JP2003192441A - Boride sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a boride sintered compact which is sintered by using a binder, is provided with wear resistance required, e.g. for cutting heat-treated steel, and can reduce the working cost of steel or the like. <P>SOLUTION: The boride sintered compact contains Al, one element M selected from the groups Ia and IIa in the Periodic Table, and borides consisting of boron. The boride sintered compact has a composition consisting of 50 to 75 vol.% borides expressed by AlX<SB>1</SB>M<SB>y</SB><SB>1</SB>BZ<SB>12</SB>, and the balance bonding phase with inevitable impurities. The bonding phase consists of at least one kind selected from the carbides, nitrides, carbonitrides and borides of the group IVa, Va and VIa metals or a compound of their solid solutions. The borides expressed by AlX<SB>1</SB>M<SB>y</SB><SB>1</SB>BZ<SB>12</SB>are mutually joined via the above bonding phase in the structure of the sintered compact. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a boride sintered body suitable for wear resistant materials and cutting tools. In particular, it relates to a high-hardness boride sintered body that is most suitable for machining and wear-resisting tools and cutting tools for steel and cast iron.

[0002]

_2. Description of the Related Art Ceramic tools made of Al ₂ O ₃ and Si ₃ N ₄ used for cutting tools have a high hardness of Hv 1600 to 2400 and show good wear resistance when cutting iron-based materials, but have a toughness. poor. Therefore, although it is used for cutting cast iron with good machinability, in cutting steel, a sufficient life cannot be obtained due to a decrease in fracture resistance.

Cemented carbide tools have a sintered body hardness of
Hv1500 to 2000, which is lower than that of ceramics, and further contains metallic Co. Therefore, when cutting steel hardened to a hardness of about HRc40 by heat treatment, wear resistance and fracture resistance are poor and sufficient tool life cannot be obtained.

On the other hand, there is a cBN sintered body as a high-hardness cutting tool, and it is known to show high performance in cutting hardened steel hardened to a hardness of HRc50 or higher by quenching. In addition, cBN sintered bodies have a life equivalent to or longer than that of ceramic tools and cemented carbide tools, even when cutting general heat-treated steel with HRc 30 to 50. However, because cBN, which is synthesized under ultra-high pressure using an ultra-high-pressure high-temperature generator with high manufacturing cost, is used as the raw material, and because it is sintered under ultra-high pressure, the tool unit price is high and the processing cost is high. Not commonly used.

On the other hand, the Journal of H. Werheit et al.
Alloys and Compounds, 202 (1993) 269-281, Al
As a ternary boride containing, the hardness of a single crystal of AlLiB ₁₄ is Hv29.
It is shown that the hardness of the single crystal of 50 and AlMgB ₁₄ is as high as Hv2790. This paper discloses a method of dissolving magnesium and boron in a large amount of aluminum melt to precipitate crystals.

The technique described in USP6099605 is known as another conventional technique. This publication discloses that Al, Mg, and B element powders are blended in a stoichiometric composition, and after being refined by a mechanical alloying method, 30% by weight of TiB ₂ is added and sintered by hot pressing. It shows that a high hardness sintered body of Hv3800-4600 can be obtained.

[0007]

[Problems to be Solved by the Invention]
The technology disclosed in USP has the following problems. The technique of the above-mentioned paper has a problem that it is not possible to obtain a dense sintered body containing a small amount of impurities. The technique of this paper is
AlMgB ₁₄ particles of several tens of μm or more can be generated. More specifically, the minimum particle size is 50 μm and the maximum reaches 2 mm. However, AlMgB ₁₄ is difficult to sinter, and a dense sintered body cannot be obtained from such coarse particles.

Further, if such coarse particles are made fine and a high pressure and high temperature apparatus is used, a dense sintered body can be obtained. However, it takes a long time to reduce the size of coarse particles, and it is difficult to control the composition because impurities such as 3% by weight or more are mixed in from the grinding container or the grinding medium (balls). Furthermore, since the sintered body thus obtained has low toughness,
A steel material having a hardness of HRc40 or more does not have sufficient performance due to chipping even after continuous cutting.

On the other hand, the technique described in USP6099605 has a problem in that it is impossible to obtain a sintered body having sufficient hardness and toughness due to the inclusion of impurities. With steel crushing balls
Since mechanical alloying is performed with a high energy type pulverizer containing raw material powders of Al, Mg and B, it is unavoidable that impurities are mixed in the pulverization ball and the container material. for that reason,
It has been confirmed that iron reacts with the raw material boron to produce FeB _{49, which} is mixed therein. Since such a boride of iron is a brittle material and has a high reactivity with steel materials, when using this sintered body as a cutting tool, both the wear resistance and fracture resistance of the cutting edge are reduced. There is.

In mechanical alloying, an oxidative reaction is likely to occur, and there is a risk of explosion due to a rapid oxidative reaction. Therefore, a mixed raw material containing a group Ia or IIa metal such as Li or Na is miniaturized into a sintered body. Is virtually impossible to obtain.

Therefore, the main object of the present invention is to obtain a boride sintered by using a binder, which has the wear resistance required for cutting of heat-treated steel and can reduce the processing cost of steel and the like. To provide a union.

[0012]

The present invention achieves the above object by defining the composition of the binder and the particle size of the raw material.

That is, the boride sintered body of the present invention is made of Al
And an element M selected from the groups Ia and IIa of the periodic table
And a boride sintered body containing a boride composed of boron.
The boride sintered body is composed of 50 to 75% by volume of boride having a composition of Al _{X ≤ 1} M _{y ≤ 1} B _{Z ≥ 12} , and the balance is a binder phase and inevitable impurities. The binder phase is composed of at least one selected from carbides, nitrides, carbonitrides and borides of Group IVa, Va and VIa metals, or a solid solution compound thereof. The boride represented by Al _{X ≤ 1} M _{y ≤ 1} B _{Z ≥ 12} is bonded to each other through the binder phase in the structure of the sintered body.

Conventionally, a sintered body containing a boride having a composition represented by Al _{X ≤ 1} M _{y ≤ 1} B _{Z ≥ 12} has Al _{X ≤ 1} excluding inevitable impurities.
Sintered body consisting only of M _{y ≤ 1} B _{Z ≥ 12} or 30% by weight
%, It is possible to obtain high hardness with a sintered body containing an additive, but sufficient strength cannot be obtained. For example, in the technique described in USP6099605, since crushing is performed by mechanical alloying so as to completely destroy the crystal structure of each raw material powder, a crushing container
This is because impurities causing embrittlement are mixed from the medium.
Also, after mechanical alloying, 30% by weight of TiB ₂ is blended to form a high hardness sintered body, but TiB ₂ is as small as 17% in volume%, and Al _{X ≤ 1} M _{y ≤ 1 which is} hard to sinter. This is because the B _{Z ≧ 12} boride particles contact each other and a sufficient bond strength cannot be obtained.

In the present invention, the content of ternary boride is 50 to 75.
By making the volume% and the remaining 25 to 50% by volume the binder, the ternary borides are strongly bonded through the binder phase. In particular, a fine ternary boride powder whose crystal structure is not broken is used as a raw material to improve the difficulty of sintering. As a result, a sintered body having high hardness and fracture resistance suitable for a cutting tool can be obtained.

The sintered body of the present invention comprises 50 to 75% by volume of a ternary boride represented by Al _{X ≤1} M _{y ≤1} B _Z ≥12, the balance being a binder phase and unavoidable impurities. More specific ternary boride compositions include AlMgB ₁₄ and AlLiB ₁₄ . For AlMgB ₁₄ , the more accurate structure is Al _{0.7 5} Mg _0.78 B ₁₄ .

The binder phase is composed of one or a mixture of carbides, nitrides, carbonitrides and borides of Group IVa, Va and VIa metals, or a solid solution compound. More specifically, a material containing at least one of Ti, Zr carbides, nitrides, carbonitrides, and borides is preferable.

[0018] inevitable impurities, in general, a system containing a AlMgB _14, oxides of Al and Mg, an oxide of MgAl ₂ 0 ₄ and binding phase metal elements seen. In the system containing AlLiB ₁₄ , oxides of Al and Li, AlLiO ₂ and oxides of binder phase metal elements are found.

The maximum grain size of the ternary boride constituting the sintered body is
It is preferably 5 μm or less. By constructing a sintered body from such a fine ternary boride, a sintered body having a strength required to obtain wear resistance and chipping resistance in cutting steel can be obtained.
The more preferable maximum particle size of the ternary boride is 2 μm or less.
Also, the hardness of the sintered body that is preferable as a cutting tool is Hv25 GPa.
That is all.

In the above boride sintered body, boride particles having a maximum particle size of 5 μm or less are pressure: 150 MPa or more and 10 GPa or less, temperature: 1
It is obtained by sintering at 000 ° C or higher and 1500 ° C or lower. The more preferable maximum particle diameter of the boride particles is 3 μm or less.

By using fine boride particles, a dense and high-hardness sintered body can be obtained. Such a boride particle can be made into a state in which the crystal structure is not destroyed as much as possible and the amount of impurities is small by not crushing or crushing for a short time. More preferable range of sintering pressure is 1 GPa or more
It is 5 GPa or less, more preferably 1 GPa or more and 3 GPa or less.
A more preferable range of the sintering temperature is 1200 to 1400 ° C. The sintering holding time is preferably about 15 to 60 minutes.

The fine boride particles used as the raw material powder for the sintered body are obtained by a method of obtaining fine boride particles from the beginning without crushing, and by first obtaining coarse particles and then pulverizing them to obtain fine particles. There are two ways.

The method without pulverization is as follows: boron: maximum particle size 3
75-91 atomic% below μm, Al: 4-21 atomic%, Periodic Table Ia
And a raw material having a composition of one element M selected from the group IIa: 3 to 6 atom% in a gas atmosphere of an inert gas other than nitrogen at a temperature of 1300 ° C. or lower.

By using boron having a maximum particle size of 3 μm or less as a raw material, the maximum particle size of the obtained boride particles can be suppressed to 5 μm or less. More preferably, the maximum particle size is 1 μm or less using boron as a raw material, and the maximum particle size of the obtained boride particles is 3
It should be less than μm.

Conventionally, AlMgB ₁₄ contains a large amount of Al for crystal growth. For example, the content of Al is about 80 to 91 atomic%. In the present invention, the content of Al is reduced as much as possible, and a composition is selected so that fine boride particles can be obtained. Al is
If it exceeds 21 atomic%, crystal grain growth occurs, and coarse boride grains tend to be formed.

Table 1 shows a composition example of AlMgB _{14 in} which fine particles of boride particles were obtained by the above method while changing the Al content. Composition No. 1 in Table 1 is a stoichiometric composition of AlMgB ₁₄ , and fine boride particles were obtained, but some oxides were also observed. In No. 2, the obtained particles were fine particles, and the amount of oxide was very small, which was preferable AlMgB ₁₄ . Furthermore, even with No.3, fine AlMgB ₁₄ could be synthesized.
The grain size is coarser than that of o.2, and the amount of Al that can produce preferable fine particles is considered to be 21 atom%.

[0027]

[Table 1]

The atmosphere for the heat treatment is an inert gas atmosphere. However, nitrogen is excluded. Usually, it is preferable to use argon.

The heat treatment temperature is theoretically the melting point of Al (660.
4 ° C) or higher to 1300 ° C or lower. 130
Synthesis at a temperature higher than 0 ° C. is not preferable because AlB ₁₂ is also synthesized at the same time. Optimal synthesis temperature is 1200-13
It is around 00 ℃, especially around 1200 ℃. The holding time is preferably about 30 to 90 minutes.

According to this method, fine boride particles can be obtained without crushing, and it is possible to avoid a decrease in the content of boride when impurities are mixed during grinding to form a sintered body. it can.

Next, the method of pulverization is as follows. First, boron: 75 to 91 atomic% with a maximum particle size of 40 μm or less, Al: 4 to 21 atomic%, one element M selected from groups Ia and IIa of the periodic table: A raw material having a composition of 3 to 6 atomic% is heat-treated at a temperature of 1300 ° C. or lower in an inert gas atmosphere other than nitrogen, and the maximum particle size is 50
Boride particles having an average particle size of 15 μm or less are obtained. Subsequently, the boride particles having a maximum particle size of 50 μm or less are crushed to obtain boride particles having a maximum particle size of 5 μm or less.

The composition of the raw materials, the atmosphere in the heat treatment, and the temperature are the same as in the case of the method without pulverization. Here, since the grain size of boron as the raw material is coarse, the synthesized grain size of boride is also large, but the maximum grain size is 50 μm or less and the average grain size is 1
When the particle size is 5 μm or less, the maximum particle size can be reduced to 5 μm or less in a short time even if the crushing process is used. If the crushing time is short, the boride powder can be obtained with almost no impurities mixed therein. Then, by using the boride particles containing few impurities, the sinterability is also improved, and a dense sintered body can be obtained.

The crushing is preferably carried out under the condition that impurities are not mixed in as much as possible. Examples of crushing conditions using a ball mill include balls: made of alumina, diameter 3 to 6 m
m, crushing time: 4 to 10 hours. It is preferable to carry out the pulverization in a short time as much as possible.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. (Example 1) Purity 99.9%, maximum particle size 3μm or less amorphous boron powder, purity 99.9%, maximum particle size 40μm or less aluminum powder, purity 99.9%, maximum particle size 180μm or less magnesium powder 85 atomic% , 10 atom% and 5 atom% were mixed and mixed. Place this mixed powder in a high-purity alumina crucible, set it in a high-temperature atmosphere heating furnace, and hold it at 1200 ° C for 1 hour in a high-purity argon gas atmosphere of 99.99% or more. 2 μm of AlMgB ₁₄ powder was obtained. Further, similarly to the above 99.9% purity, by a less amorphous boron powder maximum particle size of 1 [mu] m, 2 [mu] m in maximum particle size, to obtain a AlMgB _{1 4} powder 0.7μm in average particle size.

Using each of the above particles, the set shown in Table 2 was used.
TiN particles having a maximum particle size of 3 μm or less were mixed. these
The mixed powder of
Ball mill made by filling with balls made of Na and ethanol
And mixed homogeneously. 1 x 10 of this mixed powder⁻³Pa vacuum
Medium, dried at 600 ℃, then pressed into pellets
did. Place this compact in a Mo container, and
Using a temperature device, hold at a pressure of 2GPa and temperature of 1350 ℃ for 30 minutes.
To obtain a sintered body. X-ray diffraction measurement results of the obtained sintered body and
Table 2 also shows the measurement results of Vickers hardness. X-ray diffraction measurement
As a result, in all the sintered bodies, AlMgB₁₄And TiN, TiB₂But
Was observed. Other than these substances, MgA1 ₂0_FourAnd A1₂0₃of
In some sintered bodies, a peak was observed.

Next, when the structures of these sintered bodies were observed with a scanning electron microscope, it was found that the fine AlMgB ₁₄ particles were bonded to each other via a binder phase.

As a comparative example, a sintered body containing no binder by the above method (Comparative Example 1-7), and TiN was used as a binder.
Sintered bodies containing 10% by volume and 20% by volume (Comparative Examples 1-8 and 1-9) were produced. Table 2 also shows the results of the X-ray diffraction measurement and the hardness measurement. In addition, when the structure was observed with a scanning electron microscope, AlMgB ₁₄ was in many places in contact with each other even when the binder was included, and most of the binder was present at the triple points between the particles.

A chip for cutting was produced using the above sintered body as a cutting edge. Heat-treated carbon steel SCM435 (HRc30) round bar (φ150 × 300m) using these cutting chips
Perimeter cutting of m) was performed for 20 minutes. Cutting condition is V = 300m / mi
n, d = 0.5mm, f = 0.2mm / rev, dry type. Table 2 shows the results of the flank wear amount of the present invention example and the comparative example after cutting for 20 minutes.

[0039]

[Table 2]

As is clear from Table 2, all of the examples of the present invention have a hardness of 25 GPa or more and a small flank wear amount, and it is understood that they are sintered bodies having excellent hardness.

Example 2 AlMgB ₁₄ having a maximum particle size of 2 μm or less
Particles and binder particles having a maximum particle size of 3 μm or less were blended in the composition shown in Table 3. High-pressure high-temperature sintering was performed on these mixed powders in the same manner as in Example 1 to obtain a sintered body. X of the obtained sintered body
Table 3 shows the line diffraction measurement results and the Vickers hardness measurement results. In all the sintered bodies, a binder compounded with AlMgB ₁₄ and a boride of a metal element forming the binder were observed. In addition to the above substances, peaks of MgA1 ₂ O ₄ and A1 ₂ O ₃ were observed.

As a comparative example, as shown in Table 3, a sintered body having a compounding ratio of the binder of 50% by volume or more (Comparative Example 2-9) and 10-2.
Sintered bodies having 3% by volume (Comparative Examples 2-10 to 2-12) were also prepared.

A cutting tip having the above sintered body as a cutting edge was produced. Heat-treated carbon steel SCM435 (HRc30) round bar (φ150 × 300m) using these cutting chips
A work material with four V-shaped grooves in (m) was prepared and intermittent cutting was performed. Cutting conditions are V = 250m / min, d = 0.2mm, f = 0.1
5mm / rev, dry type. Table 3 shows the fracture lives of the tools of the present invention and comparative examples.

[0044]

[Table 3]

As is clear from Table 3, all of the examples of the present invention have a hardness of 25 GPa or more and have a long defect life.
It can be seen that the sintered body has both hardness and toughness.

Example 3 A crystalline boron powder having a purity of 99.9% and a maximum particle size of 1 μm or less so that the composition ratios of boron, aluminum and lithium are 82 at%, 13 at%, and 5 at%.
Aluminum with a purity of 99.9% and a maximum particle size of 300 μm or less -28
Atomic% lithium alloy powder was mixed and mixed at 70% by weight and 30% by weight, respectively. Put this mixed powder in a high-purity alumina crucible and set it in a high temperature atmosphere heating furnace.
In the above high-purity argon gas atmosphere, the temperature was maintained at 1180 ° C. for 1 hour to obtain AlLiB ₁₄ powder having a maximum particle size of 2 μm and an average particle size of 0.8 μm.

This powder had the composition shown in Table 4 and the maximum particle size
ZrN particles of 2 μm or less were blended. These mixed powders are
In a ball mill container made of Luconia, balls made of zirconia,
Fill with ethanol, ball mill and mix homogeneously
did. 1 x 10 of this mixed powder ⁻³Dry at 600 ° C in Pa vacuum
After being dried, it was pressed into pellets. This molding
Put the body in a Mo container, and use this container with a high pressure and high temperature device.
The pressure to 2GPa and the temperature to 1400 ℃ for 30 minutes to obtain a sintered body.
It was X-ray diffraction measurement results and Vickers hardness of the obtained sintered body
Table 4 shows the measurement results of the degree. Al in all sintered bodies
LiB₁₄And ZrN, ZrB₂Was observed. In addition to the above substances, Al
LiO₂And A1₂O₃Was observed.

Next, when the structures of these sintered bodies were observed with a scanning electron microscope, it was found that the AlLiB ₁₄ particles were bonded to each other via a binder phase.

As a comparative example, a sintered body containing no binder by the above method (Comparative Example 3-5), and further using ZrN 20 as a binder.
A sintered body containing 3% by volume (Comparative Example 3-6) was produced. These x
Table 4 also shows the results of the line diffraction measurement and the hardness measurement.

A chip for cutting was produced using the above sintered body as a cutting edge. Heat-treated carbon steel SCM435 (HRc30) round bar (φ150 × 300m) using these cutting chips
m) was continuously cut for 10 minutes. Cutting condition is V = 400m /
It is a dry type with min, d = 0.2 mm, f = 0.15 mm / rev. Table 4 shows the results of damage to the cutting edges of the present invention example and the comparative example.

[0051]

[Table 4]

As is clear from Table 4, all of the examples of the present invention have a hardness of 25 GPa or more and a small flank wear amount, indicating that they are sintered bodies having excellent hardness.

[0053]

As described above, the sintered body of the present invention is
By forming a structure in which borides, whose composition is Al _{X ≤ 1} M _{y ≤ 1} B _{Z ≥ 12} , are mutually bonded by a binder, they have excellent wear resistance and chipping resistance when used as a cutting tool. With sex.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3C046 FF31 FF40 FF43                 4G001 BA01 BA03 BA05 BA06 BA24                       BA25 BA26 BA37 BA38 BA39                       BA43 BA44 BA45 BA57 BB01                       BB03 BB05 BB06 BB24 BB25                       BB26 BB37 BB38 BB39 BB43                       BB44 BB45 BB57 BC13 BD12                       BD18

Claims (6)

[Claims] 1. A boride sintered body containing a boride consisting of Al, one element M selected from groups Ia and IIa of the periodic table, and boron, wherein the boride sintered body comprises: Boride whose composition is represented by Al _{X ≤ 1} M _{y ≤ 1} B _{Z ≥ 12} is 50 to 75% by volume and the balance consists of a binder phase and unavoidable impurities, and the binder phase is IVa, Va, or a VIa group metal. Carbides, nitrides, carbonitrides and borides consisting of at least one selected from these or solid solution compounds thereof, the boride represented by Al _{X ≤ 1} M _{y ≤ 1} B _{Z ≥ 12} in the sintered body structure A boride sintered body, which is bonded to each other through the binder phase. 2. The boride sintered body according to claim 1, wherein the element M is Mg. 3. The boride sintered body according to claim 1, wherein the element M is Li. 4. The binder phase is a carbide or nitride of Ti or Zr,
2. The boride sintered body according to claim 1, which is mainly composed of at least one kind of carbonitride. 5. The boride having a composition represented by Al _{X ≦ 1} M _{y ≦ 1} B _{Z ≧ 12} is composed of particles of 5 μm or less.
The boride sintered body according to 1. 6. Al oxides and elements as unavoidable impurities
2. The boride sintered body according to claim 1, comprising at least one selected from an oxide of M, an oxide of B and Al, and a complex oxide of elements M and B.