JP2006152422A - Boron-doped diamond film, and diamond-coated cutting tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve oxidation resistance and lubricity of a diamond film. <P>SOLUTION: Since boron is doped in a boron-doped diamond film 20 at the rate of 0.5-1.0 atom%, a layer of an oxide of boron (for example, B<SB>2</SB>O<SB>3</SB>) is deposited on the surface of the diamond film 20 when being oxidized, the progress of oxidation into the film is suppressed by the layer of the oxide, the oxidation resistance of the film 20 is improved, the friction coefficient is reduced and the lubricity is improved. Early wear or peeling of the film caused by the oxidation is suppressed and excellent durability can be obtained even when cutting a composite material containing an iron material or cutting a heat-resistant alloy such as a titanium alloy with the cutting point being hot. Further, since the lubricity is also improved, heat generation caused by the friction is suppressed, the durability of the film 20 is improved in this aspect, and the quality of a worked surface of a work is improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diamond film coated on a predetermined member such as a processing tool, and more particularly to a technique for improving oxidation resistance and lubricity.

A diamond coating tool in which a surface of a base material such as cemented carbide is coated with a diamond coating has been proposed as a cutting tool such as an end mill, a bite, a tap, a drill, or other processing tools. The tools described in Patent Document 1 and Patent Document 2 are an example, and such a diamond-coated tool has a very high hardness and provides excellent wear resistance and welding resistance. In Patent Document 3 and Patent Document 4, in order to give conductivity or improve oxidation resistance, when diamond is crystal-grown by a microwave plasma CVD (chemical vapor deposition) method or the like, A technique for doping boron (boron; B) is described.
Japanese Patent No. 2519037 JP 2002-79406 A JP 2004-193522 A Japanese Patent Laid-Open No. 10-146703

  However, for diamond coatings coated on the surface of tool base materials, etc., boron doping has not yet been proposed, and since oxidation resistance is low and lubricity is poor, composite materials including iron-based materials are not suitable. In cutting or cutting of a heat-resistant alloy such as a titanium alloy that has a high cutting point, the diamond coating may wear early due to oxidation, and sufficient durability may not be obtained. In addition, the heat generation due to friction may reduce the durability, and the work surface quality of the work material may be impaired.

  The present invention has been made against the background described above, and its object is to improve the oxidation resistance and lubricity of a diamond film coated on the surface of a predetermined member.

  In order to achieve such an object, the first invention is a diamond film coated on the surface of a predetermined member, and is characterized in that boron is doped.

  The second invention is characterized in that in the boron-doped diamond film of the first invention, the boron is doped at a ratio of 0.05 to 2.0 atomic%.

  The third invention relates to a diamond coated processing tool in which a surface of a predetermined tool base material is coated with a diamond coating, and the diamond coating is applied to the surface of a processing portion for performing a predetermined processing as described in the first or second invention. A boron-doped diamond film is coated.

  Boron-doped diamond is a p-type semiconductor having positively charged holes in which some carbon atoms are replaced by boron atoms. Further, the atomic% of boron is the ratio of the number of atoms replaced with boron atoms, and is examined by, for example, secondary ion mass spectrometry.

In such a boron-doped diamond film, when the surface is oxidized, a layer of boron oxide (for example, B ₂ O ₃ ) is formed on the surface, so that the oxide layer oxidizes the inside of the film. Is suppressed, the oxidation resistance of the coating is improved, and the coefficient of friction is reduced to improve the lubricity. As a result, even in cutting of composite materials including iron-based materials and cutting of heat-resistant alloys such as titanium alloys with high cutting points, early wear and delamination of the coating due to oxidation are suppressed, resulting in excellent durability. Sex can be obtained. In addition, since the lubricity is improved, heat generation due to friction is suppressed. In this respect, the durability of the coating is improved and the work surface quality of the work material is improved.

  In the diamond coating tool of the third invention in which the boron-doped diamond film is coated on the surface of the processed portion, substantially the same effect as described above can be obtained.

  The boron-doped diamond coating of the present invention is preferably applied to a processing tool such as a cutting tool that requires wear resistance, oxidation resistance, and lubricity, that is, a diamond coating processing tool. For example, it can be used as a processing tool.

  In the case of a diamond-coated tool, a superhard tool material such as cemented carbide is preferably used as a tool base material to be coated with a boron-doped diamond coating, but other tool materials such as high-speed tool steel may also be used. it can. In order to improve the adhesion, a predetermined pretreatment such as roughening the surface of the tool base material or providing another coating as a base can be performed.

  Further, when the film thickness of the boron-doped diamond film is less than 5 μm, sufficient wear resistance cannot be obtained. On the other hand, if it exceeds 25 μm, it is easy to peel off, and therefore it is preferably in the range of 5 to 25 μm, preferably about 10 to 20 μm. Is appropriate. When applied to other than the processing tool, it is appropriately determined according to the material and purpose of the coating target. The boron-doped diamond film and a hard film made of an intermetallic compound such as TiAlN, or other films can be alternately laminated, and it is sufficient that the boron-doped diamond film is provided at least on the uppermost part.

  A CVD method is suitably used for coating the boron-doped diamond film, and a microwave plasma CVD method is particularly desirable, but other CVD methods such as a hot filament CVD method and a high-frequency plasma CVD method can also be used. Regarding boron doping techniques, various techniques conventionally known as boron doping techniques for diamond, such as those described in Patent Document 3 and Patent Document 4, can be employed.

  The boron-doped diamond film is formed by, for example, a nucleation process and a crystal growth process, and can be formed into a target film thickness by performing the crystal growth for a predetermined time. For example, as described in Patent Document 2, By repeating the generation step and the crystal growth step, it is possible to form a boron-doped diamond film having a microcrystal and a multilayer structure.

  If the doping amount (content) of boron is less than 0.05 atomic%, the effect of improving oxidation resistance and lubricity cannot be obtained sufficiently. On the other hand, if it exceeds 2.0 atomic%, the original diamond coating has the resistance to resistance. Since properties such as abrasion are impaired, the range of 0.05 to 2.0 atomic% is appropriate, and about 0.5 to 1.0 atomic% is desirable, but doping more than 2.0 atomic% Is also possible. This doping amount does not necessarily have to be constant throughout the boron-doped diamond coating, for example, the doping amount is increased continuously or stepwise with the crystal growth of the diamond coating so that the doping amount increases as the surface increases. Various modes are possible, such as laminating many layers and few layers alternately to form a multilayer structure.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an end mill 10 as a diamond coating tool to which the present invention is applied, specifically, a diamond coated cutting tool. FIG. 1 (a) is a front view seen from a direction perpendicular to the axis, and FIG. FIG. 4 is a cross-sectional view of the vicinity of the surface of the blade portion 14. The end mill 10 is a four-blade square end mill, and the tool base 12 is made of cemented carbide, and the tool base 12 is provided with a shank and a blade 14 integrally in the axial direction. Yes. The blade portion 14 corresponds to a processed portion, and includes an outer peripheral blade 16 and a bottom blade 18 as cutting edges, and the surface of the blade portion 14 is doped with boron at a rate of 0.5 to 1.0 atomic%. A boron-doped diamond coating 20 (hereinafter simply referred to as diamond coating 20) is coated with a film thickness of about 20 μm. The shaded area in FIG. 1A represents the diamond film 20 coated on the surface of the tool base material 12.

  In order to improve the adhesion of the diamond coating 20 after the end mill 10 forms the tool base material 12 having the outer peripheral edge 16 and the bottom edge 18 as a cutting edge by grinding the cemented carbide or the like, The surface of the blade portion 14 of the base material 12 is roughened. As the surface roughening treatment, for example, chemical erosion such as electrolytic polishing or sand blasting with an abrasive such as SiC is suitable. Then, using the microwave plasma CVD apparatus 30 of FIG. 2, diamond particles are doped on the surface of the roughened blade portion 14 while doping boron with a vapor phase synthesis method, specifically, a microwave plasma CVD method. The diamond film 20 is formed and grown.

  The microwave plasma CVD apparatus 30 of FIG. 2 includes a reaction furnace 32, a microwave generator 34, a source gas supply device 36, a vacuum pump 38, and an electromagnetic coil 40. A table 42 is provided in the cylindrical reaction furnace 32, and a plurality of tool base materials 12 to be coated with the diamond coating 20 are supported by a work support tool 44, and each blade 14 is disposed in an upward posture. It is like that. The microwave generator 34 is a device that generates a microwave of, for example, 2.45 GHz, and the tool base material 12 is heated by introducing the microwave into the reaction furnace 32, and the microwave generator 34. The heating temperature is adjusted by controlling the electric power.

The source gas supply device 36 is for supplying source gases such as methane (CH ₄ ), hydrogen (H ₂ ), and carbon monoxide (CO) into the reaction furnace 32, and controls the gas cylinders and flow rates thereof. In this embodiment, in order to dope boron, for example, a liquid obtained by dissolving boron oxide in methanol can be mixed with the raw material gas and supplied into the reaction furnace 32. It is like that. The vacuum pump 38 is for sucking and depressurizing the gas in the reaction furnace 32, so that the pressure value in the reaction furnace 32 detected by the pressure gauge 46 becomes a predetermined pressure value determined in advance. The motor current of the vacuum pump 38 is feedback controlled. The electromagnetic coil 40 is arranged in an annular shape on the outer peripheral side of the reaction furnace 32 so as to surround the inside of the reaction furnace 32.

And the coating process of the diamond film 20 consists of a nucleation process and a crystal growth process, and while adjusting the flow volume of methane and hydrogen in the nucleation process, the surface temperature of the tool base material 12 is 700 degreeC-900 degreeC. The microwave generator 34 is adjusted so that the set temperature is determined within the range, and the gas pressure in the reaction furnace 32 is determined within the range of 2.7 × 10 ² Pa to 2.7 × 10 ³ Pa. The vacuum pump 38 is operated so as to reach the set pressure, and this state is continued for a predetermined time. As a result, a nucleus layer serving as a starting point for crystal growth of diamond is attached to the surface of the tool base material 12. In the crystal growth process, for example, the flow rate of methane and hydrogen is adjusted so that the concentration of methane is set within a range of 1% to 4%, and the surface temperature of the tool base 12 is 800 ° C. 900 to adjust the microwave generator 34 so as to set the temperature defined in the range of ° C., ranges gas pressure in the reaction furnace 32 is ^{1.3 × 10 3 Pa~6.7 × 10 3} Pa Then, the vacuum pump 38 is operated so as to have a set pressure determined in the above, and this state is continued for a predetermined time to grow diamond crystals starting from the nuclei, whereby a diamond film 20 having a substantially complete diamond crystal structure is formed. It is formed with a predetermined film thickness.

  Further, when supplying the raw material gas such as hydrogen during the coating process of the diamond film 20, a liquid obtained by dissolving the boron oxide in methanol is mixed with the raw material gas and supplied into the reaction furnace 32 at a predetermined flow rate. Then, boron is doped into the diamond coating 20 at a ratio of 0.5 to 1.0 atomic%. The doping amount of boron can be adjusted by changing the supply flow rate of the liquid in which boron oxide is dissolved.

In the end mill 10 of this embodiment, since the diamond coating 20 is doped with boron in a proportion of 0.5 to 1.0 atomic%, the surface of the diamond coating 20 is subjected to oxidation. A layer of boron oxide (for example, B ₂ O ₃ ) is formed, and the progress of oxidation inside the coating is suppressed by the oxide layer, so that the oxidation resistance of the diamond coating 20 is improved and the friction coefficient is increased. Smaller and better lubricity. As a result, even in cutting of composite materials including iron-based materials and cutting of heat-resistant alloys such as titanium alloys that have high cutting points, early wear and delamination of the diamond coating 20 due to oxidation are suppressed and excellent. Durability will be obtained. Further, since the lubricity is improved, heat generation due to friction is suppressed, and in this respect as well, the durability of the diamond coating 20 is improved and the work surface quality of the work material is improved.

  Incidentally, FIG. 3 shows a two-blade square end mill in which a diamond film doped with boron at a ratio of 0.5 to 1.0 atomic% is coated with a film thickness of 20 μm. When an oxidation test was carried out using a conventional product in which a diamond film without boron doping was coated with a film thickness of 20 μm, the results shown in FIG. 4 were obtained. In the oxidation test, the sample was heated to 750 ° C. at a heating rate of 15 ° C./min, held at 750 ° C. for 30 minutes, and then naturally cooled to room temperature to examine the state of the coating (disappeared area). The end mill on the left side of FIG. 4 is a conventional product without boron dope, and the diamond coating disappears by about 100% due to oxidation or peeling due to a difference in thermal expansion from the tool base material. Only about 10% has disappeared and most of it remains. The black part of FIG. 4 is a diamond film, and in the product of the present invention, the diamond film remained with a film thickness of 17 to 18 μm even at the bottom edge part at the tip.

  FIG. 5 shows that a diamond film doped with boron at a ratio of 0.5 to 1.0 atomic% and a diamond film without boron dope are each peeled off from a base material, prepared as a single film, and measured before and after heating to oxidize. It is the result of having investigated the mass loss (%) by. The test was heated to each test temperature (700 ° C., 725 ° C., 750 ° C., 775 ° C., 800 ° C.) at a rate of temperature increase of 15 ° C./min, held at that test temperature for 30 minutes, and then naturally cooled to room temperature. The change in mass was measured. As is apparent from FIG. 5, the oxidation starts at about 700 ° C. without boron doping, whereas the oxidation starts at about 775 ° C. with boron doping, and a difference of about 75 ° C. is recognized.

  In FIG. 4 in which the oxidation test was performed at 750 ° C., approximately 100% of the film disappeared in the comparative product without boron doping, and about 10% of the film disappeared even in the boron-doped product of the present invention. The film disappears more than the above test results, but in the case of FIG. 4, it is considered that peeling due to the difference in thermal expansion from the tool base material has an effect.

  FIG. 6 shows a case where the friction coefficient of a pin coated with a diamond film doped with boron in a proportion of 0.5 to 1.0 atomic% and a pin coated with a diamond film not doped with boron were examined. , (A) is the test condition, and (b) is the test result. As is apparent from the test results, the friction coefficient of the boron-doped diamond coating was about 2/3 compared to the diamond coating without boron doping.

FIG. 7 shows a two-blade square end mill of the present invention in which a diamond film doped with boron in a proportion of 0.5 to 1.0 atomic% is coated to a thickness of 20 μm, and a diamond film without boron doping is 20 μm. In the case where a durability test of a cutting operation was performed on gray cast iron (FC250) using a conventional product I coated with a film thickness of II and a conventional product II coated with a TiAlN film, (a) is a machining condition, b) is the test result. As is apparent from the test results, the boron-doped diamond coating can provide excellent durability as well as a TiAlN coating and a diamond coating without boron doping.

  FIG. 8 shows the product of the present invention in which a diamond film doped with boron at a ratio of 0.5 to 1.0 atomic% is coated with a film thickness of 20 μm, and a diamond film without boron doping is 20 μm for a two-blade ball end mill. When a durability test of cutting work is performed on spheroidal graphite cast iron (FCD500) using a conventional product coated with a film thickness of (a), (a) shows the processing conditions, and (b) shows the test results. As is apparent from the test results, the boron-doped diamond coating provides superior durability compared to the diamond coating without boron doping.

  FIG. 9 shows a product of the present invention in which a diamond film doped with boron in a proportion of 0.5 to 1.0 atomic% is coated at a film thickness of 20 μm and a diamond film without boron doping of 20 μm for a two-blade square end mill. When a durability test of cutting is performed on a carbon steel for mechanical structure (S50C) using a conventional product coated with a film thickness of (a), (a) is a processing condition, and (b) is a test result. Also in this case, the boron-doped diamond coating can provide superior durability as compared to the diamond coating without boron doping.

  As mentioned above, although the Example of this invention was described in detail based on drawing, this is an embodiment to the last, and this invention implements in the aspect which added various change and improvement based on the knowledge of those skilled in the art. Can do.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the end mill which is one Example of this invention, (a) is the front view seen from the direction orthogonal to an axial center, (b) is sectional drawing of the surface vicinity of a blade part. It is a schematic block diagram explaining an example of the microwave plasma CVD apparatus which coats a diamond film. It is a figure which shows the external appearance photograph of the 2 end blade square end mill coated with the boron dope diamond film. It is a figure which shows the external appearance photograph (right side) after performing the oxidation test to the tool of FIG. 3 compared with the case where the diamond film without boron dope is coated (left side). It is a figure which shows the result of having investigated the difference (change ratio of mass) of the diamond film by the presence or absence of boron dope at several test temperature. It is a figure explaining the result of having investigated the difference in the friction coefficient of the diamond film by the presence or absence of boron dope, (a) is a test method, (b) is a test result. It is a figure explaining the result which investigated the difference in durability of a boron dope diamond film and the conventional film about gray cast iron, (a) is a test method, (b) is a test result. It is a figure explaining the result which investigated the difference in durability of a boron dope diamond film and a diamond film without boron dope about spheroidal graphite cast iron, (a) is a test method, (b) is a test result. It is a figure explaining the result of investigating the difference in durability between a boron-doped diamond coating and a diamond coating without boron doping for carbon steel for mechanical structure, (a) is a test method, and (b) is a test result.

Explanation of symbols

  10: End mill (diamond coating processing tool) 12: Tool base material 14: Blade portion (processing portion) 20: Boron-doped diamond coating

Claims (3)

A diamond coating coated on the surface of a given member,
A boron-doped diamond film characterized by being doped with boron.   The boron-doped diamond film according to claim 1, wherein the boron is doped at a ratio of 0.05 to 2.0 atomic%.   A diamond-coated machining tool, wherein the boron-doped diamond coating according to claim 1 or 2 is coated on a surface of a processing portion for performing predetermined processing.

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