JPH01270570A - Production of cubic boron nitride sintered compact - Google Patents

Abstract

PURPOSE:To prevent reverse rearrangement of cubic BN to hexagonal BN powder and improve high-temperature stability and thermal conductivity by sintering a cubic BN powder containing Si and B in specific conditions. CONSTITUTION:<=5wt.% Si and 0.01-1.0wt.% B are added to hexagonal BN and the blend is heated at 1300-1600 deg.C under 40-60kb pressure in the presence of a catalyst expressed by the formula LiMBN2 (M is alkaline earth metal) and then unreacted hexagonal BN and catalyst, etc., are separated and pulverized to provide a cubic BN powder containing Si and B having <=30mum particle size, which is then sintered under >=50kb pressure at >=1600 deg.C.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing a strong sintered body by hot-pressing cubic boron nitride (hereinafter referred to as cBN) powder using a high-temperature, high-pressure device. It is.

(Prior Art) cBN is used as cutting tools and grinding tools for iron-based alloys, and its production volume is increasing year by year. In order to use cBN as a tool, cBN particles are often hardened with a binder, but there are problems such as a decrease in hardness due to the binder.The general method for sintering cBN without a binder is as follows. For example, °old gh-pressure sinter
ingof cBN',YitlSheB ct at
: Eur, Symp, PowdMetall,
5th [3] '78 p201-211, the higher the pressure, the higher the performance of the sintered body, and the temperature should be within the appropriate temperature and pressure range within which the cBN phase is stable, for example, 77 kb. In this case, the temperature is 1830℃.

However, these conditions are harsher than the cBN synthesis conditions of 50kb and around 1500℃, and sintering under these conditions requires synthesis equipment that is currently operated at a pressure of about 50kb. often requires separate sintering equipment.

Another method is a sintering method using a catalyst as disclosed in Japanese Patent Publication No. 59-5547.

Still another method is to use additives such as TiN and Afi that react with cBN particles or have good wettability with c[lN, and sinter at around 1500°C for 50kb or more. . This method is the main IX of the sintering densification reaction! Plastic deformation of lPA c[IN particles does not occur sufficiently. Therefore, to compensate for insufficient sintering, 10 volumes of additives are usually added. (It is necessary to use 2 and 10) (Konaru 3,
As a result, the hardness of sintering (I) decreases to less than 60% of that of the crystal ('c [!N sintering], Ike Ueda, Abstracts of the 25th High Pressure Conference, 86th hundred 84th
Reference) Regarding 6cBN, described in JP-A-62-197357 as belonging to the sintering technology without a binder in 1.
[There is a sintering method that uses IN (boron, also known as IN). Pressure 5 exemplified in this method
0 kb, temperature 1500' (achieved sintered strip 1'1 relaxation) index.

Korote, E, Rapoport (ANCPA (015
] 91071ANN, C1l1M (PaC11l I
O[7], 607 ('85) is a recent hll
The equilibrium line of N(6)1 crystal nitride (J ion) H'cBH is given by p=o, o3TI0.3fP:kb, T:K), and furthermore, P・0.0235T-0 ,3
It is said that there is a possibility of a shift to Takanohin. Therefore, there is a margin of several kb regarding the stability of cBN as exemplified in JP-A-62-197357-15001. It cannot be said that sufficient stability has been achieved in the remaining valleys.
pHAAbl Noj, 7 (1986) T? As mentioned in
A pressure margin of is not considered to provide sufficient stability.

On the other hand, A, 11. Ma3ypcl+ko(lji
According to (1 bid, No, 5.12°84), h
It is said that it is possible to shift the BNHcBN equilibrium line to a high temperature of several hundred degrees by adding nitrogen to the cBN single crystal.

In general, σ) additives to the sintered body, in addition to the above-mentioned action of easing the sintering conditions and significantly reducing the hardness, also increase the bonding strength of cBN grains. If this bonding force is sufficient, the toughness of the sintered compact σ) becomes single crystal, and the toughness increases by L. In this case, the toughness of one standing dead is c [lN particles are equal to Gai (J and high,
Therefore, if a sufficiently large sintered JJ (4) is manufactured using fine CON without additives, the hardness will be close to that of the TJI crystal, and the toughness will be 31 mm as a single crystal, providing a cQN sintered body. I can do two things.

If sintering without additives is attempted, c[l
There is some research that focuses on the plastic deformation of CBN particles when the N particles are sintered densely ([ Effects of sintering conditions on the properties of polycrystalline c [ltJ, [1, c, i++n+uoj, l0PIII
K., METAjAl, 1986. No, 1. p
71-75 (1986)). The pressure is limited by the capacity of the press equipment, but the temperature can be increased relatively easily by improving insulation techniques, so the temperature is not a constraint on the production of c[IN sintered bodies, but Pressure is a constraint.

This document states that the temperature condition 1!1 for obtaining a sintered body in which properties such as density and hardness are saturated is 2800~2800 at a pressure of 80 kb.
It states that it is 3000K.

(Problem to be Solved by the Invention) The above-mentioned pressure condition 1゛ (-80 kb corresponds to sintering conditions that are too high for industrially carrying out the sintering of c[IN).

When the sintering pressure of cBll is set to a relatively low pressure, the pressure becomes c[
There is a possibility that it will be one level below the IN stability limit. The currently elucidated cBNMH[ltJ (hexagonal nitrogen [hyboron)] equilibrium line P=0.03T lOj (fil-L,
If P is pressure (kb) and 'r is temperature (in), and P = 50 kb, then T = 2010, and at the temperature specified in Note 2170, it falls into the hBN stability region.

Therefore, the present inventor conducted research with the aim of providing a method for sintering c[IN] at a relatively low pressure.

Although the method using only boron-rich eDN does not have any negative effects due to components other than B and N acting as impurities, it is difficult to reliably prevent conversion to hllN due to the sintering driving force generated by defects. be. Therefore, the present inventors utilized the sintering driving force due to defects in boron-rich cBN, and
We studied a method of achieving high-temperature stability in the same c[lN particle by adding i-1 diluted metal as taught by Ukoike.

As a result, the c
[It has been found that synthesizing IN and performing sintering using its powder as a raw material is advantageous for prosthesis, and the properties of the sintered body are also similar to clay.

(Means to solve the problem) Impact of Si on the production process and physical properties of rcBN polycrystals 9
”, A, M, 11a3ypcnko et al. I C1lE
PXC11EPXTBEPjblEAnb1. NO5,
12C84), cBN can be obtained by adding Sl.
It states that the stability region is increased by approximately 500°C. Also, A, M, Ma3ype++kolt! ! The paper states that when 15% or less silicon is added to directly convert hBN to cBN to obtain c[IN polycrystals, the conversion is accelerated by the addition of silicon.

When applied to the cBN sintering process, adding less than 1% of silicon fine powder classified to 1 μm or less to the raw material cBN powder and pot pressing at approximately 50 kb at 2000°C, there was no reversal to hBN. However, metal Si was precipitated and interfered with the sintering of the c[IN particles, making it impossible to obtain a satisfactory sintered body.

This means that the sintering inhibiting effect of silicon must be removed while utilizing the anti-reversal effect of silicon on hBN. This was achieved by dissolving silicon throughout the cBN particles and using cBN powder as a raw material from which excess silicon that did not dissolve in the solid solution was removed.Based on this knowledge, the present inventor filed a patent application filed in 2
The boron-rich c[
We proposed a method in which cBN containing Si or silicon nitride (hereinafter collectively referred to as 5i-cBN) is added to IN to perform sintering.

In this sintering method, it is thought that in a raw material in which boron ridge c[IN and 5i-cBN are mixed as separate particles, each effect appears independently but simultaneously in parallel during sintering. According to subsequent research, excess boron and Si coexisting in the same cBN particle did not cancel each other's effects;
In N, it was found that excess boron imparts easy sinterability to 1ζ, and Si contained in the crystal provides high temperature stability.

Based on this knowledge, by crushing and classifying cubic boron nitride containing 81 B in advance and using the obtained powder as a sintering raw material, the
It has now become possible to produce a c[IN sintered body with a strip 1' which is below the reverse transition temperature of J1cBN at 0°C or higher, which was previously insufficient for sintering.

c [Means for obtaining raw materials for IN sintered bodies are disclosed in JP-A-59-199513 and JP-A-59= by the present applicant.
This is possible by combining 199514. In other words, 5% by weight of hexagonal boron nitride (hereinafter referred to as 118N)
Add the following B and 0.01 to 1.0% by weight of metal Si or compound Si (in terms of Si weight if compound is added) and add L + M [1N2 (However, 1 is a high temperature (1300 ~1600℃), high pressure (40~60℃)
kb), and then by removing unreacted hBN, catalyst, etc. from this cBN by means such as specific gravity separation, a raw material for a cBN sintered body can be obtained.

If necessary, this raw material is preferably reduced to less than 30 μI.
Further pulverize. In this synthesis method, 5% or more of B
Even if -1Si is added in an amount exceeding 1%, it is meaningless as it will be removed in the refining step, and if both amounts are less than 0.01%, there will be no effect on sintering. 50kb or more of the above raw materials 2,1600
It is possible to obtain a strong sintered body by sintering at a temperature of ℃ or higher.

(Function) It is thought that Si, together with excess B, contributes to the formation of N defects. On the other hand, silicon preliminarily dissolved in boron-rich cQN has a solid solubility limit of 1000 to 1500 ppI1.
1, and the lattice constant of high purity c[IN is a.

- Increase compared to 3,616 people.

Solid solute increases the high temperature stability of cBN, thereby c
[The lN particles are plastically deformed, conditions are established, and cBN can be sintered without additives even under relatively low pressure conditions, which were conventionally unsuitable for sintering. On the other hand, the excess Si that is not in solid solution is h
c from BN [although not harmful to IN synthesis, c
Since silicon is harmful to the sintering of BN, it is necessary to exist in the form of solid solution or ultrafine particulate inclusions.

Part or all of B, which is present in excess of the QN composition in cBN as a sintering raw material, causes N defects in the crystal lattice, and as a result, when pressed into Hono 1, it promotes plastic deformation of the c[IN crystal. , it is estimated that one high-density sintered piece will be produced.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

<Example) Example 1 Boron 0.05 tw/l)%, silicon 0005% based on hllN.

A green compact of a powder mixture to which LiCa[1lt710% (all powder particle sizes are 325, under mesh) as a catalyst was held at a pressure of 50 kb and an altitude of 1450°C for 10 minutes to synthesize ctlN, and then conduct specific gravity separation. unreacted by h
BN etc. were separated and purified. The obtained cBN was analyzed by plasma excitation emission spectrometry to determine B and Si.
They were 436% (theoretical 436% for 1st shift) and 5 PPM. This cBN is crushed and the part with a particle size of 20μ or less is 60k
b. Pot pressing was carried out for 30 minutes at 1700°C, and the density of the obtained sintered body was measured by the school method. In addition, the density of the sintered body in which hBN was detected by the X-ray diffraction method is shown in Table 1 along with other σ) Examples and Comparative Examples.

Example 2 In Example 1, the c[IN obtained by synthesizing the c[IN synthesis raw material h[l11] with 45% boron and 09% (double element) without changing other conditions. The analysis showed that ll-
46.0%.

It became 5i-600PI'll. Similarly to the previous example, c
This sintered body of BN was obtained. hBN cannot be detected from the sintered body.

Comparative Example 1 The same treatment as in Example 1 was performed except that the addition of boron to h(IN) was omitted.

Comparative Example 2 The same treatment as in Example 1 was performed for a pond in which the addition of lithium to hBN was omitted.

(The following is a blank space) Table 1 <Effects of the invention> As shown in the examples, according to the present invention, extremely high-density c
hB of cBI+, which can be obtained by pressing [IN sintered body or low-temperature water/), and which may already be formed at a relatively low temperature of 1700°C (pot press temperature in the example)
Countertransference to N is prevented.

Furthermore, since silicon hardly exists as a grain boundary substance or alone, the thermal conductivity of the present sintered body is comparable to that of a single crystal, and it can be applied to heat dissipation substrates and the like.

Claims (1)

[Claims] 1. A method for producing a cubic boron nitride sintered body, comprising sintering cubic boron nitride powder containing Si and B under conditions of a pressure of 50 kb or more and a temperature of about 1600° C. or more.