JP5488878B2 - Hard carbon film coated cutting tool - Google Patents

Description

  The present invention relates to a hard carbon film-coated cutting tool, in particular, a high adhesion strength between a tool substrate made of a tungsten carbide base cemented carbide and a hard carbon film formed on the surface of the tool base. The present invention relates to a hard carbon film-coated cutting tool that exhibits excellent wear resistance over a long period of use by having excellent lubricity, slidability, and welding resistance.

Conventionally, a hard carbon film-coated tool in which a hard carbon film is coated on a tool base made of a tungsten carbide (hereinafter referred to as WC) base cemented carbide is known.
For example, according to Patent Document 1, a polycrystalline diamond or diamond-like carbon film having a self-shaped surface is formed as an innermost layer on the surface of a tool base, and an amorphous hard carbon film is coated as an outer layer to smooth the surface. Thus, a hard carbon film-coated tool having improved welding resistance and peel resistance in cutting of an Al alloy or the like is known.
According to Patent Document 2, diamond layers 5 having a small non-diamond carbon content and mixed layers 6 are alternately laminated on the surface of the tool base, thereby suppressing the epitaxial growth of diamond, such as an Al alloy or the like. A hard carbon film-coated tool in which the toughness, fracture resistance, and wear resistance of a diamond film in cutting is known.

Japanese Patent Publication No. 6-23431 JP-A-6-297207

  In recent years, the FA of cutting devices has been remarkably improved. On the other hand, there is a strong demand for labor saving and energy saving and further cost reduction for cutting processing, and accordingly, cutting conditions have become increasingly severe. The above-mentioned conventional hard carbon film-coated tool does not cause any special problems when used for cutting under normal conditions, but it has specific strength and specific rigidity compared to general metal materials. When used for cutting CFRP, which is excellent in cutting, and soft and highly weldable Al alloys, etc., the adhesion strength between the tool base and the hard carbon film is not satisfactory. In addition, CFRP is a composite material of carbon fiber and epoxy resin, so tool wear is severe. Also, Al alloys and the like have insufficient lubricity at the time of cutting, so they are welded to the cutting edge. There was a problem that it was easy to occur and the tool life was shortened.

  In view of the above, the present inventor has not only excellent adhesion strength to the tool base, but also lubricity, sliding, in cutting of difficult-to-cut materials such as CFRP or highly weldable Al alloy. As a result of earnest research to develop a hard carbon film coated tool that has excellent wear resistance and long-term use, the following knowledge about the laminated structure of hard carbon film Got.

FIG. 1 shows a schematic diagram of a side cross section of a hard carbon film coated tool of the present invention.
As a first layer of a hard carbon film having a laminated structure, a fine diamond layer having an average particle size of 0.1 μm or less and a film thickness of 0.5 to 6 μm is formed on the surface of a tool base made of a WC-based cemented carbide.
By adopting the fine diamond layer as the first layer of the hard carbon film, the difference in thermal expansion between the WC-based cemented carbide alloy and the hard carbon film generated during the formation of the hard carbon film is reduced. Thereby, it aims at minimizing hard carbon film peeling at the WC base cemented carbide interface.
Pure diamond has a very low coefficient of thermal expansion, 1.1 (× 10 ⁻⁶ / K) at 100 to 1000 ° C. However, when a non-diamond component such as a graphite component is mixed in this, the coefficient of thermal expansion gradually increases.
FIG. 3 shows the results of Raman spectroscopic analysis using an Ar laser with a wavelength of 512 nm.
In the present fine diamond film forming method, as shown in the Raman spectroscopic analysis result of FIG. 3A, the peak of 1140 (cm ⁻¹ ) indicating that a fine diamond is formed and a crystal having many defects. A peak at 1350 (cm ⁻¹ ) is detected. Since the peak at 1350 (cm ⁻¹ ) is derived from a defect, it indicates that amorphous carbon or nanoparticles having low crystallinity are present.
As described above, this fine diamond film is a film containing a non-diamond component in its crystal grain boundary, and shows a higher thermal expansion coefficient than that of pure diamond.
Thereby, the difference in thermal expansion between the WC-based cemented carbide substrate and the hard carbon film is reduced, and it is possible to reduce the peeling between the WC-based cemented carbide and the hard carbon film due to the difference in thermal expansion.

The diamond film with better crystallinity has better wear resistance, but the self-formation has developed, so the contact area with the work material will be reduced, and on the contrary, the wear resistance will be lowered and the finished surface accuracy will also be improved Since it deteriorates, it is necessary to form a DLC film having excellent surface smoothness and lubricity as the outermost layer of the hard carbon film.
In this case, if the film directly under the DLC film is a crystalline diamond film, the DLC film traces the self-shaped shape of the crystalline diamond film immediately below, so a fine diamond layer is formed directly under the DLC film. It is desirable to arrange.

When forming a fine diamond layer directly on the surface of the tool base and a DLC film as the outermost layer of the hard carbon film, aiming to extend the tool life by increasing the thickness of the hard carbon film, From the viewpoint of reducing the residual internal stress formed in the hard carbon film, the laminated structure of the hard carbon film has a fine diamond layer and a second layer as the first layer from the tool base side as shown in FIG. It is desirable to sequentially form a medium diamond layer, a crystalline diamond layer as a third layer, a fine diamond layer as a fourth layer (a layer immediately below the outermost layer), and a DLC layer as the outermost layer.
With such a laminated structure, residual internal stress generated in the hard carbon film can be relaxed.

  In order to further increase the adhesion strength between the tool substrate and the hard carbon film formed on the tool substrate, the adhesion strength at the interface between the tool substrate and the hard carbon film is physically increased by roughening the surface of the substrate. In this case, in order not to form voids at the interface, the hard carbon film needs to be a fine diamond layer.

This invention has been made based on the above findings,
“( 1 ) In a hard carbon film-coated cutting tool in which a hard carbon film is coated on the surface of a tool base made of a tungsten carbide base cemented carbide,
In order from the tool substrate side, the hard carbon film has a fine diamond layer as the first layer, a medium diamond layer as the second layer, a crystalline diamond layer as the third layer, a fine diamond layer as the fourth layer, and the outermost layer. It consists of a DLC layer as a surface layer ,
The first layer is a fine diamond layer having an average particle size of 0.1 μm or less and an average film thickness of 0.5 to 6 μm,
The second layer is a medium-diameter diamond layer containing 10 to 50% of diamonds grown in a columnar shape,
The third layer is a crystalline diamond layer containing 50% to 95% of columnar grown diamond,
The fourth layer is a fine diamond layer having an average particle size of 0.1 μm or less and an average film thickness of 0.1 to 5 μm,
The outermost layer, the hard matter carbon film coated cutting tool characterized in that it is composed of DLC layer with an average thickness of 0.1～6Myuemu.
( 2 ) The hard carbon film-coated cutting tool according to (1) , wherein the surface roughness of the tool base made of a tungsten carbide-based cemented carbide is Ra: 0.01 to 3.0 μm. "
It has the characteristics.

  Next, the coating layer of the hard carbon film-coated tool of the present invention will be described in detail.

Among the hard carbon films of the present invention, in order from the surface of the tool base (see FIG. 1), the fine diamond layer of the first layer, the medium diamond layer of the second layer, the crystalline diamond layer of the third layer, and the fourth layer The fine diamond layer can be formed by, for example, a hot filament CVD method in a mixed gas atmosphere of methane and hydrogen.
In addition, the fifth (outermost layer) DLC layer can be formed by, for example, a high-frequency plasma CVD method.

Fine diamond layer (first layer in FIG. 1):
A fine diamond layer (first layer) is formed by vapor deposition on the tool substrate surface made of a WC-based cemented carbide by, for example, hot filament CVD under the following conditions.
Deposition pressure: 20-50 torr,
H ₂ flow rate: 3000 sccm,
CH ₄ flow rate: 130 sccm,
Filament voltage value: 180 V,
Deposition temperature: 600-1100 ° C.
The fine diamond layer (first layer) formed under the above conditions has an average particle size of 0.1 μm or less, and a graphite component or an amorphous component is mixed between the crystal grains. The coefficient of thermal expansion is large (the coefficient of thermal expansion of pure diamond is about 1.1 × 10 ⁻⁶ (K)).
Therefore, the thermal expansion difference from the WC-based cemented carbide, which is the tool base, is smaller than that of pure diamond, and the residual stress between the tool base and the fine diamond layer (first layer) after film formation is reduced. As a result, adhesion strength between the tool base and the fine diamond layer (first layer) is improved, and peeling of the hard carbon film is reduced.
If the thickness of the fine diamond layer (first layer) is less than 0.5 μm, the effect of improving the adhesion strength is small. On the other hand, if the thickness exceeds 6 μm, the wear resistance tends to decrease. The film thickness of the diamond layer (first layer) was set to 0.5 to 6 μm. A preferable film thickness is 1 to 3 μm.
In addition, the average particle diameter of the diamond crystal grain as used in the field of this invention measures the crystal grain diameter in the center part of the film thickness of each layer with a scanning electron microscope (SEM), and the average value is an average grain diameter of each layer. Defined as being.

FIG. 3 shows the result of Raman spectroscopic analysis of the bottom and middle positions shown in FIG. 2 for the fine diamond film formed under different conditions.
In addition, the wavelength of the used laser beam is 512 nm.
The film forming conditions in FIG.
“Film formation pressure: 30 torr, methane concentration: 4.0% (CH ₄ flow rate: 125 sccm, H ₂ flow rate: 3000 sccm), filament voltage value: 180 V”,
Also, the film forming conditions in FIG.
“Film formation pressure: 8 torr, methane concentration: 4.1% (CH ₄ flow rate: 65 sccm, H ₂ flow rate: 1500 sccm), filament voltage value: 180 V”
It is.
The hard carbon film of the present invention mentions surface smoothness as one of the important items.
However, when a large amount of ballast diamond is generated, the surface smoothness is impaired. Therefore, it is necessary to minimize the generation of ballast diamond.
Here, the present inventor has found that the conditions for generating the ballast diamond are derived from the film quality of the lowermost layer of the diamond film.
It is well known that ballast diamonds are likely to occur when the hard carbon film crystal grains are composed of fine diamond. However, particularly in the case of 512 nm wavelength Raman spectroscopic analysis, when the hard film bottom position shows a Raman spectrum as shown in FIG. 3B, the rate of occurrence of ballast diamond is very high, whereas FIG. When a peak at 1333 (cm ⁻¹ ) is detected as in a), it has been found that the incidence is low. At this time, the Raman spectrum at the position of the hard carbon film middle indicates that the peak of 1333 (cm ⁻¹ ) is detected under the conditions of FIG. b) Both spectra are almost similar. That is, the inventors have found that the origin of ballast diamond is affected by the film quality of the lowermost diamond film.
As a supplement, for gentle peaks shown in FIG. 3 (b) in 1350 ^{(cm -1)} are contained the peak of 1333 ^{(cm -1),} can not be confirmed peaks of 1333 as spectrum ^{(cm -1).}
For the above reasons, the fine diamond layer employed in the first hard carbon film layer of the present invention was formed under the conditions showing a Raman spectrum as shown in FIG.

Medium grain diamond layer ((second layer in FIG. 1)):
An intermediate diamond layer (second layer) is deposited on the surface of the fine diamond layer (first layer) by, for example, a hot filament CVD method under the following conditions.
Deposition pressure: 20-50 torr,
H ₂ flow rate: 3000 sccm,
CH ₄ flow rate: 95 sccm,
Filament voltage value: 180 V,
Deposition temperature: 600-1100 ° C.
By forming a film under the above conditions, a medium-diameter diamond layer (second layer) containing 10 to 50% of diamonds grown in a columnar shape is formed.
Here, the diamond film grown in a columnar shape is defined as “a diamond film having a continuous area of 1 μm or more and a length of 2 μm or more in the major axis direction in the IPF map in SEM-EDX”. .
The medium grain diamond layer is formed between the crystalline diamond layer formed as the third layer thereon and the fine diamond diamond layer as the first layer, thereby forming a hard carbon film as a thick film. Even in this case, the residual stress between the first and third layers of the hard carbon film is relieved, which contributes to the improvement of the interlayer adhesion strength.
The medium-diamond diamond layer has intermediate wear resistance between the first layer and the third layer, but if the film thickness is 1 μm or less, the residual stress mitigating action is small, while if the film thickness exceeds 5 μm, it is hard. The film thickness increases as the entire carbon film increases, so that the film stress increases and the hard carbon film is easily peeled off from the substrate. Therefore, the film thickness of the medium grain diamond layer is preferably 1 to 6 μm.

Crystalline diamond layer ((third layer in FIG. 1)):
The crystalline diamond layer is formed on the surface of the medium grain diamond layer (second layer) by, for example, a hot filament CVD method under the following conditions.
Deposition pressure: 20-50 torr,
H ₂ flow rate: 3000 sccm,
CH ₄ flow rate: 75 sccm,
Filament voltage value: 180 V,
Deposition temperature: 600-1100 ° C.
By forming the film under the above conditions, a crystalline diamond layer (third layer) containing 50 to 95% of diamond grown in a columnar shape is formed.
The crystalline diamond layer (third layer) has high hardness and exhibits excellent wear resistance, but if its film thickness is less than 1 μm, the effect of improving wear resistance is small, while its film thickness exceeds 5 μm. As a result, the crystal grains are likely to be coarsened, resulting in loss of smoothness on the surface of the hard carbon film, conversely causing a decrease in wear resistance, and an increase in the film thickness of the hard carbon film as a whole. Since the carbon film is easily peeled off from the substrate, the thickness of the crystalline diamond layer (third layer) is preferably 1 to 5 μm.

Fine diamond layer ((fourth layer in FIG. 1)):
The fine diamond layer ((fourth layer)) can be formed on the surface of the crystalline diamond layer (third layer), for example, under the same conditions as the fine diamond layer ((first layer)).
Deposition pressure: 20-50 torr,
H ₂ flow rate: 3000 sccm,
CH ₄ flow rate: 75 sccm,
Filament voltage value: 180 V,
Deposition temperature: 600-1100 ° C.
The fine diamond layer ((fourth layer)) is located between the crystalline diamond layer (third layer) and the DLC layer (fifth layer, outermost layer) in the same manner as the fine diamond layer ((first layer)). The surface roughness of the crystalline diamond layer (third layer) is traced to the DLC layer (fifth layer, outermost layer) as it is, and the surface of the DLC layer (fifth layer, outermost layer) is simultaneously obtained. Prevents loss of smoothness.
In addition, the fine diamond layer (fourth layer) is formed when a crack or the like occurs in the outermost layer (fifth layer) of the hard carbon film during cutting. (3rd layer → 2nd layer → 1st layer) It has the function of preventing the propagation and propagation.
If the film thickness of the fine diamond layer (fourth layer) is less than 0.1 μm, it will not be possible to prevent the surface smoothness of the DLC layer (fifth layer, outermost layer) from being deteriorated. The effect of preventing propagation is small. On the other hand, if the film thickness exceeds 5 μm, the wear resistance of the hard carbon film as a whole tends to decrease, so the film of the fine diamond layer (fourth layer) The thickness was determined to be 0.1 to 5 μm. A preferable film thickness is 0.5 to 2 μm.

DLC layer (fifth layer in FIG. 1):
A diamond film with better crystallinity has better wear resistance, but because the self-shaped shape has developed, there may be a decrease in wear resistance due to a decrease in the contact area with the work material. In particular, in cutting of difficult-to-cut materials such as CFRP or a highly weldable Al alloy, it tends to have a short life due to the occurrence of defects, welding, and the like.
Therefore, as the outermost surface of the hard carbon film, a DLC layer having excellent lubricity with the work material and low weldability with the work material is formed.
The DLC layer can be formed using, for example, a normal high-frequency plasma CVD apparatus under the conditions that the discharge output is 150 (W), the film formation temperature is 100 to 200 ° C., and the reaction gas is CH ₄ .
Since the DLC layer traces the shape of the layer immediately below it, it is desirable to dispose the fine diamond layer (fourth layer) as the layer immediately below the DLC layer in terms of surface smoothness and lubricity. .
When the film thickness of the DLC layer is less than 0.1 μm, the excellent lubricity and welding resistance cannot be sufficiently exhibited. On the other hand, when the film thickness exceeds 6 μm, the wear resistance tends to decrease. Therefore, the film thickness of the DLC layer was determined to be 0.1 to 6 μm. A preferred film thickness is 0.1 to 2 μm.

Tool surface properties:
By forming the fine diamond layer (first layer) on the surface of the tool base made of WC cemented carbide, it is possible to prevent the occurrence of peeling based on the residual stress derived from the thermal expansion difference between the tool base and the hard carbon film. it can.
However, when cutting difficult-to-cut materials such as CFRP or highly weldable Al alloy, a large load acts on the cutting edge, so a stronger bond strength is required between the tool base and the hard carbon film. However, this requirement can be met by roughening the surface roughness of the tool base made of the WC cemented carbide to Ra: 0.01 to 3.0 μm.
That is, if the surface roughness of the tool base surface is within the above numerical range, the fine diamond of the first layer formed on the tool base fills the rough surface voids of the base surface, and the tool is physically bonded. The adhesion strength between the substrate and the hard carbon film (the fine diamond layer of the first layer) can be increased.
When the surface roughness is out of the above numerical range, voids are formed at the interface between the fine diamond layer (first layer) and the tool base surface, so that the adhesion strength can be further improved. Absent.

  The hard carbon film-coated tool of the present invention has a fine diamond layer (first layer), a medium diamond layer (second layer), a crystalline diamond layer on a tool base surface having a predetermined surface roughness made of a WC cemented carbide. By forming a hard carbon film having a laminated structure of (third layer), fine diamond layer (fourth layer) and DLC layer (fifth layer, outermost layer), the adhesion strength between the tool base and the hard carbon film is increased. Not only is it improved, but it also has lubricity, slidability, and welding resistance, so the hard carbon film coated tool of this invention can be cut into CFRP with high specific strength, high rigidity, or Al alloy with high weldability. Even when used in the above, it exhibits excellent wear resistance over a long period of use, and the tool life can be extended.

It is a schematic explanatory drawing which shows the layer structure (cross section) of the hard carbon film | membrane coated tool of this invention. It is a cross-sectional photograph of the hard carbon film which shows the Raman spectrum measurement site | part of the Raman spectroscopic analysis result shown in FIG. (A), (b) is a Raman spectrum chart at the time of forming into a film on different conditions about the fine diamond layer (1st layer) of the hard carbon film coating tool of this invention. It is a graph which shows the relationship between cutting time and flank wear width.

Next, the hard carbon film-coated tool of the present invention will be specifically described with reference to examples.
Here, although the case where a hard carbon film coating tool is applied as an insert is described, this invention is not limited to this, It is possible to apply to various cutting tools.

  As the raw material powder, an average particle diameter: 0.8 μm fine WC powder, 1.3 μm TaC powder, 1.2 μm NbC powder, and 1.8 μm Co powder were prepared. : 6% by mass, TaC: 0.5% by mass, NbC: 0.5% by mass, balance: WC, added with wax, mixed by ball milling in acetone for 24 hours, and dried under reduced pressure The green compact is pressed into various green compacts of a predetermined shape at a pressure of 100 MPa, and these green compacts are subjected to a predetermined temperature in the range of 1370 to 1470 ° C. at a temperature increase rate of 7 ° C./min in a 6 Pa vacuum atmosphere. The temperature was raised to a temperature, held at this temperature for 1 hour, and then sintered under furnace cooling conditions to produce a WC-based cemented carbide tool substrate having a size of 10 mm × 10 mm × 2.5 mm.

Next, the surface of the tool base was ultrasonically cleaned in acetone and dried, and then etching with an acid solution and / or etching with an alkali solution was performed to adjust the surface roughness Ra to 0.5 to 1.0 μm. Thereafter, a fine diamond layer (first layer), a medium diamond layer (second layer), a crystalline diamond layer (third layer), a fine diamond having a predetermined average particle diameter and a predetermined film thickness under the following film formation conditions By laminating a layer (fourth layer) and a DLC layer (fifth layer, outermost layer),
The hard carbon film-coated cutting tool of the present invention having a laminated structure shown in Table 1 (hereinafter referred to as the present tool) was produced.
<< Film formation conditions >> Hot filament method Fine diamond layer: Deposition pressure 30 torr,
Reaction gas flow rate CH ₄ 130 sccm,
H ₂ 3000 sccm,
Filament voltage value 180 V,
Medium grain diamond layer: Deposition pressure 30 torr,
Reaction gas flow rate CH ₄ 95 sccm,
H ₂ 3000 sccm,
Filament voltage value 180 V,
Crystal diamond layer: Deposition pressure 30 torr,
Reaction gas flow rate CH ₄ 75 sccm,
H ₂ 3000 sccm,
Filament voltage value 180 V,
<< Film Formation Conditions >> High Frequency Plasma CVD Method DLC Layer: Film Formation Pressure 2 Pa,
Source gas CH ₄
High frequency power 100 W,

For the purpose of comparison, by forming a hard carbon film on the surface of the above tool base under the following film formation conditions,
A hard carbon film-coated cutting tool (hereinafter referred to as a comparative example tool) of a comparative example having a laminated structure shown in Table 2 was produced.
<< Film formation conditions >> Hot filament method Diamond layer: Film formation pressure 30 torr,
Reaction gas flow rate CH ₄ 95 sccm,
H ₂ 3000 sccm,
Filament voltage value 180 V,

Next, with respect to the hard carbon films of the tool of the present invention and the comparative tool, the thickness of each layer and the average particle diameter of the fine diamond were measured with a scanning electron microscope.
Table 1 shows the measurement results.

Next, for the tool of the present invention and the comparative tool,
Work material: A390-T6 round bar,
Cutting speed: 600 m / min. ,
Cutting depth: 0.15 mm,
Under the conditions, a wet turning test of the aluminum silicon alloy A390 was performed, and the relationship between the cutting time (min) and the flank wear width (mm) for each tool was examined.
The result is shown in FIG.

From the results shown in Table 1 and FIG. 4, the tool of the present invention has a fine diamond layer (first layer) and a medium diamond layer (second layer) on the surface of the tool base made of WC cemented carbide and having a predetermined surface roughness. ), Crystalline diamond layer (third layer), fine diamond layer (fourth layer), and DLC layer (fifth layer, outermost layer) to form a hard carbon film to form a tool base and hard carbon In addition to improving adhesion strength between films, it also has lubricity, slidability, and welding resistance, so when used for cutting specific strength, non-rigid CFRP or Al alloy with high weldability, etc. However, it has excellent wear resistance over a long period of use, and the tool life can be extended.
On the other hand, the comparative tool that does not have the layer structure defined in the present invention has a short tool life due to peeling or chipping of the hard carbon film in the cutting of the Al alloy.

  As described above, the hard carbon film-coated tool of the present invention is not only for cutting under normal conditions, but also for cutting of CFRP having a higher specific strength and specific rigidity than a metal material or Al alloy having a high weldability. However, since it exhibits excellent peeling resistance, fracture resistance, and wear resistance over a long period of use, and it is possible to increase the thickness of the hard carbon film, It can fully satisfy the labor-saving and energy-saving of cutting and cost reduction.

Claims (2)

In a hard carbon film coated cutting tool in which a hard carbon film is coated on the surface of a tool base made of a tungsten carbide base cemented carbide,
In order from the tool substrate side, the hard carbon film has a fine diamond layer as the first layer, a medium diamond layer as the second layer, a crystalline diamond layer as the third layer, a fine diamond layer as the fourth layer, and the outermost layer. It consists of a DLC layer as a surface layer ,
The first layer is a fine diamond layer having an average particle size of 0.1 μm or less and an average film thickness of 0.5 to 6 μm,
The second layer is a medium-diameter diamond layer containing 10 to 50% of diamonds grown in a columnar shape,
The third layer is a crystalline diamond layer containing 50% to 95% of columnar grown diamond,
The fourth layer is a fine diamond layer having an average particle size of 0.1 μm or less and an average film thickness of 0.1 to 5 μm,
The outermost layer, the hard matter carbon film coated cutting tool characterized in that it is composed of DLC layer with an average thickness of 0.1～6Myuemu. 2. The hard carbon film-coated cutting tool according to claim 1 , wherein the surface roughness of the tool base made of a tungsten carbide-based cemented carbide is Ra: 0.01 to 3.0 μm.

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