Coated cutting tools

Abstract

To provide a coated cutting tool which has improved defect resistance and wear resistance, and a long tool life.SOLUTION: A coated cutting tool contains a base material and a coating layer formed on a surface of the base material. The coating layer contains a lower layer, a lower α type Al2O3 layer, an intermediate layer and an upper α type Al2O3 layer in this order toward the surface of the coating layer from the base material side. The lower layer contains Ti compound layer comprising Ti compound of Ti, and at least one element selected from a group comprising C, N, O and B, and an average thickness of the lower layer falls within a specific range. The lower α type Al2O3 layer has an average thickness T1 which falls within a specific range, and satisfies conditions represented by specific formulae 1 and 2. The intermediate layer contains one or more layers of Ti compound layer comprising Ti compound of Ti and at least one element selected from a group comprising C, N, O and B, and has an average thickness which falls within a specific range. The upper α type Al2O3 layer has an average thickness T2 which falls within a specific range, and satisfies conditions represented by specific formula 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a coated cutting tool. [Background technology]

[0002] It is well known that coated cutting tools, which have been conventionally formed by depositing a coating layer with a total thickness of 3 to 20 μm onto the surface of a substrate made of cemented carbide or the like using chemical vapor deposition, have been used for cutting steel, cast iron, and other materials. As for the coating layer, for example, a single layer or a multi-layer coating consisting of two or more types selected from the group consisting of Ti carbides, nitrides, carbonitrides, carbonoxides, carbonitrates, and carbonitrates, and aluminum oxide (Al2O3), is known.

[0003] For example, Patent Document 1 describes a surface-coated cutting tool comprising a substrate and a coating formed on the substrate, wherein the coating comprises an α-Al2O3 layer containing a plurality of α-Al2O3 crystal grains, the α-Al2O3 layer comprising a lower layer disposed on the substrate side, an intermediate layer disposed on the lower layer, and an upper layer disposed on the intermediate layer, the lower layer comprising, in crystal orientation mapping using an electron beam backscatter diffraction apparatus for the cross-sectional polished surface of the α-Al2O3 layer, the area ratio of (001) oriented α-Al2O3 crystal grains A surface-coated cutting tool has been proposed in which the ratio is less than 35%, the area ratio of (001) oriented α-Al2O3 crystal grains in the intermediate layer is 35% or more in crystal orientation mapping, the area ratio of (001) oriented α-Al2O3 crystal grains in the upper layer is less than 35%, the thickness of the α-Al2O3 layer is 4 to 18 μm, the thickness of the intermediate layer accounts for 50% or more of the thickness of the α-Al2O3 layer, and the thickness of both the lower and upper layers is 1 μm or more. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2017 / 061058 [Overview of the project] [Problems that the invention aims to solve]

[0005] In recent years, cutting processes have increasingly involved higher speeds, higher feed rates, and deeper cuts, and the increased strength of workpieces has led to a demand for improved chipping resistance and wear resistance of tools compared to conventional methods. In particular, in recent years, there has been an increase in cutting processes that place loads on coated cutting tools, such as high-speed cutting of steel. The coated cutting tool described in Patent Document 1 has a low proportion of (110) orientation in the upper α-type Al2O3 layer, resulting in insufficient thermal shock resistance and room for improvement in chipping resistance. Furthermore, the coated cutting tool described in Patent Document 1 does not control the direction of the (110) orientation of the upper α-type Al2O3 layer relative to the (001) oriented intermediate α-type Al2O3 layer, resulting in insufficient suppression of crack initiation and propagation during cutting and room for improvement in chipping resistance.

[0006] This invention has been made in view of the above circumstances, and aims to provide a coated cutting tool with improved chipping resistance and wear resistance, resulting in a longer tool life. [Means for solving the problem]

[0007] Through extensive research, the inventors discovered that by configuring coated cutting tools in a specific way, it is possible to improve their fracture resistance and wear resistance, thereby extending the tool life of coated cutting tools. This led to the completion of the present invention.

[0008] In other words, the gist of this invention is as follows: [1] A coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, The coating layer comprises, in this order, a lower layer, a lower α-type Al2O3 layer, an intermediate layer, and an upper α-type Al2O3 layer, from the substrate side toward the surface of the coating layer. The lower layer comprises one or more Ti compound layers, each consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the lower layer is 3.00 μm or more and 15.00 μm or less. The average thickness T1 of the lower α-type Al2O3 layer is 2.00 μm or more and 15.00 μm or less. In the lower α-type Al2O3 layer, the following condition (1) is satisfied: 60 ≤ RSA < 100 (1) (In formula (1), RSA is the ratio (in area %) of the cross-sectional area of ​​particles in the lower α-type Al2O3 layer in a direction perpendicular to the surface of the substrate, where the orientation difference A, which is the angle between the normal to the surface of the substrate and the normal to the (001) plane of the particles in the lower α-type Al2O3 layer, is 0 degrees or more and 15 degrees or less, when the total area of ​​the entire cross-section is 100 area %.) In the lower α-type Al2O3 layer, the following condition (2) is satisfied: 15≦average angle β≦45 (2) (In equation (2), the average angle β (degrees) is expressed by the following equation (2-1).)

[0009]

number

[0010] (In formula (2-1), L n In an observation field that includes a cross-section of the lower α-type Al2O3 layer perpendicular to the surface of the substrate, the lowest point of each recess and the highest point of each convex on the surface of the lower α-type Al2O3 layer opposite to the substrate are identified, and the length (μm) of the nth line segment from the left in the observation field is represented by a line segment formed by connecting the lowest point of each identified recess with the highest point of the convex adjacent to the lowest point of the recess. n This represents the nth angle (in degrees) from the left of the observation field, among the angles formed by each of the created line segments and the straight line parallel to the substrate surface. However, the region of the observation field is defined as each (L) in the direction parallel to the substrate surface. n ×cosβ n This refers to the region where the total length of the ) is 50 μm or more. Said intermediate layer comprises one or more Ti compound layers formed of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O and B, the average thickness of said intermediate layer is 0.05 µm or more and 1.00 µm or less, the average thickness T2 of said upper α-type Al2O3 layer is 0.50 µm or more and 5.00 µm or less, said upper α-type Al2O3 layer satisfies the condition represented by the following formula (3), 50<RSB<100 (3) (In formula (3), RSB is the area percentage (unit: area%) of the cross-sectional area of particles, in a cross-section of said upper α-type Al2O3 layer in a direction perpendicular to the surface of said base material, where the orientation difference B formed between the normal line of the line segment created when obtaining said average angle β (unit: degree) and the normal line of the (110) plane of particles of said upper α-type Al2O3 layer is 0 degree or more and 15 degrees or less, where the total area of the entire cross-section is defined as 100 area%. However, said orientation difference B is determined for each divided region, by dividing said upper α-type Al2O3 by respective normal lines of the base material surface passing through each of the lowest points of said specified recessed portions and each of the highest points of said protruding portions in the observation visual field for obtaining said average angle β (unit: degree).) A coated cutting tool. [2] In said lower α-type Al2O3 layer, among the lowest points of individual said recessed portions on the surface of said lower α-type Al2O3 layer on the opposite side to said base material in the observation visual field for obtaining said average angle β (unit: degree), the average particle diameter of particles in a direction parallel to the surface of said base material at a position 0.2 µm from the lowest point located closest to said base material side toward said base material side is 0.3 µm or more and 2.0 µm or less, The coated cutting tool according to [1].[ [3] the ratio of the average thickness T1 of said lower α-type Al2O3 layer to the average thickness T2 of said upper α-type Al2O3 layer (T1 / T2) is 1.0 or more and 12.0 or less, The coated cutting tool according to [1] or [2].[ [4] the average thickness of said coating layer is 8.00 µm or more and 25.00 µm or less, A coated cutting tool according to any one of [1] to [3]. [5] wherein the base material is cemented carbide, cermet, ceramics or cubic boron nitride sintered body, A coated cutting tool according to any one of [1] to [4]. Effects of the Invention

[0011] According to the present invention, a coated cutting tool having improved fracture resistance and wear resistance and a long tool life can be provided. Brief Description of Drawings

[0012] [Figure 1] It is a schematic diagram showing an example of the coated cutting tool of the present invention. Mode for Carrying Out the Invention

[0013] Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. However, the present invention is not limited to the following present embodiment. Various modifications can be made to the present invention without departing from the gist thereof. In the drawings, the same elements are denoted by the same reference numerals, and duplicate descriptions are omitted. Unless otherwise specified, positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown in the drawings.

[0014] [Coated cutting tool] The coated cutting tool of the present embodiment is a coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, wherein the coating layer includes, in this order from the base material side toward the surface of the coating layer, a lower layer, a lower α-type Al₂O₃ layer, an intermediate layer, and an upper α-type Al₂O₃ layer, the lower layer includes one or more Ti compound layers formed of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O and B, an average thickness of the lower layer is 3.00 µm or more and 15.00 µm or less, and an average thickness T₁ of the lower α-type Al₂O₃ layer is 2.00 µm or more and 15.00 µm or less, In the lower α-type Al2O3 layer, the conditions expressed by the following formula (1) are satisfied, 60 ≤ RSA < 100 (1) (In formula (1), RSA is the ratio (in area %) of the cross-sectional area of ​​particles in the lower α-type Al2O3 layer perpendicular to the surface of the substrate, where the orientation difference A, which is the angle between the normal to the surface of the substrate and the normal to the (001) plane of the particles in the lower α-type Al2O3 layer, is between 0 degrees and 15 degrees, when the total area of ​​the entire cross-section is 100%.) In the lower α-type Al2O3 layer, the conditions expressed by the following formula (2) are satisfied, 15≦average angle β≦45 (2) (In equation (2), the average angle β (degrees) is expressed by the following equation (2-1).)

[0015]

number

[0016] (In formula (2-1), L n β represents the length (μm) of the nth line segment from the left in the observation field, which is formed by connecting the lowest point of each recess and the highest point of a convexity on the surface of the lower α-type Al2O3 layer opposite the substrate in an observation field that includes a cross-section of the lower α-type Al2O3 layer perpendicular to the surface of the substrate, and drawing a straight line connecting the lowest point of each identified recess and the highest point of a convexity adjacent to the lowest point of the recess. n This represents the nth angle (in degrees) from the left of the observation field, among the angles formed between each created line segment and a straight line parallel to the substrate surface. However, the area of ​​the observation field is defined in the direction parallel to the substrate surface, for each (L n ×cosβ n This refers to the region where the total length of the ) is 50 μm or more. The intermediate layer comprises one or more Ti compound layers, each consisting of Ti and at least one element selected from the group consisting of C, N, O, and B; the average thickness of the intermediate layer is 0.05 μm or more and 1.00 μm or less; and the average thickness T2 of the upper α-type Al2O3 layer is 0.50 μm or more and 5.00 μm or less. The upper α-type Al2O3 layer satisfies the condition expressed by the following formula (3). 50 <RSB<100 (3) (In equation (3), RSB is the ratio (in area %) of the cross-sectional area of ​​particles whose orientation difference B is between 0 degrees and 15 degrees, when the total area of ​​the entire cross-section of the upper α-type Al2O3 layer perpendicular to the surface of the substrate is 100 area %, and the angle between the normal of the line segment created when determining the average angle β (degrees) and the normal of the (110) plane of the particles in the upper α-type Al2O3 layer is 0 degrees or more. However, the orientation difference B is determined for each divided region by dividing the upper α-type Al2O3 layer into sections using the normals of the substrate surface that pass through the lowest point of each recess and the highest point of each convex part in the observation field used to determine the average angle β (degrees).)

[0017] By adopting the above-described configuration, the coated cutting tool of this embodiment can improve chipping resistance and wear resistance, thereby extending tool life. The factors contributing to the superior fracture resistance and wear resistance of such coated cutting tools are not fully understood, but are presumed to be as follows. However, the factors are not limited to those listed below. The coated cutting tool of this embodiment has excellent wear resistance and resistance to plastic deformation due to the average thickness of the lower layer being 3.00 μm or more, and excellent chipping and fracture resistance due to the suppression of peeling of the coating layer by the average thickness of the lower layer being 15.00 μm or less. Furthermore, the coated cutting tool of this embodiment has excellent wear resistance and resistance to plastic deformation due to the average thickness T1 of the lower α-type Al2O3 layer being 2.00 μm or more, and excellent chipping and fracture resistance due to the suppression of peeling of the coating layer by the average thickness T1 of the lower α-type Al2O3 layer being 15.00 μm or less. Furthermore, the coated cutting tool of this embodiment has excellent wear resistance and resistance to plastic deformation because the progression of crater wear is suppressed by the RSA of the lower α-type Al2O3 layer being 60 area % or more, and the formation of the lower α-type Al2O3 layer is facilitated by the RSA being less than 100 area %. Furthermore, in this embodiment, the coated cutting tool has an average angle β of 15 degrees or more in the lower α-type Al2O3 layer, which improves the adhesion between the lower α-type Al2O3 layer and the upper α-type Al2O3 layer via the intermediate layer, resulting in excellent chipping resistance and fracture resistance. Also, if the average angle β is 45 degrees or less, the surface irregularities of the coating layer are reduced, which lowers the cutting resistance, resulting in excellent wear resistance and fracture resistance. In addition, in this embodiment, the coated cutting tool has an average angle β in the lower α-type Al2O3 layer that is in the range of 15 degrees to 45 degrees, which suppresses the propagation of cracks during cutting, thus improving fracture resistance. Furthermore, in this embodiment, the coated cutting tool has an average thickness of 0.05 μm to 1.00 μm in the intermediate layer, which allows the RSB value to be easily set within a predetermined range. Furthermore, in this embodiment, the coated cutting tool has improved thermal shock resistance and thus improved fracture resistance because the average thickness T2 of the upper α-type Al2O3 layer is 0.50 μm or more, and peeling of the coating layer is suppressed, resulting in excellent chipping and fracture resistance. In addition, in this embodiment, the coated cutting tool has improved thermal shock resistance and thus improved fracture resistance because the RSB of the upper α-type Al2O3 layer is greater than 50 area%, and the formation of the upper α-type Al2O3 layer is easier because the RSB is less than 100 area%. The combined effects described above result in a coated cutting tool of this embodiment that offers improved fracture resistance and wear resistance, leading to a longer tool life.

[0018] In general, in the prior art, for example, as in Patent Document 1, a single-layer α-type Al2O3 layer may be configured such that the lower side is oriented to the (001) plane and the upper side is oriented to the (110) plane (this configuration will also be referred to as "Configuration A" below). In this case, it tends to be difficult to increase the orientation ratio of either the lower side or the upper side, or both. In this embodiment, in view of the above circumstances, in order to simultaneously provide a lower α-type Al2O3 layer oriented on the (001) plane so that the RSA is within a specific range, and an upper α-type Al2O3 layer oriented on the (110) plane so that the RSB is within a specific range, an intermediate layer containing a Ti compound layer is formed between the lower α-type Al2O3 layer and the upper α-type Al2O3 layer (this configuration will also be referred to as "Configuration B" below). The coated cutting tool of this embodiment is presumed to possess the effects of both an α-type Al2O3 layer oriented on the (001) side, which has excellent wear resistance, and an α-type Al2O3 layer oriented on the (110) side, which has excellent fracture resistance, by forming an intermediate layer in this manner. Furthermore, the inventors discovered that in configuration B, controlling the surface irregularities of the lower α-type Al2O3 layer improves the adhesion between the lower and upper sides of the α-type Al2O3 layer. Specifically, by further controlling the "average angle β (degrees)" of the lower α-type Al2O3 layer in configuration B to a range of 15 degrees to 45 degrees (this configuration will also be referred to as "configuration C" below), the inventors found that the fracture resistance is even better, leading to the completion of the present invention.

[0019] Figure 1 is a schematic cross-sectional view partially showing an example of a coated cutting tool according to this embodiment. The coated cutting tool 7 has a base material 1 and a coating layer 6 formed on the surface of the base material 1. In the coating layer 6, the lower layer 2, the lower α-type Al2O3 layer 3, the intermediate layer 4, and the upper α-type Al2O3 layer 5 are stacked upwards in this order from the base material 1 side.

[0020] The substrate in this embodiment is not particularly limited as long as it can be used as a substrate for a coated cutting tool. Examples of such substrates include cemented carbide, cermet, ceramics, and cubic boron nitride sintered bodies. Among these, cemented carbide is preferred as the substrate. Using such a substrate tends to result in coated cutting tools with superior fracture resistance and wear resistance.

[0021] In this embodiment, the coating layer comprises, in order from the substrate side toward the surface of the coating layer, a lower layer, a lower α-type Al2O3 layer, an intermediate layer, and an upper α-type Al2O3 layer, and may also include an outer layer if necessary. The average thickness of the coating layer is not particularly limited, but is preferably between 8.00 μm and 25.00 μm. When the average thickness of the coating layer is 8.00 μm or more, it tends to have excellent abrasion resistance and resistance to plastic deformation, and when it is 25.00 μm or less, the adhesion of the coating layer improves, and it tends to have excellent chipping resistance and resistance to chipping. From a similar viewpoint, the average thickness of the coating layer is more preferably between 8.50 μm and 24.60 μm, and even more preferably between 15.40 μm and 21.30 μm.

[0022] [Lower layer] In this embodiment, the lower layer includes one or more Ti compound layers, each consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. By having the above lower layer between the substrate and the lower α-type Al2O3 layer, the adhesion and wear resistance of the coated cutting tool are improved.

[0023] The Ti compound layer in the lower layer is not particularly limited, but examples include a TiC layer made of TiC (hereinafter also simply referred to as the "TiC layer"), a TiN layer made of TiN (hereinafter also simply referred to as the "TiN layer"), a TiCN layer made of TiCN (hereinafter also simply referred to as the "TiCN layer"), a TiCO layer made of TiCO (hereinafter also simply referred to as the "TiCO layer"), a TiCNO layer made of TiCNO (hereinafter also simply referred to as the "TiCNO layer"), a TiON layer made of TiON (hereinafter also simply referred to as the "TiON layer"), and a TiB2 layer made of TiB2 (hereinafter also simply referred to as the "TiB2 layer"). From the viewpoint of achieving the effects of the present invention more effectively and reliably, it is preferable that the Ti compound layer in the lower layer includes a TiN layer, a TiCN layer, a TiCO layer, and / or a TiCNO layer.

[0024] The lower layer may consist of one layer or multiple layers (for example, two or three layers). From the viewpoint of achieving the effects of the present invention more effectively and reliably, it is preferable that the lower layer be composed of multiple layers, more preferably two or more layers, even more preferably three or more layers, and still more preferably three layers. When the lower layer consists of three layers, a TiC layer or TiN layer may be provided as the first layer on the surface of the substrate, a TiCN layer may be provided as the second layer on the surface of the first layer, and a TiCNO layer or TiCO layer may be provided as the third layer on the surface of the second layer. Among these, it is preferable that the lower layer has a TiN layer as the first layer on the surface of the substrate, a TiCN layer as the second layer on the surface of the first layer, and a TiCNO layer or TiCO layer as the third layer on the surface of the second layer.

[0025] In this embodiment, the average thickness of the lower layer is 3.00 μm or more and 15.00 μm or less. When the average thickness of the lower layer is 3.00 μm or more, it exhibits excellent abrasion resistance and resistance to plastic deformation, and when it is 15.00 μm or less, peeling of the coating layer is suppressed, and it exhibits excellent chipping resistance and fracture resistance. From a similar viewpoint, the average thickness of the lower layer is preferably 3.20 μm or more and 14.80 μm or less, and more preferably 4.50 μm or more and 14.30 μm or less.

[0026] The average thickness of the lower layer is measured by the following method. In the method for measuring the average angle β, of the lowest points of recesses and highest points of convexities on the surface opposite the substrate of the lower α-type Al2O3 layer, the three lowest points of recesses with the smallest shortest distance from the substrate surface are identified in order from the side with the smallest shortest distance, and the three highest points of convexities with the largest shortest distance from the substrate surface are identified in order from the side with the largest shortest distance. A normal to the substrate surface is drawn passing through these six identified points, and the arithmetic mean of the lengths these normals traverse the lower layer is taken as the average thickness of the lower layer. In this embodiment, the average thickness of each layer is determined using the six identified points, as in the method described above: the three lowest points of recesses with the smallest shortest distance from the substrate surface are identified in order from the side with the smallest shortest distance, and the three highest points of convexities with the largest shortest distance from the substrate surface are identified in order from the side with the largest shortest distance. In other words, a normal to the substrate surface is drawn passing through the six identified points, and the arithmetic mean of the lengths these normals traverse each layer is taken as the average thickness of each layer. More precisely, the "normal to the substrate surface" mentioned above refers to the normal to a straight line approximately parallel to the substrate surface in the method for measuring the average angle β.

[0027] When the lower layer is formed of the first to third layers as described above, the average thickness of the first layer formed on the surface of the substrate is preferably 0.10 μm or more and 1.00 μm or less, from the viewpoint of further improving chipping resistance and / or abrasion resistance. From the same viewpoint, the average thickness of the first layer is more preferably 0.20 μm or more and 0.50 μm or less.

[0028] When the lower layer is formed of the first to third layers as described above, the average thickness of the second layer formed on the surface of the first layer is preferably 3.00 μm or more and 14.00 μm or less from the viewpoint of further improving chipping resistance and / or wear resistance. From the same viewpoint, the average thickness of the second layer is more preferably 3.80 μm or more and 13.50 μm or less, and even more preferably 4.30 μm or more and 12.50 μm or less.

[0029] When the lower layer is formed of the first to third layers as described above, the average thickness of the third layer formed on the surface of the second layer is preferably 0.10 μm or more and 1.00 μm or less from the viewpoint of further improving chipping resistance and / or wear resistance. From the same viewpoint, the average thickness of the third layer is more preferably 0.10 μm or more and 0.80 μm or less, and even more preferably 0.10 μm or more and 0.50 μm or less.

[0030] The Ti compound layer is a layer made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, but it may also contain trace amounts of elements other than those mentioned above, as long as the effects of the lower layer are achieved.

[0031] [Lower α-type Al2O3 layer] In this embodiment, the lower α-type Al2O3 layer includes an α-type Al2O3 layer made of α-type Al2O3. The lower α-type Al2O3 layer has an average thickness T1 of 2.00 μm or more and 15.00 μm or less, satisfies the conditions expressed in equation (1) above, and satisfies the conditions expressed in equation (2) above.

[0032] The average thickness T1 of the lower α-type Al2O3 layer is 2.00 μm or more and 15.00 μm or less. An average thickness T1 of 2.00 μm or more of the lower α-type Al2O3 layer provides excellent abrasion resistance and resistance to plastic deformation, while an average thickness T1 of 15.00 μm or less suppresses peeling of the coating layer, resulting in excellent chipping resistance and fracture resistance. From a similar viewpoint, the average thickness T1 of the lower α-type Al2O3 layer is preferably 2.80 μm or more and 14.80 μm or less, and more preferably 4.00 μm or more and 14.00 μm or less.

[0033] The average thickness T1 of the lower α-type Al2O3 layer is measured by the following method. In the measurement method of average angle β, among the determined lowest points of concave portions and highest points of convex portions on the surface of the lower α-type Al₂O₃ layer opposite to the base material, select 3 lowest points of concave portions that have a smaller shortest distance from the base material surface in order from the side with the smaller shortest distance, and select 3 highest points of convex portions that have a larger shortest distance from the base material surface in order from the side with the larger shortest distance. Draw normal lines of the base material surface passing through the determined 6 points, and take the arithmetic mean of the lengths of these normal lines crossing the lower α-type Al₂O₃ layer as the average thickness of the lower α-type Al₂O₃ layer.

[0034] The lower α-type Al₂O₃ layer satisfies the condition represented by the following formula (1). 60≦RSA<100 (1) (In formula (1), RSA refers to, in a cross-section of the lower α-type Al₂O₃ layer in a direction perpendicular to the surface of the base material, when the total area of the entire cross-section is 100 area%, it is the proportion of the cross-sectional area (unit: area%) of particles whose orientation difference A, which is the angle formed between the normal line of the base material surface and the normal line of the (001) plane of the particles in the lower α-type Al₂O₃ layer, is 0° or more and 15° or less.)

[0035] In the lower α-type Al₂O₃ layer, when RSA is 60 area% or more, the progress of crater wear is suppressed, so that the layer is excellent in wear resistance and plastic deformation resistance. In addition, when RSA is less than 100 area%, the formation of the lower α-type Al₂O₃ layer is facilitated. From the same viewpoint, RSA is preferably 63 area% or more and 96 area% or less, and more preferably 70 area% or more and 90 area% or less.

[0036] The lower α-type Al₂O₃ layer satisfies the condition represented by the following formula (2). 15≦average angle β≦45 (2) (In formula (2), the average angle β (degrees) is represented by the following formula (2-1).)

[0037] [Mathematics]

[0038] (In formula (2-1), L nβ represents the length (μm) of the nth line segment from the left in the observation field, which is formed by connecting the lowest point of each recess and the highest point of a convexity on the surface of the lower α-type Al2O3 on the opposite side of the substrate in an observation field that includes a cross-section of the lower α-type Al2O3 layer perpendicular to the surface of the substrate, and drawing a straight line connecting the lowest point of each identified recess and the highest point of a convexity adjacent to the lowest point of the recess. n This represents the nth angle (in degrees) from the left of the observation field, among the angles formed between each created line segment and a straight line parallel to the substrate surface. However, the area of ​​the observation field is defined in the direction parallel to the substrate surface, for each (L n ×cosβ n This refers to the region where the total length of the ) is 50 μm or more.

[0039] In the lower α-type Al2O3 layer, if the average angle β is 15 degrees or more, the adhesion between the lower α-type Al2O3 layer and the upper α-type Al2O3 layer via the intermediate layer is improved, resulting in excellent chipping resistance and fracture resistance. Furthermore, if the average angle β in the lower α-type Al2O3 layer is 45 degrees or less, the surface irregularities of the coating layer are reduced, lowering cutting resistance, resulting in excellent wear resistance and fracture resistance. In addition, by setting the average angle β in the lower α-type Al2O3 layer to a range of 15 degrees to 45 degrees, crack propagation during cutting is suppressed, thus improving fracture resistance.

[0040] Furthermore, the coated cutting tool of this embodiment exhibits particularly excellent fracture resistance when the average angle β in the lower α-type Al2O3 layer is controlled to a range of 15 degrees or more and 45 degrees or less (this configuration will also be referred to as "Configuration C" below), and the configuration in which the average angle β is further controlled to a range of 22 degrees or more and 38 degrees or less (this configuration will also be referred to as "Configuration D"). In configuration C, the larger the average angle β in the lower α-type Al2O3 layer, the lower the ratio of the upper α-type Al2O3 layer's orientation toward the (110) plane relative to the normal to the substrate surface tends to decrease. Therefore, it can be predicted that, generally, a larger average angle β in the upper α-type Al2O3 layer improves adhesion, but decreases chipping resistance and makes it difficult to improve fracture resistance. However, in reality, it has been found that configuration D among configuration C exhibits particularly excellent fracture resistance. In this regard, it is presumed that by specifically using configuration D among configuration C, an effect of improving fracture resistance other than adhesion is obtained. The cause is not clear, but it is estimated as follows: Generally, the (012) plane is known as a cleavage plane in Al2O3 with an α-type crystal structure, and it tends to be prone to fracture by cracking. In a lower α-type Al2O3 layer oriented to the (001) plane so that RSA is within a specific range, the (012) plane is tilted at approximately 58 degrees with respect to the substrate surface (32 degrees with respect to the normal to the substrate surface). Furthermore, generally speaking, the (110) plane of Al2O3 with an α-type crystal structure has a smaller coefficient of thermal expansion compared to other planes. For this reason, orientation toward the (110) plane is thought to have the effect of suppressing the initiation and propagation of cracks perpendicular to the (110) plane due to thermal shock. Based on the two points above, in configuration D, cracks are less likely to occur in the upper α-type Al2O3 layer during cutting due to thermal shock in a direction between 22 and 38 degrees relative to the substrate surface, and the probability of cracks propagating in the direction along the cleavage plane of the lower α-type Al2O3 layer is reduced. Therefore, it is considered that chipping resistance during cutting, which is subject to thermal shock, is also improved, and that it has excellent fracture resistance.

[0041] The average angle β is measured by the following method. The cross-section of the lower α-type Al2O3 layer perpendicular to the substrate surface is observed using a FE-SEM to obtain an image of the lower α-type Al2O3 layer. In this process, the direction approximately parallel to the substrate surface is made parallel to the left-right direction of the observed image. More specifically, "Obtaining an observation image such that the direction approximately parallel to the substrate surface is parallel to the left-right direction of the observation image" means that the interface between the coating layer and the substrate crosses the observation image from the left edge to the right edge, and the straight line connecting the interface between the coating layer and the substrate at the left edge and the interface between the coating layer and the substrate at the right edge is parallel to the left-right direction of the observation image. The above straight line refers to a straight line approximately parallel to the substrate surface. In the observed image, a straight line approximately parallel to the substrate surface is drawn at a position closer to the substrate than the surface of the lower α-type Al2O3 layer opposite the substrate. In the observed image, the surface of the lower α-type Al2O3 layer opposite the substrate is observed to have a continuous pattern from left end to right end where the shortest distance between the surface and the straight line approximately parallel to the substrate surface is small and where it is large. From left end to right end of the observed image, identify all points where the shortest distance between the surface of the lower α-type Al2O3 layer opposite the substrate and the aforementioned straight line changes from a large portion to a small portion, and define these as the lowest points of each recess. From left end to right end of the observed image, identify all points where the shortest distance between the surface of the lower α-type Al2O3 layer opposite the substrate and the aforementioned straight line changes from a small portion to a large portion, and define these as the lowest points of each recess. Draw line segments connecting the lowest points of each identified recess to the highest points of the convex portions adjacent to the lowest points of the recesses. The length of each line segment and the angle between that line segment and a line approximately parallel to the substrate surface are determined individually. In this process, the length of the nth line segment from the left in the observation field is L. n This is expressed as follows, and the angle between the nth line segment and the line approximately parallel to the substrate surface is β. n This is how it is expressed. Substitute the obtained value into equation (2-1), and the calculated value is taken as the average angle β.

[0042] In this embodiment, the lower α-type Al2O3 layer includes an α-type Al2O3 layer made of α-type Al2O3, but it may also contain components other than α-type Al2O3 as long as the effects of the present invention are achieved.

[0043] In the lower α-type Al2O3 layer, it is preferable that the average particle size in the direction parallel to the substrate surface, at a position 0.2 μm toward the substrate from the lowest point of each recess on the surface of the lower α-type Al2O3 layer opposite to the substrate in the observation field for determining the average angle β (degrees), is between 0.3 μm and 2.0 μm. In the lower α-type Al2O3 layer, if the average particle size is 0.3 μm or more, it tends to be easier to control the RSB value within a predetermined range. Furthermore, in the coated cutting tool of this embodiment, if the average particle size in the lower α-type Al2O3 layer is 2.0 μm or less, the adhesion between the lower α-type Al2O3 layer and the upper α-type Al2O3 layer via the intermediate layer is improved, resulting in a tendency for superior chipping resistance and fracture resistance. From a similar viewpoint, it is more preferable that the average particle size in the lower α-type Al2O3 layer is 0.4 μm or more and 1.9 μm or less, and even more preferable that it is 0.7 μm or more and 1.6 μm or less.

[0044] [Middle class] In this embodiment, the intermediate layer comprises one or more Ti compound layers, each consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, with an average thickness of 0.05 μm or more and 1.00 μm or less. As mentioned above, in general, a single-layer α-type Al2O3 layer is sometimes configured such that the lower side is oriented to the (001) plane and the upper side is oriented to the (110) plane (this configuration will also be referred to as "Configuration A" below). In this case, it tends to be difficult to increase the orientation ratio of either the lower side or the upper side, or both. In this embodiment, by forming an intermediate layer containing a Ti compound layer between the lower α-type Al2O3 layer and the upper α-type Al2O3 layer in the coating layer (this configuration will also be referred to as "Configuration B" below), it is possible to simultaneously arrange the lower α-type Al2O3 layer oriented on the (001) plane so that the RSA is within a specific range, and the upper α-type Al2O3 layer oriented on the (110) plane so that the RSB is within a specific range, and it is presumed that the effects of both can be obtained.

[0045] The intermediate layer comprises one or more Ti compound layers, preferably one or more Ti compound layers, each comprising a Ti compound made of Ti and at least one element selected from the group consisting of C, N, O, and B.

[0046] The Ti compound layer in the intermediate layer is not particularly limited, but examples include a TiC layer made of TiC (hereinafter also simply referred to as the "TiC layer"), a TiN layer made of TiN (hereinafter also simply referred to as the "TiN layer"), a TiCN layer made of TiCN (hereinafter also simply referred to as the "TiCN layer"), a TiCO layer made of TiCO (hereinafter also simply referred to as the "TiCO layer"), a TiCNO layer made of TiCNO (hereinafter also simply referred to as the "TiCNO layer"), a TiON layer made of TiON (hereinafter also simply referred to as the "TiON layer"), and a TiB2 layer made of TiB2 (hereinafter also simply referred to as the "TiB2 layer"). From the viewpoint of achieving the effects of the present invention more effectively and reliably, it is preferable that the Ti compound layer in the intermediate layer includes a TiCO layer and / or a TiCNO layer.

[0047] The intermediate layer may consist of one layer or multiple layers (for example, two or three layers). From the viewpoint of achieving the effects of the present invention more effectively and reliably, it is preferable that the intermediate layer consists of one layer.

[0048] The average thickness of the intermediate layer is 0.05 μm to 1.00 μm. This provides excellent fracture resistance. From a similar viewpoint, the average thickness of the intermediate layer is preferably 0.05 μm to 0.90 μm, and more preferably 0.20 μm to 0.80 μm. Furthermore, by keeping the average thickness of the intermediate layer within the above range, the RSB (area %) in the upper α-type Al2O3 layer can be easily adjusted to a predetermined range.

[0049] The average thickness of the intermediate layer is measured by the following method. In the method for measuring the average angle β, of the lowest point of the recesses and highest point of the convexities on the surface opposite the substrate of the lower α-type Al2O3 layer, three lowest points of the recesses with the smallest shortest distance from the substrate surface are identified, starting from the side with the smallest shortest distance, and three highest points of the convexities with the largest shortest distance from the substrate surface are identified, starting from the side with the largest shortest distance. A normal to the substrate surface is drawn passing through these six identified points, and the arithmetic mean of the lengths over which these normals cross the intermediate layer is taken as the average thickness of the intermediate layer.

[0050] [Top α-type Al2O3 layer] In this embodiment, the upper α-type Al2O3 layer has an average thickness T2 of 0.50 μm or more and 5.00 μm or less, and the upper α-type Al2O3 layer satisfies the condition represented by formula (3) above.

[0051] In this embodiment, the average thickness T2 of the upper α-type Al2O3 layer is 0.50 μm or more and 5.00 μm or less. In this embodiment, the coated cutting tool has improved thermal shock resistance and fracture resistance when the average thickness T2 of the upper α-type Al2O3 layer is 0.50 μm or more, and excellent chipping resistance and fracture resistance when the average thickness T2 of the upper α-type Al2O3 layer is 5.00 μm or less, and peeling of the coating layer is suppressed. From a similar viewpoint, it is preferable that the average thickness T2 of the upper α-type Al2O3 layer is 0.60 μm or more and 4.50 μm or less, and more preferable that it is 0.80 μm or more and 2.20 μm or less.

[0052] The average thickness T2 of the upper α-type Al2O3 layer is measured by the following method. In the method for measuring the average angle β, of the lowest points of the recesses and highest points of the convexities on the surface opposite the substrate of the lower α-type Al2O3 layer, the three lowest points of the recesses with the smallest shortest distance from the substrate surface are identified in order from the side with the smallest shortest distance, and the three highest points of the convexities with the largest shortest distance from the substrate surface are identified in order from the side with the largest shortest distance. A normal to the substrate surface is drawn passing through these six identified points, and the arithmetic mean of the lengths over which these normals cross the upper α-type Al2O3 layer is taken as the average thickness of the upper α-type Al2O3 layer.

[0053] In this embodiment, the upper α-type Al2O3 layer satisfies the condition represented by the following formula (3). 50 <RSB<100 (3) (In equation (3), RSB is the ratio (in area %) of the cross-sectional area of ​​particles whose orientation difference B is between 0 degrees and 15 degrees, when the total area of ​​the entire cross-section of the upper α-type Al2O3 layer perpendicular to the surface of the substrate is 100 area %, and the angle between the normal of the line segment created when determining the average angle β (degrees) and the normal of the (110) plane of the particles in the upper α-type Al2O3 layer is 0 degrees or more. However, the orientation difference B is determined for each divided region by dividing the upper α-type Al2O3 layer into sections using the normals of the substrate surface that pass through the lowest point of each recess and the highest point of each convex part in the observation field used to determine the average angle β (degrees).)

[0054] In this embodiment, if the RSB of the coated cutting tool in the upper α-type Al2O3 layer exceeds 50 area%, the thermal shock resistance is improved, and thus the fracture resistance is improved. Furthermore, if the RSB is less than 100 area%, the formation of the upper α-type Al2O3 layer becomes easier. From a similar viewpoint, it is preferable that the RSB is 52 area% or more and 91 area% or less, and more preferable that it is 54 area% or more and 82 area% or less.

[0055] In this embodiment, the upper α-type Al2O3 layer includes an α-type Al2O3 layer made of α-type Al2O3, but it may also contain components other than α-type Al2O3 as long as the effects of the present invention are achieved.

[0056] In this embodiment, the ratio of the average thickness T1 of the lower α-type Al2O3 layer to the average thickness T2 of the upper α-type Al2O3 layer (T1 / T2) is preferably 1.0 or more and 12.0 or less. In this embodiment, when T1 / T2 is 1.0 or greater, the progression of crater wear is suppressed, and the coated cutting tool tends to have excellent wear resistance and resistance to plastic deformation. When T1 / T2 is 12.0 or less, thermal shock resistance is improved, and therefore fracture resistance tends to be improved. From a similar viewpoint, it is more preferable that T1 / T2 is 1.3 or more and 10.7 or less, and even more preferable that it is 3.5 or more and 9.3 or less.

[0057] [External layer] In this embodiment, the coating layer may include an outer layer on the interface opposite to the substrate of the upper α-type Al2O3 layer (i.e., the surface of the upper α-type Al2O3 layer). Including an outer layer in the coating layer can improve wear resistance. It also allows for easy identification of the corner that has been used. The outer layer is preferably a layer of a compound consisting of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, Si, and Y, and at least one element selected from the group consisting of C, N, O, and B (preferably C and / or N), as this tends to result in excellent wear resistance. From a similar viewpoint, it is more preferable for the outer layer to be a layer of a compound consisting of at least one element selected from the group consisting of Ti, Nb, Cr, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B, and even more preferable for it to be a layer of a compound consisting of at least one element selected from the group consisting of Ti, Cr, Al, and Si, and at least one element selected from the group consisting of C, N, and O. Among these, specific examples of the outer layer are preferably a TiN layer made of TiN, a TiCNO layer made of TiCNO, and a TiCN layer made of TiCN.

[0058] The average thickness of the outer layer is not particularly limited and may be, for example, 0.1 μm or more and 5.0 μm or less. From the viewpoint of achieving the effects of the present invention more effectively and reliably, the average thickness of the outer layer is preferably 0.15 μm or more and 3.0 μm or less, and more preferably 0.2 μm or more and 3.0 μm or less.

[0059] The average thickness of the outer layer is measured by the following method. In the method for measuring the average angle β, of the lowest point of a recess and the highest point of a convex portion on the surface opposite the substrate of the lower α-type Al2O3 layer, three lowest points of recesses with the smallest shortest distance from the substrate surface are identified, starting from the side with the smallest shortest distance, and three highest points of convex portions with the largest shortest distance from the substrate surface are identified, starting from the side with the largest shortest distance. A normal to the substrate surface is drawn passing through these six identified points, and the arithmetic mean of the lengths over which these normals cross the outer layer is taken as the average thickness of the outer layer.

[0060] [Measurement methods for RSA and RSB] In this embodiment, as a method for measuring RSA and RSB, for example, the cross-section to be measured can be observed with an electrolytic emission scanning electron microscope (FE-SEM), and the cross-sectional area of ​​particles with a specific orientation difference can be measured using an electron backscattering imaging device (EBSD) attached to the FE-SEM. RSA and RSB may be calculated by measuring the orientation difference in the same way, except that the crystal planes being measured are different. More specifically, they can be determined, for example, by the method described in the examples below.

[0061] [Method for forming a coating layer] The method for forming the coating layer in the coated cutting tool of this embodiment is not particularly limited, but examples include the following methods. However, the method for forming each layer is not limited thereto.

[0062] For example, the lower Ti compound layer is formed by the following method. A Ti compound layer consisting of a Ti nitride layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-10.0 mol%, N2: 20-60 mol%, and H2: the remainder, at a temperature of 850-950°C and a pressure of 300-400 hPa.

[0063] A Ti compound layer consisting of a Ti carbide layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 1.5-3.5 mol%, CH4: 3.5-5.5 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 70-80 hPa.

[0064] A Ti compound layer consisting of a Ti carbonitride layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-7.0 mol%, CH3CN: 0.5-1.5 mol%, and H2: the remainder, at a temperature of 800-900°C and a pressure of 60-80 hPa.

[0065] A Ti compound layer consisting of a Ti carbonitroxide layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 3.0-4.0 mol%, CO: 0.5-1.0 mol%, N2: 30-40 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 50-150 hPa.

[0066] A Ti compound layer consisting of a Ti carbon oxide layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 1.0-2.0 mol%, CO: 2.0-3.0 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 50-150 hPa.

[0067] After the lower layer is formed, an α-type Al2O3 layer of the lower α-type Al2O3 layer is formed on its surface. For example, this layer can be formed by the following method. First, a lower layer consisting of one or more Ti compound layers is formed on the surface of the substrate. Next, the surface of the layer furthest from the substrate (the non-substrate layer) is oxidized. Subsequently, a lower α-type Al2O3 layer is formed on the surface of the layer furthest from the substrate through a nucleation process.

[0068] More specifically, oxidation of the surface of the layer furthest from the substrate may be carried out under conditions where the raw material composition is CO2: 0.3 to 1.0 mol%, H2: the remainder, the temperature is 950 to 1050°C, and the pressure is 50 to 60 hPa (oxidation step 1). The oxidation treatment time in this case is preferably 1 to 5 minutes.

[0069] Subsequently, a nucleation step is performed to form nuclei on the surface of the layer furthest from the substrate. The nucleation step may be carried out by chemical vapor deposition under the following conditions: the raw material composition is AlCl3: 1.0-5.0 mol%, CO2: 0.5-2.5 mol%, CO: 0.5-2.5 mol%, HCl: 1.0-3.0 mol%, H2: the remainder, the temperature is 950-1050°C, and the pressure is 60-80 hPa (nucleation step 1). In this case, the processing time for nucleation step 1 is preferably 1-10 minutes.

[0070] Subsequently, a lower α-type Al2O3 layer is formed on the surface of the lower layer. The following describes the case in which the lower α-type Al2O3 layer is formed in three stages. The first stage of forming the α-type Al2O3 layer of the lower α-type Al2O3 layer may be carried out by chemical vapor deposition under the following conditions: the raw material composition is AlCl3: 1.5~2.5 mol%, CO2: 1.0~2.5 mol%, HCl: 3.0~6.0 mol%, H2S: 0.05~0.10 mol%, H2: remainder, the temperature is 970~1030°C, and the pressure is 60~80 hPa (film formation step 1). In this case, the processing time for film formation step 1 is preferably such that the thickness of the film formed by film formation step 1 becomes 5%~15% of the average thickness of the target lower α-type Al2O3 layer, and more preferably 10%.

[0071] Furthermore, after the film formation step 1, the second stage of forming the α-type Al2O3 layer of the lower α-type Al2O3 layer may be carried out by chemical vapor deposition under the following conditions: the raw material composition is AlCl3: 2.0~4.0 mol%, CO2: 1.0~2.5 mol%, HCl: 2.0~4.0 mol%, H2S: 0.6~1.0 mol%, H2: remainder, the temperature is 970~1030°C, and the pressure is 60~80 hPa (film formation step 2). In this case, the processing time for film formation step 2 is preferably such that the thickness of the film formed by film formation step 2 becomes 50%~70% of the average thickness of the target lower α-type Al2O3 layer, and more preferably 60%.

[0072] Furthermore, after the film formation step 2, the third stage of the α-type Al2O3 layer of the lower α-type Al2O3 layer may be formed by chemical vapor deposition under the following conditions: the raw material composition is AlCl3: 4.0~7.0 mol%, CO2: 1.5~3.0 mol%, HCl: 0.3~0.8 mol%, H2S: 0.6~1.0 mol%, H2: remainder, the temperature is 930~970°C, and the pressure is 100~140 hPa (film formation step 3). In this case, the processing time for film formation step 3 is preferably such that the thickness of the film formed by film formation step 3 becomes 25%~35% of the average thickness of the target lower α-type Al2O3 layer, and more preferably 30%.

[0073] To keep RSA (area %) within a predetermined range, the proportion of H2S in the raw material composition can be controlled in film deposition step 1 and / or film deposition step 2. Specifically, for example, increasing the proportion of H2S in the raw material composition of film deposition step 1 and / or film deposition step 2 tends to increase RSA.

[0074] In the lower α-type Al2O3 layer, in order to keep the average particle size within a predetermined range in the direction parallel to the substrate surface at a position 0.2 μm toward the substrate side from the lowest point of each recess on the surface of the lower α-type Al2O3 layer opposite to the substrate in the observation field for determining the average angle β (degrees), the proportions of CO2 and / or HCl in the raw material composition can be controlled in the film formation process 1. Specifically, for example, by decreasing the proportion of CO2 or increasing the proportion of HCl in the raw material composition of the film formation process 1, the average particle size tends to increase.

[0075] To keep the average angle β within a predetermined range, the proportions of AlCl3 and / or HCl in the raw material composition can be controlled during the film formation process 3. Specifically, for example, increasing the proportion of AlCl3 or decreasing the proportion of HCl in the raw material composition of the film formation process 3 tends to increase the average angle β.

[0076] Next, an intermediate layer is formed on the surface of the lower α-type Al2O3 layer, comprising one or more Ti compound layers made of Ti and at least one element selected from the group consisting of C, N, O, and B. The intermediate layer can be formed, for example, by the following method.

[0077] For example, a Ti compound layer consisting of a Ti carbonitroxide layer as an intermediate layer can be formed by chemical vapor deposition using a raw material composition of TiCl4: 4.0-7.0 mol%, CO: 2.0-4.0 mol%, N2: 30-40 mol%, H2: the remainder, at a temperature of 930-970°C and a pressure of 80-120 hPa.

[0078] The Ti compound layer, consisting of a Ti carbon oxide layer as an intermediate layer, can be formed by chemical vapor deposition using a raw material composition of TiCl4: 4.0-7.0 mol%, CO: 2.0-4.0 mol%, and H2: the remainder, at a temperature of 930-970°C and a pressure of 80-120 hPa.

[0079] After the intermediate layer is formed, an α-type Al2O3 layer of the upper α-type Al2O3 layer is formed on its surface. For example, this layer can be formed by the following method. First, the surface of the intermediate layer is oxidized. Then, a nucleation process is carried out to form an upper α-type Al2O3 layer on the surface of the intermediate layer.

[0080] More specifically, oxidation of the surface of the intermediate layer may be carried out under conditions where the raw material composition is CO2: 0.3 to 1.0 mol%, H2: the remainder, the temperature is 950 to 1050°C, and the pressure is 50 to 60 hPa (oxidation step 2). The oxidation treatment time in this case is preferably 1 to 5 minutes.

[0081] Subsequently, a nucleation process is performed to form nuclei on the surface of the intermediate layer. The nucleation process may be carried out by chemical vapor deposition under the following conditions: the raw material composition is AlCl3: 3.0-7.0 mol%, CO2: 2.0-5.0 mol%, HCl: 3.0-5.0 mol%, H2: the remainder, the temperature is 950-1050°C, and the pressure is 70-90 hPa (nucleation process 2). In this case, the processing time for nucleation process 2 is preferably 1-10 minutes.

[0082] Subsequently, the formation of the upper α-type Al2O3 layer may be carried out by chemical vapor deposition under the following conditions: the raw material composition is AlCl3: 2.0-4.0 mol%, CO2: 4.0-7.0 mol%, HCl: 1.0-2.5 mol%, H2S: 0.05-0.10 mol%, H2: remainder, the temperature is 930-970°C, and the pressure is 100-140 hPa (film formation step 4).

[0083] To keep the RSB (area %) within a predetermined range, the proportion of CO in the raw material composition during the intermediate layer formation process and the proportion of CO2 in the raw material composition during the film deposition process 4 should be controlled. Specifically, increasing the proportion of CO in the raw material composition during the intermediate layer formation process or increasing the proportion of CO2 in the raw material composition during the film deposition process 4 tends to increase the RSB. Furthermore, if the average thickness of the intermediate layer is kept within a predetermined range, the RSB tends to increase.

[0084] An outer layer, such as a TiCNO layer, TiN layer, or TiCN layer, may be formed on the surface of the upper α-type Al2O3 layer, if necessary. The outer layer can be formed, for example, by the following method.

[0085] The TiN layer, which serves as the outer layer, can be formed by chemical vapor deposition using a raw material composition of TiCl4: 5.0-10.0 mol%, N2: 20-60 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 300-400 hPa.

[0086] The TiCN layer, which serves as the outer layer, can be formed by chemical vapor deposition using a raw material composition of TiCl4: 4.0-8.0 mol%, CH3CN: 0.5-2.0 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 60-80 hPa.

[0087] The TiCNO layer, which serves as the outer layer, can be formed by chemical vapor deposition using a raw material composition of TiCl4: 3.0-4.0 mol%, CO: 0.5-1.0 mol%, N2: 30-40 mol%, and H2: the remainder, at a temperature of 950-1050°C and a pressure of 80-120 hPa.

[0088] The coated cutting tools of this embodiment are thought to have the effect of extending tool life compared to conventional tools, at least due to their superior fracture resistance and wear resistance (however, the factors that can extend tool life are not limited to those mentioned above). Specifically, examples of coated cutting tools of this embodiment include replaceable cutting inserts for milling or turning, drills, and end mills. [Examples]

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0090] [Inventions 1-27 and Comparative Products 1-17] As a base material, a cemented carbide alloy with the composition 88.5%WC-6.7%Co-1.4%TiC-0.6%TiN-0.5%TaC-2.0%NbC-0.2%ZrC-0.1%Cr3C2 (all by mass%) was prepared, machined into an insert shape from CNMG120408. After round honing of the cutting edge ridge of this base material using a SiC brush, the surface of the base material was cleaned.

[0091] After cleaning the surface of the substrate, a coating layer was formed by chemical vapor deposition. First, the substrate was placed in the thermal chemical vapor deposition apparatus, and under the raw material composition, temperature, and pressure conditions shown in Table 1, a first layer with the composition shown in Tables 14 and 15 was formed on the surface of the substrate to the average thickness shown in Tables 14 and 15. Next, under the raw material composition, temperature, and pressure conditions shown in Table 1, a second layer, as shown in Tables 14 and 15, was formed on the surface of the first layer to the average thickness shown in Tables 14 and 15. Then, under the raw material composition, temperature, and pressure conditions shown in Table 1, a third layer, as shown in Tables 14 and 15, was formed on the surface of the second layer to the average thickness shown in Tables 14 and 15. This formed a lower layer consisting of three layers. Subsequently, under the raw material composition, temperature, and pressure conditions shown in Table 2, the surface of the third layer was subjected to oxidation treatment for the time shown in Table 2.

[0092] Next, the nucleation process for the lower α-type Al2O3 layer was carried out on the surface of the oxidized third layer under the raw material composition, temperature, and pressure conditions shown in Table 2, for the time shown in Table 2. Subsequently, a film deposition process 1 was carried out on the surface of the third layer under the raw material composition, temperature, and pressure conditions shown in Tables 4 and 5. Then, a film deposition process 2 was carried out under the raw material composition, temperature, and pressure conditions shown in Tables 6 and 7. Then, a film deposition process 3 was carried out under the raw material composition, temperature, and pressure conditions shown in Tables 8 and 9, so that the average thickness T1 of the lower α-type Al2O3 layer would be the average thickness shown in Tables 14 and 15. The layer formed in film deposition process 1 was formed to have a thickness of 10% of the desired average thickness T1 of the lower α-type Al2O3 layer, the layer formed in film deposition process 2 was formed to have a thickness of 60% of the desired average thickness T1 of the lower α-type Al2O3 layer, and the layer formed in film deposition process 3 was formed to have a thickness of 30% of the desired average thickness T1 of the lower α-type Al2O3 layer. However, as an exception, in comparative product 12, the layer formed in film deposition step 1 was formed to have a thickness of 10% of the desired average thickness T1 of the lower α-type Al2O3 layer, and the layer formed in film deposition step 2 was formed to have a thickness of 90% of the desired average thickness T1 of the lower α-type Al2O3 layer.

[0093] Next, an intermediate layer was formed on the surface of the lower α-type Al2O3 layer under the raw material composition, temperature, and pressure conditions shown in Tables 10 and 11, such that the overall average thickness was as shown in Tables 16 and 17. Subsequently, the surface of the intermediate layer was subjected to oxidation treatment under the raw material composition, temperature, and pressure conditions shown in Table 3, for the time shown in Table 3.

[0094] Next, a nucleation process for the upper α-type Al2O3 layer was carried out on the surface of the oxidized intermediate layer under the raw material composition, temperature, and pressure conditions shown in Table 3, for the time shown in Table 3. Subsequently, an upper α-type Al2O3 layer was formed on the surface of the intermediate layer under the raw material composition, temperature, and pressure conditions shown in Tables 12 and 13, by adjusting the deposition time so that the average thickness T2 of the upper α-type Al2O3 layer was the average thickness shown in Tables 16 and 17. However, comparative samples 11 and 12 did not form an intermediate layer or an upper α-type Al2O3 layer.

[0095] Furthermore, for Inventions 24 to 26, Comparative Products 11 and 12, an outer layer with the composition described in Tables 16 and 17 was formed on the surface of the upper α-type Al2O3 layer under the raw material composition, temperature, and pressure conditions shown in Table 1, so as to have the average thickness described in Tables 16 and 17. Thus, coated cutting tools, inventions 1-27 and comparative inventions 1-17, were obtained.

[0096] The thickness of each layer in the sample was determined by the method described above. The measurement results are shown in Tables 14 to 17.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] Table 4

[0101] Table 5

[0102] Table 6

[0103] Table 7

[0104] Table 8

[0105] Table 9

[0106] Table 10

[0107] Table 11

[0108] Table 12

[0109] Table 13

[0110] [Table 14]

[0111] [Table 15]

[0112] [Table 16]

[0113] [Table 17]

[0114] [Measurement of average angle β] The average angle β was measured using the method described above.

[0115] [Measurement and calculation of RSA and RSB] For RSA and RSB, the following measurement cross-sections were observed using an electrolytic emission scanning electron microscope (FE-SEM) under the conditions described below. The total cross-sectional areas of particles with orientation difference A between 0 and 15 degrees, and the total cross-sectional areas of particles with orientation difference B between 0 and 15 degrees, were measured using the electron backscattering imaging device (EBSD) attached to the FE-SEM, according to the "(Method for measuring the cross-sectional area of ​​particles with a specific orientation difference)" described below. From the obtained values, RSA was calculated as the ratio of the cross-sectional area of ​​particles whose orientation difference A, which is the angle between the normal to the surface of the substrate and the normal to the (001) plane of the particles in the lower α-type Al2O3 layer, is between 0 degrees and 15 degrees, when the total area of ​​the entire cross-section in the lower α-type Al2O3 layer perpendicular to the surface of the substrate is set to 100 area %. In the cross-section of the upper α-type Al2O3 layer perpendicular to the surface of the substrate, assuming the total area of ​​the entire cross-section is 100 area%, the RSB was calculated as the ratio of the cross-sectional area of ​​particles whose orientation difference B, which is the angle between the normal of the line segment created when determining the average angle β (degrees) and the normal of the (110) plane of the particles in the upper α-type Al2O3 layer, is between 0 degrees and 15 degrees. However, the orientation difference B was calculated for each divided region by dividing the upper α-type Al2O3 layer into sections using the normals of the substrate surface that pass through each lowest point of the identified recess and each highest point of the convex portion within the observation field used to determine the average angle β (degrees). The measurement results are shown in Tables 18 and 19. (conditions) • Method for machining the measurement cross-section RSA and RSB: Coated cutting tools were polished using diamond paste to obtain a cross-sectional microstructure perpendicular to the surface of the substrate. Then, finish polishing was performed using colloidal silica to obtain a mirror-polished surface of the cross-sectional microstructure. • Measurement cross-section RSA: Cross-section of the lower α-type Al2O3 layer perpendicular to the surface of the substrate. RSB: Cross-section of the upper α-type Al2O3 layer perpendicular to the surface of the substrate. ·Direction difference RSA: Orientation difference A (angle between the normal to the surface of the substrate and the normal to the (001) plane of the particles in the lower α-type Al2O3 layer (unit: degrees)) RSB: Azimuth Difference B (The angle between the normal of the line segment created when determining the average angle β (degrees) and the normal of the (110) plane of the particles in the upper α-type Al2O3 layer (unit: degrees))

[0116] (Method for measuring the cross-sectional area of ​​particles with a specific orientation difference) The sample was placed in the FE-SEM. The sample was irradiated with an electron beam at an incidence angle of 70 degrees, with an acceleration voltage of 15 kV and an irradiation current of 1.0 nA. The orientation difference and cross-sectional area of ​​each particle were measured in a measurement range of 30 μm × 50 μm with an EBSD setting of a step size of 0.05 μm. The cross-sectional area of ​​a particle within the measurement range was defined as the sum of the pixels corresponding to that cross-sectional area. That is, in each layer, the sum of the cross-sectional areas of particles in the range of 0 degrees to 15 degrees based on orientation difference A or orientation difference B was calculated by totaling the pixels occupied by the particle cross-sections corresponding to each range and converting them to area.

[0117] [Average particle size of α-type Al2O3 particles in the lower α-type Al2O3 layer] For the obtained inventions 1-27 and comparative products 1-17, the average particle size of the α-type Al2O3 particles constituting the lower α-type Al2O3 layer was measured using an EBSD attached to the FE-SEM. Specifically, a coated cutting tool was polished using diamond paste to obtain a cross-sectional structure parallel to the surface of the substrate. Then, finish polishing was performed using colloidal silica to obtain a mirror-polished surface of the cross-sectional structure. The sample with the cross-sectional structure was set in the FE-SEM, and the sample was irradiated with an electron beam at an incident angle of 70 degrees with an acceleration voltage of 15 kV and an irradiation current of 1.0 nA. Measurements were performed in a measurement range of 30 μm × 50 μm with an EBSD setting of a step size of 0.05 μm. Using EBSD, the average particle size of particles in the lower α-type Al2O3 layer of a coated cutting tool was measured in a direction parallel to the substrate surface, at a position 0.2 μm toward the substrate from the lowest point of each recess on the surface of the lower α-type Al2O3 layer opposite the substrate in the observation field used to determine the average angle β (degrees). More specifically, first, if there was an orientation difference of 5 degrees or more between adjacent measurement points, that point was defined as a grain boundary. The region enclosed by the grain boundary was defined as one crystal grain, and the average grain size was calculated. A straight line was drawn parallel to the surface of the substrate at a position 0.2 μm toward the substrate from the lowest point located closest to the substrate. Next, the number of crystal grains contained within the range of the straight line was determined. The value obtained by dividing the length of the straight line by the number of crystal grains was taken as the average grain size of α-type Al2O3 in the lower α-type Al2O3 layer. In this case, the length of the straight line was set to 40 μm. The obtained average grain size results are shown in Tables 18 and 19.

[0118] [Table 18]

[0119] [Table 19]

[0120] The obtained samples were used to perform the following cutting tests and evaluations.

[0121] [Cutting Test 1] • Insert: CNMG120408 (ISO standard) Base material composition: 88.5%WC-6.7%Co-1.4%TiC-0.6%TiN-0.5%TaC-2.0%NbC-0.2%ZrC-0.1%Cr3C2 (mass%), ·Work material: S45C, • Workpiece shape: round bar, ·Cutting speed: 350m / min, • Cutting depth: 2.0 mm, Feed rate: 0.3mm / rev, • Coolant: Water-soluble coolant, • Evaluation item: Tool life was defined as the machining time (minutes) until the maximum flank wear width of the sample reached 0.3 mm. The better the wear resistance and resistance to plastic deformation, the longer the tool life (machining time) in this cutting test.

[0122] [Cutting Test 2] • Insert: CNMG120408 (ISO standard) Base material composition: 88.5%WC-6.7%Co-1.4%TiC-0.6%TiN-0.5%TaC-2.0%NbC-0.2%ZrC-0.1%Cr3C2 (mass%), ·Work material: S45C, • Workpiece shape: A round bar with four equally spaced grooves on its outer surface. ·Cutting speed: 240m / min, • Cutting depth: 1.5mm, Feed rate: 0.15mm / rev, • Coolant: Water-soluble coolant, • Evaluation criteria: Tool life was defined as the point at which the sample fractured, and the number of impacts until tool life was measured. The better the fracture resistance, the longer the tool life (more impacts) in this cutting test.

[0123] The results of the evaluations obtained are shown in Tables 20 and 21. For cutting test 1, the processing time was evaluated as "A" for 28 minutes or more, "B" for 20 minutes or more but less than 28 minutes, and "C" for less than 20 minutes. For cutting test 2, the number of impacts was evaluated as "A" for 10,000 or more, "B" for 7,000 or more but less than 10,000, and "C" for less than 7,000.

[0124] [Table 20]

[0125] [Table 21]

[0126] As shown in Tables 20 and 21, the invention received a rating of B or higher in both Cutting Test 1 and Cutting Test 2. Based on these results, the coated cutting tool comprises a base material and a coating layer formed on the surface of the base material, wherein the coating layer includes, in order from the base material side toward the surface of the coating layer, a lower layer, a lower α-type Al2O3 layer, an intermediate layer, and an upper α-type Al2O3 layer, the lower layer includes one or more Ti compound layers made of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B, the average thickness of the lower layer is 3.00 μm or more and 15.00 μm or less, the average thickness T1 of the lower α-type Al2O3 layer is 2.00 μm or more and 15.00 μm or less, and the lower α-type A The invention, which satisfies the conditions represented by formula (1) in the I2O3 layer, satisfies the conditions represented by formula (2) in the lower α-type Al2O3 layer, and includes one or more Ti compound layers in the intermediate layer, which consist of Ti and at least one element selected from the group consisting of C, N, O, and B, with an average thickness of the intermediate layer of 0.05 μm or more and 1.00 μm or less, and an average thickness T2 of the upper α-type Al2O3 layer of 0.50 μm or more and 5.00 μm or less, and satisfies the conditions represented by formula (3) in the upper α-type Al2O3 layer, was found to have excellent fracture resistance and wear resistance and a long tool life. [Industrial applicability]

[0127] The coated cutting tool of the present invention has excellent fracture resistance and wear resistance, which extends tool life compared to conventional tools, and therefore has high potential for industrial application. [Explanation of Symbols]

[0128] 1...Base material, 2...Lower layer, 3...Lower α-type Al2O3 layer, 4...Middle layer, 5...Upper α-type Al2O3 layer, 6...Coating layer, 7...Coated cutting tool

Claims

1. A coated cutting tool comprising a base material and a coating layer formed on the surface of the base material, The coating layer consists of a lower layer and a lower α-type Al layer, extending from the substrate side toward the surface of the coating layer. 2 O 3 Layers, intermediate layers, and upper α-type Al 2 O 3 The layers and are included in this order. The lower layer comprises one or more Ti compound layers, each consisting of a Ti compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the lower layer is 3.00 μm or more and 15.00 μm or less. The lower α-type Al 2 O 3 The average thickness T1 of the layer is 2.00 μm or more and 15.00 μm or less. The lower α-type Al 2 O 3 In the layer, the following condition expressed by equation (1) is satisfied, 60 ≤ RSA < 100 (1) (In formula (1), RSA is the lower α-Al in the direction perpendicular to the surface of the base material when measured under the conditions of a measurement range of 30 μm × 50 μm and a step size of 0.05 μm 2 2O 3 In the cross-section of the layer, when the total area of the entire cross-section is defined as 100 area%, the lower α-Al 2 2O 3 is the area percentage (unit: area%) of the cross-sectional area of particles whose orientation difference A, which is the angle formed between the normal line of the base material surface and the normal line of the (001) plane of the particles of the layer, is 0 degrees or more and 15 degrees or less.) The lower α-type Al 2 O 3 In the layer, the following condition expressed by equation (2) is satisfied, 15≦average angle β≦45 (2) (In equation (2), the average angle β (degrees) is expressed by the following equation (2-1).) [Math 1] (In formula (2-1), L n This refers to the lower α-type Al in the direction perpendicular to the surface of the substrate when measured under the conditions of a measurement range of 30 μm × 50 μm and a step size of 0.05 μm. 2 O 3 In the observation field including the cross-section of the layer, the lower α-type Al 2 O 3 The lowest point of each recess and the highest point of each protrusion on the surface of the layer opposite to the substrate are identified, and the length (μm) of the nth line segment from the left in the observation field is represented by a line segment formed by connecting the lowest point of each identified recess with the highest point of the protrusion adjacent to the lowest point of the recess. n This represents the nth angle (in degrees) from the left of the observation field, among the angles formed by each of the created line segments and the straight line parallel to the substrate surface. However, the region of the observation field is defined as each (L) in the direction parallel to the substrate surface. n ×nosβ n This refers to a region where the total length of the elements is 50 μm or more. The aforementioned intermediate layer comprises one or more Ti compound layers, each consisting of a Ti compound comprising Ti and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the intermediate layer is 0.05 μm or more and 1.00 μm or less. The aforementioned upper α-type Al 2 O 3 The average thickness T2 of the layer is 0.50 μm or more and 5.00 μm or less. The aforementioned upper α-type Al 2 O 3 In the layer, the following conditions are satisfied: 50<RSB<100 (3) (In formula (3), RSB is the upper α-type Al in the direction perpendicular to the surface of the substrate when measured under the conditions of a measurement range of 30 μm × 50 μm and a step size of 0.05 μm) 2 O 3 In the cross-section of the layer, if the total area of ​​the entire cross-section is set to 100 area%, the normal of the line segment created when determining the average angle β (degrees) and the upper α-type Al 2 O 3 This is the percentage of the cross-sectional area (unit: area %) of particles whose orientation difference B, which is the angle made with the normal of the (110) plane of the particle in the layer, is between 0 degrees and 15 degrees. However, the orientation difference B is determined in the observation field for determining the average angle β (degrees), where the upper α-type Al 2 O 3 The layers are divided by the normals to the surface of the substrate that pass through the lowest points of the recesses and the highest points of the protrusions, and the region is determined for each divided area. Coated cutting tools.

2. The lower α-type Al 2 O 3 In the layer, the lower α-type Al in the observation field for determining the average angle β (degrees) 2 O 3 The average particle size in the direction parallel to the surface of the substrate at a position 0.2 μm toward the substrate from the lowest point of each recess on the surface of the layer opposite to the substrate is 0.3 μm or more and 2.0 μm or less. The coated cutting tool according to claim 1.

3. The aforementioned upper α-type Al 2 O 3 The lower α-type Al relative to the average thickness T2 of the layer 2 O 3 The ratio of the average layer thickness T1 (T1 / T2) is between 1.0 and 12.

0. A coated cutting tool according to claim 1 or claim 2.

4. The average thickness of the coating layer is 8.00 μm or more and 25.00 μm or less. A coated cutting tool according to claim 1 or claim 2.

5. The substrate is a cemented carbide, cermet, ceramic, or cubic boron nitride sintered body. A coated cutting tool according to claim 1 or claim 2.

Images