JPH03174366A - Boride/alumina-based sintered body and production thereof - Google Patents

Abstract

PURPOSE:To enhance strength by mixing boride of one or more kinds selected from among groups IVa, Va, VIa metallic elements in the periodic table, two or more kinds of compds. selected from among these metallic elements, boron and O2 and Al2O3 at the ratio of specified volume and molding the mixture and roasting the molded body. CONSTITUTION:A powdery raw material is obtained by mixing 30-95vol.% (hereinafter shown in %) boride of one or more kinds of groups IVa, Va, VIa metallic elements such as TiB2 having <=3mum mean particle diameter, <=20% compd. of two or more kinds selected from among the above-mentioned metallic elements, boron and O2 such as B2O3 having <=2mum mean particle diameter and 5-70% Al2O3 powder having <=3mum mean particle diameter or substance such as 9Al2O3.B2O3 wherein Al2O3 is produced by roasting and one or all parts thereof consist of acicular particles and thereafter grinding the mixture. This powdery raw material is pressure-molded and thereafter the molded body is roasted at 1400-1900 deg.C in the reductive atmosphere wherein inert gas such as Ar or carbon is present. Thereby a boride/Al2O3-based sintered body is obtained wherein 5% or more consist of a circular particles having >=1.5 aspect ratio.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention relates to ceramics whose main components are metal elements boride and aluminum oxide, and more specifically, ceramics with excellent wear resistance and toughness, particularly for use in iron manufacturing and refining. Related jigs and tools, jigs for nonferrous refined aluminum molten metal, and ceramics suitable for cutting tools.

[Prior art and its problems 1 Ceramic materials such as alumina (AlzCh) sintered bodies have traditionally been used as metal materials because they have superior mechanical properties such as wear resistance compared to metal materials. It is used as an alternative material for various structural parts.

However, in recent years, ceramics have been required to have even higher properties, and various improvements have been proposed for aluminum sintered bodies by combining them with other ceramics.

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

[Problem to be Solved by the Invention 1] However, 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.

In recent years, attempts have been made to mix it with metal and sinter it to improve its toughness, but this method has the problem that the strength at high temperatures drops dramatically and the properties of metal borides cannot be utilized. there were.

Furthermore, 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.

[Means for Solving the Problems 1] As a result of repeated studies, the inventor solved the above problems by adding aluminum oxide and a small amount of boron oxide as a binder for boride. I found out that I can get it.

Furthermore, the present inventors solved the above-mentioned drawbacks in terms of toughness by forming acicular particles of aluminum oxide added to boride, a metal element, and obtained a material that maintains high hardness and toughness even at high temperatures. Ta.

That is, the present invention uses Va and Va of the periodic table as a manufacturing method.
, a mixture consisting of 30 to 95 volume % of at least one boride selected from group VIa metal elements, 5 to 70 volume % of aluminum oxide or a substance that produces aluminum oxide by firing, and 20 volume % or less of boron oxide. After molding, it is fired at a temperature of 1400 to 190°C,
The sintered body contains the metal boride, aluminum oxide, and at least two selected from the metal elements, boron, and oxygen.
A boride-aluminum oxide sintered body in which at least 5% by volume of the aluminum oxide is comprised of acicular particles having an aspect ratio of 1.5 or more. It is characterized by:

The present invention will be explained in detail below.

The sintered body of the present invention is produced by mixing a small amount of boron oxide with at least one type of boride selected from metallic elements of groups 1 Va, Va, and ■a of the periodic table and aluminum oxide, molding, and then sintering the mixture. do.

The boride powder of the metal element has an average particle size of 3 μm or less, preferably 1 μm or less. Specific examples of this boride include TiB, ZrB, HfB2, and TaB.

NbBz, CrB,, WB, MO! 05, etc., and these may be borides of metal elements having a non-stoichiometric composition, or may be a mixture of two or more thereof.

On the other hand, the average particle size of aluminum oxide powder is preferably 3 μm or less, preferably 1 μm or less. In addition, instead of the alkhenium oxide powder, a substance that generates aluminum oxide upon firing, such as aluminum metal or 9A1zOs.
Aluminum borate represented by B2O3 or 2A1203.2BzO3 can also be used.

Further, boron oxide is added as a sintering aid to the main component consisting of the metal boride component and aluminum oxide component. This boron oxide preferably has an average particle size of 5 μm or less.

These powders contain at least one boride selected from metal elements in groups 1 Va, Va, and VIa of the periodic table.
5% by volume, especially 50-85% by volume, 5-70% by volume of aluminum oxide or a substance that produces aluminum oxide by calcination, especially 15% by volume.
~50% by volume, boron oxide not more than 20% by volume, especially 1-5
Mixed in volume %. Sintering is difficult when the metal boride exceeds 95 volume % or the aluminum oxide component exceeds 5 volume %, and conversely, when the metal boride exceeds 30 volume % or the aluminum oxide component exceeds 70 volume %. This is because the hardness of the obtained sintered body decreases and the properties of the metal boride cannot be exhibited. In addition, boron oxide is 2
If it exceeds 0% by volume, the properties of the sintered body will deteriorate.

Further, according to the present invention, the toughness of the sintered body can be further improved by replacing all or part of the aluminum oxide component with acicular particles. The acicular particles used include aluminum oxide whiskers and substances that generate alumina whiskers when heated during sintering, such as 9Al□0. - Aluminum borate whiskers having the chemical formula 2B202, etc. can be mentioned. These preferably have an average diameter (breadth axis) of 2 μm or less, particularly 0.2 to 0.7 μm, and an average aspect ratio expressed by major axis/breadth axis of 3 to 100, particularly preferably 10 to 30. used. These acicular particles have an aspect ratio of 1.5 or more in the sintered body, and the proportion of the particles is 5% by volume or more, especially 2% by volume.
It is desirable to mix it so that it is 0 volume% or more.

The reason why the average diameter is limited to the above range is that if it is 2 μm or less, grain growth during sintering will not become excessive and high bending strength can be maintained. The growth is significant, making it difficult to control the particle size.
Strength decreases, toughness varies, and boundary wear on the flank surface tends to increase when used as a cutting tool.

On the other hand, if the average aspect ratio is smaller than 3, the effect of fiber reinforcement is small and the toughness decreases, and if it is larger than 100, it is difficult to handle the raw material and cannot be uniformly dispersed, so the toughness tends to decrease. You can use it without any problem if you mix it while crushing some of it.

The above-mentioned raw material powders are mixed within the above-mentioned range, then molded into a desired shape by well-known molding means such as press molding, extrusion molding, injection molding, cast molding, cold isostatic pressing, etc., and then fired.

As the firing method, a normal firing method, a hot press method, a hot isostatic pressure firing method, etc. are applied, and the firing method is a reducing atmosphere in which an inert gas such as Ar or He or carbon, etc. is present at a temperature of 1400 to 1900°C. In order to obtain a particularly high-density sintered body, sintering with a theoretical density ratio of 96% or more can be performed using the normal sintering method or the hot press method. Power your body,
Further, hot isostatic pressure firing may be performed.

According to the above calcination, most of the metal boride and aluminum oxide remain as they are and are sintered, but some of the metal boride decomposes and reacts with oxygen in the system, resulting in the formation of metal oxides and oxides. Boron etc. are generated.

On the other hand, when aluminum metal is used instead of aluminum oxide, it reacts with oxygen or boron in the system during sintering to produce aluminum boride or aluminum oxide such as AIB, and when aluminum borate is used, ,
Aluminum borate separates into aluminum oxide and boron oxide at around 1400°C.

Boron oxide added to the raw material evaporates at temperatures above 1500°C along with boron oxide separated from other raw materials during the sintering process, but both act as sintering aids and help increase the density of the sintered body. promote. However, if a large amount of boron oxide is contained in the sintered body, it will reduce the hardness and strength of the sintered body, so the content is preferably 20% by volume or less, preferably 5% by volume or less.

The sintered body obtained by the above manufacturing method contains an aluminum oxide phase, a phase consisting of borides of Group 1 Va, Va, and ■a metal elements of the periodic table, and boron oxide produced in the sintering process and the metal oxides. The above-mentioned metals such as boron,
It is composed of a compound phase consisting of at least two or more types selected from oxygen. According to the invention, aluminum oxide is contained in an amount of 5 to 70% by volume, in particular 15 to 50% by volume, said metal boride is contained in an amount of 30 to 95% by volume, in particular 50 to 85% by volume, and at least one selected from said metals, boron and oxygen. The compound phase consisting of two or more types is 20% by volume or less, especially 1 to 5% by volume.
Excellent properties can be obtained by having a proportion of .

Further, according to the present invention, AlzO +
By creating a sintered body with a fine structure in which acicular particles such as whiskers are dispersed, the toughness of the sintered body can be further improved. Specifically, it is desirable that aluminum oxide crystal particles having an aspect ratio of 1.5 or more are present in the sintered body in a proportion of 5% by volume or more, particularly 20% by volume or more, based on the whole.

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), periodic table 1 Va, Va,
Boride of Via group metal element (particle size 200 mesh or less)
, using boron oxide (particle size 200 mesh or less), aluminum oxide whiskers (average particle size 0.7 μm, average aspect ratio 15) and aluminum borate whiskers (average particle size 0.7 μm, average aspect ratio 20), Table 1. After weighing in the proportions shown, the mixture was mixed and ground in a rotary mill for 12 hours.

The slurry after mixing was dried and used as a raw material for hot pressing.

This raw material is filled into a carbon mold and kept at a predetermined temperature for 1 hour.
Hot press bottom hole with a pressure of 300Kg/cm
A bending test piece based on IS was prepared.

Each obtained sample was polished to 3 based on JISR1601.
The point bending strength is improved by polishing to a mirror finish.
KIC and Vickers hardness were measured by M method.

Furthermore, the content of particles with an aspect ratio of 1.5 or more in the aluminum oxide particles was determined from the electron micrograph.

The results are shown in Table 1.

(Left below) According to Table 1, sample 1.9 consisting of a single metal boride.
All of No. 12.19 to No. 23 had poor sinterability, and their flexural strength was 35 kg/im" or less, and their toughness and Vickers hardness could not be measured due to voids.

Further, in the case of sample Nα8 in which the amount of boron oxide exceeds 20% by volume, no improvement effect on the properties is observed, and furthermore, in the case of sample Nα8 in which the amount of aluminum oxide exceeds 70% by volume, the hardness is low and the object of the present invention cannot be achieved.

In contrast, all the samples of the present invention exhibited excellent properties, with a bending strength of 35 Kg/m1 or more and a toughness (K+c) of 3.
A hardness of 5 MPa·+a'' or more and a Vickers hardness of 1750 or more were achieved.

[Effect of the invention 1 As detailed above, according to the present invention, the periodic table No. 1 Va,
By adding aluminum oxide and boron oxide to borides of group Va and VIa metal elements, the sinterability can be improved and a composite sintered body having high hardness, strength, and toughness can be obtained.

Due to its characteristics, this sintered body exhibits excellent effects as a tool for iron refining, a jig for non-ferrous refined aluminum molten metal, and a cutting tool, but it can also be applied to various other industrial parts and materials. .

Claims (4)

[Claims] (1) 30 to 95 volume % of at least one boride selected from group IVa, Va, and VIa metal elements of the periodic table, 5 to 70 volume % of aluminum oxide, and the metal element, boron,
A boride-aluminum oxide sintered body comprising 20% by volume or less of a compound comprising at least two species selected from oxygen. (2) At least 5% by volume of the sintered body is comprised of acicular particles having an aspect ratio of 1.5 or more.
A boride-aluminum oxide sintered body as described in 2. (3) 30 to 95 volume % of at least one boride selected from group IVa, Va, and VIa metal elements of the periodic table; 5 to 70 volume % of aluminum oxide or a substance that produces aluminum oxide upon firing; 1. A method for producing a boride-aluminum oxide sintered body, which comprises molding a mixture comprising 20% by volume or less of boron and then firing it at a temperature of 1400 to 1900°C. (4) The boride according to claim 3, wherein part or all of the aluminum oxide or the substance that generates aluminum oxide upon firing is comprised of acicular particles.
A method for producing an aluminum oxide sintered body.