DIAMOND-COATED CEMENTED CARBIDE CUTTING TOOL

Abstract

In this diamond-coated cemented carbide cutting tool, (1) an average particle size of WC particles is 0.5 to 0.9 m, (2) (R.sub.z) being 0.5 to 1.0 m, a maximum distance between the concave and convex () is 0.5 to 1.5 m, a length (Y.sub.e) is 0.5 to 2.0 m, (3) a sum of areas of WC particles, which satisfies (L.sub.1) being 0.4 to 0.8 m, (L.sub.2) being 0.2 to 0.4 m, and (L.sub.1)/(L.sub.2) being 1.5 to 2.5, is 70 area % or more, (4) an average grain size of diamond crystals in a region of 0.5 to 1.5 m from the body interface is 0.1 to 0.3 m, and (5) columnar crystals satisfying at least one of: a ratio of crystals, which has a growth direction shifted in 10 degrees or less from the diamond film thickness direction, being 90% or more; or an orientation ratio of <110> being 30 to 70%.

Claims

1. A diamond-coated cemented carbide cutting tool comprising: a WC-based cemented carbide body containing 3 to 15 mass % of Co that is coated with a diamond film, wherein, in a cross section of the diamond-coated cemented carbide cutting tool in a diamond film thickness direction, (1) an average particle size of WC particles constituting the WC-based cemented carbide body is 0.5 to 0.9 m, (2) a maximum height difference (R.sub.z) of concave and convex of an interface of the WC-based cemented carbide body contacting the diamond film is 0.5 to 1.0 m, a maximum distance () between adjacent concave and convex of the WC-based cemented carbide body at the interface is 0.5 to 1.5 m, and a length (Y.sub.e) of the diamond film in the thickness direction in a region where a binder phase of the WC-based cemented carbide body is removed is 0.5 to 2.0 m, (3) when a sum of areas occupied by individual WC particles contacting the diamond film at the interface is defined as 100 area %, a sum of areas of WC particles, which satisfies a maximum value (L.sub.1) of vertex-to-vertex distances of the WC particles at a body interface being 0.4 to 0.8 m, a minimum value (L.sub.2) of a diameter of an inscribed-circle inscribed in the WC particle or distances between tangents of opposing faces being 0.2 to 0.4 m, and (L.sub.1)/(L.sub.2) being 1.5 to 2.5, is 70 area % or more, (4) an average grain size of diamond crystals in a region of 0.5 to 1.5 m from the WC-based cemented carbide body interface toward the diamond film is 0.1 to 0.3 m, and (5) the diamond-coated cemented carbide cutting tool comprises columnar crystals, which contact the top of the diamond crystals and constitute the diamond film, the columnar crystals satisfy at least one of: a ratio of crystals, which has a growth direction shifted in 10 degrees or less from the diamond film thickness direction, being 90% or more; and an orientation ratio of <110> being 30 to 70%.

2. The diamond-coated cemented carbide cutting tool according to claim 1, wherein an average film thickness of the diamond film is 3 to 30 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a schematic view of a thickness direction cross-section (vertical cross-section) of a diamond film showing that the properties of concave and convex of a cemented carbide body affect the properties of concave and convex of the diamond film.

[0025] FIG. 2 is an enlarged schematic view of a vertical cross-section of a diamond-coated tool according to an embodiment of the present invention (the scale is not accurate because the view is a schematic view, and in order to emphasize the presence of a binder phase, the area thereof is illustrated larger than its actual size).

[0026] FIG. 3 is a view illustrating the distance between the concave and convex of WC particles at the interface between the diamond film and the WC-based cemented carbide body.

[0027] FIG. 4 is a schematic view of the shape of the WC particles in a region in which the binder phase of FIG. 2 is removed, and is a view illustrating the maximum value (L.sub.1) of vertex-to-vertex distances of WC particle sizes and the diameter of an inscribed-circle inscribed in the WC particles or the minimum distance between the tangents of opposing faces (L.sub.2).

DETAILED DESCRIPTION OF THE INVENTION

[0028] As described above, the present invention is based on the new finding that by achieving improvement in the adhesion of a diamond film to a cutting tool body, a reduction in strain included therein, and high smoothness of the outer surface thereof, chipping of the diamond film tool can be suppressed, the peeling resistance of the diamond film is improved, and thus the tool life is extended.

[0029] Here, the adhesion of the diamond film is achieved by setting, in a WC-based cemented carbide body which is a body, each factor of (1) the Co content, (2) the average particle size of WC particles, (3) the maximum height difference (R.sub.2) of the concave and convex of a body interface, (4) the maximum distance () between adjacent concave and convex of the WC-based cemented carbide body at the interface, (5) the length (Y.sub.e) of the diamond film in the thickness direction in a region in which a binder phase of the WC-based cemented carbide body is removed, (6) the maximum value (L.sub.1) of vertex-to-vertex distances of the WC particles contacting with the diamond film at the interface, and the diameter of an inscribed-circle inscribed in the WC particle or the minimum distance between the tangents of opposing faces (L.sub.2), (7) (L.sub.1)/(L.sub.2), and (8) the area ratio of the WC particles corresponding to (6) and (7) to a predetermined value. On the other hand, the smoothness of the surface of the diamond film is achieved by, in addition to setting the factors that affect the adhesion to the predetermined values, (9) causing the average grain size of diamond crystals in a region of 0.5 to 1.5 m from the body interface toward the diamond film to be 0.1 to 0.3 m, and (10) including columnar crystals constituting the diamond film, which contact the top of the diamond crystals (contact the diamond crystals described in (9)), and satisfy at least one of a proportion a ratio of columnar crystals, which has a growth direction shifted in 10 degrees or less from the diamond film thickness direction(the ratio of columnar crystals in which the angle between the growth direction and the thickness direction of the diamond film is 10 degrees or less):, being 90% or more; and an orientation ratio of <110> being 30 to 70%.

[0030] For this reason, in the present invention, in order to cause the diamond film to obtain predetermined adhesion, while controlling the factors that affect the adhesion, by also considering the influence of the factors that affect the adhesion on the smoothness, the optimum range of each factor is found to achieve improvement in the adhesion, a reduction in strain, and improvement in the smoothness, so that the feature of the invention is to obtain a cutting tool made of diamond-coated cemented carbide in which the occurrence of chipping is suppressed, peeling resistance is improved, and the tool life is long.

[0031] Hereinafter, an embodiment of the present invention will be described in detail, including the description of the optimum range of each factor.

[0032] 1. WC-Based Cemented Carbide Body (Cutting Tool Body)

[0033] First, a WC-based cemented carbide body 1 will be described.

[0034] (1) Co Content

[0035] The WC-based cemented carbide body 1 of the present embodiment contains WC and Co, and the Co content is 3 to 15 mass %. The reason for determining the numerical range of the Co content is as follows. In a case where the Co content in the cemented carbide included in the body 1 is less than 3 mass %, the toughness of the cutting tool body 1 decreases, and fracturing is likely to occur during cutting, which is not preferable. On the other hand, when 15 mass % is exceeded, the volume ratio occupied by voids in a region in which Co is removed after etching increases, and the region in which Co is removed becomes fragile, so that the adhesion between the diamond film and the tool surface decreases, which is not preferable. Therefore, the Co content in the cemented carbide is set to 3 to 15 mass %. The Co content is preferably set in a range of 5 to 7 mass %.

[0036] (2) Average Particle Size of WC

[0037] The average particle size of WC of the WC-based cemented carbide body 1 of the present embodiment is 0.5 to 0.9 m. The reason why the average particle size is set to this range is that when the average particle size is less than 0.5 m, the toughness of the body 1 decreases, and when the average particle size exceeds 0.9 m, the concave and convex of the body after etching in a pretreatment step become large, which adversely affects the smoothness of a diamond film 2 and easily causes chipping. The average particle size of WC is preferably set in a range of 0.6 to 0.8 m.

[0038] Here, the particle size of WC is the same at any part of the body 1 which has not been subjected to the etching, and is determined as follows. That is, in a cross-section (a cutting plane along the thickness direction of the diamond film 2 (a direction perpendicular to the surface of the diamond film 2)) in a 50-m square region on the body side separated by 10 m from the surface of the body 1 (an interface 3 with the diamond film 2), regarding the particle size of individual WC particles 1a which have not been subjected to etching, crystal orientations are measured by electron backscatter diffraction patterns (EBSD) under the condition of a step size of 0.1 m, a position where the crystal orientations of adjacent measurement points are shirted by 5 degrees is regarded as a grain boundary, and a region surrounded by grain boundaries is regarded as one particle. Then, at each of three random parts in the body cross-section, the number of WC particles 1a included in a 10-m line segment (overlapping a 10-m line segment) is counted, 10 m is divided by the number of WC particles 1a obtained, and the average value of the three obtained numerical values is taken as the average particle size of WC.

[0039] (3) Maximum Height Difference of Body Interface

[0040] The maximum height difference (R.sub.z) of concave and convex of the body surface (maximum value of the concave and convex of the body surface) according to JIS B 0601-1994 obtained by cutting an edge tip, polishing the cross-section of the edge tip (cutting plane along the thickness direction of the diamond film 2) with a cross-sectional polisher (hereinafter, referred to as CP), and observing three 50-m square regions including the interface 3 between the body 1 and the film 2 with a scanning electron microscope is 0.5 to 1.0 m. The reason why R.sub.z is set to be in this range is that when R.sub.z is less than 0.5 m, the anchor effect of the body interface to the diamond film 2 is not sufficient and there is a concern that sufficient adhesion of the diamond film 2 to the body 1 may not be obtained, and when R.sub.z exceeds 1.0 m, the smoothness of the diamond coating may be adversely affected and chipping may easily occur. The maximum height difference (R.sub.z) is preferably set in a range of 0.6 to 0.8 m.

[0041] (4) Maximum Value (Maximum Distance Between Concave and Convex) of Distances Between Adjacent Concave and Convex of Body Interface

[0042] The maximum value () of the distances between adjacent concave and convex of the body interface (body surface) obtained by cutting an edge tip, polishing the cross-section of the edge tip (cutting plane along the thickness direction of the diamond film) with CP, and observing three 50-m square regions including the interface 3 between the body 1 and the film 2 with the scanning electron microscope is 0.5 to 1.5 m. The reason why is set to be in this range is that when is less than 0.5 m, there is a concern that the smoothness of the diamond film 2 may not be secured, and when exceeds 1.5 m, the adhesion of the diamond film 2 to the body 1 may become insufficient. is preferably set in a range of 0.7 to 1.2 m. is defined as the distance between concave and convex between which the height difference satisfies a range of 0.5 to 1.5 m. The distance between the concave and convex is shown in FIG. 3 for reference.

[0043] (5) Length (Y.sub.e) of Diamond Film 2 in the Thickness Direction in Region in Which Binder Phase of Body is Removed

[0044] In order to form the diamond film 2 on the cemented carbide body 1, it is necessary to remove Co, which is a binder phase component of the cemented carbide body 1, from the interface 3 between the cemented carbide body 1 and the diamond film 2. In a cross-sectional observation image obtained by cutting the edge tip of a diamond-coated tool (diamond-coated tool), polishing the cross-section of the edge tip (cutting plane along the thickness direction of the diamond film) with CP, and observing three 50-m square regions including the interface 3 between the body 1 and the film 2 with the scanning electron microscope, as illustrated in FIG. 2, the length of the diamond film 2 in the film thickness direction from an uppermost WC particle 1a of the WC body 1 to the deepest bottom of the WC body 1 in the region in which the binder phase 1b of the body 1 is removed by etching with an acid or the like is taken as Y.sub.e. In a case where Y.sub.e is less than 0.5 m, the Co layer is not sufficiently removed from the surface of the cemented carbide body, so that Co diffuses into the interface 3 between the cemented carbide body 1 and the film 2 at the time of diamond deposition, resulting in a reduction in the adhesion of the diamond film 2. In addition, in a case where Y.sub.e exceeds 2.0 m, the interface 3 between the cemented carbide body 1 and the film 2 becomes fragile, and the body side is easily cracked, which causes peeling. Therefore, the value of Y.sub.e is set to 0.5 to 2.0 m. The value of Y.sub.e is preferably set in a range of 0.7 to 1.5 m.

[0045] (6) Maximum Value (L.sub.1) of Vertex-To-Vertex Distances of WC Particle of Body Interface, and Diameter of Inscribed-circle inscribed in WC Particle of Corresponding Particle or Minimum Value of Distances between Tangents of Opposing Faces (L.sub.2)

[0046] L.sub.1 represents the value of the maximum distance (maximum length) connecting the vertices of the corresponding WC particle 1a, and is 0.4 to 0.8 m. The maximum length (L.sub.1) of the WC particle 1a depends on the particle size of the WC particle 1a, and since WC is eroded by etching, the range thereof is defined in a range not exceeding the WC particle size. When the maximum length does not fall within this range, good adhesion of the diamond film 2 cannot be obtained. L.sub.1 is preferably set in a range of 0.5 to 0.7 m.

[0047] On the other hand, L.sub.2 is the diameter of the inscribed-circle inscribed in the corresponding WC particle 1a or the minimum value of the distance between the tangents of the opposing faces. L.sub.2 is the maximum value of the diameter of the inscribed-circle inscribed in the corresponding WC particle when the number of vertices constituting the cross-sectional shape of the WC particle 1a of the corresponding particle is three. And L.sub.2 and is the minimum value of the distance between the tangents of the opposing faces (sides opposing each other in the cross-section) when the number of vertices constituting the cross-sectional shape of the WC particle 1a of the corresponding particle is four. The range of L.sub.2 is 0.2 to 0.4 m. When L.sub.2 is less than 0.2 m, the body strength in the region in which the binder phase 1b of the body 1 is removed cannot be obtained, and a crack tends to occur in the region in which the binder phase 1b of the body 1 is removed. When L.sub.2 exceeds 0.4 m, the anchor effect of the body interface to the diamond film 2 cannot be sufficiently obtained, and there is a concern that sufficient adhesion to the body 1 may not be obtained. L.sub.2 is preferably set in a range of 0.25 to 0.35 m.

[0048] The definition of the maximum value (L.sub.1) of the vertex-to-vertex distances of the WC particle 1a and the diameter of the inscribed-circle inscribed in the corresponding WC particle or the minimum value of the distances between the tangents of the opposing faces (L.sub.2) is illustrated in FIG. 4 for reference.

[0049] (7) Ratio between Maximum Value (L.sub.1) of Vertex-To-Vertex Distances of WC Particle at Body Interface and Diameter of Inscribed-circle inscribed in WC Particle of Corresponding Particle or Minimum Value of Distances between Tangents of Opposing Faces (L.sub.2)

[0050] The ratio (L.sub.1)/(L.sub.2) between the maximum value (L.sub.1) of the vertex-to-vertex distances of the WC particles 1a of the body 1 that contact the diamond film 2 and the diameter of the inscribed-circle inscribed in the WC particle 1a of the corresponding particle or the minimum value of the distances between the tangents of the opposing faces (L.sub.2) is 1.5 to 2.5. The reason why the ratio is set to be in this range is that when the ratio is less than 1.5, the anchor effect to the diamond film 2 may not be sufficient and sufficient adhesion of the diamond film 2 may not be obtained, and when the ratio exceeds 2.5, there is a concern that the smoothness of the diamond film 2 may be impaired and chipping may easily occur. (L.sub.1)/(L.sub.2) is preferably set in a range of 1.7 to 2.2.

[0051] Regarding the maximum value (L.sub.1) of the vertex-to-vertex distances of the WC particle 1a at the body interface and the diameter of the inscribed-circle inscribed in the WC particle 1a of the corresponding particle or the minimum value of the distances between the tangents of the opposing faces (L.sub.2), in a vertical cross-section (cutting plane along the thickness direction of the diamond film) of the body 1 corresponding to a region of 10 m from the interface of the body 1 and 50 m in the direction parallel to the body surface, crystal orientations are measured by electron backscatter diffraction (EBSD) under the condition of a step size of 0.1 m, a position where the crystal orientations of adjacent measurement points are shifted by 5 degrees is regarded as a grain boundary, a region surrounded by grain boundaries is regarded as one particle of the WC particle 1a, and for all the WC particles 1a in the same vertical cross-section, (L.sub.1) and (L.sub.2) of the particles in the same vertical cross-section are obtained.

[0052] (8) Area Ratio of WC Particles Satisfying (6) and (7)

[0053] Regarding the area ratio of WC particles 1a satisfying (6) and (7) described above, in a vertical cross-section (cutting plane along the thickness direction of the diamond film) observation image obtained by observing three 50-m square regions including the interface 3 between the diamond film 2 and the body 1, when the sum of the areas occupied by individual WC particles 1a that contact the diamond film 2 at the interface 3 is regarded as 100 area %, if the area occupied by the WC particles 1a satisfying (6) and (7) described above among such WC particles 1a is not 70 area % or more, the adhesion and smoothness of the diamond film 2 cannot be obtained even if the regulations (6) and (7) are satisfied. The area ratio is preferably 85 area % or more, and more preferably set in a range of 90 to 100 area %.

[0054] 2. Diamond Film

[0055] Next, the diamond film 2 will be described.

[0056] (1) Average Film Thickness of Diamond Film

[0057] The average film thickness of the diamond film 2 is the average value of five film thicknesses measured in a region of 50 m in the horizontal direction to the body surface (direction parallel to the body surface), and the value is desirably set in a range of 3 to 30 m. By setting the average film thickness to be in this range, sufficient wear resistance and peeling resistance can be further exhibited for long-term usage, and rounding of the edge is more reliably eliminated, so that predetermined machining accuracy can be obtained. The average film thickness of the diamond film 2 is more preferably set in a range of 8 to 18 m.

[0058] (2) Average Grain Size of Diamond Crystals in Region of 0.5 to 1.5 m from Body Interface Toward Diamond Film

[0059] In a cross-sectional observation image obtained by cutting the edge tip of a diamond-coated tool, polishing the cross-section of the edge tip (cutting plane along the thickness direction of the diamond film) with CP, and observing three 50-m square regions including the interface 3 between the body 1 and the film 2 with the scanning electron microscope, the average grain size of the diamond crystals in a region of 0.5 to 1.5 m from the body interface toward the diamond film 2 along the thickness direction of the diamond film 2, that is, in a growth initial region (diamond film growth initial stage 2b in FIG. 2) of the diamond film 2 is set to 0.1 to 0.3 m. The average grain size of the diamond crystals is the average value of numerical values obtained by counting the number of diamond crystal grains included in a 3-m line segment (overlapping a 3-m line segment) at each of three random parts in the growth initial region observed with angle selective backscattered electrons (ASB), and dividing 3 m by the obtained number of diamond crystal grains. The reason why the average grain size is set to be in this numerical range is that when the average grain size is less than 0.1 m, satisfactory adhesion cannot be obtained, and when the average grain size exceeds 0.3 m, the diamond grains on the outer surface side of the grains do not grow in a columnar shape, that is, in the thickness direction of the diamond film 2. The average grain size of the diamond crystals in the growth initial region of the diamond film 2 is preferably set in a range of 0.15 to 0.25 m.

[0060] (3) In Columnar Crystals Constituting Diamond Film, Ratio of Diamond Crystals in Growth Directions Shifted at Angle of 10 Degrees or Less from Thickness Direction of Diamond Film and <110> Orientation Ratio

[0061] The crystal structure of the film 2 as illustrated in FIG. 2 can be checked by the structure observation by ASB. The diamond film 2 grows in a columnar shape in a diamond film growth late stage 2a, the growth ratio (hereinafter, aspect ratio) of the crystal grain size in the film thickness direction to that in the horizontal direction exceeds 3, and the aspect ratio increases with the film thickness.

[0062] The shift of the growth direction of the crystal grain of the film 2 and the <110> orientation ratio are measured as follows. Regarding the growth direction of the diamond film 2, in a structure observation image of the film 2 obtained by cutting the edge tip of a diamond-coated tool, polishing the cross-section of the edge tip (cutting plane along the thickness direction of the diamond film) with CP, and observing three 30-m square film cross-sectional regions by ASB, a value obtained by dividing the area occupied by the crystals, in which the shift of the growth direction (the major axis direction of the columnar crystal) of the film 2 from the film thickness direction is 10 degrees or less, by the total area of the film 2 in the measurement region is taken as the ratio of the shift of the angle of 10 degrees or less. In addition, by irradiating individual crystal grains present in the three measurement ranges of the film cross-sectional polished surface perpendicular to the film surface in the 30-m square film cross-sectional regions with electron beams by EBSD, the inclination angle between the angle formed by the normal to the (110) face of the individual crystal grains of the film 2 and the film thickness direction is measured, and the sum of frequencies where the inclination angle is in a range of 0 to 20 is taken as the <110> orientation ratio. In the columnar crystals constituting the diamond film 2, at least a ratio of diamond crystals, in which the shift in angle of the growth direction measured by the above method from the normal direction of the body 1 (the thickness direction of the diamond film) is 10 degrees or less, 90% or more, or a <110> orientation ratio of 30% to 70%. The reason for this numerical range is that when the ratio of the columnar crystals in which the growth direction is in the thickness direction of the diamond film 2 is less than 90%, the diamond crystals significantly come off during cutting due to strain included in the diamond film 2, and chipping easily occurs. In addition, when the <110> orientation ratio is less than 30%, the wear resistance of the diamond film 2 is insufficient, and when the <110> orientation ratio exceeds 70%, the diamond crystal grains are coarsened, the impact resistance decreases, and chipping easily occurs. However, in a state where the <110> orientation ratio of the film 2 is less than 30% or exceeds 70%, when the area occupied by crystals in which the shift of the growth direction of the film 2 is within 10 degrees exceeds 90%, predetermined cutting performance can be obtained. Furthermore, even in a state where the area occupied by the crystals, in which the shift of the growth direction of the film 2 is 10 degrees or less, does not exceed 90%, when the <110> orientation ratio is 30% or more and 70% or less, predetermined cutting performance can be obtained. Therefore, at least one of the two may be satisfied. The ratio of the columnar crystals, in which the shift of the shift in angle of the growth direction from the thickness direction of the diamond film is 10 degrees or less, is preferably 93% or more, and more preferably 95% or more and 100% or less. The <110> orientation ratio is preferably 40% or more and 60% or less.

EXAMPLES

[0063] Next, examples will be described.

[0064] Here, a diamond-coated end mill will be described as a specific example of the diamond-coated tool according to the present invention, but the present invention is not limited thereto, and can be applied to various diamond-coated tools such as diamond-coated alloy inserts and diamond-coated drills as a matter of course.

[0065] (A) Manufacturing Process of Body

[0066] As raw material powders, a WC powder, a Co powder, a TaC powder, and a NbC powder or Cr.sub.3C.sub.2 powder having a predetermined average particle size in a range of 0.5 to 0.9 m were mixed in the ratios shown in Table 1, paraffin as a binder, and toluene, xylene, mesitylene, tetralin, or decalin as a solvent were added, and the mixture was blended in acetone by a ball mill for 24 hours and was decompressed and dried. Thereafter, extrusion press forming was performed to obtain round bar green compacts each having a diameter of 10 mm and a length of 150 mm, and these round bar green compacts were sintered under the sintering condition that the round bar green compacts were held in a vacuum atmosphere at 1 Pa at a temperature of 1380 C. to 1500 C. for one to two hours, whereby sintered bodies were obtained. Thereafter, the sintered bodies were polished to manufacture WC-based cemented carbide sintered bodies.

[0067] Next, the WC-based cemented carbide sintered bodies were ground so that a groove-forming portion had an outer diameter dimension of 10 mm and a length of 100 mm, whereby end mill bodies made of WC cemented carbide (hereinafter, simply referred to as end mill bodies) were manufactured.

[0068] (b) Etching Step

[0069] Next, etching was performed on the surface of the end mill body in order to form fine concave and convex satisfying the respective numerical ranges of R.sub.z, , L.sub.1, L.sub.2, (L.sub.1)/(L.sub.2), and area %.

[0070] The etching was performed in two steps of alkali etching and acid etching. The alkali etching was performed by electrolytic etching, and the acid etching was performed by immersing the body in dilute nitric acid.

[0071] Specifically, the following is performed.

[0072] (First Pretreatment Step)

[0073] Electrolytic etching was performed on the end mill body in 1 L of an etching solution containing NaOH (4 to 8 g) for 10 to 20 minutes in a state where current flows to cause the amount of current per unit area to become 1.5 to 2.5 A/dm.sup.2, whereby SC on the body surface was removed.

[0074] (Second Pretreatment Step)

[0075] The end mill body was immersed in 1 L of a solution of dilute nitric acid (0.5 vol %) for 8 to 12 seconds at room temperature (23 C.), whereby a portion of the metal binder phase primarily containing Co near the surface of the drill body was removed by acid etching.

[0076] (c) Pretreatment Step for Film Formation of Diamond Film

[0077] As a pretreatment for deposition of a diamond film, in order to promote nucleation of diamond at the initial stage of diamond deposition, the end mill body subjected to the above-mentioned etching was subjected to ultrasonication in an ethyl alcohol solution containing a diamond powder having a particle size of 1 m for 10 minutes.

[0078] (d) Deposition Step

[0079] The end mill body subjected to the pretreatments was loaded into a hot filament CVD apparatus. The flow rate ratio between hydrogen gas and methane gas was adjusted at a filament temperature of 2050 C. to 2100 C. and a gas pressure of 1 to 3 Torr (133.3 to 399.9 Pa) to maintain the body temperature at 750 C. to 800 C. for a predetermined time (see Table 2), and deposition was performed under initial deposition conditions (for example, from the start of deposition to 300 minutes) such that the grain size of diamond grains in a region of 0.5 to 1.5 m from the body interface toward the diamond film became 0.1 to 0.3 m. Thereafter, the flow rate ratio between hydrogen gas and methane gas was adjusted at a filament temperature of 2100 C. to 2150 C. and a gas pressure of 5 to 8 Torr (666.6 to 1066.4 Pa) to maintain the body temperature at 850 C. to 900 C. for a predetermined time (see Table 2), and deposition was performed under deposition conditions (late deposition conditions) such that diamond grew in a columnar shape, whereby diamond film end mills of the present invention (hereinafter, referred to as present invention end mills) were prepared.

[0080] For comparison, raw material powders containing a WC powder having a predetermined average particle size in a range of 0.4 to 1.2 m were mixed in the proportions shown in Table 1, and in the step described in (a), drill bodies were manufactured. Thereafter, processes of the steps corresponding to (b) to (d) described above (details are shown in Table 2) were performed, whereby diamond film end mills of comparative examples (hereinafter, referred to as comparative end mills) were prepared.

[0081] In Table 2, the Preceding pretreatment step is to remove a portion of the binder phase near the body surface in 1 L of a solution of dilute nitric acid (0.5 vol %) for 8 to 15 seconds at room temperature (23 C.), and precedes the first pretreatment step described above. The diagonal lines in Table 2 indicate that the corresponding steps were not performed. Comparative end mill 15 and comparative end mill 18 did not obtain a diamond film.

[0082] Table 3 shows the WC particle size, R.sub.z, , Y.sub.e, L.sub.1, L.sub.2, and (L.sub.1)/(L.sub.2) of the body, the area % of WC particles, the average film thickness of the diamond film, the grain size in the region of 0.5 to 1.5 m, the ratio of columnar crystals within 10 degrees, and the <110> orientation ratio in the present invention end mills obtained according to Table 2 and the comparative end mills.

[0083] In Table 3, diagonal lines indicate that the corresponding items could not be measured.

TABLE-US-00001 TABLE 1 Composition of cutting tool body (mass %) Kind Co TaC NbC Cr.sub.3C.sub.2 WC Body composition A 3.0 0.3 0.2 Balance Body composition B 7.0 0.4 Balance Body composition C 5.5 0.3 0.2 Balance Body composition D 12.0 0.4 0.4 Balance Body composition E 10.0 0.4 0.2 Balance Body composition F 15.0 0.5 0.5 Balance Body composition G 10.0 0.6 0.2 Balance Body composition H 5.0 0.3 Balance Body composition I 9.0 0.3 0.5 Balance Body composition J 8.0 0.4 0.2 Balance Body composition K 17.0* 0.5 0.8 0.9 Balance Body composition L 2.0* 0.6 0.4 0.5 Balance (Note) *in the columns indicates that the value is not included in the scopes defined by the instant claims.

TABLE-US-00002 TABLE 2 Deposition conditions Pretreatment conditions Initial stage Late stage Preceding Second Concentration Concentration pretreatment First pretreatment step pretreatment of methane of methane step Concentration Amount step gas with gas with Treatment of alkali of Treatment Treatment respect to respect to time solution current time time hydrogen gas Deposition hydrogen gas Deposition Kind Body (sec) (M) (A/dm.sup.2) (min) (sec) (vol %) time (hr) (vol %) time (hr) Present invention G 0.2 1.5 15 8 3.0 1.5 2.0 32 end mill 1 Present invention F 0.1 1.5 10 8 3.5 1.0 2.5 30 end mill 2 Present invention C 0.2 1.5 10 10 3.5 1.5 2.0 37 end mill 3 Present invention B 0.1 1.5 15 10 3.5 1.0 2.0 40 end mill 4 Present invention A 0.2 1.5 15 8 3.0 4.0 1.5 38 end mill 5 Present invention H 0.2 2.0 20 8 3.0 3.0 1.5 36 end mill 6 Present invention I 0.2 2.0 20 8 3.5 3.5 1.5 23 end mill 7 Present invention J 0.2 2.0 20 10 3.0 3.0 1.5 19 end mill 8 Present invention C 0.2 1.5 10 8 3.5 3.5 1.5 25 end mill 9 Present invention F 0.2 2.0 10 10 3.5 3.5 2.0 30 end mill 10 Present invention E 0.1 1.5 15 10 3.5 3.0 2.0 25 end mill 11 Present invention J 0.2 1.5 15 10 3.0 3.5 1.5 60 end mill 12 Present invention D 0.1 2.0 20 8 2.5 3.0 2.0 30 end mill 13 Present invention G 0.2 1.5 10 10 3.0 3.5 1.5 25 end mill 14 Present invention A 0.1 2.0 15 10 3.5 3.5 2.0 30 end mill 15 Present invention I 0.2 1.5 15 8 3.0 2.0 1.5 6 end mill 16 Present invention H 0.2 2.0 15 8 3.0 2.0 2.0 25 end mill 17 Present invention B 0.2 2.0 20 10 3.5 2.0 1.5 15 end mill 18 Present invention F 0.2 1.5 15 8 2.5 2.0 2.0 4 end mill 19 Present invention H 0.2 2.0 20 10 2.5 3.0 1.5 70 end mill 20 Comparative end D 0.2 2.0 20 3 2.0 3.0 2.0 30 mill 1 Comparative end G 0.2 2.0 15 20 2.0 4.0 1.5 50 mill 2 Comparative end A 0.1 1.5 5 5 3.5 4.0 2.0 30 mill 3 Comparative end E 0.2 1.5 30 8 2.0 3.0 1.5 25 mill 4 Comparative end B 0.2 1.0 30 8 2.5 4.0 2.0 20 mill 5 Comparative end F 0.2 3.0 10 10 2.5 4.0 1.5 15 mill 6 Comparative end H 0.05 1.5 15 8 2.0 3.0 2.0 10 mill 7 Comparative end C 0.3 1.5 20 10 3.5 3.0 2.0 20 mill 8 Comparative end J 0.2 2.0 15 8 3.0 4.0 1.5 30 mill 9 Comparative end I 0.2 1.5 20 10 2.5 4.0 2.0 20 mill 10 Comparative end K* 0.2 2.0 15 8 2.0 4.0 1.5 20 mill 11 Comparative end L* 0.2 1.5 20 10 2.0 3.0 2.0 30 mill 12 Comparative end B 0.2 1.0 20 10 3.0 3.0 2.0 30 mill 13 Comparative end C 0.2 1.0 3 10 2.5 3.0 1.5 25 mill 14 Comparative end A 0.2 1.5 20 2.5 4.0 2.0 20 mill 15 Comparative end G 8 2.0 4.0 2.0 40 mill 16 Comparative end E 10 3.0 4.0 1.5 20 mill 17 Comparative end C 2.0 4.0 1.5 20 mill 18 Comparative end J 10 0.2 2.0 15 10 2.5 3.0 2.0 20 mill 19 Comparative end E 15 0.2 1.5 15 10 2.0 3.0 1.5 30 mill 20 Comparative end C 6 0.2 2.0 20 10 2.5 3.0 2.0 20 mill 21 Comparative end I 5 0.2 1.5 20 10 2.5 3.5 1.5 30 mill 22 Comparative end C 0.2 1.5 15 10 4.0 3.0 2.0 20 mill 23 Comparative end A 0.2 2.0 20 10 1.0 3.0 1.5 20 mill 24 Comparative end C 0.2 2.0 20 10 0 0 1.0 50 mill 25 (Note) *in the columns indicates that the value is not included in the scopes defined by the instant claims.

TABLE-US-00003 TABLE 3 Body WC average Area ratio of WC particles particle size R.sub.s Y.sub.a L.sub.1 L.sub.2 simultaneously satisfying Kind (m) (m) (m) (m) (m) (m) (L.sub.1/L.sub.2) three left columns (%) Present invention end mill 1 0.6 0.5 0.6 0.8 0.5 0.3 1.7 80 Present invention end mill 2 0.5 0.6 0.5 1.5 0.4 0.2 2.0 90 Present invention end mill 3 0.5 0.6 0.6 1.2 0.4 0.2 2.0 90 Present invention end mill 4 0.6 0.5 0.8 0.9 0.5 0.2 2.5 90 Present invention end mill 5 0.7 0.6 0.6 0.6 0.6 0.3 2.0 90 Present invention end mill 6 0.9 1.0 0.9 0.9 0.7 0.4 1.8 80 Present invention end mill 7 0.8 0.9 1.1 0.8 0.7 0.3 2.3 80 Present invention end mill 8 0.9 0.9 1.2 1.2 0.8 0.4 2.0 80 Present invention end mill 9 0.6 0.5 0.5 0.6 0.5 0.2 2.5 90 Present invention end mill 10 0.7 0.8 0.8 1.0 0.6 0.3 2.0 80 Present invention end mill 11 0.9 1.0 1.0 1.0 0.8 0.4 2.0 80 Present invention end mill 12 0.6 0.7 0.7 0.8 0.5 0.2 2.5 80 Present invention end mill 13 0.7 0.8 0.9 1.0 0.6 0.3 2.0 80 Present invention end mill 14 0.6 0.6 0.6 0.7 0.5 0.2 2.5 80 Present invention end mill 15 0.7 0.7 0.8 0.9 0.6 0.3 2.0 70 Present invention end mill 16 0.5 0.6 0.7 0.8 0.4 0.2 2.0 80 Present invention end mill 17 0.6 0.6 0.6 0.7 0.5 0.2 2.5 90 Present invention end mill 18 0.7 0.8 0.9 1.0 0.6 0.3 2.0 90 Present invention end mill 19 0.6 0.7 0.7 0.8 0.5 0.2 2.5 90 Present invention end mill 20 0.6 0.7 0.7 1.5 0.5 0.2 2.5 80 Comparative end mill 1 0.6 1.5* 0.6 0.3* 0.5 0.2 2.5 80 Comparative end mill 2 0.5 1.3* 0.4 2.5* 0.4 0.2 2.0 80 Comparative end mill 3 0.5 0.2* 0.5 0.5 0.4 0.2 2.0 70 Comparative end mill 4 0.6 2.0* 0.6 0.8 0.5 0.2 2.5 50* Comparative end mill 5 0.6 0.3* 0.7 0.8 0.5 0.2 2.5 80 Comparative end mill 6 0.5 1.8* 0.5 1.2 0.4 0.2 2.0 30* Comparative end mill 7 0.6 0.3* 0.7 0.8 0.5 0.2 2.5 80 Comparative end mill 8 0.6 1.6* 0.6 1.5 0.5 0.2 2.5 90 Comparative end mill 9 1.3* 2.0* 1.6* 0.8 1.2* 0.3 4.0* 80 Comparative end mill 10 0.4* 0.3* 0.3* 1.5 0.3* 0.3 1.0* 90 Comparative end mill 11 0.7 0.6 0.5 0.8 0.6 0.3 2.0 80 Comparative end mill 12 0.6 0.7 0.7 1.5 0.5 0.2 2.5 90 Comparative end mill 13 0.6 0.5 0.6 1.2 0.5 0.1* 5.0* 80 Comparative end mill 14 0.7 0.4* 0.5 1.0 0.6 0.5* 1.2* 90 Comparative end mill 15 0.6 0.7 0.8 0.5 0.2 2.5 0* Comparative end mill 16 0.5 0.8 0.4 0.3 1.3* 0* Comparative end mill 17 0.6 1.5 0.5 0.2 2.5 0* Comparative end mill 18 0.5 0.4 0.4 1.0* 0* Comparative end mill 19 0.5 1.6* 1.3 1.5 0.4 0.2 2.0 80 Comparative end mill 20 0.7 1.7* 1.6* 1.5 0.6 0.2 3.0 80 Comparative end mill 21 0.5 1.6* 0.9 1.5 0.4 0.2 2.0 70 Comparative end mill 22 0.6 1.8* 0.7 1.5 0.5 0.2 2.5 70 Comparative end mill 23 0.5 0.6 0.5 1.5 0.4 0.2 2.0 80 Comparative end mill 24 0.6 0.7 0.7 1.5 0.5 0.2 2.5 90 Comparative end mill 25 0.6 0.8 0.8 1.5 0.5 0.2 2.5 90 Diamond film Ratio of columnar crystals having growth direction at angle of Average Average grain 10 degrees or less <110> film size in region with respect to orientation thickness of 0.5 to 1.5 thickness direction of ratio Kind (m) m (m) diamond film (%) (%) Present invention end mill 1 15 0.2 90 20* Present invention end mill 2 12 0.2 90 20* Present invention end mill 3 15 0.2 90 15* Present invention end mill 4 16 0.2 90 20* Present invention end mill 5 18 0.1 80* 50 Present invention end mill 6 15 0.1 80* 60 Present invention end mill 7 10 0.1 70* 70 Present invention end mill 8 8 0.1 80* 70 Present invention end mill 9 12 0.1 90 50 Present invention end mill 10 14 0.2 90 40 Present invention end mill 11 12 0.2 100 70 Present invention end mill 12 28 0.1 100 40 Present invention end mill 13 12 0.2 100 70 Present invention end mill 14 13 0.1 95 50 Present invention end mill 15 14 0.3 100 30 Present invention end mill 16 3 0.1 90 50 Present invention end mill 17 11 0.2 90 30 Present invention end mill 18 7 0.3 90 50 Present invention end mill 19 2** 0.2 90 30 Present invention end mill 20 32** 0.2 90 50 Comparative end mill 1 14 0.3 90 50 Comparative end mill 2 24 0.1 90 30 Comparative end mill 3 14 0.1 90 50 Comparative end mill 4 13 0.2 80* 30 Comparative end mill 5 10 0.2 100 30 Comparative end mill 6 8 0.2 70* 40 Comparative end mill 7 6 0.2 90 40 Comparative end mill 8 10 0.1 90 30 Comparative end mill 9 14 0.1 30* 10* Comparative end mill 10 10 0.2 90 80* Comparative end mill 11 10 0.2 90 30 Comparative end mill 12 14 0.2 100 40 Comparative end mill 13 14 0.2 80* 40 Comparative end mill 14 10 0.2 90 50 Comparative end mill 15 Comparative end mill 16 18 0.2 80* 30 Comparative end mill 17 10 0.1 90 40 Comparative end mill 18 Comparative end mill 19 10 0.2 90 40 Comparative end mill 20 14 0.2 80* 30 Comparative end mill 21 10 0.2 80* 40 Comparative end mill 22 14 0.2 90 40 Comparative end mill 23 10 0.05* 90 50 Comparative end mill 24 10 0.4* 30* 50 Comparative end mill 25 22 1.0<* 30* 50 (Note) *in the columns indicates that the value is not included in the scopes defined by the instant claims. **in the columns indicates that the value is not included in the scopes defined by the instant claims.

[0084] Next, using the present invention end mills 1 to 20 and comparative end mills 1 to 25 (all of which had an outer diameter of 10.0 mm), a CFRP high-speed groove machining test was performed under the following conditions. The conventional cutting speed described in the following conditions is a cutting speed at which the efficiency (generally, the number of parts that can be machined until the tool life, and the like) is optimum in a case of using a coated tool in the related art.

[0085] Cutting speed: 300 m/min

[0086] Cutting conditions: Air blow

[0087] Overhang: 25 mm

[0088] Feed per tooth: 0.03 mm/tooth

[0089] In the cutting test, when abnormal noise of cutting was generated and the load during cutting showed an abnormality, the test was interrupted, and the presence or absence of peeling/fracture was checked. In a case where peeling, fracture, or the like was confirmed, the machining length up to that point was taken as the machining life.

[0090] In addition, those in which fracturing had not occurred until the machining length became 25 m, the wear state of the flank face on the center of the cutting edge was normal (no fracture or chipping), and the length of burrs or the delamination width around the machined hole did not exceed 1 mm were regarded as an acceptable condition of the present invention end mills.

[0091] Table 4 shows the results of these evaluations.

TABLE-US-00004 TABLE 4 Test results Cutting length Type (m) Wear state Present invention end mill 1 30 Normal wear Present invention end mill 2 30 Normal wear Present invention end mill 3 30 Normal wear Present invention end mill 4 30 Normal wear Present invention end mill 5 30 Normal wear Present invention end mill 6 30 Normal wear Present invention end mill 7 30 Normal wear Present invention end mill 8 30 Normal wear Present invention end mill 9 30 Normal wear Present invention end mill 10 30 Normal wear Present invention end mill 11 30 Normal wear Present invention end mill 12 30 Normal wear Present invention end mill 13 30 Normal wear Present invention end mill 14 30 Normal wear Present invention end mill 15 30 Normal wear Present invention end mill 16 30 Normal wear Present invention end mill 17 30 Normal wear Present invention end mill 18 30 Normal wear Present invention end mill 19 25 Normal wear Present invention end mill 20 25 Normal wear Comparative end mill 1 <1 Chipping Comparative end mill 2 20 Chipping Comparative end mill 3 <1 Chipping Comparative end mill 4 15 Chipping Comparative end mill 5 15 Chipping Comparative end mill 6 15 Chipping Comparative end mill 7 10 Chipping Comparative end mill 8 15 Chipping Comparative end mill 9 10 Chipping Comparative end mill 10 15 Chipping Comparative end mill 11 <1 Chipping Comparative end mill 12 15 Chipping Comparative end mill 13 15 Chipping Comparative end mill 14 15 Chipping Comparative end mill 15 <1 Fracture Comparative end mill 16 <1 Chipping Comparative end mill 17 <1 Chipping Comparative end mill 18 <1 Fracture Comparative end mill 19 20 Chipping Comparative end mill 20 15 Chipping Comparative end mill 21 15 Chipping Comparative end mill 22 20 Chipping Comparative end mill 23 15 Chipping Comparative end mill 24 15 Chipping Comparative end mill 25 5 Chipping

[0092] From the results shown in Table 4, it can be seen that in the present invention end mills, both the Co content in the body and the average particle size of the WC particles were within the predetermined ranges, the maximum height difference between the concave and convex of the body interface contacting with the diamond film or the maximum distance between the concave and convex and the length in the thickness direction of the diamond film in the region in which the binder phase of the body was removed were respectively within the predetermined ranges, 70 area % or more of the WC particles at the interface satisfied in the predetermined range the maximum value of the vertex-to-vertex distances and the diameter of the inscribed-circle inscribed therein or the minimum value of the distances between the tangents of the opposing faces, (maximum value of vertex-to-vertex distances of WC particles at body interface)/(diameter of inscribed-circle inscribed in WC particle or minimum value of distances between tangents of opposing faces), in addition, the average film thickness of the diamond film, the maximum height difference between the concave and convex, and the average grain size of the diamond crystals in the range of 0.5 to 1.5 m from the body interface satisfied the predetermined values, and in the diamond columnar crystals at least one of the ratio of the crystals at an angle in the predetermined range with respect to the film thickness direction or the <110> orientation ratio satisfied the predetermined value, so that adhesion and smoothness of the diamond film could be secured and excellent chipping resistance and wear resistance were exhibited. Therefore, the cutting tools made of diamond-coated cemented carbide of the present invention were improved in tool life for hard-to-cut materials such as CFRP. Contrary to this, it can be seen that comparative end mills which lacked one or more items to be satisfied by the cutting tools made of diamond-coated cemented carbide of the present invention could not secure adhesion and smoothness of the diamond film, and thus had a short cutting length, chipping occurred, and a short tool life.

INDUSTRIAL APPLICABILITY

[0093] The cutting tool made of diamond-coated cemented carbide of the present invention can be applied not only to end mills made of diamond-coated cemented carbide, but also to various diamond-coated tools such as inserts made of diamond-coated cemented carbide and drills made of diamond-coated cemented carbide. For this reason, since the cutting tool made of diamond-coated cemented carbide of the present invention exhibits excellent edge tip strength and wear resistance, the cutting tool made of diamond-coated cemented carbide of the present invention can satisfactorily cope with energy saving during cutting and a further reduction in costs, and thus the industrial applicability thereof is extremely large.

REFERENCE SIGNS LIST

[0094] 1 cemented carbide body

[0095] 1a WC particle

[0096] 1b binder phase

[0097] 2 diamond film

[0098] 2a diamond film growth late stage

[0099] 2b diamond film growth initial stage

[0100] 3 interface between cemented carbide body and diamond film