirmed that the optimum film thickness per layer in the laminated film composed of the TiCN layer layer and the CrCN layer layer is 3 to 9 nm. However, even if the film thickness per layer is 2.7 nm or less or about 10.2 nm or more, the film hardness is higher than that of the conventional CrN film having pores (Comparative Example 2) and there are no pores. It is excellent in wear resistance and seems to be usable for the top ring of diesel engines. In the laminated film, dislocations cause plastic deformation by moving in the layer and at the boundary between layers. Therefore, reducing the thickness of each layer has the effect of increasing the dislocation accumulation (Hall Petch type strengthening mechanism) and lattice strain at the interface of the layers, increasing the hardness of the laminated film, and improving wear resistance. Let However, it is considered that if the layer spacing is too small, boundary slip between layers occurs, resulting in a sudden decrease in hardness, resulting in a deterioration in wear resistance.

  Next, samples No. 1-3 and No. 1-7 of Example 1, Samples No. 2-3C and No. 2-9 of Example 2, and piston ring of Comparative Example 1.2 were simultaneously used in a diesel engine. Table 4 shows the results of actual machine evaluation. The engine was a high-load diesel engine with a cylinder inner diameter of φ135 × 6 cylinders similar to the previous one, and was run for 100 hours N at a load of 4/4. The results are shown in Table 4. Comparative Example 1 Except for the piston ring of the coating, the piston ring of the present invention was free from chipping or peeling of the coating. Also, the wear amount was 2.6 to 3.8 μm, which was more than that of Comparative 2.

Table 4 shows the results of actual machine evaluation.

When the ion plating film is on the nitride layer in the longitudinal section of the steel piston ring In the longitudinal section of a steel piston ring, there is a nitride layer only on both sides of the piston ring When there is no nitride layer in the longitudinal section of a steel piston ring. Schematic diagram of arc ion ion plating equipment used in this case Figure showing the relationship between the arc current of the TiCN layer and the film deposition rate Example of film peak in X-ray diffraction Schematic diagram of wear test

Explanation of symbols

11: Piston ring

12: Gas inlet
13: Exhaust port
14: Vacuum container
15: Arc power supply
16: First target
17: Arc power supply
18: Second target
19: Bias power supply
20: Rotating table
21: Heater 21

Claims (3)

A piston ring having a laminated film by an ion plating method on at least an outer peripheral sliding surface, wherein the laminated film includes a compound layer composed of Ti, carbon, and nitrogen and a compound layer composed of Cr, carbon, and nitrogen. A piston ring characterized by being alternately laminated. 2. The piston ring according to claim 1, wherein the carbon concentration of the laminated coating is 4 to 8% by weight. The piston ring according to claim 1 or 2, wherein the laminated film is formed by alternately laminating the compound layers of 3 to 9 nm.

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