A cubic boron nitride sintered body, and a tool having a coated cubic boron nitride sintered body.

Abstract

To provide a cubic boron nitride sintered body and a covered cubic boron nitride sintered body capable of extending the tool life, by having excellent wear resistance and defect resistance.SOLUTION: A cubic boron nitride sintered body containing cubic boron nitride and a binder phase, wherein in the cross-sectional structure, the content ratios of the cubic boron nitride and the binder phase are within a predetermined range, and the binder phase includes a Ti compound phase containing a predetermined compound, an Al compound phase containing a predetermined compound, and a W compound phase containing WC, the average particle size of the W compound phase is 0.5 μm or more and 3.0 μm or less, the content ratios of the Ti compound phase and the Al compound phase relative to the entire binder phase are within a predetermined range, the content ratio X1 of the W compound phase is 2.0 area % or more and 30.0 area % or less, and in a range extending 300 nm from the interface between the cubic boron nitride and the binder phase toward the binder phase side, the content ratio X2 of the W compound phase relative to the entire binder phase is greater than the content ratio X1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cubic boron nitride sintered body and a tool having a coated cubic boron nitride sintered body. [Background technology]

[0002] A cubic boron nitride sintered body contains cubic boron nitride (hereinafter also referred to as "cBN") and a binder phase. Conventionally, cubic boron nitride sintered bodies containing a Ti compound as the binder phase material have been widely used as tools using cBN sintered bodies for cutting iron-based workpieces such as steel and cast iron. This is because cubic boron nitride sintered bodies containing a Ti compound have low affinity with iron-based workpieces and excellent reactive wear resistance.

[0003] Therefore, in recent years, cBN sintered bodies containing various Ti compounds have been proposed. For example, Patent Document 1 proposes a cutting tool made of a cBN-based sintered body in which at least the cutting edge is formed by a cBN-based sintered body containing cBN particles as a hard phase and Ti compound particles as a binding phase, wherein the average particle size of the Ti compound particles is 250 nm or less, and a W-Co phase in which W and Co components coexist exists at the interface of the Ti compound particles and at the interface between the Ti compound particles and the cBN particles, and the W-Co phase exists without interruption between the cBN particles, thereby forming a heat transfer path. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-28929 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, conventional cubic boron nitride sintered bodies containing Ti compounds have low thermal conductivity and toughness, and there is room for improvement. Recent machining processes demand high efficiency, with a greater emphasis on high speed, high feed rates, and deep cuts. Therefore, in recent machining processes, there is a need to improve the chipping resistance and wear resistance of tools compared to conventional methods.

[0006] Against this backdrop, Patent Document 1 describes a cBN sintered body that has improved thermal conductivity and excellent wear resistance due to the presence of a continuous W-Co phase between cBN particles. However, the content ratio and / or particle size of the W-Co phase, which is presumed to be present in a certain proportion near the surface of the cBN particles, have not been sufficiently investigated, so there is room for improvement in fracture resistance.

[0007] The present invention aims to provide a cubic boron nitride sintered body and a coated cubic boron nitride sintered body that have excellent wear resistance and fracture resistance, and can extend tool life. [Means for solving the problem]

[0008] Through extensive research into extending tool life, the inventors discovered that by segregating a W compound phase containing WC near the surface of cBN particles in a cubic boron nitride sintered body containing a Ti compound, and by controlling its particle size, it is possible to improve fracture resistance, thereby extending tool life. This led to the completion of the present invention. [1] A cubic boron nitride sintered body comprising cubic boron nitride and a bonding phase, When the cross-sectional structure of the cubic boron nitride sintered body was observed, the content of cubic boron nitride was 10.0 area% to 60.0 area% of the total 100 area% of the cubic boron nitride sintered body, and the content of the binding phase was 40.0 area% to 90.0 area%. The bonded phase comprises a Ti compound phase, an Al compound phase, and a W compound phase. The Ti compound phase contains a compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The Al compound phase contains a compound of Al and at least one element selected from the group consisting of C, N, O, and B. The W compound phase contains WC. The average particle size of the W compound phase is 0.5 μm or more and 3.0 μm or less. In the cross-sectional structure, the content ratio of the Ti compound phase is 60.0 area% or more and 90.0 area% or less, the content ratio of the Al compound phase is more than 0.0 area% and 20.0 area% or less, and the content ratio X1 of the W compound phase is 2.0 area% or more and 30.0 area% or less, with respect to 100 area% of the entire bonding phase. In the cross-sectional structure, in the range from the interface between the cubic boron nitride and the bonding phase to a distance of 300 nm toward the bonding phase side, the content ratio X2 of the W compound phase with respect to 100 area% of the entire bonding phase is greater than the content ratio X1. Cubic boron nitride sintered body. [2] The W compound phase further contains at least one of a compound of W and at least one element selected from the group consisting of C, N, O, and B (excluding WC), and a compound of W and Co and at least one element selected from the group consisting of C, N, O, and B. The cubic boron nitride sintered body according to [1]. [3] The ratio of the content ratio X2 to the content ratio X1 is 1.10 or more and 2.10 or less. The cubic boron nitride sintered body according to [1] or [2]. [4] The content ratio X2 is 3.0 area% or more and 45.0 area% or less. The cubic boron nitride sintered body according to any one of [1] to [3]. [5] Let the X-ray diffraction peak intensity of the (101) plane of WC in the bonding phase be I WC and the X-ray diffraction peak intensity of the (004) plane of WB2 be I WB2 When it is set as, I WCand I WB2 I for the sum WB2 The ratio is between 0.00 and 0.03. A cubic boron nitride sintered body as described in any one of [1] to [4]. [6] The W compound phase further comprises a compound of W and Co with at least one element selected from the group consisting of C, N, O, and B, wherein the content ratio (atomic ratio) of the Co element to the total content ratio of the W and Co elements is 0.05 or more and 0.50 or less. The cubic boron nitride sintered body described in [1] to [5]. [7] A cubic boron nitride sintered body according to any one of items [1] to [6], and a coating layer formed on the surface of the cubic boron nitride sintered body, The coating layer is a single layer or a laminate of two or more layers, comprising at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the entire coating layer is 0.5 μm or more and 8.0 μm or less. Coated cubic boron nitride sintered body. [8] A tool comprising a cubic boron nitride sintered body or a coated cubic boron nitride sintered body as described in any one of items [1] to [7]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a cubic boron nitride sintered body and a coated cubic boron nitride sintered body that have excellent wear resistance and fracture resistance, thereby extending tool life. [Modes for carrying out the invention]

[0010] The following describes in detail embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment"), but the present invention is not limited to the embodiments described below. The present invention can be modified in various ways without departing from its spirit.

[0011] [Cubic boron nitride sintered body] The cBN sintered body of this embodiment is a cBN sintered body containing cBN and a binder phase, and when the cross-sectional structure of the cBN sintered body is observed, the cBN content is 10.0 area% to 60.0 area% of the total 100 area% of the cBN sintered body, and the binder phase content is 40.0 area% to 90.0 area%. The binder phase contains a Ti compound phase, an Al compound phase, and a W compound phase, the Ti compound phase contains a compound of Ti and at least one element selected from the group consisting of C, N, O, and B, and the Al compound phase contains a compound of Al and at least one element selected from the group consisting of C, N, O, and B. The W compound phase contains WC, the average particle size of the W compound phase is 0.5 μm or more and 3.0 μm or less, in the cross-sectional structure, the content of the Ti compound phase is 60.0 area% or more and 90.0 area% or less relative to 100 area% of the total area of ​​the binder phase, the content of the Al compound phase is greater than 0.0 area% and 20.0 area% or less, the content X1 of the W compound phase is 2.0 area% or more and 30.0 area% or less, and in the cross-sectional structure, in the range from the interface between cBN and the binder phase to a distance of 300 nm toward the binder phase, the content X2 of the W compound phase relative to 100 area% of the total area of ​​the binder phase is greater than the content X1.

[0012] By adopting this configuration, the cBN sintered body of this embodiment can improve wear resistance and fracture resistance, thereby extending tool life. The factors contributing to the improved wear resistance and fracture resistance of the cBN sintered body in this embodiment, resulting in a longer tool life, are not fully understood, but the inventors speculate that these factors are as follows. However, the factors are not limited to these. In this embodiment, the cBN sintered body has a cBN content of 10.0 area% or more relative to the total area of ​​the cBN sintered body, resulting in a high content of cBN, which has excellent mechanical strength, and therefore mainly excellent fracture resistance. On the other hand, in this embodiment, the cBN sintered body has a cBN content of 60.0 area% or less, resulting in a low content of cBN, which has poor reactivity with iron, and therefore mainly excellent wear resistance. Furthermore, in this embodiment, the cBN sintered body has a binder phase content of 40.0 area% or more, resulting in a relatively low content of cBN, which has poor reactivity with iron, and therefore mainly excellent wear resistance. On the other hand, in this embodiment, the cBN sintered body has a binder phase content of 90.0 area% or less, resulting in a relatively high content of cBN, which has excellent mechanical strength, and therefore mainly excellent fracture resistance. Furthermore, the cBN sintered body of this embodiment has excellent wear resistance, mainly because the Ti compound phase contains a compound of Ti and at least one element selected from the group consisting of C, N, O, and B, and the content of the Ti compound phase is 60.0 area% or more relative to 100.0 area% of the total bonding phase, thereby improving its reactivity with iron. On the other hand, the cBN sintered body of this embodiment has excellent wear resistance, mainly because the thermal conductivity is improved, by having a Ti compound phase content of 90.0 area% or less. Furthermore, the cBN sintered body of this embodiment has excellent chipping resistance, mainly because the Al compound phase contains a compound of Al and at least one element selected from the group consisting of C, N, O, and B, and the content of the Al compound phase is greater than 0.0 area% relative to 100.0 area% of the total bonding phase, thereby improving its sinterability. On the other hand, the cBN sintered body of this embodiment has excellent wear resistance and / or fracture resistance because the Al compound phase content is 20.0 area% or less, resulting in a low content of Al2O3, which has poor thermal conductivity, and / or AlN, which has poor mechanical strength. Furthermore, the cBN sintered body of this embodiment has excellent wear resistance because the W compound phase contains WC, and the W compound phase content X1 is 2.0 area% or more relative to the total bonding phase of 100.0 area%, thus improving the thermal conductivity of the cBN sintered body. MutuallyThe hardness of the cBN sintered body is improved by having a W compound phase content X1 of 30.0 area% or less, resulting in superior wear resistance. In this embodiment, the cBN sintered body has a W compound phase content X2 relative to 100 area% of the total binder phase in the range from the interface between cBN and the binder phase to a distance of 300 nm toward the binder phase, which is greater than the above content X1. As a result, the proportion of WC, which has a smaller difference in thermal expansion coefficient with cBN compared to the Ti compound phase and Al compound phase, is higher near the surface of the cBN particles. This reduces strain and stress concentration due to thermal stress near the interface between cBN and the binder phase, thus improving fracture resistance. Furthermore, in this embodiment, the toughness of the cBN sintered body is improved by having an average particle size of the W compound phase of 0.5 μm or more, resulting in superior wear resistance. Moreover, the effects of making the above content X2 higher than the content X1 can be effectively and reliably achieved. thing Because the average particle size of the phase is 3.0 μm or less, the hardness of the cBN sintered body is improved, resulting in superior wear resistance.

[0013] The cBN sintered body of this embodiment contains cBN and a binder phase. The cBN content is between 10.0 area% and 60.0 area%, and the binder phase content is between 40.0 area% and 90.0 area%. In the cBN sintered body of this embodiment, the total content of cBN and the binder phase is 100.0 area%.

[0014] In the cBN sintered body of this embodiment, the content ratio (area %) of cBN and the binder phase can be determined by taking a scan electron microscope (SEM) image of any cross-section and analyzing the captured SEM image with commercially available image analysis software. Specifically, it can be determined by the method described in the examples below.

[0015] [Cubic boron nitride (cBN)] In the cBN sintered body of this embodiment, a cBN content of 10.0 area% or more relative to 100.0 area% of the total cBN sintered body results in a high content of cBN, which has excellent mechanical strength, and therefore primarily excellent fracture resistance. On the other hand, a cBN content of 60.0 area% or less results in a low content of cBN, which has poor reactivity with iron, and therefore primarily excellent wear resistance. From a similar viewpoint, a cBN content of 15.0 area% to 50.0 area% is preferable, and a cBN content of 20.0 area% to 40.0 area% is more preferable.

[0016] [Binded phase] In the cBN sintered body of this embodiment, the binder phase content is 40.0 area% or more relative to 100.0 area% of the total cBN sintered body. This results in a relatively low content of cBN, which has poor reactivity with iron, and therefore exhibits excellent wear resistance. On the other hand, if the binder phase content is 90.0 area% or less, the content of cBN, which has excellent mechanical strength, becomes relatively high, and therefore exhibits excellent fracture resistance. From a similar viewpoint, the binder phase content is preferably 50.0 area% to 85.0 area%, and more preferably 60.0 area% to 80.0 area%.

[0017] The cBN sintered body of this embodiment has a bonding phase comprising a Ti compound phase, an Al compound phase, and a W compound phase. The content of the Ti compound phase is 60.0% to 90.0% of the total bonded phase area (100.0% area). A Ti compound phase content of 60.0% or more improves reactivity with iron, resulting in superior wear resistance. Conversely, a Ti compound phase content of 90.0% or less improves thermal conductivity, also resulting in superior wear resistance. From a similar viewpoint, a Ti compound phase content of 62.9% to 87.9% is preferable, and 67.1% to 82.4% is more preferable.

[0018] In the cBN sintered body of this embodiment, the Ti compound phase preferably contains at least one selected from the group consisting of TiC, TiCN, TiN, and TiB2. The inclusion of such compounds in the Ti compound phase tends to result in excellent reactive wear resistance. From a similar viewpoint, the Ti compound phase is more preferably to contain at least one selected from the group consisting of TiC, TiCN, and TiB2, even more preferably to contain TiC or TiB2, and even more preferably to contain TiC and TiB2.

[0019] The content of the Al compound phase is between 0.0 area% and 20.0 area% relative to 100.0 area% of the total bonding phase. A content of Al compound phase greater than 0.0 area% improves sinterability, resulting in superior fracture resistance. On the other hand, a content of Al compound phase of 20.0 area% or less reduces the content of Al2O3, which has poor thermal conductivity, and / or AlN, which has poor mechanical strength, resulting in superior wear resistance and / or fracture resistance of the cBN sintered body. From a similar viewpoint, the content of Al compound phase is preferably between 2.2 area% and 16.0 area%, and more preferably between 3.0 area% and 12.9 area%.

[0020] In the cBN sintered body of this embodiment, the Al compound phase preferably contains at least one selected from the group consisting of Al2O3, AlN, and AlB2. When the Al compound phase contains such compounds, the sinterability of the cBN sintered body is improved, and it tends to have excellent fracture resistance. From a similar viewpoint, the Al compound phase is more preferably selected from the group consisting of Al2O3 and AlN, and even more preferably contains Al2O3.

[0021] The W compound phase content X1 is between 2.0 area% and 30.0 area% relative to 100.0 area% of the total bonding phase. A W compound phase content X1 of 2.0 area% or more improves the thermal conductivity of the cBN sintered body, resulting in superior wear resistance. On the other hand, the W compound... MutuallyThe hardness of the cBN sintered body is improved by having a content ratio X1 of 30.0 area% or less, and thus it is mainly excellent in wear resistance. From a similar viewpoint, the content ratio of the W compound phase is preferably 2.2 area% or more and 27.7 area% or less, more preferably 5.0 area% or more and 26.0 area% or less, and even more preferably 6.1 area% or more and 22.0 area% or less.

[0022] In the cBN sintered body of this embodiment, the W compound phase contains WC, and more preferably further contains at least one of the following: a compound of W and at least one element selected from the group consisting of C, N, O, and B (excluding WC), and a compound of W and Co and at least one element selected from the group consisting of C, N, O, and B. The compound of W and at least one element selected from the group consisting of C, N, O, and B more preferably contains at least one selected from the group consisting of W boride, W carbide (excluding WC), W and Co boride, and W and Co carbide, and more preferably contains W carbide (excluding WC) and / or W and Co carbide. Here, examples of compounds included in the W compound phase other than WC are Co3W3C, Co6W6C, W2Co 21 Examples include B6, CoWB, W2C and WB, and WC in which Co is dissolved. When the W compound phase contains such compounds, stress concentration near the interface between cBN and the binder phase is relieved, and the bonding force between cBN and the binder phase is improved, resulting in a tendency for superior fracture resistance. From a similar viewpoint, it is more preferable to include at least one selected from the group consisting of Co3W3C, Co6W6C, and WC in which Co is dissolved, even more preferable to include at least one selected from the group consisting of Co3W3C and WC in which Co is dissolved, and even more preferable to consist of at least one selected from the group consisting of Co3W3C and WC in which Co is dissolved.

[0023] In the cBN sintered body of this embodiment, the binder phase preferably includes a Ti compound phase, an Al compound phase, and a W compound phase, and further preferably includes a metal containing at least one element selected from the group consisting of W, Co, Ni, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta, and / or a compound of at least one element selected from the group consisting of Co, Ni, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta, and at least one element selected from the group consisting of C, N, O, and B. The further inclusion of such components in the binder phase promotes the reaction sintering between cubic boron nitride and the binder phase, and tends to yield a cubic boron nitride sintered body with excellent wear resistance and fracture resistance. Examples of metals containing at least one element selected from the group consisting of W, Co, Ni, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta, and compounds of at least one element selected from the group consisting of Co, Ni, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta and at least one element selected from the group consisting of C, N, O, and B include VC, VN, Cr3C2, CrN, Cr2N, ZrC, ZrN, ZrO2, NbC, NbN, Mo2C, HfC, HfC, TaC, TaN, Mo, Co, CoAl, and Ni. Among these, it is more preferable to include CrN, VC, NbN, or Mo2C from the same viewpoint as described above. Furthermore, when such compounds are included, their content is preferably 0.1 area% to 10.0 area% and more preferably 0.5 area% to 9.0 area% based on 100 area% of the total bonded phase.

[0024] In this embodiment, the cBN sintered body preferably has a content ratio X2 of the W compound phase relative to 100% of the total area of ​​the binder phase in the range from the interface between cBN and the binder phase to a distance of 300 nm toward the binder phase side, which is between 3.0 area% and 45.0 area%. When the above content ratio X2 is 3.0 area% or more, the content ratio of WC, which has a smaller difference in thermal expansion coefficient with cBN compared to Ti compounds and Al compounds, is increased near the cBN, thereby easing stress concentration near the interface between cBN and the binder phase. As the bonding strength between cBN and the binder phase is improved, the fracture resistance tends to be even better. On the other hand, when the above content ratio X2 is 45.0 area% or less, the proportion of the Ti compound phase and / or Al compound phase near the cBN particles is relatively higher. As the sinterability of the cBN sintered body is improved, the wear resistance and fracture resistance tend to be even better. From a similar viewpoint, the above content ratio X2 is more preferably 4.5 area% or more and 42.0 area% or less, and even more preferably 8.0 area% or more and 39.0 area% or less. In the definition of content ratio X2, "the entire bonded phase" means the entire bonded phase in the range from the interface between cBN and the bonded phase to a distance of 300 nm toward the bonded phase, and "content ratio of W compound phase X2" means the content ratio of the W compound phase in the range from the interface between cBN and the bonded phase to a distance of 300 nm toward the bonded phase. Furthermore, if the bonded phase region is narrow and there is a double overlap between the range from the interface between cBN and the bonded phase to a distance of 300 nm toward the bonded phase and the range from another interface between cBN and the bonded phase to a distance of 300 nm toward the bonded phase, the area of ​​the overlapping portion is not counted twice. Similarly, if there is a triple or more overlapping portion, the area of ​​the overlapping portion is not counted three or more times.

[0025] The ratio of the content ratio X2 to the content ratio X1 is preferably 1.10 or more and 2.10 or less. When the ratio of the content ratio X2 to the content ratio X1 is 1.10 or more, the effect of alleviating strain and stress concentration due to thermal stress near the interface between cBN and the bonding phase is more effective and reliable, and the defect resistance tends to improve. Further, when the ratio of the content ratio X2 to the content ratio X1 is 2.10 or less, the thermal conductivity in the bonding phase is improved, so that the wear resistance tends to be excellent. From the same viewpoint, the ratio of the content ratio X2 to the content ratio X1 is more preferably 1.20 or more and 2.01 or less, and even more preferably 1.30 or more and 1.90 or less.

[0026] In the bonding phase, the X-ray diffraction peak intensity of the (101) plane of WC is I WC and the X-ray diffraction peak intensity of the (004) plane of WB2 is I WB2 . When WC and I WB2 are used, the ratio of I WB2 to the sum of I WC and I WB2 is preferably 0.00 or more and 0.03 or less. The ratio I WB2 / (I WB2 +I WC +I WB2 ) being 0.00 or more and 0.03 or less indicates that the W compound phase does not contain WB2 or, even if it contains WB2, the value of the above ratio is 0.03 or less, suppressing the formation of a boride of W with low mechanical strength, improving the toughness of the cBN sintered body, and thus tending to be even more excellent in defect resistance. From the same viewpoint, the above ratio I WB2 / (I WC +I WB2 ) is more preferably 0.00 or more and 0.02 or less, even more preferably 0.00 or more and 0.01 or less, and even more preferably 0.00.

[0027] When the W compound phase further contains compounds of W and Co with at least one element selected from the group consisting of C, N, O, and B, the ratio of the Co element to the total ratio of the W and Co elements (atomic ratio) is preferably 0.05 or more and 0.50 or less. When the above atomic ratio Co / (W+Co) in the W compound phase is 0.05 or more, the toughness of the W compound phase is improved, and the toughness of the cBN sintered body is improved, resulting in a tendency for even better fracture resistance. Furthermore, when the above atomic ratio Co / (W+Co) is 0.50 or less, the hardness of the W compound phase is improved, and the hardness of the cBN sintered body is improved, resulting in a tendency for even better wear resistance. From a similar viewpoint, the above atomic ratio Co / (W+Co) is more preferably 0.10 or more and 0.43 or less, and even more preferably 0.20 or more and 0.38 or less.

[0028] In this embodiment, the composition and X-ray diffraction peak intensity of each compound in cBN and the bonded phase can be identified using a commercially available X-ray diffraction analyzer. For example, by using a Rigaku X-ray diffractometer (product name "SmartLab") and performing X-ray diffraction measurements of a 2θ / θ focused optical system using Cu-Kα rays under predetermined conditions, the composition of the bonded phase can be identified. Suitable measurement conditions include, for example, output: 45kV, 200mA, incident solar slit: 5°, diverging longitudinal slit: 2 / 3°, diverging longitudinal limiting slit: 5mm, scattering slit: 2 / 3°, receiving solar slit: 5°, receiving slit: 0.3mm, sampling width: 0.02°, scan speed: 1° / min, and 2θ measurement range: 30~90°.

[0029] In this embodiment, the cBN sintered body may inevitably contain impurities. Examples of impurities are not particularly limited, but include lithium, calcium, silicon, and magnesium contained in the raw material powder. Typically, the content of unavoidable impurities is 1% by mass or less of the total cBN sintered body. Therefore, unavoidable impurities have little effect on the characteristic values ​​of the cBN sintered body.

[0030] [Method for manufacturing cubic boron nitride sintered bodies] The cBN sintered body of this embodiment can be manufactured, for example, by the following method. As raw material powders, cubic boron nitride (cBN) powder, TiC powder, TiCN powder, TiN powder, WC powder, Co powder, Al powder, CrN powder, VC powder, NbN powder, Mo2C powder, etc. are prepared. Here, by increasing the average particle size of the WC powder, the average particle size of the resulting W compound can be increased, and the above I WB2 / ( I WC +I WB2 The value of ) can be reduced. Furthermore, by appropriately adjusting the proportion of each raw material powder, the content ratio (area %) of cBN and the binder phase in the resulting cBN sintered body can be controlled to within the above specific range. Furthermore, by appropriately adjusting the proportion of each raw material powder, the content ratio of the Co element (atomic ratio Co / (W+Co)) relative to the total content ratio of W and Co elements in the W compound phase can be controlled to within the above specific range. In addition, increasing the blending ratio of WC and Co tends to increase the above content ratio X2.

[0031] Here, the surface of the cBN powder is modified with an anionic polymer, and the surface of the WC powder and Co powder is modified with a cationic polymer (modification step). The surface-modified cBN powder, WC powder, and Co powder are stirred in ethanol for 1 to 24 hours to cause electrostatic adsorption of the powders, and then centrifugation is performed to remove excess polymer (stirring step).

[0032] By performing the modification and stirring steps as described above, the content ratio X2 tends to be larger than the content ratio X1. Furthermore, by performing the modification and stirring steps and increasing the processing time of the stirring step, the ratio of content ratio X2 to content ratio X1 (X2 / X1) tends to increase. In addition, by reducing the average particle size of the WC powder and then performing the modification and stirring steps, the ratio of content ratio X2 to content ratio X1 (X2 / X1) tends to increase. When the ratio (X2 / X1) increases by these methods, the content ratio X2 also tends to increase. When a method to increase the content ratio X2 is implemented, the above I WB2 / ( I WC +I WB2 The value of ) tends to be large.

[0033] Next, each prepared raw material powder is placed in a cylinder for a ball mill together with alumina balls, hexane solvent, and paraffin and mixed. By appropriately adjusting the proportion of each raw material powder, the content of the Ti compound phase (area %), the content of the Al compound phase (area %), and the content of the W compound phase X1 (area %) in the binding phase can be controlled to the above-mentioned specific range.

[0034] The raw material powder, mixed in a ball mill, is filled into a high-melting-point metal capsule made of Zr under a nitrogen atmosphere in a glove box. To remove moisture and organic components adsorbed on the surface of the filled raw material powder, vacuum heat treatment is performed with the capsule open. After vacuum heat treatment, the capsule is sealed, and the raw material powder filled in the capsule is sintered at high temperature and pressure. The conditions for high-temperature sintering are, for example, pressure: 4.0~7.0 GPa, temperature: 1200~1500°C, sintering time: 20~60 minutes. Here, if the temperature during sintering is controlled to be high, the above I WB2 / ( I WC +I WB2 The value of ) tends to be large.

[0035] Furthermore, for a more specific manufacturing method, the method described in the examples below may be used.

[0036] [Coated cubic boron nitride sintered body] The coated cubic boron nitride sintered body of this embodiment comprises the cubic boron nitride sintered body described above and a coating layer formed on the surface of the cubic boron nitride sintered body, wherein the coating layer is a single layer or a stack of two or more layers containing at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B, and the average thickness of the entire coating layer is 0.5 μm or more and 8.0 μm or less. The abrasion resistance of the cubic boron nitride sintered body is further improved by forming a coating layer on its surface. Furthermore, the coated cubic boron nitride sintered body of this embodiment, in which the coating layer has the above-mentioned components and composition, exhibits excellent abrasion resistance. Moreover, when the average thickness of the entire coating layer is 0.5 μm or more, abrasion resistance is mainly improved, and when the average thickness is 8.0 μm or less, the occurrence of defects due to peeling is suppressed, thus exhibiting excellent defect resistance. From this viewpoint, the average thickness of the entire coating layer is preferably 1.0 μm or more and 6.5 μm or less, and more preferably 1.5 μm or more and 6.0 μm or less.

[0037] Examples of compounds that form the coating layer include TiCN, TiC, TiN, TiAlN, TiSiN, CrN, and NbN. The coating layer may have a structure in which multiple layers with different compositions are alternately stacked. In this case, the average thickness of each layer is, for example, 5 nm to 500 nm.

[0038] The thickness of each layer constituting the coating layer, as well as the overall thickness of the coating layer, can be measured from the cross-sectional structure of the coated cubic boron nitride sintered body using an optical microscope, scanning electron microscope (SEM), or transmission electron microscope (TEM). The average thickness of each layer and the overall thickness of the coating layer in the coated cubic boron nitride sintered body can be determined by measuring the thickness of each layer and the overall thickness of the coating layer from three or more cross-sections located approximately 50 μm from the cutting edge of the surface facing the metal evaporation source toward the center of that surface, and then calculating the average value.

[0039] Furthermore, the composition of each layer constituting the coating layer can be measured from the cross-sectional structure of the coated cubic boron nitride sintered body using methods such as EDS or wavelength-dispersive X-ray analysis (WDS).

[0040] The method for manufacturing the coating layer in the coated cubic boron nitride sintered body of this embodiment is not particularly limited, but examples include chemical vapor deposition, ion plating, arc ion plating, sputtering, and ion mixing. Among these, arc ion plating is even more preferable because it provides superior adhesion between the coating layer and the cubic boron nitride sintered body.

[0041] [tool] The tool of this embodiment includes the cubic boron nitride sintered body or the coated cubic boron nitride sintered body described above. The tool of this embodiment may have the same configuration as known tools, except for the inclusion of the cubic boron nitride sintered body or coated cubic boron nitride sintered body. Since the cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment has excellent wear resistance and fracture resistance, tools containing them can be used, for example, as cutting tools or wear-resistant tools, and are preferably used as cutting tools. It is even more preferable that the cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment be included in cutting tools for carburized and quenched steel. When the cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment is included in cutting tools or wear-resistant tools, tool life can be extended compared to conventional tools. [Examples]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0043] (Example 1) [Weighing of raw material powder] Cubic boron nitride (cBN) powder, TiC powder, TiCN powder, TiN powder, WC powder, Co powder, Al powder, CrN powder, VC powder, NbN powder, and Mo2C powder were prepared and weighed according to the ratios shown in Tables 1 and 2 below. The average particle sizes were 2.0 μm (cBN powder), 2.0 μm (TiC powder), 2.0 μm (TiCN powder), 2.0 μm (TiN powder), 1.0 μm (Co powder), 0.5 μm (Al powder), 2.0 μm (Cr2N powder), 2.0 μm (VC powder), 2.0 μm (NbN powder), and 2.0 μm (Mo2C powder), respectively. The average particle size of the WC powder is shown in Table 3. The average particle size of the raw material powder was measured using the Fisher Sub-Sieve Sizer (FSSS) method as described in ASTM standard B330.

[0044] [Table 1]

[0045] [Table 2]

[0046] [Table 3]

[0047] [Modification process] Of the weighed raw material powders, the surface of the cBN powder was modified with sodium polystyrene sulfonate, an anionic polymer, and the WC powder and Co powder were modified with polydiallyldimethylammonium chloride, a cationic polymer.

[0048] [Agitation process] Next, the surface-modified cBN powder, WC powder, and Co powder were stirred in ethanol for 1 to 24 hours to induce electrostatic adsorption between the powders. After stirring, centrifugation was performed to remove excess polymer. Note that the modification and stirring steps were not performed for comparative samples 8 and 11.

[0049] [Table 4]

[0050] [Mixing process] The raw material powder after the stirring process and the remaining raw material powder after weighing were placed in a cylinder for a ball mill along with alumina balls, hexane solvent, and paraffin, and mixed for 6 hours. In comparative samples 8 and 11, the modification and stirring processes were not performed, and the above mixing process was carried out using the weighed raw material powder.

[0051] [Filling process and drying process] The mixed raw material powder was filled into a high-melting-point metal capsule made of Zr (hereinafter simply referred to as "capsule") in a glove box under a nitrogen atmosphere. To remove moisture and organic components adsorbed on the surface of the filled raw material powder, vacuum heat treatment was performed with the capsule open. After vacuum heat treatment, the capsule was sealed.

[0052] [Sintering process] Next, the raw material powder filled in the capsules was sintered under high temperature and high pressure for 40 minutes. The conditions for high-pressure sintering are shown in Table 5 below.

[0053] [Table 5]

[0054] [Analysis using SEM images] For cBN sintered bodies obtained by high-pressure sintering, the content ratio (area %) of cBN and the binder phase was determined by analyzing cross-sectional microstructure images of the cBN sintered bodies taken with a scanning electron microscope (SEM) using commercially available image analysis software. More specifically, the cBN sintered bodies were mirror-polished in a direction perpendicular to their surface. Next, the mirror-polished surface of the cBN sintered body, magnified at 5000x, was observed using a backscattered electron image with an SEM. Using an energy-dispersive X-ray analyzer (EDS) attached to the SEM, the black regions were identified as cBN, and the gray and white regions as the binder phase. Furthermore, within the binder phase, the dark gray regions were identified as the Al compound phase, the light gray regions as the Ti compound phase, and the white regions as the W compound phase. Subsequently, microstructure images of the above cross-section of cBN were taken using an SEM. The microstructure images were taken to include a 20 μm × 20 μm field of view, and a total of 20 field of view images were obtained. Using image analysis software, the occupied area of ​​cBN and the bonded phase was determined from the tissue images, and the content percentage (area %) was calculated from these occupied areas. Similarly, the content percentage (area %) of the Ti compound phase, the Al compound phase, and the W compound phase X1 (area %) in the bonded phase were calculated from the tissue images, based on the content percentage of each phase relative to the occupied area of ​​the bonded phase. Each value was the average of the values ​​obtained from 20 fields of view of the tissue images. Furthermore, if the bonded phase contained materials other than the Al compound phase, Ti compound phase, and W compound phase, these were identified by combining the analysis results of EDS mapping images, and the occupied area of ​​each was determined to calculate the content percentage (area %). Furthermore, by analyzing microstructure images of the same field of view as described above, the occupied area of ​​the bonded phase and the occupied area of ​​the W compound phase were determined in the range from the interface between cubic boron nitride and the bonded phase to a distance of 300 nm toward the bonded phase, respectively. The content ratio X2 (area %) of the W compound phase relative to 100% of the total bonded phase area in the above range was then measured. From the obtained values, the ratio of X2 to X1 was calculated. Here, the mirror-polished surface of the cBN sintered body refers to the surface of the cBN sintered body or the cross-section of the cBN sintered body obtained by mirror-polishing an arbitrary cross-section. The method for obtaining the mirror-polished surface of the cBN sintered body was polishing using diamond paste. The results obtained above are shown together in Table 6.

[0055] Also, in the case where the W compound phase contains the Co element, the content ratio (atomic ratio) of the Co element with respect to the total content ratio of the W element and the Co element was calculated as follows. First, in the same observation field as the microstructure photograph of the cBN sintered body taken by SEM as described above, EDS analysis of the entire field of view was performed to measure the content ratio (atomic ratio) of the W element and the Co element contained in the cBN sintered body. From the obtained values, the content ratio of the Co element with respect to the total content ratio of the W element and the Co element (in the table, denoted as atomic ratio Co / (W + Co)) was calculated. Furthermore, by image analysis of the microstructure photograph of the cubic boron nitride sintered body taken by SEM, the area of the W compound particles in the cross-sectional microstructure was determined, and the diameter of a circle with an area equal to that area was defined as the particle size of the W compound. The average value of the particle sizes of the W compound particles present in the microstructure photograph was determined as the average particle size of the W compound. These measurement results are shown in Table 7.

[0056] [Analysis of Composition by X-ray Diffraction (XRD)] Regarding the bonding phase contained in the cBN sintered body obtained by the sintering process, analysis of the composition by X-ray diffraction (XRD) was performed. The composition of the bonding phase was identified using an X-ray diffractometer (product name "SmartLab") manufactured by Rigaku Corporation. Specifically, X-ray diffraction measurement of the 2θ / θ convergent optical system using Cu-Kα rays was performed under the following conditions to identify the composition of the bonding phase. [X-ray Diffraction Measurement Conditions] Output: 45 kV, 200 mA, Incident-side Soller slit: 5°, Divergent vertical slit: 2 / 3°, Divergent vertical limiting slit: 5 mm, Scattering slit 2 / 3°, Receiving-side Soller slit: 5°, Receiving slit: 0.3 mm, Sampling width: 0.02°, Scan speed: 1° / min, 2θ measurement range: 30 to 90°. The analysis results are shown in Table 6. In Table 6, only the phases for which clear peaks were obtained by X-ray diffraction measurement are identified and shown. Analysis using EDS revealed the presence of a W compound phase containing both W and Co elements in all samples except for Invention 33 and Comparative Sample 8. Furthermore, it was determined that Invention 28 and Comparative Sample 12 contained Co3W3C. On the other hand, clear peaks of phases containing both W and Co elements could not be identified in samples other than Invention 28, Invention 33, Comparative Sample 8, and Comparative Sample 12. Therefore, it is presumed that these samples contain Co3W3C or WC in which Co is solid-dissolved (referred to as CoW compound in the table) in proportions that are not detectable by X-ray diffraction measurement. Furthermore, from the X-ray diffraction pattern obtained by the above X-ray diffraction measurement, the X-ray diffraction peak intensity of the (10¹) plane of WC (I WC ), and the X-ray diffraction peak intensity of the (004) plane of WB2 in the bonded phase (I WB2 ) and also I WC and I WB2 I for the sum WB2 The ratio was calculated. (In the table, I WB2 / ( I WC +I WB2 ) is noted. )The X-ray diffraction peaks for each crystal plane were obtained by referring to the following ICDD cards. These results are shown in Tables 6 and 7. WC: No. 00-051-0939 WB2: No.01-089-3928

[0057] [Table 6]

[0058] [Table 7]

[0059] [Manufacturing of cutting tools] The cBN sintered body obtained above was cut using a wire electrical discharge machine to match the insert shape of the tool as defined in ISO standard CNGA120408. The cut cBN sintered body was brazed to a base metal made of cemented carbide. The brazed tool was then honed to obtain a cutting tool.

[0060] The obtained samples were used to perform the following cutting tests and evaluations. [Cutting Test] Workpiece material: SCM415H carburized and hardened steel (HRC60) Workpiece shape: round bar, Machining method: External turning, Cutting speed: 200m / min, Feed rate: 0.15mm / rev, Cutting depth: 0.12mm, Coolant: Used (water-soluble coolant), Evaluation criteria: When the wear width of the tool's flank surface reaches 0.10 mm, or when it breaks, the tool is considered to have been removed. Tool life was defined as the machining time until tool life was reached. Furthermore, the wear width of the tool's flank surface was 0. The type of damage to a sample that reached 0.10 mm and reached the end of its tool life is defined as "normal wear," and the type of damage that resulted in chipping of the tool is defined as "normal wear." The damage pattern of samples that reached the end of their lifespan was defined as "loss." The results of the above test are shown in Table 8.

[0061] [Table 8]

[0062] The results shown in Table 8 indicate that the cutting tool using the invented cBN sintered body exhibits superior wear resistance and fracture resistance compared to the comparative cutting tool using the cBN sintered body, resulting in a longer tool life.

[0063] (Example 2) Next, as shown in Table 9, the surfaces of the cubic boron nitride sintered bodies of Invention 2, Invention 7, Invention 15, and Invention 19 obtained in Example 1 were subjected to ion bombardment treatment, and then a coating layer was formed by arc ion plating. When forming the first and second layers, they were formed in this order on the surface of the cubic boron nitride sintered body. For Inventions 41, 47, 51, 55, and 59, which contain two types of compounds in the composition of the first layer, layers of each compound with a thickness of 50 nm per layer were alternately and repeatedly formed to achieve the average thickness of the first layer. The respective treatment conditions were as follows. The composition and average thickness of the coating layer are as shown in Table 9 below.

[0064] [Conditions for ion bombardment treatment] • Substrate temperature: 500℃, • Pressure: Ar gas atmosphere at 2.7 Pa Voltage: -400V, ·Current: 40A, • Duration: 30 minutes.

[0065] [Coating layer formation conditions] • Substrate temperature: 500℃, • Pressure: Nitrogen (N2) gas atmosphere at 3.0 Pa (nitride layer), or a mixed gas atmosphere of nitrogen (N2) gas and acetylene gas (C2H2) gas at 3.0 Pa (carbonitride layer) Voltage: -60V, ·Current: 120A.

[0066] [Table 9]

[0067] The obtained coated cubic boron nitride sintered body was subjected to a cutting test in the same manner as in Example 1, and the invention was evaluated. The results are shown in Table 10.

[0068] [Table 10]

[0069] As shown in Table 10, coated cBN sintered bodies with a coating layer formed on the surface (inventions 40-59) exhibited even greater wear resistance and fracture resistance than cBN sintered bodies without a coating layer (inventions 2, 7, 15, 19), resulting in a longer tool life. [Industrial applicability]

[0070] The cubic boron nitride sintered body and the coated cubic boron nitride sintered body of the present invention have excellent wear resistance and fracture resistance, which extends tool life compared to conventional tools, and therefore have high potential for industrial application.

Claims

1. A cubic boron nitride sintered body comprising cubic boron nitride and a bonding phase, When the cross-sectional structure of the cubic boron nitride sintered body was observed, the content of cubic boron nitride was 10.0 area% to 58.0 area% of the total 100 area% of the cubic boron nitride sintered body, and the content of the binding phase was 42.0 area% to 90.0 area%. The bonded phase comprises a Ti compound phase, an Al compound phase, and a W compound phase. The Ti compound phase comprises a compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The Al compound phase comprises a compound of Al and at least one element selected from the group consisting of C, N, O, and B. The W compound phase includes WC, The average particle size of the W compound phase is 0.5 μm or more and 3.0 μm or less. In the cross-sectional structure, the content of the Ti compound phase is 60.0 area% or more and 90.0 area% or less relative to 100 area% of the total area of ​​the binder phase, the content of the Al compound phase is greater than 2.2 area% and 16.0 area% or less, and the content X1 of the W compound phase is 2.2 area% or more and 30.0 area% or less. The total content ratio of the Ti compound phase, the Al compound phase, and the W compound phase is 91.9% or more and 100.0% or less by area. In the cross-sectional structure, in the range from the interface between the cubic boron nitride and the bonding phase to a distance of 300 nm toward the bonding phase, the content ratio X2 of the W compound phase relative to 100% of the total area of ​​the bonding phase is greater than the content ratio X1. The aforementioned content ratio X2 is 4.5 area% or more and 42.0 area% or less. Cubic boron nitride sintered body.

2. The W compound phase further comprises at least one of the following: a compound of W and at least one element selected from the group consisting of C, N, O, and B (excluding WC), and a compound of W and Co and at least one element selected from the group consisting of C, N, O, and B. The cubic boron nitride sintered body according to claim 1.

3. The ratio of the content ratio X2 to the content ratio X1 is 1.10 or more and 2.10 or less. The cubic boron nitride sintered body according to claim 1.

4. The X-ray diffraction peak intensity of the (10¹) plane of WC in the bonded phase is I WC WB 2 The X-ray diffraction peak intensity of the (004) plane is I WB2 In that case, I WC and I WB2 I for the sum WB2 The ratio is between 0.00 and 0.

03. The cubic boron nitride sintered body according to claim 1.

5. The W compound phase further comprises a compound of W and Co and at least one element selected from the group consisting of C, N, O, and B, wherein the content ratio (atomic ratio) of the Co element to the total content ratio of the W and Co elements is 0.05 or more and 0.50 or less. The cubic boron nitride sintered body according to claim 1.

6. A cubic boron nitride sintered body according to any one of claims 1 to 5, and a coating layer formed on the surface of the cubic boron nitride sintered body, The coating layer is a single layer or a laminate of two or more layers, comprising at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B. The average thickness of the entire coating layer is 0.5 μm or more and 8.0 μm or less. Coated cubic boron nitride sintered body.

7. A tool comprising a cubic boron nitride sintered body according to any one of claims 1 to 5.

8. A tool comprising a coated cubic boron nitride sintered body as described in claim 6.

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