JP2006150572A - Boron doped diamond coating film, and diamond coated cutting tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the oxidation resistance and the lubricity of a diamond coating film. <P>SOLUTION: Because the boron doped diamond coating film 20 is doped with 0.5 to 1.0 atm.% of boron, a layer of boron oxide (e.g., B<SB>2</SB>O<SB>3</SB>) is formed on the surface of the diamond coating film 20 when it has been oxidized. Because the progress of the oxidation into the inside of the coating film is suppressed by means of the layer of the boron oxide, the oxidation resistance of the coating film 20 is improved, and also the coefficient of friction of the coating film 20 is reduced and its lubricity is improved. Particularly, the diamond coating film 20 according to the present example is composed of fine crystal grains having a grain size smaller than 1 μm; therefore, the surface of the diamond coating film 20 is smoother than those of usual diamond coating films, and further the layer of boron oxide is formed on the surface of the diamond coating film 20. As a result, the coefficient of friction becomes furthermore small, and the excellent lubricity can be achieved. <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 the diamond coating.

  In order to achieve such an object, the first invention is a diamond film coated on the surface of a predetermined member, which is composed of microcrystalline diamond having a crystal grain size of 2 μm or less and doped with boron. It is characterized by being.

  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 microcrystalline 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. In particular, since diamond is microcrystalline in the present invention, the surface is smoother than that of a normal diamond coating, and a boron oxide layer is formed on the surface, so that the friction coefficient is further reduced. Excellent lubricity can be obtained. As a result, in the cutting of composite materials including iron-based materials and the cutting of heat-resistant alloys such as titanium alloys where the cutting point is high, early wear and delamination of the diamond coating due to oxidation are suppressed and excellent. Durability can be obtained. In addition, since the lubricity is improved, heat generation due to friction is suppressed. In this respect, the durability of the diamond 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 microcrystalline boron-doped diamond film can be formed by repeating a nucleation step and a crystal growth step as described in Patent Document 2, for example. The crystal grain size is 2 μm or less, preferably 1 μm or less. The crystal grain size is the maximum diameter in a direction perpendicular to the crystal growth direction, and the crystal grain size of all diamonds is preferably 2 μm or less, but at least 80 of the crystal grain size on the surface or a predetermined cross section. % Or more may be 2 μm or less. Further, if the length dimension in the crystal growth direction is 2 μm or less, the crystal grain size in the direction perpendicular to the crystal growth direction is generally 2 μm or less. Even if the dimension in the crystal growth direction is larger than 2 μm, the crystal grain size may be 2 μm or less.

  If the boron doping amount (content) is less than 0.05 atomic%, the effects of oxidation resistance and lubricity cannot be obtained sufficiently, while if it exceeds 2.0 atomic%, the wear resistance of the original diamond coating is present. In the range of 0.05 to 2.0 atomic% is preferable, and about 0.5 to 1.0 atomic% is preferable, but doping more than 2.0 atomic% may be performed. Is possible. This doping amount does not necessarily have to be constant throughout the boron-doped diamond film. For example, the doping amount is increased continuously or stepwise so that the doping amount is increased toward the surface, or a large number of layers and a few layers are alternated. Various forms are possible, such as laminating 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 processing portion, and includes an outer peripheral blade 16 and a bottom blade 18 as cutting blades, and the surface of the blade portion 14 forms a multilayer structure with microcrystals having a crystal grain size of 1 μm or less. In addition, a boron-doped diamond film 20 (hereinafter simply referred to as diamond film 20) doped with boron at a ratio of 0.5 to 1.0 atomic% 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.

As shown in FIG. 3, the coating process of the diamond film 20 using such a microwave plasma CVD apparatus 30 is performed including a step R1 of the nucleus deposition process and a step R2 of the crystal growth process. In the nuclear attachment step of Step R1, the flow rate of methane and hydrogen is adjusted so that the concentration of methane is set within a range of 10% to 30%, and the surface temperature of the tool base 12 is 700 ° C. The microwave generator 34 is adjusted so that the set temperature is set in a range of ˜900 ° C., and the gas pressure in the reaction furnace 32 is in a 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 determined in the above, and this state is continued for 0.1 to 2 hours. As a result, a nucleus layer serving as a starting point of diamond crystal growth is attached to the surface of the tool base material 12 or the surfaces of a large number of diamond crystals that have been crystal-grown by the crystal growth process in step R2.

In the crystal growth process of Step R2, 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 The vacuum pump 38 is operated so that the set pressure is set within the predetermined range, and the state is maintained for a predetermined time so that the crystal grain size of diamond is maintained at 1 μm or less, specifically, the diamond crystal. This is continued for a predetermined processing time shorter than a predetermined time for which the length (length dimension in the crystal growth direction) is 1 μm. That is, in the crystal growth process of this embodiment, if the length dimension in the crystal growth direction is 1 μm or less, the crystal grain size in a plane substantially perpendicular to the crystal growth direction is maintained at 1 μm or less.

  Then, in the next step R3, whether or not the film thickness of the diamond coating 20 crystal-grown on the surface of the tool base material 12 has reached a predetermined set film thickness (20 μm in this embodiment), For example, the determination is made based on the number of executions of step R2, and the above steps R1 and R2 are repeated until the set film thickness is reached. During the execution of Step R1, the crystal growth of diamond is stopped, and a new nucleus layer is formed on the crystal. In the subsequent crystal growth process (Step R2), the diamond crystal below the nucleus layer is formed. The diamond film 20 is not regrown but is newly grown from a new nucleus as a starting point, so that the diamond film 20 having a multi-crystal structure with a crystal grain size and a crystal length of both 1 μm or less is formed as a tool base material. 12 surfaces are coated.

  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. In particular, since the diamond coating 20 of the present embodiment is a microcrystal having a crystal grain size of 1 μm or less, the surface is smoother than that of a normal diamond coating, and a boron oxide layer is formed on the surface. As a result, the friction coefficient is further reduced and excellent lubricity is obtained. 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.

  4A is a boron-doped diamond film having a normal crystal grain size (coarse crystal), that is, diamond is grown until a predetermined film thickness is obtained by a single crystal growth process (step R2 in FIG. 3). FIG. 4 (b) is an electron micrograph of the surface of the diamond coating 20 of this example, and the difference in the crystal grain size of the diamond is clear.

  FIG. 5 shows the results of examining the surface roughness (contour curve) of the boron-doped diamond film having the same normal crystal grain size (coarse crystal) as in FIG. 4 and the diamond film 20 of this example. FIG. 5 (a) shows a case of a diamond film having a normal crystal grain size, and its maximum height Rz is 3.0 μm, while FIG. 5 (b) shows the product of the present invention and its maximum height. Rz is 0.7 μm, and it can be seen that an extremely smooth coating surface can be obtained. From this, it is estimated that the surface roughness of the work surface of the work material is greatly improved.

  FIG. 6 shows the durability of the cutting process on an aluminum alloy (ADC12) using a drill coated with the same diamond film as the diamond film 20 (product of the present invention) and a conventional product coated with a microcrystalline diamond film without boron dope. (A) shows the processing conditions and (b) shows the test results. As is apparent from the test results, the present invention product doped with boron can provide a durability approximately twice that of the conventional product without boron doping.

  FIG. 7 shows a diamond film having a normal crystal grain size (coarse crystal) without boron doping, a microcrystalline diamond film without boron doping, and a microcrystalline diamond film with boron doping formed under the same conditions as the diamond coating 20. When the respective friction coefficients were examined using coated pins, (a) is the test condition and (b) is the test result. As is apparent from the test results, the boron-doped microcrystalline diamond film has a lower friction coefficient than a coarse-crystal diamond film as well as a boron-doped microcrystalline diamond film. This is presumably because a boron oxide layer is formed on the surface of the diamond coating.

  FIG. 8 shows a diamond film having a normal crystal grain size (coarse crystal) prepared by doping boron at a ratio of 0.5 to 1.0 atomic% and non-boron-doped diamond film. It is the result of peeling off from the material and heating, measuring the mass before and after heating, and examining the mass loss (%) due to oxidation. 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. 8, 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. Although this test result relates to a diamond film having a normal crystal grain size (coarse crystal), the difference in oxidation resistance is considered to be due to the presence or absence of boron doping, so the same applies to the microcrystalline diamond of the present invention. It is estimated that the result of is obtained.

  FIG. 9 is an external view photograph of a two-blade square end mill coated with a diamond film having a normal crystal grain size (coarse crystal) doped with boron at a ratio of 0.5 to 1.0 atomic% in a film thickness of 20 μm. When an oxidation test was performed using this boron-doped product and a non-boron-doped product in which a diamond film having a normal crystal grain size (coarse crystal) without boron doping was coated with a film thickness of 20 μm, the results shown in FIG. 10 were obtained. 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. 10 is a non-boron-doped product, and the diamond film disappears by about 100% due to oxidation or peeling due to a difference in thermal expansion from the tool base material, whereas the right-side boron-doped product has a 10% Most of it remains, just disappearing. The black portion in FIG. 10 is the diamond coating, and in the boron-doped product, the diamond coating remained at a thickness of 17 to 18 μm even at the bottom edge portion at the tip. This case is also related to a diamond film having a normal crystal grain size (coarse crystal), but since the difference in oxidation resistance is considered to be due to the presence or absence of boron doping, the same result is obtained for the microcrystalline diamond of the present invention. Presumed to be obtained.

  In FIG. 8, at 750 ° C., the disappearance of the film is 0% for the boron-doped product, and the disappearance of the film is about 8 to 10% even for the non-boron-doped product. In FIG. 10, it is considered that peeling due to a difference in thermal expansion from the tool base material has an influence.

  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 flowchart explaining the procedure at the time of coating a microcrystal diamond film using the apparatus of FIG. It is a figure which compares and shows the electron micrograph of the surface of the diamond film of a normal crystal grain size (coarse crystal), and the electron micrograph of the surface of a microcrystal diamond film. It is a figure which compares and shows the surface roughness (contour curve) of the diamond film of a normal crystal grain diameter (coarse crystal), and the surface roughness (contour curve) of a microcrystal diamond film. It is a figure explaining the result of investigating the difference in durability of the diamond film by the presence or absence of boron dope, (a) is processing conditions, (b) is a test result. 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 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 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. 9 compared with the tool (left side) which coated the diamond film without boron dope.

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 comprising a microcrystalline diamond having a crystal grain size of 2 μm or less and 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%.   3. A diamond-coated machining tool, characterized in that the surface of a machined part to be subjected to predetermined machining is coated with the microcrystalline boron-doped diamond film according to claim 1 or 2.

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