JP6996064B2 - Surface coating cutting tool and its manufacturing method - Google Patents

Description

The present invention relates to a surface-coated cutting tool and a method for manufacturing the same.

Conventionally, a surface-coated cutting tool having a base material and a coating film covering the base material has been known to include one or both of a TiCN layer and a TiC layer as a coating film.

Geun-Woo, Park, 1 others, "Structural and Mechanical Properties of Multilayered CVD TiC / TiCN Coatings with Variations of Multilayer Period", Materials Science Forum, Switzerland, Trans Tech Publications, 2007, vols.534-536, p.1233 -1236 (Non-Patent Document 1) discloses a coating film containing a laminated structure of TiC and TiCN formed on a cemented carbide by a CVD method (chemical vapor deposition method) as a coating film for a cutting tool. There is.

Anongsack Paseuth, 4 others, "Microstructure, mechanical properties, and cutting performance of TiC _x N _1-x coatings with various x values alloyed by moderate temperature chemical vapor deposition", Surface & Coatings Technology, Switzerland, Elesevier, 2014, vol. 260, p.139-147 (Non-Patent Document 2) discloses a coating film made of TiC _x N _1-x formed on a cemented carbide by a CVD method as a coating film for a cutting tool.

Geun-Woo, Park, 1 others, "Structural and Mechanical Properties of Multilayered CVD TiC / TiCN Coatings with Variations of Multilayer Period", Materials Science Forum, Switzerland, Trans Tech Publications, 2007, vols.534-536, p.1233 -1236 Anongsack Paseuth, 4 others, "Microstructure, mechanical properties, and cutting performance of TiCxN1-xcoatings with various x values sintered by moderate temperature chemical vapor deposition", Surface & Coatings Technology, Switzerland, Elesevier, 2014, vol.260, p. 139-147

In Non-Patent Document 1, a gas containing CH ₄ is used as a raw material gas for the TiCN layer and the TiC layer in the CVD method. CH ₄ does not thermally decompose unless it is about 1000 ° C. or higher. Therefore, the CVD method using CH ₄ is performed under high temperature conditions of 1000 ° C. or higher. Under this condition, mutual diffusion is likely to occur between the base material made of cemented carbide and the coating during the formation of the coating, and the η layer, which is an embrittlement layer, is likely to be formed at the interface between the base material and the coating.

Further, in Non-Patent Document 1, since the CVD method is performed under a high temperature condition of 1000 ° C. or higher, the atoms vapor-deposited on the substrate easily move on the substrate, so that the direction of crystal growth is difficult to be constant and the particles are granular. Crystals are easy to grow. In a film made of granular crystals, the number of fracture starting points increases due to the large number of crystal interfaces, the film tends to fall off due to brittle fracture, and the chipping resistance of the film decreases.

In Non-Patent Document 2, in the CVD method, TiCl ₄ , CH ₃ CN, C ₂ H ₄ , N ₂ and H ₂ are used as the raw material gas for the TiC _x N _1-x layer, and the gas is formed under a temperature condition of 840 ° C. The membrane is made. Under this condition, the content of C in the TiC _x N _1-x layer tends to be large (for example, 0.65 <x <0.9). In the TiC _x N _1-x layer, when the C content is increased, the hardness is improved, but the chipping resistance is lowered. Further, in the TiC _x N _1-x layer, when the C content is increased, the oxidation start temperature tends to decrease, and there is room for improvement in the oxidation resistance.

Further, in Non-Patent Document 2, since the coating film is strongly oriented on the (422) surface having a high Young's modulus, the coating film is easily broken and there is room for improvement in chipping resistance.

Further, in Non-Patent Document 2, since the film formation temperature is low, C ₂ H ₄ in the raw material gas aggregates and carbonizes, and is mixed as free carbon in the TiC _x N _1-x layer. When free carbon is contained in the film, the film becomes sparse and the fracture starting point increases, so that the chipping resistance of the film decreases.

Therefore, an object of the present invention is to provide a surface-coated cutting tool having excellent wear resistance and chipping resistance and a method for manufacturing the same.

The surface-coated cutting tool according to one aspect of the present invention is
[1] A surface-coated cutting tool comprising a base material and a coating film covering the base material.
The coating comprises a first hard layer having a plurality of columnar crystals.
Each of the columnar crystals has the following formula (1).
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
The first unit layer represented by and the following formula (2)
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
It has a multi-layer structure in which the second unit layer shown by is alternately laminated, and has a multi-layer structure.
In the columnar crystal, the layer closest to the substrate is the first unit layer, which is a surface coating cutting tool.

The method for manufacturing a surface-coated cutting tool according to another aspect of the present invention is as follows.
[2] The method for manufacturing a surface-coated cutting tool according to the above [1].
The process of preparing the base material and
A step of forming a film on the base material is provided.
The step of forming the coating film includes a first unit layer forming step and a second unit layer forming step.
The first unit layer forming step and the second unit layer forming step are carried out by a chemical vapor deposition method under conditions of a reaction temperature of 800 ° C. or higher and 950 ° C. or lower and a pressure of 0.05 atm or higher and 1.0 atm or lower. ,
In the first unit layer forming step, the following formula (1) is used using the first raw material gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ .
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
Forming the first unit layer indicated by
In the second unit layer forming step, the following formula (2) is used using the second raw material gas containing TiCl ₄ , C ₂ H ₄ and H ₂ .
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
Forming the second unit layer indicated by
The first unit layer forming step and the second unit layer forming step are methods for manufacturing a surface-coated cutting tool, which are started from the first unit layer forming step.

According to the above aspect, it is possible to provide a surface-coated cutting tool having excellent wear resistance and chipping resistance and a method for manufacturing the same.

It is an SEM (scanning electron microscope) photograph of the cross section of the coating film of the surface coating cutting tool according to the embodiment of the present invention. It is a figure which shows typically the cross section of the coating film of the surface coating cutting tool shown in FIG. 1. It is an SEM (scanning electron microscope) photograph which magnifies and shows the part containing a columnar crystal in FIG. It is a figure which shows typically the part containing the columnar crystal shown in FIG. It is an optical micrograph of the cross section of the coating of the surface coating cutting tool which concerns on one Embodiment of this invention.

[Explanation of Embodiment of the present invention]
First, embodiments of the present invention will be listed and described.

The surface-coated cutting tool according to one aspect of the present invention is
(1) A surface-coated cutting tool including a base material and a coating film that covers the base material.
The coating comprises a first hard layer having a plurality of columnar crystals.
Each of the columnar crystals has the following formula (1).
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
The first unit layer represented by and the following formula (2)
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
It has a multi-layer structure in which the second unit layer shown by is alternately laminated, and has a multi-layer structure.
In the columnar crystal, the layer closest to the substrate is the first unit layer, which is a surface coating cutting tool.

According to the present invention, it is possible to provide a surface-coated cutting tool having excellent wear resistance and chipping resistance.

(2) The lamination period of the multilayer structure is preferably 20 nm or more and 4000 nm or less. According to this, it is possible to suppress delamination in a multilayer structure, and it is possible to provide a surface-coated cutting tool having excellent wear resistance, heat resistance and chipping resistance.

(3) It is preferable that x in the formula (1) and y in the formula (2) satisfy the relationship of y−x ≧ 0.25. According to this, the wear resistance and the chipping resistance of the surface-coated cutting tool can be improved in a well-balanced manner.

(4) The first hard layer preferably contains 1.0% by volume or less of free carbon. According to this, the wear resistance and the chipping resistance of the surface-coated cutting tool can be further improved.

The method for manufacturing a surface-coated cutting tool according to another aspect of the present invention is as follows.
(5) The method for manufacturing a surface-coated cutting tool according to any one of (1) to (4) above.
The process of preparing the base material and
A step of forming a film on the base material is provided.
The step of forming the coating film includes a first unit layer forming step and a second unit layer forming step.
The first unit layer forming step and the second unit layer forming step are carried out by a chemical vapor deposition method under conditions of a reaction temperature of 800 ° C. or higher and 950 ° C. or lower and a pressure of 0.05 atm or higher and 1.0 atm or lower. ,
In the first unit layer forming step, the following formula (1) is used using the first raw material gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ .
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
Forming the first unit layer indicated by
In the second unit layer forming step, the following formula (2) is used using the second raw material gas containing TiCl ₄ , C ₂ H ₄ and H ₂ .
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
Forming the second unit layer indicated by
The first unit layer forming step and the second unit layer forming step are methods for manufacturing a surface-coated cutting tool, which are started from the first unit layer forming step.

According to the present invention, it is possible to provide a surface-coated cutting tool having excellent wear resistance and chipping resistance.

(6) In the first unit layer forming step, the content of H ₂ gas in the first raw material gas is 60% by volume or more and 98% by volume or less, and in the second unit layer forming step, in the second raw material gas. _The content of H2 gas is preferably 90% by volume or more and 99% by volume or less. According to this, it is possible to suppress the mixing of free carbon into the first unit layer and the second single layer.

[Details of Embodiments of the present invention]
A specific example of the surface-coated cutting tool according to the embodiment of the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

In the present specification, when a compound is represented by a chemical formula, if the atomic ratio is not particularly limited, it includes all conventionally known atomic ratios, and is not necessarily limited to those in the stoichiometric range. For example, when simply writing "TiCN", the atomic ratio of "Ti", "C" and "N" is not limited to 50:25:25, and when writing "TiC", "Ti" and "C" are also used. The atomic ratio of "" is not limited to the case of 50:50, and any conventionally known atomic ratio is included.

<Surface coating cutting tool>
The surface-coated cutting tool according to the embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a diagram showing a cross section of a coating film of a surface-coated cutting tool according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a cross section of a coating film of the surface-coated cutting tool shown in FIG. FIG. 3 is an enlarged SEM (scanning electron microscope) photograph showing a portion including columnar crystals in FIG. 1. FIG. 4 is a diagram schematically showing a portion including a columnar crystal shown in FIG.

As shown in FIG. 1, the surface-coated cutting tool 10 according to the embodiment of the present invention includes a base material 1 and a coating film 2 that covers the base material 1. The coating film 2 preferably covers the entire surface of the base material 1, but even if a part of the base material 1 is not covered with the coating film 2 or the composition of the coating film 2 is partially different, the present embodiment is used. It does not deviate from the range.

The surface-coated cutting tool of the present embodiment includes a drill, an end mill, a cutting tip with a replaceable cutting edge for a drill, a cutting tool with a replaceable cutting edge for an end mill, a cutting tool with a replaceable cutting edge for milling, a cutting tool with a replaceable cutting edge for turning, a metal saw, and the like. It can be suitably used as a cutting tool such as a gear cutting tool, a reamer, and a tap.

<Base material>
As the base material 1 used in the surface-coated cutting tool 10 of the present embodiment, any conventionally known base material of this type can be used. For example, cemented carbide (for example, WC-based cemented carbide, WC, as well as those containing Co or added with a carbonitride such as Ti, Ta, Nb), cermet (TiC, TiN, TiCN, etc.) are mainly used. Can be either a component), high-speed steel, ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cubic boron nitride sintered body, or diamond sintered body. preferable.

Among these various base materials, it is particularly preferable to select WC-based cemented carbide and cermet (particularly TiCN-based cermet). This is because these base materials have an excellent balance between hardness and strength particularly at high temperatures, and have excellent characteristics as base materials for surface-coated cutting tools for the above-mentioned applications.

<Coating>
The coating film 2 included in the surface-coated cutting tool 10 of the present embodiment may include another layer as long as it includes at least one first hard layer 3. Examples of other layers include an underlayer 5 (TiN, TiC, TiBN, etc.), an intermediate layer 6 (TiBNO, TiCNO, etc.), an alumina layer 7, an outermost layer 8 (TiN, TiCN, TiC, etc.), and the like. can.

The coating film 2 has an action of improving various properties such as wear resistance and chipping resistance by coating the base material 1.

The coating film 2 preferably has a total thickness of 6 to 30 μm, preferably 6 to 25 μm. If the thickness is less than 6 μm, the wear resistance may be insufficient, and if it exceeds 30 μm, the coating is frequently peeled off or broken when a large stress is applied between the coating and the substrate in the intermittent processing. It may occur.

<First hard layer>
In the present embodiment, the first hard layer 3 has a plurality of columnar crystals 4. As shown in FIG. 4, in each of the columnar crystals 4, one layer of the first unit layer 4a and one layer of the second unit layer 4b are alternately laminated, and as a whole, one or more first unit layers 4a and one or more layers are laminated. It has a multilayer structure including one or more second unit layers 4b. In the columnar crystal 4, the layer closest to the base material 1 is the first unit layer 4a.

The first unit layer 4a has the following formula (1).
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
It has the composition shown by.

The second unit layer 4b has the following formula (2).
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
It has the composition shown by.

By having such a structure, the first hard layer 3 shows an excellent effect that wear resistance and chipping resistance are improved in a well-balanced manner. The reason for this is presumed to be as follows (i) to (vi).

(I) Since the first hard layer 3 contains a plurality of columnar crystals 4, it has fewer grain boundaries than the case where it is composed of granular crystals, the fracture starting point is reduced, and the film is less likely to fall off or be chipped. Therefore, the first hard layer 3 has excellent chipping resistance.

(Ii) Generally, in a layer made of TiCN, the smaller the atomic ratio of carbon to the total of carbon and nitrogen, the better the chipping resistance and heat resistance, but the wear resistance tends to decrease. On the other hand, in the layer made of TiCN, the larger the atomic ratio of carbon to the total of carbon and nitrogen, the better the wear resistance, but the chipping resistance and the heat resistance tend to decrease. In the first hard layer 3, the first unit layer 4a made of TiCN having a relatively low carbon content and the second unit layer 4b made of TiCN or TiC having a relatively high carbon content are alternately laminated. Since it is included, wear resistance and chipping resistance are improved in a well-balanced manner, and heat resistance is also improved.

(Iii) Since the first hard layer 3 has a multilayer structure of the first unit layer 4a and the second unit layer 4b, the intragranular propagation of cracks (propagation of cracks inside the columnar crystal 4) is suppressed. be able to. This improves the chipping resistance of the first hard layer 3.

(Iv) Since the lattice constants of the first unit layer 4a and the second unit layer 4b are different, distortion occurs in the crystal lattices of the first unit layer 4a and the second unit layer 4b, and the first unit layer 4a and the second unit layer 4b are distorted as compared with the case where there is no distortion. The hardness of the 1st unit layer 4a and the 2nd unit layer 4b becomes higher. This improves the wear resistance of the first hard layer 3.

(V) In the columnar crystals 4 contained in the first hard layer 3, the layer closest to the substrate is the first unit layer 4a. This indicates that the first unit layer 4a was first formed when the columnar crystals 4 were formed on the base material 1 by, for example, the CVD method. The first unit layer 4a is a layer made of TiCN having a relatively low carbon content, and has the largest TC (422) in the orientation index TC (hkl). Therefore, the columnar crystal 4 having a multilayer structure formed by alternately laminating the second unit layer 4b and the first unit layer 4a on the first unit layer 4a is oriented on the (422) plane, and the columnar crystal 4 is oriented. Grow uniformly in the direction perpendicular to the surface of the substrate (the thickness direction of the coating film 2). As a result, the variation in strength in the columnar crystals 4 is reduced, and the wear resistance and chipping resistance of the first hard layer 3 are improved.

(Vi) The columnar crystals 4 contained in the first hard layer 3 are oriented toward the (422) plane, which is the closest packed plane of the rock salt type crystal structure and has a high Young's modulus, which is close to the (111) plane. This improves the wear resistance of the first hard layer 3.

In the present embodiment, the first hard layer 3 may be composed of only a plurality of columnar crystals 4, or may include other crystal regions such as granular crystals together with the columnar crystals 4. When the first hard layer 3 contains other crystal regions, the volume ratio of the columnar crystals 4 in the first hard layer 3 is preferably 50% by volume or more, more preferably 70% by volume or more, and further preferably 100% by volume. preferable. If the volume ratio of the columnar crystals 4 is less than 50%, the effect of improving the wear resistance and chipping resistance of the first hard layer derived from the columnar crystals may not be obtained.

The presence of columnar crystals in the first hard layer 3 and the volume ratio of the columnar crystals 4 in the first hard layer 3 are confirmed by observing the cross section of the coating film using an SEM (scanning electron microscope). can do. Specifically, the cross section of the coating film is CP-processed by Ar etching, and the processed surface is observed with a field emission scanning electron microscope SU6600 manufactured by Hitachi, Ltd. at a magnification of 10000 times. It can be confirmed that the crystal part is present. Further, the area ratio of the columnar crystal portion and the non-columnar crystal portion can be calculated, and the area ratio of the columnar crystal portion can be used as the volume ratio of the columnar crystal in the first hard layer.

The columnar crystals 4 contained in the first hard layer 3 are grown in a direction substantially perpendicular to the surface of the substrate (that is, in the thickness direction of the coating film), and have, for example, a width (diameter) of 30 nm or more and 500 nm or less and a length. It has a shape of 1000 nm or more and 10000 nm or less. The granular crystal is not a crystal grown in one direction like a columnar crystal, but a crystal having a substantially spherical or amorphous shape and having a particle size of 100 nm or more and 1000 nm or less. The size of columnar crystals and granular crystals can be calculated from Scherrer's formula based on the measurement results of X-ray analysis (XRD).

The average particle size of the columnar crystals 4 is preferably 30 nm or more and 80 nm or less, and more preferably 30 nm or more and 60 nm or less. If the average particle size of the columnar crystals is less than 30 nm, the grain boundaries may increase in the first hard layer and the chipping resistance may decrease. On the other hand, if the average particle size exceeds 80 nm, the wear resistance may decrease. Here, the average particle size of the granular crystal is a value derived from the half width of the (422) peak of TiC measured by XRD (out-of-plane) using Scherrer's equation (constant K = 0.9). Means. The average particle size of the columnar crystals is synonymous with the width (diameter) of the columnar crystals.

The aspect ratio of the columnar crystal 4 is preferably 40 or more. If the aspect ratio is less than 40, the wear resistance under high temperature cutting conditions tends to decrease. The upper limit of the aspect ratio is not particularly limited, but is preferably 400 or less from the viewpoint of manufacturing. Here, the aspect ratio means a value obtained by dividing the width (diameter) of the columnar crystal by the length of the columnar crystal.

The average particle size and aspect ratio of the columnar crystals 4 can be measured as follows. First, the cross section of the coating film 2 is mirror-processed to etch the grain boundaries of the first hard layer 3 having the columnar crystals 4. Then, at a portion corresponding to 1/2 of the film thickness of the first hard layer 3, the width of each crystal in the horizontal direction with the substrate is set as the particle size, and the particle size of each crystal is measured using SEM to obtain an average value. Ask. The number of measurement points is 20. The film thickness of the first hard layer 3 is divided by the obtained average value, and this calculated value is used as the aspect ratio of the columnar crystal.

In the present embodiment, each of the columnar crystals 4 has the following formula (1).
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
The first unit layer 4a represented by the following formula (2)
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
The columnar crystal 4 has a multilayer structure in which the second unit layers 4b shown in the above are alternately laminated, and the layer closest to the base material 1 in the columnar crystal 4 is the first unit layer 4a.

The first unit layer 4a has a composition of TiC _x N _z-x (where 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20). This composition means that the atomic ratio of carbon to the total of carbon and nitrogen is relatively low. Generally, in a layer made of TiCN, the smaller the atomic ratio of carbon to the total of carbon and nitrogen, the better the chipping resistance and heat resistance. Therefore, the columnar crystal 4 including the first unit layer 4a has excellent chipping resistance and heat resistance.

In TiC _{x Nz-x} , when x is less than 0.45, sufficient hardness cannot be obtained and wear resistance becomes insufficient. On the other hand, when x is 0.70 or more, the compositions of the first unit layer 4a and the second unit layer 4b are close to each other. It is not possible to obtain the effect of improving the wear resistance and the chipping resistance in a well-balanced manner. x is preferably in the range of 0.45 ≦ x ≦ 0.65, more preferably in the range of 0.50 ≦ x ≦ 0.60. The atomic ratio of "Ti" and the total of "C" and "N" in TiC _x Nz _-x is 0.80 when "Ti" is 1. It is preferably ~ 1.10.

The second unit layer 4b has a composition of TiC yNA _{-y (} where 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20). This composition means that in the layer made of TiCN, the atomic ratio of carbon to the total of carbon and nitrogen is relatively high, or the layer is made of TiC containing no N. In the layer made of TiCN, the larger the atomic ratio of carbon to the total of carbon and nitrogen, the better the wear resistance. Therefore, the columnar crystal 4 including the second unit layer 4b has excellent wear resistance.

From the viewpoint of increasing the effect of improving the wear resistance and the chipping resistance in a well-balanced manner, the difference in the concentration of carbon and nitrogen in the first unit layer 4a and the second unit layer 4b is increased, that is, the absolute value of yx. It is desirable to increase the value. y is preferably in the range of 0.85 ≦ y <1, more preferably in the range of 0.90 ≦ y <1.00. The atomic ratio of "Ti" and the total of " _C " and "N" in TiC _yNA is 0.80 when "Ti" is 1. ~ 1.20.

The composition of the first unit layer 4a TiC _x N _z-x (where 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20) and the composition TiC of the second unit layer 4b. It is preferable that _y in yNAy (where 0.70 ≦ y ≦ 1 and 0.80 ≦ _A ≦ 1.20) satisfies the relationship of yx ≧ 0.25. According to this, in the columnar crystal 4, it is possible to obtain the effect that the excellent chipping resistance derived from the first unit layer and the excellent wear resistance derived from the second unit layer are improved in a well-balanced manner. The value of y-x is more preferably in the range of 0.30 ≦ y-x ≦ 0.50, and further preferably in the range of 0.35 ≦ y-x ≦ 0.50.

The composition of the first unit layer 4a and the second unit layer 4b (atomic ratio of titanium, carbon, nitrogen), and the composition of the other layers in the coating are determined by using an EPMA (Electron Probe Microanalyzer) device for the cross section of the coating. It can be confirmed by measuring.

In the columnar crystals 4 contained in the first hard layer 3, the layer closest to the substrate is the first unit layer 4a. This indicates that the first unit layer 4a was first formed when the columnar crystals 4 were formed on the base material 1 by the CVD method. The first unit layer 4a is a layer made of TiCN having a relatively low carbon content, and has the largest TC (422) in the orientation index TC (hkl). Therefore, the columnar crystal 4 having a multilayer structure formed by alternately laminating the second unit layer 4b and the first unit layer 4a on the first unit layer 4a is oriented on the (422) plane, and the columnar crystal 4 is oriented. Grow uniformly in the direction perpendicular to the surface of the substrate (the thickness direction of the coating film 2). As a result, the variation in strength in the columnar crystals 4 is reduced, and the chipping resistance and wear resistance of the first hard layer 3 are improved.

Further, the columnar crystal 4 is oriented to the (422) plane close to the (111) plane, which has a high Young's modulus on the close-packed plane of the rock salt type crystal structure. This improves the wear resistance of the first hard layer 3.

Here, the orientation index TC (hkl) is defined by the following formula (3).

In formula (3), I (hkl) indicates the X-ray diffraction intensity of the (hkl) plane, and I ₀ (hkl) is based on the JCPDS standard (Joint Committee on Powder Diffraction Standards) (hkl). The average value of the X-ray powder diffraction intensity of TiC and TiN constituting the surface is shown. Note that (hkl) is the eight planes of (111), (200), (220), (311), (331), (420), (422), and (511), and is the right-hand side of the equation (3). The curly braces indicate the average value of these eight planes.

The maximum TC (422) in the orientation index TC (hkl) means that the TC (422) shows the maximum value when the orientation index TC (hkl) is obtained from the equation (3) for all eight surfaces. This means that the columnar crystals are strongly oriented to the (422) plane. By making the (422) plane the orientation plane in this way, the columnar crystals grow in a direction perpendicular to the surface of the substrate. As a result, the variation in strength in the columnar crystals is reduced, and the chipping resistance and wear resistance of the first hard layer are improved.

The orientation index TC (422) of the (422) plane of the columnar crystal 4 is preferably 1.5 or more and 6.0 or less, and more preferably 3.0 or more and 6.0 or less. According to this, the uniformity of the columnar crystals becomes good, and the chipping resistance and the wear resistance of the first hard layer are improved.

In a multilayer structure in which the first unit layer 4a and the second unit layer 4b are alternately laminated, the lamination period is preferably 20 nm or more and 4000 nm or less. If the lamination period is less than 20 nm, it may be difficult to form a uniform film with a small film thickness. On the other hand, when the film thickness exceeds 4000 nm, the hardness difference (strength difference) between the first unit layer 4a and the second unit layer 4b becomes excessive, delamination occurs, and it is difficult to obtain sufficient chipping resistance. There is. Here, the stacking period means the total thickness of one adjacent first unit layer 4a and one second unit layer 4b. The lamination period is more preferably 50 nm or more and 500 nm or less, and further preferably 50 nm or more and 200 nm or less.

In the multilayer structure, the ratio of the thickness of the adjacent 1st unit layer 4a and the 1st layer 2nd unit layer 4b is preferably in the range of 1: 1 to 3: 1. According to this, the wear resistance and the chipping resistance of the first hard layer are improved in a well-balanced manner.

In the multilayer structure, the number of repetitions of the stacking cycle is preferably 10 or more and 1000 or less, and more preferably 100 or more and 500 or less. According to this, by laminating the first unit layer and the second unit layer, the effect of improving the wear resistance and the chipping resistance in a well-balanced manner can be sufficiently obtained. The number of repetitions is a value that means the number of cycles in the entire multilayer structure when the combination of the first unit layer of one adjacent layer and the second unit layer of one layer is one cycle.

The thickness of the first unit layer 4a of one layer is preferably 10 nm or more and 200 nm or less, and more preferably 20 nm or more and 100 nm or less. According to this, the effect of improving the chipping resistance and the heat resistance by the first unit layer can be sufficiently obtained.

The thickness of the second unit layer 4b of one layer is preferably 10 nm or more and 200 nm or less, and more preferably 20 nm or more and 100 nm or less. According to this, the effect of improving the wear resistance by the second unit layer can be sufficiently obtained.

The total thickness of the first hard layer 3 is preferably 3 μm or more and 15 μm or less, and more preferably 4 μm or more and 10 μm or less. If the thickness is less than 3 μm, sufficient wear resistance may not be exhibited in continuous machining, and if it exceeds 15 μm, chipping resistance may not be stable in intermittent cutting.

In the columnar crystal, the first unit layer 4a and the second unit layer 4b are alternately laminated to form a multilayer structure. As shown in FIG. 5, the cross section of the coating film is observed with an optical microscope. The difference in contrast can be confirmed as indicating a multi-layer structure. It can also be confirmed by observing the cross section of the coating film using an SEM (scanning electron microscope), EPMA (electron probe microanalyzer) or TEM (transmission electron microscope).

The stacking period, the thickness of the first unit layer, the thickness of the second unit layer, and the thickness of the first hard layer can be measured by observing the cross section of the coating film using an SEM (scanning electron microscope). .. Specifically, the film thickness can be specified by observing at an acceleration voltage of 10 kV using a field emission scanning electron microscope SU6600 manufactured by Hitachi, Ltd. and measuring the length of the columnar crystal region at a magnification of 5000 times.

The amount of free carbon in the first hard layer 3 is preferably 1.0% by volume or less. Here, the free carbon does not exist as a TiC or TiCN compound, and means a CC-bonded amorphous carbon or free carbon. If the amount of free carbon in the first hard layer exceeds 1.0% by volume, cracks are likely to occur starting from the free carbon, and the chipping resistance of the first hard layer may decrease. The amount of free carbon is more preferably 0.1% by volume or less, and most preferably free carbon is not contained. The amount of free carbon can be measured using an XPS (X-ray Photoelectron Spectroscopy) device. Specifically, it can be calculated from the position and intensity ratio of the C-1s spectrum of XPS. (The binding energy of the binding carbon (TiC) is 281.3 to 281.7 eV, and the binding energy of the non-bonding carbon (free carbon) is 283.8 to 284.7 eV).

The hardness of the first hard layer 3 as measured by the nanoindenter method is preferably 26 GPa or more and 35 GPa or less, and more preferably 28 GPa or more and 34 GPa or less. According to this, the first hard layer has sufficient hardness. The hardness is measured by a method conforming to ISO14577, and the measured load is 10 mN (1 g). The hardness of the first hard layer is measured by applying a load from the normal direction of the cross section in the cross section of the base material. Ten measurement points are set at equal intervals from the substrate direction to the film thickness direction, and the average value of the hardness at the ten points is taken as the hardness of the first hard layer.

<Other layers>
The coating film 2 of the present embodiment can include a layer other than the first hard layer 3. Examples of such other layers include, but are not limited to, the base layer 5, the intermediate layer 6, the alumina layer 7, the outermost surface layer 8, and the like.

The base layer 5 is formed directly above the base material in order to improve the adhesion between the base material and the coating film. The base layer 5 is made of TiN, TiBN, etc., and preferably has an average thickness of 0.1 to 2.0 μm.

The intermediate layer 6 is formed between the first hard layer 3 and the alumina layer 7 in order to improve the adhesion between the two layers. The intermediate layer 6 is made of TiCNO, TiBNO, etc., and preferably has an average thickness of 0.3 to 3.0 μm.

The alumina layer 7 is formed on the surface side of the first hard layer 3 because it has excellent oxidation resistance, wear due to heat generated during high-speed cutting of steel (oxidative wear), and excellent welding resistance during cutting of castings. Ru. The alumina layer 7 is made of α-type aluminum oxide or the like, and preferably has an average thickness of 2 to 15 μm.

The outermost surface layer 8 is formed on the outermost surface of the coating film to indicate whether or not the cutting edge has been used. The outermost surface layer 8 is made of TiN, TiCN, TiC and the like, and preferably has an average thickness of 0.3 to 2.0 μm.

<Manufacturing method of surface covering cutting tool>
The method for manufacturing a surface-coated cutting tool according to an embodiment of the present invention includes a step of preparing a base material and a step of forming a film on the base material.

The step of forming the coating film includes a first unit layer forming step and a second unit layer forming step. The first unit layer forming step and the second unit layer forming step are carried out under the conditions of a reaction temperature of 800 ° C. or higher and 950 ° C. or lower and a pressure of 0.05 atm or higher and 1.0 atm or lower by a chemical vapor deposition method. In the first unit layer forming step, the following formula (1) is used using the first raw material gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ .
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
The first unit layer indicated by is formed. In the second unit layer forming step, the following formula (2) is used using the second raw material gas containing TiCl ₄ , C ₂ H ₄ and H ₂ .
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
The second unit layer indicated by is formed. The first unit layer forming step and the second unit layer forming step are started from the first unit layer forming step. The first hard layer described above can be formed by such a method.

<Process to prepare the base material>
As the base material, the base material described above is prepared.

<Step of forming a film>
Next, a coating is formed on the substrate to obtain a surface-coated cutting tool. In the present embodiment, the first unit layer 4a and the second unit layer 4b of the coating film are formed by alternately supplying the first raw material gas and the second raw material gas into the reaction chamber of the chemical vapor deposition apparatus. .. Since the first unit layer is formed by the first raw material gas and the second unit layer is formed by the second raw material gas, the first unit layer forming step and the second unit layer forming step are alternately performed. It is possible to form a first hard layer including a multilayer structure in which one unit layer and a second unit layer are alternately laminated. An underlayer can be formed directly above the base material in order to improve the adhesion between the base material and the coating film.

In the step of forming the coating film, the first unit layer forming step and the second unit layer forming step start from the first unit layer forming step. As a result, the layer closest to the base material in the multilayer structure becomes the first unit layer. As described above, the first unit layer has the maximum TC (422) in the orientation index TC (hkl). Therefore, the multilayer structure formed by alternately laminating the second unit layer and the first unit layer on the first unit layer is oriented on the (422) plane, has a low Young's modulus, and has excellent wear resistance. Have.

The first source gas contains TiCl ₄ , CH ₃ CN, N ₂ and H ₂ . The second source gas contains TiCl ₄ , C ₂ H ₄ and H ₂ . Although the second raw material gas does not contain nitrogen, the second unit layer may contain nitrogen. The reason for this is that when the gas supplied to the reaction chamber is changed from the first raw material gas to the second raw material gas, nitrogen in the first raw material gas remains in the reaction chamber, and this nitrogen becomes the second raw material gas. It is thought that it is mixed.

In the conventional method (for example, Non-Patent Document 1), a gas containing CH ₄ is used as a raw material gas in order to form a layer made of TiCN or TiC by the CVD method. Since CH ₄ does not thermally decompose unless it is about 1000 ° C. or higher, the CVD method using CH ₄ has been performed under high temperature conditions of 1000 ° C. or higher.

Under this condition, the obtained layer made of TiCN or TiC is composed of granular crystals, and the fracture starting point increases due to the large number of grain boundaries, and cracks develop from this fracture starting point to cause the film to fall off or chip. There was a case. Further, during the formation of the coating film, mutual diffusion may occur between the base material made of cemented carbide and the coating film, and the η layer, which is an embrittlement layer, may be formed at the interface between the base material and the coating film.

In the production method according to the present embodiment, CH ₄ is not used as the raw material gas, but C ₂ H ₄ which decomposes at about 800 ° C. is used. Therefore, the reaction temperature of the CVD method is set to a low temperature of 800 ° C. or higher and 950 ° C. or lower. Can be done. Under this condition, the first unit layer and the second unit layer contain columnar crystals and the grain boundaries are reduced, so that the chipping resistance is improved. Further, since the η layer is not formed at the interface between the base material and the coating film, the adhesion between the base material and the coating film is improved. If the reaction temperature is less than 800 ° C., chlorine in the raw material gas may remain in the first unit layer and the second unit layer, and the hardness may decrease. On the other hand, when the reaction temperature exceeds 950 ° C., granular crystals are likely to be formed. In addition, an η layer may be formed at the interface between the base material and the coating film. The reaction temperature is preferably 800 ° C. or higher and 900 ° C. or lower, and more preferably 830 ° C. or higher and 900 ° C. or lower, from the viewpoint of the film forming speed and the crystal grain size.

There is also another conventional method (Non-Patent Document 2) that does not use CH ₄ as a raw material gas. In this technique, a gas containing TiCl ₄ , CH ₃ CN, C ₂ H ₄ , N ₂ and H ₂ was used as a raw material gas in order to form a layer made of TiCN by the CVD method. In this case, the reaction temperature can be lowered to a low temperature of 840 to 900 ° C., but C ₂ H ₄ in the raw material gas may aggregate and carbonize, and may be mixed as free carbon in the layer made of TiCN. .. Since free carbon serves as a starting point for fracture, there is a possibility that the chipping resistance of the coating film may decrease.

As a result of investigating a method for suppressing the mixing of free carbon into the coating film, the present inventors have increased the content of H ₂ gas in the first raw material gas to 60% by volume or more and 98% by volume in the first unit layer forming step. Hereinafter, it has been found that it is effective to set the content of H ₂ gas in the second raw material gas to 90% by volume or more and 99% by volume or less in the second unit layer forming step. Here, the flow rate of H ₂ gas is the flow rate of H ₂ gas in the first unit layer forming step and the second unit layer forming step, and is used when forming the first unit layer and the second unit layer in the reaction chamber. Values at temperature and pressure.

When the content of H ₂ gas in the first raw material gas and the content of H ₂ gas in the second raw material gas are within the above ranges, C ₂ H contained in the first raw material gas and the second raw material gas Since ₄ is diffused by the H ₂ gas, it is possible to suppress the aggregation and carbonization of C ₂ H ₄ , and thus the mixing of free carbon into the first hard layer. In the first unit layer forming step, the content of H ₂ gas in the first raw material gas is more preferably 80% by volume or more and 98% by volume or less. In the second unit layer forming step, the content of H ₂ gas in the second raw material gas is more preferably 95% by volume or more and 99% by volume or less.

In the first unit layer forming step, the flow rate of the entire first raw material gas is preferably 10 times or more and 30 times or less the volume of the reaction chamber per minute, preferably 10 times or more and 25 times or more, from the viewpoint of the uniformity of the first unit layer. Double or less is more preferable. Further, the flow rate of the entire second raw material gas in the second unit layer forming step is preferably 10 times or more and 30 times or less the volume of the reaction chamber per minute, preferably 10 times or more, from the viewpoint of the uniformity of the second unit layer. 25 times or less is more preferable. Here, the flow rate of the raw material gas is a value at a temperature and a pressure when forming the first unit layer and the second unit layer in the reaction chamber.

The contents of TiCl ₄ , CH ₃ CN, N ₂ and H ₂ in the first raw material gas can be appropriately changed according to the desired composition of the first unit layer. For example, the composition of the first raw material gas is such that TiCl ₄ is 0.5% by volume or more and 2.5% by volume or less, CH ₃ CN is 0.1% by volume or more and 1.0% by volume or less, and N ₂ is 5% by volume or more. H ₂ can be the balance in an amount of 40% by volume or less.

The contents of TiCl ₄ , C ₂ H ₄ and H ₂ in the second raw material gas can be appropriately changed according to the desired composition of the second unit layer. For example, the composition of the second raw material gas is such that TiCl ₄ is 0.5% by volume or more and 4.0% by volume or less, C ₂ H ₄ is 0.5% by volume or more and 5.0% by volume or less, and H ₂ is the balance. be able to.

In the first unit layer forming step and the second unit layer forming step, the pressure in the reaction chamber is 0.05 atm or more and 1.0 atm or less. According to this, a film containing columnar crystals can be stably formed at a reaction temperature of 800 ° C. or higher and 950 ° C. or lower. The pressure is preferably 0.1 atm or more and 0.5 atm or less.

When the coating film in the present embodiment includes layers other than the first unit layer and the second unit layer, these other layers can be formed by a conventionally known chemical vapor deposition method or physical vapor deposition method. From the viewpoint that the first unit layer and the second unit layer can be continuously formed in one chemical vapor deposition apparatus, the other layers are preferably formed by the chemical vapor deposition method.

The present embodiment will be described more specifically by way of examples. However, these embodiments do not limit the present embodiment.

[Sample 1 to Sample 27]
<Preparation of base material>
As a raw material powder for the base material, a mixed powder containing 0.5% by weight of TiC, 0.5% by weight of Cr _{3C 2} , 10% by weight of Co, and 89% by weight of WC was prepared. The mixed powder is formed into a predetermined shape and then sintered at 1300 to 1500 ° C. for 1 to 2 hours to form a cemented carbide substrate having a shape of CNMG120408N-GZ (manufactured by Sumitomo Electric Hardmetal Corp.). Got

<Formation of film>
TiN layer (base layer), first hard layer (multilayer structure of first unit layer and second unit layer), TiCNO layer (intermediate layer), Al _2O on the substrate of each sample by chemical vapor deposition method. _Three layers (alumina layer) and a TiN layer (outermost surface layer) were formed in this order. In Samples 2 to 27, in the step of forming the first hard layer, the film formation was started from the first unit layer, and then the second unit layer and the first unit layer were alternately formed. In sample 1, in the step of forming the first hard layer, only the first unit layer was formed, and the second unit layer was not formed. Table 1 shows the raw material gas composition and the film forming conditions (reaction chamber pressure, reaction chamber temperature, flow rate) of the base layer, the intermediate layer, the alumina layer, and the outermost surface layer. The raw material gas composition of the first unit layer and the second unit layer, the film forming conditions (reaction chamber pressure, reaction chamber temperature, flow rate, and in Table 2, the flow rate "x" is the entire first raw material gas per minute. It is shown that the flow rate and the flow rate of the entire second raw material gas are x times the volume of the reaction chamber)), and the stacking period are shown in Table 2.

When each sample was observed with an SEM (scanning electron microscope), a multilayer structure was confirmed in Samples 2 to 27.

The composition of the first unit layer and the second unit layer of each sample was measured using an EPMA device. In all the samples, the first unit layer is represented by TiC _x N _z-x (where 0.45 ≤ x <0.7 1 and z = 1.0), and the second unit layer is TiC. It is indicated by yNA _{-y (} where 0.70≤y≤1 and A = 1.0). The values of "x", "y" and "yx" in the above formula are shown in the "Composition" column of Table 3.

The free carbon content in the first hard layer of each sample was measured using an XPS device. The results are shown in Table 3.

The film thickness of each sample was measured using an SEM (scanning electron microscope). The results are shown in Table 3.
The X-ray diffraction intensity of the columnar crystals of each sample was measured using an XRD (X-ray diffraction) device, and the orientation index TC (422) of the (422) plane was calculated. The results are shown in Table 3.

The aspect ratio of the columnar crystals of each sample was measured by the following procedure. First, the cross section of the coating film was mirror-processed to etch the grain boundaries of the first hard layer having columnar crystals. Then, at a portion corresponding to 1/2 of the film thickness of the first hard layer, the width of each crystal in the horizontal direction with the substrate is set as the particle size, and the particle size of each crystal is measured using SEM to obtain an average value. rice field. The number of measurement points was 20. The film thickness of the first hard layer was divided by the obtained average value, and this calculated value was taken as the aspect ratio of the columnar crystal. The results are shown in Table 3.

The hardness of the first hard layer of each sample was measured by a method conforming to ISO14577, and the measured load was 10 mN (1 g). The hardness of the first hard layer was measured by applying a load from the normal direction of the cross section in the cross section of the base material. Ten measurement points were set at equal intervals from the substrate direction to the film thickness direction, and the average value of the hardness at the ten points was taken as the hardness of the first hard layer.

<Performance evaluation>
The cutting performance of each sample was evaluated as follows.

For the surface coating cutting tool of each sample, measure the cutting time (minutes) (however, rounded off to the nearest whole number) until the cutting edge chipping or flank wear amount (Vb) reaches 0.30 mm under the following cutting conditions, and the cutting edge The final damage morphology was observed. The results are shown in Table 3.

It is shown that the longer the cutting time until the chipping or flank wear amount (Vb) becomes 0.30 mm, the better the wear resistance and the chipping resistance.

In the final damage form, "normal wear" means a damage form (having a smooth wear surface) consisting only of wear without chipping, chipping, etc., and "cutting edge chipping" occurs in the cutting edge portion. Means a big chip.

<Cutting conditions>
Work Material: FCD450-4 Groove Material Outer Diameter Continuous Cutting Peripheral Speed: 250 m / min
Feed rate: 0.30 mm / rev
Cut amount: 1.5 mm
Cutting fluid: Yes

Samples 2, Samples 3, and Samples 5 to 27 are surface-coated cutting tools according to an embodiment of the present invention, and are superior in wear resistance and chipping resistance to Samples 1 and 4 which are comparative examples.

Although the embodiments and examples of the present invention have been described as described above, it is planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or variously modified.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims, not the above-mentioned meaning, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 Base material 2 Coating 3 1st hard layer 4 Columnar crystal 4a 1st unit layer 4b 2nd unit layer 5 Underlayer 6 Intermediate layer 7 Alumina layer 8 Outermost layer 10 Surface coating cutting tool

Claims (5)

A surface-coated cutting tool comprising a substrate and a coating covering the substrate.
The coating comprises a first hard layer having a plurality of columnar crystals.
Each of the columnar crystals has the following formula (1).
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
The first unit layer represented by and the following formula (2)
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 , 0.80 ≦ A ≦ 1.20 and y ≦ A )
It has a multi-layer structure in which the second unit layer shown by is alternately laminated, and has a multi-layer structure.
In the columnar crystal, the layer closest to the substrate is the first unit layer .
A surface-coated cutting tool in which x in the formula (1) and y in the formula (2) satisfy the relationship of y−x ≧ 0.25 . The surface-coated cutting tool according to claim 1, wherein the lamination period of the multilayer structure is 20 nm or more and 4000 nm or less. The surface-coated cutting tool according to claim 1 or 2 , wherein the first hard layer contains 1.0% by volume or less of free carbon. The method for manufacturing a surface-coated cutting tool according to any one of claims 1 to 3 .
The process of preparing the base material and
A step of forming a film on the base material is provided.
The step of forming the coating film includes a first unit layer forming step and a second unit layer forming step.
The first unit layer forming step and the second unit layer forming step are carried out by a chemical vapor deposition method under conditions of a reaction temperature of 800 ° C. or higher and 950 ° C. or lower and a pressure of 0.05 atm or higher and 1.0 atm or lower. ,
In the first unit layer forming step, the following formula (1) is used using the first raw material gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ .
TiC _x N _z-x (1)
(In the formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
Forming the first unit layer indicated by
In the second unit layer forming step, the following formula (2) is used using the second raw material gas containing TiCl ₄ , C ₂ H ₄ and H ₂ .
TiC _y N _A-y (2)
(In the formula (2), 0.70 ≦ y ≦ 1 , 0.80 ≦ A ≦ 1.20 and y ≦ A )
Forming the second unit layer indicated by
The first unit layer forming step and the second unit layer forming step are started from the first unit layer forming step.
The x in the formula (1) and the y in the formula (2) satisfy the relationship of y−x ≧ 0.25.
How to manufacture surface coated cutting tools. In the first unit layer forming step, the content of H ₂ gas in the first raw material gas is 60% by volume or more and 98% by volume or less, and in the second unit layer forming step, the H ₂ gas in the second raw material gas. The method for manufacturing a surface-coated cutting tool according to claim 4 , wherein the content of the gas is 90% by volume or more and 99% by volume or less.

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