JP2005060810A - Coating material and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating material having excellent sliding properties, high hardness and high fracture toughness and solving the problem that, though, in accordance with the tightening of regulations in exhaust gas from an engine of an automobile or the like, in the sliding parts of a piston ring, a valve lifter, a diesel jet pump or the like, the sliding environment has been getting severe as shown in the increase of the load of facial pressure, the increase of a sliding rate or the like, so that the needs for the improvement of wear resistance, scuff resistance and lowering the attacking properties against the mating material have been increased, but, an ion plating film adopted as the countermeasure therefor is worn out, or further, defaced in the severe environment of the engine. <P>SOLUTION: The coating material is the one formed to a film having a multilayer structure consisting of a layer having a high nitrogen concentration and a layer having a low nitrogen concentration. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coating material excellent in tribological characteristics and coated on a sliding surface or the like, for example, a coating material used for a sliding portion of an internal combustion engine piston ring, a valve lifter, a diesel injection pump or the like. More specifically, the present invention relates to a film having a novel structure formed by controlling PVD conditions for forming a hard film.

    Due to stricter exhaust gas regulations for automobile engines and higher fuel efficiency, the sliding load of parts such as piston rings, valve lifters, and diesel injection pumps has increased heat load due to increased combustion temperature, resulting in increased surface pressure load. In addition, the sliding speed is increasing, and the environment is becoming harsh due to the adoption of low viscosity lubricating oil and the like. Therefore, there is an increasing need for the above-mentioned parts, such as increasing hardness and improving fracture toughness, improving wear resistance and scuffing resistance, and lowering the attack of the counterpart material.

    For example, with respect to piston rings, conventionally, a coating made of hard chrome plating or nitriding has been used, but an improved coating corresponding to the above needs has been proposed. That is, the chromium nitride film proposed in Patent Document 1 is a mixture of metal chromium crystals and chromium nitride crystals by ion plating excellent in tribological characteristics, and the chromium nitride film proposed in Patent Document 2 has dissolved oxygen in a solid solution. It is a chromium nitride crystal. However, the sliding member coated with the film according to the above-mentioned patent document has insufficient tribological performance due to wear, scuffing, cracking or peeling due to sliding, etc. in engines with particularly severe sliding conditions. Has led to.

  For this reason, as a further measure, by repeatedly controlling the atmospheric pressure or bias voltage in the coating every predetermined time under two predetermined setting conditions, a layer of a columnar structure having a columnar shape on the sliding surface or a predetermined Patent Document 3 discloses a chromium nitride-based coating layer having a film fractured surface crystal in which layers having a porosity of 2 mm and non-columnar dense structure layers or layers having a low porosity close to true density are alternately laminated. Yes. In Patent Document 3, as the advantages and disadvantages of each layer, the columnar structure has good chipping resistance but low scuff resistance and wear resistance, whereas the dense structure has excellent scuff resistance and wear resistance. Demonstrates low chipping resistance. By laminating a columnar structure and a dense structure to form a layered film, the other layers compensate for the shortcomings of each layer, resulting in film adhesion, friction wear resistance, It is supposed to improve corrosion wear resistance and peel resistance.

    In the chromium nitride film of Patent Document 3, a part is a columnar structure having low scuff resistance and wear resistance, and the thickness of each layer is 0.1 to 10.0 μm. Since the columnar structure having low scuff resistance is formed relatively thick as a maximum of 10 μm, when the layer of the columnar structure becomes a sliding surface under the sliding condition where scuff wear is dominant in a severe sliding environment, Since the coating is expected to wear significantly, the sliding characteristics of the chromium nitride of Patent Document 3 cannot be said to be sufficient. On the other hand, it is shown that when the thickness of each layer is reduced, the characteristics of each layer are also reduced, and the number of layers is increased, so that film formation is complicated in the process.

Patent Document 4 includes Ti _(1-x) Al _x N, 0.1 ≦ x ≦ 0.4 by changing the bias voltage in the same manner as Patent Document 3 in order to obtain a layered structure of TiAlN. An abrasion-resistant hard coating is disclosed in which a low-hardness layer and a high-hardness layer made of Ti _(1-x) Al _x N, 0.4 ≦ x ≦ 0.75 are laminated. However, in this film, since the laminated structure is obtained by changing the ratio of Ti and Al by changing the bias voltage, a considerably large residual stress is generated in the film. There is a drawback that peeling easily occurs at the interface with the base material. For this reason, the film thickness is 3 μm or less, and an example of a thickened film is not disclosed.
Japanese Patent Publication No. 6-010454 JP-A-6-265023 JP-A-8-312779 JP-A-11-61380 JP-A-6-147318

    The present invention has been made in view of the above points, and is excellent in sliding characteristics such as scuff resistance, wear resistance, chipping resistance even under a sliding environment in an engine having particularly severe sliding conditions. An object is to provide a coating material having high hardness and high fracture toughness.

In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, the layered structure is composed only of a dense structure, and a metal nitride (for example, a CrN crystal single phase or CrN + Cr ₂ N mixed) is formed of the same compound. It has been found that by laminating crystal as a multilayer having different nitrogen concentrations, the bondability between the respective layers is increased, the strain between the layers can be reduced, and the fracture toughness can be further improved. As a result, it is possible to provide a high hardness and high fracture toughness layered film of PVD that is excellent in hardness, fracture toughness, adhesion, scuff resistance, friction wear resistance and chipping resistance.

A first aspect of the present invention is a coating material obtained by depositing a film made of crystalline metal nitride on a base material, wherein the cross-sectional structure of the film is a layered structure having different nitrogen concentrations. is there.
The metal nitride is not particularly limited as long as it has crystallinity. Typical metal nitrides include CrN and TiN, but ternary metal nitrides such as TiAlN may also be used. In the present invention, the “layered structure” is a layer whose density is detected under the observation of a scanning electron microscope structure as shown in FIG. 4. For example, in the case of forming a 10 μm film, the number of layers exceeds 10, preferably 20 to 100 layers of shading are formed. Conventionally, the composition in the film formed on the sliding part is a film that changes the source gas concentration discontinuously so that the adhesion of the film is good on the substrate side and the sliding property is good on the film surface side. Although the method has been known (Patent Document 5), in the process of forming such a known film to a thickness of several μm to several tens of μm, the concentration change is limited to about five times. Further, even if the raw material gas concentration is changed, the “layered structure” referred to in the present invention is not necessarily formed.
In the present invention, when the thickness of each layer of the layered composition becomes thinner than the line analysis possible limit, an enlarged structure (structure having a thicker layer) in which the same density as the layered structure appears is formed, and N of each layer is formed. The concentration shall be analyzed or analyzed with a TEM device.
As the base material, steel materials such as stainless steel and nitride steel, aluminum, aluminum alloy, magnesium alloy, titanium and titanium alloy and other wire materials or plate materials, and castings can be preferably used.

The second aspect of the present invention is characterized in that the fracture surface of the film made of crystalline nitride has only a dense structure. The dense structure was proposed by the present applicant in Patent Document 3. The structure observation method is described in paragraph number 0032 of this patent document, and the structure formation method is described in paragraph number 0031 and the first and second sentences. The lamellar structure characterized by the present invention can be formed by a columnar structure or a dense structure described in Patent Document 3, but a dense structure having excellent scuff resistance is preferred. The dense structure of the film is a film having a substantially true density with a film porosity of 0.5% by volume or less.

A third aspect of the present invention is a coating material in which the nitrogen concentration of the film increases or decreases in the adjacent layer. Either a metal nitride having a high nitrogen concentration or a metal nitride having a low nitrogen concentration may be disposed on the surface of the covering portion.

  The layered structure of the present invention is a structure in which the concentration of nitrogen in the metal nitride and the metal is different between the upper and lower layers. In the case of forming a nitride in which N (nitrogen) is dissolved in a solid solution limit, such as a nitride such as Ti or Cr, the nitrogen concentration can be changed within this solid solution range. For example, Ti nitride has a solid solubility limit of about 28 atomic% to 55 atomic% in the δ phase (TiN) as shown in FIG. 1, and the nitrogen concentration is low on the low nitrogen concentration side outside the solid solubility limit. Ε phase up to about 25 atomic%. The coating of the present invention may contain this ε phase. When the nitrogen concentration of Ti nitride is 25 atomic% or less, metal Ti in which nitrogen is dissolved is generated, so that the scuff resistance and wear resistance are lowered. Further, when the nitrogen concentration is 55.0 atomic% or more, it is not generated as a solid phase. As described above, since each layer in the layered structure is composed of only nitride crystals having different nitrogen concentrations, the bonding between the layers is very good, and delamination does not occur, and fracture toughness is improved.

    A fourth aspect of the present invention is a coating material characterized in that each layer of the layered structure has a thickness of submicron or more and 1 μm or less. When the thickness of each layer is 1 μm or more, the interlayer strain generated between the layers increases, and the peel resistance between the layers decreases. When the film of the present invention is made of the same nitride, the difference between the layers is only the nitrogen concentration, but the interlayer strain greatly depends on the thickness of each layer. Therefore, if the thickness of each layer is large, the difference in physical properties of each layer The interfacial strain due to this increases. In the present invention, in order to obtain very excellent peel resistance, abrasion resistance, and scuff resistance, it is preferable to limit the thickness of the layer to a very thin film thickness of 1 μm or less.

    According to a fifth aspect of the present invention, a metal film or a ceramic ion plating film is interposed as a base layer between a film made of crystalline metal nitride and a substrate, or a nitride layer obtained by nitriding a substrate is provided. It is a covering material characterized by being formed as an underlayer. Normally, various types of underlayers for PVD coatings are employed, but conventional underlayers can also be applied to coatings with a layered structure of the present invention. Ti, Cr, Al or the like can be preferably used as the metal of the underlayer, and TiN, CrN, Ti—Al—N or the like can be preferably used as the ceramic of the underlayer. The nitride layer can be formed by nitriding steel by gas nitriding or gas soft nitriding. The thickness of the underlayer is preferably 5 to 90 μm. FIG. 1 shows a piston ring according to an embodiment of the present invention, wherein 1 is a piston ring material, 2 is an underlayer, 4 is a nitrided layer, and 3 is a coating of the present invention.

    A sixth aspect of the present invention is a coating material having a hardness range of a film made of crystalline metal nitride and having a Vickers hardness of 1500 to 2500. The film of the present invention is preferably formed by selecting a substance having a Vickers hardness of at least 1500 or more. As such a substance, many nitrides such as Cr—N, Ti—N, and Ti—Al—N are listed. In order to increase the hardness of the film, the film fracture surface structure is preferably dense. By laminating such a film in a layer form with a film thickness of 1 μm or less, the hardness can be increased and the Vickers hardness can be 2500 or more. Therefore, the upper limit of hardness is set to 2500 in terms of Vickers hardness. The Vickers hardness is particularly preferably 1600 to 2000.

    According to a seventh aspect of the present invention, there is provided a coating material characterized in that the total thickness of the film made of crystalline metal nitride is 1 μm to 80 μm. When the film thickness is 1 μm or less, the function as a sliding member cannot be exhibited. On the other hand, if it is 80 μm or more, it is economically wasteful, and adhesion of the film and defects in the film tend to occur. The normal multilayer film is used with a film thickness of 10 μm or less as in the example of Patent Document 4, whereas this film is different only in the nitrogen concentration between layers and the film thickness of the layer is very different. Therefore, the strain at the interface between the layers can be kept small, and the film thickness can be increased. The optimum film thickness is about 20 to 50 μm.

    An eighth aspect of the present invention is a method for manufacturing a sliding member, characterized in that a film made of crystalline metal nitride is formed by contacting a metal vapor, a reactive gas and a substrate by a PVD method. The nitrogen concentration change of the layer made of metal nitride described above is a method of changing the vapor concentration of metal vapor while keeping the evaporation amount of metal vapor constant during the coating process or changing the evaporation amount of metal vapor while keeping the nitrogen concentration constant. Either method is possible. In order to perform this change in nitrogen and / or metal concentration for a very thin layer thickness of 1 μm or less as defined in claim 4, an alternating magnetic field is generated by passing an electric current through a coil installed around the cathode, and the coil By controlling the magnetic field, the way of the arc on the cathode surface, that is, the amount of metal evaporation was controlled, and a layered structure in which a large number of layers were laminated was formed.

  As described above, the sliding member of the present invention is denser than the layered fracture surface structure disclosed in JP-A-8-312779, and the layers having different nitrogen concentrations are thinned and laminated in multiple layers. As a result, a film having higher hardness and higher fracture toughness than conventional films can be obtained. That is, it is excellent in wear resistance and can suppress cracks in the film. Therefore, it is possible to generate a thick film ion plating film required for sliding parts used in severe sliding conditions such as piston rings, valve lifters, diesel injection pumps, etc., and to improve durability. Become. The coating of the present invention can also be applied to engine parts such as cam followers, sliding parts such as compressor parts such as shoe discs, and cutting tools.

Hereinafter, the present invention will be described in detail with reference to examples.
In the examples, first, a 3.2 × 2.3 mm piston ring wire (17Cr stainless steel) was bent into a ring shape of φ95 mm and then subjected to annealing treatment. Next, rough gap clearance, rough side parallel polishing, and barrel face polishing of the piston ring outer peripheral surface were performed. Thereafter, the outer peripheral surface of the piston ring was subjected to nitriding treatment to finish the gap. This was degreased by ultrasonic cleaning. In order to improve the adhesion between the piston ring base material and the base layer, the surface of the base material is shot blasted to a surface roughness of 3.2 to 4.5 μm Rz, and dust is removed from the surface by air blow and washed. did. The piston ring 21 processed as described above was set on the ion plating holding jig 22 shown in FIG. Further, the whole was fixed by a tightening nut 23.

The piston ring assembled as described in FIG. 3 is set on the rotary table 5 as a work 4 as shown in FIG. 9, and then the inside of the vacuum chamber 11 of the film forming apparatus shown in FIG. Vacuum was drawn to about 0.03 Pa, the work 4 was rotated, and a heater (not shown) set temperature was heated at 873K. Next, after an electric field was once generated by the trigger electrode 1, an ion bombardment cleaning process was performed using the chromium target 2 having a purity of 99.9% under the setting conditions shown in Table 1. After this, the arc current 160A set by the arc power supply 8; the bias voltage −25V set by the bias power supply 10; the degree of vacuum 0.8 Pa; the N ₂ gas flow rate 120 sccm introduced from the gas inlet 7; A chromium nitride layered film having a thickness of about 15 to 25 μm was formed at 4 rpm and a heater temperature of 873 K. A chromium nitride-based film having a layer form with different nitrogen concentrations generates a magnetic field by controlling the coil magnetic field by causing a current to flow from a power source 9 to a coil installed around a cathode in a film forming apparatus with a constant nitrogen gas flow rate. Thus, a film having a multi-layered structure shown in FIG. 5 was formed by controlling how the arc on the cathode surface flew, that is, the amount of metal evaporation. After film formation, the film was gradually cooled in vacuum for about 2 hours and then removed from the furnace.

    On the other hand, all the comparative examples were formed under the same conditions as in the examples except that the magnetic field generating coil installed around the cathode in the film forming apparatus was not used. In the comparative example, since there is no influence of the magnetic field, the arc flight is uniform and the metal evaporation amount is always constant, and the layered structure as in the example does not occur.

For the piston rings on which the films of the above examples and comparative examples were formed, the 180 ° portion was cut from the joint, embedded in resin, polished to a mirror surface, and then reflected electrons from the polished surface at 1500 times with an electron microscope The SEM photograph which observed the image is shown in FIG. 4, FIG. 5, respectively. Moreover, the measurement result by the line analysis of the film | membrane of an Example is shown in FIG. In the figure, the horizontal axis represents the depth (unit: mm) from the layer surface, and the vertical axis represents the Cr and N concentrations in relative%.
In the comparative example (FIG. 5) according to the prior art, the cross-sectional structure is recognized only as a single layer, and the layered structure is not recognized. On the other hand, in the film of the example (FIG. 4) according to the present invention, a layered structure in which a large number of layers having different nitrogen concentrations, that is, about 50 layers are laminated is recognized. The number of N concentration peaks in FIG.
In addition, the peak concentration increase / decrease in N concentration was observed even in the film that did not produce a layered structure according to the comparative example, but this increase / decrease is noise generated from fluctuations in the electron concentration of the film, which is clearly smaller than that of FIG. Significant differences were observed.
7 and 8 are photographs in which a reflected electron image is observed with a scanning electron microscope at a cross section of 180 ° from the above-mentioned joint (FIG. 7: Example, magnification 1500 times, FIG. 8: Comparative example, magnification 1500 times). Indicates. The fracture surface of the embodiment of the present invention is a dense structure.

    Moreover, the torsion test which evaluates the peeling resistance of a film | membrane was done by twisting the piston ring by an Example and a comparative example to the side surface direction 180 degrees from a joint as a rotation center. As a result, neither peeling of the film nor chipping was observed up to the 180 ° twisted part in both Examples and Comparative Examples, and the adhesion with the base material was good. Furthermore, the fracture toughness of the film was evaluated by the indentation method, and the residual stress of the film was measured. The coatings of the examples according to the present invention have higher hardness than the conventional coatings. Generally, the higher the hardness, the lower the fracture toughness value, and the higher the residual stress, the higher the fracture toughness value of the coating of the present invention. The residual stress was equal to or smaller than that of the comparative example. This means that the film thickness can be increased without generating microcracks in the metal nitride layer, which is a brittle material, with excellent wear resistance. Table 2 summarizes the above results.

It is a schematic diagram showing the composition of the covering material of the present invention. It is a state diagram of Ti-N. It is the schematic of the setting jig | tool used for the Example. It is a SEM photograph (magnification x1500) of the section of the film by the example of the present invention. It is a SEM photograph (magnification x1500) of a film section of a comparative example by the prior art. It is a figure which shows the line analysis result of the film cross section by an Example. It is a SEM photograph (magnification x1500) of a dense structure film fracture surface by an example of the present invention. It is a SEM photograph (magnification x1500) of a columnar structure membrane fracture surface by conventional technology. It is the schematic of the apparatus used for the Example of this invention.

Explanation of symbols

1. Covering material2. 2. Underlayer Film 4 4. Nitride layer Tightening nut Auxiliary piece 7. Piston ring (workpiece)
8). Holding jig 9. Droplet

Claims (8)

A covering material obtained by depositing a film made of crystalline metal nitride on a base material, wherein the cross-sectional structure of the film made of crystalline metal nitride is a layered structure having different nitrogen concentrations. The coating material according to claim 1, wherein the fracture surface of the film made of the crystalline metal nitride has a dense structure. The covering material according to claim 1 or 2, wherein the nitrogen concentration increases or decreases in an adjacent layer. The coating material according to any one of claims 1 to 4, wherein a thickness of each layer forming the layered structure of the film is 1.00 µm or less. A metal film or a ceramic ion plating film is interposed as an underlayer between the crystalline metal nitride film and the base material, or a nitride layer formed by nitriding the base material is formed as an underlayer The coating material according to any one of claims 1 to 4, wherein the coating material is formed. 6. The coating material according to claim 1, wherein the film made of the crystalline metal nitride has a Vickers hardness in the range of 1500 to 2500. The coating material according to any one of claims 1 to 6, wherein the thickness of the film made of the crystalline metal nitride is in the range of 1 to 80 µm. The manufacturing method of the coating | covering material which forms the membrane | film | coat consisting of the said crystalline metal nitride of any one of Claim 1-7 by PVD method.

Images