JPH04132658A - Ceramic sintered body and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain the subject sintered compact, excellent in hardness, toughness and abrasion resistance and useful as an abrasion-resistant material or material for cutting tools by the presence of specific needlelike grains in a sintered compact composed of Al, B, O and inevitable impurities at a prescribed ratio. CONSTITUTION:A ceramic sintered compact is obtained by the presence of needlelike grains, composed of at least Al, B and O and having >=1.5 aspect ratio in a sintered compact (e.g. a sintered compact composed of Al2O3, AlB12 and aluminum borate at a prescribed ratio) composed of 30-45wt.% Al, 3.0-50wt.% B and the remainder of O and inevitable impurities in the total amount thereof.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to ceramics containing aluminum oxide or aluminum borate as a main component, and more specifically to wear-resistant materials with excellent wear resistance and toughness and for use in cutting tools. The present invention relates to a ceramic sintered body suitable as a material and a method for manufacturing the same.

(Prior art and its problems) Ceramic materials such as aluminum oxide (AI 203) sintered bodies have traditionally been superior in mechanical properties such as wear resistance compared to metal materials. It is used in various structural parts as an alternative to metal materials. Furthermore, various improvements have been proposed for A l 20 ]-based sintered bodies by combining them with other ceramics.

However, in recent years, ceramics have been required to have even higher properties, and in particular, have been required to have higher toughness.

On the other hand, there are demands for improved wear resistance and high-temperature properties in Al20:1 sintered bodies, and titanium boride, which is known as a material with particularly excellent wear resistance among ceramics, can meet these demands. Borides such as zirconium boride and A
Various research and developments are being actively conducted, such as adding it to 1□03.

Although ceramics mainly composed of borides have high hardness, their strength and toughness are low and their application fields are limited.

(Problem to be Solved by the Invention) Therefore, the present inventors first mixed aluminum oxide powder or whiskers and aluminum borate whiskers with aluminum boride in a specific ratio, and after each firing, the oxidation We discovered that by leaving aluminum whiskers in the sintered body, a unique material with high toughness while maintaining high hardness can be obtained (
(Patent Application No. 1-312735).

However, when aluminum borate whiskers are mixed into the raw material, there is a problem in that the whiskers in the raw material become entangled with each other and the moldability of the raw material is significantly reduced. Furthermore, recently, the influence of whiskers on the human body has become a problem, and it has become necessary to take strict measures against dust in the manufacturing process. All of these have been major problems in manufacturing specific products.

(Means for Solving the Problems) Therefore, the present inventors further investigated these problems and found that a specific It has been found that by selecting firing conditions, acicular particles of a compound consisting of aluminum, boron, and oxygen can be produced in the sintered body without adding whiskers to the raw material.

That is, the present invention involves firing a molded body in which aluminum oxide powder, aluminum boride powder, and aluminum borate powder are mixed in a specific quantitative ratio, and in some cases, carbon powder or an oxide of an element of group 111a of the periodic table is mixed in a specific ratio. It is characterized by obtaining a specific material having high toughness while maintaining high hardness by producing acicular particles with an aspect ratio of 1.5 or more made of aluminum, boron, and oxygen, and further The sintered body is a sintered body containing 30 to 45% by weight of aluminum and 3.0 to 50% by weight of boron, the sintered body containing at least aluminum, boron, and oxygen. It is characterized by the presence of acicular particles having an aspect ratio of 1.5 or more.

The present invention will be explained in detail below.

The method for manufacturing a ceramic sintered body of the present invention is comprised of the steps of preparing raw materials, molding, and firing, which will be described in detail below.

(Preparation of raw materials) As starting materials, aluminum oxide powder, aluminum boride 45) powder, and aluminum borate powder are used.

The aluminum oxide powder has an average particle size of 3 μm or less, especially
It is desirable to use fine grains of tm or less, and the aluminum boride powder has an average particle diameter of 200 mesh or less, preferably 3 .mu.m or less, preferably 1 .mu.m or more.

Aluminum boride generally has the chemical formula AlB1□, AlB2
Although the existence of these is recognized, any of them can be used in the present invention, and aluminum boride having a Jl-stoichiometric composition may be used, or a mixture thereof may be used.

Some currently commercially available AlB12 partially contains AIBlo, but no problem occurs in that case either.

However, AIBz is A I B +. It is preferable to use AlB12 because it is more unstable and causes oxidation and heat generation during mixing. Further, the amount of boron in the sintered body can be adjusted by adding boron powder as necessary.

On the other hand, the aluminum borate powder is 9A+.

03.2 B2O3 (AI+aB403:+) or 2
One having the chemical formula of AI203 .B2O3 (AI4B209) is used. It should be noted that these powders preferably have an average particle size of 2 μm or less, particularly O02 to 0.7 μm. This is because when the average grain size is 2 μm or less, grain growth during sintering does not become excessive and high bending strength can be maintained, and when it is larger than 2 μm, the grain growth of crystal grains during sintering is significant. This is because it becomes difficult to control the particle size, variations in toughness occur, and boundary wear on the flank surface tends to increase when used as a cutting tool.

Each of the above-mentioned raw material powders is within the range surrounded by the line segment of point A-B-C-D-E-F-A in Fig. 1 showing the ternary diagram of aluminum oxide, aluminum boride l1, and aluminum borate. It is important to mix it with

In addition, the composition at each point is expressed as (x, y, z) when each point is expressed as (x, y, z), with the weight ratio of aluminum oxide as X, aluminum boride as y, and aluminum borate as l:
A (90,10,0), B (90,0,10),
C(20080), D C0,10,90), E(0
, 6040) , F (40,60,0).

The mixing ratio was set within the above range for line segment AB.
If there is more aluminum oxide, the toughness of the sintered body will decrease,
This is because desired characteristics cannot be obtained. Furthermore, line segment C
This is because if the amount of aluminum borate is greater than D, the hardness of the sintered body will decrease. If the aluminum boride content is greater than the line segment EF, the firing temperature required to obtain a dense sintered body will be high, making it difficult to generate sword-shaped particles.

The blending ratio of aluminum boride, aluminum borate, and aluminum oxide can be set arbitrarily within the range surrounded by the line segment ABCDEFA in FIG. 1, but more preferably within the range surrounded by the line C; HI J G in FIG. It is best to mix within the range enclosed by minutes. Note that each point is G (80
10,10), H(10,10,80), 1 (1
0,50,40), J(40,50,10).

According to the present invention, in order to improve the sinterability of the mixed powder, 0.1 to 8% by weight, especially 0.3% by weight of an oxide of an element of Group 1IIa of the periodic table, in terms of oxide, is added. It is also possible to mix carbon powder in a proportion of 5% to 5% by weight, and 2% by weight or less for the purpose of suppressing grain growth and improving the strength of the sintered body.

The reason for limiting the amount of the additive described in 1- is that the amount of the oxide is 0.
If it is less than 1% by weight, it is insufficient to fully control sintering, and if it exceeds 8% by weight, voids will occur in the sintered body, which is not desirable. In addition, the elements of group 111a of the periodic table include Yb, Nd, Er, Ce, SmXY, Gd, and Dy.
and La, and the addition of Dy, Y, and Nd is particularly effective.

Further, if the amount of carbon powder added exceeds 2% by weight, voids remain in the sintered body and the strength decreases.

(Molding) Next, the aluminum boride powder, aluminum oxide powder, aluminum borate powder, and optionally carbon powder and sintering aid are mixed in a predetermined ratio, and then molded into a desired shape by a known molding means. As the shaping means, for example, press molding, extrusion molding, injection molding, casting molding, cold isostatic pressing, etc. are employed. Note that during molding, known binders and dispersants may be used to improve moldability. If desired, the binder is removed from these molded bodies in vacuum or in an inert gas such as nitrogen gas or argon gas, and then firing is performed.

(Firing) Firing may be performed under the temperature conditions described below in a reducing atmosphere in which an inert gas such as Ar or He or carbon exists, and in a pressurized or reduced pressure atmosphere thereof. As the firing method, normal pressure firing, hot pressing method, hot isostatic pressing method (HIP method), etc. are applied. After creating a sintered body with a ratio of 96% or more, an additional 100%
Hot isostatic firing may be performed under high pressure equal to or higher than atmospheric pressure.

The maximum holding temperature during firing is suitably 1,300 to 1,900°C, but optimally in the range of 1,500 to 1,750°C.

According to the present invention, whiskers made of boron, oxygen, and aluminum are produced in the sintered body by this firing, but in order to promote whisker production,
At least once during heating or cooling between 1000°C and the maximum holding temperature, set a heating rate or cooling rate of 25°C/min or less, or 1
Intermediate holding for 5 minutes or more is performed at least once during heating or cooling at a temperature from 000°C to the maximum holding temperature. According to such an operation, 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 newly generate aluminum borate and aluminum oxide. The newly generated aluminum borate and the added aluminum borate grow into acicular shapes and generate whiskers during the heating process or cooling process under the above-mentioned conditions.

The sintered body obtained by the above production method consists of aluminum, boron, oxygen, and in some cases carbon, and elements of Group Ma of the periodic table as constituent elements, but the crystal structure has an aluminum oxide or aluminum borate crystal phase. Acicular particles consisting of aluminum, boron, and oxygen are dispersed between the crystal phases, and boron oxide, aluminum borate, or glassy substances produced by them are present at the grain boundaries of the crystal phase. It is a complex complex.

According to the present invention, the optimum proportions of aluminum and boron were studied in terms of the characteristics of the sintered body, and it was found that aluminum was 30 to 45% by weight, 35 to 40% by weight, and boron was 3.0 to 50% by weight. % by weight, especially 20-40% by weight
The sintered body exhibits excellent properties, and if it contains carbon, it has a double foot% or less, and if it contains elements from group 1a of the periodic table, its oxide equivalent amount is 0. It is preferably 2 to 8% by weight or less.

That is, if the amount of aluminum is less than 0% 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 50% by weight, the hardness decreases and the abrasion resistance decreases when used as a cutting tool or a wear-resistant material. If the amount of boron is less than 10% 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 if it exceeds 50% by weight, the toughness will decrease.

Note that the oxide equivalent amounts of carbon and Group 111a elements of the periodic table are based on the same reasons as described above.

(Function) (1) The reason why the sintered body of the present invention described above has high strength, high toughness, and high hardness can be attributed to the following two factors.

■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 aluminum and boron, and the bonding force of the particles is improved.
◇The acicular aluminum borate produced in the composite reinforcement sintering process has a Young's modulus as high as that of aluminum oxide, and its theoretical strength is equivalent to that of alumina. For this reason, the toughness can be increased in the same manner as in the case of compounding acicular alumina.

Also, elements of group 111a of the periodic table, especially oy, y, Nc
By adding 1, decomposition of aluminum borate whiskers can be suppressed.

The invention will now be explained with the following examples.

(Example 1) As a raw material, A1□03 powder (average particle size of 111 m or less,
(purity 99.9% or more) and AIB+□ powder (average particle size 2
11m), aluminum borate (average particle size 07μm),
Using an oxide powder of an element of group A of the periodic table with an average diameter of 1 to 2 μm and carbon powder with an average particle diameter of 0.371 m, they were weighed at the proportions shown in Table 1 and mixed for 12 hours in a rotary mill. Shattered. The slurry after mixing was dried and used as a raw material for bot press.

This raw material was filled into a carbon mold, and fired in a press under the firing conditions of No.
A bending test piece was created based on the above.

Further, samples No. 35 to 4I in Table 1 were fired under the firing conditions of Nos. 1 to 2 shown in FIGS. 2 and 3.

Further, carbon powder was added to samples Nos. /11 to 43, and oxides of elements of group 111a of the periodic table were added to samples No. 44.45, and fired in the same manner as above.

ICP analysis was performed on each of the obtained sintered bodies to quantify the amounts of alumina J1, boron, and oxygen, and the presence or absence of whiskers with an aspect ratio of 1.5 or more was observed from electron micrographs.

In addition, as a characteristic evaluation, each sintered body was polished to JIS]6
The three-point bending strength based on 01 was measured, the Klc was measured by the IM method after mirror polishing, and the Vickers hardness was measured.

The results are shown in Table 1.

(Left below) According to Table 1, the composition is at points AB-C-D in Figure 1.
-E-F-A range exhibits excellent properties, and especially those with a composition in the range of point G -Hl-J-G have a bending strength of 70 kg/mm2 or more and a toughness of 6 MP.
A-m"" or more was achieved.

Furthermore, in a comparison of sample No. 12.35.36.37, it was found that the slower the cooling rate during firing, the higher the characteristics. Also, in the cooling process, sample No. 38
．． It has been found that similarly high properties can be obtained by holding the temperature at a temperature lower than the firing temperature, such as 39.40.

(Effects of the Invention) As detailed above, the sintered body of the present invention is a composite sintered body mainly composed of aluminum oxide, and can be imparted with high toughness while maintaining high hardness. This makes it possible to expand the field of application as wear parts for various bodies such as tools, structural parts, etc.

[Brief explanation of drawings]

FIG. 1 is a ternary diagram showing the composition of each powder of aluminum oxide, aluminum boride, and aluminum borate, and FIGS. 2 and 3 are diagrams showing firing conditions depending on temperature and time.

Claims (4)

[Claims] (1) A sintered body consisting of 30 to 45% by weight of aluminum, 3.0 to 50% by weight of boron, and the balance being oxygen and unavoidable impurities, the sintered body containing at least aluminum, boron, and The aspect ratio of oxygen is 1.
A ceramic sintered body characterized by the presence of 5 or more acicular particles. (2) 30-45% by weight of aluminum, 3.0-50% by weight of boron, 0.1-8% by weight of Group IIIa elements of the periodic table in terms of oxides, and 2% by weight or less of carbon in the total amount , a sintered body in which the remainder is oxygen and unavoidable impurities, the sintered body being characterized by the presence of acicular particles having an aspect ratio of 1.5 or more and consisting of at least aluminum, boron, and oxygen. Sintered body. (3) aluminum oxide powder, aluminum boride powder,
The weight ratio of each powder of aluminum borate powder is x
, y and z, each powder corresponds to the following points A, B, C, D, E, F x y z A (90, 10, 0) B (90, 0, 10 ) C (20, 0, 80) D ( 0, 10, 90) E ( 0, 60, 40) F (40, 60, 0) Line segment connecting A-B-C-D-E-F-A The molded body mixed within the range surrounded by is fired in an inert or reducing atmosphere to grow acicular particles with an aspect ratio of 1.5 or more consisting of at least aluminum, boron, and oxygen in the sintered body. A method for producing a ceramic sintered body characterized by the following. (4) aluminum oxide powder, aluminum boride powder,
The weight ratio of each powder of aluminum borate powder is x
, y and z, each powder corresponds to the following points A, B, C, D, E, F x y z A (90, 10, 0) B (90, 0, 10 ) C (20, 0, 80) D ( 0, 10, 90) E ( 0, 60, 40) F (40, 60, 0) Line segment connecting A-B-C-D-E-F-A is within the range surrounded by , and the periodic table group IIIa element oxide powder is 0.
．． 1 to 8% by weight and carbon powder mixed in a range of 2% by weight or less is fired in an inert or reducing atmosphere, and the sintered body is made of at least aluminum, boron, and oxygen, and has an aspect ratio of 1. A method for producing a ceramic sintered body characterized by growing acicular particles of .5 or more.