JP2017042901A - Surface-coated cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-coated cutting tool having coating with enhanced mechanical characteristics, and a further prolonged service life of the cutting tool.SOLUTION: A surface-coated cutting tool of the invention comprises: a base material, and a coating formed on the base material. The coating has an α-AlOa layer including a plurality of crystal grains of α-AlO. The α-AlOlayer includes: a lower layer part arranged on the base material side in a thickness direction with 1 μm thickness; and an upper layer part arranged on a front surface side opposite to the base material side, with 2 μm thickness. When crystal orientations are specified to crystal grains, respectively, to a cross section formed by cutting the α-AlOlayer, with a plane including a normal line of a surface of the α-Allayer, by EBSD analysis using FE-SEM, to create a color map based on the specified crystal orientation, the upper layer part includes 90% or more area which is occupied by crystal grains having a normal line direction of (001) surface within ±10° with regard to the normal line direction on the surface of the α-AlOlayer, while the lower layer part includes 50% or less of the above-mentioned area.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a surface-coated cutting tool.

Conventionally, a surface-coated cutting tool in which a coating is formed on a substrate has been used. For example, Japanese Patent Laid-Open No. 2004-284003 (Patent Document 1) describes an α whose total area of crystal grains indicating the crystal orientation of the (0001) plane is 70% or more when viewed from the normal direction of the surface of the layer. It discloses a surface-coated cutting tool having a coating comprising -al ₂ O ₃ layer.

Japanese Patent Laid-Open No. 2010-207946 (Patent Document 2) discloses that α- in which crystal grains observed on the surface of the layer have a specific size category when viewed from the normal direction of the surface of the layer. A surface-coated cutting tool having a coating comprising an Al ₂ O ₃ layer is disclosed.

JP 2004-284003 A JP 2010-207946 A

In Patent Document 1 and Patent Document 2, by having a coating including the α-Al ₂ O ₃ layer having the above-described configuration, mechanical properties such as wear resistance and fracture resistance of the surface-coated cutting tool are improved. Therefore, it is expected that the life of the cutting tool will be extended.

  However, in recent cutting work, there has been a problem that speeding up and efficiency improvement have progressed, the load applied to the cutting tool has increased, and the life of the cutting tool has been shortened. For this reason, it is required to further improve the mechanical properties of the coating film of the cutting tool and further extend the life of the cutting tool.

  The present disclosure has been made in view of such circumstances, and an object of the present disclosure is to provide a surface-coated cutting tool that improves the mechanical properties of the coating and further extends the life of the cutting tool. It is in.

A surface-coated cutting tool according to an aspect of the present disclosure is a surface-coated cutting tool including a base material and a coating film formed on the base material, and the coating film includes a plurality of α-Al ₂ O ₃ crystal grains. has a α-Al ₂ O ₃ layer comprising, the α-Al ₂ O ₃ layer in its thickness direction, and positioned at the base material side, and a lower layer portion having a thickness of 1 [mu] m, opposite the substrate side Α-Al when the α-Al ₂ O ₃ layer is cut along a plane including the normal of the surface of the α-Al ₂ O ₃ layer, the upper layer portion having a thickness of 2 μm located on the surface side _{For each} cross section of the ₂ O ₃ layer, the crystal orientation of each crystal grain is identified by electron backscatter diffraction image (EBSD) analysis using a field emission scanning microscope (FE-SEM), and a color map based on this is specified. when you create, in the color map, the upper layer portion (001) plane direction normal α-Al ₂ O ₃ layers Area occupied by the crystal grains is within ± 10 ° with respect to the normal direction of the surface is 90% lower section (001) plane law surface normal direction α-Al ₂ O ₃ layers The area occupied by crystal grains within ± 10 ° with respect to the line direction is 50% or less.

  According to the above, the mechanical properties of the coating are improved, and the life of the cutting tool can be further extended.

It is a perspective view showing an example of a surface covering cutting tool concerning one embodiment of this indication. It is the II-II sectional view taken on the line of FIG. FIG. 3 is a partially enlarged view of FIG. 2. A color map created based on the cross-section of the α-Al ₂ O ₃ layer obtained by cutting the film in a plane including the normal to the surface of the coating. The stress distribution in the thickness direction of the α-Al ₂ O ₃ layer is a graph schematically showing. It is sectional drawing which shows the shape in the thickness direction of a 2nd intermediate | middle layer roughly. It is sectional drawing which shows roughly an example of the chemical vapor deposition apparatus used for manufacture of the film which concerns on embodiment.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described. In the crystallographic description of the present specification, individual planes are indicated by (). In addition, in the present specification, the notation in the form of “A to B” means the upper and lower limits of the range (that is, A or more and B or less), the unit is not described in A, and the unit is described only in B. The unit of A is the same as the unit of B. Further, in this specification, those having no particular atomic ratio in the chemical formulas such as “TiN” and “TiCN” do not indicate that the atomic ratio of each element is only “1”, and are conventionally known. All atomic ratios are included.

[1] A surface-coated cutting tool according to an aspect of the present disclosure is a surface-coated cutting tool including a base material and a coating film formed on the base material, and the coating film includes a plurality of α-Al ₂ O _3. An α-Al ₂ O ₃ layer containing crystal grains of the α-Al ₂ O ₃ layer, the α-Al ₂ O ₃ layer being positioned on the substrate side in the thickness direction and having a thickness of 1 μm, and the substrate side and located on the opposite surface side of, and including an upper layer portion having a thickness of 2 [mu] m, a, of a cutaway of the α-Al ₂ O ₃ layer in a plane including the normal to the surface of the α-Al ₂ O ₃ layer Based on the cross-section of the α-Al ₂ O ₃ layer, the crystal orientation of each crystal grain was determined by electron backscatter diffraction image (EBSD) analysis using a field emission scanning microscope (FE-SEM). when you create a color map, the color map, the upper layer portion, the normal direction of the (001) plane alpha-Al ₂ Area occupied by the crystal grains is within ± 10 ° with respect to the normal direction of the _{three-layered} surface of not less than 90%, the lower layer portion (001) surface normal direction is alpha-Al ₂ O ₃ layer The area occupied by crystal grains within ± 10 ° with respect to the normal direction of the surface is 50% or less. According to such an α-Al ₂ O ₃ layer, high wear resistance can be exhibited in the upper layer portion located on the surface side, and high adhesion to the substrate in the lower layer portion located on the substrate side. Can demonstrate its sexuality. Therefore, the surface-coated cutting tool [1] is excellent in mechanical properties and thus has a long life.

[2] In the above surface-coated cutting tool, preferably, the α-Al ₂ O ₃ layer has a stress distribution that varies in the thickness direction, and the surface side of the α-Al ₂ O ₃ layer has a compressive residual stress. The substrate side of the α-Al ₂ O ₃ layer has a tensile residual stress. In this case, the surface-coated cutting tool has a longer life.

  [3] In the surface-coated cutting tool according to [2], preferably, the stress distribution includes a first region in which an absolute value of compressive residual stress continuously increases from the surface side toward the base material side, The absolute value of the compressive residual stress is continuously reduced from the surface side to the base material side and changes to the tensile residual stress. The second region is continuously increased, and the first region and the second region are continuous via an intermediate point where the absolute value of the compressive residual stress is the largest. Such a surface-coated cutting tool has an excellent balance between wear resistance and fracture resistance.

[4] In the Al ₂ O ₃ layer of the surface-coated cutting tool of [2] and [3], preferably, the absolute value of the compressive residual stress is 1000 MPa or less, and the absolute value of the tensile residual stress is 2000 MPa or less. Such a surface-coated cutting tool has an excellent balance between wear resistance and fracture resistance.

[5] In the above surface-coated cutting tool, preferably, the coating includes a first intermediate layer between the base material and the Al ₂ O ₃ layer, and the first intermediate layer is a TiCN layer. Since the TiCN layer has high hardness, the surface-coated cutting tool including the coating having the first intermediate layer is excellent in wear resistance.

[6] In the surface-coated cutting tool according to [5], preferably, the coating includes a second intermediate layer between the first intermediate layer and the α-Al ₂ O ₃ layer, and the second intermediate layer is a TiCNO layer. Or it is a TiBN layer and the difference of the maximum thickness of the 2nd intermediate | middle layer and minimum thickness is 0.3 micrometer or more. The second intermediate layer, it is possible to exhibit the effect as an anchor for adhering the alpha-Al ₂ O ₃ layer and the first intermediate layer, it is possible to enhance the peeling resistance of the coating. Therefore, the surface-coated cutting tool including the coating having the second intermediate layer is further excellent in fracture resistance.

[7] In the surface-coated cutting tool, preferably, the coating includes a surface layer located on the outermost surface, and the surface layer is a TiC layer, a TiN layer, or a TiB ₂ layer. Thereby, the toughness of the coating is improved.

[Details of the embodiment of the present invention]
Hereinafter, one embodiment of the present invention (hereinafter referred to as “this embodiment”) will be described, but the present embodiment is not limited thereto.

[Surface coated cutting tool]
Referring to FIG. 1, a surface-coated cutting tool 10 (hereinafter simply referred to as “tool 10”) of the present embodiment has a cutting edge at which rake face 1, flank face 2, rake face 1 and flank face 2 intersect. And a ridge line portion 3. That is, the rake face 1 and the flank face 2 are faces that are connected with the blade edge line portion 3 interposed therebetween. The cutting edge ridge line portion 3 constitutes a cutting edge tip portion of the tool 10. The shape of such a tool 10 depends on the shape of the base material described later.

  FIG. 1 shows a tool 10 as a cutting edge exchangeable cutting tip for turning, but the tool 10 is not limited to this, and a drill, an end mill, a cutting edge exchangeable cutting tip for a drill, a cutting edge exchangeable cutting tip for an end mill, a milling cutter. It can be suitably used as a cutting tool such as a cutting edge exchangeable cutting tip for processing, a metal saw, a gear cutting tool, a reamer, and a tap.

  Further, when the tool 10 is a cutting edge exchange type cutting tip or the like, the tool 10 includes those having a chip breaker and those having no chip breaker, and the cutting edge ridge line portion 3 has a sharp edge (rake face). And the ridge where the flank intersects), honing (having a sharp edge), negative land (having a chamfer), and a combination of honing and negative land.

  Referring to FIG. 2, the tool 10 has a configuration including a base material 11 and a coating 12 formed on the base material 11. In the tool 10, the coating 12 preferably covers the entire surface of the substrate 11, but a part of the substrate 11 is not covered with the coating 12 or the configuration of the coating 12 is partially different. Even so, it does not depart from the scope of the present embodiment.

〔Base material〕
With reference to FIG. 2, the base material 11 of this embodiment has a rake face 11a, a flank face 11b, and a cutting edge ridge line portion 11c where the rake face 11a and the flank face 11b intersect. The rake face 11 a, the flank face 11 b, and the cutting edge ridge line part 11 c constitute a rake face 1, a flank face 2, and a cutting edge ridge line part 3 of the tool 10.

  As the base material 11, 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 film 12 of this embodiment includes at least one α-Al ₂ O ₃ layer described in detail below. As long as the coating 12 includes the α-Al ₂ O ₃ layer, it can include other layers. The composition of the other layers is not particularly limited, and examples thereof include TiC, TiN, TiB, TiBN, TiAlN, TiSiN, AlCrN, TiAlSiN, TiAlNO, AlCrSiCN, TiCN, TiCNO, TiSiC, CrSiN, AlTiSiCO, and TiSiCN. The order of the lamination is not particularly limited.

  The coating film 12 of this embodiment has an effect of improving various characteristics such as wear resistance and fracture resistance by covering the base material 11.

  The coating 12 preferably has a thickness of 3 to 35 μm. When the thickness of the coating 12 is 3 μm or more, it is possible to suppress a reduction in tool life due to the thin thickness of the coating 12. When the thickness of the coating 12 is 35 μm or less, the chipping resistance in the initial stage of cutting can be improved.

With reference to FIG. 3, as an example of a preferable configuration of the coating film 12 of the present embodiment, the base layer 13 and the first intermediate layer are sequentially arranged from the substrate side to the surface side of the coating film 12 (from the lower side to the upper side in the figure). The coating film 12 in which the layer 14, the second intermediate layer 15, and the α-Al ₂ O ₃ layer 16 are laminated will be described.

[Α-Al ₂ O ₃ layer]
The α-Al ₂ O ₃ layer 16 of the present embodiment is a layer including crystal grains of a plurality of α-Al ₂ O ₃ (aluminum oxide whose crystal structure is α-type). That is, this layer is composed of polycrystalline α-Al ₂ O ₃ . Usually, this crystal grain has a grain size of about 50 to 3000 nm.

In addition, the α-Al ₂ O ₃ layer 16 of this embodiment satisfies the following requirements. That is, in the thickness direction, a lower layer portion that is located on the base material side and has a thickness of 1 μm, and an upper layer portion that is located on the surface side opposite to the base material side and has a thickness of 2 μm, to the cross-section of the α-Al ₂ O ₃ layer 16 of a cutaway of the α-Al ₂ O ₃ layer 16 in a plane including the normal to the surface of -al ₂ O ₃ layer 16, EBSD analysis using FE-SEM When the crystal orientation of each crystal grain made of α-Al ₂ O ₃ is specified by and a color map based on the crystal orientation is created, the upper layer portion of the color map has the normal direction of the (001) plane being α The area occupied by crystal grains (hereinafter also referred to as “(001) plane-oriented crystal grains”) within ± 10 ° with respect to the normal direction of the surface of the Al ₂ O ₃ layer is 90% or more; The area occupied by the (001) plane-oriented crystal grains is 50% or less.

Here, a specific method for creating the color map will be described with reference to FIGS. The lower surface 16b of the α-Al ₂ O ₃ layer 16 shown in FIG. 4 is a surface located on the substrate 11 side in FIG. 3, that is, a surface in contact with the second intermediate layer 15, and the upper surface 16a is a substrate. The surface located on the surface side of the coating 12 opposite to the 11 side, that is, the surface of the α-Al ₂ O ₃ layer 16. When another surface layer or the like is formed on the α-Al ₂ O ₃ layer 16, the upper surface 16a is a surface in contact with the surface layer.

First, an α-Al ₂ O ₃ layer is formed based on the manufacturing method described later. Then, the formed α-Al ₂ O ₃ layer (including the base material) is cut so that a cross section perpendicular to the α-Al ₂ O ₃ layer is obtained (that is, the surface of the α-Al ₂ O ₃ layer). And cut so that the cut surface obtained by cutting the α-Al ₂ O ₃ layer at a plane including the normal line to is exposed). Thereafter, the cut surface is polished with water-resistant abrasive paper (containing a SiC abrasive abrasive as an abrasive).

The above cleavage is, for example alpha-Al ₂ surface of the O ₃ layer 16 (alpha-Al ₂ if O ₃ layer 16 another layer is formed thereon to a film surface) for a sufficiently large hold After being fixed in close contact with a flat plate using wax or the like, it is cut in a direction perpendicular to the flat plate with a rotary blade cutter (cut so that the rotary blade and the flat plate are as vertical as possible). ) This cutting can be performed at any part of the α-Al ₂ O ₃ layer 16 as long as it is performed in such a vertical direction, but it is preferable to cut the vicinity of the edge of the blade edge as described later. .

  In addition, the above polishing is performed using the water-resistant abrasive papers # 400, # 800, and # 1500 in order (the number (#) of the water-resistant abrasive paper means a difference in the particle size of the abrasive, and the number is The larger the particle size, the smaller the particle size of the abrasive).

Subsequently, the polished surface is further smoothed by ion milling with Ar ions. The conditions for the ion milling treatment are as follows.
Acceleration voltage: 6 kV
Irradiation angle: 0 ° from the normal direction of the surface of the α-Al ₂ O ₃ layer (that is, the linear direction parallel to the thickness direction of the α-Al ₂ O ₃ layer at the cut surface)
Irradiation time: 6 hours.

  Next, the smoothed cross section (mirror surface) is observed using an FE-SEM (product name: “SU6600”, manufactured by Hitachi High-Technologies Corporation) equipped with EBSD, and the obtained observation image is obtained. EBSD analysis. The observation location is not particularly limited, but it is preferable to observe the vicinity of the edge portion of the blade edge in consideration of the relationship with the cutting characteristics.

Also for EBSD analysis, data is collected sequentially by placing a focused electron beam onto each pixel individually. The normal of the sample surface (cross section of the smoothed α-Al ₂ O ₃ layer) is inclined by 70 ° with respect to the incident beam, and the analysis is performed at 15 kV. In order to avoid the charging effect, a pressure of 10 Pa is applied. The high current mode is used in combination with the opening diameter of 60 μm or 120 μm. Data collection is performed at a step of 0.1 μm / step for 500 × 300 points corresponding to a surface area of 50 × 30 μm on the cross section.

The EBSD analysis result is analyzed using commercially available software (trade name: “orientation Imaging microscopy Ver 6.2”, manufactured by EDAX), and the color map is created. Specifically, first, the crystal orientation A of each crystal grain included in the cross section of the α-Al ₂ O ₃ layer 16 is specified. The crystal orientation A of each crystal grain specified here is a plan view of each crystal grain appearing in the cross section of the α-Al ₂ O ₃ layer 16 from the normal direction of the cross section (direction passing through the paper surface in FIG. 4). It is the plane orientation that is sometimes observed. Then, based on the crystal orientation A of each obtained crystal grain, the plane orientation of each crystal grain in the normal direction of the surface of the α-Al ₂ O ₃ layer 16 is specified. Then, a color map is created based on the specified plane orientation. To create the color map, the “Cristal Direction MAP” method included in the software can be used. The color map is created over the entire thickness direction of the α-Al ₂ O ₃ layer 16 observed on the cut surface.

In FIG. 4, each region surrounded by a solid line and having hatched hatching is each (001) plane-oriented crystal grain, and each region surrounded by a solid line and having no hatching is (001) plane. It is a crystal grain whose normal direction is a direction other than the former. That is, in FIG. 4, the crystal grains in which the plane orientation in the normal direction of the surface of the α-Al ₂ O ₃ layer 16 is shifted by 10 ° or less from the (001) plane and the (001) plane are hatched, The crystal grains whose plane orientation in the normal direction of the surface of the α-Al ₂ O ₃ layer 16 is a plane other than the former are not hatched. Note that although there is a region shown in black in FIG. 4, this is regarded as a region of crystal grains whose crystal orientation was not specified by the above method.

Moreover, in FIG. 4, the linear distance (shortest distance) d ₁ from the virtual straight line S1 toward the base material side of the α-Al ₂ O ₃ layer 16 is 2 μm, and this is the thickness of the upper layer portion 16A. In FIG. 4, the linear distance (shortest distance) d ₂ from the virtual straight line S2 toward the surface side of the α-Al ₂ O ₃ layer 16 is 1 μm, and this is the thickness of the lower layer portion 16B. That is, in the α-Al ₂ O ₃ layer 16, the region from the surface located on the surface side to the 2 μm inner side is the upper layer portion 16 A, and the α-Al ₂ O ₃ layer 16 is located on the base material side. A region from the surface to the inner side of 1 μm is the lower layer portion 16B. The imaginary straight lines S1 and S2 are approximate straight lines of edges formed by the surface of the α-Al ₂ O ₃ layer 16.

  In the color map, the upper layer portion 16A has a ratio of the total area of the (001) -oriented crystal grains to the entire area of the upper layer portion 16A of 90% or more, and the lower layer portion 16B has the entire area of the lower layer 16B. The ratio of the total area of (001) plane-oriented crystal grains to the area is 50% or less.

The tool 10 including the α-Al ₂ O ₃ layer 16 that satisfies the above requirements is excellent in mechanical properties and has a long life. This will be described in comparison with the prior art.

Conventional, alpha-Al ₂ O ₃ layer approach that has been taken to improve the mechanical properties of, alpha-Al ₂ by controlling the mode of each crystal on the surface of the O ₃ layer alpha-Al ₂ O ₃ layer The characteristics were improved, thereby improving the characteristics of the film having the α-Al ₂ O ₃ layer. In such a conventional approach, the surface of the α-Al ₂ O ₃ layer is a portion that receives a large load due to cutting, and by controlling the properties of this portion, the properties of the entire α-Al ₂ O ₃ layer are controlled. It was based on the idea that. For this reason, no attention has been paid to the configuration in the thickness direction of the Al ₂ O ₃ layer. In particular, the fact that the uniformity of a layer produced by chemical vapor deposition (CVD) or physical vapor deposition (PVD) was to be improved was also distracted from attention to the structure in the thickness direction.

However, the present inventors considered that the breakthrough could not be achieved with the purpose of further extending the life of the cutting tool only by the conventional approach. Then, the present inventors have conducted various studies with focusing on aspects of each crystal in the thickness direction of the α-Al ₂ O ₃ layer, whereby, among the crystals constituting the α-Al ₂ O ₃ layer, It has been found that the crystal form located on the substrate side greatly contributes to the adhesion of the α-Al ₂ O ₃ layer, that is, the fracture resistance.

By further studying based on the above findings, in the α-Al ₂ O ₃ layer, the hardness of the layer itself tends to increase as the area ratio of the (001) -oriented crystal grains increases. When the area occupied by the (001) plane-oriented crystal grains is too large, the adhesion between the α-Al ₂ O ₃ layer and other layers tends to be lowered, and further, in the α-Al ₂ O ₃ layer On the contrary, it has been found that the adhesiveness tends to be increased by varying the orientation of the crystal grains.

The tool 10 according to the present embodiment is completed based on the above knowledge, and includes a coating 12 having an α-Al ₂ O ₃ layer 16 whose crystal structure specifically changes in the thickness direction. Specifically, the α-Al ₂ O ₃ layer 16 has a thickness of 2 μm, and an upper layer portion 16A having an area occupied by (001) plane-oriented crystal grains of 90% or more, a thickness of 1 μm, and ( And (001) a lower layer portion 16B having an area occupied by plane-oriented crystal grains of 50% or less.

According to the α-Al ₂ O ₃ layer 16 as described above, in the upper layer portion 16A, which is an area where cracks are likely to occur during cutting, the occurrence of cracks due to impact during cutting can be suppressed, and the toughness of the cutting tool Can be greatly improved, and thus high wear resistance can be achieved. On the other hand, it can have high adhesiveness to the layer in contact with the lower layer portion 16B. Therefore, since the coating film 12 of this embodiment is excellent in both wear resistance and fracture resistance characteristics, the mechanical characteristics of the tool 10 are improved as compared with the conventional one, and the life is extended.

  In the above-described embodiment, the area ratio in the upper layer portion 16A is more preferably 92% or more. Moreover, the upper limit of the said area ratio of 16 A of upper layer parts is not specifically limited, For example, 100% may be sufficient. The area ratio in the lower layer portion 16B is more preferably 45% or less. Moreover, the lower limit of the said area ratio of the lower layer part 16B is not specifically limited, For example, 0% may be sufficient.

[Thickness of α-Al ₂ O ₃ layer]
In the present embodiment, the α-Al ₂ O ₃ layer 16 preferably has a thickness of 3 to 25 μm. Thereby, the above excellent effects can be exhibited. The thickness is more preferably 3 to 22 μm, still more preferably 3 to 10 μm.

If the thickness of the α-Al ₂ O ₃ layer 16 is less than 3 μm, the degree of improvement in wear resistance due to the presence of the α-Al ₂ O ₃ layer 16 tends to be low. If it exceeds 25 μm, the interfacial stress due to the difference in coefficient of linear expansion between the α-Al ₂ O ₃ layer 16 and the other layers may increase, and the α-Al ₂ O ₃ crystal grains may fall off. Therefore, when the α-Al ₂ O ₃ layer 16 has an intermediate layer portion between the upper layer portion 16A and the lower layer portion 16B, the thickness of the intermediate layer portion is preferably 22 μm or less. Such a thickness can be confirmed by observation of a vertical cross section of the substrate 11 and the coating 12 using a scanning electron microscope (SEM) or the like.

Moreover, it is preferable that the ratio of the orientation crystal grain in the said color map is more than 50% in the said middle layer part. In this case, a decrease in the hardness of the α-Al ₂ O ₃ layer 16 due to the presence of the intermediate portion can be suppressed. The proportion of the middle layer is more preferably 90% or more, and still more preferably 92% or more.

[Stress distribution of α-Al ₂ O ₃ layer]
The α-Al ₂ O ₃ layer 16 of the present embodiment has a stress distribution that changes in its thickness direction, and the upper surface 16a side (that is, the surface side) of the α-Al ₂ O ₃ layer 16 has a compressive residual stress. The lower surface 16b side (that is, the base material side) of the α-Al ₂ O ₃ layer 16 preferably has a tensile residual stress. Such an α-Al ₂ O ₃ layer 16 can have higher hardness on the upper surface 16a side to which an impact is directly applied during cutting, and is greatly involved in the adhesion resistance of the α-Al ₂ O ₃ layer 16. It is possible to have higher adhesion on the lower surface 16b side. This is because the hardness of the layer tends to be increased by having compressive residual stress on the upper surface 16a side, and the α-Al ₂ O ₃ layer 16 on the lower surface 16b side by having tensile residual stress on the lower surface 16b side. This is because the stress difference with the base material 11 tends to be small.

Here, “compressive residual stress” and “tensile residual stress” are a kind of internal stress (intrinsic strain) existing in the layer. The compressive residual stress refers to a stress represented by a numerical value “−” (minus) (in this specification, the unit is represented by “MPa”). For this reason, the concept that the compressive residual stress is large indicates that the absolute value of the numerical value is large, and the concept that the compressive residual stress is small indicates that the absolute value of the numerical value is small. The tensile residual stress refers to a stress represented by a numerical value “+” (plus) (in this specification, the unit is represented by “MPa”). For this reason, the concept that the tensile residual stress is large indicates that the numerical value is large, and the concept that the tensile residual stress is small indicates that the numerical value is small. The stress distribution of the α-Al ₂ O ₃ layer 16 can be measured by a conventionally known sin ² ψ method using X-rays, a constant penetration depth method, or the like.

An example of a preferable distribution of the stress distribution is shown in FIG. In the graph of FIG. 5, the vertical axis indicates the residual stress, and the horizontal axis indicates the position in the thickness direction of the α-Al ₂ O ₃ layer 16. Regarding the vertical axis, when the value is “−”, it means that compressive residual stress exists in the α-Al ₂ O ₃ layer 16, and when the value is “+”, the α-Al ₂ O ₃ layer 16 means that there is a tensile residual stress in the layer 16. When the value is “0”, it means that there is no stress in the α-Al ₂ O ₃ layer 16.

4 and 5, the stress distribution in the thickness direction of the α-Al ₂ O ₃ layer 16 is the absolute value of the compressive residual stress from the upper surface 16a side (front surface side) to the lower surface 16b side (base material side). The absolute value of the compressive residual stress continuously decreases from the first region P ₁ where the value increases continuously, to the lower surface 16b side of the first region and from the upper surface 16a side to the lower surface 16b side. The second region P _{2 in} which the absolute value of the changed tensile residual stress is continuously increased, and the first region and the second region are the absolute values of the compressive residual stress. It is preferable to continue through an intermediate point P ₃ where becomes the largest. The intermediate point P ₃ is the lower surface 16b, in which is located close to the upper surface 16a.

Since the α-Al ₂ O ₃ layer 16 has the stress distribution as described above, the balance between the wear resistance and the fracture resistance of the α-Al ₂ O ₃ layer 16 is more excellent during intermittent cutting. . Herewith, the impact applied from the upper surface 16a side of the α-Al ₂ O ₃ layer 16 in α-Al ₂ O ₃ layer 16 is sufficiently absorbed in between the upper surface 16a side of the intermediate point P _3, the midpoint This is because the high adhesion is exhibited in the lower surface 16b side of the P _3.

In particular, regarding the α-Al ₂ O ₃ layer 16 of the present embodiment, the upper layer portion 16A located on the upper surface 16a side has an area occupied by oriented crystal grains of 90% or more and has a high orientation with respect to the (001) plane. However, when such a part has a high compressive residual stress, it tends to be excellent in both characteristics of wear resistance and toughness. On the other hand, the lower layer portion 16B located on the lower surface 16b side has an area occupied by orientation crystal grains of 50% or less and has a low orientation with respect to the (001) plane, but such a portion has a tensile residual stress. Therefore, the adhesion to the contacting layer tends to be further improved.

  In the stress distribution, the absolute value of the compressive residual stress is preferably 1000 MPa or less (that is, −1000 MPa or more and less than 0 MPa), and the absolute value of the tensile residual stress is preferably 2000 MPa or less (that is, more than 0 MPa and 2000 MPa or less). In this case, both characteristics of wear resistance and fracture resistance tend to be exhibited appropriately.

In the stress distribution, a region from the upper surface 16a to a position having a distance (linear distance) of 5 to 50% of the thickness of the α-Al ₂ O ₃ layer 16 has compressive residual stress, and other regions. Preferably has a tensile residual stress. Also in this case, the balance between wear resistance and fracture resistance is particularly excellent. The distance is more preferably 5 to 45%, and still more preferably 10 to 40%.

The intermediate point P ₃ is preferably located at a distance of 0.1 to 40% of the thickness of the α-Al ₂ O ₃ layer 16 from the upper surface 16a. In this case, the form of damage to the α-Al ₂ O ₃ layer 16 is stabilized, and for example, sudden chipping can be suppressed, so that variations in the life of the tool 10 can be reduced. For example, when the thickness of the α-Al ₂ O ₃ layer 16 is ₃ to 10 μm, the distance from the upper surface 16a of the midpoint P ₃ is preferably 0.5 to ₂ μm. The absolute value of the compressive residual stress at the midpoint P ₃ is preferably a 100～900MPa, more preferably 200～890MPa, more preferably from 350～890MPa.

[First intermediate layer]
Returning to FIG. 3, the coating film 12 according to this embodiment includes a TiCN layer as the first intermediate layer 14 between the base material 11 and the α-Al ₂ O ₃ layer 16. Since the TiCN layer is excellent in wear resistance, the wear resistance of the coating 12 can be further improved.

[Second intermediate layer]
With reference to FIG. 3, the coating 12 according to the present embodiment includes a second intermediate layer 15 between the first intermediate layer 14 and the α-Al ₂ O ₃ layer 16. As shown in FIG. 6, the second intermediate layer 15 is preferably composed of acicular crystals.

The acicular crystal is a crystal having an elongated shape like a needle because the crystal growth direction is one direction. As shown in FIG. 6, the layer made of acicular crystals has the characteristics that the thickness varies greatly and the surface shape becomes complicated. Therefore, the effect as an anchor can be exerted on the contacting layer. Therefore, by having such a second intermediate layer 15 between the base material 11 and the α-Al ₂ O ₃ layer 16, the α-Al ₂ O ₃ layer 16 may be difficult to peel from the base material 11. Therefore, the fracture resistance of the tool 10 including the coating 12 is further improved.

The second intermediate layer 15 is preferably a TiCNO layer or a TiBN layer. This is because TiCNO and TiBN can easily form needle crystals. In addition, the difference between the maximum thickness d ₃ and the minimum thickness d _{4 of} the second intermediate layer 15 is preferably 0.3 μm or more. In this case, the above characteristics are effectively exhibited. The difference is preferably 1.0 μm or less. This is because if the difference exceeds 1.0 μm, the shape of the second intermediate layer 15 may adversely affect the shape of the coating 12. In addition, the said difference can be confirmed using FE-SEM provided with said EBSD.

[Underlayer]
With reference to FIG. 3, the film 12 according to the present embodiment includes a base layer 13 that is in contact with the substrate 11. By using, for example, a TiN layer as the underlayer 13, the adhesion between the substrate 11 and the coating 12 can be further enhanced.

[Other layers]
The coating film 12 according to the present embodiment may have a surface layer on the α-Al ₂ O ₃ layer 16. The surface layer is preferably a TiC layer, a TiN layer, or a TiB ₂ layer. Although the upper surface 16a side of the α-Al ₂ O ₃ layer 16 has a high (001) orientation, a TiC layer, a TiN layer, and a TiB layer formed on the α-Al ₂ O ₃ layer 16 are used. _{The two} layers are particularly effective in suppressing crack propagation during intermittent cutting. Therefore, the coating film 12 having a surface layer having such a composition is advantageous in terms of improving toughness. Especially, since the TiN layer exhibits a clear gold color, it is easy to identify the cutting edge after cutting use, which is advantageous from the viewpoint of economy.

〔Production method〕
The tool 10 according to the above-described embodiment can be manufactured by forming the coating 12 on the surface of the substrate 11. The coating 12 can be formed by a CVD method using a chemical vapor deposition (CVD) apparatus illustrated in FIG.

  With reference to FIG. 7, the CVD apparatus 30 includes a plurality of base material setting jigs 31 for holding the base material 11 and a reaction vessel 32 made of heat-resistant alloy steel that covers the base material setting jig 31. . A temperature control device 33 for controlling the temperature in the reaction vessel 32 is provided around the reaction vessel 32. The reaction vessel 32 is provided with a gas introduction pipe 35 having a gas introduction port 34. The gas introduction pipe 35 is arranged so as to extend in the vertical direction in the internal space of the reaction container 32 in which the base material setting jig 31 is arranged, and a plurality of gas introduction pipes 35 for ejecting gas into the reaction container 32. Are provided. Using this CVD apparatus 30, each layer can be formed as follows.

  First, the base material 11 is placed on the base material setting jig 31, and the source gas for the underlayer 13 is supplied from the gas introduction pipe 35 into the reaction container 32 while controlling the temperature and pressure in the reaction container 32 within a predetermined range. To introduce. Thereby, the base layer 13 is produced on the surface of the base material 11. Similarly, by introducing the raw material gas for the first intermediate layer 14 and the raw material gas for the second intermediate layer 15 into the reaction vessel 32 in this order, the first intermediate layer 14 and the second intermediate layer are formed on the underlayer 13. 15 are formed in order.

For example, when manufacturing a TiN layer, TiCl ₄ and N ₂ can be used as source gases. When manufacturing the TiCN layer, TiCl ₄ , N ₂ and CH ₃ CN can be used. When manufacturing the TiCNO layer, TiCl ₄ , N ₂ , CO and CH ₄ can be used.

The temperature in the reaction vessel 32 when forming each layer is preferably controlled to 1000 to 1100 ° C., and the pressure in the reaction vessel 32 is preferably controlled to 0.1 to 1013 hPa. Further, HCl may be introduced together with the above source gas. By introducing HCl, the uniformity of the thickness of each layer can be improved. Note that H ₂ is preferably used as the carrier gas. Further, it is preferable to rotate the gas introduction pipe 35 by a driving unit (not shown) at the time of gas introduction. Thereby, each gas can be uniformly dispersed in the reaction vessel 32.

  Further, at least one of the above layers may be formed by MT (Medium Temperature) -CVD. Unlike the CVD method (hereinafter also referred to as “HT-CVD method”) performed at a temperature of 1000 ° C. to 1100 ° C., the MT-CVD method has a relatively mild temperature of 850 to 950 ° C. This is a method of forming a layer while maintaining a proper temperature. Since the MT-CVD method is performed at a relatively low temperature compared to the HT-CVD method, damage to the base material 11 due to heating can be reduced. In particular, it is preferable to form the TiCN layer by MT-CVD.

Next, the α-Al ₂ O ₃ layer 16 is formed on the second intermediate layer 15. The α-Al ₂ O ₃ layer 16 according to the present embodiment is formed by performing a CVD method including the following first α-Al ₂ O ₃ formation step and second α-Al ₂ O ₃ formation step. can do. In particular, the α-Al ₂ O ₃ layer 16 having the stress distribution described above can be formed by further performing a compressive residual stress applying step. Hereinafter, the first α-Al ₂ O ₃ forming step, the second α-Al ₂ O ₃ forming step, and the compressive residual stress applying step will be described in order.

First, the first α-Al ₂ O ₃ formation step is performed. As the source gas, AlCl ₃ , N ₂ , CO ₂ , and H ₂ S are used. At this time, regarding the flow rate (l / min) between CO ₂ and H ₂ S, the flow rate ratio is set so as to satisfy CO ₂ / H ₂ S ≧ 2. Thereby, the lower layer part 16B which has the above-mentioned orientation is formed. The most preferred that each flow rate of CO ₂ and H ₂ S are 0.4~2.0l / min and 0.1~0.8l / min, and most preferably from 1l / min and 0.5 l / min. The upper limit of CO ₂ / H ₂ S is not particularly limited, but is preferably 5 or less from the viewpoint of the uniformity of the layer thickness.

In the first α-Al ₂ O ₃ formation step, the film formation time is controlled so that an α-Al ₂ O ₃ layer having a thickness of at least 1 μm is formed. The first alpha-Al ₂ O ₃ formation of alpha-Al ₂ O ₃ layer formed by the process, is located in the most lower (the side contacting the second intermediate layer 15 and bottom) α-Al ₂ O ₃ This is because the layer becomes the lower layer portion 16B. For this reason, the film-forming time of the first α-Al ₂ O ₃ forming step is at least 5 minutes. On the other hand, if the film formation time is excessively long, a layer having a relatively low hardness is formed thick, which is not preferable in terms of the hardness of the coating 12, and therefore, the first α-Al ₂ O ₃ formation step is completed. The membrane time is at least 30 minutes or less.

When an α-Al ₂ O ₃ layer having a thickness of more than 1 μm is formed by the first α-Al ₂ O ₃ formation step, the lowermost layer having a thickness of 1 μm is regarded as the lower layer portion 16B. The other part is regarded as a middle layer part (first middle layer part).

Second, a second α-Al ₂ O ₃ formation step is performed. As the source gas, AlCl ₃ , N ₂ , CO ₂ , and H ₂ S are used. At this time, regarding the flow rate (l / min) between the CO ₂ gas and the H ₂ S gas, the flow rate ratio is set so as to satisfy 0.5 ≦ CO ₂ / H ₂ S ≦ 1. Thereby, the upper layer portion 16A having the above-described orientation is formed.

In the second α-Al ₂ O ₃ formation step, the film formation time is controlled so that an α-Al ₂ O ₃ layer having a thickness of at least 2 μm is formed. Of the α-Al ₂ O ₃ forming step formed by the _second α-Al ₂ O ₃ forming step, α-Al ₂ O located at the uppermost position (the side on which the surface of the coating 12 is formed is the top). _{This is because the three} layers become the upper layer portion 16A. For this reason, the film-forming time of the second α-Al ₂ O ₃ forming step is at least 30 minutes or longer. The upper limit value of the film formation time is not particularly limited, but if the thickness of the α-Al ₂ O ₃ layer 16 is excessively thick, there is a concern that crystal grains may fall off, so the second α-Al ₂ O ₃ formation step. The film formation time is preferably 500 minutes or less.

When an α-Al ₂ O ₃ layer having a thickness exceeding 2 μm is formed by the second α-Al ₂ O ₃ formation step, the uppermost layer having a thickness of 2 μm is regarded as the upper layer portion 16A. The other part is regarded as a middle layer (second middle layer).

In the first α-Al ₂ O ₃ formation step and the second α-Al ₂ O ₃ formation step, the temperature in the reaction vessel 32 is preferably controlled to 1000 to 1100 ° C., and the pressure in the reaction vessel 32 Is preferably controlled to 0.1 to 100 hPa. Further, HCl may be introduced together with the above listed source gases, and H ₂ can be used as the carrier gas. In addition, it is the same as the above that it is preferable to rotate the gas introduction pipe 35 when introducing the gas.

Third, the formed α-Al ₂ O ₃ layer 16 is subjected to a blasting process from the surface side (upper surface 16a side) to apply compressive residual stress to the α-Al ₂ O ₃ layer 16 ( Compression residual stress application step). The layer formed by the CVD method tends to have tensile residual stress as a whole, but this step can apply compressive residual stress to the surface side of the α-Al ₂ O ₃ layer 16. The α-Al ₂ O ₃ layer 16 having the stress distribution can be produced.

In blasting media projection pressure, projection time, by controlling the projection distance, it is possible to control the presence or absence of the intermediate point P ₃ in the stress distribution, and its position (distance from the upper surface 16a). In addition, by controlling the projection time, it is possible to control the region having the compressive residual stress, and thereby applying the compressive residual stress to the desired region in the thickness direction of the Al ₂ O ₃ layer 16 from the upper surface 16a. it can.

In addition, when the film 12 has a surface layer formed on the upper surface 16a of the α-Al ₂ O ₃ layer 16, it is preferable to perform a compressive residual stress applying step after the surface layer is formed. In order to form the surface layer after performing the compressive residual stress applying step, it is necessary to stop the CVD apparatus 30, to take out the base material 11 from the reaction vessel 32, and the manufacturing process becomes complicated. Since this surface layer only needs to remain on a part of the surface of the tool 10, the surface layer may be partially removed by the blast treatment.

  The coating 12 can be manufactured by the manufacturing method described above, and thus the tool 10 including the coating 12 can be manufactured.

Further, α-Al ₂ O case in _{a three-layer} base material side of the area ratio of (001) plane orientation crystal grains large, α-Al ₂ O ₃ layer a layer in contact with the substrate-side surface of the composition and the like Tend to be limited. For example, when the contacted layer is made of polycrystal, it may be difficult to form an α-Al ₂ O ₃ layer with high orientation on the layer. In contrast, the α-Al ₂ O ₃ layer 16 of the present embodiment has the lower layer portion 16B in which the area ratio of the (001) plane-oriented crystal grains is 50% or less, and thus is not subject to the above-described limitation. .

With respect to the manufacturing method described above, the aspect of each layer changes by controlling each condition of the CVD method. For example, the composition of each layer is determined by the composition of the source gas introduced into the reaction vessel 32, and the thickness of each layer is controlled by the implementation time (film formation time). In addition, the second intermediate layer 15 is preferably a needle crystal, but this can change the crystal shape into a needle crystal by controlling the flow rate of the source gas and the film formation temperature. Further, the length of each needle-like crystal can be made non-uniform by controlling the pressure during film formation, thereby causing the difference between the maximum thickness d ₁ and the minimum thickness d ₂ as described above. it can. In particular, in the α-Al ₂ O ₃ layer 16, the crystal orientation in the thickness direction is controlled by controlling the flow ratio (CO ₂ / H ₂ S) of the CO ₂ gas and the H ₂ S gas in the source gas. Sex can be changed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. Sample No. 1 to 12 correspond to examples, and sample Nos. 13 to 20 are comparative examples.

[Sample preparation]
First, sample no. 1 will be described. Made of cemented carbide with a composition (including inevitable impurities) consisting of TaC (2.0 mass%), NbC (1.0 mass%), Co (10.0 mass%) and WC (balance) as the base material A cutting tip (shape: CNMG120408N-UX, manufactured by Sumitomo Electric Hardmetal Co., Ltd., JIS B4120 (2013)) was prepared. A base layer, a first intermediate layer, a second intermediate layer, an α-Al ₂ O ₃ layer and a surface layer are formed in this order on the prepared base material using a CVD apparatus, and a coating is formed on the surface of the base material. Produced. The conditions for forming each layer are shown below. The parentheses following each gas composition indicate the flow rate (l / min) of each gas.

(Underlayer: TiN layer)
Gas: TiCl ₄ (5), N ₂ (15), H ₂ (45)
Pressure and temperature: 130 hPa and 900 ° C.

(First intermediate layer: TiCN layer)
Gas: TiCl ₄ (10), N ₂ (15), CH ₃ CN (1.0), H ₂ (85)
Pressure and temperature: 90 hPa and 860 ° C. (MT-CVD method).

(Second intermediate layer: TiCNO layer)
Gas: TiCl ₄ (0.003), CH ₄ (2.2), N ₂ (6.7), CO (0.5), HCl (1.5), H ₂ (40)
Pressure and temperature: 180 hPa and 1010 ° C.

(Α-Al ₂ O ₃ layer)
(1) CVD conditions for the first α-Al ₂ O ₃ formation process Gas: AlCl ₃ (2.5), CO ₂ (1.3), H ₂ S (0.4), H ₂ (40)
Pressure and temperature: 80 hPa and 1000 ° C
(2) CVD conditions for _second α-Al ₂ O ₃ formation step Gas: AlCl ₃ (3), CO ₂ (1.0), H ₂ S (1.4), H ₂ (38)
Pressure and temperature: 80 hPa and 1000 ° C.

(Surface layer: TiB ₂ layer)
Gas: TiCl ₄ (9), BCl ₃ (1.0), HCl (0.6), H ₂ (30)
Pressure and temperature: 70 hPa and 1000 ° C.

  Next, the following blasting treatment was performed on the cutting edge exchangeable cutting tip for turning which is a base material on which a coating film was formed. That is, while rotating the tip at 100 rpm, aluminum oxide balls having an average particle diameter of 50 μm are uniformly applied to the rake face and flank face from the 45 ° direction of the edge of the cutting edge with compressed air (projection pressure) of 0.15 MPa. Collided for 5 seconds.

As described above, sample No. 1 tool was produced. Sample No. As for 2 to 20, each tool was produced by forming a film comprising a base layer, a first intermediate layer, a second intermediate layer, an α-Al ₂ O ₃ layer and a surface layer on the same base material. . In each sample, the composition of the second intermediate layer and the surface layer was appropriately changed by changing the source gas used for forming the second intermediate layer and the surface layer. Table 1 shows the composition and thickness of each layer constituting the coating in each sample. The thickness of each layer was adjusted by appropriately adjusting the film formation time.

For the second intermediate layer and the α-Al ₂ O ₃ layer, conditions other than the source gas and the film formation time were appropriately changed. Specifically, in the second intermediate layer, the pressure during film formation was changed as shown in Table 2. Thereby, in each sample, the difference between the maximum thickness and the minimum thickness of the second intermediate layer made of acicular crystals was different as shown in Table 2.

For the α-Al ₂ O ₃ layer, by changing the flow ratio (CO ₂ / H ₂ S) of CO ₂ and H ₂ S among the gases to be introduced as shown in Table 3, the upper layer portion And the degree of orientation of the lower layer was controlled. Sample No. In all of 1 to 20, after the first α-Al ₂ O ₃ formation step was performed for 30 minutes, the second α-Al ₂ O ₃ formation step was performed for a predetermined time. And the area ratio (%) which the (001) plane orientation crystal grain accounts in the formed lower layer part and upper layer part calculated | required by the above-mentioned method. The results are shown in Table 3. In Table 3, the “first” and “second” columns indicate CO ₂ and H ₂ during the first α-Al ₂ O ₃ formation step and the second α-Al ₂ O ₃ formation step, respectively. The flow ratio with S is shown.

Referring to Table 3, sample no. 1 to 12, in the color map created by the above method, the area ratio of the (001) plane-oriented crystal grains in the upper layer part is 90% or more, and the (001) plane-oriented crystal grains in the lower layer part The area ratio occupied by was 50% or less.
On the other hand, Sample No. 13 to 20, the area ratio of the (001) plane-oriented crystal grains in the upper layer part is 90% or more, and the area ratio of the (001) plane-oriented crystal grains in the lower layer part is 50% or less. There was no one that met the condition.

In addition, the conditions for the blast treatment were also changed when the samples 1 to 20 were produced. Table 4 shows the blasting conditions for each sample. Further, with respect to the thickness direction of the α-Al ₂ O ₃ layer, residual stresses at six arbitrary points having different depths (distance from the upper surface) were measured by the above-described sin ² ψ method. Residual stress at a position having a distance of 0.5 μm from the upper surface (“upper surface side” in Table 4) and residual stress at a position having a distance of 0.5 μm from the lower surface (“lower surface side” in Table 4) Table 4 shows. In addition, regarding each depth, the residual stress in arbitrary 3 points | pieces was measured, and these average values were made into the residual stress in each depth.

Further, from the measurement result of the residual stress, it is confirmed whether or not the first region P ₁ and the second region P ₂ exist in each sample, and the sample in which the first region P ₁ and the second region P ₂ are confirmed. Determined that an intermediate point P ₃ exists. Further, from the same measurement result relates the thickness direction of the Al ₂ O ₃ layer was calculated the ratio of the area of thickness having a compressive residual stress to the thickness of the Al ₂ O ₃ layer (%). These results are shown in Table 4.

Referring to Table 4, sample no. In 9, 10 and 17, since the projection pressure was lowered in the blasting process, the intermediate point P ₃ did not exist. That is, sample no. In 9, 10, and 17, a stress distribution was observed in which the residual stress gradually changed from the compressive residual stress to the tensile residual stress from the upper surface side (front surface side) to the lower surface side (base material side). In Samples 13 to 16, since the blast treatment was not performed, the above stress distribution was not observed in the Al ₂ O ₃ layer, and there was only a tensile residual stress on the upper surface side and the lower surface side. .

Further, the sample No. in which the intermediate point P ₃ was confirmed. In 1-8, 11, 12, and 18-20, the position was a position having a distance of 0.5 μm from the surface of the α-Al ₂ O ₃ layer. Therefore, the value shown in the “upper surface side” column of Table 4 is the maximum value of the compressive residual stress of the Al ₂ O ₃ layer in each sample.

[Evaluation 1: Fracture resistance]
The chip of each sample was set on a bite of model number PCLNR2525-43 (manufactured by Sumitomo Electric Industries, Ltd.), and this was used to evaluate the fracture resistance by repeated turning of alloy steel.

  The cutting conditions are as follows. 20 chips were used for each sample, turning was performed for 20 seconds, and the ratio (number) of broken chips among all 20 chips was calculated as the breakage rate (%). The results are shown in Table 5. In Table 5, it shows that it is excellent in fracture resistance, so that a failure rate (%) is low.

Work material: SCM440 (6 grooves, φ350mm)
Cutting speed: 120 m / min
Cutting depth: 2.0mm
Cutting oil: None.

[Evaluation 2: Abrasion resistance]
The chip of each sample was set on a bite of model number PCLNR2525-43 (manufactured by Sumitomo Electric Industries, Ltd.), and the wear resistance was evaluated by repeated turning of the alloy steel using this.

  The conditions for turning are as follows. Using 20 tips for each sample, turning was performed for 15 minutes, the wear amount Vb (mm) on the flank side of all 20 tips was measured, and the average value of each sample was calculated. The results are shown in Table 5. In Table 5, it shows that it is excellent in abrasion resistance, so that the value of Vb (mm) is small.

Work material: SCr420H (φ250mm)
Cutting speed: 280 m / min
Cutting depth: 2.0mm
Feed amount: 0.2mm / rev
Cutting oil: Water-soluble oil.

  Referring to Table 5, sample no. In Nos. 1-12, Sample No. Compared with 13-17, the high fracture resistance and high abrasion resistance were confirmed. Sample No. 1 to 12, in the upper layer part, the area ratio occupied by (001) plane-oriented crystal grains is 90% or more, and in the lower layer part, the area ratio occupied by (001) plane-oriented crystal grains is 50% or less. Met. On the other hand, sample No. 13-20 did not satisfy this. From these results, sample No. 1 as an example of the present embodiment is obtained. It has been confirmed that the chips 1 to 12 have high fracture resistance and high wear resistance, and therefore have excellent mechanical properties and thus have a stable long life.

Sample No. In Nos. 13 and 16, since the area ratio of the (001) -oriented crystal grains in the lower layer portion was 50% or less, it was predicted that the fracture resistance was excellent. %Met. This is not a defect in terms of peeling from the base material of the α-Al ₂ O ₃ layer because the layer corresponding to the upper layer part contributing to the hardness does not exist, but the α-Al ₂ O ₃ layer itself is broken. It was a deficit caused by

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Rake face 2 Flank face 3 Cutting edge ridge part 10 Surface covering cutting tool 11 Base material 11a Rake face 11b Flank face 11c Cutting edge edge part 12 Coating 13 Underlayer 14 First intermediate layer 15 2nd intermediate layer 16 α-Al ₂ O ₃ Layer 16a Upper surface 16b Lower surface 16A Upper layer portion 16B Lower layer portion 30 CVD device 31 Base material setting jig 32 Reaction vessel 33 Temperature control device 34 Gas introduction port 35 Gas introduction pipe 36 Through hole P ₁ First region P ₂ Second region P ₃ Midpoint.

Claims (7)

A surface-coated cutting tool comprising a substrate and a coating formed on the substrate,
The coating has an α-Al ₂ O ₃ layer including a plurality of α-Al ₂ O ₃ crystal grains,
The α-Al ₂ O ₃ layer is located on the base material side in the thickness direction and has a thickness of 1 μm, a surface portion opposite to the base material side, and a thickness of 2 μm. And an upper layer portion having
To the cross-section obtained by cutting the α-Al ₂ O ₃ layer in a plane including the normal to the surface of the α-Al ₂ O ₃ layer, wherein the electron backscatter diffraction image analysis using a field emission scanning microscope When the crystal orientation of each crystal grain is specified and a color map based on this is created,
In the color map,
In the upper layer portion, the area occupied by the crystal grains in which the normal direction of the (001) plane is within ± 10 ° with respect to the normal direction of the surface of the α-Al ₂ O ₃ layer is 90% or more,
In the lower layer portion, the area occupied by the crystal grains in which the normal direction of the (001) plane is within ± 10 ° with respect to the normal direction of the surface of the α-Al ₂ O ₃ layer is 50% or less. Surface coated cutting tool. The α-Al ₂ O ₃ layer has a stress distribution that changes in its thickness direction,
The surface side of the α-Al ₂ O ₃ layer has a compressive residual stress,
The surface-coated cutting tool according to claim 1, wherein the base side of the α-Al ₂ O ₃ layer has a tensile residual stress. The stress distribution is
A first region in which the absolute value of the compressive residual stress continuously increases from the surface side toward the base material side;
The absolute value of the compressive residual stress is continuously reduced from the surface side toward the base material side from the surface side to the base material side with respect to the first region, and subsequently changed to the tensile residual stress, A second region in which the absolute value of the turned tensile residual stress continuously increases,
The surface-coated cutting tool according to claim 1 or 2, wherein the first region and the second region are continuous via an intermediate point where the absolute value of the compressive residual stress is the largest. The surface-coated cutting tool according to claim 2 or 3, wherein in the α-Al ₂ O ₃ layer, the absolute value of the compressive residual stress is 1000 MPa or less, and the absolute value of the tensile residual stress is 2000 MPa or less. . The coating includes a first intermediate layer between the substrate and the α-Al ₂ O ₃ layer,
The surface-coated cutting tool according to any one of claims 1 to 4, wherein the first intermediate layer is a TiCN layer. The coating includes a second intermediate layer between the first intermediate layer and the α-Al ₂ O ₃ layer,
The second intermediate layer is a TiCNO layer or a TiBN layer;
The surface-coated cutting tool according to claim 5, wherein a difference between the maximum thickness and the minimum thickness of the second intermediate layer is 0.3 μm or more. The coating includes a surface layer located on the outermost surface,
The surface-coated cutting tool according to any one of claims 1 to 6, wherein the surface layer is a TiC layer, a TiN layer, or a TiB ₂ layer.

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