JP7379221B2 - diamond coated cutting tools - Google Patents

Description

The present disclosure relates to diamond coated cutting tools.

Patent Document 1 discloses a diamond-coated cutting tool having a structure in which a polycrystalline diamond layer (film) is coated on the surface of a base material.
In this diamond-coated cutting tool, the surface roughness of the base material and the number of voids at the interface of the diamond layer are each limited to specific ranges. Here, the surface roughness of the base material means the arithmetic mean roughness Ra of the surface of the base material and the average length RSm of the roughness curve elements of the surface of the base material.
This diamond-coated cutting tool has a surface roughness within a specific range to improve the adhesion of the diamond layer to the base material due to the anchor effect.
In addition, by setting the number of voids within a specific range, this diamond-coated cutting tool alleviates residual stress caused by the difference in thermal expansion coefficient between the base material and the diamond layer, and improves the adhesion of the diamond layer to the base material. It's improving.
In this way, the diamond-coated cutting tool of Patent Document 1 improves the adhesion of the diamond layer to the base material by adjusting the surface roughness and the number of voids.

Japanese Patent Application Publication No. 2011-38150

In the diamond-coated cutting tool of Patent Document 1, the number of voids is 1×10 ³ or more and 1×10 ⁶ or less/cm. It is stated that within this range, the residual stress at the interface between the diamond layer and the base material is relaxed.
However, in the above range, the gap between the voids at the interface between the diamond layer and the base material is narrow and the number of voids is large, so that the substantial contact area between the diamond layer and the base material becomes small. Therefore, there was a risk that the peeling resistance would be insufficient.
The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a diamond-coated cutting tool in which a diamond layer has high adhesion to a base material. The present disclosure can be realized as the following forms.

[1] A diamond-coated cutting tool comprising a base material and a diamond layer covering the surface of the base material,
The base material has an average coefficient of thermal expansion x from 25°C to 600°C,
3.1×10 ^-6 /K≦x≦4.0×10 ^-6 /K
and the diamond layer has a plurality of voids extending in the crystal growth direction from a portion in contact with the base material,
In a cut surface obtained by cutting the diamond-coated cutting tool at a plane including the base material and the diamond layer, the average distance between the centers of adjacent voids is 12 μm or more and 1000 μm or less, diamond-coated cutting. tool.

[2] The diamond-coated cutting tool according to [1], wherein the base material is made of a silicon nitride sintered body or a sialon sintered body.

[3] The diamond-coated cutting tool according to [2], wherein the sialon sintered body contains 2% by mass or more and 35% by mass or less of Al in terms of oxide.

[4] The silicon nitride sintered body contains at least one selected from Ti nitrides, carbonitrides, and carbides in a total amount of 5% by mass or more and 20% by mass or less,
The diamond according to [2] or [3], wherein the sialon sintered body contains a total of 5% by mass or more and 20% by mass or less of at least one selected from Ti nitride, carbonitride, and carbide. Coated cutting tools.

[5] The diamond-coated cutting tool according to any one of [2] to [4], wherein the sialon sintered body includes a polytype crystal phase.

The diamond-coated cutting tool of the present disclosure improves the adhesion of the diamond layer to the base material by setting the thermal expansion coefficient of the base material to a specific range and by setting the average distance between the centers of adjacent voids to a specific range. This improves peeling resistance.
Furthermore, by using a sintered body having a specific composition as the base material, peeling resistance is further improved.
When the base material is composed of a sialon sintered body containing a polytype crystal phase, peeling resistance is particularly excellent.

FIG. 2 is a diagram schematically showing a SEM image of a cut surface of a diamond-coated cutting tool. FIG. 2 is an enlarged view of FIG. 1; FIG. 3 is a diagram schematically showing an example of voids.

The present invention will be explained in detail below. In this specification, descriptions using "~" for numerical ranges include the lower limit and upper limit unless otherwise specified. For example, the description "10 to 20" includes both the lower limit value of "10" and the upper limit value of "20". That is, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Diamond coated cutting tool 1
(1) Configuration of diamond-coated cutting tool 1 The diamond-coated cutting tool 1 includes a base material 3 and a diamond layer 5 covering the surface 3A of the base material 3. The base material 3 has an average coefficient of thermal expansion x from 25° C. to 600° C. that satisfies the following relational expression 1.
3.1×10 ^-6 /K≦x≦4.0×10 ^-6 /K ...Relational expression 1
Further, the diamond layer 5 has a plurality of voids 9 extending from the portion in contact with the base material 3 in the crystal growth direction. In a cut surface obtained by cutting the diamond-coated cutting tool 1 along a plane including the base material 3 and the diamond layer 5, the average distance between the centers 9A of adjacent voids 9 is 12 μm or more and 1000 μm or less. .

(2) Base material 3
(2.1) Average thermal expansion coefficient x of base material 3
As mentioned above, from the viewpoint of improving the adhesion of the diamond layer 5 to the base material 3, it is preferable that the average thermal expansion coefficient x of the base material 3 from 25° C. to 600° C. satisfies the above relational expression 1, and the following relation: It is more preferable that Expression 2 is satisfied, and even more preferable that the following Relational Expression 3 is satisfied. Note that the average coefficient of thermal expansion x can be measured using TMA (Thermo Mechanical Analysis).
3.1×10 ^-6 /K≦x≦3.7×10 ^-6 /K ...Relational expression 2
3.1×10 ^-6 /K≦x≦3.4×10 ^-6 /K ...Relational expression 3

(2.2) Preferred configuration example of base material 3 From the viewpoint of further improving peeling resistance, the base material 3 is preferably composed of a silicon nitride sintered body or a sialon sintered body. Silicon nitride (Si ₃ N ₄ ) in the silicon nitride sintered body is a ceramic crystal grain made of Si (silicon) and N (nitrogen), and is sintered by adding a sintering aid etc. to silicon nitride as a raw material. be done. Silicon nitride has an α phase with an equiaxed particle shape and a β phase with an acicular particle shape, and the properties of toughness and hardness can be controlled by the composition ratio of these. β-silicon nitride has a structure in which acicular structures are intertwined, so it has high toughness, and α-silicon nitride has an equiaxed particle shape, so it has lower toughness than β-silicon nitride, but High hardness. In the silicon nitride contained in the silicon nitride sintered body, the type and composition ratio of these crystal phases are not particularly limited.

The silicon nitride sintered body contains at least one element selected from the group consisting of Group 4 elements, rare earth elements, and Mg (magnesium) in the periodic table (hereinafter sometimes referred to as "specific elements"). May contain. The content ratio is not particularly limited, and for example, it may be contained in a range of 0.5 mol % or more and less than 2.6 mol % in terms of oxide with respect to the silicon nitride sintered body. The periodic table referred to here is based on "Inorganic Chemical Nomenclature - IUPAC 1990 Recommendations" G. J. According to "Designation of Groups of the Periodic Table" in Table I-3.2, edited by Leich, translated and written by Kazuo Yamazaki, published on March 26, 1993, published by Tokyo Kagaku Dojin Co., Ltd., page 43.

Suitable examples of the Group 4 element of the periodic table, which is one of the specific elements, include titanium (Ti), zirconium (Zr), and hafnium (Hf). Rare earth elements include scandium (Sc), yttrium (Y), lanthanides, and actinides. Examples of the lanthanoids include cerium group elements and yttrium group elements, and examples of the cerium group elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), and promethium (Pm). , and samarium (Sm). Yttrium group elements include europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and thulium ( Tm), ytterbium (Yb), and lutetium (Lu). Examples of the actinoid include actinium (Ac), thorium (Th), and the like. Note that oxide conversion refers to oxidizing an element or converting it into an oxide combined with oxygen.

One type of the specific element may be contained in the silicon nitride sintered body, or a plurality of types of the specific elements may be contained in the silicon nitride sintered body.

From the following viewpoints, the silicon nitride sintered body preferably contains at least one kind selected from Ti (titanium) nitride, carbonitride, and carbide in a total amount of 5% by mass or more and 20% by mass or less, The total content is more preferably 5% by mass or more and 15% by mass or less, and even more preferably the total content is 5% by mass or more and 10% by mass or less. When the silicon nitride sintered body contains the above compound of Ti (titanium) within the above range, further peeling resistance can be expected. That is, the matrix silicon nitride (α-silicon nitride, β-silicon nitride), which has a smaller coefficient of thermal expansion than the diamond layer 5, and the above compound of Ti (titanium), which has a larger thermal expansion than the diamond layer 5, are combined. Then, while tensile stress and compressive stress are randomly applied and the stresses cancel each other out, the thermal expansion of the entire sintered body falls within the range of relational expression 1 above, and further peeling resistance can be expected.
Preferred examples of Ti (titanium) nitrides, carbonitrides, and carbides include TiC _x N _(1-x) (0≦X≦1).

SiAlON (SiAlON) in the SiAlON sintered body is a ceramic crystal particle made of Si (silicon), Al (aluminum), O (oxygen), and N (nitrogen). Sialon is made by adding a sintering aid to raw material powder containing constituent elements such as Si, Al, O, and N, such as silicon nitride, alumina, aluminum nitride, and silica, and sintering the mixture. Sialon particles have β-sialon expressed by the composition formula Si _6-Z Al _Z O _Z N _8-Z (0<Z≦4.2) and composition formula Mx (Si, Al) ₁₂ (O, N). ₁₆ (0 < are doing. Like silicon nitride, β-sialon has a structure in which acicular structures are intertwined, so it has high toughness, whereas α-sialon has an equiaxed particle shape, so it has lower toughness than β-sialon. However, it has high hardness. In sialon, the ratio of α-sialon and β-sialon is not particularly limited.

The Sialon sintered body contains 1% by mass of a rare earth element used as a sintering aid, for example, at least one element selected from the group consisting of Sc, Y, Dy, Yb, Er, Ce, and Lu, in terms of oxide. It may contain up to 7% by mass.

From the viewpoint of further improving the peeling resistance of the diamond layer 5, the Sialon sintered body preferably contains Al (aluminum) in an oxide equivalent of 2% by mass or more and 35% by mass or less, and 5% by mass or more and 30% by mass. It is more preferable to contain 15% by mass or more and 25% by mass or less.

From the following viewpoints, it is preferable that the sialon sintered body contains at least one kind selected from Ti (titanium) nitride, carbonitride, and carbide in a total of 5% by mass or more and 20% by mass or less, and the total It is more preferable that the content is 5% by mass or more and 15% by mass or less, and even more preferably the total content is 5% by mass or more and 10% by mass or less. When the sialon sintered body contains the above compound of Ti (titanium) within the above range, further peeling resistance can be expected. That is, by combining the SiAlON sintered body of the matrix with a coefficient of thermal expansion smaller than that of the diamond layer 5 and the above compound of Ti (titanium) whose thermal expansion is larger than that of the diamond layer 5, the tensile stress and compressive stress are randomly generated. While the stress applied to the sintered body is canceled out, the thermal expansion of the entire sintered body falls within the range of relational expression 1 above, and further peeling resistance can be expected.
Preferred examples of Ti (titanium) nitrides, carbonitrides, and carbides include TiC _x N _(1-x) (0≦X≦1).

The sialon sintered body preferably contains a polytype crystal phase from the viewpoint of further improving peeling resistance. The polytype is preferably at least one selected from the group consisting of 12H, 15R, and 21R. That is, the Sialon sintered body is composed of 12H-sialon (general formula: SiAl ₅ O ₂ N ₅ ), 15R-sialon (general formula: SiAl ₄ O ₂ N ₄ ), and 21R-sialon (general formula: SiAl ₆ O ₂ It is preferable to contain at least one polytype sialon selected from the group consisting of N ₆ ).
Since the Sialon sintered body contains a polytype crystal phase, further peeling resistance can be expected. In other words, the matrix sialon (α-sialon, β-sialon), which has a smaller thermal expansion coefficient than the diamond layer 5, and the polytype sialon, which has a larger thermal expansion than the diamond layer 5, combine to reduce tensile stress and compressive stress. is applied randomly and cancels out the stress, and the thermal expansion of the entire sintered body falls within the range of relational expression 1 above, and further peeling resistance can be expected.
The polytype crystal phase contained in the Sialon sintered body can be identified by X-ray diffraction analysis of the sintered body.

(3) Diamond layer 5
As schematically shown in FIG. 1, the diamond layer 5 has a plurality of voids 9 extending in the crystal growth direction from a portion in contact with the base material 3. Here, the "crystal growth direction" refers to the vector direction in which the distance from the base point to the surface of the diamond layer 5 is the shortest when the base point is a specific point on the surface 3A of the base material 3. , meaning the upward direction in FIG. Note that FIG. 1 conceptually shows an SEM image of the cut surface of the diamond-coated cutting tool 1 observed with a SEM (Scanning Electron Microscope), and does not accurately show the actual SEM image. It's not a thing. FIG. 1 is a conceptual diagram of a SEM image of a cut surface cut in a direction perpendicular to the surface 3A of the base material 3. When observing the void 9 by SEM, the diamond-coated cutting tool 1 is cut together with the base material 3 including the diamond layer 5, and a sample for SEM observation is prepared from the cut surface using a commercially available cross-sectional sample preparation device. . Then, by observing the vicinity of the interface between the base material 3 and the diamond layer 5 of the sample under magnification using a SEM, the voids 9 can be observed.

The void 9 in the present disclosure has a width W of 100 nm or more and 500 nm or less in the direction perpendicular to the crystal growth direction (direction along the surface 3A of the base material 3, lateral direction in FIGS. 1 and 2) in the cut plane, and , the length LP in the direction along the crystal growth direction (perpendicular to the surface 3A of the base material 3, longitudinal direction in FIGS. 1 and 2) is defined as 100 nm or more and 1 μm or less. Note that the width W is the length of the gap 9 along the vertical direction (lateral direction in FIGS. 1 and 2) from the most one end side to the most other end side in the vertical direction (lateral direction in FIGS. 1 and 2). be. The length LP is the length along the crystal growth direction (vertical direction in FIGS. 1 and 2) from the most one end side to the most other end side in the crystal growth direction (vertical direction in FIGS. 1 and 2) of the void 9. . FIG. 3 illustrates a case where the shape is different from the void 9 shown in FIGS. 1 and 2, and the width W and length LP in the case of FIG. 3 are illustrated. Note that the shapes of the voids 9 shown in FIGS. 1 to 3 do not necessarily accurately represent the actual shapes.
In the diamond-coated cutting tool 1 of the present disclosure, the distance L between the centers 9A of adjacent voids 9 is The average (average interval) is 12 μm or more and 1000 μm or less, preferably 12 μm or more and 500 μm or less, and more preferably 14 μm or more and 100 μm or less. Note that the center 9A of the void 9 is the center in the vertical direction (lateral direction in FIGS. 1, 2, and 3). The interval L is the distance between the centers 9A of adjacent voids 9 in the vertical direction.
The average interval is obtained, for example, as follows. A plurality of (for example, 50) SEM images (for example, 5000x magnification) are successively obtained from the position of the cutting edge of the diamond-coated cutting tool 1 in a direction moving away from the cutting edge. That is, by connecting a plurality of SEM images, it is possible to observe the interface between the base material 3 and the diamond layer 5. The field of view of each SEM image can be, for example, 18 μm x 24 μm, but in short, it is only necessary to observe the interface at least 1000 μm from the position of the cutting edge of the diamond-coated cutting tool 1 and identify the average interval. The plurality of obtained SEM images are analyzed using WinRoof (image analysis/measurement software Mitani Shoji Co., Ltd.), and each interval L between the centers 9A of adjacent voids 9 is determined. The obtained intervals L are averaged (arithmetic mean) to obtain an average interval.

The diamond layer 5 preferably has a multilayer structure in order to reduce the surface roughness of the film and provide high film toughness. The diamond layer 5 is preferably made of polycrystalline diamond. Here, polycrystalline diamond is one in which fine diamond particles are tightly bound together. The diamond layer 5 may contain foreign atoms such as boron, nitrogen, and silicon, and unavoidable impurities other than these elements.

The method of forming the diamond layer 5 is not particularly limited. The diamond layer 5 is preferably formed by CVD (chemical vapor deposition). Examples of the CVD method include microwave plasma CVD, hot filament CVD, and high frequency plasma CVD. Among these CVD methods, the microwave plasma CVD method is preferably used because it can easily obtain a film with fine crystal grain size and low surface roughness.

The thickness of the diamond layer 5 is not particularly limited. The thickness of the diamond layer 5 is preferably 8 μm or more and 20 μm or less. If it is 8 μm or more, the adhesion will improve, and if it is 20 μm or less, it will be easier to sharpen the cutting edge, resulting in improved cutting performance.

(4) Estimated reason why the structure of the present disclosure increases the adhesion of the diamond layer 5 to the base material 3 and improves the peeling resistance The coefficient of thermal expansion of the diamond layer 5 (diamond coating) is 3.1×10 ⁻⁶ / K, and in order to reduce the residual stress, it is necessary to make the thermal expansion coefficients of the diamond layer 5 and the base material 3 as close as possible. However, when the coefficient of thermal expansion of the base material 3 is smaller than that of the diamond layer 5, tensile stress is applied to the diamond layer 5, and the adhesion of the diamond layer 5 to the base material 3 decreases. Therefore, the coefficient of thermal expansion of the base material 3 needs to be close to and larger than the coefficient of thermal expansion of the diamond layer 5. By setting the average coefficient of thermal expansion x of the base material 3 within the specific range shown in the above relational expression 1, the coefficients of thermal expansion of the diamond layer 5 and the base material 3 become close to each other, and the tensile stress applied to the diamond layer 5 is suppressed. It is presumed that the adhesion of the diamond layer 5 to the base material 3 is improved.
Furthermore, it is presumed that the diamond-coated cutting tool 1 of the present disclosure has improved peeling resistance for the following reasons. If the interval between the voids 9 at the interface of the base material 3 is narrow, the contact area between the diamond layer 5 and the base material 3 becomes small, and the adhesion of the diamond layer 5 to the base material 3 decreases. On the other hand, if the spacing between the voids 9 is too wide, residual stress will accumulate at the interface and the adhesion will deteriorate. In the diamond-coated cutting tool 1 of the present disclosure, the average distance between the centers 9A of adjacent voids 9 is adjusted to 12 μm or more and 1000 μm or less, thereby reducing the number of starting points for peeling and suppressing residual stress at the interface. It is presumed that this improves peeling resistance.
It is presumed that by improving the peeling resistance, peeling becomes less likely to occur not only at the initial stage of cutting but also when cutting continues for a long time, extending the life of the tool. Furthermore, the diamond-coated cutting tool 1 of the present disclosure can be used under more severe conditions, so it is possible to increase cutting efficiency.

2. Method for manufacturing diamond-coated cutting tool 1 The method for manufacturing diamond-coated cutting tool 1 is not particularly limited. An example of a method for manufacturing the diamond-coated cutting tool 1 is shown below.

(1) Raw materials For example, the following raw material powders are used as raw materials.
・Main component α-Si ₃ N ₄ powder ・Sintering aid Y ₂ O ₃ (yttrium oxide), Yb ₂ O ₃ (ytterbium oxide), La ₂ O ₃ (lanthanum oxide), CeO ₂ (cerium (IV oxide) ), Er ₂ O ₃ (erbium oxide), Dy ₂ O ₃ (dysprosium oxide), MgO (magnesium oxide), MgCO ₃ (magnesium carbonate), Al ₂ O ₃ (aluminum oxide), AlN (aluminum nitride), ZrO ₂ Select from (zirconium oxide), TiN (titanium nitride), TiC (titanium carbide)

(2) Preparation of base material 3 Raw material powder, an organic binder dissolved in a solvent, and a solvent are wet mixed using a ball to obtain a slurry. The slurry is dried and press-molded into a desired (tool) shape to obtain a molded body. The molded body is subjected to a degreasing treatment in a heating device under a predetermined atmosphere, for example, at 400° C. to 800° C. for 60 minutes to 120 minutes. Further, the degreased molded body is placed in a container and heated under a predetermined atmosphere, for example, at 1700° C. to 1900° C. for 120 minutes to 360 minutes, thereby obtaining a sintered body. If the theoretical density of the sintered body is less than 99%, HIP treatment (Hot Isostatic Pressing method: Hot Isostatic Pressing method) for 120 minutes to 240 minutes at 1500° C. to 1700° C. under a predetermined atmosphere of 1000 atm, for example, is performed. ) to form a dense body with a theoretical density of 99% or more. The sintered body or dense body produced in this way corresponds to the base material 3.

(3) Pre-coating treatment Before coating the diamond layer 5, a pre-coating treatment may be performed. The coating pretreatment is performed to improve the adhesion of the diamond layer 5 to the base material 3. Specifically, roughening treatment of the surface 3A of the base material 3 is exemplified. For the surface roughening treatment, chemical corrosion such as electrolytic polishing, sandblasting using abrasive grains such as SiC, etc., is used, for example.

(4) Coating diamond layer 5 (formation of diamond layer 5)
For coating the diamond layer 5, for example, a microwave plasma CVD method can be used. For example, methane (CH ₄ ), hydrogen (H ₂ ), carbon monoxide (CO), or the like is supplied as a raw material gas for coating. The coating process, for example, repeats the following two steps. The following nucleation step and crystal growth step are repeated until the set film thickness is reached, and the multilayered diamond layer 5 is coated on the surface 3A of the base material 3.
The average distance between the centers 9A of adjacent voids 9 in the diamond layer 5 can be controlled by adjusting the average coefficient of thermal expansion of the base material 3 from 25°C to 600°C. The reason why such control is possible is not clear, but it is presumed as follows. The surface 3A of the base material 3 is heated during the coating process, and is cooled after the coating process. Since the average coefficient of thermal expansion of the diamond layer 5 and the average coefficient of thermal expansion of the base material 3 are different, tensile stress or compressive stress is applied to the diamond layer 5 formed on the base material 3 during cooling, and the voids 9 are formed. This is considered to occur. Therefore, it is presumed that by adjusting the average coefficient of thermal expansion of the base material 3, the above-mentioned tensile stress or compressive stress can be controlled, and the average distance between the centers 9A of adjacent voids 9 can be controlled. It can also be controlled by adjusting the surface roughness of the base material 5 through pre-coating treatment. It is presumed that this is because the tensile stress or compressive stress applied to the diamond layer 5 is also controlled by the surface roughness.
(4.1) Nucleation step The flow rates of methane and hydrogen are adjusted so that the concentration of methane is at a predetermined set value within the range of 10% to 30%. At this time, the surface temperature of the base material 3 is set within the range of 700°C to 900°C, and the gas pressure within the reactor is set within the range of 2.5×10 ² Pa to 3.0×10 ³ Pa. This condition is continued for 0.1 to 2 hours at the set pressure determined within.
(4.2) Crystal growth process The flow rates of methane and hydrogen are adjusted so that the concentration of methane is at a predetermined set value within the range of 1% to 4%. At this time, the surface temperature of the base material 3 is set at a temperature set within the range of 800°C to 900°C, and the gas pressure within the reactor is set within the range of 1.0×10 ³ Pa to 7.0×10 ³ Pa. Crystals are grown at a predetermined pressure within the chamber.

Hereinafter, a more specific explanation will be given with reference to Examples.
Note that Experimental Examples 1 to 10 are examples, and Experimental Examples 11 to 18 are comparative examples.
In Table 1, when "*" is attached, such as "11*", it indicates that it is a comparative example.

1. Preparation of diamond-coated cutting tool (1) Preparation of base material α-Si ₃ N ₄ powder with an average particle size of 1.0 μm or less, and sintering aids Y ₂ O ₃ (yttrium oxide) and Yb ₂ O ₃ (ytterbium oxide), La ₂ O ₃ (lanthanum oxide), CeO ₂ (cerium (IV) oxide), Er ₂ O ₃ (erbium oxide), Dy ₂ O ₃ (dysprosium oxide), MgO (magnesium oxide), MgCO ₃ (magnesium carbonate), Al ₂ O ₃ (aluminum oxide), AlN (aluminum nitride), ZrO ₂ (zirconium oxide), TiN (titanium nitride), and TiC (titanium carbide) in the composition shown in Table 1. The powder was weighed to obtain a raw material powder.
A slurry was obtained by wet mixing raw material powder, a microwax-based organic binder dissolved in ethanol, and ethanol in a ball mill using Si ₃ N ₄ balls. The slurry was dried and press-molded into the shape of SPGN422 according to ISO standards to obtain a molded body.
The molded body was subjected to degreasing treatment in a heating device at 400° C. to 800° C. for 60 minutes to 120 minutes under a nitrogen atmosphere of 1 atm. Further, the degreased molded body was placed in a container made of Si ₃ N ₄ and heated in a nitrogen atmosphere at 1700° C. to 1900° C. for 120 minutes to 360 minutes to obtain a sintered body. If the theoretical density of the sintered body is less than 99%, HIP treatment is further performed at 1500°C to 1700°C for 120 to 240 minutes in a nitrogen atmosphere of 1000 atm to make it a dense body with a theoretical density of 99% or more. . The sintered body or dense body thus produced was used as a base material.

(2) Coating A microwave plasma CVD method was used for coating the diamond layer. Methane (CH ₄ ), hydrogen (H ₂ ), carbon monoxide (CO), etc. were used as raw material gases. In the coating process, the nucleation process described in section (4.1) and the crystal growth process described in section (4.2) are repeated until the set film thickness (12 μm) is reached, and a diamond layer with a multilayer structure is formed. was coated on the surface of the base material.

2. Measuring method for diamond-coated cutting tools, etc. (1) Calculation method for Al oxide content and Ti compound content The Al oxide content and Ti compound content are based on the base material. The calculation was made by measuring X-ray Fluorescence Spectrometry.
Note that the Ti compound herein means at least one selected from Ti nitrides, carbonitrides, and carbides.

(2) Crystal phase identification method Polytype SiAlON contained in the sintered body was identified by X-ray diffraction analysis of the base material. Here, polytype sialon refers to 12H-sialon (general formula: SiAl ₅ O ₂ N ₅ ), 15R-sialon (general formula: SiAl ₄ O ₂ N ₄ ), and 21R-sialon (general formula: SiAl ₆ O ₂ N ₆ ).

(3) Coefficient of thermal expansion measurement method Each base material was measured using TMA (Thermo Mechanical Analysis). The measurement conditions were R. T (25°C) to 1000°C, under Ar atmosphere, at 10°C/min.

(4) Observation method of voids Observation was performed using a scanning electron microscope (SEM). Specifically, the diamond-coated cutting tool was cut along with the base material including the diamond layer, and the interface between the diamond layer and the base material was polished by ion milling to prepare a sample for SEM observation. Then, the presence or absence of voids and the spacing between voids were measured by observing the vicinity of the interface under magnification using a SEM. At this time, 50 SEM images (5000x magnification) were successively obtained from the position of the cutting edge of the diamond-coated cutting tool in the direction away from the cutting edge. The field of view of each SEM image was 18 μm×24 μm. The obtained 50 SEM images were analyzed using WinRoof (image analysis/measurement software Mitani Shoji Co., Ltd.), and the distance between the centers of adjacent voids was determined. Then, the determined intervals were averaged to obtain an average interval.
In addition, when measuring the average spacing, the width of the void in the cut plane in the direction perpendicular to the crystal growth direction is 100 nm or more and 500 nm or less, and the length in the direction along the crystal growth direction is 100 nm or more and 1 μm or less. The air gap was used. In other words, voids that did not meet this requirement were not used for spacing measurements.

3. Cutting test of diamond-coated cutting tools (1) Test method A cutting test was conducted using each diamond-coated cutting tool. The test conditions are as follows. In the cutting test, the number of passes until the diamond layer peeled off from the diamond-coated cutting tool was measured. The higher the number of passes, the higher the evaluation. The evaluation was as follows.
<Test conditions>
・Work material: Aluminum material (AC4A-T6)
・Cutting speed: 300m/min
・Depth of cut: 1.0mm
・Feed amount: 0.25mm/rev.
・Length per 1 pass: 200mm
・Cutting environment: With cooling water

<Evaluation>
"A"...1400 passes or more "B"...1000 passes or more but less than 1400 passes "C"...900 passes or more but less than 1000 passes "D"...Less than 900 passes

(2) Test results The test results are shown in Table 1.
The average coefficient of thermal expansion x satisfies 3.1×10 ⁻⁶ /K≦x≦4.0×10 ⁻⁶ /K, and the average distance between the centers of the adjacent voids is 12 μm or more and 1000 μm or less. Experimental Examples 1 to 10 all had good evaluations of "C" or higher. ^On the other ^hand , the average coefficient of thermal expansion Experimental Examples 11 to 17 where the thickness was not 12 μm or more and 1000 μm or less were all rated as “D”, which was not good. More specifically, in Experimental Examples 1 to 10, the number of passes until peeling was at least 900, while in Experimental Examples 11 to 17, the number of passes until peeling was at most 600, and the durability was The peelability was significantly different.
Comparing Experimental Examples 1, 2, and 3, Experimental Example 3 containing 2% by mass or more and 35% by mass or less of Al in terms of oxide was evaluated higher than Experimental Examples 1 and 2 which were outside this range.
Comparing Experimental Examples 1, 2, and 4, Experimental Example 4 containing Ti nitride (TiN) from 5% by mass to 20% by mass was evaluated higher than Experimental Examples 1 and 2, which were outside this range.
Comparing Experimental Examples 3, 5, 6, 7, and 8, Experimental Examples 5, 6, 7, and 8 containing a polytype crystal phase were evaluated higher than Experiment Example 3, which did not contain a polytype crystal phase. .

The present disclosure is not limited to the embodiments detailed above, and various modifications or changes can be made within the scope of the claims of the present disclosure.

1...Diamond coated cutting tool 3...Base material 3A...Surface 5...Diamond layer 9...Void 9A...Center

Claims (4)

A diamond-coated cutting tool comprising a base material and a diamond layer coating the surface of the base material,
The base material has an average coefficient of thermal expansion x from 25°C to 600°C,
3.1×10 ^-6 /K≦x≦4.0×10 ^-6 /K
and the diamond layer has a plurality of voids extending in the crystal growth direction from a portion in contact with the base material,
In a cut surface obtained by cutting the diamond-coated cutting tool on a plane including the base material and the diamond layer, the average distance between the centers of each of the adjacent voids is 12 μm or more and 1000 μm or less,
A diamond-coated cutting tool , wherein the base material is made of a silicon nitride sintered body or a sialon sintered body . The diamond-coated cutting tool according to claim 1 , wherein the sialon sintered body contains Al in an amount of 2% by mass or more and 35% by mass or less in terms of oxide. The silicon nitride sintered body contains a total of 5% by mass or more and 20% by mass or less of at least one selected from Ti nitride, carbonitride, and carbide,
The diamond coating according to claim 1 or 2 , wherein the sialon sintered body contains a total of 5% by mass or more and 20% by mass or less of at least one selected from Ti nitride, carbonitride, and carbide. Cutting tools. The diamond-coated cutting tool according to any one of claims 1 to 3 , wherein the sialon sintered body includes a polytype crystal phase.

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