JP3882078B2 - Manufacturing method of high purity ultrafine cubic boron nitride sintered body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
Since the present invention has the second hardness after diamond and is more stable than diamond for iron-based metals, it is expected to bring technological innovation to the conventional machining field as iron-based metal cutting tools, abrasives, etc. The present invention relates to a high-purity ultrafine cBN sintered body that can be produced and a method for producing the same.
[0002]
[Prior art]
Various forms of cBN sintered bodies have been used as cutting tools and abrasives for ferrous metals. These have excellent characteristics in machining of iron-based materials and occupy an important position in the machining field, which is the modern industrial base. The cBN sintered body used so far is a composite sintered body sintered together with various sintering aids in the range of 40 to 50,000 atm. The cBN content is about 40 to 90 wt%. Various things have been developed. When used as a cutting tool, the content of cBN is controlled according to the characteristics of the work material, but in recent years high cutting performance is achieved by a high-purity sintered body with a total content of cBN and inevitable impurities of 100%. Has been found to appear (Non-Patent Documents 1 and 2).
[0003]
There are two methods for synthesizing a high-purity cBN sintered body having a total content of cBN containing no sintering aid and inevitable impurities of 100%. One is to use a low-pressure phase boron nitride such as hexagonal crystal as a raw material and proceed the sintering reaction at the same time while proceeding the phase transition to cBN which is a high-pressure phase under high pressure and high temperature. As a result, synthesis of a dense translucent cBN sintered body at 77,000 atmospheres and 2000 ° C. has been reported (Non-patent Document 3). Further, synthesis of a translucent cBN sintered body has been reported by adding a small amount of hydrochloric acid to a raw material hexagonal boron nitride under a temperature and pressure condition of 65,000 atm and 1900 ° C. (Non-patent Document 4).
[0004]
The other is a commercially available cBN powder, which is sintered without the addition of a sintering aid. It is also a dense translucent cBN sintered body in the 7.7 GPa and 2000 ° C region, and semiconductor characteristics. There has been reported synthesis of a sintered body imparted with (Non-patent Document 5, Patent Document 1). These high-purity cBN sintered bodies have high hardness, and in particular, high-purity sintered bodies synthesized at 77,000 atm and 2000 ° C have excellent cutting performance and will play an important role in the future machining field. It is expected.
[0005]
However, the conditions for synthesizing these high-purity cBN sintered bodies are as severe as 65 to 77,000 atmospheres and 1900 ° C. or higher. Considering the current industrial scale and technical level, when compared with the composite sintered body synthesized in the current low pressure region, it is based on the conventional technology in terms of stable supply and manufacturing cost as a large sintered body tool material. There is much room for improvement in the method for synthesizing a high-purity sintered body.
[0006]
On the other hand, when the sintered body is used as a cutting tool, the surface roughness of the work surface of the work material is affected by the size of the constituent particle diameter of the sintered body. For this reason, when aiming at precision processing, such as mirror finishing of material, it is desired that the particle diameter of a sintered compact is as small as possible. The particle size of the high-purity cBN sintered body obtained so far is up to about 0.5 μm even if it is a fine particle size, and synthesis of a dense high-purity sintered body with a particle size smaller than this has not been reported .
[0007]
[Non-Patent Document 1]
Yamaoka, Akaishi, Ueda, New Diamond, 22 28 (1991)
[Non-Patent Document 2]
H. Sumiya and S. Uesaka, J. Mater. Res., 35, 1181 (2000)
[Non-Patent Document 3]
M. Akaishi, et al., J. Mater. Sci. Let., 12, 1883 (1993)
[Non-Patent Document 4]
H. Sei et al., Diamond Relat. Mater., 2, 1160 (1993)
[Non-Patent Document 5]
T. Taniguchi, et.al., J. Mater. Res., 14, 162 (1999)
[Patent Document 1]
Japanese Patent No. 2725733 [0008]
[Problems to be solved by the invention]
In order to improve the efficiency of machining processes represented by the automobile industry and the like and to preserve the environment, it is required to improve the characteristics of existing cBN (cubic boron nitride) sintered body tools. In order to improve the characteristics of the tool, fine control of the sintered body structure is indispensable, and for that purpose, it is a great way to realize high purity and fine particles of cBN sintered body tools that are currently in increasing demand. it makes sense. The conventional technology made it possible to synthesize high-purity cBN sintered bodies at a pressure of 77,000 atm, pressures over 2000 ° C, and temperature range. There were problems of instability and high cost.
[0009]
The synthesis condition of the sintered body is in the range of 50,000 atm is important in terms of stable supply and spread as a tool material on the current industrial scale. For this reason, the use of a sintering aid is effective for relaxing the sintering conditions, but it becomes a factor that hinders the original characteristics of cBN as a cutting tool of the obtained sintered body. In addition, the strength of the sintered body is known to depend on the constituent particle diameter, but in the structure in which the fine particles are densely sintered, the size of the microcracks inherent in the sintered body structure is reduced, so that the sintered body is sintered. It can be expected that the strength as a body is improved, and that when used as a cutting tool, the surface roughness of the work material is improved by a tool material having a fine particle diameter.
[0010]
That is, the problem to be solved by the present invention is to relax the conventional severe sintering conditions of 6.5 GPa or more, and to provide a high-purity cBN sintered body having a fine particle size of a sintered body useful as a cutting tool material. To enable synthesis in the 50,000 atmospheres range where current industrial production technology can be applied.
[0011]
[Means for Solving the Problems]
The process of synthesizing a high-purity cBN sintered body without adding a sintering aid was examined. It was difficult to reduce the synthesis pressure in the process using the phase transition from the low-pressure phase boron nitride described above. In the pressure region, the low-pressure phase component of the raw material remains in the sintered body, and a good sintered body cannot be obtained.
[0012]
On the other hand, in the latter process of directly sintering cBN particles, no inhibiting factors such as low-pressure phase boron nitride remain in low-pressure sintering. As a result of evaluating the sintering characteristics of cBN particles having an initial particle size of 0.5 to 1.2 μm, 2 to 4 μm, and 8 to 12 μm without adding a sintering aid in the 77,000 atmospheric pressure region, the smaller the particle size, the more the particles are sintered. It was found that the lower temperature limit at which light is easy to proceed and translucency is low (T. Taniguchi, et.al., J. Mater. Res., 14, 162 (1999), T. Taniguchi Sci & Technol. High Press , in Proc.AIRAPT-17 (Univ. Press (India), 2000) pp893.).
[0013]
Among the series of sintering behavior of cBN particles found here, the formation of a dense and strong sintered body structure is based on the premise that the bonds between the constituent particles are well formed. It was noted that the effect of surface energy, which acts as a driving force when the constituent particles try to reduce their surface area, is important. That is, since the fine particles have a larger surface area than the coarse particles, the driving force for sintering is high, and it can be considered that the sintering and densification easily proceed. This idea, which was verified in the cBN particle sintering experiment in the 77,000 atmosphere region, is thought to be applicable to the sintering of cBN particles in the low pressure region. The sintering behavior of unused fine particles has not been clarified. Therefore, we attempted high-pressure sintering in the low-pressure region without adding a sintering aid, using finer cBN ultrafine particles as raw materials than those used in the 77,000-atmosphere region.
[0014]
Although there is no particle size standard based on a standardized measurement method for cBN ultrafine particles, the particle size range is 0 to 1/10, 0 to 1/4, 0 to 1/2, 0 to 1, 0 to 2, 1-3, 2-4, 4-8 are divided into the standard particle size standard (the center particle size is the intermediate value of the particle size width) is commercially available, in this specification, The particle size width of the cBN ultrafine particles is based on such classification.
[0015]
In order to advance the sintering without adding a sintering aid, it is necessary to set the sintering temperature higher in order to promote the solid phase reaction of the substance. The stability of is an important condition. The upper limit of the sintering temperature of high-pressure stable phases such as cBN and similar super-hard materials such as diamond is defined below the thermodynamically stable temperature conditions of these materials. At a temperature higher than this, reverse conversion to the low-pressure phase proceeds and a good sintered body cannot be obtained.
[0016]
Focusing on this thermodynamic stability, cBN is stable up to a higher temperature than diamond, and the sintering temperature condition in the 50,000 atm region is about 1500 ° C for diamond, whereas cBN is about 1900 ° C. Setting up to high temperatures is possible. Considering this thermodynamic stability condition, it is possible to make a working hypothesis that fine cBN particles can be sintered under a lower pressure condition than before.
[0017]
In the range of 5 to 60,000 atmospheres, commercially available cBN powders with various particle sizes ranging from 0 to 0.1 μm, 0 to 0.25 μm, and 0 to 1 μm (hereinafter referred to as “initial particle size”) range from 1400 to 2000 ° C. Then, the properties of the obtained sintered body were evaluated. When the obtained sintered body has an initial particle size of 0 to 0.25 μm and 0 to 1 μm, the characteristics are varied despite controlling the synthesis conditions, the sintered structure is inhomogeneous and the strength is also high. It was insufficient.
[0018]
On the other hand, when the initial particle size was 0 to 0.1 μm, a dense cBN sintered body was obtained without adding a sintering aid under the conditions of 50,000 atm, pressure of 1600 ° C. or higher, and temperature. The Vickers hardness of the sintered body was about 45 GPa (test load 9.8 N), and the characteristics greatly exceeded those of the cBN composite sintered body to which the sintering aid was added. The constituent particle diameter after sintering was an average particle diameter of about 0.1 to 0.2 μm, which made it possible to synthesize a high-purity ultrafine particle cBN sintered body.
[0019]
On the other hand, points to be noted in optimizing the sintering conditions of the fine particles are the aggregation state of the raw material powder and the contamination state of the particle surface. In the commercially available cBN ultrafine particle powder, primary particles are aggregated to a few microns due to aggregation. Therefore, these cBN ultrafine particles were washed. Although cBN is stable against strong acids, it is known to be etched at high temperature with an alkaline solution. The cBN ultrafine particles having a particle size in the range of 0 to 0.1 μm were cleaned with a 5 molar aqueous alkali solution, washed with pure water, and freeze-dried to obtain a raw material powder for sintering.
[0020]
This powder was subjected to high-pressure sintering in the range of 1500 to 1800 ° C. at 4.5 to 60,000 atmospheres, and the obtained sintered body was evaluated. As a result, a dense cBN sintered body was obtained without adding a sintering aid under the conditions of a lower limit of 50,000 atm, a pressure of 1600 ° C., and a temperature condition. At this time, a translucent sintered body was obtained at a sintering temperature of 1800 ° C. The Vickers hardness of the sintered body was about 45 GPa (test load 9.8 N), and the characteristics greatly exceeded those of the cBN composite sintered body to which the sintering aid was added. In addition, the average particle size of the sintered constituent particles measured by scanning and transmission electron microscope observation is about 0.1 to 0.2 μm, which enables the synthesis of translucent high-purity ultrafine particle cBN sintered bodies. It became.
[0021]
From the above experiments, high hardness having an initial particle size 50,000-60,000 atm cBN ultrafine powder 0～0.1Myuemu, pressure below 1600 ° C. or higher 1900 ° C., a dense and fine structure by sintering at a temperature We found that high-purity ultrafine particle cBN sintered bodies can be synthesized. The present invention has been made based on this finding.
[0022]
That is, the present invention intends to provide a high-hardness ultrafine particle cBN sintered body that cannot be obtained by the prior art and the prior art by adopting the configurations described in (1) to (3) below. It is.
[0023]
(1) using a cBN ultrafine particle size range 0~0.1μm as a raw material powder of ultrafine particles cBN sintered body 5-6 GPa, 1600 or 1900 ° C. under a pressure, cBN by sintering at a temperature a total of 100% of the content and unavoidable impurities, high hardness, high-purity ultrafine particle cBN sintered body having an average particle size of 0.1 ~ 0.2 μ m of the sintered body is obtained.
[0024]
(2) 50,000 atmospheres the cBN fine particles powder subjected to the cleaning treatment of the particle surface by an alkaline solution, a pressure of less than 1900 ° C. 1800 ° C. or higher, by sintering without the addition of sintering aid at a temperature , a total of 100% of the cBN content and unavoidable impurities, transparent high hardness, high-purity ultrafine particle cBN sintered body having an average particle size of 0.1 ~ 0.2 μ m of the sintered body is obtained.
[0025]
(3) If the pressure is less than 50,000 atm under the synthesis conditions (1) and (2 ) above, a good sintered body cannot be obtained regardless of the sintering temperature. Further, when the sintering temperature is lower than 1600 ° C., a strong sintered body structure cannot be obtained, and when the sintering temperature is 1900 ° C. or higher, remarkable grain growth is observed, and the strength of the sintered body decreases. For this reason, the conditions for obtaining a good sintered body are a temperature range of 1600 to less than 1900 ° C. in the range of 5 to 60,000 atmospheres, and 1800 ° C. to less than 1900 ° C. in order to obtain a translucent cBN sintered body. Become. When raw material powder having an initial particle size of 0 to 0.1 μm is used under these conditions, the average particle size of the sintered body is about 0.1 to 0.2 μm, and the Vickers hardness is about 45 GPa (test load 9.8 N). The characteristic which exceeded the characteristic of the composite sintered compact which added the conventional auxiliary agent was acquired.
[0026]
【Example】
Hereinafter, the present invention will be described based on examples and drawings.
Example 1
Commercially available particle sizes range (initial particle diameter) 0~0.1μm cBN powder was filled into a tantalum capsule high pressure vessel 5.5 GPa by a belt-type ultra high pressure generating apparatus, a pressure of 1600 ° C., 30 minutes at a temperature condition Sintered. At this time, no cBN sintering aid was added. The heating rate is about 5 ° C / min. After sintering, the pressure was reduced after cooling at about 500 ° C./min, and the sample was collected together with the tantalum capsule in the pressure vessel. The tantalum capsules were removed by mechanical or chemical treatment (hydrofluoric acid-mixed nitric acid), and the sample was collected.
[0027]
The sample was evaluated by hardness measurement, observation of the fracture surface by a scanning electron microscope (SEM) and transmission microscope (TEM), and identification of phases by X-ray diffraction after polishing with diamond abrasive grains. As shown in FIG. 1, from the X-ray diffraction pattern, the sintered body is a single phase of cBN, and has an average particle diameter of about 0.1 to 0.2 μm according to the SEM shown in FIG. 2 and the TEM observation shown in FIG. At a test load of 9.8 N, the Vickers hardness was about 45 GPa, and the obtained sintered body was shown to be a high hardness and high purity ultrafine particle cBN sintered body.
[0028]
Example 2
A commercially available cBN powder with an initial particle size of 0 to 0.1 μm was filled in a fluororesin sealed container (internal volume 100 ml) together with 2 gr of 5 mol of sodium hydroxide and held at 150 ° C. for 24 hours. After cooling this to room temperature, the alkaline solution in the fluororesin container was washed with pure water. After washing 5 times with pure water more than 100 times the initial alkaline solution, freeze drying treatment was performed on cBN ultrafine particle powder soaked in about 20 cc of pure water to obtain a raw material powder for sintering . This powder was filled into a tantalum capsule in a high-pressure vessel and subjected to the same high-pressure and high-temperature treatment as in Example 1.
[0029]
Phase identification by X-ray diffraction, structural observation of the fracture surface by SEM and TEM, and evaluation of the sintered body by Vickers hardness test on the polished surface were performed. From the X-ray diffraction pattern of the sintered body shown in FIG. 1, the sintered body is a single phase of cBN, and the average particle diameter is about 0.1 to 0.2 μm as shown in the SEM and TEM observation photographs of FIGS. It is a homogeneous structure without coarse particles due to abnormal grain growth. At a test load of 9.8 N, the Vickers hardness was about 45 GPa, and the obtained sintered body was shown to be a high hardness and high purity ultrafine particle cBN sintered body. It was also found that when the sintering temperature was 1800 ° C., the sintered body obtained under the same conditions exhibited translucency.
[0030]
Example 3
In the pretreatment of the cBN fine powder described in Example 1, anhydrous NaOH was melted in a zirconia crucible and charged with about 5 g of cBN fine particle powder while being kept at about 400 ° C. and boiled for about 3 minutes. The same cleaning treatment as in Example 2 was performed. This treatment was performed on cBN particles having an initial particle size of 0 to 0.1 μm, then washed with pure water, freeze-dried, and sintered at a high pressure of 50,000 atm and 1600 ° C. The obtained sample was a high-hardness and high-purity ultrafine particle cBN sintered body as described in Example 2.
[0031]
Comparative Example 1
In the process described in Example 1, sintered bodies were prepared using cBN particles having initial particle diameters of 0 to 0.25 μm and 0 to 1 μm as raw materials. Under the sintering conditions of 5 to 60,000 atmospheres and 1600 to 1800 ° C., the obtained sintered body has a Vickers hardness of 30 GPa (test load 9.8 N) or less, and the initial particle size 0 to 0.1 seen in Example 1 Compared to the case of μm, the strength was remarkably inferior. From the comparative example, it was clarified that the particle size of cBN is important for the high-strength ultrafine particle sintered body manufacturing method and the development of translucency.
[0032]
Comparative Example 2
In the process described in Example 1, under the sintering conditions of 45,000 atm and 1600-1800 ° C., the obtained sintered body had a Vickers hardness of 30 GPa (test load 9.8 N) or less. Further, when sintered at 1500 ° C. in the region of 50,000 to 60,000 atmospheres, the obtained sintered body had a Vickers hardness of 30 GPa (test load 9.8 N) or less. When sintered at 1900 ° C. in the same pressure region, the strength of the obtained sintered body was remarkably reduced by grain growth, and the Vickers hardness was 30 GPa (test load 9.8 N). From the comparative example, it was clarified that the optimization of the sintering temperature and pressure is important for the high-strength and light-transmitting behavior in the manufacturing method of the high purity ultrafine particle sintered body.
[0033]
In each of the examples and comparative examples, the high-purity cBN sintered body was prepared in the present invention in the region of 50,000 to 60,000 atm. Indicates that processing is important. If the raw material powder is fine, the driving force for sintering is large and sintering is likely to proceed. To achieve this effect, however, it is necessary to select an appropriate initial particle size and clean the particle surface. Preprocessing is important. In the present invention, a cBN ultrafine particle powder having an appropriate particle size is selected, and preferably subjected to an appropriate pretreatment to be cleaned, so that the sintering aid can be used in a region of 50,000 atmospheres, which is impossible with the prior art. A high hardness and high purity ultrafine particle cBN sintered body was obtained without using.
[0034]
【The invention's effect】
The present invention is valuable in that a high-purity cBN sintered body having a total content of cBN and inevitable impurities of 100% can be synthesized in the pressure and temperature range for synthesizing a normal cBN composite sintered body, and at the same time, It became possible to supply an ultrafine cBN sintered body having an average particle size of about 0.1 to 0.2 μm, which could not be obtained by the technology.
[0035]
Innovations in machining tools such as those seen in the present invention improve productivity and reduce energy consumption in the machining field, consumption of cooling water from the transition from conventional wet to dry processes, and reduction of industrial wastewater Is expected to be possible. Further, as the polishing / grinding ratio is improved, the amount of polishing waste and grinding fluid discharged is reduced as compared with the use of conventional abrasive grains. That is, the amount of waste associated with processing can be reduced, and in addition to resource saving and energy saving, a great effect such as contributing to environmental conservation can be expected.
[Brief description of the drawings]
1 is an X-ray diffraction pattern of a high-purity ultrafine particle cBN sintered body synthesized in Example 1. FIG.
FIG. 2 is a drawing-substitute scanning electron micrograph of a fracture surface of a high-purity ultrafine particle cBN sintered body synthesized in Example 1.
FIG. 3 is a transmission electron micrograph in place of a drawing of a fracture surface of a high purity ultrafine particle cBN sintered body synthesized in Example 1.

Claims (3)

Grain radial width 0~0.1μm of cubic boron nitride powder (hereinafter referred to as cBN) the cBN is thermodynamically stable 5GPa more 6GPa less, sintering at high pressure and temperature conditions of less than 1600 ° C. or higher 1900 ° C., a total of 100% of the cBN content and unavoidable impurities, producing an average particle size of you characterized by producing a sintered body of 0.1 ~ 0.2 μ m high purity ultrafine particle cBN sintered body of the sintered body mETHODS. After the cBN powder was treated with an aqueous alkaline solution or alkaline melt in producing how high purity ultrafine particle cBN sintered body according to claim 1, wherein the sintering. The cBN powder 1800 The high-purity ultrafine particles according to claim 2, wherein the sintered body has a light-transmitting property by being sintered at a temperature condition of not less than ° C. cBN A method for producing a sintered body.

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