JP2019171547A - Surface-coated cutting tool and method of manufacturing the same - Google Patents

Abstract

To provide a surface-coated cutting tool excellent in wear resistance and chipping resistance, and a method of manufacturing the same.SOLUTION: The surface-coated cutting tool is provided that comprises a base and a coating film coating the base, the coating film includes a first hard coating layer having a plurality of columnar crystals. Each columnar crystal has a multilayer structure in which a first unit layer represented by the following formula (1): TiCN(in the formula (1), 0.45≤x<0.70 and 0.80≤z≤1.20) and a second unit layer represented by the formula (2): TiCN(in the formula (2), 0.70≤y≤1 and 0.80≤A≤1.20) are alternately laminated. In the columnar crystal, a layer most adjacent to the base is the first unit layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface-coated cutting tool and a manufacturing method thereof.

  2. Description of the Related Art Conventionally, in a surface-coated cutting tool including a base material and a coating film that covers the base material, a coating film that includes one or both of a TiCN layer and a TiC layer is known.

  Geun-Woo, Park, 1 other, "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 film containing a laminated structure of TiC and TiCN formed on a cemented carbide by a CVD method (chemical vapor deposition method) as a film for a cutting tool. Yes.

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

Geun-Woo, Park, 1 other, "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 and 4 others, `` Microstructure, mechanical properties, and cutting performance of TiCxN1-xcoatings with various x values fabricated 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 source 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. For this reason, the CVD method using CH ₄ is performed under a high temperature condition of 1000 ° C. or higher. Under this condition, during the formation of the film, mutual diffusion is likely to occur between the base material made of cemented carbide and the film, and an η layer that is an embrittlement layer is likely to be formed at the interface between the base material and the film.

  Further, in Non-Patent Document 1, since the CVD method is performed under a high temperature condition of 1000 ° C. or higher, atoms deposited on the base material are likely to move on the base material, so that the crystal growth direction is difficult to be constant, and granular Crystals are easy to grow. In a film made of granular crystals, since there are many crystal interfaces, the starting point of fracture increases, 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 source gas for the TiC _x N _1-x layer, and are formed under a temperature condition of 840 ° C. The membrane is done. Under this condition, the content of C in the TiC _x N _1-x layer tends to increase (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. Furthermore, in the TiC _x N _1-x layer, when the C content increases, the oxidation start temperature tends to decrease, and there is room for improvement in oxidation resistance.

  Further, in Non-Patent Document 2, since the coating is strongly oriented in the (422) plane having a high Young's modulus, the coating 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 source 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 has a sparse structure 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 excellent in wear resistance and chipping resistance and a method for producing the same.

The surface-coated cutting tool according to an 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 includes 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 Formula (1), it is 0.45 <= x <0.70 and 0.80 <= z <= 1.20)
A first unit layer 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)
A second unit layer indicated by a multi-layer structure alternately stacked,
In the columnar crystal, the layer closest to the substrate is the first unit layer, which is a surface-coated cutting tool.

A method for producing a surface-coated cutting tool according to another aspect of the present invention is as follows.
[2] A method for producing a surface-coated cutting tool according to [1] above,
Preparing a substrate;
Forming a film on the substrate,
The step of forming the coating 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 performed by a chemical vapor deposition method under conditions of a reaction temperature of 800 ° C. or more and 950 ° C. or less and a pressure of 0.05 atm or more and 1.0 atm or less. ,
In the first unit layer forming step, using the first source gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ , the following formula (1)
TiC _x N _z-x (1)
(In Formula (1), it is 0.45 <= x <0.70 and 0.80 <= z <= 1.20)
Forming a first unit layer represented by
In the second unit layer forming step, a second source gas containing TiCl ₄ , C ₂ H ₄ and H ₂ is used, 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)
Forming a second unit layer represented by
The first unit layer forming step and the second unit layer forming step are a method for manufacturing a surface-coated cutting tool, which is started from the first unit layer forming step.

  According to the said aspect, the surface-coated cutting tool excellent in abrasion resistance and chipping resistance, and its manufacturing method can be provided.

It is a SEM (scanning electron microscope) photograph of the section of the coat of the surface covering cutting tool concerning one embodiment of the present invention. It is a figure which shows typically the cross section of the film of the surface coating cutting tool shown by FIG. It is a SEM (scanning electron microscope) photograph which expands and shows the part containing the columnar crystal in FIG. It is a figure which shows typically the part containing the columnar crystal shown by FIG. It is an optical microscope photograph of the cross section of the film of the surface coating cutting tool which concerns on one embodiment of this invention.

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

The surface-coated cutting tool according to an 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 includes 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 Formula (1), it is 0.45 <= x <0.70 and 0.80 <= z <= 1.20)
A first unit layer 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)
A second unit layer indicated by a multi-layer structure alternately stacked,
In the columnar crystal, the layer closest to the substrate is the first unit layer, which is a surface-coated cutting tool.

  According to the present invention, a surface-coated cutting tool having excellent wear resistance and chipping resistance can be provided.

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

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

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

A method for producing a surface-coated cutting tool according to another aspect of the present invention is as follows.
(5) A method for producing a surface-coated cutting tool according to any one of (1) to (4) above,
Preparing a substrate;
Forming a film on the substrate,
The step of forming the coating 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 performed by a chemical vapor deposition method under conditions of a reaction temperature of 800 ° C. or more and 950 ° C. or less and a pressure of 0.05 atm or more and 1.0 atm or less. ,
In the first unit layer forming step, using the first source gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ , the following formula (1)
TiC _x N _z-x (1)
(In Formula (1), it is 0.45 <= x <0.70 and 0.80 <= z <= 1.20)
Forming a first unit layer represented by
In the second unit layer forming step, a second source gas containing TiCl ₄ , C ₂ H ₄ and H ₂ is used, 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)
Forming a second unit layer represented by
The first unit layer forming step and the second unit layer forming step are a method for manufacturing a surface-coated cutting tool, which is started from the first unit layer forming step.

  According to the present invention, a surface-coated cutting tool having excellent wear resistance and chipping resistance can be provided.

(6) In the first unit layer forming step, the content of H ₂ gas in the first source gas is 60% by volume or more and 98% by volume or less, and in the second unit layer forming step, The content of H ₂ gas is preferably 90% by volume or more and 99% by volume or less. According to this, it can suppress that free carbon mixes in a 1st unit layer and a 2nd single layer.

[Details of the embodiment of the present invention]
A specific example of a surface-coated cutting tool according to an embodiment of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

  In the present specification, when a compound is represented by a chemical formula, when the atomic ratio is not particularly limited, any conventionally known atomic ratio is included, and is not necessarily limited to a stoichiometric range. For example, when “TiCN” is simply written, the atomic ratio of “Ti”, “C”, and “N” is not limited to 50:25:25. Also, when “TiC” is written, “Ti” and “C” Is not limited to the case of 50:50, and any conventionally known atomic ratio is included.

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

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

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

<Base material>
As the base material 1 used for 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, including WC, including Co, or including carbonitrides such as Ti, Ta, Nb), cermet (TiC, TiN, TiCN, etc.) 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 substrates, it is particularly preferable to select a WC-based cemented carbide or cermet (particularly TiCN-based cermet). This is because these substrates are particularly excellent in the balance between hardness and strength at high temperatures, and have excellent characteristics as substrates for surface-coated cutting tools for the above applications.

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

  The coating 2 has an effect of improving various properties such as wear resistance and chipping resistance by coating the substrate 1.

  The coating 2 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. If it exceeds 30 μm, peeling or breaking of the coating frequently occurs when a large stress is applied between the coating and the substrate in intermittent processing. 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, each of the columnar crystals 4 is formed by alternately laminating one first unit layer 4a and one second unit layer 4b, and as a whole, one or more first unit layers 4a and 4 It has a multilayer structure including one or more second unit layers 4b. In the columnar crystal 4, the layer closest to the substrate 1 is the first unit layer 4 a.

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

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 these.

  Said 1st hard layer 3 shows the outstanding effect that abrasion resistance and chipping resistance improve with sufficient balance by having such a structure. The reason is presumed to be as follows (i) to (vi).

  (I) Since the first hard layer 3 includes a plurality of columnar crystals 4, there are fewer grain boundaries than in the case where the first hard layer 3 is composed of granular crystals, the number of fracture starting points is reduced, and the coating is less likely to fall off or be lost. 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 wear resistance improves as the atomic ratio of carbon to the total of carbon and nitrogen increases, but the chipping resistance and heat resistance tend to decrease. The first hard layer 3 is formed by alternately laminating first unit layers 4a made of TiCN having a relatively small carbon content and second unit layers 4b made of TiCN or TiC having a relatively large carbon content. Therefore, 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 crystals 4) is suppressed. be able to. Thereby, the chipping resistance of the first hard layer 3 is improved.

  (Iv) Since the first unit layer 4a and the second unit layer 4b have different lattice constants, distortion occurs in the crystal lattices of the first unit layer 4a and the second unit layer 4b, compared with the case where there is no distortion. The hardness of the 1 unit layer 4a and the 2nd unit layer 4b becomes high. Thereby, the wear resistance of the first hard layer 3 is improved.

  (V) In the columnar crystal 4 included in the first hard layer 3, the layer closest to the substrate is the first unit layer 4a. This indicates that when the columnar crystal 4 is formed on the substrate 1 by, for example, the CVD method, the first unit layer 4a is formed first. The first unit layer 4a is a layer made of TiCN having a relatively low carbon content, and TC (422) is the maximum in the orientation index TC (hkl). Accordingly, the columnar crystal 4 having a multilayer structure formed by alternately stacking the second unit layer 4b and the first unit layer 4a on the first unit layer 4a is oriented in the (422) plane, and the columnar crystal 4 Grow uniformly in the direction perpendicular to the surface of the substrate (in the thickness direction of the coating 2). Thereby, the dispersion | variation in the intensity | strength in the columnar crystal 4 becomes small, and the abrasion resistance and chipping resistance of the 1st hard layer 3 improve.

  (Vi) The columnar crystals 4 included in the first hard layer 3 are oriented in the (422) plane close to the (111) plane having a high Young's modulus in the close-packed plane of the rock salt type crystal structure. Thereby, the wear resistance of the first hard layer 3 is improved.

  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 includes 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 100% by volume. preferable. When 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 using an SEM (scanning electron microscope). can do. Specifically, the cross section of the film is CP processed by Ar etching, and the processed surface is observed at a magnification of 10,000 times using a field emission scanning electron microscope SU6600 manufactured by Hitachi, Ltd. It can be confirmed that a crystal part exists. Furthermore, 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 set as the volume ratio of the columnar crystal in the first hard layer.

  The columnar crystals 4 included in the first hard layer 3 are grown in a direction substantially perpendicular to the substrate surface (that is, the thickness direction of the film), and have a width (diameter) of 30 nm to 500 nm, for example. Has a shape of 1000 nm to 10,000 nm. Note that the granular crystal is not a crystal grown in one direction like a columnar crystal but has a substantially spherical or irregular shape and a particle size of 100 nm to 1000 nm. The size of the columnar crystal or granular crystal can be calculated from the Scherrer equation based on the measurement result 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. When the average grain size of the columnar crystals is less than 30 nm, the grain boundaries increase in the first hard layer, and chipping resistance may be lowered. On the other hand, if the average particle size exceeds 80 nm, the wear resistance may be reduced. Here, the average particle size of the granular crystals is a value derived from the half-value width of the (422) peak of TiC measured by XRD (out-of-plane) using Scherrer's formula (constant K = 0.9). Means. The average grain size of the columnar crystal is synonymous with the width (diameter) of the columnar crystal.

  The aspect ratio of the columnar crystal 4 is preferably 40 or more. When 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 grain size and aspect ratio of the columnar crystal 4 can be measured as follows. First, the cross section of the coating 2 is mirror-finished, and the grain boundaries of the first hard layer 3 having the columnar crystals 4 are etched. Then, at a location corresponding to 1/2 of the film thickness of the first hard layer 3, the width of each crystal in the horizontal direction with respect to the base material is defined as the grain size, and the grain size of each crystal is measured using an 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 taken 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 Formula (1), it is 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 second unit layer 4b shown in FIG. 2 has a multilayer structure in which the second unit layers 4b are alternately stacked. In the columnar crystal 4, the layer closest to the substrate 1 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 sum of carbon and nitrogen is relatively low. In general, 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 N _z-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. Therefore, by stacking the first unit layer and the second unit layer having different compositions, The effect of improving the wear resistance and chipping resistance in a balanced manner cannot be obtained. x is preferably in the range of 0.45 ≦ x ≦ 0.65, and more preferably in the range of 0.50 ≦ x ≦ 0.60. Note that the atomic ratio of “Ti” and the sum of “C” and “N” in TiC _x N _z-x is such that when “Ti” is 1, the sum of “C” and “N” is 0.80. It is preferable to be set to ˜1.10.

The second unit layer 4b has a composition of TiC _y N _A-y (where 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20). This composition means that the layer made of TiCN has a relatively high atomic ratio of carbon to the total of carbon and nitrogen, or is a layer made of TiC not containing N. In a layer made of TiCN, the greater 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 chipping resistance in a balanced manner, the concentration difference between carbon and nitrogen in the first unit layer 4a and the second unit layer 4b is increased, that is, the absolute value of xy It is desirable to increase the value. y is preferably in the range of 0.85 ≦ y <1, and more preferably in the range of 0.90 ≦ y <1.00. Note that the atomic ratio of “Ti” and the sum of “C” and “N” in TiC _y N _A-y is “ ₀ ” when “Ti” is 1, and the sum of “C” and “N” is 0.80. ~ 1.20.

_{X in} the composition TiC _x N _{z-x of} the first unit layer 4a (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 y} N _A-y (where 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20) satisfy the relationship of y−x ≧ 0.25. According to this, in the columnar crystal 4, it is possible to obtain an 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 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, and nitrogen) and the composition of the other layers in the coating were determined using an EPMA (Electron Probe Microanalyzer) apparatus. This can be confirmed by measuring.

  In the columnar crystal 4 included in the first hard layer 3, the layer closest to the substrate is the first unit layer 4a. This indicates that when the columnar crystal 4 is formed on the substrate 1 by the CVD method, the first unit layer 4a is first formed. The first unit layer 4a is a layer made of TiCN having a relatively low carbon content, and TC (422) is the maximum in the orientation index TC (hkl). Accordingly, the columnar crystal 4 having a multilayer structure formed by alternately stacking the second unit layer 4b and the first unit layer 4a on the first unit layer 4a is oriented in the (422) plane, and the columnar crystal 4 Grow uniformly in the direction perpendicular to the surface of the substrate (in the thickness direction of the coating 2). Thereby, the dispersion | variation in the intensity | strength in the columnar crystal 4 becomes small, and the chipping resistance and abrasion resistance of the 1st hard layer 3 improve.

  The columnar crystals 4 are oriented in the (422) plane close to the (111) plane having a high Young's modulus at the close-packed plane of the rock salt type crystal structure. Thereby, the wear resistance of the first hard layer 3 is improved.

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

In formula (3), I (hkl) represents the X-ray diffraction intensity of the (hkl) plane, and I ₀ (hkl) is (CP1) according to JCPDS standard (Joint Committee on Powder Diffraction Standards (powder X-ray diffraction standard)). 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 sides of (111), (200), (220), (311), (331), (420), (422), and (511), and is the right side of equation (3). The curly brackets indicate the average value of these eight surfaces.

  In the orientation index TC (hkl), TC (422) is the maximum. When the orientation index TC (hkl) is obtained by the equation (3) for all the eight surfaces, TC (422) shows the maximum value. This means that the columnar crystals are strongly oriented in the (422) plane. As described above, when the (422) plane becomes an orientation plane, columnar crystals grow in a vertical direction with respect to the substrate surface. Thereby, the dispersion | variation in the intensity | strength in a columnar crystal becomes small, and the chipping resistance and abrasion resistance of a 1st hard layer improve.

  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 is improved, and the chipping resistance and wear resistance of the first hard layer are improved.

  In the multilayer structure in which the first unit layers 4a and the second unit layers 4b are alternately stacked, the stacking 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, if 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 lamination period means the total thickness of one adjacent first unit layer 4a and one adjacent second unit layer 4b. The lamination period is more preferably 50 nm to 500 nm, and still more preferably 50 nm to 200 nm.

  In the multilayer structure, the ratio of the thicknesses of the adjacent first unit layer 4a and the adjacent second unit layer 4b is preferably in the range of 1: 1 to 3: 1. According to this, the wear resistance and 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, it is possible to sufficiently obtain the effect of improving the wear resistance and the chipping resistance in a balanced manner. The number of repetitions is a value that means the number of periods in the entire multilayer structure when the combination of one adjacent first unit layer and one second unit layer is one period.

  The thickness of one first unit layer 4a 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 heat resistance by the first unit layer can be sufficiently obtained.

  The thickness of one second unit layer 4b 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 wear resistance by the second unit layer can be sufficiently obtained.

  The overall 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 film is observed with an optical microscope. The difference in contrast can be confirmed as indicating a multilayer structure. Moreover, it can also confirm by observing the cross section of a film using SEM (scanning electron microscope), EPMA (electron beam 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 using an SEM (scanning electron microscope). . Specifically, the film thickness can be defined 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 an enlargement magnification of 5000 times.

  The amount of free carbon in the first hard layer 3 is preferably 1.0% by volume or less. Here, free carbon does not exist as TiC or TiCN compound, but means C—C bonded amorphous carbon or free carbon. If the amount of free carbon in the first hard layer exceeds 1.0% by volume, cracks tend to occur starting from free carbon, and the chipping resistance of the first hard layer may be reduced. The amount of free carbon is more preferably 0.1% by volume or less, and most preferably free carbon is not included. The amount of free carbon can be measured using an XPS (X-ray photoelectron spectroscopy) apparatus. Specifically, it can be calculated from the position and intensity ratio of the XPS C-1s spectrum. (The binding energy of binding carbon (TiC) is 281.3 to 281.7 eV, and that of non-binding carbon (free carbon) is 283.8 to 284.7 eV).

  The first hard layer 3 has a hardness measured by a nanoindenter method of 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. In addition, the measurement of hardness is performed by the method based on ISO14577, and a measurement load shall be 10 mN (1g). 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 regular intervals from the substrate direction along the film thickness direction, and the average value of the hardness at the 10 points is defined as the hardness of the first hard layer.

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

  The underlayer 5 is formed immediately above the base material in order to improve the adhesion between the base material and the coating. The underlayer 5 is made of TiN, TiBN, or the like, and preferably has an average thickness of 0.1 to 2.0 μm.

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

  The alumina layer 7 is excellent in oxidation resistance, and has excellent wear resistance due to heat (oxidation wear) generated during high-speed cutting of steel and welding resistance during cutting of castings. The 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 in order to show the discriminability of whether or not the cutting edge is used. The outermost surface layer 8 is made of TiN, TiCN, TiC or the like, and preferably has an average thickness of 0.3 to 2.0 μm.

<Method for manufacturing surface-coated cutting tool>
The manufacturing method of the surface coating cutting tool which concerns on one embodiment of this invention comprises the process of preparing a base material, and the process of forming a film on a base material.

The step of forming the coating 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 performed by a chemical vapor deposition method under conditions of a reaction temperature of 800 ° C. or more and 950 ° C. or less and a pressure of 0.05 atm or more and 1.0 atm or less. In the first unit layer forming step, using the first source gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ , the following formula (1)
TiC _x N _z-x (1)
(In Formula (1), it is 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, a second source gas containing TiCl ₄ , C ₂ H ₄ and H ₂ is used, 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)
To form a second unit layer. 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.

<Step of preparing a substrate>
As a base material, the base material demonstrated above is prepared.

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

  In the step of forming a 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 substrate in the multilayer structure is the first unit layer. As described above, the first unit layer has the largest 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 in the (422) plane, has a low Young's modulus, and 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 . The second source gas does not contain nitrogen, but the second unit layer may contain nitrogen. The reason for this is that when the gas supplied into the reaction chamber is changed from the first source gas to the second source gas, nitrogen in the first source gas remains in the reaction chamber, and this nitrogen becomes the second source gas. It is thought to be mixed.

In a conventional method (for example, Non-Patent Document 1), a gas containing CH ₄ is used as a source gas in order to form a layer made of TiCN or TiC by a 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 these conditions, the obtained layer of TiCN or TiC is composed of granular crystals, and because there are many grain boundaries, the starting point of fracture increases, and cracks develop from this starting point of breakage, resulting in dropouts and defects of the coating. There was a case. Further, during the formation of the coating film, mutual diffusion occurs between the substrate made of the cemented carbide and the coating film, and an η layer that is an embrittlement layer may be formed at the interface between the substrate and the coating film.

In the manufacturing method according to the present embodiment, C ₂ H ₄ that decomposes at about 800 ° C. is used as the source gas without using CH ₄ , so that the reaction temperature of the CVD method is set to a low temperature of 800 ° C. or higher and 950 ° C. or lower. Can do. 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. Moreover, since the η layer is not formed at the interface between the substrate and the coating, the adhesion between the substrate and the coating 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 substrate and the coating. 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 formation rate and the crystal grain size.

There is another conventional method (Non-Patent Document 2) that does not use CH ₄ as a source gas. In this technique, a gas containing TiCl ₄ , CH ₃ CN, C ₂ H ₄ , N _2, and H ₂ is used as a source gas in order to form a layer made of TiCN by a CVD method. In this case, although the reaction temperature can be lowered to 840 to 900 ° C., 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 is a starting point of fracture, the chipping resistance of the coating may be reduced.

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

The content of H ₂ gas of the first source gas, and, when the content of H ₂ gas in the second raw material gas is in the range of the, C ₂ H contained in the first material gas and second material gas _{Since 4} is diffused by H ₂ gas, it is possible to suppress C ₂ H ₄ from agglomerating and carbonizing, thereby preventing free carbon from being mixed into the first hard layer. In the first unit layer forming step, the content of H ₂ gas in the first source gas is more preferably 80% by volume to 98% by volume. In the second unit layer forming step, the content of H ₂ gas in the second source gas is more preferably 95% by volume to 99% by volume.

  In the first unit layer forming step, the flow rate of the entire first source gas is preferably 10 to 30 times the volume of the reaction chamber per minute, from the viewpoint of uniformity of the first unit layer, and preferably 10 to 25 times. Even less than double is more preferable. In addition, the flow rate of the entire second source 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 from the viewpoint of the uniformity of the second unit layer. 25 times or less is more preferable. Here, the flow rate of the source gas is a value in temperature and pressure when the first unit layer and the second unit layer are formed in the reaction chamber.

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

The contents of TiCl ₄ , C ₂ H ₄ and H ₂ in the second source gas can be appropriately changed according to the desired composition of the second unit layer. For example, the composition of the second source gas is such that TiCl ₄ is 0.5 volume% to 4.0 volume%, C ₂ H ₄ is 0.5 volume% to 5.0 volume%, 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, at a reaction temperature of 800 ° C. or higher and 950 ° C. or lower, a film containing columnar crystals can be formed stably. The pressure is preferably from 0.1 atm to 0.5 atm.

  When the film in this Embodiment contains layers other than a 1st unit layer and a 2nd unit layer, these other layers can be formed by a conventionally well-known chemical vapor deposition method or a physical vapor deposition method. From the viewpoint that the first unit layer and the second unit layer can be formed continuously in one chemical vapor deposition apparatus, the other layers are preferably formed by chemical vapor deposition.

  The present embodiment will be described more specifically with reference to examples. However, the present embodiment is not limited to these examples.

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

<Formation of coating>
A TiN layer (underlying layer), a first hard layer (a multilayer structure of a first unit layer and a second unit layer), a TiCNO layer (intermediate layer), Al ₂ O are formed on the base material of each sample by chemical vapor deposition. _Three layers (alumina layer) and TiN layer (outermost surface layer) were formed in this order. In Samples 2 to 27, in the first hard layer forming step, 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 formation process of 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 film forming conditions (reaction chamber pressure, reaction chamber temperature, flow rate) of the underlayer, intermediate layer, alumina layer, and outermost layer. Source gas composition of first unit layer and second unit layer, film forming conditions (reaction chamber pressure, reaction chamber temperature, flow rate, in Table 2, the flow rate “x” is the total of the first source gas per minute. It shows that the flow rate and the flow rate of the entire second source gas are x times the volume of the reaction chamber.) And the stacking cycle are shown in Table 2.

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

The composition of the first unit layer and the second unit layer of each sample was measured using an EPMA apparatus. In all samples, the first unit layer is represented by TiC _x N _z-x (where 0.45 ≦ x <0.70 and z = 1.0), and the second unit layer is TiC _y N _1-A (where 0.70 ≦ y ≦ 1 and A = 1.0). The values of “x”, “y” and “y−x” 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 apparatus. The results are shown in Table 3.

The film thickness of each sample was measured using 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) apparatus, 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 crystal of each sample was measured by the following procedure. First, the cross section of the coating was mirror-finished to etch the grain boundaries of the first hard layer having columnar crystals. Then, at a position corresponding to 1/2 of the film thickness of the first hard layer, the width of each crystal in the horizontal direction with respect to the base material is defined as the particle size, and the average value is obtained by measuring the particle size of each crystal using SEM. It was. In addition, the measurement location was 20 locations. 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 based on ISO14577, and the measurement 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 regular intervals from the substrate direction along the film thickness direction, and the average value of the hardness at the 10 points was defined as the hardness of the first hard layer.

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

  For the surface-coated cutting tool of each sample, the cutting edge (tips) until the cutting edge chipping or flank wear amount (Vb) reaches 0.30 mm (but rounded off after the decimal point) is measured and the cutting edge is measured under the following cutting conditions. The final damage form was observed. The results are shown in Table 3.

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

  In the final damage form, “normal wear” means a damage form (having a smooth wear surface) that does not cause chipping or chipping but only wear, and “tip chipping” occurs at the cutting edge. It means a big lack.

<Cutting conditions>
Work material: FCD450-4 groove material outer diameter continuous cutting peripheral speed: 250 m / min
Feeding speed: 0.30mm / rev
Cutting depth: 1.5mm
Cutting fluid: Yes

  Samples 2 to 27 are surface-coated cutting tools according to an embodiment of the present invention, and were superior in wear resistance and chipping resistance to Sample 1 as a comparative example.

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

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 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 surface layer 10 Surface coating cutting tool

Claims (6)

A surface-coated cutting tool comprising a substrate and a coating that covers the substrate,
The coating includes 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 Formula (1), it is 0.45 <= x <0.70 and 0.80 <= z <= 1.20)
A first unit layer represented by the following formula (2):
TiC _y N _1-A (2)
(In the formula (2), 0.70 ≦ y ≦ 1 and 0.80 ≦ A ≦ 1.20)
A second unit layer indicated by a multi-layer structure alternately stacked,
In the columnar crystal, the surface-coated cutting tool, wherein the layer closest to the base material is the first unit layer.   The surface-coated cutting tool according to claim 1, wherein a 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, wherein x in the formula (1) and y in the formula (2) satisfy a relationship of y−x ≧ 0.25.   The surface-coated cutting tool according to any one of claims 1 to 3, wherein the first hard layer includes free carbon in an amount of 1.0% by volume or less. It is a manufacturing method of the surface covering cutting tool according to any one of claims 1 to 4,
Preparing a substrate;
Forming a film on the substrate,
The step of forming the coating 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 performed 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, using the first source gas containing TiCl ₄ , CH ₃ CN, N ₂ and H ₂ , the following formula (1)
TiC _x N _z-x (1)
(In formula (1), 0.45 ≦ x <0.70 and 0.80 ≦ z ≦ 1.20)
Forming a first unit layer represented by
In the second unit layer forming step, a second source gas containing TiCl ₄ , C ₂ H _4, and H ₂ is used, 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)
Forming a second unit layer represented by
The said 1st unit layer formation process and the said 2nd unit layer formation process are the manufacturing methods of the surface coating cutting tool started from the said 1st unit layer formation process. In the first unit layer forming step, the content of H ₂ gas in the first source gas is 60% by volume to 98% by volume, and in the second unit layer forming step, H ₂ gas in the second source gas is used. The method for producing a surface-coated cutting tool according to claim 5, wherein the content of is from 90% by volume to 99% by volume.