JP7610782B2 - Surface-coated cutting tools - Google Patents

Description

The present invention relates to a surface-coated cutting tool (hereinafter sometimes referred to as a coated tool).

2. Description of the Related Art Conventionally, coated tools have been known in which a coating layer is formed on the surface of a tool substrate such as a tungsten carbide (hereinafter abbreviated as WC)-based cemented carbide, and are known to exhibit excellent wear resistance.
In order to improve the durability of the coated tool, various proposals have been made for improving the coating layer.

For example, Patent Document 1 describes a coated tool having a surface of a tool substrate coated with any one of nitrides, carbonitrides, oxynitrides, and oxycarbonitrides of (Al _1-x V _x ) (x is 0.24 to 0.45), and it is said that the coated tool prevents chipping and breakage of the cutting edge and peeling of the coating layer and has good wettability.

JP 2005-271106 A

The present invention was made in consideration of the above circumstances and proposals, and aims to provide a coated tool with improved chipping resistance.

The surface-coated cutting tool according to an embodiment of the present invention comprises:
A tool substrate and a coating layer on a surface of the tool substrate,
1) The coating layer has an average layer thickness of 1.0 to 20.0 μm, and comprises a composite nitride layer or composite carbonitride layer of V and Al, in which, when the composition is expressed by the composition formula (V _1-x Al _x ) (C _y N _1-y ), the average x content x _avg is 0.76 to 0.95 and the average y content y _avg is 0.000 to 0.015,
2) The composite nitride layer or composite carbonitride layer has composite nitride or composite carbonitride crystal grains having a NaCl type face-centered cubic structure,
3) In a frequency distribution of inclination angles of the normal direction of each {110} plane of the crystal grain relative to the normal direction of the surface of the tool base, inclination angles in the range of 0 to 45 degrees are divided into increments of 0.25 degrees, the maximum frequency is present in one of the 0 to 10 degree divisions, and the sum of the frequency distributions of the 0 to 10 degree divisions accounts for 45% or more of the total sum of frequencies of the inclination angle distribution.

Furthermore, the surface-coated cutting tool according to the above embodiment may satisfy one or more of the following items (1) to (7). However, it does not satisfy both (4) and (5) at the same time.

(1) The crystal grains are columnar crystals having an area-weighted average crystal grain width of 0.1 to 2.0 μm and an area-weighted average aspect ratio of 2.0 to 10.0, and include those having a repeated change in the Al content ratio within the grains, taking maximum and minimum values along any one of the equivalent crystal orientations represented by <001>, and a difference Δx between the average value of the maximum values and the average value of the minimum values of x is 0.03 to 0.10.

(2) The crystal grains are columnar crystals with an average crystal grain width of 0.1 to 2.0 μm and an average aspect ratio of 2.0 to 10.0, and have a repeating change in which the Al content ratio has a maximum value and a minimum value along one of the equivalent crystal orientations represented by <001>, the average interval of the repeating change is 3 to 100 nm, and the change width x0 of x in a plane perpendicular to the orientation is 0.01 or less.

(3) The lattice constant a of the crystal grains satisfies the relationship 0.05a _VN + 0.95a _AlN ≦a ≦ 0.24a _VN + 0.76a _AlN with respect to the lattice constant a _VN of cubic VN and the lattice constant a _AlN of cubic AlN.

(4) The complex nitride or complex carbonitride layer is composed only of crystal grains of the complex nitride or complex carbonitride having the NaCl type face-centered cubic structure .

(5) The composite nitride or composite carbonitride layer contains microcrystalline grains having a hexagonal crystal structure, the area ratio of the microcrystalline grains is 30% or less, and the average grain size is 0.01 to 0.30 μm.

(6) Between the tool substrate and the V and Al composite nitride layer or composite carbonitride layer, there is a lower layer consisting of one or more Ti compound layers selected from the group consisting of a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer, and a carbonitride oxide layer, and having a total average layer thickness of 0.1 to 20.0 μm.

(7) An upper layer including at least an aluminum oxide layer is present on the upper portion of the composite nitride layer or composite carbonitride layer with a total average layer thickness of 1.0 to 25.0 μm.

As a result of the above, it is possible to obtain a surface-coated cutting tool with improved chipping resistance.

1 is a schematic diagram showing a vertical cross section of a coating layer of a surface-coated cutting tool according to an embodiment of the present invention. FIG. FIG. 2 is a diagram showing a schematic diagram of a change in the content ratio in a crystal grain of a NaCl type face-centered cubic structure having a repeated change in the content ratio of Al. FIG. 2 is a schematic diagram showing repeated changes in the Al content. FIG. 2 is a schematic perspective view of a portion of a gas supply pipe of an example of an apparatus for manufacturing the surface-coated cutting tool according to the present embodiment. FIG. 5 is a schematic cross-sectional view of the gas supply pipe of FIG. 4 . 5 is a schematic cross-sectional view showing a gas nozzle of the gas supply pipe of FIG. 4. FIG. 13 is a graph showing the frequency distribution of the inclination angle between the normal direction of the surface of the tool base body in Example 8 and the normal direction of the {110} plane of a crystal grain having a NaCl type face-centered cubic structure.

The inventors have investigated coated tools coated with a composite nitride layer of V and Al or a composite carbonitride layer (hereinafter sometimes referred to as a (VAl)(CN) layer) and found that simply coating with a composite nitride layer of V and Al or a composite carbonitride layer does not provide sufficient chipping resistance.

As a result of further investigation, it was discovered that chipping resistance can be improved by orienting the normal direction of the {110} plane of the (VAl)(CN) layer in a specific manner perpendicular to the surface of the tool base (normal direction to the surface of the tool base).

Hereinafter, a surface-coated cutting tool according to an embodiment of the present invention will be described.
In this specification and claims, when a numerical range is expressed as "L to M" (where L and M are both numerical values), the range includes an upper limit value (M) and a lower limit value (L), and the upper limit value (M) and the lower limit value (L) have the same units.

I. Coating Layer The coating layer (2) of this embodiment is present on the surface of the tool substrate (1) and includes a (VAl)(CN) layer (3) as shown in Figure 1. A lower layer (4) may be present between the tool substrate (1) and the (VAl)(CN) layer (3), and an upper layer (5) may be present on the surface of the (VAl)(CN) layer.
The following description will focus on the (VAl)(CN) layer.

1. (VAl)(CN) Layer (1) Average Layer Thickness The average layer thickness of the (VAl)(CN) layer is preferably 1.0 to 20.0 μm. The reason is that if the average layer thickness is less than 1.0 μm, the average layer thickness is too thin to ensure sufficient wear resistance over long-term use, while if the average layer thickness exceeds 20.0 μm, the crystal grains of the (VAl)(CN) layer tend to become coarse, making chipping more likely to occur.

(2) Composition When the composition of the (VAl)(CN) layer is expressed by the composition formula (V _1-x Al _x )(C _y N _1-y ), it is preferable that the average x content x _avg is 0.76 to 0.95 and the average y content y _avg is 0.000 to 0.015.

The reason is as follows: if x _avg is less than 0.76, the wear resistance of the (VAl)(CN) layer is insufficient, while if it exceeds 0.95, the (VAl)(CN) layer is easily embrittled and its chipping resistance is reduced. Also, when y _avg is within the above range, the adhesion between the (VAl)(CN) layer and the tool base or the lower layer described later is improved, the impact during cutting is mitigated, and the chipping resistance of the coating layer is reliably improved.

Although the ratio of (V _1-x Al _x ) to (C _y N _1-y ) is not particularly limited, it is preferable that the ratio of (V _1-x Al _x ) to (C _y N _1-y ) is 0.8 to 1.2 when (V 1-x Al x ) is 1. The reason for this is that if the ratio of (C _y N _1-y ) to (V _1-x Al _x ) is within the above range, the object of the present invention can be achieved more reliably.

(3) NaCl-type face-centered cubic structure The (VAl)(CN) layer preferably contains crystal grains having a NaCl-type face-centered cubic structure. That is, in a longitudinal section (a section perpendicular to the surface of the tool base when the surface is treated as a flat surface ignoring minute irregularities on the surface of the tool base), the area ratio of crystal grains having a NaCl-type face-centered cubic structure is 60% or more, more preferably 80% or more, and all crystal grains (area ratio is 100%) may have a NaCl-type face-centered cubic structure.

(4) Gradient distribution in the normal direction of the {110} plane For the (VAl)(CN) layer, electron backscatter diffraction (EBSD) was used to determine the gradient distribution in the normal direction of the {110} plane for crystal grains having a NaCl-type face-centered cubic structure.
[1] Measure the inclination angle of the normal direction of the {110} plane of this crystal grain (direction 7 in FIG. 2) with respect to the normal direction of the surface of the tool base;
[2] Divide the inclination angles within the range of 0 to 45 degrees into increments of 0.25 degrees,
[3] When the frequency distribution of the inclination angle is calculated by tallying up the frequencies in each category,
In the determined inclination angle frequency distribution, it is preferable that the highest peak (maximum frequency) is in one of the sections in the range of 0 to 10 degrees, and that the sum of the frequencies in this range of 0 to 10 degrees is 45% or more of the sum of the frequencies in the range of 0 to 45 degrees.
This ratio is more preferably 50% or more, and even more preferably 55% or more.
By having such a distribution of the inclination angles, the toughness is improved while the wear resistance is maintained, and therefore the chipping resistance of the coating layer is reliably improved.

When calculating the distribution of the number of inclination angles, in the case of an ideal random orientation, the number of inclination angles is normalized so that it is a constant value regardless of the inclination angle between the normal direction of a certain crystal plane and the normal direction of the surface of the tool base.

Here, the surface of the tool base is defined as the average line of the interface roughness between the tool base and the coating layer in the observation image of the longitudinal section. In other words, when the tool base has a flat surface like an insert, element mapping is performed on the longitudinal section using energy dispersive X-ray spectroscopy (EDS), and the interface between the coating layer (if a lower layer, as described below, exists, the lower layer is used instead of the coating layer) and the tool base is determined by performing known image processing on the obtained element map, and the average line is arithmetically determined for the roughness curve of the interface between the coating layer and the tool base thus obtained, and this is defined as the surface of the tool base. The direction perpendicular to this average line is defined as the direction perpendicular to the tool base (layer thickness direction).

Even if the tool base has a curved surface like a drill, if the tool diameter is sufficiently large compared to the thickness of the coating layer, the interface between the coating layer and the tool base in the measurement area will be approximately flat, so the surface of the tool base can be determined using a similar method. That is, for example, in the case of a drill, element mapping is performed using EDS on the longitudinal section of the coating layer in a section perpendicular to the axial direction, and the interface between the coating layer and the tool base is determined by performing known image processing on the obtained element map, and the average line is arithmetically determined for the roughness curve of the interface between the coating layer and the tool base thus obtained, and this is taken as the surface of the tool base. The direction perpendicular to this average line is taken as the direction perpendicular to the tool base (layer thickness direction).

(5) Average Grain Width and Aspect Ratio The crystal grains having a NaCl type face-centered cubic structure in the (VAl)(CN) layer are more preferably columnar crystals having an average crystal grain width of 0.1 to 2.0 μm and an average aspect ratio of 2.0 to 10.0.

The reason for this is that when the average grain width is smaller than 0.1 μm, the increase in grain boundaries reduces plastic deformation resistance and oxidation resistance, leading to abnormal damage. On the other hand, when the average grain width W is greater than 3.00 μm, the toughness is likely to decrease due to the presence of coarsely grown particles.

In addition, when the average aspect ratio of the granular crystals is smaller than 2.0, the interface (grain boundary) is likely to become the starting point of fracture due to the shear stress generated on the surface of the coating layer during cutting, causing chipping. On the other hand, when the average aspect ratio exceeds 10.0, micro-chipping occurs on the cutting edge during cutting, and when chipping occurs in the adjacent columnar structure, the resistance to the shear stress generated on the surface of the coating layer is likely to be small, and the columnar structure breaks, causing the damage to progress rapidly and resulting in large chipping.

Here, the method of calculating the average grain width and the average aspect ratio will be described.
First, the grain boundaries are determined in a 50 μm observation field (longitudinal section) parallel to the tool substrate of the coating layer. The method of determining the grain boundaries is to use an electron backscatter diffraction device to analyze the observation field plane two-dimensionally at intervals of 0.01 μm to obtain measurement points having a crystal lattice of a NaCl type face-centered cubic structure in the observation field plane. Among the measurement points having the crystal lattice of the NaCl type face-centered cubic structure, if there is an orientation difference of 5 degrees or more between adjacent measurement points (hereinafter referred to as pixels), or if adjacent pixels do not have a crystal lattice of a NaCl type face-centered cubic structure, the boundary between the pixels is defined as a grain boundary.

The area surrounded by the grain boundary is then defined as one crystal grain. However, a single pixel that has an orientation difference of 5 degrees or more from all of its adjacent pixels is not considered a crystal grain; a pixel that is connected to two or more pixels is treated as a crystal grain. In this way, the grain boundary determination is performed and the crystal grains are identified.

Next, for a certain crystal grain i, the maximum length H _i in the direction perpendicular to the surface of the tool base (layer thickness direction), the grain width W _i which is the maximum length in the direction parallel to the surface of the tool base, and the area S _i are obtained. The aspect ratio A _i of the crystal grain i is calculated as A _i =H _i /W _i . In this manner, the grain widths W ₁ to W _n (n≧20) of at least 20 or more (i=1 to 20 or more) crystal grains in the observation field are area-weighted averaged by [Math. 1] to obtain the average grain width W of the crystal grains. Similarly, the aspect ratios A ₁ to A _n (n≧20) of the crystal grains are obtained and area-weighted averaged by [Math. 2] to obtain the average aspect ratio A of the crystal grains.

(6) Repeated Change in Al Content [1] Maximum and Minimum Values As shown in FIG. 2, it is more preferable that the crystal grains (6) having a NaCl-type face-centered cubic structure in the (VAl)(CN) layer have a repeating change in the Al content (i.e., the V content) along one of the equivalent crystal orientations (10) represented by <001>, in which the Al content (i.e., the V content) has a maximum value in a region (8) where the Al content is relatively high and a minimum value in a region (9) where the Al content is relatively low.

Here, the Al content (i.e., the V content) refers to, for example, the change shown diagrammatically in FIG. 3. In FIG. 3, the maximum and minimum values are the same, and the interval between adjacent maximum and minimum values is also the same, but the repeated change in the Al content in this specification and claims means that the Al content changes so that it alternates between maximum and minimum values, and the maximum and minimum values may or may not be the same, and the interval between adjacent maximum and minimum values may or may not be the same.

It is more preferable that the difference between the average value of the maximum value and the average value of the minimum value in the Al content ratio, that is, the difference (Δx) of x in the above-mentioned composition formula: (V1 _{- xAlx} )( _{CyN1 -y} ), is 0.03 to 0.10. This causes appropriate distortion in the crystal grains having a NaCl-type face-centered cubic structure, and reliably improves the hardness of the coating layer.

That is, if Δx is less than 0.03, the aforementioned distortion is small and the coating layer may not have sufficient hardness, whereas if it exceeds 0.10, the distortion becomes too large, increasing lattice defects and decreasing the hardness of the coating layer.

[2] Interval of Repeated Changes The average value of the interval between the repeated maximum and minimum values is more preferably 3 to 100 nm, because if it is less than 3 nm, the toughness of the coating layer may decrease, whereas if it exceeds 100 nm, improvement in the hardness of the coating layer may not be expected.

The interval between the repetition of the maximum and minimum values is determined by performing a line analysis along one of the equivalent crystal orientations represented by <001> of the crystal grains, measuring the Al content, and graphing the results. Note that a known noise removal method (e.g., the moving average method) is used for graphing and analysis.

That is, as shown in FIG. 3, a straight line m is drawn across the curve showing the repeated changes in the Al content. This straight line m is drawn so that the area of the region surrounded by the curve is equal above and below line m. Then, for each region where line m crosses the curve showing the repeated changes in the Al content, the maximum or minimum value of the Al content is found, and the distance between the two is measured. The measured values at multiple points are averaged to find the average distance of the repeated changes in the Al content in (VAl)(CN).

[3] Plane perpendicular to the direction of repeated change Furthermore, in a plane perpendicular to the direction of repeated change between the maximum and minimum values of the Al content (a plane having the direction of repeated change as its normal line; in FIG. 2, a plane having the direction of number (10) as its normal line), the variation range of x in the composition formula (V _1-x Al _x ) (C _y N _1-y ) (i.e., the difference between the maximum and minimum values) x0 is more preferably 0.01 or less.
When x0 is within this range, the hardness and chipping resistance of the coating layer are improved more reliably.

(7) Lattice constant of crystal grains having a NaCl-type face-centered cubic structure When an X-ray diffraction test is performed on a (VAl)(CN) layer using an X-ray diffractometer with Cu-Kα radiation as a radiation source to determine the lattice constant a of crystal grains having a NaCl-type face-centered cubic structure, it is more preferable that the lattice constant a satisfies the relationship of 0.05a _VN + 0.95a _AlN = 4.050≦a≦0.24a _VN + 0.76a _AlN = 4.068, where a VN of cubic _VN (JCPDS00-035-0768) is 4.1392 Å and a AlN of cubic _AlN (JCPDS00-046-1200) is 4.0450 Å. When this relationship is satisfied, by exhibiting a higher hardness, the (VAl)(CN) layer has a better impact resistance in addition to a better wear resistance.

(8) Microcrystal grains having a hexagonal crystal structure When the (VAl)(CN) layer is observed in a vertical cross section, each of the crystal grains having a NaCl-type face-centered cubic structure may be a columnar crystal, and the microcrystal grains having a hexagonal crystal structure may be present at the grain boundaries in an area ratio of 30% or less.

When fine crystal grains with a hexagonal crystal structure are present at an area ratio of 30% or less, slippage at the grain boundaries of crystal grains with a NaCl-type face-centered cubic structure is suppressed, and the toughness of the coating layer is reliably improved. However, if the area ratio exceeds 30%, the number of crystal grains with a NaCl-type face-centered cubic structure decreases, and the hardness of the coating layer may decrease.

The average grain size of the microcrystal grains having a hexagonal crystal structure is more preferably 0.01 to 0.30 μm. This is because if the average grain size is less than 0.01 μm, the aforementioned grain boundary sliding may not be sufficiently suppressed, while if it exceeds 0.30 μm, the distortion within the coating layer may become large, causing the hardness of the coating layer to decrease.

Here, the average grain size is calculated by finding the area of the microcrystal grains and taking the diameter of the circle that corresponds to this area.

2. Lower layer The coating layer including the (VAl)(CN) layer of this embodiment sufficiently achieves the above-mentioned object, but when a lower layer is provided which is made of one or more Ti compound layers selected from the group consisting of Ti carbide layers, nitride layers, carbonate layers and carbonitride layers and has a total average thickness of 0.1 to 20.0 μm, the coated tool exhibits more excellent properties in combination with the effects of this layer. However, when a lower layer is provided which is made of one or more Ti compound layers selected from the group consisting of Ti carbide layers, nitride layers, carbonate layers and carbonitride layers, if the total average thickness of the lower layer is less than 0.1 μm, the function of the lower layer is not fully exhibited, whereas if it exceeds 20.0 μm, the crystal grains tend to become coarse, making chipping more likely to occur.

3. Upper layer In addition, when an upper layer having a total average layer thickness including an aluminum oxide layer of 1.0 to 25.0 μm is provided on the coating layer including the (VAl)(CN) layer of this embodiment, the excellent properties of the coated tool are further exhibited, which is preferable. If the total average layer thickness is less than 1.0 μm, the function of the upper layer is not fully exhibited, while if it exceeds 25.0 μm, chipping is likely to occur.

II. Material of the Tool Base (1) Any material that is a conventionally known material for a tool base can be used as long as it does not impede the achievement of the object of the present invention. For example, the material is preferably any one of cemented carbide (WC-based cemented carbide, WC, Co, and carbonitrides of Ti, Ta, Nb, etc.), cermet (TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), and cBN sintered body.

(2) Shape The shape of the tool body is not particularly limited as long as it is a shape usable as a cutting tool, and examples of the shape include the shapes of an insert and a drill.

III. Manufacturing Method The (VAl)(CN) layer of this embodiment can be manufactured by a CVD method using, for example, a gas group A consisting of _NH3 gas and _H2 gas, and a gas group B consisting of _VCl4 , _AlCl3 , _N2 , and _H2 .

Here, gas group A and gas group B are supplied separately in the space inside the reaction vessel of the thermal CVD device up to just before the object to be deposited, and then gas group A and gas group B are mixed and reacted just before the object to be deposited. This is effective for uniformly supplying gas species with high reactivity to each other over the deposition area to deposit a uniform film. The detailed technical content is disclosed, for example, in Patent Publication No. 6511798.

The film forming apparatus described in this publication has a gas supply pipe as shown in FIGS. 4 to 6, and its structure will be described below.
As shown in Figures 4 and 5, the gas supply pipe (11), which is a cylindrical pipe that rotates at a predetermined rotational speed around its center (13), has its interior divided into approximately two equal parts by a partition member (12) extending along its axial direction, and has a gas group A flow section (14) and a gas group B flow section (15).

The gas supply pipe (11) is provided with multiple gas group A nozzles (16) and gas group B nozzles (17) along the height direction, which constitute a pair of nozzles (20) located at approximately the same height as shown in FIG. 4.

The gas group A nozzle (16) and the gas group B nozzle (17) shown in FIG. 5 belong to the same nozzle pair (20), and the angle between the center (18) of the outer peripheral opening end of the gas group A nozzle (16) and the center (19) of the outer peripheral opening end of the gas group B nozzle (17) is α.

As shown in FIG. 6, the relative angle around the axis between the raw gas group A nozzles 16 in two nozzle pairs (20) adjacent to each other in the height direction (axial direction) is β1, and the relative angle around the axis between the raw gas group B nozzles 17 in two nozzle pairs (20) adjacent to each other in the height direction (axial direction) is β2. The relative angles around the axis between the gas group A nozzle (16) and the gas group B nozzle (17) adjacent to each other in the height direction (axial direction) are γ1 and γ2, respectively.

IV. Measurement method (1) Average layer thickness After determining the surface of the tool base as described above, measurements are made along multiple analysis lines (e.g., five lines) in a direction perpendicular to the surface of the tool base. The average layer thickness of the (VAl)(CN) layer is determined by determining the layer thickness for each analysis line and averaging it to determine the average layer thickness, which is defined as the boundary with the adjacent layer where Al atoms appear and their content rate becomes 1 atomic %.

(2) Composition The composition of the (VAl)(CN) layer is determined as follows.
The average Al content x _avg is determined by irradiating a polished surface of a sample with an electron beam from the surface side of the sample using an electron probe microanalyzer (EPMA), and calculating the average Al content x _avg from the 10-point average of the characteristic X-ray analysis results obtained.

The average content ratio y _avg of C was determined by secondary ion mass spectroscopy (SIMS). An ion beam was irradiated to a 70 μm×70 μm area from the surface side of the sample, and the concentration of the components released by the sputtering action was measured in the depth direction.

(3) Crystal grains having a NaCl-type face-centered cubic structure The crystal structure of the (VAl)(CN) layer is identified by electron beam diffraction using a transmission electron microscope (TEM), it is confirmed that it is a NaCl-type face-centered cubic structure, and its area ratio is calculated.

(4) Tilt Angle Number Distribution Regarding the tilt angle number distribution of the (VAl)(CN) layer, the longitudinal section is set as the polished surface in the lens barrel of a field emission scanning electron microscope (FE-SEM), and an electron beam with an accelerating voltage of 15 kV and an irradiation current of 1 nA is irradiated to each of the crystal grains having a NaCl type face-centered cubic structure present within the measurement range of the polished cross-sectional surface at an incident angle of 70 degrees on the polished surface.

Using the EBSD method, the inclination angle of the normal to the {110} crystal plane of the (VAl)(CN) layer relative to the normal to the tool base surface (the direction perpendicular to the tool base surface at the polished surface) is measured at intervals of 0.01 μm/step for the coating layer within a measurement range of 50 μm in length horizontally to the tool base surface and along a cross section perpendicular to the tool base surface up to the layer thickness.

Then, based on the measurement results, the measured tilt angles within the range of 0 to 45 degrees are divided into 0.25 degree increments, and the number of degrees within each division is tallied to confirm the presence of a peak in the number of degrees (highest number of degrees) within the range of 0 to 10 degrees, and to determine the percentage of the number of degrees within the range of 0 to 10 degrees.

The present invention will be explained below with reference to examples, but the present invention is not limited to these examples. In other words, an insert cutting tool using a WC-based cemented carbide as the tool base will be given, but the material of the tool base may be as described above, and the shape of the tool base may be a drill or the like, as described above.

1. Manufacturing of tool base body As raw material powders, WC powder, TiC powder, TaC powder, NbC powder, _Cr3C2 powder and Co powder, all having an average particle size of 1 to ₃ μm, were prepared. These raw material powders were mixed according to the composition shown in Table 1, and wax was added thereto, and the mixture was mixed in acetone using a ball mill for 24 hours. The mixture was dried under reduced pressure and then pressed into a green compact of a predetermined shape at a pressure of 98 MPa.

The compact was then vacuum sintered in a vacuum of 5 Pa at a specified temperature in the range of 1370 to 1470°C for 1 hour. After sintering, tool bases A to C made of WC-based cemented carbide with the insert shape of Mitsubishi Materials Corporation's LOGU1207040PNER-M were manufactured.

2. Film formation A (VAl)(CN) layer was formed on the surface of each of the tool substrates A to C using a CVD apparatus to obtain Examples 1 to 10 shown in Tables 5 and 6. The film formation conditions were as shown in Table 2, and were generally as follows:

Reaction gas composition (the content ratio of gas components is expressed as volume % with the total of gas group A and gas group B being 100 volume %):
Gas group A _NH3 : 2.0-3.0%, _H2 : 55-60%
Gas group B: AlCl ₃ : 0.6 to 0.9%, VCl ₄ : 0.2 to 0.3%,
Al(CH ₃ ) ₃ : 0.0 to 0.5%, N ₂ : 0.0 to 12.0%,
_H2 : Residual reaction atmosphere pressure: 4.5 to 5.0 kPa
Reaction atmosphere temperature: 700 to 850°C

Here, gas group A and gas group B were supplied as source gas A and source gas B, respectively, in the CVD apparatus described in the above-mentioned Japanese Patent No. 6511798. The rotation speed of the gas supply pipe and the nozzle angle of the gas supply pipe were as follows:
Gas supply pipe rotation speed: 5 to 20 rpm
Gas supply pipe nozzle angle:
α: 180°
β1 and β2: 155°
γ1 and γ2: 25°

For Examples 4 to 10, the lower layer and/or upper layer shown in Table 4 were formed under the conditions shown in Table 3.

For comparison, a (VAl)(CN) layer was formed on the surface of tool substrates A to C under the film-forming conditions shown in Table 2, and Comparative Examples 1 to 10 shown in Tables 5 and 6 were obtained.
In the comparative example process, the source gas was not separated into two systems but was supplied into the reaction chamber of the thermal CVD device from one gas supply pipe. Therefore, a gas supply pipe was used that did not have a distinction between the gas group A nozzle (16) and the gas group B nozzle (17) and did not have a nozzle pair (20).
In addition, for Comparative Examples 4 to 10, the lower layer and/or the upper layer shown in Table 4 were formed under the conditions shown in Table 3.

The average Al content x _avg and the average C content y _avg were calculated for the above-mentioned Examples 1 to 10 and Comparative Examples 1 to 10 using the above-mentioned method. In addition, in each distribution of the number of inclination angles made by the normal line of the {110} plane with respect to the normal direction of the surface of the tool base, it was confirmed whether the maximum frequency of the number of inclination angles was in the range of 0 to 10 degrees, and the proportion of the frequency in which the inclination angle was in the range of 0 to 10 degrees was obtained. Furthermore, the presence or absence of repeated changes in the Al content along the equivalent orientation represented by <001> of the composition change of Al, the difference between the average maximum value and the average minimum value of the Al content, the average repetition interval, and further the change in the Al content in the plane perpendicular to the orientation were also measured.

In addition, the proportion of crystal grains having a NaCl type face-centered cubic structure, the lattice constants of TiN and AlN having a NaCl type face-centered cubic structure, and the area proportion of fine crystal grains present at the grain boundaries of columnar crystals having a NaCl type face-centered cubic structure were measured.
The average layer thickness was determined by observing the longitudinal section of each constituent layer using a scanning electron microscope (magnification: 5000 times), measuring the layer thickness at five points within the observation field, and averaging the results.

These results are summarized in Tables 5 and 6. Figure 7 shows the frequency distribution of the inclination angle between the normal direction of the surface of the tool base in Example 8 and the normal direction of the {110} plane of the crystal grains of the NaCl type face-centered cubic structure.

Next, for Examples 1 to 10 and Comparative Examples 1 to 10, a wet face milling test was carried out on alloy steel SCM440 while the specimens were clamped to the tip of a tool steel cutter with a cutter diameter of 32 mm using a fixture, and the flank wear width of the cutting edge was measured.

Cutting test: Wet face milling Workpiece material: JIS/SCM440 Width Cutting speed: 190m/min
Cutting depth: 6.0 mm
Cut ae: 20mm
Feed per blade: 0.12 mm/blade Cutting time: 80 minutes

The results of the cutting test are shown in Table 7. For Comparative Examples 1 to 10, the cutting edge fracture caused the tool to reach the end of its life, so the time to reach the end of its life is shown.

As is clear from the results shown in Table 7, none of the examples experienced chipping at the cutting edge, and chipping resistance was improved, demonstrating excellent cutting performance over a long period of time.
In contrast, in all of Comparative Examples 1 to 10, chipping occurred at the cutting edge, and the cutting edge reached the end of its useful life in a short period of time.

1 Tool base body 2 Coating layer 3 (VAl)(CN) layer 4 Lower layer 5 Upper layer 6 Crystal grains having a NaCl type face-centered cubic structure in the (VAl)(CN) layer 7 Normal direction of the {110} plane of the crystal grains having a NaCl type face-centered cubic structure in the (VAl)(CN) layer 8 Region with a relatively high Al content 9 Region with a relatively low Al content 10 Equivalent crystal orientation represented by <001> 11 Gas supply pipe 12 Partition member 13 Center of gas supply pipe 14 Gas group A flow section 15 Gas group B flow section 16 Gas group A nozzle 17 Gas group B nozzle 18 Center of the outer peripheral opening end of the gas group A nozzle 19 Center of the outer peripheral opening end of the gas group B nozzle 20 Angle β1 Angle β2 Angle γ1 Angle γ2 Angle

Claims (8)

A surface-coated cutting tool having a tool substrate and a coating layer on a surface of the tool substrate,
1) The coating layer has an average layer thickness of 1.0 to 20.0 μm, and comprises a composite nitride layer or composite carbonitride layer of V and Al, in which, when the composition is expressed by the composition formula (V _1-x Al _x ) (C _y N _1-y ), the average x content x _avg is 0.76 to 0.95 and the average y content y _avg is 0.000 to 0.015,
2) The composite nitride layer or composite carbonitride layer has composite nitride or composite carbonitride crystal grains having a NaCl type face-centered cubic structure,
3) In a frequency distribution of inclination angles of the normal direction of each {110} plane of the crystal grain relative to the normal direction of the surface of the tool base, the inclination angles in the range of 0 to 45 degrees are divided into increments of 0.25 degrees, and the maximum frequency is present in any of the inclination angle distributions of 0 to 10 degrees, and the sum of the frequency distributions of the inclination angle distributions of 0 to 10 degrees accounts for 45% or more of the sum of the frequencies of the entire inclination angle distribution.
A surface-coated cutting tool comprising: The surface-coated cutting tool according to claim 1, characterized in that the crystal grains are columnar crystals having an area-weighted average crystal grain width of 0.1 to 2.0 μm and an area-weighted average aspect ratio of 2.0 to 10.0, and have a repeated change in the Al content rate within the grains along any one of equivalent crystal orientations represented by <001>, with the Al content rate taking maximum and minimum values, and a difference Δx between the average value of the maximum values and the average value of the minimum values of x being 0.03 to 0.10. The surface-coated cutting tool according to claim 1 or 2, characterized in that the crystal grains are columnar crystals with an average crystal grain width of 0.1 to 2.0 μm and an average aspect ratio of 2.0 to 10.0, and have repeated changes in the Al content ratio along one of the equivalent crystal orientations represented by <001>, with the average interval of the repeated changes being 3 to 100 nm, and the change width x0 of x in a plane perpendicular to the orientation being 0.01 or less. The surface-coated cutting tool according to any one of claims 1 to 3, characterized in that the lattice constant a of the crystal grains satisfies the relationship _0.05aVN + _0.95aAlN ≦a≦ _0.24aVN + 0.76aAlN, where _aVN is the lattice constant of cubic VN and _aAlN is the lattice constant of cubic _AlN . 5. The surface-coated cutting tool according to claim 1, wherein the composite nitride or composite carbonitride layer is composed only of crystal grains of the composite nitride or composite carbonitride having a NaCl type face-centered cubic structure . The surface-coated cutting tool according to any one of claims 1 to 4, characterized in that the composite nitride or composite carbonitride layer contains fine crystal grains having a hexagonal crystal structure, the area ratio of the fine crystal grains is 30% or less, and the average grain size is 0.01 to 0.30 μm. A surface-coated cutting tool according to any one of claims 1 to 6, characterized in that a lower layer is present between the tool substrate and the V and Al composite nitride layer or composite carbonitride layer, the lower layer being made of one or more Ti compound layers selected from the group consisting of a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer and a carbonitride oxide layer, and having a total average layer thickness of 0.1 to 20.0 μm. The surface-coated cutting tool according to any one of claims 1 to 7, characterized in that an upper layer including at least an aluminum oxide layer is present on the upper portion of the composite nitride layer or composite carbonitride layer, with a total average layer thickness of 1.0 to 25.0 μm.

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