JPS6131360A - Manufacture of composite sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a high-density composite sintered body containing aluminum nitride and boron nitride.

Specifically, a molded body of a mixed powder consisting of aluminum nitride powder, boron nitride powder, and at least one metal or metal compound selected from Group IIa metals and Group IIIa metals of the periodic table is heated at 2 to 100 atmospheres. Under nitrogen gas atmosphere,
Provided is a method for producing a composite sintered body, characterized in that sintering is performed at a temperature of 1750 to 2400°C.

So-called non-oxide ceramics such as silicon nitride and silicon carbide are ceramics that have recently attracted particular attention as high-temperature, high-strength materials, but once these sintered bodies are sintered, it is difficult to give them an arbitrary shape by post-processing. This has become extremely difficult, and this problem is considered to be one of the major practical difficulties.

For this reason, in the field of oxides, glass ceramics in which many fine mica crystals are precipitated in glass, and so-called mica ceramics obtained by hot pressing natural or synthetic mica powder have recently been developed. These ceramics are machinable ceramics that can be cut with ordinary tools and ground, and are useful as ceramics with improved workability. Furthermore, among non-oxidizing ceramics, hexagonal boron nitride has a layered graphite structure, so its sintered body can be cut and ground with ordinary tools, and has been in practical use for a long time. However, although the above-mentioned various machinable ceramics have the advantage of being easy to process, they also have the fundamental drawback of being ``soft'' and ``weak'', which prevents them from being widely used as ceramics. It's not.

As a result of intensive research into non-oxide machinable ceramics, the present inventors have discovered a new material consisting of aluminum nitride, boron nitride, and at least one metal compound selected from Group 1a metals or Group 1IIa metals of the periodic table. We have already developed and proposed a composite sintered body. The composite sintered body is a sintered body in which crystal grains with polygonal mechanical fracture surfaces are closely packed, and thin layered crystal grains are interposed in part or all of the grain interface of the packed particles. It is a revolutionary ceramic that can be cut at high speed with ordinary tools, and has a bending strength of 35 to 9/xi or more depending on the composition, which is comparable to high-strength ceramics. As a result of intensive research into the manufacturing method of the composite sintered body, the present inventors found that aluminum nitride powder, boron nitride powder and
At least one selected from Group Ia metals or Group 11a metals
By sintering a compact of a mixed powder of a metal compound under nitrogen gas pressure, the mechanical strength and thermal conductivity of the resulting sintered compact are improved while machinability with ordinary tools is maintained. They discovered this and completed the present invention.

That is, the present invention provides a molded body of a mixed powder consisting of aluminum nitride powder, boron nitride powder, and at least one metal or metal compound selected from Group IA metals and Group I Ja metals of the periodic table. This is a method for producing a composite sintered body, characterized by sintering at a temperature of 1750 to 2400°C in a nitrogen gas atmosphere at atmospheric pressure.

Any type of aluminum nitride powder can be used as the aluminum nitride powder of the present invention, but in order to obtain a dense composite sintered body, it is necessary to It is preferable that the average particle diameter of the aggregated particles measured by a method such as 500 μm or less is 5 μm or less. Powders with a diameter of 3 μm or less, most preferably 2 μm or less are used. Particularly suitable is a powder containing 70 volumes or more of particles of 3 μm or less. In addition, when obtaining a composite sintered body with high thermal conductivity, the AIN content ft (A
(calculated from the nitrogen content of JN powder) is 90% by weight and 7%
The above aluminum nitride powders are preferably employed, and more preferably powders having a weight of 94 ≦ or more, and even more preferably 7% or more by weight of 97 are employed.

The aluminum nitride powder suitably used in the present invention is a powder with an average particle diameter of 2 μm or less, containing 70% by volume or more of particles with a size of 3 μm or less, and containing 3.0% or less of nitride, Moreover, the aluminum nitride powder contains 0.5% by weight or less of cationic impurities when the aluminum nitride composition is MN. When such aluminum nitride powder is used, it is preferably used in the present invention because it can improve the thermal conductivity of the resulting cast sintered body and suppress a decrease in mechanical strength at high temperatures. In particular, the powder has an average particle diameter of 2 μm or less, contains 70% by volume or more of particles of 3 μm or less, has an oxygen content of 1.5% by weight or less, and contains cationic impurities when the aluminum nitride composition is AJN. The use of aluminum nitride powder having a content of 0.3% by weight or less is particularly preferred in the present invention because it significantly improves the thermal conductivity of the resulting composite sintered body and suppresses the decrease in mechanical strength at high temperatures. used for.

The method for producing the aluminum nitride powder is not particularly limited, and any known method can be employed. For example, a method of nitriding metal aluminum in nitrogen and then pulverizing it, a method of reducing and nitriding alumina, a method of arc discharging metal aluminum in nitrogen, a method of gas phase reaction between IJ C13 and NH3,
(NH4).

A method using thermal decomposition of AlF6, 1107!3, NH3, etc. can be adopted.

The boron nitride powder is not particularly limited, and any powder can be used. Typical examples that are generally suitably used are as follows.

Generally, the boron nitride powder preferably used has a purity of 99.9%. (At 1% by weight or more, the average particle size is 5 μm)
These are as follows. Further, the method for producing the boron nitride powder is not particularly limited, and any known method can be employed.

For example, (1) H3BO3 or H&2B4 in the presence of urea
A method of manufacturing by heating 07 at 500 to 950°C in an NH3 atmosphere.

(2) A method of manufacturing by reacting BO and NH3.

(3) A method in which the Fe-B alloy is heated at a temperature of 500 to 1400°C, and then Fθ is dissolved and removed using, for example, an acid.

etc. can be adopted.

In addition, at least one metal or metal compound selected from Group IIa metals and Group 111a metals of the Periodic Table (hereinafter sometimes simply referred to as sintering aids) is not particularly limited and is a known one. can be used. Typical examples that are particularly preferably used are as follows. The periodic table I
As metals of Group Ia, beryllium, calcium, strontium, barium, etc. are generally preferred, and yttrium or lanthanum group metals are preferred, with yttrium being more specific.

Lanthanum, cerium, praseodymium, neodymium.

Preferred are promethium, samarium, europium, trithium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and especially yttrium, lanthanum, cerium, neodymium, and the like. These metal compounds from Group IIa or Group 111a of the periodic table are not particularly limited, and the metal compounds known above can be used as sintering aids for aluminum nitride powder and/or boron nitride powder. Generally, for example, nitrates,
Compounds such as carbonates, halides, and oxides are preferably used.

Further, the composition ratio of each component constituting the composite sintered body of the present invention can be selected from a wide range depending on the desired properties of the composite sintered body. Generally, for example, aluminum nitride is 50 to 9
7 parts by weight, preferably 65 to 95 parts by weight, boron nitride in the range of 3 to 50 parts by weight, preferably 5 to 35 parts by weight, and selected from metals of group IIa and group 11a of the periodic table. It is preferable to select the amount of at least one metal or metal compound in an amount of 4 to 10 parts by weight, preferably 0.2 to 5 parts by weight.

The aluminum nitride powder, nitride powder, and sintering aid described above are mixed, shaped, and subjected to sintering under nitrogen gas pressure. Here, the sintering aid does not necessarily need to be added to the aluminum nitride powder or boron nitride powder, and the sintering aid is not necessarily added to the aluminum nitride powder or boron nitride powder in advance so that the sintering aid is included in the powder. It may be mixed into the manufacturing raw materials.

The aluminum nitride powder in the present invention.

The mixing of the boron nitride powder and the sintering aid is not particularly limited, and may be dry mixing or wet mixing. A particularly preferred embodiment is wet mixing, ie mixing in the wet state using a liquid dispersion medium. The liquid dispersion medium is not particularly limited, and commonly used water, alcohols, hydrocarbons, or mixtures thereof are preferably used. In particular, lower alcohols having carbon atoms of 4 or less, such as methanol, ethanol, and butanol, are most preferably employed industrially.

In addition, the wet mixing device used for the above mixing is not particularly limited and any known device may be used. However, when used for mixing particularly high purity aluminum nitride powder and boron nitride powder, It is preferable to choose one that does not produce any impurity components. For example, the material may be aluminum nitride itself, polyethylene, polyurethane,
Plastic materials such as nylon or materials coated with these materials may be selected.

Further, when obtaining the composite sintered body, addition and mixing of a binder, a deflocculant, a plasticizer, etc. in addition to the raw materials may be appropriately employed as necessary.

As a specific embodiment of sintering in the present invention, the mixed powder containing the aluminum nitride powder, boron nitride powder, and sintering aid is formed by a suitable molding method such as a dry press method, a rubber press, an extrusion method, an injection method, The most commonly used method is to form the desired shape by a doctor blade sheet forming method or the like, then place it on a suitable pod material or the like and sinter it at high temperature under nitrogen pressure. As another embodiment, a method may be adopted in which the mixed powder consisting of the aluminum nitride powder, boron nitride powder, and sintering aid is sintered under gas pressure while applying a mechanical pressure of 50 to 50 (l). .

The nitrogen gas pressure employed in the present invention is in the range of 2 to 100 atmospheres. When sintering under 2 atmospheres, that is, around atmospheric pressure or under reduced pressure, it is often difficult to improve the thermal conductivity and mechanical strength of the composite sintered body due to the heat dissipation of AJH at high temperatures. Further, a gas pressure of 100 atmospheres or more is not preferable because it does not bring about any improvement in effectiveness and is accompanied by equipment difficulties. The nitrogen gas pressure that can be suitably employed is in the range of 4 to 20 atmospheres. Further, in the present invention, the nitrogen gas atmosphere only needs to be mainly nitrogen gas, and there is no problem even if it partially contains gases such as argon and helium.

Sintering of the present invention is carried out at 1750-2400°C, preferably at 180°C.
It is carried out in a temperature range of 0 to 2300°C.

At a temperature of 1750° C. or lower, it may be difficult to improve the thermal conductivity and mechanical strength of the composite sintered body, and at a temperature of 2400° C. or higher, thermal decomposition of AIH increases, which is undesirable.

The selection of sintering temperature depends on the particle size of aluminum nitride powder and boron nitride powder.

It may be determined appropriately based on nitrogen gas pressure.

The sintering time varies depending on the sintering temperature, but is usually 30 minutes to 1
Selected from a range of 0 hours.

As is clear from the mechanical fracture surface of the composite sintered body obtained by the method of the present invention shown in FIG. 1 of the attached drawing, the mechanical fracture surface is filled with polygonal crystal grains. It is composed of thin layered crystal grains interposed in part or all of the grain interface of the filled particles.

The crystal grains whose mechanically fractured surfaces are polygonal in FIG. 1 are sintered crystal grains of aluminum nitride. The aluminum nitride sintered grains are formed by a close packing of fine grains whose mechanical fracture surfaces are distinguished from each other by clear contours, The contour is polygonal, and the fine crystals have an average particle diameter of 0.3D-1,8 when the average particle diameter at the fracture surface defined by the clear contour is defined as D (μrIL).
At least 70% of the crystal grains have a particle size in the range D. Said Q, 3D A-1
, 81, that is, an aluminum nitride sintered body that has polygonal particles of relatively uniform size on the fracture surface has not been known so far. .

1. The main feature of the external appearance of the mechanically fractured surface of aluminum nitride is that the crystal planes covered with dust on the fractured surface of individual particles form a relatively smooth flat surface. This means that the crystal grains often contain foreign phases (usually appearing as small circular depressions on the fracture surface) that are formed due to the incorporation of impurities or gaseous phases.
It shows that there is no.

Furthermore, from FIG. 1, it is clear that the grains filled with polygonal crystal grains made of aluminum nitride have thin layered crystal grains interposed in part or all of the grain interface. These thin layered crystal grains are sintered crystal grains made of boron nitride.

As clearly shown in Figure 1, on the mechanically fractured surface of the sintered body, thin layer-like crystal grains made of boron nitride existing at the grain interface of the aluminum nitride particles form the machinable ceramic of the composite sintered body of the present invention. It is estimated that this is an important factor that gives the properties of That is, the thin layered crystal grains made of boron nitride present at the grain interface of the aluminum nitride particles absorb the force applied from the outside during cutting, prevent the aluminum nitride sintered body from breaking, and improve the composite sintered body. We believe that this enables high-speed cutting using ordinary tools.

At least one metal compound selected from Group 11a metals and Group 111a metals of the periodic table cannot be confirmed from photographs of mechanically fractured fracture surfaces of the ventralized sintered bodies obtained in the present invention. . The metal compound can generally be analyzed using an X-ray microanalyzer or a fluorescent X-ray analyzer. In addition, the content may be confirmed as a decreased ftt compared to the amount of the metal compound or the substance that can become the metal compound mixed with the aluminum nitride powder and boron nitride powder before the sintering process.

That is, it is considered that a part of the metal compound or a substance that can become the metal compound may sublimate during sintering.

However, although the amount thereof present is small, the metal compound in the ventral sintered body obtained by the present invention functions to assist in sintering the aluminum nitride powder and the boron nitride powder, and also serves to assist the sintering of the aluminum nitride powder and the boron nitride powder. It is thought that this, together with the powder, is a factor that gives these composite sintered bodies the properties of machinable ceramics.

The ventralized sintered body obtained by the present invention is a sintered body of high density and high purity, and generally has a purity of, for example, 90% or more, preferably 95% or more, and 25g/- or more, preferably 2.0g/- or more.
7g/all! The density will be higher than that.

Sintering under nitrogen gas pressure according to the present invention has a remarkable effect on improving the thermal conductivity and mechanical strength of the composite sintered body, as will be clear from the examples described below. This is because pressurized nitrogen gas suppresses the thermal decomposition of AIH during sintering at high temperatures, accelerating sintering, and ultimately eliminating a large amount of pores in the sintered body. it is conceivable that.

Like the normal pressure sintering method, the sintering method under pressurized nitrogen according to the present invention enables the production of products with complex shapes in large quantities, and therefore has extremely high industrial value. The present invention will be specifically illustrated below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Aluminum nitride powder 80 with an average particle diameter of 1.31 μm and 3 μm or less accounts for 90 volume i% and has the composition shown in Table 1.
20 parts by weight of hexagonal boron nitride powder and 3 parts by weight of barium nitrate with an average particle size of 2.5 μm and a particle size of 5 μm or less in a proportion of 95 volume ijk% and a purity of 995%. - The coated balls were uniformly mixed in a ball mill using ethanol as a dispersion medium. After drying the obtained mixed powder, about 1
2Ii was rubber pressed at a pressure of 2000% to form a disc-shaped molded product with an outer diameter of 40 tnxp-# about 6.3 mm. This molded body was placed in a graphite container whose inner wall was coated with boron nitride powder, and heated under nitrogen gas pressure of 98 atmospheres for 2 hours.
It was baked at a temperature of 200°C for 3 hours. The density of the obtained white sintered body was z931/cd. A columnar test piece of about 3 square inches was cut out from this sintered body, finished with No. 1500 sandpaper, and crossheaded at a speed of 05 m/min.

Table I Ag'N powder analysis value AIM content 97.8% Element content"g <5 (PPM) cr
21 (')sl 125
(〃) Zn 9 (tr) Fe
20 (#) cu <s
(〃) Mn 5 (〃) N1 27 (〃) T1 <5 (#) Co <s (#)
AI 64.8 (wt%)N
33.4 (#) 0 1.1 (#) 0 0.11 (#) As a result of measuring the 3-point bending strength of 20 spans, the average value was 4
2kl? /mm was obtained. Also, from the same sample, the diameter is about 1
A disc-shaped sample with 0 fins and a thickness of 2.511 II was cut out, and its thermal conductivity at room temperature was determined by the sea sun flash method and was 93 W/mK. Furthermore, when the workability of the ventral ML structure obtained in this example was investigated, it was found that both drilling with a carbide drill and high-speed cutting with a carbide cutting tool were easily performed, and the material was free-cutting.

Example 2 Aluminum nitride, boron nitride and Periodic Table Ia
Table 2 shows the results of sintering in the same manner as in Example 1 while changing the composition ratio of the group metal compound or the group 111a metal compound.

Example 3 The same mixed powder 129 of aluminum nitride powder, boron nitride powder and barium nitrate as used in Example 1 was coated with boron nitride powder on the inner wall and had an inner diameter of 40 mm.
Filled in a graphite mold of
Sintered at ℃ for 3 hours. The density of the obtained sintered body is 2.95
1! iI/cI! It was easy to cut."
Further, the bending strength and thermal conductivity of this sintered body were measured under the same conditions as in Example 1, and were each 441'J/mx.

Example 4 As aluminum nitride, the average particle size is 1.8 μm and 3μ
m or less accounts for 75% by volume, and Fe0.
A mixed powder was prepared in the same manner as in Example 1, except that aluminum nitride powder containing 0.07%, 810.03%, and 08% TiO with an oxygen content of 2.1 wt% was used. This mixed powder was molded into a disc shape under the same conditions as in Example 1, and the molded body was heated at 215 m
Sintering was carried out at a temperature of 0° C. for 3 hours. The obtained sintered body has a density of 2
．． At 89 Jil/7, it was a machinable ceramic that could be easily drilled and ground using a carbide drill or cutting tool.

Moreover, the bending strength and thermal conductivity of this sintered body are each 31
kg/*ml 47 w/ax.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph showing the sintered body particle structure of the mechanically fractured surface of the composite sintered body prepared in Real Gloss Example 1.

Claims (1)

[Claims] A compact of a mixed powder consisting of aluminum nitride powder, boron nitride powder, and at least one metal or metal compound selected from group IIa metals and group IIIa metals of the periodic table is heated at 2 to 100 atmospheres. under a nitrogen gas atmosphere of 175
A method for producing a composite sintered body, characterized by sintering at a temperature of 0 to 2400°C.