Cubic boron nitride sintered body, and, tool with covered 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] Cubic boron nitride sintered compacts contain cubic boron nitride (hereinafter also referred to as "cBN") and a binder phase. Conventionally, cubic boron nitride sintered compacts containing Ti compounds as binder phase materials have been widely used as tools using cBN sintered compacts for cutting ferrous workpieces such as steel and cast iron. This is because cubic boron nitride sintered compacts containing Ti compounds have low affinity with ferrous workpieces and have excellent reactive wear resistance.

[0003] For this reason, cBN sintered bodies containing various Ti compounds have been proposed in recent years. 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 binder phase, characterized in that the average particle size of the Ti compound particles is 250 nm or less, a W-Co phase in which W and Co components coexist is present at the interfaces between the Ti compound particles and between the Ti compound particles and the cBN particles, and the W-Co phase exists continuously between the cBN particles, thereby forming a heat transfer path. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-28929 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional cubic boron nitride sintered bodies containing Ti compounds have low thermal conductivity and toughness, leaving room for improvement. In recent years, there has been a demand for higher efficiency in cutting processes, with increasing speed, feed rate, and depth of cut becoming more pronounced. For this reason, cutting processes in recent years have required tools with improved chipping resistance and wear resistance compared to conventional methods.

[0006] In light of this background, the invention of 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 and / or grain size of the W-Co phase, which is presumed to exist in a constant proportion near the surface of the cBN particles, have not been fully investigated, leaving room for improvement in fracture resistance.

[0007] An object of the present invention is to provide a cubic boron nitride sintered body and a coated cubic boron nitride sintered body that have excellent wear resistance and chipping resistance and can extend tool life. [Means for solving the problem]

[0008] The inventors of the present invention have conducted extensive research into extending tool life and have found that in a cubic boron nitride sintered body containing a Ti compound, by segregating a W compound phase containing WC near the surface of cBN particles and controlling the particle size, it is possible to improve fracture resistance, thereby extending tool life, and have completed the present invention. [1] A cubic boron nitride sintered body comprising cubic boron nitride and a binder phase, When the cross-sectional structure of the cubic boron nitride sintered body is observed, the content of the cubic boron nitride is 10.0 area % or more and 60.0 area % or less, and the content of the binder phase is 40.0 area % or more and 90.0 area % or less, relative to 100 area % of the entire cubic boron nitride sintered body; the binder phase includes 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 W compound phase has an average grain size of 0.5 μm or more and 3.0 μm or less, In the cross-sectional structure, with respect to 100 area % of the entire binder phase, 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, In the cross-sectional structure, within a range of 300 nm from the interface between the cubic boron nitride and the binder phase toward the binder phase, a content ratio X2 of the W compound phase relative to 100% by area of ​​the entire binder phase is larger 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. [1] A cubic boron nitride sintered body according to the present invention. [3] The ratio of the content ratio X2 to the content ratio X1 is 1.10 or more and 2.10 or less. [1] or [2]. A cubic boron nitride sintered body. [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] The X-ray diffraction peak intensity of the (101) plane of WC in the binder phase is I WC and the X-ray diffraction peak intensity of the (004) plane of WB2 is I WB2 When I WCand I WB2 I for the sum of WB2 The ratio is 0.00 or more and 0.03 or less, The cubic boron nitride sintered body according to any one of [1] to [4]. [6] the W compound phase further contains a compound of W and Co with at least one element selected from the group consisting of C, N, O and B, and the content ratio (atomic ratio) of Co element to the total content ratio of W element and Co element is 0.05 or more and 0.50 or less; A cubic boron nitride sintered body according to any one of [1] to [5]. [7] [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, 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; 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 the cubic boron nitride sintered body or the coated cubic boron nitride sintered body according to any one of [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 chipping resistance, thereby enabling an extension of tool life. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail, but the present invention is not limited to the following embodiment. The present invention can be modified in various ways without departing from the gist of the present invention.

[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 content of cBN is 10.0 area % or more and 60.0 area % or less, and the content of the binder phase is 40.0 area % or more and 90.0 area % or less, relative to 100 area % of the entire cBN sintered body, 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 includes WC, and the average grain size of the W compound phase is 0.5 μm or more and 3.0 μm or less; in a cross-sectional structure, the content ratio of the Ti compound phase is 60.0 area % or more and 90.0 area % or less, and the content ratio of the Al compound phase is more than 0.0 area % and 20.0 area % or less, relative to 100 area % of the entire binder phase; 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 of 300 nm from the interface between the cBN and the binder phase toward the binder phase in the cross-sectional structure, the content ratio X2 of the W compound phase relative to 100 area % of the entire binder phase is larger than the content ratio X1.

[0012] By adopting such a configuration, the cBN sintered body of this embodiment can improve the wear resistance and chipping resistance, and as a result, the tool life can be extended. The factors that enable the cBN sintered body of this embodiment to have improved wear resistance and fracture resistance and a long tool life are not clear in detail, but the present inventors speculate that the factors are as follows, although the factors are not limited to these. The cBN sintered body of this embodiment has a cBN content of 10.0 area % or more relative to the total area of ​​the cBN sintered body (100.0 area %), which results in a high content of cBN, which has excellent mechanical strength, and therefore has excellent fracture resistance. On the other hand, the cBN sintered body of this embodiment has a cBN content of 60.0 area % or less, which results in a low content of cBN, which has poor reactivity with iron, and therefore has excellent wear resistance. Furthermore, the cBN sintered body of this embodiment has a binder phase content of 40.0 area % or more, which results in a relatively low content of cBN, which has poor reactivity with iron, and therefore has excellent wear resistance. On the other hand, the cBN sintered body of this embodiment has a binder phase content of 90.0 area % or less, which results in a relatively high content of cBN, which has excellent mechanical strength, and therefore has excellent fracture resistance. Furthermore, the cBN sintered body of this embodiment has a Ti compound phase containing a compound of Ti and at least one element selected from the group consisting of C, N, O, and B. The Ti compound phase accounts for 60.0 area% or more of the total binder phase (100.0 area%), thereby improving reactivity resistance with iron and thereby providing excellent wear resistance. The cBN sintered body of this embodiment has a Ti compound phase content of 90.0 area% or less, thereby improving thermal conductivity and thereby providing excellent wear resistance. The cBN sintered body of this embodiment has an Al compound phase containing a compound of Al and at least one element selected from the group consisting of C, N, O, and B. The Al compound phase accounts for more than 0.0 area% of the total binder phase (100.0 area%), thereby improving sinterability and thereby providing excellent fracture resistance. 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, which reduces the content of Al2O3, which has poor thermal conductivity, and / or the content of 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 100.0 area % of the entire binder phase, improving the thermal conductivity of the cBN sintered body. On the other hand, the W compound content X1 is 30.0 area % or less, improving the hardness of the cBN sintered body, improving the wear resistance.In the cBN sintered body of this embodiment, the W compound phase content ratio X2 relative to the total area of ​​the binder phase (100% by area) is greater than the content ratio X1 within a range extending 300 nm from the interface between the cBN and the binder phase toward the binder phase. This increases the content of WC, which has a smaller difference in thermal expansion coefficient from cBN than the Ti compound phase and Al compound phase, near the surface of the cBN particles. This reduces strain and stress concentration due to thermal stress near the interface between the cBN and the binder phase, thereby improving primarily fracture resistance. Furthermore, the cBN sintered body of this embodiment has an average grain size of 0.5 μm or more, which improves the toughness of the cBN sintered body, thereby providing excellent wear resistance. Furthermore, the effects of increasing the content ratio X2 above the content ratio X1 can be effectively and reliably achieved. Meanwhile, the average grain size of the W compound phase is 3.0 μm or less, which improves the hardness of the cBN sintered body, thereby providing excellent wear resistance.

[0013] The cBN sintered body of this embodiment contains cBN and a binder phase. The cBN content is 10.0 area % or more and 60.0 area % or less, and the binder phase content is 40.0 area % or more and 90.0 area % or less. 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 binder phase can be determined by photographing an arbitrary cross section with a scanning electron microscope (SEM) and analyzing the SEM photograph 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, the cBN content is 10.0 area% or more relative to the total area of ​​the cBN sintered body (100.0 area%). This increases the content of cBN, which has excellent mechanical strength, and therefore provides excellent fracture resistance. On the other hand, when the cBN content is 60.0 area% or less, the content of cBN, which has poor resistance to reactivity with iron, is reduced, and therefore provides excellent wear resistance. From the same perspective, the cBN content is preferably 15.0 area% or more and 50.0 area% or less, and more preferably 20.0 area% or more and 40.0 area% or less.

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

[0017] In the cBN sintered body of this embodiment, the binder phase includes a Ti compound phase, an Al compound phase, and a W compound phase. The content of the Ti compound phase is 60.0 area % or more and 90.0 area % or less, relative to 100.0 area % of the entire binder phase. When the content of the Ti compound phase is 60.0 area % or more, resistance to reactivity with iron is improved, resulting in excellent wear resistance. On the other hand, when the content of the Ti compound phase is 90.0 area % or less, thermal conductivity is improved, resulting in excellent wear resistance. From the same viewpoint, the content of the Ti compound phase is preferably 62.9 area % or more and 87.9 area % or less, and more preferably 67.1 area % or more and 82.4 area % or less.

[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. When the Ti compound phase contains such a compound, it tends to have excellent reactive wear resistance. From the same viewpoint, the Ti compound phase more preferably contains at least one selected from the group consisting of TiC, TiCN, and TiB2, even more preferably contains TiC or TiB2, and even more preferably contains TiC and TiB2.

[0019] The content of the Al compound phase is greater than 0.0 area% and less than 20.0 area% relative to 100.0 area% of the entire binder phase. When the content of the Al compound phase exceeds 0.0 area%, sinterability is improved, resulting in excellent fracture resistance. On the other hand, when the content of the Al compound phase is less than 20.0 area%, the content of Al2O3, which has poor thermal conductivity, and / or the content of AlN, which has poor mechanical strength, is reduced, resulting in excellent wear resistance and / or fracture resistance of the cBN sintered body. From the same perspective, the content of the Al compound phase is preferably greater than 2.2 area% and less than 16.0 area%, and more preferably greater than 3.0 area% and less than 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 a compound, the sinterability of the cBN sintered body improves, and therefore the cBN sintered body tends to have excellent fracture resistance. From the same viewpoint, the Al compound phase more preferably contains at least one selected from the group consisting of Al2O3 and AlN, and even more preferably contains Al2O3.

[0021] The W compound phase content X1 is 2.0 area% or more and 30.0 area% or less, relative to 100.0 area% of the entire binder phase. When the W compound phase content X1 is 2.0 area% or more, the cBN sintered body has improved thermal conductivity, mainly resulting in excellent wear resistance. On the other hand, when the W compound content X1 is 30.0 area% or less, the cBN sintered body has improved hardness, mainly resulting in excellent wear resistance. From the same perspective, the W compound phase content 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 preferably 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 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 a boride of W, a carbide of W (excluding WC), a boride of W and Co, and a carbide of W and Co, and even more preferably contains a carbide of W (excluding WC) and / or a carbide of W and Co. Here, examples of compounds contained in the W compound phase other than WC include Co3W3C, Co6W6C, and W2Co. 21 Examples of the W compound phase include B6, CoWB, W2C and WB, and WC with Co dissolved therein. When the W compound phase contains such compounds, stress concentration near the interface between the cBN and the binder phase is alleviated, improving the bonding strength between the cBN and the binder phase, and therefore the W compound phase tends to have excellent fracture resistance. From the same viewpoint, it is more preferable for the W compound phase to contain at least one selected from the group consisting of Co3W3C, Co6W6C, and WC with Co dissolved therein, even more preferable for the W compound phase to contain at least one selected from the group consisting of Co3W3C and WC with Co dissolved therein, and even more preferable for the W compound phase to consist of at least one selected from the group consisting of Co3W3C and WC with Co dissolved therein.

[0023] In the cBN sintered body of this embodiment, the binder phase preferably contains a Ti compound phase, an Al compound phase, and a W compound phase, and further contains 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 with at least one element selected from the group consisting of C, N, O, and B. When the binder phase further contains such components, reactive sintering between the cubic boron nitride and the binder phase is promoted, and a cubic boron nitride sintered body with excellent wear resistance and chipping resistance tends to be obtained. Examples of the 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 the compound of at least one element selected from the group consisting of Co, Ni, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta with at least one element selected from the group consisting of C, N, O, and B include VC, VN, CrC, CrN, CrN, ZrC, ZrN, ZrO, NbC, NbN, MoC, HfC, HfC, TaC, TaN, Mo, Co, CoAl, and Ni. Among these, CrN, VC, NbN, or MoC is more preferred for the same reasons as described above. Furthermore, when such a compound is contained, its 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 entire binder phase.

[0024] In the cBN sintered body of this embodiment, the W compound phase content ratio X2 is preferably 3.0 area% or more and 45.0 area% or less within a range of 300 nm from the interface between the cBN and the binder phase toward the binder phase, relative to the total area ratio of the binder phase (100 area%). By setting the content ratio X2 to 3.0 area% or more, the content ratio of WC, which has a smaller difference in thermal expansion coefficient from cBN than Ti compounds and Al compounds, increases near the cBN, thereby alleviating stress concentration near the interface between the cBN and the binder phase. The bonding strength between the cBN and the binder phase is improved, which tends to further improve fracture resistance. On the other hand, by setting the content ratio X2 to 45.0 area% or less, the proportion of the Ti compound phase and / or Al compound phase in the vicinity of the cBN particles is relatively high. The sinterability of the cBN sintered body is improved, which tends to further improve wear resistance and fracture resistance. From the same viewpoint, the 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 the content ratio X2, "the entire binder phase" refers to the entire binder phase within a range extending from the interface between the cBN and the binder phase toward the binder phase at a distance of 300 nm, and "the content ratio X2 of the W compound phase" refers to the content ratio of the W compound phase within a range extending from the interface between the cBN and the binder phase toward the binder phase at a distance of 300 nm. Furthermore, if the binder phase region is narrow and there is a double overlap between a range extending from the interface between the cBN and the binder phase toward the binder phase at a distance of 300 nm and another range extending from another interface between the cBN and the binder phase toward the binder phase at a distance of 300 nm, the area of ​​the overlapping portion is not counted twice. Similarly, if there are triple or more overlapping portions, the area of ​​the overlapping portion is not counted twice or more.

[0025] The ratio of the content percentage X2 to the content percentage X1 is preferably 1.10 or more and 2.10 or less. When the ratio of the content percentage X2 to the content percentage X1 is 1.10 or more, the effect of alleviating strain and stress concentration due to thermal stress near the interface between the cBN and the binder phase is more effectively and reliably achieved, and chipping resistance tends to be improved. Furthermore, when the ratio of the content percentage X2 to the content percentage X1 is 2.10 or less, the thermal conductivity in the binder phase is improved, and therefore wear resistance tends to be excellent. From the same viewpoint, the ratio of the content percentage X2 to the content percentage 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 binder 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 I WC and I WB2 I for the sum of WB2 It is preferable that the ratio is 0.00 or more and 0.03 or less. WC and I WB2 I for the sum of WB2 Ratio of I WB2 / (I WC +I WB2 ) is 0.00 or more and 0.03 or less, the W compound phase does not contain WB2, or even if it does contain WB2, the above ratio is 0.03 or less, which indicates that the formation of W borides, which have low mechanical strength, is suppressed, and the toughness of the cBN sintered body is improved, which tends to make the fracture resistance even better. 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 a compound of W, Co, and at least one element selected from the group consisting of C, N, O, and B, the content ratio (atomic ratio) of Co relative to the total content ratio of W and Co is preferably 0.05 to 0.50. When the 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 compact is improved, tending to further improve chipping resistance. Furthermore, when the 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 compact is improved, tending to further improve wear resistance. From the same viewpoint, the atomic ratio Co / (W+Co) is more preferably 0.10 to 0.43, and even more preferably 0.20 to 0.38.

[0028] In this embodiment, the composition and X-ray diffraction peak intensity of each compound in the cBN and binder phase can be identified using a commercially available X-ray diffraction measurement device. For example, the composition of the binder phase can be identified by performing X-ray diffraction measurement using a 2θ / θ focusing optical system with Cu-Kα radiation using an X-ray diffraction device manufactured by Rigaku (product name "SmartLab") under specified conditions. Measurement conditions are preferably set as follows: output: 45 kV, 200 mA, incident side Soller slit: 5°, divergence vertical slit: 2 / 3°, divergence 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°.

[0029] In this embodiment, the cBN sintered body may unavoidably contain impurities. Examples of impurities include, but are not limited to, lithium, calcium, silicon, and magnesium contained in the raw material powder. Typically, the content of unavoidable impurities is 1 mass% or less of the entire cBN sintered body. Therefore, the unavoidable impurities have almost no effect on the properties of the cBN sintered body.

[0030] [Method for manufacturing sintered cubic boron nitride] The cBN sintered body of this embodiment can be produced, 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, MoC powder, etc. are prepared. Here, by increasing the average particle size of the WC powder, the average particle size of the obtained W compound can be increased, and the above-mentioned I WB2 / (I WC +I WB2 ) can be reduced. In addition, by appropriately adjusting the ratio of each raw material powder, the content ratio (area %) of cBN and binder phase in the obtained cBN sintered body can be controlled within the above-mentioned specific range. In addition, by appropriately adjusting the ratio of each raw material powder, the content ratio of Co element to the total content ratio of W element and Co element in the W compound phase (atomic ratio Co / (W+Co)) can be controlled within the above-mentioned specific range. Furthermore, by increasing the compounding ratio of WC and Co, the content ratio X2 tends to increase.

[0031] Here, the surfaces of the cBN powder are modified with an anionic polymer, and the WC powder and Co powder are 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 electrostatically attract each other, and then centrifuged to remove excess polymer (stirring step).

[0032] By carrying out such a modification step and agitation step, the content ratio X2 tends to be larger than the content ratio X1. In addition, by carrying out the modification step and agitation step and lengthening the processing time of the agitation step, the ratio (X2 / X1) of the content ratio X2 to the content ratio X1 tends to be larger. Furthermore, by carrying out the modification step and agitation step after reducing the average particle size of the WC powder, the ratio (X2 / X1) of the content ratio X2 to the content ratio X1 tends to be larger. When the ratio (X2 / X1) is increased by these methods, the content ratio X2 also tends to be larger. When a method for increasing the content ratio X2 is carried out, the above I WB2 / (I WC +I WB2 ) tends to be large.

[0033] Next, the prepared raw material powders are mixed in a ball mill cylinder together with alumina balls, hexane solvent, and paraffin. By appropriately adjusting the ratio of each raw material powder, the content ratio (area %) of the Ti compound phase, the content ratio (area %) of the Al compound phase, and the content ratio X1 (area %) of the W compound phase in the binder phase can be controlled within the above-mentioned specific ranges.

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

[0035] As a more specific production 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 above-mentioned cubic boron nitride sintered body and a coating layer formed on the surface of the cubic boron nitride sintered body, the coating layer being a single layer or a laminate 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. Forming a coating layer on the surface of the cubic boron nitride sintered body further improves the wear resistance of the cubic boron nitride sintered body. Furthermore, the coated cubic boron nitride sintered body of this embodiment, in which the coating layer has the above-mentioned components and structure, has excellent wear resistance. Furthermore, when the average thickness of the entire coating layer is 0.5 μm or more, the wear resistance is improved, and when the average thickness is 8.0 μm or less, the occurrence of defects due to peeling is suppressed, resulting in excellent defect resistance. From this perspective, 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 or more and 500 nm or less.

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

[0039] 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 EDS or wavelength dispersive X-ray analyzer (WDS).

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

[0041] [tool] The tool of this embodiment includes the above-mentioned cubic boron nitride sintered body or the above-mentioned coated cubic boron nitride sintered body. The tool of this embodiment may have the same configuration as a known tool, except for including the cubic boron nitride sintered body or coated cubic boron nitride sintered body. The cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment has excellent wear resistance and chipping resistance, so tools including them can be used, for example, as cutting tools or wear-resistant tools, and cutting tools are particularly preferred. The cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment is more preferably included in cutting tools for carburized and hardened 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, the tool life can be extended compared to conventional tools. [Example]

[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 raw 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 MoC powder were prepared and weighed out according to the ratios shown in Tables 1 and 2. The average particle sizes of these powders 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 (CrN powder), 2.0 μm (VC powder), 2.0 μm (NbN powder), and 2.0 μm (MoC powder), respectively, and the average particle size of the WC powder was as shown in Table 3. The average particle size of the raw material powder was measured by the Fisher method (Fisher Sub-Sieve Sizer (FSSS)) according to the American Society for Testing and Materials (ASTM) standard B330.

[0044] [Table 1]

[0045] [Table 2]

[0046] [Table 3]

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

[0048] [Mixing process] Next, the surface-modified cBN powder, WC powder, and Co powder were stirred in ethanol for 1 to 24 hours to electrostatically attract the powders to each other. After stirring, the powders were centrifuged to remove excess polymer. Note that the modification and stirring processes were not performed on Comparative Products 8 and 11.

[0049] [Table 4]

[0050] [Mixing process] The raw material powder after the stirring step and the remaining raw material powder after weighing were placed in a cylinder for a ball mill together with alumina balls, hexane solvent, and paraffin and mixed for 6 hours. Note that for Comparative Products 8 and 11, the modification step and stirring step were not performed, and the above mixing step was performed using 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 nitrogen atmosphere in a glove box. In order to remove moisture and organic components adsorbed on the surface of the filled raw material powder, a vacuum heat treatment was carried out with the capsule open. After the vacuum heat treatment, the capsule was sealed.

[0052] [Sintering process] The raw material powder packed in the capsule was then sintered at high temperature and high pressure for 40 minutes. The high pressure sintering conditions are shown in Table 5 below.

[0053] [Table 5]

[0054] [SEM image analysis] The cBN and binder phase content (area %) of cBN sintered bodies obtained by high-pressure sintering was determined by analyzing cross-sectional microstructure photographs 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 perpendicular to their surfaces. Next, the mirror-polished surfaces of the cBN sintered bodies were observed using backscattered electron images magnified at 5000x using 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 were identified 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. Then, microstructure photographs of the above cross sections of the cBN were taken using the SEM. The microstructure photographs were taken to cover a 20 μm × 20 μm field of view, resulting in a total of 20 fields of view. Using image analysis software, the occupied areas of the cBN and binder phase were determined from the structural photographs, and the content ratios (area %) were calculated from the occupied areas. Similarly, the content ratios (area %) of the Ti compound phase, the Al compound phase, and the W compound phase X1 (area %) in the binder phase were calculated from the content ratios of each phase relative to the area occupied by the binder phase. Each value was the average of the values ​​obtained from 20 fields of view of the structural photographs. When the binder 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 the EDS mapping images, and the occupied areas of each were determined to calculate the content ratios (area %). Furthermore, the structural photograph of the same field of view as above was analyzed, and the area occupied by the binder phase and the area occupied by the W compound phase were determined within a range of 300 nm from the interface between the cubic boron nitride and the binder phase toward the binder phase side, and the content ratio X2 (area %) of the W compound phase relative to the total area 100% of the binder phase within the above range was measured. From the obtained value, the ratio of X2 to X1 was calculated. Here, the mirror-polished surface of the cBN sintered body refers to a cross section of the cBN sintered body obtained by mirror-polishing the surface or any cross section of the cBN sintered body. The mirror-polished surface of the cBN sintered body was obtained by polishing with diamond paste. The results obtained above are combined and shown in Table 6.

[0055] Also, in the case where the W compound phase contains Co element, the content ratio (atomic ratio) of Co element to the total content ratio of W element and 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, and the content ratios (atomic ratios) of W element and Co element contained in the cBN sintered body were measured. From the obtained values, the content ratio of Co element to the total content ratio of W element and Co element (denoted as atomic ratio Co / (W + Co) in the table) 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 the same area as 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 focusing 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°, Divergence vertical slit: 2 / 3°, Divergence 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. Table 6 identifies and shows only phases for which clear peaks were obtained in X-ray diffraction measurement. Analysis using EDS confirmed the presence of a W compound phase containing both W and Co elements in all samples except for Invention Product 33 and Comparative Product 8, and further confirmed the presence of Co3W3C in Invention Product 28 and Comparative Product 12. However, because clear peaks of a phase containing both W and Co could not be identified in samples other than Invention Product 28, Invention Product 33, Comparative Product 8, and Comparative Product 12, it is presumed that these samples contain Co3W3C or WC with Co solid solution (referred to as CoW compound in the table) at a level not detectable by X-ray diffraction measurement. In addition, from the X-ray diffraction pattern obtained by the above X-ray diffraction measurement, the X-ray diffraction peak intensity (I WC ), and the X-ray diffraction peak intensity of the (004) plane of WB2 in the binder phase (I WB2 ) and also I WC and I WB2 I for the sum of WB2 The ratio of I WB2 / (I WC +I WB2 ) The X-ray diffraction peaks of each crystal plane were referenced 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] [Cutting tool manufacturing] The cBN sintered body obtained above was cut using a wire electric discharge machine to fit the tool shape of the insert shape specified in ISO standard CNGA120408. The cut cBN sintered body was joined to a base metal made of cemented carbide by brazing. The brazed tool was then honed to obtain a cutting tool.

[0060] The obtained samples were subjected to the following cutting test and evaluated. [Cutting test] Work material: SCM415H carburized steel (HRC60), Workpiece shape: round bar, Processing method: external turning, Cutting speed: 200m / min, Feed: 0.15mm / rev, Cutting depth: 0.12 mm, Coolant: Use (water-soluble coolant), Evaluation item: When the tool flank wear width reaches 0.10 mm or when it is chipped, the tool is considered to be finished. The tool life was measured as the machining time until the tool life was reached. The damage type of the specimen that reached 0.10mm and reached the end of the tool life was defined as "normal wear" and the damage type of the specimen that reached chipping was defined as "normal wear". The damage type of the sample that reached the end of its life was designated as "fault." The results of the above tests are shown in Table 8.

[0061] [Table 8]

[0062] The results shown in Table 8 show that cutting tools using the inventive cBN sintered body have superior wear resistance and chipping resistance and have a longer tool life than cutting tools using the comparative cBN sintered body.

[0063] Example 2 Next, as shown in Table 9, the surfaces of the cubic boron nitride sintered bodies of Invention Products 2, 7, 15, and 19 obtained in Example 1 were subjected to ion bombardment treatment, and then coating layers were 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 Invention Products 41, 47, 51, 55, and 59, whose first layer composition contained two compounds, layers of each compound were formed alternately, each 50 nm thick, to achieve the average thickness of the first layer. The processing conditions for each were as follows. The composition and average thickness of the coating layer were as shown in Table 9 below.

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

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

[0066] [Table 9]

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

[0068] [Table 10]

[0069] The results shown in Table 10 show that the coated cBN sintered compacts (Inventions 40 to 59) with a coating layer formed on the surface have superior wear resistance and chipping resistance and have a longer tool life than the cBN sintered compacts (Inventions 2, 7, 15, and 19) without a coating layer formed on the surface. [Industrial Applicability]

[0070] The cubic boron nitride sintered body and coated cubic boron nitride sintered body of the present invention have excellent wear resistance and chipping resistance, and can extend the tool life compared to conventional tools, and in that respect have high industrial applicability.

Claims

1. A cubic boron nitride sintered body comprising cubic boron nitride and a binder phase, When a cross-sectional structure of the cubic boron nitride sintered body is observed, the content of the cubic boron nitride is 10.0 area % or more and 60.0 area % or less, and the content of the binder phase is 40.0 area % or more and 90.0 area % or less, relative to 100 area % of the entire cubic boron nitride sintered body; the binder phase includes 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 includes WC, the W compound phase has an average grain size of 0.5 μm or more and 3.0 μm or less, In the cross-sectional structure, with respect to 100 area % of the entire binder phase, a content ratio of the Ti compound phase is 60.0 area % or more and 90.0 area % or less, a content ratio of the Al compound phase is more than 0.0 area % and 20.0 area % or less, and a content ratio X1 of the W compound phase is 2.0 area % or more and 30.0 area % or less, In the cross-sectional structure, within a range of 300 nm from the interface between the cubic boron nitride and the binder phase toward the binder phase, a content ratio X2 of the W compound phase relative to 100% by area of ​​the entire binder phase is larger 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.

3. 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.

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

4. The content ratio X2 is 3.0 area% or more and 45.0 area% or less, 3. The cubic boron nitride sintered body according to claim 1.

5. The X-ray diffraction peak intensity of the (101) plane of WC in the binder phase is expressed as I WC And WB 2 The X-ray diffraction peak intensity of the (004) plane of WB2 When I WC and I WB2 I for the sum of WB2 The ratio is 0.00 or more and 0.03 or less, 3. The cubic boron nitride sintered body according to claim 1.

6. the W compound phase further contains a compound of W and Co with at least one element selected from the group consisting of C, N, O and B, and the content ratio (atomic ratio) of Co element to the total content ratio of W element and Co element is 0.05 or more and 0.50 or less; 3. The cubic boron nitride sintered body according to claim 1.

7. A cubic boron nitride sintered body according to any one of claims 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, 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; 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 the cubic boron nitride sintered body according to any one of claims 1 to 6.

9. A tool comprising the coated cubic boron nitride sintered body of claim 7.

Images