JP2010024103A - Method for producing high-purity boron nitride sintered compact having high hardness and high toughness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a high-purity boron nitride sintered compact, which is low in cleavage property, is excellent in crack propagation suppressing action and includes high hardness and high toughness. <P>SOLUTION: The high-purity boron nitride sintered compact containing a trace quantity of wurtzite type boron nitride is produced by cleaning the surface of fine wurtzite type boron nitride powder having ≤0.5 μm particle diameter with a supercritical fluid containing no oxygen and using solid polyvinylidene chloride, polyvinyl chloride and polyethylene as fluid sources and sintering under a high-pressure high-temperature condition of ≥5 GPa and ≥1,400°C without adding a sintering aid. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a high-purity boron nitride sintered body having a high hardness and high toughness having a low cleaving property and an excellent crack propagation suppressing action, and particularly when applied as a cutting tool material of a different composite material. Furthermore, the present invention relates to a method for producing a high-purity boron nitride sintered body that is excellent not only in chipping resistance and wear resistance but also in the finished surface accuracy of a work material and that exhibits excellent cutting performance over a long period of use.

Conventionally, a boron nitride sintered body, for example, cubic boron nitride (hereinafter referred to as cBN) is used as a tool material having low affinity with a work material for cutting of an iron-based work material such as high hardness steel. Alternatively, it is well known that wurtzite boron nitride (hereinafter referred to as wBN) is used.
These boron nitride sintered bodies are generally manufactured as a sintered body by, for example, mixing cBN powder or wBN powder with a sintering aid such as metal or ceramic and performing ultra-high pressure and high temperature treatment. However, since this sintered body contains a sintering aid, it is inferior in hardness, thermal conductivity, etc. compared to cBN or wBN, and it can be said that the original characteristics of cBN and wBN are sufficiently exhibited. There wasn't.

  Therefore, as one of the manufacturing methods for obtaining a boron nitride sintered body having better characteristics, a cBN powder having a particle size width of 0.5 to 2 μm is made of a fluid containing no oxygen and is used as a solid source as a fluid source. High purity purified by supercritical fluid using one or more of vinylidene chloride, polyvinyl chloride and polyethylene, and sintered under high pressure and high temperature conditions of 5 GPa and 1400 ° C or higher without adding sintering aid A method for producing a cBN sintered body has been proposed. According to this production method, it has been reported that a high-purity cBN sintered body having high hardness and no abnormal grain growth and excellent heat resistance can be obtained. ing.

  In addition, a method for producing a sintered body using wBN powder as a raw material without using a binder component is also known, but in such a case, an ultrahigh pressure of 8 to 9 GPa is required. Since expensive equipment is required, the cost is high. Furthermore, even under sintering under such ultra-high pressure, only 50% or less of wBN is phase-transformed to cBN, and cBN Since the phase transition to is incomplete, the excellent properties of cBN as a sintered body have not been sufficiently exhibited.

Japanese Examined Patent Publication No. 62-41192 Japanese Patent No. 3132649 JP 2007-70148 A “Powder Metallurgy and Metal Ceramics” Vol. 37, no. 1-2 (1998) 48-54

cBN has hardness comparable to that of diamond and is also thermally and chemically stable. Therefore, cBN is currently used as a cutting tool material for ferrous materials such as high-speed steel, die steel, and cast iron. For example, a cutting tool made of a high-purity cBN sintered body shown in Patent Document 3 is excellent in cutting of iron-based work materials such as high-speed steel, die steel, and cast iron. Exhibits wear resistance.
However, recently, for example, dissimilar composite materials have been used to reduce the weight of automobile components. However, such dissimilar composite materials (for example, ductile cast iron-aluminum alloy composite materials) When a cBN sintered body is used as the cutting tool material, cracks are likely to occur due to a high load acting on the cutting blade, while the cBN sintered body has a high cleaving property and has no crack (crack) propagation suppressing action. Since it is sufficient, cracks (cracks) propagate through the cBN sintered body to cause chipping, chipping, etc. in the cutting tool, leading to damage and shortening the tool life. .
Therefore, the present invention has a low cleaving property and an excellent crack propagation suppressing action that can improve cutting characteristics and extend the tool life even when applied as a cutting tool material of a different composite material. Another object of the present invention is to provide a new production method capable of easily and inexpensively obtaining a high-purity boron nitride sintered body having high hardness and high toughness.

  The present inventors diligently studied the raw material powder and production conditions when producing a high-purity boron nitride sintered body, and obtained the following knowledge.

In the method for producing a sintered body disclosed in Patent Document 3, cBN powder having a particle size width of 0.5 to 2 μm is used as a raw material powder and sintered without using a binder phase component. Although a high-purity cBN sintered body has been obtained, the cBN sintered body obtained by this method has a high degree of cleaving although it has a high hardness as described above, and this is used as a cutting tool material of a heterogeneous composite material. When used, the tool life was short because it was liable to be damaged by chipping and the like.
Therefore, the present inventors have disclosed the above Patent Document 3 without using a cBN powder as a raw material powder but using a wurtzite boron nitride (wBN) powder as a raw material powder and without using a binder phase component. It has been found that a high-purity boron nitride sintered body having a high hardness and a high toughness having a low cleaving property and an excellent crack propagation suppressing effect can be obtained by performing the same treatment as the method.
The “high-purity boron nitride sintered body” in the present invention refers to a boron nitride sintered body sintered without using a sintering aid. The wBN powder as the raw material powder may be a wBN powder produced by a method well known to those skilled in the art that instantaneously creates a high-pressure and high-temperature state for hBN with an explosive and causes phase transition to the high-pressure phase wBN.

That is, the present invention uses fine wurtzite boron nitride (wBN) powder as a raw material powder and performs sintering at a relatively low pressure (about 5 to 7 GPa) and high temperature without using a binder phase component. The present inventors have found that a high-purity boron nitride sintered body containing a very small amount of fine wBN and compressed hBN (hereinafter referred to as comp.hBN) and the balance being cBN can be produced.
The above comp. hBN is normal-pressure hexagonal boron nitride (hBN) generated by a reverse phase transition during the sintering of wBN. When the diffraction peak position of (002) is obtained by X-ray diffraction, normal hBN is obtained. It is called compressed hBN (compressed hBN (comp-hBN)) because it shows a peak at a position shifted to the higher angle side from the diffraction peak position of the crystal and the c-axis of the hexagonal crystal is compressed and shortened.

  The high-purity boron nitride sintered body produced by the present invention has a low cleaving property, an excellent crack propagation suppressing action, and has a high hardness and high toughness. Therefore, this is a composite of ductile cast iron-aluminum alloy. When used as a cutting tool material of different composite materials such as materials, it is possible to improve the finish surface accuracy of the work material, and at the same time, without causing chipping, chipping, breakage, etc. Excellent wear resistance and tool life can be extended.

The present invention has been made based on the above findings,
"The surface of wurtzite-type boron nitride fine powder with a particle size of 0.5 μm or less is made of a fluid that does not contain oxygen, and one or more of solid polyvinylidene chloride, polyvinyl chloride, and polyethylene are used as the fluid source. Characterized in that it is cleaned with a supercritical fluid and sintered under high pressure and high temperature conditions of 5 GPa or more and 1400 ° C. or more under the thermodynamic stability condition of cubic boron nitride without adding a sintering aid. Of manufacturing a high-purity boron nitride sintered body containing wurtzite-type boron nitride. "
It is characterized by.

  The present invention will be described in detail below.

Wurtzite boron nitride (wBN) fine powder:
As described above, the wurtzite boron nitride (wBN) fine powder as the raw material powder can be formed by instantaneously creating a high pressure and high temperature state in the hBN powder with an explosive, and the resulting wBN powder. Are formed as fine particles having a particle size of 0.5 μm or less. Since this wBN fine particle powder hardly causes grain growth even during sintering under ultra-high pressure and high temperature, the resulting high purity boron nitride sintered body has a small particle size (approximately 0.5 μm or less). As a result, when used as a cutting tool material, cutting can be performed with a low surface roughness (for example, Ry 2.00 μm or less) without roughening the surface of the work material, and the finished surface accuracy of the work material can be improved. Can be increased.

Cleaning:
In order to enhance the sinterability of the above wBN fine powder, the surface is made of a fluid containing no oxygen, and an ultra-high-performance material using one or more of solid polyvinylidene chloride, polyvinyl chloride and polyethylene as a fluid source. When cleaned and sintered with a critical fluid, the surface of the fine powder is activated, and the high-purity boron nitride sintered body in which the fine powder is firmly bonded to each other even without the addition of a sintering aid (binding phase component). Is formed.
The high-purity boron nitride sintered body is mostly composed of cBN in which wBN of the raw material powder undergoes phase transition during sintering, but a part of the wBN of the raw material powder undergoes phase transition to cBN. It is particularly important in the present invention that wBN is contained in the sintered body as it is.
The other part of the raw powder wBN undergoes a reverse phase transition to comp-hBN and remains in the sintered body as comp-hBN, but the amount of comp-hBN is very small (less than about 10 vol%). Thus, the properties of the sintered body are not adversely affected.
In the production method of the present invention, the raw material powder composed of wBN is not completely phase-transformed into cBN, and by intentionally containing a small amount of wBN in the sintered body, the cleavage property is high and crack propagation is suppressed. The characteristics of the 100% cBN sintered body inferior in action can be improved, and a high-purity boron nitride sintered body having high hardness and high toughness can be produced.

Sintering conditions:
In the production of a conventional cBN sintered body, sintering was performed under ultra-high pressure and high temperature conditions of 6 GPa or more and 1700 ° C. or more. However, in the present invention, the conventional technology is used without adding a sintering aid. Compared with relatively relaxed conditions, that is, high pressure and high temperature conditions of 5 GPa or more and 1400 ° C. or more, abnormal grain growth is achieved by sintering under such relaxed conditions. It is possible to obtain a high-purity boron nitride sintered body having a fine and dense sintered structure and containing a small amount of wBN.
From the point that the phase transition from wBN to cBN is not carried out completely and a small amount of wBN is left to be contained, while the amount of comp-hBN formed is suppressed to a very small amount (less than about 10 vol%). Is preferably 5 to 7 GPa, 1400 to 1900 ° C., and 5 to 30 minutes.
By sintering under high pressure and high temperature, that is, conditions of 5 GPa or more and 1400 ° C. or more, preferably 5 to 7 GPa, 1400 to 1900 ° C., and 5 to 30 minutes, the particle powders are strongly bonded to each other. A high-purity boron nitride sintered body having a fine and dense sintered structure with a particle size of 1 μm or less is obtained.
The manufactured high-purity boron nitride sintered body has a low cleavage property, an excellent crack propagation suppressing effect, a high hardness and a high toughness, and is made of a heterogeneous composite material such as a ductile cast iron-aluminum alloy. When used as a cutting tool material, it has excellent finished surface accuracy (Ry 2.00 μm or less) and exhibits excellent wear resistance over a long period of use without causing chipping, chipping, etc. .

FIG. 1 shows an example of a capsule for filling a wBN fine particle powder which is a raw material powder in the production of a high purity boron nitride sintered body according to the present invention.
Inside the Ta capsule 1, wBN fine powder 2 having a particle size of 0.5 μm or less, Ta foil 3, and polyvinylidene chloride 4 are alternately stacked, and a graphite disk 5 is arranged above and below. In a specific example, a Ta capsule was used for the sample container, and a graphite disk was placed under the capsule. After placing three Ta foils on a graphite disk, 500 mg of wBN fine powder having a particle size of 0.5 μm or less is weighed, and 2.2 mg of polyvinylidene chloride is laminated on the wBN fine powder. 500 mg of wBN fine powder having the same particle size width was filled on vinylidene, and three Ta foil discs were placed on the wBN fine powder. Further, two 500 mg of wBN fine powder having a particle size of 0.5 μm or less was weighed, 2.2 mg of polyvinylidene chloride was sandwiched between the wBN fine powder, and the wBN fine powder was covered with Ta foil. .
As the fluid source, not only polyvinylidene chloride but also one or more of polyvinylidene chloride, polyvinyl chloride, and polyethylene can be used.

As described above, the present invention uses a wurtzite-type boron nitride (wBN) fine particle powder having a particle size width of 0.5 μm or less as a raw material powder for sintering, and this surface is used as a solid source of polyvinylidene chloride, poly Cleaned with supercritical fluid using vinyl chloride and polyethylene, relatively relaxed high pressure and high temperature conditions of 5 GPa or more and 1400 ° C. or more under the thermodynamic stability condition of cubic boron nitride without adding sintering aid ( Preferably, by sintering at 5 to 7 GPa, 1400 to 1900 ° C. for 5 to 30 minutes, a fine and dense sintered structure in which the particle powder is firmly bonded without abnormal grain growth is obtained. As a result, it is possible to produce a high-purity boron nitride sintered body containing a small amount of wBN having a low cleavage property, excellent crack propagation suppressing action, high hardness and high toughness.
When the high-purity boron nitride sintered body obtained by this manufacturing method is used as a tool material for cutting a heterogeneous composite material composed of a composite material of ductile cast iron and an aluminum alloy, for example, In addition to improving the accuracy of the finished surface, it offers excellent wear resistance over a long period of use without fear of chipping, chipping or breaking of the tool, improving cutting characteristics and extending the tool life. Can do.

  Below, the manufacturing method of the highly purified boron nitride sintered compact which has the high hardness and toughness of this invention is demonstrated concretely based on an Example.

As shown in FIG. 1, a wBN fine particle powder having a particle size of 0.5 μm or less is stratified into a layer having a diameter of 11.2 mm, and a 1.5 mg disk made of a supercritical fluid source shown in Table 1 is placed thereon. Then, the same amount of wBN fine powder was pressure-filled thereon. This wBN fine powder was filled into a Ta capsule together with other wBN fine powder. Graphite disks were placed above and below the Ta capsule. The capsules were subjected to high-pressure and high-temperature treatment together with the pressure medium under the conditions shown in Table 2 to produce high-purity boron nitride sintered bodies (referred to as sintered bodies of the present invention) 1 to 10 having a thickness of 0.5 to 2 mm. .
For the manufactured sintered bodies 1 to 10 of the present invention, first, a powder sample is prepared, an X-ray diffraction pattern is measured by X-ray diffraction, and peak intensities I of cBN, wBN and comp-hBN in the sintered body are determined. Asked. FIG. 2 shows an X-ray diffraction chart of the sintered body 3 of the present invention measured by Bruker AXSMXP18VAHF.
Moreover, after grinding the sintered compact surface, it grind | polished using a diamond paste as an abrasive | polishing agent, and measured the Vickers hardness Hv of the surface of this invention sintered compact 1-10 after grinding | polishing.
Table 3 shows values of the peak intensity I and the Vickers hardness Hv.
Furthermore, the sintered structure after polishing of the sintered bodies 1 to 10 of the present invention was observed with a scanning electron microscope.

For comparison, cBN powder having a particle size of 0.5 to 1.5 μm is layered with a diameter of 11.2 mm, and a 1.5 mg disk made of the supercritical fluid source shown in Table 1 is placed thereon. Then, the same amount of cBN powder was pressure-filled thereon. This cBN powder was filled with Ta capsule together with other cBN powders. Graphite disks were placed above and below the Ta capsule. This capsule was subjected to high-pressure and high-temperature treatment under the conditions shown in Table 2 together with the pressure medium, and high-purity cBN sintered bodies (referred to as comparative example sintered bodies) 1 to 10 having a thickness of 0.5 to 2.0 mm as comparative examples. Manufactured.
About the manufactured comparative example sintered compacts 1-10, while performing the peak intensity measurement by X-ray diffraction and the Vickers hardness Hv measurement similarly to the case of this invention sintered compact 1-10, the surface is ground and polished. Then, the structure was observed.
FIG. 3 shows an X-ray diffraction chart of the comparative sintered body 3 measured by Bruker AXSMXP18VAHF. In addition, Table 4 shows the peak intensity and Hv for the comparative sintered bodies 1 to 10.

When the X-ray diffraction charts of the sintered bodies 1 to 10 of the present invention and the comparative sintered bodies 1 to 10 were compared, there was a great difference between the two in terms of the peak intensity shown in the chart.
The X-ray diffraction charts of the sintered bodies 1 to 10 of the present invention show almost the same tendency as that shown in FIG. 2, and the X-ray diffraction charts of the sintered bodies 1 to 10 of the comparative examples show almost the same tendency as that shown in FIG. For example, in FIG. 2, cBN peak intensity I (cBN) = 23083 (43.3 degrees), wBN peak intensity I (wBN) = 756 (40.8 degrees), and comp-hBN peak intensity I In contrast to (hBN) = 872 (28.5 degrees), FIG. 3 shows that cBN peak intensity I (cBN) = 15294 is only 43.3 degrees, and wBN and comp− The peak intensity of hBN is not seen.
Accordingly, the sintered bodies 1 to 10 of the present invention contain a small amount of wBN and comp-hBN, whereas the comparative sintered bodies 1 to 10 contain wBN and comp-hBN. It can be seen that almost 100% is composed of cBN.
Moreover, about the hardness Hv of this invention sintered compact 1-10 and comparative example sintered compact 1-10, a big difference was not seen evidently from the result of Table 3, Table 4, and it was substantially equivalent.
In addition, the sintered structures of the sintered bodies 1 to 10 of the present invention are fine and dense structures in which almost no cracks are present inside the sintered bodies and particle powders having a particle diameter of 1 μm or less are firmly bonded. However, in Comparative Example sintered bodies 1 to 10, although there were almost no cracks in the sintered body, a coarse structure in which coarse particles were bonded was formed.

  Next, the sintered bodies 3, 5 and 9 of the present invention are divided into equilateral triangles having a side of 3 mm by a wire electric discharge machine, and further Co: 5 mass%, TaC: 5 mass%, WC: remaining composition And a brazing portion (corner portion) of a WC-based cemented carbide insert body having the shape of CIS standard CNMA120408 in mass%, Cu: 26%, Ti: 5%, Ni: 2.5%, Ag: After brazing using a brazing material of an Ag alloy having the remaining composition and processing the outer periphery to a predetermined dimension, the cutting edge is subjected to honing processing with a width of 0.13 mm and an angle of 25 °, and finish polishing is further performed. As a result, high-purity boron nitride cutting tools (referred to as tools of the present invention) 1 to 3 having an ISO standard CNMA120408 insert shape were produced.

  For comparison, cBN cutting tools (referred to as comparative example tools) 1 to 3 having the insert shape of ISO standard CNMA120408 were manufactured in the same manner as described above for the comparative example sintered bodies 3, 5 and 9.

The present invention tools 1 to 3 and comparative tools 1 to 3 are all screwed to the tip of the tool steel tool with a fixing jig.
Work material: FCD450 and A390T6 heterogeneous composite round bar,
Cutting speed: 200 m / min. ,
Cutting depth: 0.15 mm,
Feed: 0.07 mm / rev. ,
Wet high-speed cutting of a different composite material of ductile cast iron and Al-17% Si alloy under the conditions of the above, and the flank wear width of each cutting edge after the cutting time of 1 minute, 3 minutes, 5 minutes and 10 minutes ( mm).
The values are shown in Table 5.

Further, the surface roughness Ry of the work material after cutting for 10 minutes was measured by a surf test SJ-201P manufactured by Mitutoyo.
The values are also shown in Table 5.

    As is apparent from Table 5, all of the inventive tools 1 to 3 exhibit excellent wear resistance without causing breakage or breakage, and the finished surface accuracy of the work material is high (surface roughness Ra). In contrast, the comparative tools 1 to 3 showed almost the same characteristics as the tools 1 to 3 of the present invention, but the comparative tool 2 partly within the cutting test time. Chipping has occurred, and the finishing surface accuracy of the work material was inferior to that of the inventive tools 1 to 3 for any of the comparative tools 1 to 3.

As described above, according to the production method of the present invention, fine wBN powder is used as a raw material powder for producing a high-purity boron nitride sintered body, and a small amount of wBN is contained in the sintered body after sintering. By doing so, it is possible to obtain a high-purity boron nitride sintered body having low cleaving property, excellent crack propagation suppressing action, high hardness and high toughness.
For example, when this high-purity boron nitride sintered body is applied as a cutting tool material of a different composite material, the cutting tool made of the high-purity boron nitride sintered body has a finished surface accuracy of the work material. In addition to being able to improve, it also has excellent chipping resistance and wear resistance, and exhibits excellent cutting performance over a long period of use.

FIG. 3 is a schematic cross-sectional view of a capsule for filling a wBN fine particle powder that is a raw material powder in the production of a high-purity boron nitride sintered body according to the present invention. The X-ray diffraction chart measured about this invention sintered compact 3 is shown. The X-ray diffraction chart measured about the comparative example sintered compact 3 is shown.

Explanation of symbols

1: Ta capsule 2: wBN powder 3: Ta foil 4: Polyvinylidene chloride 5: Graphite disk

Claims (1)

  The surface of wurtzite-type boron nitride fine powder having a particle size of 0.5 μm or less is made of a fluid that does not contain oxygen, and one or more of solid polyvinylidene chloride, polyvinyl chloride, and polyethylene are used as a fluid source. It is cleaned with a supercritical fluid and sintered under high pressure and high temperature conditions of 5 GPa or more and 1400 ° C. or more under the thermodynamic stability condition of cubic boron nitride without adding a sintering aid. A method for producing a high-purity boron nitride sintered body containing wurtzite boron nitride.

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