cutting tools

Abstract

A cutting tool comprising a substrate and a coating provided on the substrate, the coating including an α-Al2O3 layer, the α-Al2O3 layer having a thickness of 3 μm or more and 20 μm or less, a rectangular measurement field of view that is continuous from a virtual line L1 to a virtual line L2 and that is provided on a cross section of the coating along a normal to the surface of the coating, has a length of 30 μm in a first direction along the surface of the coating, and a length of the coating in a second direction perpendicular to the first direction that includes the entire thickness of the α-Al2O3 layer along the second direction, the number of first Σ3-type crystal grain boundaries intersecting with the imaginary line L3 is 5 or more, the imaginary line L1 is an imaginary line that is located 0.5 μm away from a first interface of the α-Al2O3 layer that is located on the substrate side toward the α-Al2O3 layer side, the imaginary line L2 is an imaginary line that is located 0.5 μm away from a second interface of the α-Al2O3 layer that is located on the surface side of the coating toward the α-Al2O3 layer side, and the imaginary line L3 is an imaginary line that is the same distance from the imaginary line L1 and the imaginary line L2.

Description

[Technical Field]

[0001] The present disclosure relates to cutting tools. [Background technology]

[0002] Cutting tools have traditionally been used in which a coating is formed on a substrate. Aluminum oxide with an α-crystal structure (hereinafter also referred to as "α-Al2O3") has been used as a coating material due to its excellent mechanical properties (Patent Document 1 and Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-131058 [Patent Document 2] Japanese Patent Publication No. 2023-101044 Summary of the Invention

[0004] A cutting tool according to the present disclosure is a cutting tool including a substrate and a coating provided on the substrate, wherein the coating includes an α-Al2O3 layer, the α-Al2O3 layer having a thickness of 3 μm or more and 20 μm or less, and a rectangular measurement field from imaginary line L1 to imaginary line L2 in a cross section of the coating taken along a normal to the surface of the coating, the length of the coating in a first direction along the surface of the coating being 30 μm, and the length of the coating in a second direction perpendicular to the first direction including the entire thickness of the α-Al2O3 layer along the second direction. the number of first Σ3-type crystal grain boundaries that are continuous and intersect with a virtual line L3 is 5 or more, the virtual line L1 is a virtual line that is located 0.5 μm away from a first interface of the α-Al2O3 layer that is located on the substrate side toward the α-Al2O3 layer side, the virtual line L2 is a virtual line that is located 0.5 μm away from a second interface of the α-Al2O3 layer that is located on the surface side of the coating, and the virtual line L3 is a virtual line that is the same distance from the virtual line L1 and the virtual line L2. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic view showing an example of a cross section of a cutting tool according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a method for measuring the number of first Σ3 type crystal grain boundaries. [Figure 3] FIG. 3 is an enlarged view of the region near the interface between the α-Al2O3 layer and the first layer in the cross section of the coating. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] In the techniques of Patent Documents 1 and 2, as the cutting tool is used, crater wear occurs, which involves the shedding of α-Al2O3 particles, and the tool life tends to decrease.

[0007] Therefore, an object of the present disclosure is to provide a cutting tool having a coating including an α-Al2O3 layer, which cutting tool has a long tool life.

[0008] [Effects of this disclosure] According to the present disclosure, it is possible to provide a cutting tool having a coating including an α-Al2O3 layer, and having a long tool life.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) A cutting tool according to the present disclosure is a cutting tool including a substrate and a coating provided on the substrate, wherein the coating includes an α-Al2O3 layer, and the thickness of the α-Al2O3 layer is 3 μm or more and 20 μm or less, and a rectangular measurement field extending from a virtual line L1 to a virtual line L2 in a rectangular measurement field, the rectangular measurement field being provided on a cross section of the coating along a normal to the surface of the coating, the length of the first direction along the surface of the coating being 30 μm, and the length of the coating in a second direction perpendicular to the first direction including the entire thickness of the α-Al2O3 layer along the second direction, and the number of first Σ3-type crystal grain boundaries intersecting with imaginary line L3 is 5 or more, the imaginary line L1 is an imaginary line that is distanced 0.5 μm from a first interface of the α-Al2O3 layer located on the substrate side toward the α-Al2O3 layer side, the imaginary line L2 is an imaginary line that is distanced 0.5 μm from a second interface of the α-Al2O3 layer located on the surface side of the coating, and the imaginary line L3 is an imaginary line that is distanced the same from imaginary line L1 and imaginary line L2.

[0010] According to the present disclosure, it is possible to provide a cutting tool having a coating including an α-Al2O3 layer, and having a long tool life.

[0011] (2) In the above (1), the number of the first Σ3-type grain boundaries may be equal to or less than 100. This suppresses the detachment of α-Al2O3 particles during use of a cutting tool, which occurs when the α-Al2O3 particles are excessively refined, and improves the wear resistance of the α-Al2O3 layer.

[0012] (3) In the above (1) or (2), the number of all grain boundaries that intersect with the virtual line L3 in the measurement field may be 20 or more. This prevents the grain size of the α-AlO particles from becoming coarse, improving the wear resistance of the α-AlO layer.

[0013] (4) In any of the above (1) to (3), the α-Al2O3 layer may have an orientation index TC(hkl) of TC(0 0 12) of 5 or more. This improves the wear resistance of the α-Al2O3 layer.

[0014] (5) In any one of the above (1) to (4), the coating further includes a first layer disposed between the substrate and the α-Al2O3 layer, and the first layer may be a TiCN layer, thereby improving the wear resistance and chipping resistance of the coating.

[0015] (6) In any of (1) to (5) above, the coating further includes a second layer disposed on the principal surface of the α-Al2O3 layer opposite the principal surface closest to the substrate, and the second layer may include at least one selected from the group consisting of a TiN layer, a TiCN layer, and a TiCNO layer. When the second layer is at least one of a TiN layer and a TiCN layer, it is easy to identify the corners of the cutting tip after use (identifying the used portion). When the second layer includes a TiCNO layer, when a TiCN layer is disposed directly on the α-Al2O3 layer and a TiN layer or a TiCN layer is disposed directly on the TiCN layer, the adhesion between the α-Al2O3 layer and the second layer is improved, thereby suppressing wear progression in the early stages of cutting.

[0016] [Details of the embodiments of the present disclosure] Specific examples of cutting tools according to the present disclosure will be described below with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0017] In the present disclosure, the notation in the form "A to B" means greater than or equal to A and less than or equal to B, and when no unit is specified for A and only a unit is specified for B, the unit of A and the unit of B are the same.

[0018] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0019] In this disclosure, when one or more numerical values ​​are listed as the lower and upper limits of a numerical range, the combination of any one numerical value listed in the lower limit with any one numerical value listed in the upper limit is also disclosed.

[0020] In this disclosure, "comprises," "includes," "has," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even a configuration expressed in closed terms may include additional elements that are normally incidental impurities or unrelated to the subject technology.

[0021] To deepen understanding of the present disclosure, the structure of the α-Al2O3 layer will be described first. "Grain boundaries" exist between the α-Al2O3 particles contained in the α-Al2O3 layer.

[0022] The grain boundaries in the α-Al2O3 layer include CSL grain boundaries and general grain boundaries. The CSL grain boundaries consist of Σ3-type grain boundaries, Σ7-type grain boundaries, Σ11-type grain boundaries, Σ17-type grain boundaries, Σ19-type grain boundaries, Σ21-type grain boundaries, Σ23-type grain boundaries, and Σ29-type grain boundaries.

[0023] Σ3-type grain boundaries have the lowest grain boundary energy among the CSL grain boundaries of α-Al2O3. Therefore, the higher the proportion of Σ3-type grain boundaries in the α-Al2O3 layer, the better the mechanical properties, including the plastic deformation resistance, of the α-Al2O3 layer.

[0024] In both Patent Document 1 and Patent Document 2, the amount of Σ3 type grain boundaries in the α-Al2O3 layer is controlled to improve tool life. However, when the present inventors used the cutting tools described in Patent Documents 1 and 2 to cut chromium-molybdenum steel, they found that crater wear accompanied by the shedding of α-Al2O3 particles occurred, resulting in a decrease in tool life. The present inventors investigated the reasons for this and discovered the following.

[0025] In Patent Document 1, the proportion of Σ3 type grain boundaries is increased in the lower part of the α-Al2O3 layer close to the substrate, but the proportion of Σ3 type grain boundaries is low in the upper part of the α-Al2O3 layer, which causes α-Al2O3 particles to fall off in the upper part, making it prone to crater wear.

[0026] In Patent Document 2, the α-Al2O3 layer is formed in two separate steps: a first step and a second step. As a result, the Σ3 type grain boundaries in the region formed in the first step are not continuous with the Σ3 type grain boundaries in the region formed in the second step, and if a crack propagates in the α-Al2O3 layer, α-Al2O3 particles fall off, making it susceptible to crater wear.

[0027] As a result of extensive research based on the above findings, the present inventors have found that the tool life of a cutting tool can be improved by controlling the amount of Σ3 type grain boundaries in the α-Al2O3 layer as well as the morphology of the Σ3 type grain boundaries. The cutting tool of the present disclosure will be described below.

[0028] [Embodiment 1: Cutting tool] A cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "this embodiment") will be described with reference to FIG. 1. The cutting tool according to this embodiment includes a substrate 10 and a coating 15 provided on the substrate 10. The coating 15 includes an α-Al2O3 layer 11. The thickness of the α-Al2O3 layer 11 is 3 μm or more and 20 μm or less. In a rectangular measurement field R1 provided on a cross section of the coating 15 along a normal to the surface P1 of the coating 15, the length of the coating 15 in a first direction along the surface P1 of the coating 15 is 30 μm, and the length of the coating 15 in a second direction perpendicular to the first direction includes the entire thickness of the α-Al2O3 layer 11 along the second direction, the number of first Σ3 type grain boundaries that are continuous from the imaginary line L1 to the imaginary line L2 and intersect with the imaginary line L3 is 5 or more. The imaginary line L1 is an imaginary line that is 0.5 μm away from the first interface S1 located on the substrate 10 side of the α-Al2O3 layer 11 toward the α-Al2O3 layer 11. The imaginary line L2 is an imaginary line that is 0.5 μm away from the second interface S2 located on the surface P1 side of the coating 15 of the α-Al2O3 layer 11 toward the α-Al2O3 layer 11. The imaginary line L3 is an imaginary line that is the same distance from the imaginary line L1 and the imaginary line L2.

[0029] 1, the first layer 12 is provided directly below the α-Al2O3 layer 11, and therefore the interface between the α-Al2O3 layer 11 and the first layer 12 corresponds to the first interface S1. If the first layer 12 is not provided directly below the α-Al2O3 layer 11, and the α-Al2O3 layer 11 is provided directly on the substrate 10, then the interface between the α-Al2O3 layer 11 and the substrate 10 corresponds to the first interface S1. If the first layer 12 is not provided directly below the α-Al2O3 layer 11, and the α-Al2O3 layer 11 is provided directly on another layer, such as an intermediate layer, then the interface between the α-Al2O3 layer 11 and the other layer corresponds to the first interface S1.

[0030] In Fig. 1, the second layer 13 is provided directly on the α-Al2O3 layer 11, and therefore the interface between the α-Al2O3 layer 11 and the second layer 13 corresponds to the second interface S2. If the second layer 13 is not provided directly on the α-Al2O3 layer 11 and the α-Al2O3 layer 11 is the outermost layer of the coating, the surface of the α-Al2O3 layer 11 corresponds to the second interface S2.

[0031] The cutting tool of the present disclosure has a coating including an α-Al2O3 layer and can have a long tool life. The reason for this is presumed to be as follows. In the cutting tool of the present disclosure, the number of first Σ3 type grain boundaries that are continuous from the imaginary line L1 to the imaginary line L2 and intersect with the imaginary line L3 in the measurement field of view R1 is five or more. The first Σ3 type grain boundaries are an indicator of the amount of Σ3 type grain boundaries in the α-Al2O3 layer that are continuous from the region of the α-Al2O3 layer close to the substrate to the region close to the surface of the coating. If there are many first Σ3 type grain boundaries in the α-Al2O3 layer, α-Al2O3 particles are less likely to fall off during use of the cutting tool, and crater wear is suppressed. This improves the tool life of the cutting tool of the present disclosure.

[0032] <Cutting tool configuration> As shown in FIG. 1, the cutting tool 1 of this embodiment includes a substrate 10 and a coating 15 provided on the substrate 10. The coating 15 includes an α-Al2O3 layer 11. The coating 15 may cover at least a portion of the substrate that is involved in cutting, or may cover the entire substrate. The portion of the substrate that is involved in cutting refers to an area of ​​the substrate surface that is within 1.5 mm from the cutting edge. It is within the scope of the present disclosure even if a portion of the substrate is not covered with this coating or if the coating has a partially different configuration.

[0033] <Cutting tool applications> The cutting tool of the present disclosure may be, for example, a drill, an end mill, an indexable cutting tip for a drill, an indexable cutting tip for an end mill, an indexable cutting tip for a milling cutter, an indexable cutting tip for a turning cutter, a metal saw, a gear cutting tool, a reamer, or a tap.

[0034] <Base material> The substrate includes a cutting face and a flank, and any conventionally known substrate of this type can be used. The material of the substrate may be, for example, cemented carbide (for example, a WC-based cemented carbide such as a WC-Co-based cemented carbide, where the cemented carbide can contain carbonitrides of Ti, Ta, Nb, etc.), cermet (a material mainly composed of TiC, TiN, TiCN, etc.), high-speed steel, ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cubic boron nitride sintered body, or diamond sintered body.

[0035] The substrate material may be a cemented carbide (particularly a WC-based cemented carbide) or a cermet (particularly a TiCN-based cermet). Substrates made of cemented carbide or cermet have an excellent balance of hardness and strength at high temperatures and have excellent properties as substrates for cutting tools used in the above applications. When a WC-based cemented carbide is used as the substrate, its structure may contain free carbon and abnormal layers called η phase or ε phase.

[0036] The substrate may have a surface that has been modified. For example, in the case of a cemented carbide, a de-β layer may be formed on the surface, and in the case of a cermet, a surface-hardened layer may be formed. The substrate exhibits the desired effect even when its surface has been modified.

[0037] When the cutting tool is an indexable cutting insert, the substrate may or may not have a chip breaker. The shape of the cutting edge ridge can be any of a sharp edge (the ridge where the rake face and flank intersect), a honed edge (a sharp edge with a radius), a negative land (a chamfered edge), or a combination of a honed edge and a negative land.

[0038] <Coating> <Coating composition> The coating includes an α-Al2O3 layer provided on the substrate. Coating 15 may be made of an α-Al2O3 layer. In this case, the α-Al2O3 layer is provided directly on the substrate, and the main surface of the α-Al2O3 layer opposite to the main surface closest to the substrate corresponds to the outermost surface of the coating.

[0039] As shown in FIG. 1, the coating 15 may further include a first layer 12 disposed between the substrate 10 and the α-Al 2 O 3 layer 11 .

[0040] As shown in FIG. 1, the coating 15 may further include a second layer 13 disposed on the major surface of the α-Al 2 O 3 layer 11 opposite the major surface closest to the substrate 10 .

[0041] As shown in FIG. 1, the coating 15 may include an intermediate layer (not shown) disposed between the first layer and the α-Al 2 O 3 layer.

[0042] <Total coating thickness> The total thickness of the coating may be 5 μm or more and 30 μm or less, 7 μm or more and 20 μm or less, or 10 μm or more and 15 μm or less. When the average thickness of the total coating is 5 μm or more, the abrasion resistance of the coating is improved. When the average thickness of the total coating is 30 μm or less, the peeling resistance of the coating is improved.

[0043] The total thickness of the coating is measured by obtaining a cross-sectional sample parallel to the normal direction of the substrate surface and observing the sample with a scanning transmission electron microscope (STEM), such as JEM-2100F (product name) manufactured by JEOL Ltd.

[0044] In this disclosure, "thickness" refers to an average thickness. The specific measurement method is as follows: A cutting tool is cut along a cross section parallel to the normal direction of the surface to obtain a sample with the cross section of the coating exposed. The sample is observed with a scanning transmission electron microscope (STEM). The observation magnification is 5000x. A rectangular measurement field of view of (30 μm in the direction parallel to the substrate surface) × (a distance including the entire thickness of the coating) is set in the STEM image, and the thickness width is measured at 10 points in the measurement field, and the average value is taken as the "thickness." The thickness of each layer described below is also measured in the same way.

[0045] <α-Al2O3 layer> <Thickness of α-Al2O3 layer> The thickness of the α-Al2O3 layer is 3 μm or more and 20 μm or less, and may be 5 μm or more and 15 μm or less, or 7 μm or more and 12 μm or less.

[0046] <Composition of α-Al2O3 layer> In this embodiment, the α-Al2O3 layer contains a plurality of α-Al2O3 (aluminum oxide having an α-type crystal structure) particles. The α-Al2O3 layer may be composed of a plurality of α-Al2O3 particles. The α-Al2O3 layer may contain unavoidable impurities as long as the effects of this embodiment are not impaired. Examples of the unavoidable impurities include chlorine (Cl). The content of the unavoidable impurities in the α-Al2O3 layer may be 3 mass% or less. The content of the unavoidable impurities in the α-Al2O3 layer is measured by secondary ion mass spectrometry (SIMS).

[0047] The grain boundaries in the α-AlO layer of this embodiment include CSL grain boundaries and general grain boundaries. The CSL grain boundaries consist of Σ3-type grain boundaries, Σ7-type grain boundaries, Σ11-type grain boundaries, Σ17-type grain boundaries, Σ19-type grain boundaries, Σ21-type grain boundaries, Σ23-type grain boundaries, and Σ29-type grain boundaries. The scope of the present disclosure does not deviate from the case where one or more grain boundaries other than the Σ3-type grain boundaries are not observed, as long as the effects of the present disclosure are not impaired.

[0048] ≪Σ3 type grain boundary≫ In the α-Al2O3 layer of this embodiment, the number of first Σ3 type grain boundaries in the measurement field of view R1 is 5 or more. From the viewpoint of improving crater wear resistance, the number of first Σ3 type grain boundaries in the measurement field of view R1 may be 5 or more and 100 or less, 10 or more and 75 or less, or 20 or more and 50 or less.

[0049] The method for measuring the number of first Σ3 type grain boundaries in the measurement field of view R1 will be described with reference to Figs. 2 and 3. Fig. 2 is a diagram for explaining the method for measuring the number of first Σ3 type grain boundaries. Fig. 2 schematically shows an example of a cross section of a coating. Fig. 3 is a diagram for explaining a method for setting the first interface. Fig. 3 shows an enlarged view of the region near the interface between the α-Al2O3 layer and the first layer in the cross section of the coating.

[0050] (A1) The cutting tool is cut with a diamond wire along the normal to the rake face of the substrate to expose the cross section of the α-Al2O3 layer. The cutting position is set at a position where the surface of the cutting tool is smooth and includes the cutting edge of the cutting tool. The exposed cross section is subjected to ion milling using Ar ions to make the cross section mirror-finished. The ion milling conditions are as follows: the acceleration voltage is 6 kV; the irradiation angle is 0° from a straight line parallel to the thickness direction of the α-Al2O3 layer in the cross section of the α-Al2O3 layer; and the irradiation time is 6 hours.

[0051] (A2) The mirror-finished cross section is observed at 5000x magnification using a field emission scanning electron microscope (EF-SEM) to obtain a backscattered electron diffraction (EBSD) image. The SEM conditions are as follows: the normal to the cross section is tilted 70° relative to the incident beam; the analysis is performed at 15 kV; a pressure of 10 Pa is applied to avoid charging effects; a high current mode is used in conjunction with an aperture diameter of 60 μm or 120 μm; and the step size is 0.1 μm / step.

[0052] (A3) Data processing is performed on the EBSD image to obtain a first image in which the Σ3 grain boundary is distinguished from other grain boundaries in the EBSD image. Data processing is performed with and without noise filtering. Noise filtering and grain boundary character distribution are determined using commercially available software (trade name: "Orientation Imaging Microscopy Ver. 6.2" by EDAX). Analysis of the grain boundary character distribution is based on data available from Grimmer (H. Grimmer, R. Bonnet, Philosophical Magazine A 61 (1990), 493-509). The Brandon criterion (ΔΘ<Θ(Σ)-0.5, where Θ=15°) is used to allow for a margin of error from the theoretical value (D. Brandon Acta metall. 14 (1966), 1479-1484).

[0053] (A4) A rectangular measurement field of view R1 is set in the first image, the length of which in a first direction along the surface P1 of the coating 15 is 30 μm, and the length of which in a second direction perpendicular to the first direction of the coating 15 includes the entire thickness of the α-Al2O3 layer 11 along the second direction.

[0054] (A5) In the first image, an imaginary line L1 is set at a distance of 0.5 μm from the first interface S1 located on the substrate 10 side of the α-Al2O3 layer 11 toward the α-Al2O3 layer side, an imaginary line L2 is set at a distance of 0.5 μm from the second interface S2 located on the surface P1 side of the α-Al2O3 layer coating 15 toward the α-Al2O3 layer side, and an imaginary line L3 is set at the same distance from the imaginary line L1 and the imaginary line L2.

[0055] 3, the first interface S1 is deemed to be a line S11 that passes through the valley bottom B of the first interface S1 and is the same distance from an imaginary line LB that is parallel to the main surface 10a of the substrate 10 and that passes through the peak T of the first interface S1 and is also parallel to the main surface 10a of the substrate 10. When the actual second interface S2 is uneven, the second interface S2 is deemed to be a line that passes through the valley bottom B of the second interface S2 and is the same distance from an imaginary line that is parallel to the main surface of the substrate and that passes through the peak T of the second interface S2 and is also parallel to the main surface of the substrate.

[0056] (A6) Within the measurement field of view R1, the number of first Σ3 type crystal grain boundaries that are continuous from the virtual line L1 to the virtual line L2 and intersect with the virtual line L3 is counted. Seven first Σ3 type crystal grain boundaries are observed within the measurement field of view R1 shown in Figure 2. A specific counting method will be explained using Figure 3. In Figure 3, the thick lines within the measurement field of view R1 indicate Σ3 type crystal grain boundaries.

[0057] The Σ3 type grain boundary a1 is continuous as a single line from the imaginary line L1 to the imaginary line L2 and intersects with the imaginary line L3. In this case, the number of first Σ3 type grain boundaries intersecting with the imaginary line L3 is one.

[0058] The Σ3 type grain boundary a2 and the Σ3 type grain boundary a3 merge at a position closer to the substrate than the imaginary line L3 to form a single Σ3 type grain boundary, which intersects with the imaginary line L3 as a single boundary. In this case, the number of first Σ3 type grain boundaries intersecting with the imaginary line L3 is one.

[0059] The Σ3 type grain boundary a4 branches off at a position closer to the surface of the coating than the imaginary line L3 to form two Σ3 type grain boundaries, each of which continues to the imaginary line L2. In this case, the number of first Σ3 type grain boundaries intersecting with the imaginary line L3 is one.

[0060] The Σ3 type grain boundary a5 branches into two Σ3 type grain boundaries at a position closer to the substrate than the imaginary line L3, and each of the two Σ3 type grain boundaries continues to the imaginary line L2. In this case, the number of first Σ3 type grain boundaries that intersect with the imaginary line L3 is two.

[0061] The Σ3 type grain boundary a6 and the Σ3 type grain boundary a7 merge at a position closer to the surface of the coating than the imaginary line L3 to form a single Σ3 type grain boundary, which intersects with the imaginary line L3 as a single boundary. In this case, the number of first Σ3 type grain boundaries intersecting with the imaginary line L3 is two.

[0062] (A7) The number of the first Σ3 type crystal grain boundaries is measured in three mutually non-overlapping measurement visual fields R1. The average of the numbers of the first Σ3 type crystal grain boundaries in the three measurement visual fields R1 is calculated. In the present disclosure, this average corresponds to the number of the first Σ3 type crystal grain boundaries in the measurement visual field.

[0063] It was confirmed that similar results could be obtained even when the above measurements were performed on the same sample by arbitrarily setting multiple measurement fields.

[0064] In the above-described measurement field of view provided in the α-AlO layer of this embodiment, the number of all grain boundaries intersecting with the virtual line L3 may be 20 or more, 20 to 150, 40 to 150, or 50 to 100.

[0065] The method for measuring the number of all grain boundaries that intersect with the virtual line L3 in the measurement field of view is described below. An EBSD image is obtained using the same methods as (A1) and (A2) of the method for measuring the number of first Σ3-type grain boundaries in the measurement field of view R1. Data processing is performed on the EBSD image to obtain a second image in which all grain boundaries are displayed in the SEM image. The measurement field of view R1 and the virtual line L3 are set in the second image using the same methods as (A4) and (A5) above. The number of all grain boundaries that intersect with the virtual line L3 in the measurement field of view R1 is measured. This measurement is performed for three measurement fields of view R1 that do not overlap with each other. The average number of grain boundaries in the three measurement fields of view R1 is calculated. In the present disclosure, this average corresponds to the number of all grain boundaries that intersect with the virtual line L3 in the measurement field of view.

[0066] It was confirmed that similar results could be obtained even when the above measurements were performed on the same sample by arbitrarily setting multiple measurement fields.

[0067] Orientation Index In the α-Al2O3 layer of this embodiment, the orientation index TC(hkl) (TC(0 0 12)) may be 5 or more, 5 or more and 8 or less, or 7 or more and 8 or less. The orientation index TC(hkl) is expressed by the following formula (1).

[0068]

number

[0069] In equation (1), I(hkl) represents the X-ray diffraction intensity of the (hkl) reflection plane, and I0(hkl) represents the standard intensity according to ICDD PDF card number 00-010-0173. Furthermore, n in equation (1) represents the number of reflections used in the calculation, which is 8 in this embodiment. The (hkl) planes used for reflection are (012), (104), (110), (0 0 12), (113), (024), (116), and (300).

[0070] ICDD (registered trademark) is an abbreviation for International Centre for Diffraction Data, and PDF (registered trademark) is an abbreviation for Powder Diffraction File.

[0071] The above-described measurement of TC(hkl) can be performed by analysis using an X-ray diffractometer. TC(hkl) can be measured, for example, using a SmartLb / a (registered trademark) manufactured by Rigaku Corporation (scan speed: 21.7° / min, step: 0.01°, scan range: 15 to 140°) under the following conditions. In this embodiment, the measurement results of TC(hkl) using an X-ray diffractometer are referred to as "XRD results."

[0072] Characteristic X-ray: Cu-Kα Tube voltage: 45kV Tube current: 200mA Filter: Multi-layer mirror Optics: Concentration method X-ray diffraction method: θ-2θ method When using an X-ray diffraction device, X-rays are irradiated onto the flank of the cutting tool. Since the rake face is usually uneven, while the flank is flat, it is preferable to irradiate the flank with X-rays to eliminate disturbance factors. In particular, X-rays are irradiated onto a portion of the flank extending approximately 2 to 4 mm from the cutting edge ridge. This increases the reproducibility of the results. In this embodiment, the TC(hkl) value of the α-Al2O3 layer on the flank of the substrate is the same as the TC(hkl) value of the α-Al2O3 layer on the rake face of the substrate.

[0073] It was confirmed that similar results could be obtained even when the above measurements were performed on the same sample by arbitrarily setting multiple measurement fields.

[0074] <First layer> The coating 15 of this embodiment may further include a first layer 12 disposed between the substrate 10 and the α-Al2O3 layer 11. The first layer corresponds to an underlayer. The first layer 12 may be provided directly on the substrate 10. The α-Al2O3 layer 11 may be provided directly on the first layer 12. The first layer 12 may be a TiCN layer or a TiN layer, or may be a TiCN layer.

[0075] The average thickness of the first layer may be 0.1 μm or more and 20 μm or less, which further improves the wear resistance and chipping resistance of the coating.

[0076] <Second layer> The coating 15 of this embodiment may further include a second layer 13 disposed on the principal surface of the α-AlO layer 11 opposite the principal surface closest to the substrate 10. The second layer corresponds to a surface layer. The principal surface of the second layer opposite the principal surface closest to the substrate corresponds to the outermost surface of the coating. The second layer may be a TiN layer, a TiCN layer, or a TiCNO layer.

[0077] The second layer may have an average thickness of 0.05 μm or more and 1 μm or less, which improves the adhesion between the second layer and the adjacent layer.

[0078] <Middle class> The coating 15 may include an intermediate layer (not shown) disposed between the first layer and the α-Al2O3 layer. The intermediate layer may be in contact with the first layer and the α-Al2O3 layer. The intermediate layer may be a TiCN layer or a TiCNO layer. The TiCN layer and the TiCNO layer have excellent wear resistance, and therefore can impart more suitable wear resistance to the coating. The average thickness of the intermediate layer may be 1 μm or more and 20 μm or less.

[0079] <Cutting tool manufacturing method> The cutting tool of this embodiment can be manufactured by forming a coating on a substrate by chemical vapor deposition (CVD). Of the coating, the α-Al2O3 layer can be formed, for example, by the following method. Note that the layers of the coating other than the α-Al2O3 layer can be formed under conventionally known conditions.

[0080] The process for forming the α-Al2O3 layer includes a first step and a second step. The conditions throughout the process for forming the α-Al2O3 layer are a temperature of 1000°C and a pressure of 70 hPa. The gas flow rate (total gas flow rate) in the first step is 70 to 90 L / min, and the gas flow rate (total gas flow rate) in the second step is 100 to 130 L / min.

[0081] The source gases used are AlCl3, HCl, CO2, CO, H2S, and H2. From the start of film formation, the compounding ratio of the source gases is changed depending on the thickness of the α-Al2O3 layer formed. Specifically, it is as follows.

[0082] The first step is the process of forming the α-Al2O3 layer from the start of deposition to a thickness of 1.5 μm. In this step, the source gas is composed of 1.3-1.7 volume % AlCl3, 1.8-2.2 volume % HCl, 1.3-1.7 volume % CO2, 2.2-2.8 volume % CO, and the remaining volume % H2, where the total source gas is taken as 100 volume %. The CO content of the source gas, 2.2-2.8 volume %, is higher than the CO content (e.g., 0-1 volume %) used in conventional source gas deposition of α-Al2O3 layers.

[0083] The second step is the formation of an α-Al2O3 layer with a thickness of more than 1.5 μm and not more than 20 μm. In this step, the source gas is mixed with 0.8-1.2 volume percent AlCl3, 0.5-4.0 volume percent HCl, 3.5-4.0 volume percent CO2, 1.0-5.5 volume percent CO, 0.5-0.7 volume percent H2S, and the remaining volume percent H2, where the total source gas is taken as 100 volume percent. In this step, the deposition temperature is set high at 1000°C, and the ratios of CO, HCl, CO2, and H2S are controlled within the above ranges to increase the number of Σ3 grain boundaries and suppress coarsening of the α-Al2O3 particles.

[0084] When transitioning from the first process to the second process, the total gas flow rate is gradually increased over 240 seconds from the point when the thickness of the α-Al2O3 layer reaches 1.5 μm, which facilitates the continuous formation of Σ3 grain boundaries between the α-Al2O3 layer formed in the first process and the α-Al2O3 layer formed in the second process. [Example]

[0085] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0086] <Preparing the substrate> A substrate was prepared. The raw material powders for the substrate (TaC powder: 2.0 mass%, NbC powder: 1.0 mass%, Co powder: 10.0 mass%, WC: remainder) were uniformly mixed, pressure-molded into a predetermined shape, and sintered at 1300 to 1500°C for 1 to 2 hours to obtain a substrate made of cemented carbide (shape: model number CNMG120408N-UX (manufactured by Sumitomo Electric Hardmetal Industries, Ltd.)). "WC: remainder" indicates that WC accounts for the remainder of the compounded composition (mass%).

[0087] <Coating formation> A coating was formed on the surface of the substrate obtained above to produce a cutting tool. Specifically, the substrate was set in a CVD apparatus, and a coating was formed on the substrate by CVD.

[0088] <<Formation of the first layer>> For samples with "TiCN" listed in the "Composition" column of "First Layer" in Table 3, a TiCN layer was formed on the substrate. The thickness of the first layer is as shown in Table 3. The conditions for forming the TiCN layer are as follows: Raw material gas composition: TiCl4: 8.5 vol%, CH3CN: 0.5 vol%, CO: 1.65 vol%, N2: 10.0 vol%, HCl: 2.0 vol%, H2: remaining vol% when the total raw material gas is 100 vol% Raw gas flow rate: 120 L / min Pressure: 70hPa Temperature: 850℃

[0089] <Formation of α-Al2O3 layer> Next, an α-Al2O3 layer was formed directly on the first layer or directly on the substrate. The process of forming the α-Al2O3 layer includes a first step and a second step.

[0090] The first step is the formation process from the start of film formation to the region where the thickness of the α-Al2O3 layer reaches 1.5 μm. The film formation conditions (pressure, temperature, total gas flow rate) and raw material gas composition in the first step are as shown in Table 1.

[0091] The second step is a step of forming an α-Al2O3 layer with a thickness exceeding 1.5 μm. The film formation conditions (pressure, temperature, total gas flow rate) and source gas composition in the second step are as shown in Table 2. The second step was terminated when the thickness of the α-Al2O3 layer formed in the second step reached the thickness shown in the "Thickness" column in Table 2.

[0092] For samples marked "Yes" in the "Transition step" column in Table 1, the total gas flow rate was gradually changed over 240 seconds when transitioning from the first step to the second step, starting from the point when the α-Al2O3 layer thickness reached 1.5 μm. For samples marked "No" in the "Transition step" column in Table 1, the gas flow rate was switched without any particular control over the change in gas flow rate.

[0093] <<Formation of the second layer>> Next, for samples with "TiN, TiCN" listed in the "Composition" column of the "Second Layer" in Table 3, a TiN layer and a TiCN layer were formed in the above order directly on the α-Al2O3 layer. The thickness of each layer is as shown in Table 3. The conditions for forming the TiN and TiCN layers are as follows:

[0094] Conditions for forming the TiN layer Raw material gas composition: TiCl4: 4.0% by volume, N2: 42.5% by volume, H2: remaining volume % when the total raw material gas is 100% by volume Raw gas flow rate: 80 L / min Pressure: 70hPa Temperature: 1000℃

[0095] Conditions for forming the TiCN layer Raw material gas composition: TiCl4: 8.5 vol%, CH3CN: 0.5 vol%, CO: 1.65 vol%, N2: 10.0 vol%, HCl: 2.0 vol%, H2: remaining vol% when the total raw material gas is 100 vol% Raw gas flow rate: 120 L / min Pressure: 90hPa Temperature: 1000℃

[0096] Through the above steps, cutting tools of each sample were obtained.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] [evaluation] <Number of first Σ3 type grain boundaries> In the α-AlO layer of each sample cutting tool, the number of first Σ3 type grain boundaries in the measurement field described in embodiment 1 was measured. The specific measurement method was as described in embodiment 1. The results are shown in the "Number of first Σ3 type grain boundaries" column in Table 3.

[0101] <Number of all grain boundaries that intersect with the virtual line L3> In the α-AlO layer of each sample cutting tool, the number of all grain boundaries that intersect with the virtual line L3 in the measurement field of view described in embodiment 1 was measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Total number of grain boundaries" column in Table 3.

[0102] <Orientation index TC(0 0 12)> The orientation index TC (0 0 12) was measured for the α-Al2O3 layer of each sample cutting tool. The specific measurement method is as described in embodiment 1. The results are shown in Table 3.

[0103] <Cutting test> Using each sample cutting tool, cutting tests were carried out under the following conditions. The exposed area of ​​the substrate on the rake face (mm 2 ) was measured. 2 The time when this limit was exceeded was defined as the tool life. The results are shown in Table 3. The longer the tool life, the better the crater wear resistance of the cutting tool.

[0104] ≪Cutting conditions≫ Work material: SCM415 Processing: Round bar external diameter turning Cutting speed: 500m / min Feed rate: 0.2 mm / rev Depth of cut: 2.0 mm Cutting fluid: Water-soluble cutting oil

[0105] <Consideration> The cutting tools of Samples 1 to 12 correspond to Examples. The cutting tools of Samples 1-1 to 1-3 correspond to Comparative Examples. It was confirmed that the cutting tools of Samples 1 to 12 had longer tool life than the cutting tools of Samples 1-1 to 1-3.

[0106] In the α-Al2O3 layer of sample 1-1, the proportion of Σ3 type grain boundaries was high in the lower part close to the substrate, but the proportion of Σ3 type grain boundaries was low in the upper part of the α-Al2O3 layer, and the number of primary Σ3 type grain boundaries was small. As a result, α-Al2O3 particles fell off in the upper part, making it prone to crater wear.

[0107] In the α-Al2O3 layer of sample 1-2, the Σ3-type grain boundaries in the region formed in the first process were not continuous with those in the region formed in the second process, and the number of first Σ3-type grain boundaries was small. As a result, as cracks propagated in the Al2O3 layer, α-Al2O3 particles fell off, making it susceptible to crater wear.

[0108] In the α-Al2O3 layer of sample 1-3, the proportion of Σ3-type grain boundaries was low throughout the entire region, and the number of primary Σ3-type grain boundaries was small. As a result, as cracks propagated in the α-Al2O3 layer, α-Al2O3 particles fell off, making it susceptible to crater wear.

[0109] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0110] 10 base material, 10a main surface, 11 α-Al2O3 layer, 12 first layer, 13 second layer, 15 coating, S1 first interface, S2 second interface, R1 measurement field of view, a1,a2,a3,a4,a5,a6,a7 Σ3 type grain boundary.

Claims

1. A cutting tool comprising a base material and a coating provided on the base material, The aforementioned coating is α-Al ２ O ３ Including layers, The α-Al ２ O ３ The layer thickness is between 7 μm and 20 μm. A cross-section of the coating along the normal to the surface of the coating is provided, with a length of 30 μm in the first direction along the surface of the coating, and a length of α-Al in the second direction perpendicular to the first direction of the coating. ２ O ３ In a rectangular measurement field that includes the entire thickness of the layer along the second direction, The number of first Σ3-type crystal grain boundaries that are continuous from virtual line L1 to virtual line L2 and intersect virtual line L3 is 5 or more. The virtual line L1 is the α-Al ２ O ３ from the first interface located on the substrate side of the layer to the α-Al ２ O ３ a virtual line with a distance of 0.5 μm to the layer side, The virtual line L2 is the α-Al ２ O ３ From the second interface located on the surface side of the coating layer, the α-Al ２ O ３ This is a virtual line with a distance of 0.5 μm to the layer side. A cutting tool in which the virtual line L3 is a virtual line that is the same distance from the virtual lines L1 and L2.

2. The cutting tool according to claim 1, wherein the number of the first Σ3-type crystal grain boundaries is 100 or less.

3. The cutting tool according to claim 1 or claim 2, wherein the number of all grain boundaries intersecting the virtual line L3 in the measurement field is 20 or more.

4. The α-Al ２ O ３ The cutting tool according to claim 1 or claim 2, wherein the layer has an orientation index TC(hkl) where TC(0 0 12) is 5 or greater.

5. The coating comprises the substrate and the α-Al ２ O ３ It further includes a first layer placed between the layers, The cutting tool according to claim 1 or claim 2, wherein the first layer is a TiCN layer.

6. The aforementioned coating is the α-Al ２ O ３ The layer further includes a second layer disposed on the main surface opposite to the main surface of the layer that is close to the substrate, The cutting tool according to claim 1 or claim 2, wherein the second layer includes at least one selected from the group consisting of a TiN layer, a TiCN layer, and a TiCNO layer.

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