JP2840688B2 - Manufacturing method of aluminum oxide sintered body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ceramic containing aluminum oxide as a main component, and more particularly, to an aluminum oxide material excellent in wear resistance and toughness, particularly suitable for a cutting tool. The present invention relates to a method for producing a sintered body.

(Prior art and its problems) Ceramic materials such as aluminum oxide (Al ₂ O ₃ ) -based sintered materials should have better mechanical properties such as wear resistance than metal materials. It is used as various structural parts as a material replacing metal materials. Various improvements have also been proposed for Al ₂ O ₃ sintered bodies by combining them with other ceramics.

However, recently, even higher properties have been required for ceramics, and the current materials are particularly insufficient in toughness.

On the other hand, there is also a demand for improving the abrasion resistance and high-temperature characteristics of Al ₂ O _3. Research and development of a system to which a compound is added is actively performed.

(Problems to be Solved by the Invention) Such boride-based ceramics have high hardness, but have low strength and toughness, and their application fields are limited.

For example, titanium boride has been considered promising as a material for cutting tools because of its high hardness and good thermal conductivity.
A method for improving toughness could not be found, and it was not practical. Further, zirconium boride is expected to be used as a crucible for molten metal because of its low reactivity with metals, but its application field as a structural material is limited because of its low strength.

Aluminum boride is known to have a high hardness like other borides, but its physical properties are often unknown.

Therefore, the present inventors have studied the improvement of the sinterability and characteristics of aluminum boride among the above metal borides.As a result, aluminum oxide was mixed with aluminum boride at a specific ratio, It has been found that a specific material having high toughness can be obtained while maintaining high hardness by firing under a specific sintering condition and decomposing part or all of aluminum boride (Japanese Patent Application No. Hei. No. 312735). However, this material has a problem that the composition of the sintered body is difficult to control because boron is easily scattered during sintering, and the characteristics are not stable.

(Means for Solving the Problem) The present inventors have made various studies on this problem, and found that Mg, Ca, Cr, Mn, and F
It has been found that the properties of the sintered body can be stabilized by adding a compound of at least one element selected from e, Co, Ni and an element of Group IIIa of the periodic table.

That is, the present invention provides aluminum boride of 15 to 95% by weight,
Aluminum oxide or a substance that produces aluminum oxide by firing is added at a ratio of 3 to 90% by weight in terms of aluminum oxide to be produced, and Mg, Ca, C
At least one of r, Mn, Fe, Co, Ni and Group IIIa element of the periodic table is mixed at a ratio of 0.1 to 8% by weight in terms of oxide, and after molding, a temperature of 1400 to 1900 ° C. In particular, in the above configuration, it is possible to cause needle-like particles in the sintered body by using aluminum oxide or a needle-like thing as a compound that generates aluminum oxide by firing, Thereby, the toughness of the sintered body can be further improved.

 Hereinafter, the present invention will be described in detail.

The method for producing the aluminum oxide-based sintered body of the present invention comprises the steps of preparing, molding, and firing raw materials described in detail below.

(Adjustment of Raw Materials) As starting materials, use is made of aluminum boride powder and aluminum oxide powder or a compound powder that forms aluminum oxide by firing.

Aluminum boride powder has an average particle size of 200 mesh or less,
Desirably, it is a powder of 3 μm or less, optimally 1 μm or less, and may generally be aluminum boride of formula AlB ₁₂ , AlB ₂ or a non-stoichiometric composition, or a mixture thereof. Some of the currently marketed AlB ₁₂ partially contains AlB ₁₀ , but in that case, no problem occurs.

On the other hand, aluminum oxide powder or a substance that produces aluminum oxide by firing has an average particle diameter of 3 μm.
Hereinafter, it is particularly desirable to use fine particles of 1 μm or less.

Further, according to the present invention, the toughness of the sintered body can be further increased by using a needle-shaped substance as aluminum oxide or a substance that produces aluminum oxide by firing. Specifically, acicular aluminum oxide,
Alternatively needles aluminum borate having the formula of _{9Al 2 O 3 · 2B 2 O} 3 as a material for generating the needles aluminum oxide by heating in the sintering is used. These needle-like substances have an average diameter (minor diameter) of 2 μ or less, particularly 0.7 to 0.2.
It is preferable that the average of the aspect ratios represented by the major axis / minor axis is 3 to 100, particularly 10 to 30. The reason why the average diameter is specified to be 2 μm or less is that the grain growth at the time of sintering does not become excessive and a high resistance strength can be maintained. This is because it is difficult to control the diameter, the toughness varies, and when used as a cutting tool, the flank boundary wear tends to increase. On the other hand, if the average of the aspect ratios is less than 3, the effect of fiber reinforcement is small, and there is no effect of improving toughness.
If it is larger than 0, the handling of the raw material is difficult, and it cannot be uniformly dispersed, so that the toughness tends to decrease. In this case, if a part of the whisker is mixed while being crushed, it can be used without any problem.

Each of the above raw material powders has an aluminum boride powder of 15 to 95%.
%, Preferably 30 to 80% by weight, aluminum oxide powder or a substance which forms aluminum oxide by firing is mixed at a ratio of 3 to 90% by weight, preferably 20 to 70% by weight in terms of aluminum oxide. In order to obtain a particularly high hardness material, 55-80% by weight of aluminum boride,
The optimum content is 20 to 45% by weight of aluminum oxide, and particularly 30 to 55% by weight of aluminum boride and 45 to 70% by weight of aluminum oxide to obtain a material having high toughness.

The reason for setting the mixing ratio within the above range is that sintering is difficult when aluminum boride exceeds 95% by weight, and when aluminum boride is less than 15% by weight, the hardness of the sintered body decreases,
This is because desired characteristics cannot be obtained. If the amount of aluminum oxide is less than 3% by weight, there is no effect of toughening, and if it exceeds 90% by weight, the hardness decreases.

The needle-like substance added in place of the aluminum oxide powder for the purpose of increasing toughness is desirably replaced at a rate of 10% by weight or more based on the total amount of aluminum oxide.

According to the present invention, as a sintering aid, Mg, Ca, Cr,
It is important to contain at least one selected from Mn, Fe, Co, Ni and an element of Group IIIa of the periodic table in an amount of 0.1 to 8% by weight, particularly 0.3 to 5% by weight in terms of oxide,
If the amount of the auxiliary agent is less than 0.1% by weight, sintering is insufficient, and a stable sintered body cannot be obtained even in characteristics. If the amount exceeds 8% by weight, voids are generated in the sintered body, which is not desirable. In particular, Yb, Nd, Er, C
e, Sm, Y, Cd, Dy and La.

(Molding) The above-mentioned aluminum boride, aluminum oxide and sintering aid are mixed at a predetermined ratio, and then molded into a desired shape by a known molding means. As molding means, for example, press molding,
Extrusion molding, injection molding, casting molding, cold isostatic pressing and the like are employed. At the time of molding, a known binder or dispersant may be used to improve moldability. After sintering, these molded bodies are removed in a vacuum or an inert gas such as nitrogen gas or argon gas as required.

(Firing) The firing may be performed at a temperature of 1200 to 1900 ° C. for 0.5 to 6.0 hours in a reducing atmosphere in which an inert gas such as Ar, He or the like or carbon is present, and a pressurized or reduced pressure atmosphere thereof. As the firing means, normal pressure firing, hot pressing method, hot isostatic pressing method (HIP method), etc. are applied. After preparing a sintered body having a ratio of 96% or more, hot isostatic firing may be further performed under a high pressure of 500 atm or more.

According to the above firing, part or all of the aluminum boride in the raw material is separated into aluminum and boron, and the aluminum reacts with oxygen in the system to produce aluminum oxide, and boron also reacts with oxygen in the system. It reacts to produce boron oxide and a glassy substance consisting of aluminum, oxygen and boron. These boron compounds form a liquid phase together with the sintering aid component to promote sintering, but at this time, some of the boron is volatilized. Also, the aluminum oxide as a raw material remains almost as it is with some grain growth.

The sintered body obtained by the above-described manufacturing method has aluminum oxide as a main phase, and boron oxide or aluminum borate or a glassy substance made of aluminum, boron, oxygen, or the like is generated as a subphase at the grain boundaries. Further, the sintering aid component also forms a subphase component. According to the present invention, when the optimum ratio of aluminum and boron was examined in terms of the properties as a sintered body, aluminum was 10 to 50% by weight, particularly 20 to 40% by weight, boron was 10 to 50% by weight, and Especially 20
Sinters present in a proportion of 4040% by weight showed excellent properties.

That is, if the amount of aluminum is less than 10% by weight, the hardness and toughness decrease, and the aluminum cannot be used as a structural material.
If it exceeds 50% by weight, the hardness is reduced, and when used as a cutting tool or a wear-resistant material, the wear property is reduced. 10 boron
If the amount is less than 10% by weight, the hardness becomes almost the same as that of a normal aluminum oxide sintered body, and there is no effect of adding boron.

According to the present invention, the needle-like substance is used as a raw material, and in particular, aluminum oxide crystal particles having an aspect ratio of 1.5 or more are present in a sintered body at a rate of 5% by volume or more, particularly 20% by volume or more, thereby achieving a higher level. Toughness can be improved.

(Operation) The following two factors can be considered as reasons why the above-mentioned sintered body has high strength, high toughness and high hardness.

Improvement of particle bonding strength During sintering, part or all of aluminum boride is decomposed to produce active aluminum and boron. New particles which are firmly bonded by the aluminum and boron are formed, and the particle bonding force is improved.

Complexity of particle shape In conventional alumina, many crystal particles are almost spherical,
Destruction was occurring from those grain boundaries. In the material of the present invention, the particles are sintered together with the decomposition generation reaction described in the above, so that the particle shape is complicated and complicated. Therefore, the development of new cracks is prevented, and as a result, the fracture toughness is improved. The addition of acicular alumina or a substance that produces acicular alumina by decomposition is further promoted to complicate the particle shape, and has a complicated structure of acicular crystals, thereby further improving toughness.

In addition, by the addition of the sintering aid described above, the decomposition reaction is further promoted, and a liquid phase component reduced by the volatilization of boron is supplied to thereby stably obtain a high-density sintered body. .

 Hereinafter, the following example of the present invention will be described.

(Example 1) Al ₂ O ₃ powder (average particle size of 1 μm or less, purity 9
9.9%), AlB ₁₂ powder (average particle size 2μm) and acicular Al
Table 1 shows ₂ O ₃ (average particle size 0.7 μm, average aspect ratio 15), acicular aluminum borate (average particle size 0.7 μm, average aspect ratio 20) and sintering aid having an average particle size of 1 to 2 μm. And then mixed and pulverized for 12 hours with a rotary mill. The slurry after mixing was dried to obtain a raw material for hot pressing.

This raw material is filled in a carbon mold and heated at 1680 ° C for 1 hour for 30 hours.
Hot press firing was performed at a pressure of 0 kg / cm ² to prepare a bending test piece based on JIS.

Each obtained sample was polished to obtain a three-point bending strength based on JIS1601, and polished to a mirror surface to obtain K1 by IM method.
c and Vickers hardness were further measured.

In addition, ICP analysis was performed on the sintered body, the amounts of Al and B were quantified, and the content of particles having an aspect ratio of 1.5 or more in the sintered body was determined by surface analysis from an electron micrograph.

 The results are shown in Table 1.

According to Table 1, a sample consisting only of aluminum boride
Compared with the comparative example of No. 1, the samples No. ₂ to 7 to which the Al ₂ O ₃ component and the sintering aid were added showed significantly improved characteristics.

In addition, in Samples 9 to 15 to which acicular aluminum borate was added as an Al ₂ O ₃ component, the characteristics were improved except for Sample No. 9 in which the amount of boron was too large and Sample No. 15 in which the amount of boron was too small.

AlB ₁₂ and Al without sintering aid in Sample Nos. 16 to 24
_For sample No. 16 composed of a combination of ₂ O _{3, as} the sintering aid was added, the characteristics improved, but the amount of the aid was 8 wt 9 according to a comparison between sample Nos. 40 to 54, Al ₂ O ₃ Al ₂ O ₃ as a component
Needle-like as Al ₂ O ₃ component than sample No. 40-54 using particles
It is understood that the use of Al ₂ O ₃ has higher properties, especially toughness.

(Effects of the Invention) As described in detail above, according to the method for producing an aluminum oxide-based sintered body of the present invention, part or all of aluminum boride is decomposed to generate active aluminum and boron, which are strongly bonded. New particles are formed, the particle bonding force is improved, and the particle shape becomes complicated and intricate, so that the toughness is improved, and the obtained aluminum oxide-based composite sintered body has high hardness. And high toughness can be imparted, thereby expanding the field of application as various body wear parts and structural parts including tools.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C04B 35/00-35/22

Claims (2)

(57) [Claims] 1. An aluminum boride of 15 to 95% by weight and aluminum oxide or a substance capable of producing aluminum oxide by calcination are added at a ratio of 3 to 90% by weight in terms of aluminum oxide to be produced. , Ca, Cr, Mn,
At least one of Fe, Co, Ni and Group IIIa element of the periodic table is mixed at a ratio of 0.1 to 8% by weight in terms of oxide, and after molding, firing at a temperature of 1400 to 1900 ° C. A method for producing an aluminum oxide-based sintered body, characterized in that: 2. The method for producing an aluminum oxide sintered body according to claim 1, wherein all or a part of said aluminum oxide or a substance which forms aluminum oxide by firing is made of acicular crystal grains.