Coated cemented carbide and tools

Abstract

The coated cemented carbide comprises a substrate made of cemented carbide and a diamond layer disposed directly on at least a portion of the substrate, wherein the cemented carbide contains tungsten carbide particles and cobalt, the substrate comprises an outer region having a gradient composition in which the cobalt content increases from the interface with the diamond layer toward the interior of the substrate, and an inner region located more toward the interior of the substrate than the outer region, wherein the cobalt content in the inner region is 2 mass% or more, and the percentage (T2 / T1)×100 of the standard deviation T2 μm of the thickness of the outer region relative to the average thickness T1 μm of the outer region is 30% or less.

Description

[Technical Field]

[0001] The present disclosure relates to coated cemented carbides and tools. [Background technology]

[0002] Conventionally, coated cemented carbide, which includes a substrate made of cemented carbide and a diamond layer disposed directly on at least a portion of the substrate, has been used as a material for cutting tools and the like (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 03-094062 [Patent Document 2] International Publication No. 2004 / 031437 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-038150 Summary of the Invention

[0004] The coated cemented carbide of the present disclosure comprises: A coated cemented carbide comprising a substrate made of cemented carbide and a diamond layer disposed directly on at least a portion of the substrate, The cemented carbide includes tungsten carbide particles and cobalt; the substrate includes an outer region having a gradient composition in which the cobalt content increases from the interface with the diamond layer toward the interior of the substrate, and an inner region located closer to the interior of the substrate than the outer region; the cobalt content in the inner region is 2% by mass or more; The percentage (T2 / T1)×100 of the standard deviation T2 μm of the thickness of the outer region to the average thickness T1 μm of the outer region is 30% or less. [Brief explanation of the drawings]

[0005] [Figure 1]FIG. 1 is a diagram schematically showing a cross section of a coated cemented carbide according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged view of region II in FIG. [Figure 3] FIG. 3 is a perspective view illustrating one embodiment of a tool. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] When a coated cemented carbide having a substrate made of cemented carbide and a diamond layer disposed directly on at least a portion of the substrate is used as a material for a tool such as a cutting tool, the resistance to peeling of the diamond layer from the substrate (i.e., "peeling resistance") may be insufficient. Therefore, when such a coated cemented carbide is used for a tool such as a cutting tool, the tool life may be insufficient.

[0007] Therefore, an object of the present disclosure is to provide a coated cemented carbide having excellent peeling resistance and a tool made of the coated cemented carbide.

[0008] [Effects of this disclosure] According to the present disclosure, it is possible to provide a coated cemented carbide having excellent peeling resistance and a tool made of the coated cemented carbide.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The coated cemented carbide of the present disclosure is A coated cemented carbide comprising a substrate made of cemented carbide and a diamond layer disposed directly on at least a portion of the substrate, the cemented carbide includes tungsten carbide particles and cobalt; the substrate includes an outer region having a gradient composition in which the cobalt content increases from the interface with the diamond layer toward the interior of the substrate, and an inner region located closer to the interior of the substrate than the outer region, The cobalt content in the internal region is 2% by mass or more, The percentage (T2 / T1)×100 of the standard deviation T2 μm of the thickness of the outer region to the average thickness T1 μm of the outer region is 30% or less.

[0010] According to the present disclosure, it is possible to provide a coated cemented carbide having excellent peeling resistance and a tool made of the coated cemented carbide.

[0011] (2) In the above (1), the average thickness T1 of the outer region may be 1 μm or more and 5 μm or less, thereby providing a coated cemented carbide having better peeling resistance and a tool made of the coated cemented carbide.

[0012] (3) In the above (1) or (2), the average thickness of the diamond layer may be 3 μm or more and 28 μm or less, thereby providing a coated cemented carbide having superior peeling resistance and a tool made of the coated cemented carbide.

[0013] (4) In any one of the above (1) to (3), in a cross section of the coated cemented carbide taken along the normal direction of the surface of the diamond layer, the substrate has a recess having a depth of 1 μm or more at the interface between the substrate and the diamond layer, The average width of the recess at a depth of 1 μm from the recess may be 1 μm or more and 3 μm or less, thereby making it possible to provide a coated cemented carbide having superior peeling resistance and a tool made of the coated cemented carbide.

[0014] (5) In (4) above, in a rectangular field of view provided on the cross section, which includes the interface between the substrate and the diamond layer, and which has a length of 80 μm along the normal to the surface of the diamond layer and a length of 110 μm along the surface of the diamond layer, the number of first indentations whose width at a depth of 1 μm from the indentation exceeds 10 μm may be 1 or less. This makes it possible to provide a coated cemented carbide having superior peeling resistance and a tool made of the coated cemented carbide.

[0015] (6) In any of the above (1) to (5), the content of the tungsten carbide particles in the cemented carbide may be 90% by mass or more and 98% by mass or less, thereby providing a coated cemented carbide having superior peeling resistance and a tool made of the coated cemented carbide.

[0016] (7) In any of the above (1) to (6), the content of cobalt in the cemented carbide may be 2% by mass or more and 10% by mass or less, thereby providing a coated cemented carbide having better peeling resistance and a tool made of the coated cemented carbide.

[0017] (8) The tool of the present disclosure is made of the coated cemented carbide described in (1) to (7) above.

[0018] According to the present disclosure, a tool made of a coated cemented carbide having excellent peeling resistance can be provided.

[0019] [Details of the embodiments of the present disclosure] A specific example of a coated cemented carbide according to one embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference symbols 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.

[0020] In this disclosure, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and if no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0021] 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.

[0022] [Embodiment 1: Coated cemented carbide] A coated cemented carbide according to an embodiment of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a diagram schematically showing a cross section of a coated cemented carbide according to an embodiment of the present disclosure. Figure 2 is an enlarged view of region II in Figure 1. One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is A coated cemented carbide (3) comprising a substrate (1) made of cemented carbide and a diamond layer (2) disposed directly on at least a portion of the substrate (1), The cemented carbide includes tungsten carbide particles and cobalt; the substrate 1 includes an outer region R2 having a gradient composition in which the cobalt content increases from the interface with the diamond layer 2 toward the interior of the substrate 1, and an inner region R1 located closer to the interior of the substrate 1 than the outer region R2; The cobalt content in the internal region R1 is 2% by mass or more, The percentage (T2 / T1)×100 of the standard deviation T2 μm of the thickness of the outer region R2 to the average thickness T1 μm of the outer region R2 is 30% or less.

[0023] According to the present disclosure, it is possible to provide a coated cemented carbide 3 having excellent peeling resistance and a tool made of the coated cemented carbide 3. The reason for this is presumed to be as follows.

[0024] In the coated cemented carbide 3 of this embodiment, the substrate 1 includes an outer region R2 having a gradient composition in which the cobalt content increases from the interface with the diamond layer 2 toward the interior of the substrate 1, and an inner region R1 located closer to the interior of the substrate 1 than the outer region R2, the cobalt content of the inner region R1 being 2 mass% or more, and the percentage (T2 / T1)×100 of the standard deviation T2μm of the thickness of the outer region R2 relative to the average thickness T1μm of the outer region R2 being 30% or less. This allows the variation in thickness of the outer region R2 to be kept sufficiently low, thereby improving the adhesion between the substrate 1 and the diamond layer 2 and thereby improving the peeling resistance of the coated cemented carbide 3.

[0025] ≪Base material≫ The coated cemented carbide 3 includes a substrate 1 made of a cemented carbide. The cemented carbide includes tungsten carbide particles and cobalt. The cemented carbide may further include nickel. The cemented carbide may further include other components within a range that does not impair the effects of the present disclosure. Examples of other components include carbides, nitrides, or carbonitrides containing at least one element selected from the group consisting of titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), hafnium (Hf), and molybdenum (Mo), as well as inevitable impurities. Examples of inevitable impurities include iron (Fe), calcium (Ca), oxygen (O), and sulfur (S).

[0026] The content of tungsten carbide particles in the cemented carbide alloy may be 90% by mass or more and 98% by mass or less. This ensures a sufficient area of the contact interface between the tungsten carbide particles, which have high adhesion, and the diamond particles in the diamond layer 2 described below, thereby further improving the peeling resistance of the coated cemented carbide alloy 3. The content of tungsten carbide particles in the cemented carbide alloy may be 91% by mass or more and 97% by mass or more, or 92% by mass or more and 96% by mass or less. The tungsten carbide particles include at least one of "pure WC particles (including WC containing no impurity elements and WC containing impurity elements below the detection limit)" and "WC particles containing impurity elements intentionally or unavoidably contained therein, as long as the effects of the present disclosure are not impaired." The impurity content of the tungsten carbide particles (when two or more elements constituting the impurities are present, the total content of these elements) is less than 0.1% by mass. The content of impurity elements in the tungsten carbide particles is measured by ICP optical emission spectroscopy (Inductively Coupled Plasma Emission Spectroscopy, measuring device: "ICPS-8100" (trademark) manufactured by Shimadzu Corporation).

[0027] The cobalt content in the cemented carbide may be 2% by mass or more and 10% by mass or less, thereby suppressing the generation of graphite due to the presence of cobalt, and further improving the peeling resistance of the coated cemented carbide 3. The cobalt content in the cemented carbide may be 3% by mass or more and 9% by mass or less, or 4% by mass or more and 8% by mass or less.

[0028] The composition of the base material 1 can be determined by determining the content of each component in the internal region R1 using ICP optical emission spectroscopy (measuring device: Shimadzu Corporation's "ICPS-8100" (trademark)) and calculating the average (arithmetic mean) of the content of each component in the internal region R1.

[0029] In the first embodiment, the average particle size of the tungsten carbide particles is not particularly limited. The average particle size of the tungsten carbide particles can be, for example, 0.5 μm or more and 3 μm or less. It has been confirmed that the coated cemented carbide 3 of the first embodiment can have excellent peeling resistance regardless of the average particle size of the tungsten carbide particles.

[0030] The average particle size of the tungsten carbide particles can be determined by the following steps (A1) to (H1). (A1) An arbitrary position of the coated cemented carbide 3 is cut out to expose a cross section, which is then mirror-polished using a cross-section polisher (manufactured by JEOL Ltd.). (B1) The region of the substrate 1 on the mirror-finished surface of the coated cemented carbide 3 is analyzed using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) (apparatus: Carl Zeiss Gemini450 (trademark)) to identify the elements contained in the substrate 1. (C1) A region of the substrate 1 on the mirror-finished surface of the coated cemented carbide 3 is photographed with a scanning electron microscope (SEM) to obtain a backscattered electron image. The photographed region of the photographed image is set to the center of the region of the substrate 1 in the cross section of the coated cemented carbide 3, that is, a position that does not include areas with properties that are clearly different from the bulk portion, such as near the interface between the diamond layer 2 and the substrate 1 (a position where the entire photographed region is the bulk portion of the substrate 1). The observation magnification is 5000x. The measurement conditions are an acceleration voltage of 3 kV, a current value of 2 nA, and a working distance (WD) of 5 mm. (D1) The photographed area in (C1) above is analyzed using an energy dispersive X-ray analyzer attached to an SEM (SEM-EDX), the distribution of the elements identified in (B1) above in the photographed area is identified, and an element mapping image is obtained. (E1) The backscattered electron image obtained in (C1) above is imported into a computer and binarized using image analysis software (OpenCV, SciPy). The binarization is performed so that only the tungsten carbide particles are extracted from the tungsten carbide particles and binder phase in the backscattered electron image. The binarization threshold varies depending on the contrast, so it is set for each image. (F1) By superimposing the elemental mapping image obtained in (D1) above on the binarized image obtained in (E1) above, the region where tungsten carbide particles exist is identified on the binarized image. Specifically, the region shown in white in the binarized image and containing tungsten (W) and carbon (C) in the elemental mapping image corresponds to the region where tungsten carbide particles exist. (G1) A rectangular measurement field of view of 12.0 μm × 8.2 μm is set in the image after the binarization process. Using the image analysis software, the outer edge of each tungsten carbide particle in the measurement field is identified, and the circle-equivalent diameter (Heywood diameter: diameter equivalent to a circle with equal area) of each tungsten carbide particle is calculated. (H1) Based on all tungsten carbide particles in the above measurement field, calculate the equivalent diameter D50 of the circle with the same area of the tungsten carbide particles.

[0031] It has been confirmed that as long as the same coated cemented carbide 3 is measured by the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0032] <Inner and outer areas> The substrate 1 includes an outer region R2 having a gradient composition in which the cobalt content increases from the interface with the diamond layer 2 toward the interior of the substrate 1, and an inner region R1 located closer to the interior of the substrate 1 than the outer region R2. The cobalt content in the inner region R1 is 2 mass % or more. The substrate 1 may consist of the outer region R2 and the inner region R1.

[0033] The percentage (T2 / T1)×100 of the standard deviation T2 μm of the thickness of the outer region R2 relative to the average thickness T1 μm of the outer region R2 is 30% or less. This improves the peeling resistance of the coated cemented carbide 3. The percentage (T2 / T1)×100 may be 1% or more and 30% or less, 3% or more and 25% or less, or 5% or more and 20% or less.

[0034] The average thickness T1 of the outer region R2 may be 1 μm or more and 5 μm or less, thereby further improving the peeling resistance of the coated cemented carbide 3. The average thickness T1 of the outer region R2 may be 1.5 μm or more and 4.5 μm or less, or the average thickness T1 of the outer region R2 may be 2 μm or more and 4 μm or less.

[0035] The standard deviation T2 μm of the thickness of the outer region R2 may be 0.2 μm or more and 1.5 μm or less, thereby further improving the peeling resistance of the coated cemented carbide 3. The standard deviation T2 μm of the thickness of the outer region R2 may be 0.25 μm or more and 1.25 μm or less, or 0.3 μm or more and 1.0 μm or less.

[0036] The average thickness T1 μm of the outer region R2 and the standard deviation T2 μm of the thickness of the outer region R2 can be determined by the following steps (A2) to (E2). (A2) The coated cemented carbide 3 is cut along a plane perpendicular to the surface of the diamond layer 2 to obtain a cross section, and the cross section is polished. (B2) Using an electron microscope, images are taken of two fields of view in a rectangular field of view of 25 μm length×40 μm width so that the diamond layer 2 and the substrate 1 are included. (C2) EDX (energy dispersive X-ray spectroscopy) line analysis is performed. Line analysis is performed with a width of approximately 8 μm, from the center point of the thickness of the diamond layer 2 to a point in the substrate 1 where the bonding phase has not been removed. The direction of the line analysis is perpendicular to the interface between the diamond layer 2 and the substrate 1. In the line analysis, the end point is the internal region where no voids are observed, extending from the above-mentioned center point beyond the external region where voids have occurred. Measurements are performed at any five points within one field of view. (D2) EDX analysis is used to obtain numerical data on the concentration profiles of tungsten atoms (W) and cobalt atoms (Co) in a CSV file, etc. (E2) Fitting is performed on the concentration profile. First, fitting is performed with "y = const." for the region where the concentrations of W and Co are constant (Step I). Let W: F(x) = a, Co: G(x) = b. Here, by confirming that the Co concentration in the fitting is 2 mass%, it is determined that the cobalt content in the internal region is 2 mass% or more. Next, fitting is performed with the linear function "y = ax + b" for the region where a concentration gradient of W and Co exists (Step II). The region to be fitted is the region that is centered at 50% of the constant value obtained in the fitting in Step I and falls within a certain range (for example, 50% ± 20% or 50% ± 30%) around it. Let W: H(x) = cx + d, Co: I(x) = ex + f. Next, the thickness of the external region R2 is calculated (Step III). The difference between the solution of H(x) = 0 (x coordinate where the W concentration rises) and the solution of G(x) = I(x) (x coordinate where the Co concentration starts to drop) is defined as the thickness of the outer region R2. Data is acquired from 10 arbitrary locations, and the average thickness T1 and standard deviation T2 are determined by calculating the average thickness and standard deviation.

[0037] As long as the same coated cemented carbide 3 is measured using the above method, it has been confirmed that there is no variation in the measurement results even if the measurement location is changed arbitrarily or the range of the fitting area in Step II is changed arbitrarily within the above range.

[0038] <Dent in the substrate> In a cross section of the coated cemented carbide 3 taken along the normal direction to the surface of the diamond layer 2, the substrate 1 may have a recess with a depth of 1 μm or more at the interface between the substrate 1 and the diamond layer 2, and the average width of the recess at a depth of 1 μm may be 1 μm or more and 3 μm or less. This suppresses the occurrence of local crack initiation points and provides an anchor effect due to the appropriate unevenness, thereby further improving the peeling resistance of the coated cemented carbide 3. The average width of the recess at a depth of 1 μm may be 1.5 μm or more and 2.5 μm or less.

[0039] The average width of the recess at a depth of 1 μm can be determined by the following steps (A3) to (D3). (A3) The coated cemented carbide 3 is cut along a plane perpendicular to the surface of the diamond layer 2 to obtain a cross section, and the cross section is polished. (B3) Using an electron microscope, two fields of view are taken, each measuring 80 μm vertically and 110 μm horizontally, so that the diamond layer 2 and the substrate 1 are included. The surface of the diamond layer 2 is imaged so that it is parallel to the edge of the image (Figure 2). (C3) Connect the two points on the WC grains that are closest to the surface of the diamond layer 2 within the field of view with a straight line L1, and draw a parallel line L2 at a distance of 1 μm from this line L1 on the substrate 1 side (Figure 2). (D3) Identify the areas of the diamond layer 2 located beyond the parallel line L2 on the substrate 1 side, measure the number of such areas and the length of the line segment on the parallel line L2 in each area (in other words, the width W1 of the depression at a depth of 1 μm from the depression), and calculate the average length of the line segment in a total of two fields of view to determine the average width of the depression (Figure 2).

[0040] It has been confirmed that as long as the same coated cemented carbide 3 is measured by the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0041] In a rectangular field of view provided on the cross section, which includes the interface between the substrate 1 and the diamond layer 2, and which has a length of 80 μm along the normal to the surface of the diamond layer 2 and a length of 110 μm along the surface of the diamond layer 2, the number of first indentations whose width at a depth of 1 μm from the indentation exceeds 10 μm may be 1 or less. This ensures a contact area between the substrate 1 and the diamond layer 2 and ensures the anchor effect between the substrate 1 and the diamond layer 2, thereby further improving the peeling resistance of the coated cemented carbide 3. The number of first indentations may be 0 or more and 1 or less, 0 or more and 0.8 or less, or 0 or more and 0.6 or less.

[0042] The number of first recesses can be determined by the following steps (A4) to (B4). (A4) Execute steps (A3) to (C3) above. (B4) A region of the diamond layer 2 located beyond the parallel line on the substrate 1 side is identified, and the number of primary dents in that region whose line segment length on the parallel line (in other words, the width of the dent at a depth of 1 μm) exceeds 10 μm is counted. The number of primary dents is determined by calculating the average value (arithmetic mean) of the two fields of view.

[0043] It has been confirmed that as long as the same coated cemented carbide 3 is measured by the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0044] <Diamond layer> <Diamond layer composition> The coated cemented carbide 3 includes a diamond layer 2 disposed directly on at least a portion of the substrate 1. Here, "directly on" is not limited to the front side of the coated cemented carbide 3 (i.e., the upper surface side of the substrate 1) during use, but also encompasses the back side of the coated cemented carbide 3 (i.e., the lower surface side of the substrate 1) during use. The diamond layer 2 refers to a layer containing diamond. The diamond may be polycrystalline diamond. Here, polycrystalline diamond refers to diamond particles of approximately 10-odd nanometers to several micrometers tightly bonded together. The diamond layer 2 may contain graphite, amorphous carbon, silicon atoms (Si), inevitable impurities (e.g., copper atoms (Cu), iron atoms (Fe), nickel atoms (Ni)), etc., as long as the effects of the present disclosure are not impaired. The presence of components other than diamond in the diamond layer 2 can be identified by X-ray diffraction (XRD), Raman spectroscopy, secondary ion mass spectrometry (SIMS), etc.

[0045] The coated cemented carbide 3 includes a diamond layer 2 disposed directly on at least a portion of the substrate 1. The average thickness of the diamond layer 2 may be 3 μm or more and 28 μm or less. This can alleviate local stress concentration when a load is applied to the diamond layer 2, thereby further improving the peeling resistance of the coated cemented carbide 3. The average thickness of the diamond layer 2 may be 4 μm or more and 27 μm or less, or may be 5 μm or more and 26 μm or less. The average thickness of the diamond layer 2 can be adjusted by appropriately changing the deposition time in the diamond layer formation step.

[0046] The average thickness of the diamond layer 2 can be determined, for example, by using a scanning electron microscope (SEM) to measure any five points on a cross-sectional sample parallel to the normal direction of the surface of the diamond layer 2 and averaging the thicknesses measured at the five points. For example, a focused ion beam device, a cross-section polisher device, etc. can be used to prepare the cross-sectional sample.

[0047] ≪Applications of coated cemented carbide≫ The coated cemented carbide 3 of this embodiment can be used for tools (cutting tools, saw blades, wear-resistant parts, etc.), molds, etc. Examples of cutting tools include cutting tools for general-purpose machining. More specifically, examples include drills, end mills, turning tools, indexable inserts, indexable cutting tips for drills, indexable cutting tips for end mills, indexable cutting tips for milling, indexable cutting tips for turning, metal saws, gear cutting tools, reamers, taps, etc.

[0048] [Embodiment 2: Method for manufacturing coated cemented carbide] The coated cemented carbide of this embodiment comprises, in this order, a step of preparing a substrate intermediate made of cemented carbide (hereinafter also referred to as the "substrate intermediate preparation step"), a step of performing a surface treatment on the surface of the substrate intermediate to obtain a substrate (hereinafter also referred to as the "surface treatment step"), and a step of forming a diamond layer on the substrate by chemical vapor deposition to obtain a coated cemented carbide (hereinafter also referred to as the "diamond layer formation step").

[0049] ≪Preparation process≫ In the preparation step, an intermediate substrate made of a cemented carbide is prepared. The intermediate substrate made of a cemented carbide may be prepared by manufacturing using a conventionally known method, or may be prepared by purchasing a commercially available product.

[0050] <Surface treatment process> In the surface treatment step, a substrate is obtained by performing a surface treatment on the surface of the substrate intermediate body made of cemented carbide. The surface treatment is performed by etching. Prior to the etching treatment, the surface treatment may further include a "sandblasting treatment" in which particles of alumina or silicon carbide are sprayed onto the substrate intermediate body, a "lapping treatment" in which the surface roughness of the substrate intermediate body is reduced, or both.

[0051] In the sandblasting process, the particle size may be, for example, 5 μm or more and 40 μm or less. This allows the "number of first recesses" described in embodiment 1 to be adjusted to a desired range. In the sandblasting process, the blasting pressure may be 0.1 MPa or more and 0.4 MPa or less.

[0052] Specific examples of lapping include mechanical polishing and ion milling. Examples of mechanical polishing include the AERO LAP (registered trademark) mirror polishing device. The lapping time may be, for example, 1 minute or more and 4 minutes or less. This allows the "average recess width" described in embodiment 1 to be adjusted to a desired range.

[0053] The etching treatment is performed by immersing the intermediate substrate in a mixed acid of sulfuric acid and nitric acid to dissolve a portion of the surface of the intermediate substrate. The etching treatment is performed while stirring the mixed acid. This allows the cobalt content in the outer region to be adjusted to a desired range, and the percentage (T2 / T1) × 100 of the standard deviation of the thickness of the outer region (T2 μm) relative to the average thickness (T1 μm) of the outer region directly below the diamond layer to be adjusted to a desired range. The sulfuric acid concentration in the mixed acid may be 10% by mass or more and 98% by mass or less, and the nitric acid concentration may be 10% by mass or more and 70% by mass or less. The time for which the intermediate substrate is immersed in the mixed acid (in other words, the etching treatment time) may be 0.5 minutes or more and 60 minutes or less. By adjusting the time for which the intermediate substrate is immersed in the mixed acid within the above range, the average thickness (T1 μm) of the outer region can be adjusted to a desired range. The stirring speed may be 100 rpm or more and 300 rpm or less.

[0054] <Diamond layer formation process> In the diamond layer formation process, a diamond layer is formed on a substrate by chemical vapor deposition to obtain a coated cemented carbide. Specifically, first, a seeding treatment is performed by applying diamond seed crystals to the surface of the substrate. At this time, the diamond seed crystals are dispersed in water at a concentration of 0.01 g / L or more, and the substrate is immersed in this diamond seed crystal aqueous solution.

[0055] The average particle size of the diamond seed crystals is preferably 0.005 μm or more and 0.5 μm or less. This results in an optimal diamond nucleation density, a lower average void area ratio in the diamond layer, and improved peeling resistance of the diamond layer. Here, "average particle size" refers to the median diameter (d50) in the volume-based particle size distribution (volume distribution). The particle size of each crystal grain used to calculate the average particle size of the diamond seed crystals is measured using a field emission scanning electron microscope (FE-SEM).

[0056] Next, a diamond layer is formed by CVD on the surface of the substrate on the side where the diamond seed crystal is seeded, to obtain a coated cemented carbide. Any conventionally known CVD method can be used as the CVD method. For example, microwave plasma CVD, plasma jet CVD, hot filament CVD, etc. can be used.

[0057] For example, a diamond layer can be formed on the substrate by placing the substrate in a hot filament CVD apparatus, introducing methane gas and hydrogen gas into the apparatus in a volumetric ratio of 0.5:99.5 to 10:90, and maintaining the substrate temperature at 700°C or higher and 900°C or lower.

[0058] [Embodiment 3: Tools] A tool according to an embodiment of the present disclosure will be described with reference to Fig. 3. Fig. 3 is a perspective view illustrating one aspect of the tool. The tool 10 according to this embodiment is made of the coated cemented carbide according to the first embodiment.

[0059] According to the present disclosure, it is possible to provide a tool made of a coated cemented carbide having excellent peeling resistance, for the reasons described in the first embodiment.

[0060] An example of the tool 10 of the present disclosure is a cutting tool having the shape shown in FIG.

[0061] <Tool manufacturing method> The method for manufacturing the tool 10 of the present disclosure can be carried out in the same manner as a conventionally known method, except that the coated cemented carbide described in the first embodiment is used. [Example]

[0062] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0063] <Production of coated cemented carbide> The coated cemented carbide samples 1 to 20 and 101 were produced by carrying out the following steps in the following order.

[0064] <Preparation process> As a substrate intermediate made of cemented carbide, a turning insert was prepared, whose material was WC-Co (cemented carbide) and whose shape was tool model number SNGN120408. The WC content and Co content in the WC-Co were adjusted to the contents [mass%] listed in Table 3.

[0065] <Surface treatment process> A substrate was obtained by performing a surface treatment on the surface of the turning cutting insert (substrate intermediate) under the conditions listed in Table 1. The sandblasting, lapping, and etching treatments were performed in this order. In Table 1, 0 rpm in the "Stirring speed [rpm]" column under "Etching treatment" means that no stirring was performed during the etching treatment. When stirring was performed during the etching treatment, the stirring was performed using a magnetic stirrer. In the etching treatment, a mixed acid containing sulfuric acid and nitric acid in a volume ratio of 1:3 was used. When lapping was performed, the surface of the substrate intermediate was polished using a dry shot mirror polisher for the time listed in Table 1.

[0066] <Diamond layer formation process> First, the surface of the substrate was seeded with diamond seed crystals. Next, a diamond layer was formed on the substrate by chemical vapor deposition under the conditions shown in Table 2 until the average thickness of the diamond layer reached the value shown in Table 3. The concentration of methane gas relative to hydrogen gas was 1% by volume.

[0067] According to the above procedure, coated cemented carbide samples 1 to 20 and 101 were produced.

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3]

[0071] <Characteristics evaluation of coated cemented carbide> <Average thickness T1 of the outer region and standard deviation T2 of the thickness of the outer region> For each of the coated cemented carbide samples, the average thickness T1 of the outer region was determined by the method described in embodiment 1. The results are shown in the "Average thickness T1 [μm]" column of the "Outer region" section of Table 3. In addition, for each of the coated cemented carbide samples, the standard deviation T2 of the thickness of the outer region was determined by the method described in embodiment 1. The results are shown in the "Standard deviation T2 [μm]" column of the "Outer region" section of Table 3.

[0072] <Average width of dent> For each coated cemented carbide sample, the average width of the dents at a depth of 1 μm from the dents was determined by the method described in embodiment 1. The results obtained are shown in the "Average width of dents [μm]" column of Table 3.

[0073] <Number of first recesses> For each coated cemented carbide sample, the number of primary dents having a width of more than 10 μm at a depth of 1 μm from the dents was determined by the method described in embodiment 1. The results obtained are shown in the "Number of primary dents" column in Table 3.

[0074] <Tungsten carbide particle content and cobalt content> For each of the coated cemented carbide alloy samples, the content of tungsten carbide particles in the cemented carbide alloy was determined by the method described in embodiment 1. The results are shown in the "WC particle content [mass%]" column of Table 3. Furthermore, for each of the coated cemented carbide alloy samples, the content of cobalt in the cemented carbide alloy was determined by the method described in embodiment 1. The results are shown in the "Co content [mass%]" column of Table 3.

[0075] <Cutting test> Using the coated cemented carbide of each sample as a cutting tool, milling was performed on the top surface of the following workpiece under the following conditions. Milling was performed until the diamond layer peeled off from the cutting tool, and the machined area until the peeling occurred was determined. The results obtained are shown in the "Cutting test" column of Table 3 under "Machined area [mm 2 The larger the processed area, the better the peel resistance. <Cutting conditions> Work material: A390 (aluminum alloy) Cutting speed Vc: 500m / min Feed per tooth: 0.2 mm / rev Cutting depth: 0.5 mm Cutting fluid: Water-soluble coolant

[0076] The coated cemented carbide samples 1 to 20 correspond to Examples. The coated cemented carbide sample 101 corresponds to Comparative Example. The results in Table 3 show that the coated cemented carbide samples 1 to 20 have superior peeling resistance compared to the coated cemented carbide sample 101.

[0077] From the above, it was found that the coated cemented carbide samples 1 to 20 had excellent peeling resistance.

[0078] Although the embodiments and examples of the present disclosure have been described above, it is originally intended that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways.

[0079] 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 embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0080] 1 base material, 2 diamond layer, 3 coated cemented carbide, R1 internal area, R2 external area, L1 straight line, L2 parallel line, W1 width, 10 tool, 1a rake face, 1b flank face, 1c cutting edge face

Claims

1. A coated cemented carbide comprising a substrate made of cemented carbide and a diamond layer disposed directly on at least a portion of the substrate, the cemented carbide includes tungsten carbide particles and cobalt; the substrate includes an outer region having a gradient composition in which the cobalt content increases from the interface with the diamond layer toward the interior of the substrate, and an inner region located closer to the interior of the substrate than the outer region, the cobalt content in the internal region is 2% by mass or more; The average thickness T of the outer region １ the standard deviation T of the thickness of the outer region, in μm ２ Percentage of μm (T ２ / T １ ) × 100 is 30% or less, The coated cemented carbide, wherein the average thickness T 1 of the outer region is 1 μm or more and 5 μm or less.

2. 2. The coated cemented carbide according to claim 1, wherein the average thickness of the diamond layer is 3 μm or more and 28 μm or less.

3. In a cross section of the coated cemented carbide taken along a normal direction to the surface of the diamond layer, the substrate has a recess having a depth of 1 μm or more at an interface between the substrate and the diamond layer, 3. The coated cemented carbide according to claim 1, wherein an average width of the recess at a depth of 1 μm from the recess is 1 μm or more and 3 μm or less.

4. 4. The coated cemented carbide according to claim 3, wherein in a rectangular field of view provided on the cross section, which includes an interface between the substrate and the diamond layer, and which has a length of 80 μm along the normal direction to the surface of the diamond layer and a length of 110 μm along the surface of the diamond layer, the number of first indentations whose width at a depth of 1 μm from the indentation exceeds 10 μm is 1 or less.

5. 3. The coated cemented carbide according to claim 1, wherein the content of the tungsten carbide particles in the cemented carbide is 90% by mass or more and 98% by mass or less.

6. 3. The coated cemented carbide according to claim 1, wherein the content of cobalt in the cemented carbide is 2% by mass or more and 10% by mass or less.

7. A tool made of the coated cemented carbide according to claim 1 or 2.