JPH05301776A - Cubic boron nitride-based sintered compact - Google Patents

Abstract

PURPOSE:To improve the toughness and remarkably improve performance in, e.g. intermittent cutting and heavy cutting without producing a boron compound due to the use of a binder unreactive with BN. CONSTITUTION:The objective sintered compact comprises 30-85vol.% cubic boron nitride and the remainder composed of a mixture of silicon nitride with aluminum nitride, aluminum oxide and silicon oxide or compounds thereof, or 30-85vol.% cubic boron nitride and the remainder composed of a mixture of silicon nitride with aluminum nitride and a rare earth metallic oxide or compounds thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cubic boron nitride sintered body which is used, for example, in a cutting tool and has excellent hardness and toughness.

[0002]

2. Description of the Related Art Cubic Boron Nitride (hereinafter abbreviated as cBN) has the highest hardness next to diamond,
Moreover, unlike diamond, it has no affinity with iron-based metals, so it is used especially in the processing of iron-based high hardness materials.

As a cutting tool using such cBN, there are a cBN bonded with a metal such as cobalt (Co) and a cubic boron nitride sintered body bonded with a ceramic such as titanium nitride (TiN). It has been used (Japanese Patent Publication Sho 5)
2-43846 gazette etc.).

[0004]

However, in such a cubic boron nitride sintered body using Co or TiN as a binder, BN reacts with Co or TiN, and Co ₂₁ W ₂
It contains boron compounds such as B ₆ and TiB ₂ . Since this boron compound has a high hardness but is a very brittle substance, it impairs the toughness of the sintered body. Therefore, the cutting tools using the cubic boron nitride sintered material up to now cannot obtain satisfactory performance, especially for applications requiring toughness such as intermittent cutting and heavy cutting. It was

[0005]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies to improve the toughness of a cubic boron nitride sintered body, and as a result,
The inventors have found that when a specific binder is selected so that a brittle boron compound is not formed as a reaction product phase of BN and the binder, the toughness is significantly improved, and the present invention has been completed.

That is, the cubic boron nitride sintered body of the present invention contains 30 to 85% by volume of cubic boron nitride, and the balance is a mixture or compound of silicon nitride, aluminum nitride, aluminum oxide and silicon oxide. It is a thing. In this case, it is desirable that the remaining compound is mainly composed of a sialon crystal containing Si, Al, O and N.

Further, cubic boron nitride is added in an amount of 30 to 85% by volume.
It is contained and the balance consists of a mixture or compound of silicon nitride, aluminum nitride and a rare earth metal oxide. At this time, it is preferable that the remaining compound is mainly composed of a sialon crystal containing Si, Al, O, N and a rare earth metal element, or mainly composed of this and a silicon nitride crystal. In this case, α sialon is produced.

The cubic boron nitride is contained in an amount of 30 to 85% by volume because the content of cBN in the sintered body must be 30% by volume or more in order to utilize the original characteristics of cBN. %, The hardness of the sintered body decreases,
This is because the abrasion resistance is impaired. On the other hand, if it exceeds 85% by volume, the hardness is high, but the toughness is lowered, and it becomes unusable for practical use.

The remaining portion of the cubic boron nitride is silicon nitride,
The reason why it is composed of a mixture or compound of aluminum nitride, aluminum oxide and silicon oxide is that they do not react with BN and do not form a brittle boron compound. The compound constituting the balance is Si
_6-x Al _x O _x N _8-x (0 <X ≦ 4.2) or Si _6-
x Al _{x + Y} O _x N _{8-x + Y} (0 <X <6, 2 ≦ Y ≦ 12)
It is desirable to be the subject.

In the case where the balance consists mainly of Si _6-x Al _x O _x N _8-x , the X value is 0 <X≤4.2.
The reason for limiting the X value to the above range is that all of them are particularly excellent in hardness and toughness. Also,
When the balance is mainly composed of Si _6-x Al _{x + Y} O _x N _{8-x + Y} , the X value and the Y value are 0 <X ≦ 6, 2 ≦ Y ≦ 12.
The reason for limiting the X value and the Y value to the above ranges is that they are particularly excellent in hardness and toughness.

Further, since the balance is composed of silicon nitride, aluminum nitride and rare earth metal oxide, these also do not produce a boron compound, and the binder phase itself is high because it contains a rare earth metal in particular. This is because the strength of the sintered body is high and the heat resistance is excellent, so that the characteristics of the entire sintered body can be improved. The remaining compound in the present invention is M _x (Si, Al) ₁₂ (O, N) ₁₆ (provided that M _x
Is preferably a rare earth metal element, 0 <X ≦ 2) as a main component, or a substance mainly containing this and silicon nitride. Here, 0 <X ≦ 2 is set because the hardness and toughness are particularly excellent in this range. The rare earth metals used in the present invention include Sc, Y, La, Ce, Pr and N.
d, Sm, Gd, Tb, Dy, Ho, Er, Yb, etc.

The cubic boron nitride sintered body of the present invention is characterized in that no metal powder is added. That is, conventionally, cB
When sintering N, it is widely practiced to add a metal element such as Al as an auxiliary agent, but the addition of such a metal element is unnecessary in the present invention. Rather, Al
When a metal element such as Si is added as an auxiliary agent, Si is added from the binder phase.
Is deposited, resulting in deterioration of the properties of the sintered body, that is, toughness, strength and the like. Therefore, according to the cubic boron nitride sintered body of the present invention, it is also a great feature that metals such as Al and Si are substantially absent.

As the method for producing the cubic boron nitride sintered body of the present invention, the raw material powder is cBN powder, and other desired Si ₃ N ₄ , AlN, Al ₂ O ₃ , SiO ₂ , Li.
₂ O, CaO, Y ₂ O ₃ , rare earth element oxides, etc. are prepared, weighed to the specific composition described above, and mixed sufficiently. Then, the mixed powder is molded into a predetermined shape. As the molding means, known molding means such as press molding, injection molding, casting molding, extrusion molding can be used.

Next, the above-mentioned compact is sintered using a high temperature and high pressure generator at high temperature and high pressure as disclosed in, for example, Japanese Patent Publication No. 39-8948. That is, the cubic boron nitride sintered material of the present invention is obtained by holding at a pressure of 3.5 to 6 GPa and a temperature of 1300 to 1800 ° C. for 15 to 120 minutes.

[0015]

In the cubic boron nitride sintered body of the present invention, since a binder that does not react with BN is used, no boron compound is generated, which improves the toughness of the sintered body. When used as a cutting tool, the performance in intermittent cutting and heavy cutting can be greatly improved. Furthermore, since silicon nitride, aluminum nitride, and a rare earth metal oxide are used as the binder phase, the toughness is improved without forming a boron compound, and the binder phase itself has high strength, high hardness, and excellent heat resistance. Further, it is possible to obtain a sintered body having further excellent characteristics, and it is possible to significantly improve the performance during cutting as compared with the conventional case.

[0016]

【Example】

Example 1 As a raw material powder, cBN (average crystal grain size 2 to 4 μm),
And Si ₃ N ₄ , Al ₂ O ₃ , AlN, and SiO ₂ powders, which are weighed and mixed at a ratio shown in Table 1 to form a predetermined shape, and thereafter, an ultrahigh pressure and high temperature generator is used to 1
The pressure and temperature shown in (1) were maintained for a predetermined period of time and baked.

[0017]

[Table 1]

Then, the cubic boron nitride sintered body was taken out, mirror-polished, and microscopically observed by SEM (scanning electron microscope). As a result, a dense structure without pores was shown.

The fracture toughness of the obtained sintered body was measured by the indentation method with a Vickers hardness and a Vickers hardness diamond indenter at a load of 20 kg. further,
The crystal phase was examined by the X-ray diffraction method.

Then, a dry interrupted cutting test was performed on each sample under the following cutting conditions.

(Intermittent cutting test) Work material SKD11 (H _RC 60.5 mm width, with 4 grooves) Cutting speed 100 m / min Cutting depth 0.2 mm Feed 0.1 mm / rev Cutting time 5 min The above experimental results are shown in Table 2 Shown in.

[0022]

[Table 2]

In Table 2, the cutting test results are
When there was no defect even after intermittent cutting for 5 minutes, it was evaluated as ◯, and when it was damaged, it was evaluated as x.

According to Tables 1 and 2, the cubic boron nitride sintered body of the present invention has a hardness of 2300 or more and a toughness of 6.4.
It was at least MPa · m ^1/2 . In addition, there was no loss even after intermittent cutting for 5 minutes. On the other hand, in the samples No. 9 and 9, the boron compound was generated, the hardness and toughness were low, and defects were generated. The crystal phase of sample No. 8 could not be identified.

Example 2 As raw material powder, cBN (average crystal grain size 2 to 4 μm),
And _{Si 3 N 4, Al 2 O} 3, AlN, and SiO ₂ powder, the powder containing _{Er 2 O 3, Yb 2 O} 3, Y 2 O 3 were weighed in a ratio shown in Table 3, these predetermined After forming into a shape, using an ultrahigh pressure and high temperature generator, the pressure shown in Table 3
The temperature was maintained for a predetermined period of time and the firing was performed.

[0026]

[Table 3]

Then, the cubic boron nitride sintered body was taken out and subjected to mirror finishing, and the structure was observed in the same manner as in Example 1. As a result, a dense structure without pores was shown.

In addition, for the obtained sintered body, Example 1
Similarly to, the Vickers hardness and the fracture toughness were measured and the crystal phase was examined.

Then, a dry interrupted cutting test was performed on each sample under the following cutting conditions.

(Intermittent cutting test) Work material SKD11 (H _RC 60.5 mm width, with 4 grooves) Cutting speed 100 m / min Cutting depth 0.2 mm Feed 0.1 mm / rev Cutting time 5 min The above results are shown in Table 4. Show.

[0031]

[Table 4]

From Tables 3 and 4, the cubic boron nitride sintered body of the present invention has a hardness of 2350 or more and a toughness of 6.9.
That was all. On the other hand, Sample No. 15 was not broken in the cutting test, but could not be cut in 1 minute due to abrasion. Further, Samples No. 18 and 18 had a boron compound, which had low hardness and toughness, and had a defect. The crystal phase of sample No. 17 could not be identified.

[0033]

As described in detail above, according to the present invention, since the binder does not react with BN and has high hardness and high toughness, the performance in, for example, interrupted cutting and heavy cutting is significantly improved. can do. Further, by further using a rare earth metal oxide as one component in the binder, it is possible to improve the strength and hardness and heat resistance of the binder, thereby significantly improving the performance during cutting as compared with the conventional case. be able to.

Claims (4)

[Claims] 1. A cubic boron nitride calcined material containing 30 to 85% by volume of cubic boron nitride, and the balance consisting of a mixture of silicon nitride, aluminum nitride, aluminum oxide, silicon oxide or a compound thereof. Union. 2. The cubic boron nitride sintered body according to claim 1, wherein the remaining compound is mainly composed of a sialon crystal containing Si, Al, O, and N. 3. A cubic boron nitride sintered body containing 30 to 85% by volume of cubic boron nitride, and the balance being a mixture or compound of silicon nitride, aluminum nitride and a rare earth metal oxide. .. 4. The cubic boron nitride sintered body according to claim 3, wherein the remaining compound is mainly composed of a sialon crystal containing Si, Al, O, N and a rare earth metal element.