JP2020157455A - Diamond-coated cemented carbide tool - Google Patents

Abstract

To provide a diamond-coated cemented carbide tool which suppresses chipping, defects, detachment and the like, even in high-speed and high-feed cutting work of hard-to-cut materials, such as CFRP/AI materials, and which exhibits excellent wear resistance over a long period of use.SOLUTION: In a diamond-coated cemented carbide tool, a surface of a tool substrate is coated with a diamond film. The tool substrate comprises a composition containing 72.4-93.6 mass% of WC, 4.0-12.0 mass% of Co, 2.4-15.6 mass% of Cr, 1.0 mass% or less of a grain growth inhibitor, and the balance of inevitable impurities. Further, at an interface of the tool substrate and the diamond film, an interface layer is provided containing nitride and/or carbonitride of Cr, and the interface layer covers 50 area% or more of the tool substrate.SELECTED DRAWING: None

Description

The present invention is a high-speed, high-feed cutting process for a difficult-to-cut composite material (hereinafter referred to as "CFRP / Al material") composed of CFRP (carbon fiber reinforced plastic) and Al alloy, etc., on which a high load acts on the cutting edge. Also related to diamond-coated cemented carbide tools with reduced burrs during cutting and improved tool life.

Conventionally, a diamond-coated cemented carbide tool (hereinafter, sometimes referred to as a "diamond-coated tool") in which a diamond film is coated on a tool substrate made of a WC-based cemented carbide is known, and its characteristics as a tool are improved. Various proposals have been made to do so.

For example, Patent Document 1 describes a polycrystalline diamond having a diamond film on the surface of a substrate made of tungsten carbide cemented carbide containing 3 to 6% by mass of Co, etched with Murakami's reagent and then etched with sulfuric acid and hydrogen peroxide. Covering tools are listed.

Further, for example, Patent Document 2 describes a cutting tool provided with a base material made of WC and Co, an intermediate layer applied thereto, and a diamond film applied to the intermediate layer by a CVD method. The intermediate layer mainly contains metal, the metal portion of the intermediate layer is mainly composed of W and / or Cr, and the intermediate layer is defined by an Rz value of 0.5 μm to 3.0 μm. A diamond-coated tool is described that has a surface roughness to be formed.

Further, for example, in Patent Document 3, the amount of bonded phase between the surface of the cemented carbide up to 100 μm is reduced as compared with the amount of bonded phase inside the cemented carbide, and a diamond film is formed on the surface of the cemented carbide. A diamond-coated tool characterized by being coated is described.

In addition, for example, in Patent Document 4, a diamond film having an average thickness of 3 to 30 μm is formed on the surface of a tool substrate made of a WC-based cemented carbide containing WC particles and a Co-bonded phase of 3 to 15% by mass. In the diamond-coated tool, (a) the WC particles are a mixture of fine WC particles and coarse WC particles, and the average particle size is 0.5 to 2.5 μm, and (b) the tool. In the vertical cross-sectional observation perpendicular to the flank surface, in the vertical cross-sectional observation 50 μm square from the tip of the cutting edge with the flank surface as one side, at least from the interface between the diamond film on the flank surface and the tool substrate, 1 to the inside of the tool substrate. In the region where a part of the Co-bonded phase was removed in the region having a depth of 5 μm and a part of the Co-bonded phase was removed, the bonding interface length between the WC particles was 0.20 or more of the peripheral length of the WC particles. Described are diamond coated tools characterized by 60 or less.

Then, for example, Patent Document 5 describes a hard phase mainly composed of WC particles, a bonded phase mainly composed of Co that bonds the hard phases, and one selected from Cr, Nb, Zr, V, and Ti. The WC particles containing the above elements include fine particles having an average particle size of 0.4 μm to 0.6 μm measured by the Fisher method and 1.2 μm to 1 having an average particle size measured by the Fisher method. It is substantially composed of coarse particles of .4 μm, and the fine particles and the coarse particles have a mass ratio of the fine particles / the coarse particles = 25/75 to 15/85, and the content of Co is A diamond coating tool is described in which the content is 0.7% by mass to 2% by mass and the content of the element is 0.09% by mass to 0.9% by mass.

Japanese Patent No. 3504675 Special Table 2013-532227 Japanese Patent No. 2539922 Japanese Unexamined Patent Publication No. 2016-87726 Japanese Unexamined Patent Publication No. 2017-39954

In recent years, there has been an increasing demand for surface quality in cutting, and for example, burrs (uncut fibers) are not allowed in drilling and trimming of CFRP / Al materials.
Therefore, in the past, cutting tools were given a rounded cutting edge called honing for the purpose of suppressing the occurrence of sudden defects, but recently, in order to improve the sharpness to ensure surface quality, the cutting edge Sharpening is being promoted.
However, when the cutting edge of the diamond-coated tool described in each of the patent documents is sharpened, there are problems as described below.

That is, in the diamond-coated tool described in Patent Document 1, since Co on the surface of the tool substrate is removed by immersing in acid, the vicinity of the surface of the tool substrate becomes an embrittlement phase, resulting in insufficient strength of the cutting edge. In particular, in high-speed high-feed cutting of CFRP / Al materials, the diamond film may fall off or chipping may occur.

Further, the diamond-coated tool described in Patent Document 2 is provided with an intermediate layer by the PVD method, but the adhesion between the tool substrate and the intermediate layer is not sufficient, and the diamond film may peel off. , CFRP / Al material does not have a sufficient tool life in high-speed high-feed cutting.

Further, the diamond-coated tool described in Patent Document 3 is difficult to balance the improvement of the adhesion strength between the diamond film and the tool substrate and the suppression of the decrease in strength, and is used for high-speed high-feed cutting of difficult-to-cut materials such as CFRP / Al materials. As described above, when it is used for cutting in which a strong impact is repeatedly applied to the cutting edge in a short period of time, abnormal damage such as chipping, chipping, and peeling is likely to occur, and the life of the cutting edge is reached early. Further, in manufacturing this covering tool, since the tool substrate is processed in a carburizing atmosphere of 1400 ° C., which exceeds the liquid phase appearance temperature of the coupled phase, this covering tool requires high precision dimensional accuracy. Difficult to use for.

In addition, the diamond-coated tool described in Patent Document 4 has improved adhesion between the diamond film and the tool substrate and has a long life, but requires a treatment for silicifying Co existing on the surface of the tool substrate. , The process of forming a diamond-coated tool is complicated.

The diamond-coated tool described in Patent Document 5 does not require a process of silicifying Co existing on the surface of the tool substrate, and can simplify the process of forming the diamond-coated tool, but is a CFRP / Al material. When used under cutting conditions where a strong impact is repeatedly applied to the cutting edge in a short period of time, such as high-speed, high-feed cutting of difficult-to-cut materials such as, abnormal damage such as chipping, chipping, and peeling is likely to occur, and it is early. There was a problem that it reached the end of its life.

The present invention suppresses chipping, chipping, peeling, etc. even in high-speed high-feed cutting of difficult-to-cut materials such as CFRP / Al materials in which a high load acts on the cutting edge, and provides excellent wear resistance for a long period of time. It is an object of the present invention to provide a diamond-coated cemented carbide tool that can be exhibited in the future.

The present inventor causes chipping, chipping, peeling, etc. even when subjected to cutting conditions in which a high load acts on the cutting edge, such as high-speed high-feed cutting of difficult-to-cut materials such as CFRP / Al materials. In order to provide a diamond-coated cemented carbide tool that suppresses and exhibits abrasion resistance, the composition of the tool substrate (WC cemented carbide) and the structure of the interface of the tool substrate at the interface between the tool substrate and the diamond film are examined. Was done. As a result, when the content ratio of Cr contained in the WC cemented carbide is made larger than the conventional ratio and a predetermined amount of a layer containing a nitride and / or carbonitride of Cr is formed at the interface, a diamond film is formed. Adhesion to the tool substrate is improved, and even when subjected to cutting conditions where a high load acts on the cutting edge, such as high-speed high-feed cutting of difficult-to-cut materials such as CFRP / Al materials, chipping and chipping We have obtained a new finding that it suppresses peeling and exhibits excellent wear resistance.

The present invention has been made based on the above findings.
"(1) A diamond-coated cemented carbide tool in which the surface of the tool substrate is coated with a diamond film.
The tool substrate contains WC: 72.4 to 93.6% by mass, Co: 4.0 to 12.0% by mass, Cr: 2.4 to 15.6% by mass, and a grain growth inhibitor: 1.0% by mass. Has a composition containing less than% and the balance is an unavoidable impurity.
The tool substrate has an interface layer containing Cr nitride and / or carbonitride at the interface with the diamond film.
The interface layer covers 50 area% or more of the tool substrate.
A diamond-coated cemented carbide tool characterized by this.
(2) The tool substrate is characterized in that Co is MCo mass% and Cr is MCr mass%, respectively, and when they are contained, 0.6 ≦ M _Cr / M _Co ≦ 1.3. Diamond-coated cemented carbide tools described in.
(3) The above-mentioned (3), wherein the interface layer has an average thickness of 0.5 to 3.0 μm, has columnar crystal grains, and the average particle width of the columnar crystal grains is 500 nm or more. The diamond-coated cemented carbide tool according to 1) or (2).
(4) The radius of curvature of the ridge line where the rake face and the flank surface of the tool substrate intersect with each other in a cross section perpendicular to an arbitrary flank surface of the tool cutting edge is 5 μm or less. A diamond-coated cemented carbide tool described in any of. "
Is.

The diamond-coated cemented carbide tool of the present invention suppresses peeling of the diamond film even in high-speed, high-feed cutting of difficult-to-cut materials such as CFRP / Al materials, and improves the life of the tool.

Hereinafter, the present invention will be described in detail. In addition, in this specification and claims, when a numerical range is expressed as "X to Y", the range shall include upper and lower numerical values (that is, X or more and Y or less), and X shall be used. When there is no description of the unit and the unit is described only in Y, the unit of X is the same as the unit of Y.

1. 1. Tool Base In the present invention, the tool base has a composition including a hard phase containing WC and a bonded phase containing Co, and the composition thereof will be described.

Hard phase:
The content ratio of WC constituting the hard phase is 72.4 to 93.6% by mass. The reason for setting this range is that when the WC content is less than 72.4% by mass, the hardness of the tool base is insufficient, while when it exceeds 93.6% by mass, the toughness of the tool base is lowered and cutting is performed. This is because chipping and defects sometimes occur. The content ratio of WC is more preferably 79.3 to 92.0% by mass.

Bonding phase:
The content ratio of Co constituting the bonded phase is 4.0 to 12.0% by mass. The reason for setting this range is that if it is less than 4.0% by mass, the toughness of the tool base is lowered and chipping or chipping occurs during cutting, while if it exceeds 12.0% by mass, the hardness of the tool base becomes low. This is because it is insufficient and vulnerable. The content ratio of Co is more preferably 5.0 to 9.0% by mass.

Cr content:
The conventional purpose of containing Cr is to suppress the growth of hard particles (hard phase), and a small amount of Cr is contained in the tool base. However, in the present invention, the purpose is to improve the adhesion between the tool base and the diamond film. Therefore, it is contained in a large amount of 2.4 to 15.6% by mass instead of the conventional small amount. By containing this large amount, the adhesion between the tool substrate and the diamond film is dramatically improved, and even in high-speed high-feed cutting of difficult-to-cut materials such as CFRP / Al material, the peeling of the diamond film is suppressed and the tool life is extended. improves. The Cr content is more preferably 4.5 to 15% by mass.

Here, Cr exists as a nitride and / or carbonitride as a layered interface layer in the vicinity of the surface of the tool substrate (for example, within a range of 3 μm from the surface of the tool substrate) by the gas nitriding treatment after the formation of the tool substrate. Is preferable. The presence of the interface layer improves the adhesion between the tool substrate and the diamond film.

The interface layer preferably covers 50 area% or more of the tool substrate. The reason is that if it is less than 50 area%, the adhesion between the tool substrate and the diamond film is not sufficient. Here, covering 50 area% or more of the tool substrate is as follows. A cross section in the direction perpendicular to an arbitrary flank surface near the cutting edge (a vertical cross section in the film thickness direction) is processed by a Cross-sector Polisher (CP), and the processed cross section is processed by a scanning electron microscope at an appropriate magnification (eg,). (Magnification 1000 times), the vicinity of the tool substrate surface (the region including the cross section between the diamond film and the tool substrate) is photographed with a backscattered electron image, and the profile of the tool substrate surface is XY with image processing software (for example, ImageJ). The scanning area is horizontal by modifying the scanning area of the scanning electron microscope so that the slope of the straight line becomes ± 1 ° or less when it is output as coordinates and the value is fitted as a linear equation (Y = aX + b). Correct so that the direction (X direction) is parallel to the surface of the tool substrate. When the width of the interface layer formed on the surface of the tool substrate of 100 μm is measured in this region, it means that the width of the interface layer is 50% or more with respect to the width of the surface of the tool substrate.

The thickness of the interface layer is preferably 0.5 to 3.0 μm. The reason is that if it is less than 0.5 μm, the adhesion between the tool substrate and the diamond film cannot be sufficiently ensured, and if it exceeds 3.0 μm and the interface layer becomes too thick, stress is concentrated on the interface layer during cutting and the interface layer. This is because the destruction of
Here, the thickness of the interface layer is the same as when the area% is obtained for the cross section in the direction perpendicular to the arbitrary flank surface near the cutting edge (longitudinal cross section in the film thickness direction) as described above. After processing, the area where the interface layer is formed is photographed with a backscattered electron image near the surface of the tool substrate (the area including the interface between the diamond film and the tool substrate) at an appropriate magnification (eg, magnification 5000 times). , WC profile and interface layer profile are output as XY coordinates, and calculated from the difference.

Further, by observing the interface layer with a secondary electron image at an appropriate magnification (eg, magnification of 5000 times) with a scanning electron microscope, the grain boundaries of the interface layer can be seen, and the interface layer is a columnar crystal grain. The average particle width thereof is preferably 500 nm or more. The reason is that when the average particle width is less than 500 nm, a large amount of grain boundaries of the interface layer are present, and the bonding layer diffuses to the surface of the interface layer through the grain boundaries during the formation of the diamond film. This is because the adhesion of the diamond film is greatly reduced. The upper limit of the average particle width is preferably 10000 nm. The reason is that when the average particle width exceeds 10000 nm, the interface layer is destroyed due to stress concentration of the interface layer on the particles during cutting.

In addition, the improvement in adhesion is achieved when the Cr content is in a predetermined ratio with respect to the Co content, that is, Co is contained in Mco mass% and Cr is contained in Mcr mass%, respectively. , 0.6 ≦ Mcr / Mco ≦ 1.3 is more reliably achieved.

Content ratio of grain growth inhibitor:
The grain growth inhibitor has a function of suppressing the growth of hard particles (hard phase), and is one or more of Nb, Zr, Ti, and Ta, or one or more of these elements. One or more of the carbides, nitrides and carbonitrides of the above, for example, one or more of NbC, TaC, (Ta, Nb) C and TiCN. The grain growth inhibitor may not be contained (that is, it may be 0% by mass), but when it is contained, the grain growth can be suppressed by setting it to 1% by mass or less. The content ratio is more preferably 0.05 to 0.90% by mass.

Inevitable impurities:
There are impurities that are inevitably mixed in the manufacturing process, and these are called unavoidable impurities. It is preferable that the amount of this unavoidable impurity is small, but even if it is contained, the content ratios of WC, Co, Cr and the grain growth inhibitor satisfy the above range, and the above-mentioned interface layer is present in a predetermined area%. If so, the problem to be solved by the present invention is solved.

Curvature of the cutting edge of the tool substrate:
This curvature is preferably 5 μm or less. The reason is that if it exceeds 10 μm, the curvature of the cutting edge after the diamond film is formed becomes too large and the quality of the machined surface deteriorates. In the present invention, it is set to 5 μm or less in order to ensure the work quality. To do.
The curvature of the cutting edge of the tool base of the tool on which the diamond film is formed is measured as follows. That is, a cross section in the direction perpendicular to an arbitrary flank surface (longitudinal cross section in the film thickness direction) in the vicinity of the cutting edge including the ridge line where the rake face and the flank surface intersect is processed by CP, and the processed cross section is scanned. Observe the vicinity of the cutting edge including the ridge line where the rake face and the flank intersect with an electron microscope at an appropriate magnification (eg, 5000 times) with a reflected electron image, and the curvature of the ridge where the rake face and the flank intersect. Is measured by image analysis.
When measuring during the process of manufacturing a diamond coating tool, a laser microscope is used to measure the vicinity of the cutting edge including the ridge line where the rake face and the flank surface intersect with respect to the cutting edge after the pretreatment performed before the formation of the diamond film, which will be described later. Observe with and analyze the line segment perpendicular to the ridgeline where the rake face and the flank face intersect.

2. 2. Diamond-coated layer The thickness of the diamond-coated layer is not particularly limited, but an average layer thickness of 3 to 30 μm is preferable. The reason is that if it is less than 3 μm, sufficient wear resistance cannot be exhibited over a long period of use, while if it exceeds 30 μm, chipping, chipping, and peeling are likely to occur, the cutting edge is rounded, and the processing accuracy is lowered. Because.
Here, in the measurement of the average film thickness of the diamond film, a cross section in the direction perpendicular to the tool substrate (longitudinal cross section in the film thickness direction) is processed by CP, and the processed cross section is subjected to an appropriate magnification by a scanning electron microscope. The film thickness can be measured at (example: magnification 5000 times), and for example, the film thickness at 5 points in the observation field can be measured and averaged.

3. 3. Manufacturing Method The diamond-coated cemented carbide tool of the present invention can be manufactured, for example, as follows.
(1) Preparation of raw material powder As raw material powder, WC powder having an average particle size of 1 μm or less, Co powder having an average particle size of 1 to 3 μm, Cr powder, and, if necessary, a grain growth inhibitor are prepared.
(2) Crushing / Mixing The raw material powder is crushed / mixed with a ball mill so as to have the composition specified in the present invention to obtain a sintered raw material powder.
(3) Molding, Sintering, Cutting Processing The obtained sintered body raw material powder is molded at a predetermined pressure to prepare a molded body, which is temporarily sintered under vacuum, and then sintered by main sintering. Get the body. Then, this sintered body is cut to produce a tool base having a predetermined shape.
(4) Gas Nitriding Treatment The tool substrate having a predetermined shape thus obtained is subjected to gas nitriding treatment at 1150 to 1250 ° C. Here, since the nitriding treatment temperature does not reach the liquid phase appearance temperature of Co, a predetermined dimensional accuracy can be obtained. Further, by performing the nitriding treatment at a sufficiently high temperature, Cr nitride and / or carbonitride is generated on the tool surface.
(5) Formation of diamond coating layer A diamond coating is formed on the tool substrate.

Next, an embodiment will be described.
Here, a diamond-coated drill will be described as an example of the diamond-coated tool according to the present invention, but the present invention is not limited to this, and can be applied to various diamond-coated tools such as a diamond-coated alloy insert and a diamond-coated end mill. Needless to say.

Manufacture of tool substrates:
As raw material powders, WC powder having an average particle size of 1 μm or less, Co powder having an average particle size of 1 to 3 μm, Cr powder, and a grain growth inhibitor are prepared, and these raw material powders are fired as shown in Table 1. After compounding so as to have a post-condensation composition (SEM-EDS analysis value), wet mixing with a ball mill for 96 hours, drying, press molding into a green compact at a pressure of 100 MPa, and pre-sintering this green compact , 6 Pa vacuum, temperature: 1400 to 1500 ° C. for 1 hour, main sintering to form a round bar sintered body for forming a tool substrate with a diameter of 10 mm, and further from the round bar sintered body. , A drill-shaped tool base made of superhard alloy (tool base of the present invention) A to F having a diameter of 7 mm was produced by grinding. In Table 1, the reason why the sum of the compositions of each component is not 100% by mass is that unavoidable impurities are present.

Gas nitriding:
Subsequently, the surfaces of the tool substrates A to F were ultrasonically cleaned in ethanol and dried, and then the tool substrates were placed in a gas treatment chamber and subjected to nitriding treatment under the following conditions.
N ₂ gas partial pressure: 70-200 Torr
Temperature in the furnace: 1150 to 1250 ° C
Processing time: 1.5-5.0 hours

Cutting edge curvature measurement:
As described above, the curvature of the cutting edge of the tool substrates A to F was measured with a laser microscope, and it was confirmed that the curvature was 5 μm or less.

Preprocessing:
Subsequently, the surfaces of the tool substrates A to F were ultrasonically cleaned in ethanol, dried, and then ultrasonically treated in an isopropyl alcohol solution containing diamond powder having a particle size of 1 to 2 μm for 10 minutes.

Formation of diamond coating layer:
The pretreated tool bases A to F were charged into the thermal filament CVD apparatus. Then, the flow rate ratio of hydrogen gas and methane gas is adjusted under a filament temperature of 2000 to 2200 ° C. and a gas pressure of 2 to 6 Torr (266.6 to 800.0 Pa), and the substrate temperature is set to 750 to 900 ° C. A diamond coating film was formed over a period of time to prepare diamond-coated drills of the present invention (hereinafter, referred to as “coating tools of the present invention”) A1 to F1, respectively.

For comparison, the raw material powder containing the WC powder having an average particle size of 1 μm or less is blended so as to have the composition after sintering shown in Table 1, and the tool substrates (comparative tool substrates) a to f are added to the tool. The diamond-coated drills (hereinafter referred to as "comparative coating tools") a1 to f1 of the comparative example are respectively manufactured in the same manner as the substrates A to F and by the same process as the process for manufacturing the drill of the present invention. Made. Here, the curvature of the cutting edge of the tool bases a to f was measured with a laser microscope, and it was confirmed that the curvature was 5 μm or less. The film formation time of the diamond film was adjusted so that the average thickness of the diamond film was 12 to 14 μm.

Subsequently, the covering tools A1 to F1 of the present invention and the comparative covering tools a1 to f1 were subjected to an evaluation test of the number of drilling times under the following conditions to check the tool life.
Work material: CFRP (thickness 20 mm) and
Composite material made of Al alloy (A7075: thickness 7 mm) Cutting speed: VC = 100 m / min Feed amount: fr = 0.05 mm / rev

Tool life determination method: The drill bit and the work (work material) were observed for every 50 holes to be machined, and the life of the drill was determined when the substrate was exposed, chipped, or chipped at the tip. In addition, as a standard for maintaining processing accuracy, a processing state in which the burr height of the processed surface of the work material does not exceed 0.3 mm and delamination is suppressed within 1 mm from the processed surface is regarded as a pass judgment, and the pass judgment is satisfied. Table 2 shows the number of holes when the number of holes to be machined is not reached.

From the results shown in Table 3, since the covering tools A1 to F1 of the present invention use a tool base that satisfies the matters specified in the present invention, stable drilled holes can be obtained for a long period of time.
On the other hand, in the comparative covering tools a1 to f1 using a tool base that does not satisfy even one of the matters specified in the present invention, not only chipping and chipping occur but also the cutting length is short (machining). The number of holes is small), or it has reached the end of its useful life in a short time.

As described above, the diamond-coated cemented carbide tool of the present invention exhibits excellent welding resistance and abrasion resistance over a long period of time in cutting CFRP / Al materials, which are difficult-to-cut materials. , FA of cutting equipment, labor saving and energy saving of cutting processing, and cost reduction can be fully satisfied.

Claims (4)

A diamond-coated cemented carbide tool in which the surface of the tool substrate is coated with a diamond film.
The tool substrate contains WC: 72.4 to 93.6% by mass, Co: 4.0 to 12.0% by mass, Cr: 2.4 to 15.6% by mass, and a grain growth inhibitor: 1.0% by mass. Has a composition containing less than% and the balance is an unavoidable impurity.
The tool substrate has an interface layer containing Cr nitride and / or carbonitride at the interface with the diamond film.
The interface layer covers 50 area% or more of the tool substrate.
A diamond-coated cemented carbide tool characterized by this. According to claim 1, when Co is contained in MCo mass% and Cr is contained in MCr mass%, respectively, 0.6 ≦ M _Cr / M _Co ≦ 1.3. Diamond-coated cemented carbide tool. Claim 1 or 2 characterized in that the interface layer has an average thickness of 0.5 to 3.0 μm, has columnar crystal grains, and the average particle width of the columnar crystal grains is 500 nm or more. Diamond-coated cemented carbide tool described in. The invention according to any one of claims 1 to 3, wherein the radius of curvature of the ridge line where the rake face and the flank surface of the tool substrate intersect with each other in a cross section perpendicular to an arbitrary flank surface of the tool cutting edge is 5 μm or less. Diamond-coated cemented carbide tool.