JP7712601B2 - 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).

Conventionally, in order to extend the life of cutting tools, there have been coated tools in which a coating layer is applied to the surface of a substrate such as a tungsten carbide (hereinafter sometimes referred to as WC)-based cemented carbide, and these coated tools have improved wear resistance and the like.
In order to further improve the cutting performance of the coated tool, various proposals have been made regarding the composition and structure of the coating layer.

For example, Patent Document 1 describes a coated tool having a coating layer which is composed of one or more layers, at least one of which includes a multilayer structure in which a first unit layer made of Ti1 _{- xAlxN} and a second unit layer made of _{Ti1- yAlyN} are alternately laminated, the first unit layer having an fcc type crystal structure, x in the Ti1 _{- xAlxN} satisfies 0<x<0.65, the second unit layer having an hcp type crystal structure, and y in the Ti1 _{- yAlyN} satisfies 0.65≦y<1, and the coated tool is said to have excellent hardness and oxidation resistance.

JP 2015-124407 A

The present invention was made in consideration of the above circumstances and proposals, and aims to obtain a surface-coated cutting tool with excellent wear resistance and thermal crack resistance.

The surface-coated cutting tool according to an embodiment of the present invention comprises:
A substrate and a coating layer on the surface of the substrate,
(a) the coating layer has an underlayer in contact with the substrate, a lower layer in contact with the underlayer, and an upper layer in contact with the lower layer,
(b) the underlayer has an average thickness of 0.05 to 2.00 μm and contains a nitride or carbonitride of Ti;
(c) the lower layer has an average thickness of 0.5 to 13.5 μm;
The composite material includes a composite nitride B or a composite carbonitride B' having a structure of (Al _XB Ti _1-XB )(C _YB N _1-YB ), and the average value of XB, XB _AVG , and the average value of YB, YB _AVG , are 0.50≦XB _AVG ≦0.75 and 0.00≦YB _AVG ≦0.05, respectively;
(d) the composite nitride B or composite carbonitride B' has crystal grains B of an NaCl type face-centered cubic structure of 80% or more by area in a cross section in the thickness direction of the coating layer,
(e) the crystal grains B include crystal grains in which the XB repeatedly increases and decreases in the thickness direction, an average value ΔXB of the difference between adjacent maximum and minimum values of the XB is 0.01 to 0.05, and the interval of the repeated change in the thickness direction is 1 to 12 nm;
(f) the upper layer has an average thickness of 0.5 to 9.4 μm;
The present invention includes a complex nitride C or a complex carbonitride C' having a structure of (Al _XC Ti _1-XC ) (C _YC N _1-YC ), wherein XC _AVG , which is an average value of XC, and YC _AVG , which is an average value of YC, are 0.50≦XC _AVG ≦0.75 and 0.00≦YC _AVG ≦0.05, respectively;
(g) the composite nitride C or composite carbonitride C' has crystal grains C of NaCl type face-centered cubic structure of 80% or more by area in the cross section in the thickness direction,
(h) the crystal grains C include crystal grains in which the XC repeatedly increases and decreases in the thickness direction, an average value ΔXC of the difference between adjacent maximum and minimum values of the XC is 0.10 to 0.50, and the interval of the repeated changes in the thickness direction is 20 to 100 nm;
(i) The lower layer and the upper layer satisfy the relationship 0.00≦XB _AVG −XC _AVG ≦0.10.

Furthermore, the surface-coated cutting tool according to the above embodiment may satisfy at least one of the following (1) to (3).

(1) in the lower layer, ρB=[Cl]/([Ti]+[Al]+[C]+[N]+[Cl]), where [Q] represents the number of atoms of element Q, is 0.001 to 0.050;
In the upper layer, ρC=[Cl]/([Ti]+[Al]+[C]+[N]+[Cl]) is 0.001 to 0.010.
(2) In the coating layer, the intensity value I(200) of the 200 diffraction line of the crystal grains having a face-centered cubic crystal structure of NaCl type and the intensity value I(111) of the 111 diffraction line of the same are:
The relationship 1.0≦I(200)/I(111) is satisfied.
(3) When the area surrounded by a line l extending 25 nm into each grain from the grain boundary between two adjacent crystal grains B is defined as area α, and the area surrounded by the line l and the grain boundary is defined as area β,
0.20≦xβ≦xα-0.10 (where xα is the average value of XB in region α, and xβ is the average value of XB in a region of 50 nm diameter at any position in region β) is present in 5 to 20% by area within region β.

The surface-coated cutting tool according to the above embodiment has excellent wear resistance and thermal crack resistance.

1 is a schematic vertical cross-sectional view of a surface-coated cutting tool according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a part of repeated changes in the Al content in a vertical cross section of a coating layer of a surface-coated cutting tool according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing regions α and β.

The present inventors have intensively studied ways to provide a coated tool having a coating layer of a composite carbide or nitride of Al and Ti (hereinafter, sometimes referred to as (AlTi)CN) with better wear resistance and thermal cracking resistance.
As a result, it was discovered that a coated tool can exhibit excellent wear resistance and thermal cracking resistance by providing an (AlTi)CN layer of a prescribed average thickness having a composition with excellent wear resistance on the surface side of the coated tool, and providing an (AlTi)CN layer of a prescribed average thickness having a composition with thermal cracking resistance underneath (on the substrate side), and both (AlTi)CN layers have a prescribed repeated change in Al content.

Hereinafter, a coated tool according to an embodiment of the present invention will be described in detail.
In this specification and claims, when a numerical range is expressed as "L to M" (L and M are both numerical values), this is equivalent to "greater than or equal to L and less than or equal to M", and the range includes an upper limit (M) and a lower limit (L). When a unit is stated only for the upper limit, the unit for the lower limit is also the same.

FIG. 1 is a schematic longitudinal sectional view of a coated tool according to an embodiment of the present invention (a cross section perpendicular to the surface of the substrate, with the surface of the substrate treated as a horizontal plane, ignoring minute irregularities on the surface of the substrate). As is clear from FIG. 1, the coated tool according to this embodiment has a base layer (2) in contact with the surface of the substrate (1), a lower layer (3) in contact with the base layer (2) on the tool surface side of the base layer (2), and an upper layer (4) in contact with the lower layer (3) on the tool surface side of the lower layer (3). The base layer (2), the lower layer (3), and the upper layer (4) constitute a coating layer (5). In addition, an outermost layer (6) may be selectively provided, as described later.
Each layer will be described in turn below.

1. Underlayer The underlayer in contact with the substrate surface is made of Ti nitride or carbonitride, and serves as a layer (adhesion layer) that provides adhesion between the substrate and the lower layer.

(1) Average composition The composition of the underlayer is not particularly limited (it is not limited to a stoichiometric composition) so long as it is a nitride or carbonitride of Ti. For example, it may have a composition formula TiC _Z N _1-Z (0≦Z≦0.5). Here, if Z is more than 0.5, the hardness of the underlayer increases excessively, and the underlayer may be easily peeled off from the interface with the substrate.

The ratio of Ti to (C _Z N _1-Z ) is not particularly limited, but is preferably 1:0.8 to 1:1.2, because the object of the present invention can be reliably achieved within this range.

(2) Average thickness The average thickness of the undercoat layer is preferably 0.05 to 2.00 μm. The reason is that if it is thinner than 0.05 μm, it will not function as an adhesive layer sufficiently, while if it is 2.00 μm or more, the thickness of the adhesive layer in the coating layer will be too large, and sufficient wear resistance will not be obtained. The average thickness of the undercoat layer is more preferably 0.10 to 1.50 μm.

2. Lower Layer The lower layer provided on the tool surface side in contact with the surface of the base layer is an (AlTi)CN layer, which acts as a layer for suppressing the propagation of thermal cracks propagating toward the base material.

(1) Average Composition In the lower layer, in (Al _XB Ti _1-XB ) (C _YB N _1-YB ), it is preferable that the average XB content, XB _AVG , and the average YB content, YB _AVG , satisfy 0.50≦XB _AVG ≦0.75 and 0.00≦YB _AVG ≦0.05.

The reason is that if XB _AVG is less than 0.50, the inherent high oxidation resistance of the (AlTi)CN coating cannot be fully obtained, while if XB _AVG exceeds 0.75, it becomes difficult to obtain good adhesion with the adjacent upper layer, and the upper layer is easily peeled off, resulting in poor durability. It is more preferable that the value of XB _AVG is 0.65≦XB _AVG ≦0.75.
The C component in (AlTi)CN has the effect of improving hardness and may be contained. However, if YB _AVG exceeds 0.05, the high temperature strength of the lower layer decreases, so it is preferable to set 0.00≦YB _AVG <0.05.

The ratio of (Al _XB Ti _1-XB ) to (C _YB N _1-YB ) is not particularly limited, but is preferably 1:0.8 to 1:1.2, because the object of the present invention can be reliably achieved within this range.
The same is true for the upper layers (Al _XC Ti _1-XC ) and (C _YC N _1-YC ).

(2) Crystal grains with NaCl type face-centered cubic structure In the lower layer, the proportion of crystal grains with NaCl type face-centered cubic structure is preferably 80 area % or more. The reason is that if it is less than 80 area %, the proportion of the soft wurtzite type hexagonal structure, which is the inherent stable phase of (AlTi)CN, increases in the lower layer, and sufficient durability of the coated tool cannot be obtained. The proportion of crystal grains with NaCl type face-centered cubic structure is more preferably 90 area % or more. It may be 100 area %.

(3) Average Thickness The average thickness of the lower layer is preferably 0.5 to 13.5 μm. The reason is that if it is less than 0.5 μm, the suppression of the thermal cracking cannot be sufficiently achieved, while if it exceeds 13.5 μm, the crystal grains of the lower layer become coarse, and although wear resistance is achieved, damage accompanied by the falling off of crystal grains due to processing shock is likely to occur, leading to abnormal damage to the coated tool. The average thickness of the lower layer is more preferably 2.0 to 7.0 μm.

(4) Repeated increase and decrease of XB In the lower layer, the proportion of crystal grains in which XB repeatedly increases and decreases in the thickness direction of the coating layer is preferably 60% or more by area. The reason is that if it is less than 60% by area, the above-mentioned suppression of thermal crack propagation cannot be sufficiently obtained. The proportion of crystal grains in which XB repeatedly increases and decreases may be 100% by area.

In the repeated increase and decrease of XB, it is preferable that the average value ΔXB of the difference between adjacent maximum and minimum values is 0.01 to 0.05. The reason for setting ΔXB in this range is that if it is less than 0.01, crack propagation is not sufficiently suppressed and chipping resistance decreases, while if it exceeds 0.05, the lattice distortion occurring at the boundary between the high Al content region and the low Al content region becomes large, which becomes the starting point of fracture during cutting and causes abnormal damage such as chipping. It is more preferable that ΔXB is 0.01 to 0.03.

In addition, it is preferable that the average value of the distance between adjacent maximum and minimum values, i.e., the average distance in the thickness direction of the coating layer, is 1 to 12 nm. The reason for setting the average distance within this range is that if the average distance is less than 1 nm, the number of boundaries between regions with high Al content and regions with low Al content increases, which leads to a local decrease in adhesion strength and a tendency for plastic deformation to occur, resulting in a decrease in chipping resistance and hardness, while if it exceeds 12 nm, the cushioning effect of the lower layer to suppress crack propagation during cutting is insufficient. It is more preferable that the average distance is 1 to 5 nm.

Figure 2 is a schematic diagram showing part of an example of repeated increase and decrease in XB (repeated change in Al content). In Figure 2, the maximum and minimum values are the same, and the interval between adjacent maximum and minimum values is also the same, but repeated increase and decrease in XB may be such that XB alternates between maximum and minimum values, and the maximum and minimum values may or may not be the same value, and the interval between adjacent maximum and minimum values may or may not be the same.

Here, the average distance between the position of the maximum value in the lower layer where XB increases and decreases repeatedly and the adjacent position of the minimum value is determined by measuring the Al content in the thickness direction of the lower layer for each crystal grain having a NaCl-type face-centered cubic structure, removing noise that is not considered to be a repeated change in XB using a known means such as a low-pass filter, and graphing the result.

That is, as shown in FIG. 2, a straight line m is drawn across the curve showing the repeated increase and decrease of XB (in FIG. 2, the straight line m shows the length crossing two maximum values and two minimum values, but the length of the straight line m is not limited to this, and is the length that allows the average value of the maximum value and the minimum value and the average interval to be obtained with high accuracy). This straight line m is drawn so that the area of the region surrounded by the curve is equal on the upper side and the lower side of the straight line m (m=XB _AVG ). Then, for each region where the straight line m crosses the curve showing the repeated change of the Al content, the maximum value or the minimum value of XB is obtained, the interval between the two is measured, and the measured values at multiple points are averaged to obtain the average interval of the repeated increase and decrease of XB for each crystal grain having a NaCl type face-centered cubic structure in the lower layer. In addition, the average value of the difference between the adjacent maximum value and the minimum value in the repeated increase and decrease of the Al content ratio XB is obtained and calculated as ΔXB.

(5) Cl Content In the lower layer, it is more preferable that ρB=[Cl]/([Ti]+[Al]+[C]+[N]+[Cl]) (where [Q] represents the number of atoms of element Q) is 0.001 to 0.050.
The reason for specifying this range for ρB is that if it is less than 0.001, the lubricity of the coating layer may be insufficient, while if it exceeds 0.050, the toughness of the lower layer may be impaired, resulting in reduced chipping resistance.

(6) Relationship between the vicinity of the grain boundary of XB and other areas As shown in FIG. 3, in the lower layer, for adjacent crystal grains of NaCl type face-centered cubic structure, the area surrounded by a line l(10) 25 nm away from the grain boundary between the two crystal grains is defined as region α(8), and the area surrounded by the line l(10) and the grain boundary is defined as region β(9).
It is even more preferable that the areas satisfying 0.20≦XBβ≦XBα-0.10 account for 5 to 20% by area within region β.
Here, XBα is the average value of XB in region α, and XBβ is the average value of XB in a region of 50 nm diameter at an arbitrary position in region B.

The reasons are as follows:
Regarding the above-mentioned relational expression, if XBβ>XBα-0.10, the movement of dislocations is suppressed, and the hardness of the TiAlCN layer may not be improved sufficiently, and the effect of improving chipping resistance due to the increase in the lattice constant near the grain boundary and the application of compressive stress to the (TiAl)CN layer may be small. On the other hand, if XBβ is less than 0.20, the high-temperature oxidation resistance of the (TiAl)CN layer may be poor, and the chipping resistance may be reduced. Therefore, it is even more preferable that 0.20≦XBβ≦XBα-0.10 is satisfied.

Regarding the area percentage of the area in region β that satisfies the above-mentioned relational formula regarding the composition of region α and region β, if the percentage present in region β is less than 5 area %, the effect of improving the hardness and chipping resistance of the (TiAl)CN layer may not be sufficient, and if it exceeds 20 area %, the high-temperature oxidation resistance of the (TiAl)CN layer may be poor, resulting in a decrease in chipping resistance. Therefore, it is more preferable that this area percentage be 5 to 20 area %, and even more preferably 10 to 20 area %.

Here, a method for measuring the compositions of the regions α and β will be described.
First, the grain boundaries of the crystal grains constituting the (TiAl)CN layer are obtained and the crystal grains are specified as follows. That is, using a crystal orientation analyzer attached to a transmission electron microscope (TEM), the polished longitudinal section is irradiated with an electron beam tilted, for example, at 0.5 to 1.0 degrees with respect to the normal direction of the polished surface in a precession motion, while the electron beam is scanned at any beam diameter and interval, and electron diffraction patterns are continuously captured to analyze the crystal orientation of each measurement point. The observation field can be exemplified as a width of 50 μm in the direction parallel to the substrate surface and a thickness (average thickness) of the coating layer in the vertical direction.

The conditions for obtaining the electron beam diffraction pattern used in this measurement are, for example, an acceleration voltage of 200 kV, a camera length of 20 cm, a beam size of 2.4 nm, and a measurement step of 5.0 nm. At this time, the measured crystal orientation is measured discretely on the measurement surface, and the measurement results are used to represent the area up to the middle between adjacent measurement points, thereby obtaining the orientation distribution of the entire measurement surface. An example of the area represented by these measurement points (hereinafter sometimes referred to as a pixel) is a regular hexagon. If there is an angle difference of 5 degrees or more in the crystal orientation between adjacent pixels, or if only one of the adjacent pixels shows a NaCl-type face-centered cubic structure, the side of the area where these pixels contact is considered to be a grain boundary. Then, the part surrounded by the side considered to be a grain boundary is defined as one crystal grain. However, a single pixel that has an orientation difference of 5 degrees or more with all adjacent pixels, or that does not have an adjacent measurement point with a NaCl-type face-centered cubic structure, is not considered to be a crystal grain, and a pixel that is connected to two or more pixels is treated as a crystal grain. In this way, grain boundaries are determined and crystal grains are identified.

Next, an observation field is defined that includes at least 10 crystal grains having a NaCl type face-centered cubic structure identified by the above procedure. Based on the grain boundaries determined when identifying the crystal grains, a line l (10) is drawn using software at a distance of 25 nm from the grain boundaries of adjacent NaCl type face-centered cubic crystal grains within each crystal grain, thereby defining regions α and β. Then, area analysis is performed using Energy Dispersive X-ray Spectrometry (EDS) using a TEM (e.g., beam diameter 1 nm). For region α, XBα is calculated for all regions α within the observation field. Then, for region β, all regions β within the observation field are divided into 50 nm intervals, and area analysis (circular shapes with a diameter of 50 nm) is performed for each divided range, and the area ratio of the areas that satisfy 0.20≦XBβ≦XBα-0.10 in region β is calculated.

3. Upper layer The upper layer is an (AlTi)CN layer, which improves the wear resistance during cutting and acts as a layer that suppresses adhesion of deposits originating from the work material.

(1) Average Composition In the upper layer, in (Al _XC Ti _1-XC ) (C _YC N _1-YC ), it is preferable that XC _AVG , which is the average content of XC, and YC _AVG , which is the average content of YC, satisfy 0.50≦XC _AVG ≦0.75 and 0.00≦YC _AVG ≦0.05.

The reason is that if XC _AVG is less than 0.50, the high oxidation resistance of (AlTi)CN cannot be obtained sufficiently, while if XC _AVG is more than 0.75, the desired wear resistance and the desired suppression of adhesion cannot be obtained. It is more preferable that XC _AVG is 0.65≦XC _AVG ≦0.75. The C component in (AlTi)CN may be contained since it has the effect of improving hardness. However, if YC _AVG exceeds 0.05, the high temperature strength decreases, so YC _AVG is preferably less than 0.05.

(2) Crystal grains with NaCl type face-centered cubic structure In the upper layer, the proportion of crystal grains with NaCl type face-centered cubic structure is preferably 80 area % or more. The reason is that if it is less than 80 area %, the proportion of the soft wurtzite type hexagonal structure, which is the inherent stable phase of (AlTi)CN, increases in the upper layer, and sufficient durability of the coated tool cannot be obtained. The proportion of crystal grains with NaCl type face-centered cubic structure is more preferably 90 area % or more. It may be 100 area %.

(3) Average thickness The average thickness of the upper layer is preferably 0.5 to 9.4 μm. The reason is that if it is less than 0.5 μm, sufficient wear resistance and suppression of adhesion cannot be obtained, while if it exceeds 9.4 μm, damage in the upper layer originating from thermal cracks that progress toward the substrate during cutting processing becomes large, which may cause abnormal damage to the tool. The average thickness of the upper layer is more preferably 2.0 to 5.0 μm.

(4) Repeated increase and decrease of XC In the upper layer, the proportion of crystal grains in which XC repeatedly increases and decreases in the thickness direction of the coating layer is preferably 60% or more by area. The reason is that if it is less than 60% by area, sufficient wear resistance cannot be obtained. The proportion of crystal grains in which XC repeatedly increases and decreases may be 100% by area.

In the repeated increase and decrease of XC, it is preferable that the average value ΔXC of the difference between adjacent maximum and minimum values is 0.10 to 0.50. The reason for setting ΔXC in this range is that if it is less than 0.10, even if there is repeated increase and decrease of XB in the lower layer, the crack propagation in the upper layer is not sufficiently suppressed and chipping resistance is reduced, while if it exceeds 0.50, the lattice distortion occurring at the boundary between the high Al content region and the low Al content region in the upper layer becomes large, increasing crystal defects and reducing the hardness of the upper layer. It is more preferable that ΔXC is 0.30 to 0.50.

In addition, it is preferable that the average value of the intervals between adjacent maximum and minimum values, i.e., the average interval in the thickness direction of the coating layer, is 20 to 100 nm. The reason for setting the average interval in this range is that if the average interval is less than 20 nm, the toughness of the coating layer will not be sufficiently improved even if there are repeated increases and decreases in XB in the lower layer, while if it exceeds 100 nm, the upper layer will not be able to sufficiently suppress crack propagation during cutting, resulting in reduced chipping resistance and stiffness. It is more preferable that the average interval is 60 to 100 nm.

The definition and measurement method of the average value ΔXC of the difference between adjacent maximum and minimum values in the repeated increase and decrease of XC, and the average interval of the repeated increase and decrease of XC, are the same as those of the repeated increase and decrease of XB.

(5) Cl Content In the upper layer, it is more preferable that ρC=[Cl]/([Ti]+[Al]+[C]+[N]+[Cl]) (where [Q] represents the number of atoms of element Q) is 0.001 to 0.010.
The reason for specifying this range for ρC is that if it is less than 0.001, the lubricity of the coating layer may be insufficient, while if it exceeds 0.010, the toughness of the upper layer may be impaired, resulting in reduced chipping resistance.

4. Relationship between XB _AVG and XC _AVG (0.00≦XB _AVG -XC _AVG ≦0.10)
The upper and lower layers preferably satisfy 0.00≦XB _AVG -XC _AVG ≦0.10. If XB _AVG -XC _AVG >0.1, the difference in the average Al content becomes large, which inhibits continuous crystal growth between the lower and upper layers. It is more preferable that 0.00≦XB _avg -XC _avg ≦0.05.

5. Value of I(200)/I(111) In the lower and upper layers, it is more preferable that the intensity value I(200) of the 200 diffraction line and the intensity value I(111) of the 111 diffraction line of the crystal grains having a NaCl type face-centered cubic crystal structure satisfy the relationship 1.0≦I(200)/I(111).

In order to achieve the above-mentioned object, it is preferable that the upper layer grows continuously as if the crystal grains of the upper layer are fitted into the tips of the crystal grains of the lower layer at the interface between the lower and upper layers. Since the upper layer grows in the <111> preferential direction, the I(200)/I(111) index was used to confirm that the upper layer is growing continuously.
If I(200)/I(111) is less than 1.0, this continuous growth is not sufficient, and the suppression of thermal crack propagation in the lower layer may be insufficient.

5. Other layers (1) Outermost layer In this embodiment, an outermost layer consisting of one or more Ti compound layers selected from Ti nitride layers, carbide layers, and carbonitride layers (which are not limited to stoichiometric compositions) and having a total average layer thickness of 0.1 to 4.00 μm may be provided in contact with the upper layer (the outermost layer may not be provided). When this outermost layer is provided, the clear color of these layers makes it easy to identify corners (identify used parts) after cutting when the coated tool is an insert. Here, if the total average layer thickness is less than 0.1 μm, the purpose of providing the outermost layer is not fully achieved, while if it exceeds 4.0 μm, chipping is likely to occur.

(2) Unintended Layers When the deposition gas is switched, very small amounts of layers other than the underlying TiCN layer, Ti carbide, nitride, carbonate and oxycarbonitride layer, (AlTi)CN layer, and α-Al ₂ O ₃ layer may be produced unintentionally.

6. Composition of Substrate (1) In this embodiment, the substrate may be made of, but is not limited to, cemented carbide (WC-based cemented carbide: containing Co in addition to WC, and further containing carbonitrides of Ti, Ta, Nb, etc.), cermet (containing TiC, TiN, TiCN, etc. as main components), ceramics (silicon nitride, sialon, aluminum oxide, etc.), or cBN sintered body.

(2) Shape The shape of the substrate is not particularly limited as long as it is a shape that can be used as a cutting tool, and examples of the shape include the shapes of an insert and a drill.

7. Composition Measurement The Al contents XB, XC and C contents YB, YC in the lower and upper layers were determined by averaging the results of Auger electron analysis obtained by irradiating a vertical section of a polished cross-section of a sample with an electron beam and performing five or more line analyses in the thickness direction of the coating layer using Auger electron spectroscopy (AES).

8. Measurement of the proportion of crystal grains having a NaCl type face-centered cubic structure The area proportion of crystal grains having a NaCl type face-centered cubic crystal structure is determined for each layer by defining the crystal grain boundaries by electron backscatter diffraction as described above, and then identifying the crystal structure of each crystal grain having a NaCl type face-centered cubic crystal structure based on the diffraction image.

9. Measurement of average thickness The average thickness of each layer constituting the coating layer can be obtained by, for example, preparing a sample for observing a vertical cross section of the coating layer at any position using a focused ion beam system (FIB), a cross section polisher (CP), or the like, observing the vertical cross section at multiple positions (e.g., 5 positions) using a scanning electron microscope (SEM) or TEM, a scanning transmission electron microscope (STEM), or an energy dispersive X-ray spectrometry (EDX) attached to the SEM or TEM, and averaging the thicknesses.

10. Measurement of I(111) and I(200) It is not possible to obtain X-ray diffraction results for only the lower layer or only the upper layer, and the X-ray diffraction results for the underlayer, lower layer, and upper layer (and the outermost layer, which is optionally provided) are shown together (collectively). In other words, the X-ray diffraction results for the coating layer are shown.

The value of I(200)/I(111) is calculated as follows. For example, X-ray diffraction is performed on the coating layer surface parallel to the substrate surface using Cu-Kα1 radiation as the X-ray source under the conditions of measurement range (2θ): 20 to 120 degrees, scan step: 0.013 degrees, and measurement time per step: 0.48 sec/step, and X-ray diffraction peaks that appear between the diffraction angles of the same crystal planes shown in JCPDS00-038-1420 cubic TiN and JCPDS00-046-1200 cubic AlN (for example, 36.66 to 38.53°, 43.59 to 44.77°, 61.81 to 65.18°) are confirmed. Then, the measured X-ray diffraction peak intensities for the 200 diffraction line and the 111 diffraction line are measured to obtain I(200)/I(111), which is the ratio of the intensity I(200) of the 200 diffraction line to the intensity I(111) of the 111 diffraction line.

11. Manufacturing Method The coating layer of the coated tool of this embodiment can be manufactured by a chemical vapor deposition method under the following manufacturing conditions, for example.

(1) Production of Underlayer For example, the following production conditions 1) or 2) can be exemplified.

1) Manufacturing conditions 1
TiN layer deposition Reaction gas composition (volume %)
TiCl ₄ : 3.0-6.0%, N ₂ : 25.0-35.0%, H ₂ : balance Reaction atmosphere pressure: 4.0-12.0 kPa
Reaction atmosphere temperature: 780 to 900°C

2) Manufacturing conditions 2
TiCN layer deposition Reaction gas composition (volume %)
TiCl ₄ : 3.0-6.0%, N ₂ : 15.0-30.0%
_CH4 or _CH3CN : 0.6-2.0%, _H2 : balance Reaction atmosphere pressure: 5.0-12.0 kPa
Reaction atmosphere temperature: 780 to 900°C

(2) Production of the lower layer Reaction gas composition (volume %)
Gas group B1: _NH3 : 4.0-5.5%, _H2 : 65-76%
Gas group B2: AlCl ₃ : 0.45 to 0.90%, TiCl ₄ : 0.20 to 0.55%,
_N2 : 0.0-12.0%, _{C2H4 :} 0.0-0.5%, _H2 : residual reaction atmospheric pressure: 4.0-5.0 kPa
Reaction atmosphere temperature: 700 to 900°C
Gas supply cycle: 1.0 to 5.0 seconds Gas supply time per cycle: 0.1 to 0.2 seconds Phase difference between the supply of gas group B1 and the supply of gas group B2: 0.1 to 0.2 seconds

(3) Production of the upper layer Reaction gas composition (volume %)
Gas group C1: _NH3 : 1.5-3.0%, _H2 : 65-76%
Gas group C2: AlCl ₃ : 0.45-0.75%, TiCl ₄ : 0.20-0.55%,
_N2 : 0.0-12.0%, _{C2H4 :} 0.0-0.5%, _H2 : residual reaction atmospheric pressure: 4.0-5.0 kPa
Reaction atmosphere temperature: 700 to 900°C
Gas supply cycle: 6.0 to 10.0 seconds Gas supply time per cycle: 0.3 to 0.5 seconds Phase difference between the supply of gas group C1 and the supply of gas group C2: 0.1 to 0.3 seconds

Next, an embodiment will be described.
Here, as an example, we will describe an application to an insert cutting tool using a WC-based cemented carbide as the substrate, but the same applies when the above-mentioned material is used as the substrate, and also when applied to drills and end mills.

As raw material powders, WC powder, TiC powder, _TaC powder, NbC powder, _Cr3C2 powder and Co powder were prepared, and these raw material powders were blended as shown in Table 1. Wax was added, and the mixture was mixed in acetone with a ball mill for 24 hours, dried under reduced pressure, and then pressed into a green compact of a predetermined shape at a pressure of 98 MPa. This green compact was vacuum sintered under conditions of holding at 1420°C in a vacuum of 5 Pa for 1 hour, to produce WC-based cemented carbide substrates A to C having the ISO standard SEEN1203AFSN shape. Note that each raw material powder contained a trace amount of unavoidable impurities.

Next, the undercoat layer, lower layer, and upper layer were formed on the surfaces of these substrates A to C in order according to the manufacturing conditions shown in Tables 2 to 4, respectively, to obtain coated tools 1 to 8 of the examples shown in Table 5 (hereinafter, Examples 1 to 8). In Table 2, the deposition gas for the undercoat layer is referred to as gas group A.

For comparison, a base layer, a lower layer, and an upper layer were formed on the surfaces of substrates A to C in that order according to the manufacturing conditions shown in Tables 2 to 4, respectively, to obtain comparative coated tools 1 to 8 (hereinafter, Comparative Examples 1 to 8) shown in Table 6.

For Examples 1 to 8 and Comparative Examples 1 to 8, when determining the grain boundaries of the crystal grains that make up the TiAlCN layer by electron beam diffraction, the pixels were made to have a regular hexagonal shape.

In Tables 5 and 6, in the column "Does it satisfy 1.0 ≦ I(200)/I(111)?", "〇" indicates that it satisfies 1.0 ≦ I(200)/I(111), and "×" indicates that it does not satisfy 1.0 ≦ I(200)/I(111) (1.0 > I(200)/I(111)).

Next, for the coated tools 1-8 of the present invention and the comparative coated tools 1-8, the various tool bases A-C (ISO standard SEEN1203AFSN shape) were all clamped to the tip of an alloy steel cutter with a cutter diameter of 80 mm using a fixture, and the following wet high-speed face milling and center cut cutting tests of Ti alloys were carried out to measure the flank wear width of the cutting edge. Table 7 shows the results of the cutting tests. Note that for the comparative coated tools 1-8, chipping occurred, causing them to reach the end of their life before the end of the cutting time, so the time until the end of their life is shown.

Cutting test: Wet high-speed face milling, center cut cutting test Cutter diameter: 80 mm
Workpiece: JIS Ti-6Al-4V alloy (60 types) block Cutting speed: 100 m/min
Cut: 2.5mm
Feed: 0.25 mm/tooth Cutting time: 10 minutes

In Table 7, the cutting time (min) until the end of life for the comparative example indicates the cutting time (min) until the end of life is reached due to chipping.

As is clear from Table 7, all of the examples had a long maximum machining time, which is the time it takes for the cutting edge to break, and had excellent durability.

1 Substrate 2 Base layer 3 Lower layer 4 Upper layer 5 Covering layer 6 Outermost layer 7 Grain boundary 8 Area α
9 Area β
10 line l

Claims (4)

A surface-coated cutting tool having a substrate and a coating layer on a surface of the substrate,
(a) the coating layer has an underlayer in contact with the substrate, a lower layer in contact with the underlayer, and an upper layer in contact with the lower layer,
(b) the underlayer has an average thickness of 0.05 to 2.0 μm and contains a nitride or carbonitride of Ti;
(c) the lower layer has an average thickness of 0.5 to 13.5 μm;
The composite material includes a composite nitride B or a composite carbonitride B' having a structure of (Al _XB Ti _1-XB )(C _YB N _1-YB ), and the average value of XB, XB _AVG , and the average value of YB, YB _AVG , are 0.50≦XB _AVG ≦0.75 and 0.00≦YB _AVG ≦0.05, respectively;
(d) the composite nitride B or composite carbonitride B' has crystal grains B of an NaCl type face-centered cubic structure of 80% or more by area in a cross section in the thickness direction of the coating layer,
(e) the crystal grains B include crystal grains in which the XB repeatedly increases and decreases in the thickness direction, an average value ΔXB of the difference between adjacent maximum and minimum values of the XB is 0.01 to 0.05, and the interval of the repeated change in the thickness direction is 1 to 12 nm;
(f) the upper layer has an average thickness of 0.5 to 9.4 μm;
The present invention includes a complex nitride C or a complex carbonitride C' having a structure of (Al _XC Ti _1-XC ) (C _YC N _1-YC ), wherein XC _AVG , which is an average value of XC, and YC _AVG , which is an average value of YC, are 0.50≦XC _AVG ≦0.75 and 0.00≦YC _AVG ≦0.05, respectively;
(g) the composite nitride C or composite carbonitride C' has crystal grains C of NaCl type face-centered cubic structure of 80% or more by area in the cross section in the thickness direction,
(h) the crystal grains C include crystal grains in which the XC repeatedly increases and decreases in the thickness direction, an average value ΔXC of the difference between adjacent maximum and minimum values of the XC is 0.10 to 0.50, and the interval of the repeated changes in the thickness direction is 20 to 100 nm;
(i) The lower layer and the upper layer satisfy 0.00≦XB _AVG −XC _AVG ≦0.10. In the lower layer, ρB=[Cl]/([Ti]+[Al]+[C]+[N]+[Cl]) (where [Q] represents the number of atoms of element Q) is 0.001 to 0.050;
2. The surface-coated cutting tool according to claim 1, characterized in that in the upper layer, ρC=[Cl]/([Ti]+[Al]+[C]+[N]+[Cl]) is 0.001 to 0.010. In the coating layer, the intensity value I(200) of the 200 diffraction line of the crystal grains having a face-centered cubic crystal structure of NaCl type and the intensity value I(111) of the 111 diffraction line of the same are:
3. The surface-coated cutting tool according to claim 1, wherein the relationship: 1.0≦I(200)/I(111) is satisfied. When the area surrounded by a line l extending 25 nm into each grain from the grain boundary between two adjacent crystal grains B is defined as area α, and the area surrounded by the line l and the grain boundary is defined as area β,
4. The surface-coated cutting tool according to claim 1, wherein areas satisfying 0.20≦xβ≦xα-0.10 (where xα is an average value of XB in the area α, and xβ is an average value of XB in an area of 50 nm diameter at an arbitrary position in the area β) are present in an area β at 5 to 20% by area.