JPS6163572A - 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 producing a composite sintered body of aluminum nitride and boron nitride which has high density and particularly excellent thermal conductivity.

It has been known that it is not possible to obtain a composite sintered body using only aluminum nitride powder and boron nitride powder, and various additives have been tried to obtain such a composite sintered body.

The inventors of the present invention have worked hard to develop an excellent composite sintered body using aluminum nitride powder, and as a result, they have developed an excellent composite sintered body by blending a specific compound with aluminum nitride powder and boron nitride powder and sintering the mixture. We have already discovered and proposed that it is possible to obtain a sintered body, a so-called machinable ceramic composite sintered body, which can be cut at high speed with ordinary tools.

As a result of further research into the manufacturing method of composite sintered bodies, the present inventors found that when firing a mixed powder in which a sintering aid was added to aluminum nitride powder and boron nitride powder, the average temperature increase in a specific temperature range It was discovered that the speed significantly affects the sintering characteristics and the characteristics of the sintered body, and the present invention was completed.

That is, the present invention provides aluminum nitride powder, nitride ~ 1700
This is a method for producing a composite sintered body in which the average temperature increase rate in the temperature range of 10 to 10 b.

The aluminum nitride powder used in the invention is not limited in any way, and any aluminum nitride powder can be used. When obtaining a dense composite sintered body by the method of the present invention, the average particle size of the aluminum nitride powder as a raw material is
00, etc.) is 5μ
It is preferable that it is below m. Powders with a diameter of 3 μm or less, most preferably 2 μm or less are used. Especially 5μm
Powders containing 70% by volume or more of the following particles are suitable. In addition, when obtaining a composite sintered body with high thermal conductivity, the content of ktN (calculated from the nitrogen content of the AM powder)
It is preferable to use aluminum nitride powder of 90 wt % or more, more preferably 94 wt % or more, and preferably 97 wt % or more to obtain a sintered body with high translucency. .

The aluminum nitride powder preferably used in the present invention is a powder with an average particle size of 2 μm or less, containing 70% or more by volume of particles of 3 μm or less, and an oxygen content of 3.0% by weight or less, and The aluminum nitride powder contains 0.5 Mkg or less of cationic impurities when the aluminum nitride composition is JktN. When such aluminum nitride powder is used, the thermal conductivity of the resulting composite sintered body is significantly improved, and therefore it is preferably used in the present invention. In particular, powder with an average particle diameter of 2 μm or less, containing 70% by volume or more of particles with a diameter of 3 μm or less, and an oxygen content of 1.5
When aluminum nitride powder containing cationic impurities of 0.3% by weight or less when the aluminum nitride composition is 0.3% by weight or less is used, the thermal conductivity of the resulting composite sintered body is improved. It is particularly preferably used in the present invention because it also improves translucency.

Typical methods for producing the hyaluminum powder preferably used in the practice of the present invention are as follows.

(1) Purity 99.0 wt%, preferably 995 wt.
k □% or more, aluminum oxide fine powder containing particles with an average particle size of 2 μm or less and 3 μm or less in a ratio of 70 volume i% or more, and an ash content of up to 0.2% by weight and an average particle size of 1 μm. The fine carbon powder below the door is intimately mixed in a liquid dispersion medium, and the weight ratio of the fine aluminum oxide powder to the fine carbon powder is 1:0.36 to 1:1.
Q) The intimate mixture obtained is optionally dried and calcined under an atmosphere of nitrogen or ammonia at a temperature of 1400-1700°C; C) The fine powder obtained is then heated under an oxygen-containing atmosphere for 60°C.
Unreacted carbon is removed by heating at a temperature of 0 to 900°C.

It can be obtained by a process.

Moreover, the boron nitride powder used for manufacturing the composite sintered body of the present invention is not particularly limited, and any powder can be used.

Generally, the boron nitride powder preferably used has a boron nitride purity of 99.03 mN% or more and an average particle size of 5 μm or less. Further, the method for producing the boron nitride powder is not particularly limited, and any known method can be employed.

The mixing ratio of the aluminum nitride powder and the boron nitride powder can be selected from a wide range depending on the properties required of the composite sintered body to be obtained. In general, it is preferable to select aluminum nitride powder in the range of 50 to 97 parts by weight, preferably 65 to 95 parts by weight, and boron nitride powder in the range of 3 to 50 parts by weight, preferably 5 to 351 parts by weight. It is.

Next, as the first sintering aid, any known sintering aid used in the production of aluminum nitride sintered bodies may be used without any limitations.

In particular, the sintering aid preferably used in the present invention is at least one metal or metal compound selected from the periodic π2L group metals and the 1a group metals.

The Group 1a metal is not particularly limited, and beryllium, magnesium, calcium, strontium, and barium can be used. Industrially it is preferred to use Cal, Si, Strontium and Barium. Moreover, Group 1a metals can be used without particular limitation. For example, Yztrium (
Y), lanthanum (L, ), cerium (Ce), praseodymium (Pr), neodymium (Na), glomethium (Pm)
), samarium (am), europium (Eu),
Gadolinium (GIL), terbium (yb), sugrosium (Dy), holmium (Ho), erbium (Kr), thulium (Tm), ytterbium (Yb), and lutetium (Lu) can be suitably used.

In particular, yttrium, lanthanum, cerium, neodymium, etc. are preferably used industrially.

The metal compound used as a sintering aid in the present invention is not particularly limited to the above metal compounds, and for example, nitrates, carbonates, compounds, oxides, etc. are preferably used. be done. In the present invention, specific examples of sintering aids suitably used are as follows.

Calcium nitrate, calcium carbonate, calcium heptadide,
Calcium compounds such as calcium oxide; Strontium compounds such as strontium nitrate, strontium carbonate, strontium heptafluoride, strontium oxide; Barium compounds such as barium nitrate, barium carbonate, barium 77, barium oxide; yttrium nitrate, yttrium carbonate, fluoride Yttrium compounds such as yttrium and yttrium oxide; lanthanum nitrate, yttrium carbonate, and 7-chloride 2
Examples include ivy/lanthanum compounds such as lanthanum oxide.

The amount of the sintering aid used in the present invention may be selected in consideration of the temperature increase rate during firing, which will be described later. Converted to 0.02~5. It is preferable to mix it so that it contains Qvt%. Of course, in addition to the above-mentioned raw materials, binders, M glues, plasticizers, etc. may be added and mixed as appropriate.

The mixing of the aluminum nitride powder, boron nitride powder, and sintering aid in the present invention 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 4 or less carbon atoms, such as methanol, ethanol, and butanol, are most preferably employed industrially.

As a specific embodiment of the firing in the present invention, a mixed powder obtained by adding a sintering aid to the aluminum nitride powder and boron nitride powder is formed by a suitable molding method, such as a dry Luss method, a rubber press, an extrusion method, an injection method, By doctor blade sheet forming method etc. After molding it into the desired shape, it is placed on a suitable crucible, pod material, etc. and heated in a non-oxidizing atmosphere at vacuum or atmospheric pressure, such as nitrogen gas, helium gas, etc.
Examples include a method of firing in an atmosphere of argon gas or the like or under high pressure of nitrogen gas of about 2 to 100 atmospheres. Alternatively, directly add the mixed powder to 97a to 20 to 500
A method of firing at high temperature under a non-breathing atmosphere of vacuum or atmospheric pressure or under nitrogen gas pressure of about 2 to 100 atmospheres while applying a mechanical pressure of about 2 to 100 atmospheres is employed.

The firing temperature is 1,700 to 2,100°C, preferably 1,750 to 20,000°C in a non-oxidizing atmosphere of vacuum or atmospheric pressure.
A temperature of 50°C is preferably adopted, and under a nitrogen gas pressure of 2 to 100 atm, the temperature is 1700 to 2400°C, preferably 1750°C.
Temperatures of ˜2300° C. are preferably employed. Note that the temperature in the present invention is a value that is compensated to indicate the gas temperature within the graphite crucible by measuring the surface of the graphite crucible containing the mixed powder with a radiation thermometer.

The most important firing condition for the firing is the temperature increase rate, and in particular, the average temperature increase rate in the temperature range of 1500 to 1700 °C is set to 10 °C/min to 40'l:/1niH. This is extremely important.

The average heating rate in the temperature range of 1500-1700℃ is 10
If the temperature is less than .degree. C./win, the densification of the aluminum nitride powder becomes too slow and a sintered body with high density and high thermal conductivity cannot be obtained.

In addition, if the average temperature increase rate is faster than 40℃/win, the rate at which pores are extracted through grain boundaries while grains grow during sintering, and the rate at which pores are confined within the grains due to grain growth will increase. It is difficult to maintain a balance between the two, making it difficult to form a dense and uniform sintered body.

In addition, rapid temperature rise is undesirable because even if the density increases, the sintered body often warps. Further, a sintered material added as a sintering aid may remain in the sintered body more than necessary, impeding the thermal conductivity and translucency of the sintered body.

The above average temperature increase rate has an optimal range depending on the type and amount of the sintering aid added, so it can be determined appropriately depending on the sintering aid, but the density and temperature of the obtained sintered body Taking conductivity into consideration, it is generally 10-b, most preferably 15-b.

Furthermore, if the type and amount of sintering aids are the same, generally a higher temperature increase rate is preferable for normal pressure sintering or gas pressure sintering than for hot press sintering. becomes.

In determining the heating rate, it is important to set the heating conditions so that the sintering aid added during the heating process does not evaporate excessively, and that as little of the sintering aid component remains after sintering. It is a matter of selection.

As for the heating method, it is industrially preferable to set a single heating rate in the range of 1,500 to 1,700°C. It is also possible to choose.

The temperature increase rate until reaching 1500° C. and the temperature increase rate when it is necessary to increase the temperature from 1700° C. to the firing temperature are not particularly limited, and any temperature increase rate may be used.

However, in consideration of the density and thermal conductivity of the obtained sintered body, it is preferable that the average temperature increase rate described above is maintained even in the temperature range of 1200 to 1500°C. Also,
Industrially, it is preferable to have a single average heating rate over the entire temperature range up to the firing temperature.

After being heated to K in this way, preferably 17
It is fired at a firing temperature of 00 to 2400°C. The firing time varies depending on the firing temperature, the type and temperature of the sintering aid, and the average heating rate, but is usually selected from a range of 10 minutes to 10 hours.

With a system in which a specific sintering aid is added to the aluminum nitride powder and boron nitride powder, the average heating rate conditions for obtaining a high-density, high-quality sintered body are quite high, at 10°C to 40°C/m1n. This is a remarkable difference compared to, for example, the temperature rise rate for industrial firing of alumina, a typical fused ceramic, which is 2-b, and is a surprising result.◇ As explained above. As described above, the present inventors speculate that the reason why a composite sintered body with excellent properties can be obtained by selecting a specific average heating rate in a specific temperature range is as follows. There is. For example, Oa (N
This phenomenon will be explained using the case where 03\4H20 is used as an example.

Aluminum nitride powder and boron nitride powder are coated with oa(mow).
) When a mixed powder containing t・4fO is heated in nitrogen, ca(No3)z・4 is first heated at a low temperature below 100°C.
H@0 ridicule occurred 1), then 1°0~130°C
At a temperature of , dehydration occurs to form an anhydrous Oa(1103)z solid. The temperature was further increased (and at about 530°C, 0a (N
03) 2 melts and becomes a liquid state. And 0a(Ho3)z melted in the temperature range from this temperature to 1000℃
is unavoidably contained in aluminum nitride powder.
About 3vt% oxygen divided by about 2.2 to 6-4X At2
(equivalent to 03 minutes) and reacts with 0aksm 1-tos,,
Produces a calcium aluminate phase such as 0aO-2A403. This calcium aluminate phase is 150
It starts to melt at a temperature of 0℃ or higher, which is 1400 to 1700℃.
It is thought that it acts effectively as a sintering aid during the process where sintering progresses most at a temperature of . According to detailed studies by the present inventors, 150% of this molten calcium aluminate phase
Because the evaporation rate at temperatures above 0°C is surprisingly fast,
If the average heating rate during the heating process above 00°C is slow, excessive evaporation of the molten calcium aluminate phase will occur, and in the temperature range of 1400°C to 1700°C, the amount of calcium aluminate phase sufficient to act as an auxiliary agent will be reduced. It is thought that this makes it difficult to obtain the desired dense sintered body. At a firing holding temperature of 1700°C or higher, the molten calcium aluminate phase acts as a densification aid, and evaporates according to its vapor pressure, ultimately reducing the amount of aid remaining in the sintered body. is often 10% or less of the initial addition amount.

The composite sintered body obtained by the method of the present invention is a sintered body with high density and high thermal conductivity. That is, 2.5? /crIL
A sintered body having a density of J or higher and a thermal conductivity of 50 W/mz or higher can be obtained.

As is clear from the mechanically fractured surface of the composite sintered body obtained by the method of the present invention shown in FIG. 1 of the accompanying drawings, the mechanically fractured 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 to 1.8D, defined as D (μWL) at the fracture surface defined by the clear contour.
At least 70× of crystal grains having a particle size in the range of K are constituted by K. The 0.3D to 1.8D
A sintered body having a fractured surface in which 70% or more of particles are present in the range of , that is, a sintered body having polygonal particles of relatively uniform size on the fractured surface, has not been known so far.

Another characteristic of the appearance of the mechanically fractured surface of aluminum nitride is that the crystal planes appearing on the fractured surface of individual particles form relatively smooth flat surfaces. This indicates that the crystal grains have almost no foreign phase (which usually appears as small circular depressions on the fracture surface) that are formed due to the incorporation of impurities or gas phase. ing.

Furthermore, from FIG. 1, it is clear that thin-layered crystal grains exist in part or all of the grain interface of the particles filled with polygonal crystal grains made of li*aluminum nitride. 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 layered crystal grains made of boron nitride existing at the grain interface of the aluminum nitride particles are obtained. It is estimated that this is an important factor that gives the properties. 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, preventing the aluminum nitride sintered body from breaking, and making it possible to cut at high speed with ordinary tools. It is thought that this makes processing possible.

As explained above, the composite sintered body obtained by the manufacturing method of the present invention has high density and high thermal conductivity, and also has the characteristics that it can be cut with ordinary tools. There is. The present invention provides a method for manufacturing a composite sintered body having such excellent properties. Since it is particularly advantageously applied to the production of bodies, its industrial value is extremely large. The present invention will be specifically illustrated by examples below, but the present invention is not limited to these examples. , and aluminum nitride powder 80 having the composition shown in Table 1.
20 parts by weight of boron nitride powder with an average particle diameter of 2.5 μm, a ratio of particles with a particle size of 5 μm or less at 95% by volume, and a purity of 99.5%, and 3N parts of barium nitrate are added to nylon. The mixture was uniformly ball-milled using a nylon-coated ball and ethanol as a dispersion medium. After drying the obtained mixed powder, about 122 was rubber pressed at a pressure of 2000 KP/21 to give an outer diameter of 40
rILrrL A disc-shaped molded product with a thickness of about 6.3 mm was prepared. This compact was placed in a graphite crucible whose inner wall was coated with boron nitride powder, and heated under nitrogen gas pressure of 1 atm for 120 min.
The temperature was raised to 0°C in 40 minutes, then from 1200°C to 190°C.
19 by increasing the temperature to 0'C at a rate of 20℃/win.
It was baked at 00°C for 3 hours.

The obtained sintered body had a uniform white color, was a machinable ceramic that could be easily ground and drilled with a carbide tool, and had a density of 2.92 t/α3. The thermal conductivity of this sintered body was measured and found to be 77 W/mK. In addition, a test piece of about 3 mm square was cut out from this sintered body and
The bending strength was measured under the conditions of a crosshead speed of 0.5 mm/win and a span of 20 mm after finishing with a sand/<- bar of the number 1. The average measured value was 34 Ky.
7mm".For comparison, the same rubber press molded product as above was made from 12QO'C to 19QQ"C.
The density of the sintered body obtained was 2.44 when sintered under the same conditions except that the heating rate was 5°C/min.
t/cti", and the average value of bending strength is 7?
/ mm” Tea Tsuta.

Table 1 Aluminum nitride powder analysis value Mg content 97.8
21 (#) Sl 125 (l) Zn 9(y) IPe 20(1) Cu < 5 (l) lJn 5(1) Nl 27(#) TI < 5(l) Co
< 5 (l) A/-64,8 (vt%) N 3 Otsu 4 (l) 0 1.1' (I) Cα11 (z) Example 2 The same aluminum nitride powder as used in Example 1 and Table 2 shows the results of sintering using boron nitride powder under various conditions. Note that column 4 in Table 2 is a comparative example.

Example 5 The aluminum nitride powder, boron nitride powder, and sintering aid used in Example 1 were mixed and molded in the same manner as in Example 1, and then heated to 1200°C for 40 minutes under nitrogen gas pressure of 9.8 atmospheres. The temperature was then increased by 20℃ from 1200℃ to 2200℃.
/ III i n heating rate to 2200'
The density of the obtained white sintered body was 2.99 t/3, and the thermal conductivity was 95 W/iz. Further, in the same manner as in Example 1, a columnar test piece was cut out from this sintered body and its 3A bending strength was measured, and an average value of 46 Ky/rum was obtained.Furthermore, the workability of the sintered body obtained in this example was Upon investigation, it was found that drilling with a carbide drill and cutting with a carbide cutting tool were both easy and free-cutting.

A scanning Hiroko microscope photograph of the mechanically fractured surface of the obtained sintered body is shown in FIG.

[Brief explanation of the drawing]

FIG. 1 is a scanning wave electron micrograph showing the sintered body particle structure of the mechanically fractured surface of the composite sintered body obtained in Example 3.

Claims (1)

[Claims] When firing a mixed powder containing aluminum nitride powder, boron nitride powder, and sintering aid to obtain a composite sintered body, the average temperature increase rate in the temperature range of at least 1500 to 1700 °C is set to 10 to 40 °C / A method for manufacturing a composite sintered body, characterized in that: min.