阅读说明：本技术 烧结体及其制造方法 (Sintered body and method for producing same ) 是由 石井显人 冈村克己 于 2018-02-15 设计创作，主要内容包括：提供了一种烧结体,该烧结体包含第一相和第二相,其中第一相由立方氮化硼颗粒构成,第二相由第一材料构成,第一材料为其中Al<Sub>2</Sub>O<Sub>3</Sub>沿晶粒边界分散和/或分散在晶粒内的部分稳定ZrO<Sub>2</Sub>。当将彼此相邻且直接接触、并且与第一相的表面的至少一部分直接接触的两个以上的立方氮化硼颗粒定义为接触体时,第二相满足Dii＝Di+(2×∑d<Sub>k</Sub>(k＝1至n))和[(Dii-Di)/Dii]×100≤50,其中Di为接触体的整个圆周的长度,n为与立方氮化硼颗粒直接接触的接触点的数量,d<Sub>k</Sub>为接触点的长度,并且∑d<Sub>k</Sub>(k＝1至n)为接触点的总长度。(A sintered body is provided which comprises a first phase composed of cubic boron nitride particles and a second phase composed of the first phaseThe first material is Al 2 O 3 Partially stabilized ZrO dispersed along grain boundaries and/or within grains 2 . When two or more cubic boron nitride particles adjacent to and in direct contact with each other and in direct contact with at least a part of the surface of the first phase are defined as a contact body, the second phase satisfies Dii ═ Di + (2 × Σ d) k (k 1 to n)) and [ (Dii-Di)/Dii:))]X 100 is less than or equal to 50, where Di is the length of the entire circumference of the contact body, n is the number of contact points with which the cubic boron nitride particles are in direct contact, d k Is the length of the contact point, and ∑ d k (k 1 to n) is the total length of the contact point.)

1. A sintered body comprising a first phase and a second phase, wherein

The first phase is composed of cubic boron nitride particles,

the second phase is composed of a first material, wherein the first material is Al₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂，

The second phase is in contact with at least a portion of the surface of the first phase, and

when two or more cubic boron nitride particles adjacent to and in direct contact with each other among the cubic boron nitride particles are defined as a contact body, Di represents the length of the entire circumference of the contact body, n represents the number of contact positions where the cubic boron nitride particles are in direct contact with each other, d represents the number of the contact positions where the cubic boron nitride particles are in direct contact with each other_kIndicates the length of each of the contact positions, and ∑ d_kRepresents the total length of the contact position, wherein when k is 1 to n, the following relationships (I) and (II) are satisfied:

[(Dii-Di)/Dii]×100≤50...(II)。

2. the sintered body according to claim 1, wherein 30% by volume or more and less than 50% by volume of the first phase is contained in the sintered body, and the following relational formula (II') is satisfied:

[(Dii-Di)/Dii]×100≤3...(II')。

3. the sintered body according to claim 1, wherein the first phase is contained in the sintered body by 50% by volume or more and less than 76% by volume, and satisfies the following relational formula (II "):

[(Dii-Di)/Dii]×100≤20...(II”)。

4. the sintered body according to claim 1, wherein 76% by volume or more and less than 100% by volume of the first phase is contained in the sintered body.

5. The sintered body according to any one of claims 1 to 4, further comprising a third phase, wherein

The third phase is composed of at least one compound composed of at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements, Al and Si in the periodic table and at least one element selected from the group consisting of carbon, nitrogen and oxygen.

6. A method of manufacturing a sintered body comprising a first phase composed of cubic boron nitride particles and a second phase composed of a first material, the method comprising:

a first step of obtaining a sintered precursor by coating the cubic boron nitride particles with the first material; and

a second step of obtaining the sintered body by sintering the sintering precursor at a pressure of more than 1GPa and 20GPa or less, wherein

The first material is Al₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂。

7. The method for producing a sintered body according to claim 6, wherein

The first step comprises a first preliminary step of obtaining a granular mixture comprising the cubic boron nitride particles and a binder,

in the first step, the sintering precursor is obtained by replacing the cubic boron nitride particles with the mixture obtained in the first preliminary step and coating the mixture with the first material,

the sintered body further comprises a third phase composed of the binder,

the binder is composed of at least one compound composed of at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements, Al and Si in the periodic table and at least one element selected from the group consisting of carbon, nitrogen and oxygen.

8. The method for producing a sintered body according to claim 6 or 7, wherein

The second step includes a second preliminary step of obtaining a mixture precursor by mixing the sintering precursor and the binder, and

in the second step, the sintered body is obtained by replacing the sintering precursor with the mixture precursor obtained in the second preliminary step, and sintering the mixture precursor at a pressure of greater than 1GPa and less than or equal to 20 GPa.

Technical Field

The present invention relates to a sintered body and a method of manufacturing the sintered body. The present application claims priority based on japanese patent application No.2017-104697, filed on day 26, 5/2017, the entire contents of which are incorporated herein by reference.

Background

WO 2016/171155 (patent document 1) discloses a sintered body comprising: cubic boron nitride (hereinafter, also referred to as "cBN"); and wherein Al₂O₃Partially stabilized zirconia (hereinafter, also referred to as "ATZ") dispersed in both or either of the grain boundaries and the grains. When applied to a cutting tool, the sintered body exhibits excellent characteristics in breakage resistance in high-speed cutting.

Reference list

Patent document

Patent document 1: WO 2016/171155

Disclosure of Invention

A sintered body according to an embodiment of the present disclosure is a sintered body including a first phase composed of cubic boron nitride particles and a second phase composed of a first material, the first material being wherein Al is₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂A second phase in contact with at least a part of the surface of the first phase, and two or more cubic boron nitrides adjacent to and in direct contact with each other among the cubic boron nitride particlesThe particles are defined as a contact body, Di represents the length of the entire circumference of the contact body, n represents the number of contact positions where cubic boron nitride particles are in direct contact with each other, d_kIndicates the length of each contact position, and ∑ d_kWhen k is 1 to n, the following relationships (I) and (II) are satisfied:

[(Dii-Di)/Dii]×100≤50...(II)。

a method of manufacturing a sintered body according to an embodiment of the present disclosure is a method of manufacturing a sintered body including a first phase composed of cubic boron nitride particles and a second phase composed of a first material, the method including: a first step of obtaining a sintered precursor by coating cubic boron nitride particles with a first material; and a second step of obtaining a sintered body by sintering the sintering precursor at a pressure of more than 1GPa and 20GPa or less, wherein the first material is Al-containing₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂。

Detailed Description

[ problem to be solved by the present disclosure ]

In the technical field related to cutting tools, it may be necessary to cut difficult-to-cut materials such as centrifugally cast iron under more severe conditions in terms of cutting speed and the like. In this case, in the sintered body disclosed in patent document 1, there is room for improvement in strength and life.

The present disclosure is made in view of the above-described actual situation, and an object of the present disclosure is to provide: a sintered body improved in strength and life, and thus cutting can be performed under more severe conditions; and a method of manufacturing the sintered body.

[ advantageous effects of the present disclosure ]

According to the above description, there may be provided: a sintered body improved in strength and life, and thus cutting can be performed under more severe conditions; and a method of manufacturing the sintered body.

[ description of the embodiments ]

The present inventors have conducted studies on sintered bodies capable of cutting under more severe conditions, and have found that the strength and life of sintered bodies produced by sintering ATZ-coated cBN particles are improved because direct contact of cBN particles with each other in the sintered bodies is suppressed. Thus, the inventors have obtained a sintered body according to the present disclosure and a method of manufacturing the sintered body.

First, embodiments of the present invention are enumerated and described.

[1]A sintered body according to an embodiment of the present disclosure is a sintered body including a first phase composed of cubic boron nitride particles and a second phase composed of a first material, the first material being wherein Al is₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂The second phase is in contact with at least a part of the surface of the first phase, and when two or more cubic boron nitride particles adjacent to and in direct contact with each other among the cubic boron nitride particles are defined as a contact body, Di represents the length of the entire circumference of the contact body, n represents the number of contact positions where the cubic boron nitride particles are in direct contact with each other, d_kIndicates the length of each contact position, and ∑ d_kWhen k is 1 to n, the following relational expressions (I) and (II) are satisfied. With this configuration, the strength and life of the sintered body can be improved.

[(Dii-Di)/Dii]×100≤50...(II)

[2] The first phase is contained in the sintered body by 30 vol% or more and less than 50 vol%, and preferably satisfies the following relation (II'):

[(Dii-Di)/Dii]×100≤3...(II')。

therefore, when used as a cutting tool, the sintered body can be suitably used for a finishing step in cutting of a difficult-to-cut material.

[3] Preferably, the first phase is contained in the sintered body by 50% by volume or more and less than 76% by volume, and satisfies the following relational expression (II "):

[(Dii-Di)/Dii]×100≤20...(II”)。

therefore, when used as a cutting tool, the sintered body can be suitably used in a rough machining step in cutting of a difficult-to-cut material.

[4] The first phase is preferably contained in the sintered body at 76 vol% or more and less than 100 vol%. Therefore, when used as a cutting tool, the sintered body can be suitably used for cutting a particularly hard difficult-to-cut material.

[5] Preferably, the sintered body further comprises a third phase, wherein the third phase is composed of at least one compound composed of at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements, Al and Si in the periodic table and at least one element selected from the group consisting of carbon, nitrogen and oxygen. Therefore, a sintered body also having more excellent toughness can be provided.

[6]A method of manufacturing a sintered body according to an embodiment of the present disclosure is a method of manufacturing a sintered body including a first phase composed of cubic boron nitride particles and a second phase composed of a first material, the method including: a first step of obtaining a sintered precursor by coating cubic boron nitride particles with a first material; and a second step of obtaining a sintered body by sintering the sintering precursor at a pressure of more than 1GPa and 20GPa or less, wherein the first material is Al-containing₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂. With this constitution, a sintered body having improved strength and life can be produced.

[7] Preferably, the first step includes a first preliminary step of obtaining a granular mixture containing cubic boron nitride particles and a binder, in which a sintered precursor is obtained by replacing the cubic boron nitride particles with the mixture obtained in the first preliminary step and coating the mixture with a first material, the sintered body further containing a third phase composed of the binder composed of at least one compound composed of at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements, Al and Si in the periodic table and at least one element selected from the group consisting of carbon, nitrogen and oxygen. Therefore, a sintered body having not only further improved strength and life but also further improved toughness can be produced.

[8] Preferably, the second step includes a second preliminary step of obtaining a mixture precursor by mixing the sintering precursor and the binder, and in the second step, the sintered body is obtained by replacing the sintering precursor with the mixture precursor obtained in the second preliminary step and sintering the mixture precursor at a pressure of greater than 1GPa and less than or equal to 20 GPa. Therefore, a sintered body having further improved toughness can be produced.

[ detailed description of embodiments of the invention of the present application ]

Embodiments of the present invention (hereinafter, also referred to as "the present embodiment") are described in more detail below; however, the present embodiment is not limited thereto.

Here, in the present specification, the expression "a to B" means a range from a lower limit to an upper limit (i.e., a to B). When the unit of a is not specified and only the unit of B is specified, the unit of a is the same as the unit of B. Further, when a compound and the like are represented by a chemical formula in the present specification and there is no particular limitation on the atomic ratio thereof, it is assumed that all conventionally known atomic ratios are included. The atomic ratio is not necessarily limited to only one within the stoichiometric range. For example, when "TiC" is described, the atomic ratio of TiC is not limited to Ti: C ═ 1:1, but includes all conventionally known atomic ratios. The same applies to compounds other than "TiC".

[ sintered body ]

The sintered body according to the present embodiment includes a first phase and a second phase. The first phase is composed of cubic boron nitride particles and the second phase is composed of a first material which is Al-containing₂O₃Dispersed in one or both of the grain boundaries and the grainsPartially stabilized ZrO₂。

< first phase >)

The first phase is composed of cubic boron nitride particles. The average particle diameter of the cubic boron nitride particles is preferably 0.1 μm to 5 μm. When the average particle diameter of the cubic boron nitride particles is less than 0.1 μm, the cubic boron nitride particles tend to be insufficiently sintered because the cubic boron nitride particles tend to aggregate when the cubic boron nitride particles are mixed with other powders. When the average particle diameter of the cubic boron nitride particles is larger than 5 μm, the strength of the cubic boron nitride particles tends to be lowered due to grain growth during sintering.

The cubic boron nitride particles preferably have a uniform particle diameter in order to achieve no stress concentration and achieve high strength. Further, the particle diameter of the cubic boron nitride particles preferably exhibits a normal distribution. Further, the cubic boron nitride particles preferably exhibit a binomial particle size distribution.

Such cubic boron nitride particles are preferably contained in the sintered body at a ratio of 30 vol% or more and less than 100 vol%. When the ratio of the cubic boron nitride particles is less than 30 vol%, hardness may be decreased, resulting in a decrease in wear resistance. When the ratio of the cubic boron nitride particles is 100 vol%, the first material is not included, with the result that the characteristics based on the first material cannot be obtained.

In this context, the first phase (cubic boron nitride particles) is preferably contained in the sintered body at 30% by volume or more and less than 50% by volume. Further, the following relational expression (II') included in the range of the following relational expression (II) is also preferably satisfied:

[(Dii-Di)/Dii]×100≤3...(II')。

in this case, when used as a cutting tool, the sintered body is suitable for a finishing step in cutting of a difficult-to-cut material.

Further, the first phase is preferably contained in the sintered body by 50 vol% or more and less than 76 vol%. In particular, it is also preferable to satisfy the following relational expression (II ") included in the range of the following relational expression (II):

[(Dii-Di)/Dii]×100≤20...(II”)。

in this case, when used as a cutting tool, the sintered body is suitable for a rough machining step in cutting of a difficult-to-cut material.

The first phase is preferably contained in the sintered body at 76 vol% or more and less than 100 vol%. In this case, the sintered body is suitable for cutting a particularly hard difficult-to-cut material when used as a cutting tool.

The average particle diameter and the content (% by volume) of the cubic boron nitride particles can be confirmed as follows. Specifically, the sintered body was subjected to CP (section polisher) processing using an argon ion beam, thereby obtaining a smooth section. The cross section was observed at a high magnification of 10000x using a field emission scanning electron microscope (FE-SEM) (trade name: "JSM-7800F", supplied by Nippon electronics Co., Ltd.), to thereby determine cubic boron nitride particles in the visual field. Further, binarization processing was performed by using image analysis software (trade name: "WinRooF ver.6.5.3", supplied by Sango Co., Ltd.) to calculate the equivalent circle diameter and area of all cubic boron nitride particles in the field of view. The average value of the equivalent circle diameter was regarded as the average particle diameter, and the average value of the area was regarded as the content. Here, in the present specification, for each area determined by a cross section obtained by CP processing, assuming that the area is continuous in the depth direction, the area represents a content in volume%.

< second phase >

The second phase is composed of a first material, wherein the first material is Al₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂。

< first Material >

As mentioned above, the first material is Al₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂. In this context, the term "partially stabilized ZrO₂"has the conventional, well-known meaning, and usually means ZrO such as₂In the ZrO₂In (b), an oxide other than zirconia is solid-dissolved to reduce oxygen vacancies in the structure, so that each is a cubic crystal and a tetragonal crystal of the crystal structureThe square crystals are stable or metastable at room temperature. Examples of the oxide include calcium oxide and magnesium oxide and rare earth oxides such as yttrium oxide. Partially stabilized ZrO₂One or two or more such oxides may be included. The solid solution amount of the oxide other than zirconia is preferably ZrO₂About 1 to 4 mol%.

In the first material (second phase), ZrO is stabilized with respect to part₂Preferably, it contains 90 vol% or less of Al₂O₃. More preferably, ZrO is stabilized with respect to part₂Containing 50% by volume or less of Al₂O₃. Since the first material has such a constitution, characteristics such as high hardness, high strength, and high toughness can be obtained, so that it can be used for high-speed cutting of a difficult-to-cut material. When ZrO is stabilized with respect to part₂Containing more than 90% by volume of Al₂O₃When it is used, the toughness tends to be lowered. Al (Al)₂O₃Stabilization of ZrO with respect to part₂The lower limit of the volume ratio of (b) may be 5 volume%. When ZrO is stabilized with respect to part₂Containing less than 5% by volume of Al₂O₃When it is used, the above characteristics tend not to be obtained.

Such Al₂O₃Present in dispersed form in the partially stabilized ZrO₂Or in both or one of the grain boundaries or grains. That is, the expression "present in a dispersed manner" means fine Al₂O₃The particles are present at grain boundaries or somewhere in the grains. In other words, this means Al₂O₃Is not limited to partially stabilize ZrO₂The specific portion of (a).

Al₂O₃The particle (crystal grain) is preferably 1 μm or less, more preferably 0.5 μm or less, and further preferably 0.1 μm or less. The lower limit of the particle size is not particularly limited, since the toughness tends to be further improved as the particle size becomes smaller. However, when the particle diameter becomes too small, the toughness of the substance itself tends to decrease. Therefore, the particle diameter is preferably 0.005 μm or more. Al (Al)₂O₃Is present in the first material in a dispersed manner, so that the toughness is pronouncedAnd (5) improving. It is considered that this is due to Al₂O₃Making the structure toughened.

Al can be determined by the same method as the above-described method for determining the particle diameter and content of cubic boron nitride particles₂O₃Particle size and content (vol%). That is, by using the above FE-SEM, a smooth cross section obtained by CP processing of the sintered body using an argon ion beam was observed at a magnification of 10000 ×, and Al was calculated by binarization processing using the above image analysis software₂O₃And the average particle diameter can be obtained from the equivalent circle diameter. Further, Al calculated by binarization processing using image analysis software may be used₂O₃Each area of (1) is used as Al₂O₃Content (vol%).

Further, in the case of the first material, the above cross section was observed at a high magnification of 10000x using FE-SEM, by performing binarization processing using the above image analysis software to calculate an equivalent circle diameter and an area of the first material, an average particle diameter was obtained from the equivalent circle diameter, and each area was used as a content (volume%) of the first material.

The first material is preferably contained in the sintered body at a ratio of 10 to 80 vol%. When the ratio is less than 10 vol%, abrasion resistance and breakage resistance may be reduced. When the ratio is more than 80 vol%, hardness may be decreased, and thus wear resistance may be decreased. The ratio of the first material is more preferably 20 to 60 vol%.

As mentioned above, the first material is Al₂O₃Partially stabilized ZrO dispersed in either or both of grain boundaries and grains₂And a second phase is formed in the sintered body. However, as described below, because the ATZ generally also functions as a binder, the first material may also function as a binder. Further, in this case, the first material is preferably contained in the sintered body at a ratio of 10 to 80 vol% regardless of the effect of the first material.

< method for producing first Material >

For example, the first material can be obtained using a neutralization coprecipitation method or a sol-gel method described below.

(neutralization coprecipitation method)

The neutralization coprecipitation method is a method including the following steps a and B. This method is described, for example, in a paper published in 2013 (j.jpn.soc.powder Powder Metallurgy, vol.60, No.10, P428-435).

(step A)

Using zirconium salt, yttrium salt and aluminum salt and making zirconium oxide (ZrO)₂) And yttrium oxide (Y)₂O₃) 95:5 to 99.5:0.5 and yttria-added zirconia and alumina (Al)₂O₃) In a molar ratio of 10:90 to 95:5, thereby preparing a mixed solution. In the above description, yttrium oxide (Y) is exemplified₂O₃) As solid solution in zirconia (ZrO)₂) An oxide of (1); however, the oxide is not limited thereto.

(step B)

The mixed solution obtained in step a is neutralized by adding an alkali to the mixed solution so as to co-precipitate zirconium, yttrium, and aluminum, thereby obtaining a first material as a precipitate. The precipitate is dried, then heated at 650 to 750 ℃ for 7 to 12 hours, then calcined at 850 to 950 ℃ for 0.5 to 3 hours, and pulverized using a ball mill or the like. Thus, Y can be produced₂O₃Stabilized ZrO₂-Al₂O₃A first material powder composed of a solid solution powder.

Herein, examples of the zirconium salt in step a include: zirconium oxychloride (ZrOCl)₂) Zirconium oxynitrate (ZrO (NO)₃)₂) And the like. Examples of yttrium salts include yttrium chloride (YCl)₃) Yttrium nitrate (Y (NO)₃)₃) And the like. Examples of the aluminum salt include aluminum chloride (AlCl)₃) And the like. Further, examples of the solvent used for the mixed solution include nitric acid, hydrochloric acid, and the like.

(Sol-gel method)

The sol-gel method is a method comprising the following step X. This method is described, for example, in a paper published in 2011 (j.jpn.soc.powder better metallic, vol.58, No.12, P727-732).

(step X)

Preparing a first material as a solid solution powder by using a sol-gel method by adding 20 to 30 mol% of Al₂O₃Added to 70 to 80 mol% of ZrO₂Wherein ZrO is obtained₂Adding 0.3 mol% to 3.5 mol% of Y₂O₃. Next, the solid solution powder is calcined at a temperature of not less than the crystallization temperature and pulverized using a ball mill or the like to prepare crystalline ZrO₂A first material powder composed of a solid solution powder.

(other methods)

The first material may also be obtained by other methods than the two methods described above. That is, partially stabilized ZrO in a solvent such as ethanol by using a pulverizer such as a bead mill or a ball mill₂And Al₂O₃Mixed with each other to obtain a slurry. Then, granulation is performed using the slurry, and the first material as a granulated substance can be thereby obtained. The granulation method is not particularly limited. Examples of the granulation method include melt granulation, spray granulation, and the like.

The strength of the granulated product was improved by the following method. Further, the first material powder may be prepared by pulverization using a ball mill or the like.

(1) Sintering in a heat treatment furnace (e.g., sintering at 1000 ℃ for 3 hours in vacuum); or

(2) To the slurry at the stage before pelletization, a binder (a general binder such as PVB (polyvinyl butyral)) was added in an amount of 10 mass%.

< relationship between first phase and second phase >)

The second phase is in contact with at least a portion of the surface of the first phase. Therefore, the cubic boron nitride particles tend to be suppressed from coming into direct contact with each other, whereby the strength and life of the sintered body can be improved. This may be due to the following reasons. That is, because of the inherent low sinterability of cBN, the cBN particles contact each other when contacted with each otherGaps are easily created between the cBN grains and at triple points of the cBN grains. On the other hand, ATZ and Al₂O₃And the like, and it is difficult to leave a gap in the structure of the sintered body. Therefore, it is considered that the density of the sintered body is improved by bringing the second phase into contact with at least a part of the surface of the first phase to avoid a gap remaining in the structure of the sintered body, and as a result, the strength and life of the sintered body can be improved. The second phase may be in contact with a part or all of the surface of the first phase as long as the effects of the present disclosure are exhibited. Further, the ratio of contact should not be limited as long as the effects of the present disclosure are exhibited.

In the sintered body according to the present embodiment, when two or more cubic boron nitride particles adjacent to and in direct contact with each other are defined as a contact body, Di represents the length of the entire circumference of the contact body, n represents the number of contact positions where the cubic boron nitride particles are in direct contact with each other, d represents_kIndicates the length of each contact position, and ∑ d_kWhen k is 1 to n, the following relationships (I) and (II) are satisfied:

[(Dii-Di)/Dii]×100≤50...(II)。

in this context, Σ d_k(wherein k is 1 to n) means d₁+d₂+d₃+…+d_n. n is a natural number.

When cubic boron nitride particles are suppressed from being in direct contact with each other, the above-described formulas (I) and (II) are satisfied. Therefore, the sintered body satisfying the above formulas (I) and (II) has improved strength and life. In the following description, [ (Dii-Di)/Dii ] × 100 in the above formula (II) is also referred to as "cBN contact ratio (%)".

Herein, when 30 volume% or more and less than 50 volume% of cubic boron nitride particles are contained in the sintered body, the cBN contact ratio (%) is preferably 3 or less, more preferably 1 or less, and most preferably 0.5 or less. When 50 volume% or more and less than 76 volume% of cubic boron nitride particles are contained in the sintered body, the cBN contact ratio (%) is preferably 20 or less, more preferably 15 or less, and most preferably 10 or less. When 76% by volume or more and less than 100% by volume of cubic boron nitride particles are contained in the sintered body, the cBN contact ratio (%) is preferably 50 or less, more preferably 40 or less, and most preferably 30 or less. As an ideal value, the lower limit value of the cBN contact ratio (%) is 0. When the cBN contact ratio (%) is more than 50, the effect of improving the strength of the sintered body tends to be insufficient.

The cBN contact ratio (%) was calculated by the following manner. That is, first, a cross section obtained by CP-processing the sintered body was observed at a magnification of 10000 × using the above FE-SEM to obtain an observation image. The observed image was subjected to binarization processing using the above-mentioned image analysis software, thereby determining cBN particles. Next, two or more cBN particles adjacent to and in direct contact with each other among the determined cBN particles are defined as a contact body, and the contour of the contact body is drawn. Then, by tracing the contour, the length of the entire circumference of the contact body is determined as Di. Further, the contact positions where the cBN particles of the contact body were in direct contact with each other were manually drawn as straight lines. The number of contact positions is denoted by n and the length of each contact position is denoted by d_kTo determine Σ d as the total length of the contact position_k(wherein k is 1 to n). By determining the total length Σ d_k(where k is 1 to n) by 2, and then added to Di, thereby determining Dii (Dii + Di + (2 × Σ d)_k(where k is 1 to n)).

In summary, the cBN contact ratio (%) can be calculated by substituting the values determined as Di and Dii into the following equation: [ (Dii-Di)/Dii ]. times.100. The cBN contact ratio (%) may be an average value of values obtained by determining Di and Dii of each of all cBN particles in a contact body state among all cBN particles in the above observation image, and substituting Di and Dii into the above equation.

< contact ratio of first phase and second phase >

As described above, the second phase is in contact with at least a portion of the surface of the first phase. The contact ratio of the first phase and the second phase can be calculated by the following method: (%). That is, a cross section obtained by CP-processing the sintered body was observed at a magnification of 10000 × by using the above FE-SEM to obtain an observation image. The observation image was subjected to binarization processing using the above-described image analysis software, thereby determining cBN particles (first phase) and a cBN particle-coated first material (second phase) (using the contour pattern of the image analysis software). First, in the cBN particles identified, the circumference of the cBN particle is drawn when the cBN particle is present in a monolithic form (a state in which the cBN particle is not in contact with other cBN particles). When two or more cBN particles are brought into contact with each other to form an aggregate (containing no component other than the cBN particles), the contour of the aggregate is drawn. Next, the sum of the length of the contour line and the circumference of the single body was determined as the total length L of the cBN particles_B. Further, in the contour line and the perimeter of the monomer, the sum of the lengths of the portions of the first material (second phase) that are in direct contact with the monomer and the aggregate is determined as the total length L of the first material (second phase)_A。

As described above, the determination can be made by determining as L_AAnd L_BSubstituting the value of (A) into the formula (L)_A/L_B) X 100 to calculate the contact ratio (%) of the first phase and the second phase. By determining the L of each of all of the cBN particles and the cBN particle-coated first material in the above-described observation image_AAnd L_BAnd L is_AAnd L_BSubstituting into the above formula, thereby obtaining the contact ratio (%) of the first phase and the second phase. In this case, the contact ratio (%) of the first phase and the second phase is preferably 80% or more, more preferably 90% or more, and most preferably 95% or more. The upper limit of the contact ratio (%) of the first phase and the second phase is 100%. Herein, it is assumed that even when the first material contained in the sintered body functions as a binder, a contact portion of the first material with the first contact is contained in the total length L of the first material_AIn (1).

< third phase >)

The sintered body preferably further comprises a third phase. Specifically, the third phase is preferably composed of at least one compound composed of at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements, Al and Si in the periodic table and at least one element selected from the group consisting of carbon, nitrogen and oxygen. This third phase acts as a binder. Therefore, a sintered body also having more excellent toughness can be provided.

For example, the binder is made of Al₂O₃、MgO、SeO、Y₂O₃、HfO、TiC、TiN、TiB₂、TiCrN、ZrC、ZrN、ZrB₂、AlCrN、AlN、AlON、AlB₂、SiC、Si₃N₄、HfC、HfN、VC、VN、NbC、TaC、CrC、CrN、Cr₂N, MoC and/or WC. The binder may be composed of only one of the above-mentioned compounds, or may be composed of a combination of two or more of the above-mentioned compounds.

The average particle size of the binder is preferably 0.05 μm to 5 μm. If the average particle diameter of the binder is less than 0.05 μm, the binder is liable to aggregate when the binder is mixed with other powders, resulting in a tendency toward insufficient sintering. If the average particle diameter of the binder is greater than 5 μm, the strength tends to be reduced due to grain growth during sintering.

Further, a binder is preferably contained as the third phase in the sintered body at a ratio of 5 to 50 vol%. When the ratio of the binder is less than 5 vol%, the strength of the sintered body may not be sufficiently improved. On the other hand, when the ratio of the binder is more than 50 vol%, the ratio of cBN particles may decrease, resulting in a decrease in hardness of the sintered body. A more preferred ratio of the binder (third phase) is 10 to 30 vol%. Further, the average particle size of the binder can be determined by the same method as that for the cBN particles.

The strength of the sintered body according to the present embodiment is preferably 1.5GPa or more. The strength is referred to as bending strength σ. The bending strength σ was represented by a value of three-point bending strength measured under conditions of a span length of 8mm and a crosshead feed speed of 0.5mm/min using a three-point bending strength measuring instrument (trade name: "AG-Xplus", supplied by Shimadzu corporation). The strength of the sintered body is more preferably 1.55GPa or more. Although the upper limit of the strength of the sintered body should not be particularly limited, it is preferable that the upper limit is 2.5GPa or less based on the raw material of the sintered body.

The composition and content ratio of each component of the first phase (cBN), the second phase (first material), and the third phase (binder) in the sintered body can be determined by observing the above cross section at a high magnification of 10000X using an FE-SEM to obtain an observation image, and analyzing the observation image using a silicon drift detector (SDD; trade name: "Apollo XF", supplied by EDAX Inc), which is one of energy dispersive X-ray spectrometers (EDX) in the FE-SEM.

[ method for producing sintered body ]

The method of manufacturing a sintered body according to the present embodiment is a method of manufacturing a sintered body including a first phase composed of cubic boron nitride particles and a second phase composed of a first material. The method for manufacturing a sintered body includes: a first step of obtaining a sintered precursor by coating cubic boron nitride particles with a first material; and a second step of obtaining a sintered body by sintering the sintering precursor at a pressure of greater than 1GPa and less than or equal to 20 GPa.

< first step >)

The first step is a step of obtaining a sintered precursor by coating cubic boron nitride particles with a first material. The first material and the cubic boron nitride particles are as described above and will not be described again.

< detailed method of the first step >

In the first step of the present embodiment, as described above, a sintered precursor is obtained by coating cubic boron nitride particles (cBN particles) with a first material. For example, the sintering precursor can be obtained by the following method using a sol-gel method.

That is, first, Zr-i- (OC)₃H₇)₄、Al(OC₃H₇)₃、Y(OC₃H₇)₃And prepared predetermined amount of cBN particles in an amount such that the content thereof in the sintered body becomes 30 vol% or more and less than 100 vol% are mixed in xylene for 2 hours, and thenWherein NH is added₄OH, thereby obtaining a first mixed solution. Next, the first mixed solution was refluxed at 70 to 80 ℃ for 24 hours, thereby obtaining a first hydrolysate. The first hydrolysate was centrifuged, then washed with hot water, and then dried in vacuum at 120 ℃, to obtain a sintered precursor. By this sol-gel method, a sintered precursor in which cBN particles are coated with a first material as a solid solution powder (ATZ) in which 20 to 30 mol% of Al is present can be prepared₂O₃Solid solubility in 70 to 80 mol% ZrO₂Wherein with respect to ZrO₂，ZrO₂Containing 0.3 to 3.5 mol% of Y₂O₃。

< first preliminary step >

The first step preferably comprises a first preliminary step of obtaining a granular mixture comprising cubic boron nitride particles and a binder. In this case, in the first step, a sintered precursor is obtained by replacing cubic boron nitride particles with the mixture obtained in the first preliminary step and coating the mixture with the first material. The binding agents are as described above and will therefore not be described again.

In the first preliminary step, specifically, first, the first material powder is prepared by using a known method such as the above-described neutralization coprecipitation method. The first material powder also functions as a binder. Next, the first material powder and the cubic boron nitride particles are added to a predetermined container and mixed in the container, thereby obtaining a granular mixture. The granulated mixture (predetermined amount), Zr-i- (OC)₃H₇)₄、Al(OC₃H₇)₃And Y (OC)₃H₇)₃Mixed in xylene for 2 hours and then NH was added thereto₄OH, thereby obtaining a second mixed solution. Next, the second mixed solution was refluxed at 70 to 80 ℃ for 24 hours, thereby obtaining a second hydrolysate. The second hydrolysate was centrifuged, then washed with hot water, and then dried at 120 ℃ under vacuum, thereby obtaining a sintered precursor. By the sol-gel method, cBN particles therein can be producedA sintered precursor in which particles are coated with a first material as a solid solution powder (ATZ) in which 20 to 30 mol% of Al₂O₃Solid solubility in 70 to 80 mol% ZrO₂Wherein with respect to ZrO₂，ZrO₂Containing 0.3 to 3.5 mol% of Y₂O₃。

Then, before the second step described below is performed, the above-described sintered precursor is preferably formed into a predetermined shape, dried, and fired at 700 to 900 ℃.

< second step >

The second step is a step of obtaining a sintered body by sintering the sintering precursor at a pressure of greater than 1GPa and 20GPa or less. In the second step, the sintering precursor is more preferably sintered at a pressure of 5GPa to 20 GPa. Therefore, a sintered body having greatly improved strength and life can be produced.

The specific sintering conditions in this case are as follows. That is, the sintering precursor is sintered by holding the sintering precursor at a temperature of 1000 ℃ to 1700 ℃ and a pressure of 5GPa to 20GPa for 5 minutes to 60 minutes. However, the sintering method is not particularly limited, and hot pressing, ultra-high pressure pressing, or the like may be used.

In particular, when sintering is performed at an ultrahigh pressure of 5GPa to 20GPa, vacuum is more preferable as a gas atmosphere. In this case, the temperature increase rate is set to 50 ℃/min to 150 ℃/min.

More preferable sintering conditions in the second step are as follows: setting the heating rate in vacuum to 50-150 deg.c/min; the pressure is 5GPa to 20 GPa; setting the sintering temperature to 1000-1700 ℃; and the holding time is set to 5 to 60 minutes.

< second preliminary step >

The second step preferably comprises a second preliminary step of obtaining a mixture precursor by mixing the sintering precursor and the binder. In this case, in the second step, a sintered body is obtained by replacing the sintering precursor with the mixture precursor obtained in the second preliminary step and sintering the mixture precursor at a pressure of greater than 1GPa and 20GPa or less. The sintering conditions of the mixture precursor may be the same as those of the sintering precursor described above.

Here, also, when the method of manufacturing a sintered body according to the present embodiment includes the second preliminary step, it is more preferable that the sintered body is obtained by sintering the mixture precursor at a pressure of 5GPa or more and 20GPa or less in the second step. Therefore, a sintered body having greatly improved strength and life can be produced.

The sintering conditions of the mixture precursor in this case may be the same as those of the sintering precursor described above. That is, sintering is performed by holding the mixture precursor at a temperature of 1000 ℃ to 1700 ℃ for 5 minutes to 60 minutes under an ultra-high pressure of 5GPa to 20 GPa. Although the sintering method is not particularly limited, hot pressing, ultrahigh pressure pressing, or the like may be used.

In particular, when sintering is performed at an ultrahigh pressure of 5GPa to 20GPa, vacuum is more preferable as a gas atmosphere. In this case, the temperature increase rate is set to 50 ℃/min to 150 ℃/min.

Preferred sintering conditions for the mixture precursor are as follows: setting the heating rate in vacuum to 50-150 deg.c/min; setting the pressure to 5GPa to 20 GPa; setting the sintering temperature to 1000-1700 ℃; and the holding time is set to 5 to 60 minutes.

The binding agent used in the second pre-step is the same as the binding agent described as the binding agent used in the first pre-step.

In this way, by the sintered body manufacturing method according to the present embodiment, a sintered body having improved strength and life can be manufactured.