JPH0437652A - Ceramics sintered body - Google Patents

Abstract

PURPOSE:To provide the above sintered body having uniform characteristics and excellent hardness, toughness, etc., by constituting the sintered body of a main phase contg. Al2O3 and an auxiliary phase contg. boron, oxygen and carbon and specifying the contents of Al, boron and carbon. CONSTITUTION:This ceramic sintered body is constituted of aluminum oxide or the aluminum oxide and aluminum boride as the main phase and the auxiliary phase contg. the boron, oxygen and carbon. In addition, the aluminum exists at a ratio of 10 to 50wt.%, the boron at 1.5 to 67wt.% and the carbon at 0.05 to 8wt.% in the total weight of the sintered body. This ceramic sintered body is produced by the method of first mixing the aluminum oxide powder, the aluminum boride powder and carbon powder at such ratios at which the above- mentiond sintered body is obtainable. The mixture is then molded to a desired shape and the molding is calcined in an inert gas. The resulted sintered body is adequately used as materials for tools and materials for various kinds of industrial mechanical parts, etc.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to ceramics containing aluminum oxide or aluminum oxide and aluminum borate,
More specifically, the present invention relates to a ceramic sintered body that has excellent wear resistance and toughness and is suitable as a variety of structural materials, especially cutting tools.

(Prior art and its problems) Ceramic materials such as alumina (A IZ O3) sintered bodies have traditionally had superior mechanical properties such as wear resistance compared to metal materials. It is used in various structural parts as an alternative to metal materials.

However, in recent years, ceramics have been required to have even higher properties, and it has been proposed to improve various properties of alumina sintered bodies by combining them with other ceramics.

In addition, research and development of borides such as titanium boride and zirconium boride is being actively conducted as materials with particularly excellent wear resistance among ceramics.

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

Titanium boride has high hardness and good thermal conductivity, so it was thought to be a promising material for cutting tools, but it has not been put into practical use because no method has been found to improve its toughness.

Since zirconium boride has low reactivity with metals, it is expected to be used as crucibles for molten metal, but its low strength limits its application as a structural material.

Furthermore, although aluminum boride is a material with superior hardness compared to aluminum oxide, there are many unknown aspects, and a sintered body with excellent properties has not yet been developed.

Therefore, the present inventors first selected aluminum boride from among the borides mentioned above and proceeded with studies on improving its sinterability and properties, and found that by mixing aluminum oxide with aluminum boride, He proposed that by firing, a part or all of the aluminum boride is decomposed and aluminum oxide is produced, thereby producing ceramics that maintain high hardness and high toughness (Japanese Patent Application No. No. 312735). However, boron in this material is easily volatilized during sintering, making it difficult to control the composition of the sintered body, resulting in unstable properties, especially when creating a large sintered body. There was a problem in that each element, particularly boron, segregated, resulting in variations in properties inside and outside the sintered body.

(Means for Solving the Problems) Therefore, the present inventors further investigated the sinterability of the system proposed earlier and the improvement of its characteristics. It has been found that by adding in a certain proportion, a sintered body having homogeneous properties as a whole and high hardness and toughness can be obtained even in a large product.

That is, the sintered body of the present invention is a ceramic sintered body having a main phase of aluminum oxide or aluminum oxide and aluminum borate, and a subphase containing at least boron, oxygen, and carbon; Aluminum is 10 to 50% by weight and boron is 1.5 to 67% by weight.
, carbon is present in a proportion of 0.05 to 8% by weight. Furthermore, in the above configuration, needle-like particles are present in the sintered body, thereby further improving the toughness of the sintered body.

The present invention will be explained in detail below.

In the ceramic sintered body of the present invention, the main phase consists of aluminum oxide or aluminum oxide and aluminum borate in terms of structure, and the elements aluminum, boron, oxygen, and carbon exist in the grain boundaries, and in terms of composition, A major feature of these sintered bodies is that each element constituting the entire sintered body exists in a specific proportion.

Specifically, Otsuji contains 10 to 50% by weight of aluminum, especially 20 to 40% by weight, and 1.5 to 67% by weight of boron in the sintered body.
, especially 20-40 weight percent, carbon 0.05-8 weight percent,
In particular, from 1 to 3% by weight, the remainder being substantially constituted by oxygen. By setting the amount of each element within the above range, a sintered body can be obtained that has high strength, hardness, and toughness even if it is a large product, and has consistent strength, hardness, and toughness both inside and outside.

That is, if the amount of aluminum is less than 10% by weight, the hardness and toughness will decrease and it will no longer be possible to use it as a structural material.
When it exceeds 0% by weight, the hardness decreases and the abrasion resistance decreases when used as a cutting tool or wear-resistant material. The amount of boron is 1
If it is less than 0% by weight, the hardness will be on the same level as a normal aluminum oxide sintered body, and the addition of boron will have no effect, and 50% by weight.
Exceeding this will reduce toughness. Furthermore, if the carbon content is less than 0.05% by weight, the elements tend to be unevenly distributed within the sintered body, and variations in properties tend to occur inside and outside the sintered body.
This is because if it is less than 8% by weight, the sinterability will deteriorate and a dense body will not be obtained.

Furthermore, according to the present invention, the presence of acicular crystal grains in the sintered body greatly improves the toughness of the sintered body. Specifically, the aspect ratio is 1.5
By having the above-mentioned 11-shaped particles present in a proportion of 3 to 75% by volume, particularly 10 to 50% by volume, toughness can be improved while maintaining high hardness, and according to the examples described later, the toughness can be increased up to 10 MPa. -m"" excellent toughness can be obtained, and aluminum oxide or aluminum borate is suitable as the component forming the acicular particles.

An example of a specific manufacturing method for manufacturing the ceramic sintered body of the present invention will be described. First, the manufacturing process includes three steps: preparation of raw materials, molding, and firing.

First, in preparing the raw materials, aluminum boride powder, aluminum oxide powder, compound powder that produces aluminum oxide when fired, and carbon powder or a compound that produces carbon when fired are used as starting materials.

The aluminum boride powder is a powder with an average particle size of 200 mesh or less, preferably 3 μm or less, optimally 1 μm or less, and generally has the chemical formula AIB, 2, Al82, or even aluminum boride with a non-stoichiometric composition. often,
It may also be a mixture of these. Currently commercially available AlB12 is partially AIB+. There are some that include , but there is no problem in that case.

On the other hand, as the aluminum oxide powder or the compound powder that produces aluminum oxide upon firing, it is desirable to use fine particles with an average particle size of 3 μm or less, particularly 1 μm or less. In addition, examples of substances that generate aluminum oxide by firing include metal aluminum, aluminum borate, etc. Aluminum borate is 9Al□03.
It is represented by the chemical formula B2O3 or 2Al□03.2B203.

In addition, in the present invention, when acicular particles are present in the sintered body, acicular crystal aluminum oxide,
Alternatively, acicular aluminum borate having the chemical formula 9A1203/2B203 may be added as a substance that generates acicular aluminum oxide upon heating during sintering.

The average diameter (breadth axis) of these acicular substances is preferably 2 μm or less, particularly 0.2 to 0.7 μm, and the average aspect ratio expressed as major axis/breadth axis is 3 to 1.
00, especially those of 10 to 30 are preferably used. The reason for specifying the above average diameter to be 2 μm or less is that grain growth during sintering does not become excessive and high flexural strength can be maintained.
If it is larger than 2 μm, the grain growth of the crystal grains during sintering will be significant, making it difficult to control the grain size, causing variations in toughness, and also tending to increase boundary wear on the flank when used as a cutting tool. It's for a reason.

On the other hand, if the average aspect ratio is smaller than 3, the effect of improving the toughness is small because the effect of fiber reinforcement is small, and if it is larger than 100, the raw material is difficult to handle and cannot be uniformly dispersed, so the toughness tends to decrease. However, even in this case, it can be used without problems if the whiskers are mixed while being crushed in part.

The above-mentioned aluminum boride, aluminum oxide component and carbon component are the aluminum, boron, and carbon components in the final sintered body.
They are appropriately mixed so that the amounts of carbon and oxygen are in the proportions described above. According to these raw material powders, it is difficult to partially determine the proportion of the starting raw materials because a decomposition reaction occurs during calcination, but it is preferable to contain aluminum boride powder in an amount of 5 to 95% by weight, preferably 30% by weight. ~80% by weight, aluminum oxide powder or a substance that produces aluminum oxide by firing is 3 to 90% by weight, preferably 20 to 70% by weight in terms of aluminum oxide, and carbon powder or a substance that produces carbon powder by firing The compound is mixed in an amount of 0.05 to 8 parts by weight, particularly 1 to 3 parts by weight, in terms of carbon, per 100 parts by weight of the mixture of aluminum boride and aluminum oxide components.

The acicular particles added in place of the aluminum oxide powder for the purpose of increasing toughness are desirably contained in a ratio of 3 to 75% by volume of the total amount as particles having an aspect ratio of 1.5 or more.

Furthermore, boron oxide can be added to the above mixture at a rate of 20 weight percent or less for the purpose of improving sinterability.

Next, the aluminum boride, aluminum oxide component, and carbon component are mixed and then molded into a desired shape by a well-known molding means. As the shaping means, for example, press molding, extrusion molding, injection molding, cast molding, cold isostatic pressing, etc. are used. Known binders and dispersants may be used to improve moldability.

Thereafter, these molded bodies are degreased in vacuum or in an inert gas such as nitrogen gas or argon gas, if desired, and then fired.

Firing is performed at a temperature of 1200 to 1900°C using Ar, He,
The reaction may be carried out for 0.5 to 6.0 hours in a reducing atmosphere in which an inert gas such as carbon or carbon is present, and in a pressurized or reduced pressure atmosphere thereof. Firing methods include normal pressure firing, hot press method, and hot isostatic pressing method (HIP method).
In order to obtain a particularly high-density sintered body, a sintered body with a theoretical density ratio of 96% or more may be prepared by ordinary firing or real press method, and then hot isostatic pressure firing may be performed.

In addition, when hot-press firing is performed using a carbon mold during firing, the carbon component in the sintered body may be composed of carbon from the carbon mold, so the carbon component in the starting material must be adjusted appropriately. It is necessary to.

According to the above firing, a part or most of the aluminum boride in the raw material decomposes into aluminum and boron, and reacts with oxygen in the system to produce aluminum oxide or aluminum borate, and further aluminum, oxygen, Generates a subphase consisting of boron. On the other hand, aluminum oxide in the raw material remains as it is and is sintered.

On the other hand, when aluminum borate is used instead of aluminum oxide, it partially separates into aluminum oxide and boron oxide at around 1400°C, producing the same effect as when each is added. On the other hand, when aluminum metal is used, it reacts with oxygen or boron in the system to produce aluminum boride or aluminum oxide such as AlB2, producing the same effect as when each is added.

In the above firing process, the boron oxide produced by the separation and reaction of each compound is emitted once at temperatures above 1500°C.
Both exhibit the effect of sintering aids and promote high densification of the sintered body. However, if a large amount of boron oxide is contained in the sintered body, the hardness and strength will decrease, so it is desirable that the boron oxide content in the sintered body is 20% by weight or less.

According to the manufacturing method described above, as shown in FIGS. 1 and 2, the crystalline phase is aluminum oxide or a main phase consisting of aluminum oxide and aluminum borate, and glass consisting of aluminum, boron, oxygen, and carbon. A subphase consisting of a crystalline phase such as 870 or 870 is formed.

(Function) The following three factors are considered to be the reason why the ceramic sintered body of the present invention described above has high strength, high toughness, and high hardness.

■Improvement of particle bonding strength During sintering, part or all of aluminum boride decomposes and active aluminum and boron are generated.

New particles are formed that are strongly bonded to each other by this aluminum and boron, and the bonding force of the particles is improved.

■Complicated particle shape In conventional aluminum oxide, many of the crystal grains were close to spherical, and destruction occurred from the grain boundaries, but in the sintered body of the present invention, the crystal particles were destroyed along with the decomposition and formation reaction described in (■). Because it is sintered, the particles have a complex shape. Therefore, new rack development is prevented, and as a result, fracture toughness is improved. Furthermore, if acicular aluminum oxide or a substance that generates acicular aluminum oxide through decomposition is added, the complexity of the particle shape will be further promoted, and the toughness will be dramatically improved because the acicular crystals will have an intricate structure. improves.

■ Promotion of gasification of boron oxide The boron oxide produced by the separation and reaction of each compound in the above firing process evaporates at temperatures above 1500°C.
Both exhibit the effect of sintering aids and promote high densification of the sintered body. However, in large products, constituent elements, especially boron oxide as a compound, are unevenly distributed in the sintered body, resulting in uneven hardness and strength characteristics, especially between the inside and outside. The presence of carbon powder promotes the gasification of boron oxide in a reducing atmosphere, and the conversion of aluminum borate to A I 20 :1 progresses.

This reduces the segregation of components and provides a sintered body with uniform properties.

The invention will now be explained with the following examples.

(Example 1) As raw materials, aluminum oxide powder (average particle size 1 μm or less, purity 99.9% or more) and AIB+2 powder (particle size 2
00 mesh or less), acicular aluminum oxide (average particle size 0.7 μm, average aspect ratio 15), and aluminum borate (average particle size 0.7 μm, average aspect ratio 20)
Carbon powder with an average particle size of 0 μm was weighed in the proportions shown in Table 1, and then mixed and ground in a rotary mill for 12 hours. The slurry after mixing was dried and used as a raw material for Hontopress. Fill a carbon mold with this raw material and
Hot press firing was performed at 800°C for 1 hour at a pressure of 300 kg/cm2.

Each of the obtained samples was polished to a mirror-like state, and the Klc and Vickers hardness of the inside and surrounding parts of the sintered body were measured by the IM method.

In addition, ICP analysis was performed on the sintered body, and A1, B and C
The content of particles having an aspect ratio of 1.5 or more was determined by surface analysis from electron micrographs.

The results are shown in Table 1.

Among the samples in Table 1, the X-ray diffraction patterns of No. 2.3 are shown in FIG. 1 and FIG. 2, respectively.

As is clear from Figures 1 and 2, a crystalline phase of aluminum oxide is observed in the sintered body, and as the carbon content increases, the crystalline phase of aluminum oxide and aluminum borate increases as shown in Figure 2. Seed crystalline phases were mainly detected.

According to Table 1, sample N to which no carbon was added.

Material N containing large amounts of 1, Nα24, and A1
o, 13, there were differences in characteristics between the inside and the periphery.

In addition, even in the system with carbon added, sample N
In a sintered body in which the carbon content exceeds 8% by weight, such as No. 7.20, poor sintering resulted in deterioration of properties such as bending strength.

Sample No. 8.9, in which no acicular particles were added to the sintered body of the present invention, had the characteristics of a -C-like aluminum oxide sintered body (hardness of 17.0 MPa or less, toughness of 3.0 MPa).
−m”” or less).

Sample No. 15 consisting of AIB, □ alone had insufficient sinterability and poor properties.

In the systems containing acicular particles, it was confirmed that the toughness was improved in all cases, but the hardness was low in sample pit 13 where the amount of aluminum exceeded 50% by weight.

In addition, sample No. in which the amount of boron is less than 1.5% by weight,
At 23, the hardness is comparable to that of aluminum oxide alone,
Sample No. 18, which contained more than 67% by weight, had high hardness but deteriorated flexural strength and toughness.

Compared to these comparative examples, the sintered bodies of the present invention in which carbon was added and each element was within the range of the present invention were able to suppress the difference in properties in both hardness and toughness to within 20%. In the samples of the present invention, sintered bodies with excellent properties with no variation in properties inside and outside were obtained, and the bending strength was 60.
kg/mm2 or more, toughness 4. Achieves OMPa-m"' or higher, Pinkers hardness of 1700 kg/mm2 or higher, and toughness of 5 to 10.5 M by incorporating acicular particles.
Pa-m"2 or more was achieved.

(Effects of the Invention) As detailed above, according to the present invention, by further containing carbon in a sintered body composed of aluminum, boron, and oxygen and having aluminum oxide as the main phase, high hardness The internal and external properties of the sintered body can be made uniform while maintaining toughness.

Thereby, the range of application as a material for various large-sized industrial machine parts including tool materials can be further expanded.

[Brief explanation of drawings]

1 and 2 both show the X-ray diffraction pattern of the ceramic sintered body of the present invention, and FIG. 1 shows the
Sample No. 2 and FIG. 2 are those of sample No. 3. Figure 1 Figure 2 Patent applicant (663) Kyocera Corporation 20 (°)

Claims (2)

[Claims] (1) A ceramic sintered body composed of aluminum oxide, or aluminum oxide and aluminum borate as the main phase, and a subphase containing at least boron, oxygen, and carbon, and the total amount of the sintered body contains 10 to 50% aluminum.
% by weight, boron 1.5-67% by weight, carbon 0.05-67% by weight
A ceramic sintered body characterized by being present in a proportion of 8% by weight. (2) The ceramic sintered body according to claim 1, wherein acicular crystal grains are present in the sintered body.