JP5207116B2 - Hard coating with excellent lubrication characteristics and metal plastic working tools - Google Patents

Description

  The present invention relates to a hard film excellent in lubricity with respect to a functional film coated on a work surface in contact with other materials, for example, in a jig such as a mold. And it is related with the tool for metal plastic working formed by coat | covering these hard films on a working surface.

  Conventionally, for example, in the case of jigs and tools used for metal plastic working, the work surface slides violently with the workpiece, causing significant wear on the surface. For this reason, a measure for increasing the wear resistance is widely performed by applying some surface treatment to the work surface of the jig. Of these, coating (coating) technology makes a great contribution to improving the service life of molds and cutting tools because a hard film having a Vickers hardness exceeding 1000 HV can be formed on the substrate surface with good adhesion.

However, in such jigs and tools, not only the wear resistance of the surface is improved, but also the work material does not cause adhesion, particularly as in the working environment of the plastic working tool described above. It is very effective to improve the lubrication characteristics. In this problem, for example, titanium (Ti) carbide is actively used as a film on the surface of jigs and tools because it has both high wear resistance and sliding properties. The titanium carbide film is formed mainly by a chemical vapor deposition method (CVD method) (Non-Patent Document 1), but otherwise, an arc ion plating method which is a kind of physical vapor deposition method (PVD method). (Non-patent Document 2). In addition to vanadium carbide (VC) films, in addition to the conventional TD treatment, forming means by the arc ion plating method has been proposed (Patent Document 1).
Techno Knowledge Network (2006) [Technical information site operated by National Institute of Advanced Industrial Science and Technology] (Internet <URL: http://www.techno-qanda.net/dsweb/Get/Document-5294>) Toyo Curing Website (2003) (Internet <URL: http://www.toyokoka.com/bumon/arkion/arkion.htm>) JP 2002-371352 A

  The conventional hard coatings proposed in Non-Patent Documents 1 and 2 have both high wear resistance and sliding characteristics. However, in the recent manufacturing industry in which reduction of manufacturing cost is strongly required for cost reduction, a higher level of film characteristics has been required when using the tool. In particular, increasing the lubrication characteristics of the coating and suppressing the adhesion of the workpiece are major issues for further increasing the tool life.

  Therefore, the present invention provides a hard coating having higher lubrication characteristics and a metal plastic working tool in which the hard coating is coated on the work surface, which cannot be obtained by a conventional method.

  The inventors of the present invention have made detailed studies in order to achieve a hard film exhibiting higher lubrication characteristics than the current situation. As a result, it was found that even with a hard film that has been proposed in the past, the lubricating properties of the film can be drastically improved by having a certain amount of carbon-carbon bond structure present in the film. . And in addition to this innovative knowledge, the present invention was reached by investigating the effect of the carbon-carbon bond distribution state present in the film.

That is, the present invention provides a hard film is coated on the substrate surface in contact with another material, the surface of the hard coating present below 3 0 atomic% on 10 atomic% or more carbon atoms having carbon-carbon bonds, and the The ratio of carbon atoms is a hard film excellent in lubrication characteristics characterized by gradually decreasing from the surface of the hard film toward the surface of the substrate. This carbon atom preferably includes both a carbon atom having a sp ² crystal structure and a carbon atom having a sp ³ crystal structure. At this time, the type of the hard coating is preferably a metal carbide or metal carbonitride, and further, the amount of carbon forming these is preferably 20 atomic% or more. The metal carbide or metal carbonitride is more preferably titanium carbide or titanium carbonitride. In addition, it is preferable that the oxygen concentration of the hard coating is 15 atomic% or less.

  Further, it is preferable to form a film made of metal nitride, specifically titanium nitride, between the surface of the substrate and the hard film. And this invention is a metal plastic working tool characterized by coat | covering these hard films on a working surface.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the hard film which has a lubrication characteristic higher than before, and the tool for metal plastic working which applied it.

  The greatest feature of the present invention is that the lubricating properties of the coating can be dramatically improved by making the hard coating contain carbon atoms having carbon-carbon bonds. And in the thickness direction of the hard coating, it was also found that the concentration distribution of carbon atoms having a bond between carbons is important for exerting the function as the total hard coating. is there.

First, the structure of the “carbon atom having a carbon-carbon bond” to be introduced into the hard film of the present invention is a so-called diamond or graphite (sp ² and / or sp ³ bond structure of carbon atoms). Graphite) or DLC (Diamond Like Carbon). And while sp ³ structure diamond is excellent in high hardness, sp ² structure graphite is particularly excellent in lubricity, so that carbon atoms constituting these bond structures can be replaced with, for example, conventional metal carbide / nitride / If dispersed in a modified film such as carbonitride, higher lubricating properties can be added to the basic properties. Among these, a metal carbide film such as titanium carbide (TiC) is preferable as a form capable of achieving excellent lubrication characteristics with a high hardness as high as 3000 HV.

In the present invention, it is necessary for carbon atoms having carbon-carbon bonds to be present at 10 atomic% or more on the surface of the hard coating in order to obtain sufficient lubrication characteristics. As the range that does not impair the properties of the base film itself and 30 atomic% or less. In this qualitative and quantitative measurement, for example, analysis of the film surface by using Raman spectroscopy and X-ray photoelectron spectroscopy (hereinafter referred to as XPS) in combination can be used. In other words, at each analytical spectrum peak that does not appear in a normal hard coating, the presence of sp ² or sp ³ carbon-carbon bond structures can be accurately grasped by Raman spectroscopy. Here, in the present invention, the crystal structure of both sp ² and sp ³ appears in this analytical spectrum peak, that is, the sp ² structure out of the total amount of carbon atoms having a carbon-carbon bond. It is desirable that both graphite and sp ³ diamond are included, or that DLC having both sp ² and sp ³ structures is included.

And after confirming the presence of the carbon atom of the said structure, what is necessary is just to quantify the carbon atom amount which has the carbon-carbon bond which occupies in a film | membrane from the XPS spectrum applicable to the bond energy. Here, in performing XPS, it is considered that the surface of the hard coating is not a little contaminated. Therefore, it involves an operation of exposing the clean surface by sputtering in advance as long as the surface information is not impaired. desirable. In the present invention, the surface dug down by sputtering for 10 minutes on the basis of sputtering of 1 nm / min with a high-purity SiO ₂ standard sample can be used as the “hard film surface”.

  Furthermore, what is characteristic of the present invention is the concentration distribution of carbon atoms having carbon-carbon bonds as described above over the thickness direction of the hard coating. In other words, if the hard coating contains too many carbon atoms with carbon-carbon bonds, the residual compressive stress inside the coating increases and the adhesion of the hard coating is increased. Decreases. However, if the number of carbon atoms contained in the hard coating is decreased in order to improve the adhesion of the hard coating, the lubrication characteristics are inferior on the surface (working surface) side of the hard coating. Therefore, by gradually decreasing the amount of carbon atoms having carbon-carbon bonds from the surface side of the hard coating to the substrate side, the sliding characteristics are improved on the surface side of the hard coating and the adhesion is good on the substrate side. A hard film can be formed.

Here, also in the qualitative and quantitative determination of the “state in which carbon atoms having carbon-carbon bonds are gradually decreasing” according to the present invention, as described above, it is necessary to follow the measuring procedure for the same carbon amount existing on the surface of the hard coating. Good. That is, the presence of the carbon-carbon bond structure of sp ² or sp ³ may be confirmed by Raman spectroscopy. First, in the “hard film surface” that was dug down by sputtering for 10 minutes on the basis of sputtering of 1 nm / min with a high-purity SiO ₂ standard sample, the surface was further dug down after quantifying the amount of carbon atoms by XPS. The same XPS analysis is performed in step 1, and this may be repeated appropriately. Then, in the present invention, measurement is performed on the sputtered surface from the outermost surface of the hard coating toward the substrate for 10 minutes and 100 minutes, and if it is confirmed that these two data are gradually reduced, the above-mentioned lubrication characteristics are obtained. The effect of coexistence and adhesion is fully exhibited. If the above-mentioned gradual decrease is confirmed on the 3rd, 10th, 100th and 200th sputter surfaces, it is more certain.

  In addition, if the basic material of the hard coating is a metal carbide or metal carbonitride as described above, it is excellent in various mechanical properties during use. Therefore, not only the lubricating properties but also the total required properties as a hard coating. Can exert sufficient effects. Specifically, a hard film in which the amount of carbon forming metal carbide or metal carbonitride occupies 20 atomic% or more is sufficient, but preferably 25 atomic% or more.

  And as a metal which comprises this carbide | carbonized_material or carbonitride, titanium is preferable. Titanium has a high ability to form carbides (carbonitrides), and the formed titanium carbides (TiC) and carbonitrides (TiCN) have very high hardness. Due to the presence of carbon atoms responsible for the carbon-carbon bond, a film having both lubricating properties and high hardness can be obtained. Among these, metal carbide (titanium carbide) is more preferable as a form capable of achieving excellent lubrication characteristics with high hardness as high as 3000 HV.

  If excessive oxygen is mixed in the hard film, it forms a large amount of metal oxide in the film and makes the film brittle. Therefore, in the present invention, it is desirable to regulate the oxygen concentration of the hard coating to 15 atomic% or less, including impurities.

  In the present invention, it is preferable to form an intermediate film made of a metal nitride between the substrate surface and the hard film from the viewpoint of further improving the adhesion between them. In this case, as the metal nitride, a nitride mainly composed of a metal element such as titanium or chromium can be applied. However, in consideration of its own hardness, titanium nitride is desirable. And about this, if a hard film | membrane is a metal carbide and metal carbonitride, it is preferable to match | combine with the metal element seed | species which comprises it for the further adhesive improvement.

  Furthermore, if titanium nitride is applied to the above intermediate film, it exhibits a special color called gold, so the hard film on it is coated with a film of a different color so that the hard film is used during use. Since the gold layer is exposed when the surface wears, the wear state (life) of the coating itself can be judged by color. For this reason, it is preferable to apply titanium nitride between the substrate surface and the hard coating. Of these, the combination of adopting silver-colored titanium carbide for the hard coating is more desirable for improving both the film characteristics and the color judgment ability.

  As a substrate for surface treatment, a plate-shaped test piece (width 15 mm × length 18 mm × thickness 2 mm) of JIS high-speed tool steel SKH51 adjusted to a hardness of 64 HRC and a disk-shaped test piece (diameter 20 mm × thickness 5 mm) ) Was prepared. The plate-shaped test piece is used for analyzing the coated film, and the disk-shaped test piece is used for evaluating the lubrication characteristics. In addition to these, a test piece (coated surface 30 mm × 30 mm) for evaluating the adhesion of the film was also prepared. And after carrying out mirror surface mechanical polishing of these planes, alkali ultrasonic cleaning was performed.

Next, a sample No. 1 in which these three kinds of substrates are combined as one set. 1 is heated and degassed in a vacuum at a temperature of 773 K and 1 × 10 ⁻³ Pa in an arc ion plating apparatus having a chamber volume of 1.4 m ³ (the insertion space for the processed product is 0.3 m ³ ). After that, cleaning with Ar plasma was performed at a temperature of 723K. Various reaction gases were introduced into the apparatus, arc discharge was generated on a pure Ti target, and coating was performed by arc ion plating under 723K. A bias voltage of −100 V is applied to the substrate during coating, and the thickness of the intermediate film, which is a titanium nitride formed directly on the substrate, is approximately 1 to 2 μm, and the titanium carbide is formed thereon. The coating time was adjusted so that the thickness of the hard film was about 2 to 3 μm. The coating conditions are shown in Table 1. As a reference sample, sample No. 1 in which a film was formed directly on the substrate by the CVD method. 2 and Sample No. 2 in which a film was formed directly on the substrate by the TD method. 3 is placed.

First, the structure was analyzed using the coating film formed on the surface of the plate-shaped test piece. First, the bonding structure of carbon existing on the surface of the film (the surface of the hard film in sample No. 1) was identified by Raman spectroscopy. The apparatus used was JEOL Ltd. model JRS-System2000. A high-purity Si standard sample is measured in advance, and the Raman peak intensity of Si appearing in a Raman shift of 520 cm ⁻¹ by a He—Ne laser (wavelength 633 nm) falls within the range of 70,000 to 80,000. After confirming this, the laser light output at that time is measured with 100% laser light, and the Raman shift range from 1000 cm ⁻¹ to 2000 cm ^{−1 is} scanned once over 40 seconds. did. As a result, sample no. In 1, both sp ² and sp ³ bond peaks indicating bonds between carbons appeared. Sample No. which is a reference sample. 2 and no. In No. 3, the peak itself indicating a bond between carbons did not appear.

Next, after confirming the result of the Raman spectroscopic analysis, the surface analysis by XPS of the coating film (hard film in sample No. 1) was subsequently performed. The apparatus used was AXIS-HS manufactured by Kratos Analytical Limited. Al was used for the X-ray source, the acceleration voltage was 15 kV, and the emission current was 7 mA. The measurement area is 0.5 mm × 0.2 mm, and the surface layer was dug down from the outermost layer for 10 minutes (about 10 nm; based on 1 nm / minute sputtering with a high-purity SiO ₂ standard sample) by sputtering immediately before the measurement. The site where impurities were removed was measured. And sample No. of this invention. With respect to 1, the measurement was also performed for each part dug down for 50 minutes, 100 minutes, 150 minutes, 200 minutes, and 300 minutes.

  The lubrication characteristics were evaluated by measuring the dynamic friction coefficient when the counterpart material was JIS bearing steel SUJ2, using a coating film on the surface of the disk-shaped test piece formed under the same conditions as those of the plate-shaped test piece. The test condition is a disk-shaped test piece using a ball-on-disk friction tester (Tribometer manufactured by CSM Instruments), pressing a SUJ2 ball (diameter 6 mm) against the coating film with a load of 2N at room temperature and in the air. Was rotated at a speed of 150 mm / sec. The test distance was 100 m, and the friction coefficient was the average of the values at the test distances of 10 m, 20 m, 30 m, 40 m, 50 m, 60 m, 70 m, 80 m, 90 m, and 100 m.

  Furthermore, the coating film on the surface of the adhesion evaluation test piece formed under the same conditions as described above was applied to the coated surface (30 mm × 30 mm) on the coated surface (30 mm × 30 mm) using a Rockwell hardness tester (Mitutoyo AR-10). An indentation was made, and the portion was observed with an optical microscope, and peeling generated around the indentation was evaluated based on the reference shown in FIG.

  Table 2 shows the composition (configuration), friction coefficient, and adhesion evaluation results of the hard film coated on each test piece. Regarding the amount of C in the table, C—O is a carbon atom bonded to O (oxygen), C—C is a carbon atom forming a bond between carbons forming the basis of the present invention, and C—Ti represents carbon atoms constituting metal Ti and carbide, respectively. Sample No. formed by CVD method and TD method was used. About 2 and 3, the carbon atom weight which has the coupling | bonding of carbon in the film | membrane surface (sputtering 10 minutes) is written in reference.

  Sample No. with a film formed by arc ion plating No. 1 has a sufficiently large number of carbon-carbon bonds existing on the hard coating surface located at the outermost surface, and a low coefficient of friction is obtained. The amount of carbon-carbon bonds decreases with an inclination toward the substrate, and an intermediate layer of titanium nitride is formed between the substrate and the substrate. Excellent adhesion.

  On the other hand, Sample No. which is a film formed by the CVD method. In addition to the fact that the carbon-carbon bond on the surface of the film 2 is small, sufficient adhesion cannot be obtained in the first place. And sample No. which is the film | membrane formed by TD method. 3 is a film mainly composed of V carbide, but in this case as well, the amount of carbon-carbon bonds on the surface of the film is small, and it is not obtained from sufficient lubrication characteristics.

  Next, a plate machining punch was prepared, and the sample No. Films were formed under the same coating conditions as those of Nos. 1 and 2, and life evaluation was performed by an actual mold test. As the punch base material, SKD11 (JIS-G-4404) whose hardness was adjusted to 58 HRC was used. The punch shape has a diameter of 75 mm and a height of 110 mm. In the test, a punch was set in a 500-ton press, and cold pressing was performed on a high-tensile steel plate (high tensile) having a tensile strength of 530 MPa and a thickness of 9.3 mm. Table 3 shows the life of each punch.

  The punch in which the hard coating of the present invention is applied to the work surface has a tool life improved by more than twice as compared with the punch to which the reference example is applied. Note that the punch to which the reference example was applied was seized early and reached the end of its life.

  As the substrate to be subjected to the surface treatment, a test piece consisting of a set of three types as used in Example 1 was prepared as Sample No. 4 was newly prepared.

These sample Nos. 4 is heated and degassed in a vacuum at a temperature of 773 K and 1 × 10 ⁻³ Pa in an arc ion plating apparatus having a chamber volume of 1.4 m ³ (the insertion space for the processed product is 0.3 m ³ ). After that, cleaning with Ar plasma was performed at a temperature of 723K. Then, a reactive gas was introduced into the apparatus, an arc discharge was generated on the pure Ti target, and coating was performed by arc ion plating under 723K. A bias voltage of −100 V was applied to the substrate during coating to form a hard film directly on the substrate. The coating time was adjusted so that the thickness of the hard film was about 2 to 3 μm. The coating conditions are shown in Table 4.

First, sample No. 1 was analyzed by Raman spectroscopy according to Example 1. Identification of the bonding structure of carbon existing on the surface of No. 4 hard coating was performed. As a result, both sp ² and sp ³ bond peaks indicating bonds between carbons appeared.

  Then, following the above, the surface analysis of the hard coating was also performed by XPS according to Example 1. Similarly, the lubrication characteristic evaluation by the measurement of the dynamic friction coefficient performed in Example 1 and the adhesion evaluation by the Rockwell indentation tester were also performed. Table 5 shows the composition (configuration) of the hard coating, the friction coefficient, and the evaluation results of the adhesion. Table 5 shows a sample No. which is a reference sample evaluated in Example 1. The results of 2 and 3 are also shown.

  Similar to Example 1, the sample No. 1 of the present invention in which a film was formed by arc ion plating. No. 4 has a sufficiently large number of carbon-carbon bonds existing on the surface of the hard film, and a low coefficient of friction is obtained. The amount of the carbon-carbon bond decreases with an inclination toward the substrate, and the adhesion to the substrate is excellent.

  INDUSTRIAL APPLICABILITY The present invention can be used for a work surface of a tool used for metal plastic working such as cold and warm forging and press working. Also, considering its sliding characteristics, it is for casting used in contact with molten metal, such as a die used for die casting and casting, or a die ring used for casting or a piston ring used for an injection machine for die casting. As a member, it can be diverted to the work surface. Further, as a tool other than the mold, it can be applied to a sliding part of a machine, a cutting blade, or the like.

It is a figure which shows the evaluation reference | standard of the peeling generation | occurrence | production situation of the adhesiveness evaluation test which applied the Rockwell hardness tester used in Example 1, 3. FIG. Invention Example No. 1 is a photomicrograph showing the results of an adhesion evaluation test 1 (state around a Rockwell indentation). Reference Example No. It is the microscope picture which showed the adhesive evaluation test result of 2 (situation around Rockwell impression). Reference Example No. 3 is a photomicrograph showing the results of 3 adhesion evaluation test results (situation around Rockwell indentation).

Claims (9)

In the hard film coated on the surface of the substrate in contact with the other material, the surface of the hard film has carbon atoms having carbon-carbon bonds of 10 atomic% to 30 atomic% , and the ratio of the carbon atoms is as follows: A hard film excellent in lubrication characteristics characterized by gradually decreasing from the surface of the hard film toward the surface of the substrate. ^2. The lubrication according to claim 1, wherein the carbon atom having a carbon-carbon bond includes both a carbon atom having a sp ² crystal structure and a carbon atom having a sp ³ crystal structure. Hard film with excellent characteristics. 3. The hard film having excellent lubricating properties according to claim 1, wherein the hard film is a metal carbide or a metal carbonitride. 4. The hard film having excellent lubrication characteristics according to claim 3 , wherein the amount of carbon forming the metal carbide or metal carbonitride is 20 atomic% or more. 5. The hard film having excellent lubricating properties according to claim 3 or 4 , wherein the metal carbide or metal carbonitride is titanium carbide or titanium carbonitride. Excellent hard film lubrication characteristics according to any one of claims 1 to 5, characterized in that the oxygen concentration is not more than 15 atomic%. Between the substrate surface and the hard coating, excellent hard film lubrication characteristics according to any one of claims 1 to 6, characterized in that to form a film comprising a metal nitride. 8. The hard film having excellent lubricating characteristics according to claim 7 , wherein the metal nitride is titanium nitride. Metal plastic working tool, characterized in that formed by coating on the working surface of the hard coating according to any one of claims 1 to 8.