JP5613970B2 - Method for synthesizing cubic boron nitride and method for producing sintered cubic boron nitride - Google Patents

Description

  The present invention relates to a cBN synthesis method for synthesizing cubic boron nitride (hereinafter referred to as cBN) from hexagonal boron nitride (hereinafter referred to as hBN), and cBN sintering using the synthesized cBN as a raw powder. The present invention relates to a method for producing a bonded body.

Conventionally, as a synthesis method for synthesizing cBN from hBN, a method using a boride containing an alkali or alkaline earth element (typically Li ₃ BN ₂ ) as a catalyst is generally known. It is also known that alloys of Al, transition metals such as Co, Ni and Fe, and mixtures thereof are effective catalysts.

  For example, Patent Document 1 reports that alloys such as NiAl, CoAl, FeNiAl, and FeNiCoAl have a catalytic action under conditions of a pressure of about 6 to 8.5 GPa and a temperature of 800 to 1600 ° C.

  In Patent Document 2, a mixture such as Fe46-Ni32-Cr21-Al 1% by mass, Ni39.2-Mn58.8-Al2% by mass, Ni49-Cr49-Al2% by mass, Fe8-Ni43-Cr47-Al2% by mass, It is reported that the catalyst is effective as a catalyst for converting the raw material hBN into cBN at a pressure of 5 to 5.5 GPa and a temperature of about 1400 to 1500 ° C.

  Non-Patent Document 1 reports that an alloy having a composition of 10% by mass of Fe90-Al previously alloyed in an arc melting furnace is effective as a cBN synthesis catalyst at about 6 GPa or more.

  It is also known that a cBN sintered body can be produced by synthesizing cBN from hBN using a catalyst and then sintering it.

For example, Patent Document 3, Co-Al mixture, Ni87-Al13% by weight mixture, WC-Co-Al, NiAl 3 alloy, such as Co67-W16.5-Al16.5 wt% to coexist with raw material hBN, pressure It has been reported that when cBN is produced by synthesis at 5.4 GPa or more and a temperature range of about 1500 to 1550 ° C., the synthesized cBN becomes a sintered body in which constituent particles are firmly bonded.

  Patent Document 4 discloses an alloy powder or mixed powder composed of one or more components selected from Mo, Al and the balance selected from Fe, Co, and Ni, and Patent Document 5 describes Cr ( Or, further, by synthesizing cBN using an alloy powder or mixed powder composed of one or more component compositions selected from Fe, Co and Ni as the metal catalyst, and Mo), Al and the balance. It is possible to synthesize cBN under low pressure conditions, and when this is used as a sintering aid to produce a cBN sintered body, the cBN sintered body has a dense structure and a high hardness. It has been reported that can be produced.

US Pat. No. 3,768,972 US Pat. No. 3,918,931 US Pat. No. 3,918,219 JP 2010-137997 A JP 2010-235369 A

“Ceramic Association Magazine” Vol. 78, no. 1 (1970) 7-14

  Since cBN has hardness comparable to diamond and is also thermally and chemically stable, cBN sintered bodies are used for cutting high-speed steel, die steel, cast iron and other iron-based work materials. It is used in a wide range of fields as a hard material for tools.

  By the way, when synthesizing cBN from hBN, as shown in the prior art, synthesis is usually performed under ultra-high pressure (5 GPa or more) and high temperature conditions. In particular, when the size of the synthesizer is increased, there are significant differences in the operational difficulty and device configuration depending on whether or not an ultra-high pressure (over 5 GPa) is required. For example, the life of a large cemented carbide, which is the central member of a mold apparatus, varies greatly depending on whether or not the operating pressure is extremely high (5 GPa or more).

  Therefore, there is a demand for a method for synthesizing cBN capable of easily synthesizing cBN under more relaxed low-pressure conditions even when the synthesis apparatus is enlarged and productivity is improved.

  On the other hand, a method for producing a cBN sintered body having a finer and finer structure is also desired for the cBN sintered body.

  As a result of intensive studies on a method for synthesizing cBN from hBN under a lower pressure condition (minimum synthesis pressure is 4 GPa), the inventors have obtained the following knowledge.

  In the synthesis of cBN from hBN, conventionally, a metal catalyst comprising an alloy or mixture of transition metals such as Fe, Ni, Co and Al was used, but the reaction mechanism was first under ultra high pressure and high temperature conditions. It is thought that the metal catalyst melts into a liquid phase and the components B (boron) and N (nitrogen) of hBN dissolve in the liquid phase, and then nucleation and growth of cBN occurs and the synthesis of cBN proceeds. Therefore, in the case where the solubility of B and N in the liquid phase is small, the conditions necessary for forming cBN are not satisfied, and if sufficient B and N are present in the liquid phase, Even if dissolved, in order to synthesize cBN by nucleating and growing cBN near the thermodynamic equilibrium condition of cBN (for example, pressure conditions of 4-5 GPa lower than the conventional synthesis pressure) Promote nucleation and growth It is considered a condition for promoting is required.

  Therefore, when the metal catalyst has an excellent B-dissolving ability and N-dissolving ability in a liquid phase state and at the same time has an action of promoting and promoting nucleation / growth of cBN, it is possible to convert cBN to It can be said that can be synthesized.

  By the way, regarding the conventionally used metal catalysts, when the action of the catalyst component is seen from the above viewpoint, transition metals such as Fe, Ni, Co and the like are several percent when they are melted and in a liquid phase state. It has the ability to dissolve a certain amount of B, and has the effect of a boron-dissolving component, while the ability to dissolve N is extremely small. , The conversion reaction to cBN becomes extremely unsatisfactory.

  Therefore, the present inventors conducted research on a metal catalyst that has an excellent ability to dissolve N and at the same time promotes and promotes nucleation / growth of cBN even under low pressure conditions. In the metal catalyst composed of alloy powder or mixed powder composed of one or more components selected from Fe, Co, and Ni, such as Cr and / or Mo and Al, and the balance, When V is contained in an amount of ˜50 mass%, the melting temperature of the metal catalyst can be lowered. Therefore, the average grain size is low in the synthesis pressure condition of 4 to 5 GPa and in the low temperature range (1200 to 1700 ° C.). It has been found that fine cBN having a diameter of 30 μm or less can be synthesized.

  The Cr and Mo components of the metal catalyst have a large ability to dissolve N in the liquid phase state. Also, by coexisting with Al, which is also a component of the metal catalyst, Promote and encourage growth. Further, in the case where Cr and Mo coexist, the solubility of nitrogen is increased by the addition of Mo, so that the generated cBN particle size is increased as compared with the case of containing Cr alone.

  In addition, Fe, Co, and Ni which are the remaining components of the metal catalyst have an action of a boron dissolving component.

  That is, as a metal catalyst for synthesizing cBN from hBN, Cr and / or Mo having an action of dissolving N, an Al component having an action of promoting and promoting cBN nucleation / growth, and the remainder dissolving B By using an alloy powder or mixed powder composed of Fe, Co, and Ni components having the function of reducing the synthesis, the minimum synthesis pressure can be reduced to 4 GPa, and in the low temperature range (1200 to 1700 ° C.), the average particle size can be reduced. It has been found that fine cBN particles having a diameter of 30 μm or less can be synthesized.

  Furthermore, the present inventors used cBN as a raw material powder, the above metal catalyst as a sintering aid, and sintered the mixed powder of the raw material powder and the sintering aid. It was also found that a dense cBN sintered body composed of fine particles of 30 μm or less and having a strong direct bond between cBN particles can be obtained.

The present invention has been made based on the above findings,
“(1) In the method for synthesizing cubic boron nitride in which cubic boron nitride is synthesized from hexagonal boron nitride under ultrahigh pressure and high temperature conditions in the presence of a metal catalyst, the metal catalyst is any one of Cr and Mo, In the case of containing two types and containing Cr alone, Cr: 10 to 55% by mass, when containing Mo alone, Mo: 10 to 50% by mass, and containing both Cr and Mo (Cr + Mo) : In the range of 10 to 50% by mass, V: 1 to 50% by mass, Al: 1.5 to 8% by mass, the balance being any one or two of Fe, Ni and Co A method for synthesizing cubic boron nitride, which is an alloy powder or a mixed powder having the above component composition, and further comprising performing the synthesis at 4 GPa or more and 1200 to 1700 ° C.

(2) In a method for producing a cubic boron nitride sintered body comprising cubic boron nitride as a raw material powder, adding a sintering aid to the raw material powder and sintering, Cr as the above-mentioned sintering aid In the case of containing only one or two of Mo and Mo and containing Cr alone, Cr: 10 to 55% by mass, when containing Mo alone, Mo: 10 to 50% by mass, Cr and Mo. When both are contained, they are contained within the range of (Cr + Mo): 10 to 50% by mass, V: 1 to 50% by mass, Al: 1.5 to 8% by mass, the balance being Fe, Ni and Co A method for producing a cubic boron nitride sintered body, comprising adding 5 to 20% by volume of an alloy powder or mixed powder composed of any one or more of the above components to a raw material powder and sintering it . "
It is characterized by.

The present invention will be described in detail below.
Components and composition of metal catalyst:
In the first aspect of the present invention, the metal catalyst may be one or two of Cr and Mo, Cr: 10 to 55% by mass, Mo: 10 to 50% by mass, (Cr + Mo): 10 to 50% by mass. In the range of V: 1 to 50% by mass, Al: 1.5 to 8% by mass, and the balance is composed of one or more of Fe, Ni and Co. It is formed as an alloy powder or a mixed powder.

  Both the Cr component and the Mo component have the action of dissolving N of hBN, which is a raw material, in a metal catalyst in a molten state (liquid phase), but if the content ratio of the Cr component and the Mo component is less than 10% by mass, When cBN is not sufficiently generated due to the low dissolution amount of Cr, on the other hand, when the content ratio of Cr component exceeds 55% by mass or when the content rate of Mo component exceeds 50% by mass, Since the melting temperature becomes too high, the solubility of N decreases under low pressure conditions of 4 to 5 GPa, and cBN is not sufficiently generated. Therefore, the content ratio of the Cr component and Mo component having an action of dissolving N is 10% to 55% by mass, preferably 20 to 40% by mass when Cr is contained alone, and Mo Is contained in an amount of 10 to 50% by mass, preferably 20 to 40% by mass.

  Further, when both the Cr component and the Mo component are contained, the solubility of N is synergistically improved. However, when the total content ratio of the Cr component and the Mo component is less than 10% by mass, In the synthesis, the action of dissolving N in the metal catalyst in the molten state (liquid phase) due to the inclusion of Cr, Mo as a component of the metal catalyst is reduced, and it becomes difficult to synthesize cBN under low pressure conditions, On the other hand, when the total content ratio of the Cr component and the Mo component exceeds 50% by mass, the composition ratio of Fe, Co, Ni, etc., which are boron-soluble components, inevitably decreases, due to an increase in melting point and a decrease in boron solubility. , CBN synthesis pressure increases. Moreover, when manufacturing a cBN sintered compact, the melting | fusing point of the metal which exists between cBN particle | grains raises, and is not preferable.

  Therefore, the total content ratio of the Cr component and the Mo component needs to satisfy 10 to 50% by mass or less.

  By containing 1 to 50% by mass of V as a component of the metal catalyst, the melting temperature of the metal catalyst can be lowered. Therefore, in a low temperature range of 1200 to 1700 ° C. and in a low pressure condition of 4 to 5 GPa. , CBN can be synthesized. However, when the V content exceeds 50% by mass, the minimum melting point exceeds about 1600 ° C., so the hBN stable region is entered in the region of pressure 4 GPa, while the V content is less than 1% by mass. Since the effect of refining cBN particles is reduced and cBN particles having an average particle size of 30 μm or less cannot be synthesized, the V content is determined to be 1 to 50% by mass. In addition, it is preferable to set it as 10-50 mass% from a viewpoint of the refinement | miniaturization effect of cBN particle | grains.

  The Al component has the effect of promoting and promoting the generation and growth of cBN nuclei, and by adding a small amount to the metal catalyst, the required pressure during cBN synthesis is greatly reduced, and cBN under low pressure conditions of 4 to 5 GPa. However, when the content ratio of the Al component is less than 1.5% by mass, cBN nucleation, growth promotion, and promoting effect are small, and cBN formation is insufficient. If it is too much, aluminum nitride may be generated, which may be an obstructive factor for cBN formation, which is not desirable for forming a sintered body. Therefore, the Al component content ratio was determined to be 1.5 to 8% by mass.

  Either one or more of Fe, Co, and Ni may be used alone or in combination of two or more thereof, and B of raw material hBN may be a molten (liquid phase) metal. It has the effect of dissolving in the catalyst.

The metal catalyst of the present invention can be used in the form of an alloy powder that is previously alloyed by an arc melting method, an atomizing method, etc. after mixing each component so as to have a predetermined composition. It can be used in the form of a mixed powder obtained by mixing and mixing so as to have the composition (mixing).
Synthesis conditions (pressure, temperature):
In the synthesis from hBN to cBN, for example, in the synthesis apparatus shown in FIG. 1, hBN, which is a raw material for synthesis, and the metal catalyst powder are coexisted, and the pressure is 4 GPa or more and the temperature is 1200 to 1700 ° C. This can be done by synthesis.

  In this invention, by using the above metal catalyst, the minimum synthesis pressure of cBN can be reduced to 4 GPa, which is much lower than the conventional synthesis method (preferably 4.4 GPa or more), Moreover, cBN can be synthesized in a low temperature range (preferably 1300 to 1600 ° C.) (Of course, the conventional method has a high synthesis pressure of 5 to 8.5 GPa and a high synthesis temperature of 1700 to 1900 ° C.) Therefore, there is an advantage that the size of the equipment is not increased and the service life of the apparatus constituent members is extended.

When the synthesis temperature is less than 1200 ° C., the metal catalyst does not dissolve, so the cBN synthesis reaction does not proceed. On the other hand, when the synthesis temperature exceeds 1700 ° C., cBN grain growth tends to occur, and the pressure of hBNＢcBN -Since it approaches the stable region of hBN in the 4-5 GPa pressure region due to temperature equilibrium, the synthesized cBN may be converted back to hBN. Therefore, the reaction synthesis temperature is 1200-1700 ° C (preferably 1300-1600). ° C).
cBN sintered body:
Conventionally, for example, as described in Patent Document _{3, WC-Co-Al,} NiAl 3, Co67-W16.5-Al16.5 wt% and a sintering aid, cBN particles are strongly bonded baked In order to produce a bonded body, it had to be performed at a pressure of 5.4 GPa or higher and a temperature of 1500 ° C. or higher. According to the present invention, the specific component used in the synthesis of cBN using cBN as a raw material powder. A metal catalyst composed of an alloy powder or a mixed powder of the composition is used as a sintering aid, and is blended into the raw material powder so that the blending ratio of the sintering aid is 5 to 20% by volume. For example, the sintering shown in FIG. When this mixed powder is arranged in a cell and sintered at a temperature range of 1200 to 1700 ° C. while being pressurized at 4.0 to 6.0 GPa, for example, the average particle size is composed of fine particles having a particle size of 30 μm or less, Strong among cBN particles A dense cBN sintered body having a solid direct bond can be obtained. That is, it can be said that the metal catalyst used at the time of cBN synthesis also has a function as a sintering aid when producing a cBN sintered body.

Here, the mixing ratio of the sintering aid is set to 5 to 20% by volume. When the mixing ratio of the sintering auxiliary is less than 5% by volume, the sintering aid is mixed with the cBN raw material when sintered. In the region where the auxiliary is not uniformly dispersed and the sintering auxiliary is insufficient, the bonding between the cBN particles cannot be sufficiently performed, and a high-strength cBN sintered body cannot be obtained.
On the other hand, when the blending ratio exceeds 20% by volume, an excess of the sintering aid exists in the gaps between the cBN particles, so that the contact surface between the cBN particles decreases, and the strong direct contact between the cBN particles. Bonding was not obtained, and as a result, a dense cBN sintered body could not be obtained. Therefore, the mixing ratio of the sintering aid was determined to be 5 to 20% by volume.

  For example, the synthesis cell shown in FIG. 1 is synthesized by the synthesis method of the present invention (as a metal catalyst, Co—40.87-Mo17.39-Cr20.87-V18.26-Al2.61 mass% Co— Using a cBN powder obtained by using a Mo-Cr-V-Al-based metal catalyst) as a raw material powder, using a Co-Mo-Cr-V-Al-based alloy having the same composition as that of the metal catalyst as a sintering aid, The content ratio of the binder is compounded so as to be 10% by volume, and this is sintered in the sintering cell shown in FIG. 2 for 60 minutes under the condition of 4.8 GPa × 1400 ° C. to thereby obtain the cBN sintered body. Manufactured.

That is, the cBN sintered body obtained by the production method of the present invention has a very dense structure and is composed of fine particles having an average particle size of 30 μm or less even when sintered at a low temperature. I understand that.
In the present invention, for the purpose of producing a sintered body composed of cBN particles having an average particle size of 30 μm or less, the cBN raw material particle size should be 30 μm or less, preferably fine particles of several μm. Similarly, in the starting state of the hBN raw material, the hBN particle size is preferably 30 μm or less.

  As described above, the present invention reduces the minimum synthesis pressure to 4 GPa by synthesizing cBN from hBN using a metal catalyst having a specific component composition, and further, synthesis is performed in a low temperature range (1200 to 1700 ° C.). By doing so, since it is possible to synthesize fine cBN particles having an average particle size of 30 μm or less, it is not necessary to increase the size of the cBN synthesizer, and the equipment cost can be reduced. Long life can be achieved.

  In addition, when cBN is used as a raw material powder and sintering is performed using an alloy powder having the same component composition as the metal catalyst and a mixed powder as a sintering aid, the average particle size can be obtained without using another sintering agent. Is composed of fine particles of 30 μm or less, and a dense cBN sintered body having a strong direct bond between the cBN particles can be manufactured, and the cost of manufacturing the cBN sintered body can be reduced.

The sample arrangement schematic of the cBN synthesis cell which synthesize | combines cBN from hBN is shown. The sample arrangement | positioning schematic of the cBN sintered compact manufacturing cell for manufacturing a cBN sintered compact using synthesized cBN as a raw material powder is shown. The X-ray-diffraction chart (cBN peak exists) of the fine particle cBN synthesized by Example 2 (pressure: 4.6 GPa, temperature: 1330 ° C., reaction time: 60 minutes) is shown. The structure photograph by the scanning electron microscope of the fine particle cBN synthesized by Example 2 (pressure: 4.6 GPa, temperature: 1330 ° C., reaction time: 60 minutes) is shown. The structure photograph by the scanning electron microscope of the coarse-grained cBN synthesized by Comparative Example 2 (pressure: 5.0 GPa, temperature: 1560 ° C., reaction time: 60 minutes) is shown.

  Hereinafter, the cBN synthesis method and the cBN sintered body manufacturing method of the present invention will be specifically described based on examples.

Example 1:
As shown in FIG. 1, an alloy powder having a component composition of Co60-Mo20-V16-Al4% by mass is prepared in advance as a metal catalyst, and is formed between two hBN molded plates (4) having a diameter of about 7 mm and a thickness of 3 mm. Sodium chloride having an outer diameter of 10 mm, an inner diameter of 7 mm, and a height of 7.6 mm (including 10% by mass of zirconia powder) so that a sandwiched metal catalyst (alloy powder) layer (3) having a thickness of about 1.6 mm is formed. It filled in the sample container of the molded object (5).

  These samples were surrounded by a graphite tubular heater (1) having an outer diameter of 12 mm, an inner diameter of 10 mm, and a height of 17.6 mm, Mo foil (2) was disposed on the inner surface, and a belt-type ultrahigh pressure device (anvil tip diameter of 21 mm, Pressurization with a cylinder inner diameter of 25 mm), and then apply power to the heater to heat it, hold it for a certain period of time, then rapidly lower the temperature, then depressurize and take out the sample, and take a scanning electron microscope, X-ray diffraction, etc. A sample was identified.

  As a result of analyzing a sample reacted at a pressure of 5.6 GPa and 1550 ° C. for 30 minutes, fine cBN particles having a cBN conversion rate of 95% or more and an average particle size of 30 μm were synthesized.

X-ray diffraction was measured with Bruxer AXSMXP18VAHF.
Further, the cBN conversion rate is obtained by obtaining the ratio of each strongest line in an X-ray diffraction pattern obtained by mixing a known amount of hBN and cBN powder in advance, and creating a test curve based on the ratio. In the X-ray diffraction pattern according to Example 2 in FIG. 3, the relative intensity of the strongest line of cBN is about 89.3%, and the volume percentage of cBN is about 95%.
In addition, the cross-section of the synthesized sample was observed by a backscattered electron image (BEI) of a scanning electron microscope (SEM), and the area ratio of cBN and metal catalyst on the observation surface (magnification: 1000 times) (the volume ratio thereafter) The approximate cBN conversion rate can be obtained by
Example 2:
As the metal catalyst, an alloy powder having a component composition of Co40.87-Mo17.39-Cr20.87-V18.26-Al2.61% by mass was used, and the pressure was 4.6 GPa and 1330 ° C. in the same manner as in Example 1. When cBN was synthesized by reacting for 60 minutes, a fine cBN particle having a cBN conversion rate of 90% or more and an average particle size of 20 μm was synthesized.

  FIG. 3 shows an X-ray diffraction chart obtained for the fine particle cBN obtained in Example 2.

FIG. 4 shows a structure photograph of the fine particle cBN obtained in Example 2 observed with a scanning electron microscope.
Example 3:
As a metal catalyst, an alloy powder having a composition of Co47-Mo20-Cr24-V6-Al 3% by mass was used and reacted at a pressure of 4.6 GPa at 1320 ° C. for 30 minutes to synthesize cBN in the same manner as in Example 1. However, cBN conversion was 80% or more, and fine particles cBN having an average particle size of 20 μm were synthesized. At the same time, a very small amount of coarse cBN having an average particle diameter of about 40 μm was synthesized. As described above, when the amount of V added was decreased, the distribution of V was partially non-uniform, and in the portion where the concentration of V was small, cBN particles grew larger than 30 μm.
Example 4:
As the metal catalyst, an alloy powder composed of Ni64-Mo16-V16-Al4% by mass was used, and cBN was synthesized by reacting at a pressure of 5.6 GPa and 1460 ° C. for 30 minutes in the same manner as in Example 1. Fine cBN particles having a cBN conversion rate of 80% or more and an average particle size of 30 μm were synthesized.
Example 5:
As a metal catalyst, an alloy powder having a composition of Ni53.04-Fe9.36-Cr20.16-V13.44-Al4 mass% was used, and the pressure was 4.0 GPa at 1315 ° C. in the same manner as in Example 1. When cBN was synthesized by reacting for 5 minutes, fine cBN having a cBN conversion rate of 90% or more and an average particle size of 25 μm was synthesized.
Example 6:
As the metal catalyst, an alloy powder composed of Co63-Cr20-V13-Al4% by mass was used, and cBN was synthesized by reacting at a pressure of 5.6 GPa and 1580 ° C. for 30 minutes in the same manner as in Example 1. Fine cBN particles having an cBN conversion rate of 80% or more and an average particle size of 10 μm were synthesized.
Example 7:
As a metal catalyst, an alloy powder having a component composition of Co40-Ni20-Cr20-V16-Al4% by mass was used and reacted at a pressure of 5.6 GPa and 1588 ° C. for 30 minutes in the same manner as in Example 1 to synthesize cBN. However, fine cBN particles having a cBN conversion rate of 80% or more and an average particle size of 5 μm were synthesized.
Example 8:
As a metal catalyst, an alloy powder having a composition of Co22-Ni50-Cr10-V10-Al 8% by mass was used and reacted at a pressure of 5.6 GPa and 1590 ° C. for 30 minutes to synthesize cBN in the same manner as in Example 1. However, fine cBN particles having a cBN conversion rate of 95% or more and an average particle size of 10 μm were synthesized.
Example 9:
As a metal catalyst, an alloy powder having a component composition of Fe18.7-Co21-Mo2.3-Cr47.4-V1.9-Al3.7% by mass was used, and in the same manner as in Example 1, a pressure of 5.6 GPa, When cBN was synthesized by reacting at 1600 ° C. for 30 minutes, fine cBN having a cBN conversion rate of 90% or more and an average particle size of 30 μm was synthesized.
Example 10:
As a metal catalyst, an alloy powder having a component composition of Fe10-Co20-Ni15-Mo50-V1-Al4% by mass was used and reacted at a pressure of 4.8 GPa and 1500 ° C. for 60 minutes in the same manner as in Example 1. When synthesized, fine cBN particles having a cBN conversion rate of 85% or more and an average particle size of 25 μm were synthesized.
Example 11:
As a metal catalyst, an alloy powder having a component composition of Fe10.2-Co29.4-Mo7.2-Cr3.2-V48.5-Al1.5% by mass was used, in the same manner as in Example 1, with a pressure of 5. When cBN was synthesized by reacting at 4 GPa and 1650 ° C. for 60 minutes, fine cBN having a cBN conversion rate of 85% or more and an average particle size of 15 μm was synthesized.
Comparative Example 1:
As shown in FIG. 1, an alloy powder (that is, containing no V component) composed of 2.5% by mass of Co46.5-Mo20-Cr31-Al is prepared in advance as a metal catalyst, and is approximately 7 mm in diameter and 3 mm thick. In order to form a sandwiched metal catalyst (alloy powder) layer (3) having a thickness of about 1.6 mm between the two hBN molded plates (4), an outer diameter of 10 mm, an inner diameter of 7 mm, and a height of 7 A 6 mm salt (containing 10% by mass of zirconia powder) compact (5) was filled into a sample container.

  These samples were surrounded by a graphite tubular heater (1) having an outer diameter of 12 mm, an inner diameter of 10 mm, and a height of 17.6 mm, Mo foil (2) was disposed on the inner surface, and a belt-type ultrahigh pressure device (anvil tip diameter of 21 mm, Pressurization with a cylinder inner diameter of 25 mm), and then apply power to the heater to heat it, hold it for a certain period of time, then rapidly lower the temperature, then depressurize and take out the sample, and take a scanning electron microscope, X-ray diffraction, etc. A sample was identified.

As a result of analyzing the sample reacted at a pressure of 4.2 GPa and 1320 ° C. for 30 minutes, the cBN conversion rate is 50% or more, but the average particle size of the obtained cBN is 80 μm coarse particles, and the fine particle cBN is It was not synthesized.
Comparative Example 2:
As a metal catalyst, an alloy powder having a composition of Co76-Mo20-Al 4% by mass (that is, containing no V component) was used and reacted at a pressure of 5.0 GPa and 1560 ° C. for 60 minutes in the same manner as in Comparative Example 1. When cBN was synthesized, the cBN conversion was 50% or more, but the average particle size of the obtained cBN was 50 μm coarse particles, and no fine cBN was synthesized.

In FIG. 5, the structure | tissue photograph observed with the scanning electron microscope of the coarse grain cBN obtained by the comparative example 2 is shown.
Comparative Example 3:
As a metal catalyst, an alloy powder (that is, containing no V component) composed of Ni 53.04-Fe 9.36-Cr 33.6-Al 4% by mass was used, and the pressure was 4.2 GPa in the same manner as in Comparative Example 1. When cBN was synthesized by reacting at 1350 ° C. for 60 minutes, the cBN conversion was 80% or more, but the average particle size of the obtained cBN was 100 μm coarse particles, and fine cBN was not synthesized. .

  In Table 1, the result of said Examples 1-11 and Comparative Examples 1-3 is shown collectively.

  From the results shown in Table 1, according to the synthesis of cBN grains using the metal catalyst of the present invention, a cBN conversion rate is high and fine cBN can be obtained in a low pressure and low temperature range.

  On the other hand, in the synthesis methods of Comparative Examples 1 to 3 using a metal catalyst containing no V component, fine cBN cannot be obtained in a low pressure and low temperature range.

ついで、上記で合成した実施例１〜１１，比較例１〜３のｃＢＮ粒子に対して、表２に示される平均粒径となるように粉砕・分級を行い、ｃＢＮ焼結体２１〜３１（実施例２１〜３１）および比較例のｃＢＮ焼結体１１〜１３（比較例１１〜１３）の原料粉末として使用した。

Next, the cBN particles of Examples 1 to 11 and Comparative Examples 1 to 3 synthesized above were pulverized and classified so as to have an average particle size shown in Table 2, and cBN sintered bodies 21 to 31 ( It was used as a raw material powder for the cBN sintered bodies 11 to 13 (Comparative Examples 11 to 13) of Examples 21 to 31) and Comparative Examples.

  As the sintering aid in the sintering experiments of Examples 21 to 31 and Comparative Examples 11 to 13, mixed powders having the same composition as the metal catalyst shown in Table 1 were used, and the content ratio of the sintering aid was carried out. In Examples 21-31, mixed powder (12) blended so as to be 5 to 20% by volume, and in Comparative Examples 11 to 13 to be 30 to 50% by volume, 0.02 mm thick Mo as shown in FIG. Filled so as to be sandwiched between sodium chloride (containing 10 wt% zirconia powder) molded body (15) having an outer diameter of 10 mm, an inner diameter of 7 mm, and a height of 7.6 mm surrounded by foil (13), and shown in Table 2 Sintering was performed under each condition.

When the obtained cBN sintered compact was observed with the scanning electron microscope, the cBN sintered compacts 21-31 (Examples 21-31) of this invention were the cBN sintered compacts 11-13 of the comparative example (comparative example 11). Compared with ˜13), a dense cBN sintered body composed of fine particles having an average particle size of 30 μm or less and having a strong direct bond between the cBN particles was formed.
Table 2 shows the average particle size of cBN in each manufactured cBN sintered body.

  As described above, according to the cBN synthesis method of the present invention and the cBN sintered body production method using cBN as a raw material powder, Cr, Mo having an action of dissolving N as a metal catalyst, and the melting temperature of the metal catalyst are set. By using an alloy powder or mixed powder composed of Fe, Co, and Ni having an action of lowering V, Al having an action of promoting and promoting cBN nucleation / growth, and the balance of B being dissolved, It is possible to synthesize fine particles (average particle size of 30 μm or less) of cBN in a lower pressure range (minimum pressure 4 GPa) and lower temperature range (1200 to 1700 ° C.), and sintering with the same component composition as the metal catalyst. By sintering using an auxiliary agent, a BN sintered body having a strong direct bond between cBN particles and having a dense fine grain structure can be produced.

DESCRIPTION OF SYMBOLS 1,11: Graphite heater 2: Mo foil 3: Metal catalyst 4: hBN raw material 5, 15: NaCl-10 mass% ZrO ₂ compact 12: Mixture of cBN + sintering aid (= metal catalyst) 13: Mo foil 14 : WC / Co alloy substrate

Claims (2)

  In the method for synthesizing cubic boron nitride in which cubic boron nitride is synthesized from hexagonal boron nitride under ultrahigh pressure and high temperature conditions in the presence of a metal catalyst, the metal catalyst contains one or two of Cr and Mo. And, when Cr is contained alone, Cr: 10 to 55% by mass, when Mo alone is contained, Mo: 10 to 50% by mass, and when both Cr and Mo are contained (Cr + Mo): 10 to 50 In addition to containing in the range of mass%, V: 1-50 mass%, Al: 1.5-8 mass%, the balance is any one or more component composition of Fe, Ni and Co A method for synthesizing cubic boron nitride, characterized in that the synthesis is performed at 4 GPa or more and 1200 to 1700 ° C.   In the method for producing a cubic boron nitride sintered body, comprising cubic boron nitride as a raw material powder, sintering by adding a sintering aid to the raw material powder, the above-mentioned sintering aids include Cr and Mo. In the case of containing either 1 type or 2 types and containing Cr alone, Cr: 10 to 55% by mass, when containing Mo alone, Mo: 10 to 50% by mass, containing both Cr and Mo In the case, (Cr + Mo): contained in the range of 10 to 50% by mass, V: 1 to 50% by mass, Al: 1.5 to 8% by mass, and the balance is any of Fe, Ni and Co A method for producing a cubic boron nitride sintered body, comprising adding 5 to 20% by volume of an alloy powder or mixed powder composed of one or more component compositions to a raw material powder and sintering.

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