JP2006002221A - Chromium-containing diamond-like carbon film and sliding member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chromium-containing diamond-like carbon film which secures a low friction coefficient even under non-lubrication and inferior lubrication as a sliding member and which has excellent adhesion and sliding properties as well, and to provide a sliding member. <P>SOLUTION: The film on the outermost surface in the material to be coated is a chromium-containing diamond-like carbon film consisting mainly of chromium and carbon. Further, the sliding member is constituted so that a substrate layer having a high chromium component is formed on the surface of the material to be coated, an intermediate layer consisting mainly of chromium and carbon in which the chromium component is lower than that in the substrate layer or is gradually reduced is formed on the substrate layer, and the outermost surface layer is coated with a chromium-containing diamond-like carbon film in which the content of chromium is lower than that in the outermost layer in the intermediate layer, and the chromium content is also 5 to 16 at%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface coating film that is applied to frictional sliding parts such as automobiles, machines, and electrical parts, and that has high adhesion and can have a low coefficient of friction even in a non-lubricated and poorly lubricated environment. .

  For parts used for friction sliding parts such as machine parts, a surface treatment that exhibits high durability even in a non-lubricated and poorly lubricated environment is desired. For such machine parts and automobile parts, low alloy steel is used as much as possible to reduce costs. Therefore, the tempering process after the quenching process is generally performed at 180 ° C. or lower. In order to provide lubrication and slidability to the surface of parts made of such materials, and to improve the use so that they can be used without friction and wear, especially in non-lubricated and inferior lubricated environments, the film is formed at a low temperature and the surface coating is low. It is desired to increase the friction coefficient, improve durability, increase toughness, and improve adhesion to the substrate.

In response to such a demand, for example, in Patent Document 1, thin films of various metal carbides, nitrides, etc. are formed by vacuum arc discharge deposition, ion plating, sputtering, etc., and sliding under lubricating oil is performed. It is a moving member. Patent Document 2 proposes a friction coefficient reduction by a diamond-like carbon film (DLC) film to which Si is added. Moreover, in the thing of patent document 3, it has a protective film excellent in abrasion resistance and adhesiveness by laminating | stacking Cr layer, Cr-carbon composition inclination layer, DLC hardness inclination layer, and hard DLC layer on a base material. A sliding member is disclosed. On the other hand, although not for a sliding member, Patent Document 3 discloses that a hard film is formed on the surface layer of a piston ring for an aluminum piston in order to reduce adhesive wear of aluminum. The hard coating is diamond-like carbon in which one or more elements selected from the group consisting of Si, Ti, W, Cr, MO, Nb, and V are dispersed at a rate of 5 to 40 atomic% (at%). The film hardness is in the range of HV700-2000. In addition, an example in which film formation is performed by ion plating is disclosed.
JP 2000-192183 A JP 2000-144426 A JP 2004-010923 A Japanese Patent No. 3355306

  However, the thing of patent document 1 is under lubricating oil, and an effect cannot be expected about the case of no lubrication. Patent Document 2 describes the properties of the Si-containing diamond-like carbon film related to the scratch limit and dynamic hardness, but the friction coefficient, which is a necessary characteristic of the sliding member, is related to the Hertz surface pressure. Is only mentioned. In addition, in Patent Document 3, a diamond-like carbon film is formed on the outermost layer with Cr having good adhesion as the lowermost layer, but whether the diamond-like carbon film on the outermost layer has the smallest friction coefficient. Not verified. Further, Patent Document 4 describes a chromium-containing diamond-like carbon film, but mainly focuses on prevention of aluminum adhesion, and does not describe a friction coefficient as a sliding member. In the examples, it is about W and Si, and Cr, Ti, Mo, Nb, V and the like are not specifically described only by suggesting that the same effect is obtained.

  The object of the present invention is to use a chromium-containing diamond-like carbon film as described above, as a sliding member, ensuring a low coefficient of friction even under non-lubricated and inferior lubrication, and having excellent adhesion and sliding characteristics. It is to provide a diamond-like carbon film (hereinafter referred to as “chromium-containing DLC film”). Furthermore, it is providing the sliding member which has a film of a low friction coefficient.

  The inventors have attempted to reduce the internal stress of the DLC film by containing metal in the DLC film, and have also improved the adhesion. However, as described above, the conventional ones have been studied for peelability and hardness, but the friction coefficient is such that the diamond-like carbon film has low friction, and the aforementioned metals such as Si, Cr, W, etc. There were some reports that the friction coefficient increased with increasing element addition. For example, the data of W1 to W4 shown in FIG. 1 are obtained by the inventors of the present invention by examining the relationship between the tungsten (W) content of the tungsten-containing diamond-like carbon film and the friction coefficient. As shown in W1 to W4 of FIG. 1, the friction coefficient is about 0.19 at a W content of 0 at%, 0.27 at 7 at%, 0.40 at 14 at%, and the friction coefficient at 20 at%. The coefficient of friction increases as the content increases to 0.48. However, the present inventor has found that in the case of a chromium-containing diamond-like carbon film other than tungsten, the chromium content is 5 to 16 at% and the friction coefficient has a minimum point. This is shown in C1 to C10 in FIG. The reason why the minimum value appears in C4 to C8 is unknown, but if the chromium content is 5 at% or less, the toughness of the DLC film is lowered, and as a result, the adhesiveness is lowered and it cannot be used. On the other hand, if the chromium content is 16 at% or more, the friction coefficient of the DLC film increases and it is not suitable for the sliding surface.

  Based on this knowledge, in the present invention, the outermost coating film of the material to be coated is a chromium-containing diamond-like carbon film mainly composed of chromium and carbon, and the chromium content is 5 to 16 at%. The above-mentioned problems have been solved by providing a chromium-containing diamond-like carbon film.

  Further, since the chromium metal has good adhesion to the iron-based substrate, the sliding member using the chromium-containing diamond-like carbon film having such a low friction coefficient is used in the invention according to claim 2. An underlayer having a large amount of chromium component is formed on the surface, and an intermediate layer mainly composed of chromium and carbon having less chromium component or gradually decreasing than the underlayer is formed on the underlayer, and chromium is formed on the outermost layer from the uppermost layer of the intermediate layer. Provided is a sliding member coated with a chromium-containing diamond-like carbon film having a low content and a chromium content of 5 to 16 at%. Thereby, it can be set as the sliding member which ensures high adhesiveness and has a chromium containing diamond-like carbon film with a low friction coefficient in the uppermost layer. In particular, a base layer mainly composed of chromium metal is formed on an iron-based metal substrate, an intermediate layer having an increased amount of carbon than the base layer is formed on the top layer, and the chromium-containing DLC film is coated on the surface layer. preferable.

  According to the present invention, since the chromium content of the chromium-containing diamond-like carbon film whose main component is the chromium and carbon is 5 to 16 at%, the friction coefficient is 0.2. It is a chromium-containing diamond-like carbon film with a low friction coefficient that can achieve the following minimum values, and it can provide good sliding characteristics with low friction even under no lubrication or inferior lubrication, which is also very beneficial from the viewpoint of energy consumption. became.

  Further, each layer mainly composed of chromium and carbon is formed on the surface of the material to be coated so that the chromium component gradually decreases, and a chromium-containing diamond-like carbon film having a chromium content of 5 to 16 at% is formed on the outermost layer. Since the coated sliding member can be secured with high adhesion and toughness, particularly with respect to ferrous metals, it can be a sliding member having a low friction coefficient. Such a chromium-containing diamond-like carbon film can be formed by a low-temperature magnetron sputtering device, an ion plating device, or the like at a temperature of, for example, about 120 to 180 ° C., and more preferably 130 to 170 ° C. Lubricating and slidability are imparted to the surface of parts made of low-alloy steel such as those performed at 180 ° C or lower, and it can be used without frictional wear even in a non-lubricated or inferior-lubricated environment. Even if it exists, it became a thing with a low friction coefficient of surface coating, durability improvement, toughness increase, and adhesiveness with a base material.

  Embodiments of the present invention will be described. A chromium target was attached to each target holder of a magnetron sputtering apparatus capable of mounting four targets, and the present invention was carried out. The magnetron sputtering apparatus is a general one and will not be described. As the test piece, a SKH51 φ20 × 5t disc was used. Prior to DLC coating, the test piece was placed in the magnetron sputtering apparatus chamber with the bottom facing down, the chamber was sealed, and the inside of the chamber was heated at 160 ° C. for degassing. Next, Ar gas of 30 cc / min was introduced into the chamber, and the test specimen surface layer was sputter cleaned with Ar ions.

  Thereafter, with the Ar gas introduced, a current of 2.0 A was passed through each sputter target to sputter evaporate chromium metal, and the upper and side surfaces of the test piece were coated with a chromium film of about 0.2 μm. Subsequently, the amount of acetylene gas was gradually increased from 0 cc / min to 20 cc / min to form a chromium carbide (CrC) film as an intermediate layer. The thickness was 0.3 to 1.2 μm. If the thickness of the underlayer is too thin or too thick, the adhesion of the outermost chromium-containing diamond-like carbon film may be hindered or the film may be damaged. Further, a DLC film containing a predetermined amount of chromium was formed on the outermost layer. At this time, the amount of Cr evaporated, that is, the chromium content was adjusted to be gradually decreased by gradually decreasing the target current value passed through each target.

  The composition of the outermost layer of the chromium-containing DLC film thus produced was analyzed by ESCA (Electron Spectroscopy for Chemical Analysis), and the chromium content was measured. Furthermore, the friction coefficient of the DLC film was measured using a pin-on-disk friction wear test apparatus with respect to the chromium-containing diamond-like carbon film, particularly the friction coefficient with respect to the chromium content of the outermost layer. Table 1 shows the measurement results of the chromium content and the friction coefficient. As a comparative example, a DLC film containing a chromium content outside the range of the present invention was prepared, and the results are shown in Table 1 as a comparative example.

  What illustrated Table 1 is shown in FIG. C1-C10 of FIG. 1 is a figure which shows the relationship between the content rate of chromium of this invention and a comparative example, and a friction coefficient. As shown in Table 1 and FIG. 1, although the C4 to C8 chromium content of the present invention is 6, 10, 14, and 16 at%, the friction coefficient is 0.14 to 0.18 and 0.2 or less. On the other hand, when the chromium contents in Comparative Examples C1 to C3 and C9 to C10 are 0, 2, 20, and 23 at%, the friction coefficients are 0.24 to 0.41 and more than 0.2. Yes.

  Furthermore, it turns out that the minimum value is included in the case of the present invention C4 to C8. In the case of tungsten shown in W1 to W4 in FIG. 1 described above, this is greatly different from the fact that the friction coefficient increases in proportion to the tungsten content. When the metal content is zero, the friction coefficient values of Cr and W are slightly different, but this is considered to be due to the film thickness, the component state of the lower layer portion on the substrate side, the presence or absence of impurities, and the like. However, it can be seen that the characteristics are completely different between W and Cr.

  Further, the durability of the above film was investigated by a pin-on-disk friction and wear test. The result is shown in FIG. FIG. 2 is a diagram showing the change of the friction coefficient with the passage of the friction test time (minutes). As can be seen from FIG. 2, Comparative Example C1 has an initial coefficient of friction of about 0.2, but the coefficient of friction gradually increases, and the maximum coefficient of friction becomes 0.3. The coefficient of friction was 0.25, and the coefficient of friction once decreased to 0.2, but then gradually increased to 0.3 and peeled off after 30 minutes. In Comparative Example C10, the coefficient of friction suddenly increased from 0.4 to 0. It rose to 6 and peeled after 8 minutes.

  On the other hand, C5 (Cr content 10 at%) of the present invention and C7 (Cr content 14 at%) of the present invention both have an initial friction coefficient of 0.2 and an early friction coefficient of about 0.15, and are stable thereafter. And showed no problem for more than 40 minutes. Further, the comparative examples show different tendencies in the change of the friction coefficient, whereas the products C5 and C7 of the present invention show almost the same and stable tendency. Thus, the present invention provides a chromium-containing diamond-like carbon film that has low friction, is stable for a long time, and is durable. In addition, even if it is a case where it does not reach 40 minutes when a friction coefficient becomes abnormally high, the test is stopped.

  3 is a partially enlarged photograph of the friction track of the present invention C7, C5 after the pin-on-disk frictional wear test (40 minutes) described above, and FIG. 4 is a comparative example of the friction track of C1, C3, C10. As shown in FIG. 3, the C7 of the present invention having the smallest friction coefficient has almost no flaw and the wear width of the friction track is small. Further, since the DLC film of the present invention is a low coefficient of friction film after a predetermined time (40 minutes) friction test, the wear of the film does not progress. On the other hand, as shown in FIG. 4, the comparative example C1 has a large friction coefficient, and the width of the friction track is wide even in the friction test time of the same time (40 minutes) as that of the present invention. Further, in the case of Comparative Example C3, the DLC film is fragile, and a part of the breakage is observed. In Comparative Example C10, the friction coefficient is the highest, the width of the friction track is the widest, burning occurs, the DLC film on the surface is scraped off, and the underlayer is completely exposed. Thus, the abrasion amount of the friction track of the disk was also less for the coating of the present invention than for the coating of the comparative example.

  In this embodiment, the magnetron sputtering method is used. However, the same result can be obtained if a similar film can be obtained, such as an ion plating method. Further, although the intermediate layer has two layers, it may be formed so that the chromium content gradually changes.

It is a figure which shows the relationship between the chromium content rate of a chromium containing diamond-like carbon membrane | film | coat of this invention and a comparative example, and a friction coefficient, and the relationship between the tungsten content rate of a tungsten containing diamond-like carbon membrane | film | coat, and a friction coefficient. It is the figure which showed the change of the friction coefficient with progress of the friction test time (40 minutes) of the chromium-containing diamond-like carbon film of this invention and the comparative example which were tested by the pin-on-disk friction wear test. It is the elements on larger scale of the friction track of this invention C7 and C5 after a pin-on-disk friction abrasion test (40 minutes). It is the elements on larger scale of the friction track of the comparative examples C1, C3, and C10 after a pin-on-disk friction abrasion test (40 minutes).

Claims (2)

Chromium-containing diamond-like carbon, wherein the coating on the outermost surface of the material to be coated is a chromium-containing diamond-like carbon film mainly composed of chromium and carbon, and the chromium content is 5 to 16 at% film. An underlayer having a high chromium component is formed on the surface of the material to be coated, and an intermediate layer mainly composed of chromium and carbon having a chromium component less than or gradually decreasing than the underlayer is formed on the underlayer, and the intermediate layer is formed on the outermost layer. The sliding member characterized by covering the chromium-containing diamond-like carbon film according to claim 1 with a chromium content less than that of the uppermost layer.