JPH06107454A - Alumina sintered body and production thereof - Google Patents

Abstract

PURPOSE:To improve chipping resistance by mixing >=1 kind of ZrO2 and HfO2, Al2O3 or MgO containing Al2O3, ZrSiO4 and SiO2 molding, sintering by heating and treating under hot isostatic pressure in a specific condition. CONSTITUTION:A slurry is prepared by wet mixing a raw material powder containing ZrO2 and/or HfO2 powder, a stabilizer such as Y2O3, Al2O3 or Al2O3 containing MgO powder, ZrSiO4 powder and SiO2 powder in a specific weight ratio. The slurry is dried and granulated by adding a molding assistant such as a wax and the granulated material is molded in a prescribed shape and the molded body is sintered in an atmosphere at 1350-1650 deg.C. Next, the sintered body is treated under hot isostatic pressure in Ar gas atmosphere of >=1000atm at >=1300 deg.C to obtain Al2O3 based sintered body excellent in chipping resistance and wear resistance composed of a matrix containing 5-40wt.% (hereafter %) tenacious phase containing ZrO2 and/or HfO2 and the mutual solid solution, 1-30% ZrSiO4, 1-20% mullite and Al2O3 or Al2O3 and spinel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly composed of alumina, and further contains zirconium oxide and / or hafnium oxide,
The present invention relates to an alumina-based sintered body containing zirconium silicate and mullite and a method for manufacturing the same. The alumina-based sintered body is suitable for, for example, a cutting tool and a tool that requires wear resistance and corrosion resistance, and is most suitable as a tool for high speed cutting of cast iron and steel.

[0002]

2. Description of the Related Art Alumina has excellent properties such as heat resistance, abrasion resistance, and chemical resistance, but has a problem of poor strength and toughness. In order to solve this problem, many alumina-based sintered bodies have been proposed in which various other substances are added to alumina. Among the alumina-based sintered bodies, the following have been proposed as sintered bodies containing alumina, zirconium oxide, zirconium silicate and mullite.

For example, in JP-A-61-247659, SiO ₂ 2.5 to 8.5 existing as mullite is disclosed.
% By weight, ZrO ₂ 3.0 to 8.0% by weight, and the balance α.
Sintered body consisting -al ₂ O ₃ is described. This alumina-based sintered body has improved wear resistance, and improved reliability and stability, and thus has the same properties as conventional Al ₂ O ₃ —MgO based sintered bodies and Al ₂ O ₃ —SiO ₂ based sintered bodies. Although the problem is solved, when used under severe conditions such as a cutting tool, the strength, toughness and thermal shock resistance are not satisfactory, there is a problem in fracture resistance, and the life is short.

Further, Japanese Patent Laid-Open No. 62-12662 discloses a partially stabilized zirconium oxide containing a stabilizer,
Sintered bodies containing mullite or alumina and mullite in the range of 0.5 to 60% internal weight are described. This sintered body suppresses the drawback of zirconium oxide, which has a large volume change, and enhances strength and toughness, but since thermal shock resistance and wear resistance at high temperatures are significantly reduced, it is Not suitable for such uses.

Further, Japanese Patent Laid-Open No. 61-26558 discloses that an alumina-based ceramics sintering raw material powder mixture containing 5 to 25% by weight of zirconium silicate powder is molded and sintered, and has excellent thermal shock resistance. A method for producing alumina-based ceramics is described. Although this sintered body has improved thermal shock resistance, which is a drawback of conventional alumina-based ceramics, it has not been improved in strength and toughness, and is used in applications such as cutting tools under harsh conditions. Can not stand.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve the problems existing in the above-mentioned alumina-based sintered body and maximize the heat resistance, wear resistance and chemical resistance of alumina. In addition to exhibiting its strength and toughness, which are its disadvantages, it provides an alumina-based sintered body that is particularly suitable for tools, with excellent wear resistance and fracture resistance at high temperatures, and excellent thermal shock resistance and plastic deformation resistance. That is.

Another object of the present invention is to provide a method for producing such an alumina-based sintered body.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive research on an alumina-zirconium oxide-based sintered body for the purpose of increasing the strength and toughness of alumina, and as a result, a starting material obtained by adding zirconium silicate to alumina. The decomposition of zirconium silicate and the reaction of mullite formation can be performed by using, to obtain a dense sintered body. Even in a system in which silicon dioxide is added to alumina, mullite is similarly formed to form a dense sintered body. By obtaining what is obtained and controlling the composition ratio of alumina, zirconium oxide, zirconium silicate and mullite present in the obtained sintered body, it has been found that the characteristics of the sintered body at a high temperature can be significantly improved. The present invention has been completed.

That is, the alumina-based sintered body of the present invention is
It is an alumina-based sintered body containing the following components (1) to (4). (1) Toughening phase 5 to 40 containing at least one of zirconium oxide, hafnium oxide and mutual solid solutions thereof
% By weight; (2) 1 to 30% by weight of zirconium silicate; (3) 1 to 20% by weight of mullite; and (4) alumina or a matrix containing alumina and spinel.

In the sintered body of the present invention, the toughening phase is zirconium oxide, hafnium oxide, or a solid solution of the two, and two or more of these may be mixed. Moreover, you may contain the stabilizer as mentioned later.

Zirconium oxide may be tetragonal, monoclinic or cubic in terms of crystal structure, or may be a mixture thereof. Of these, tetragonal zirconium oxide is particularly preferable because it has the effect of increasing the strength and toughness of the sintered body by stress-induced transformation,
Further, monoclinic zirconium oxide is also preferable because it has an effect of improving toughness by strengthening microcracks.

Hafnium oxide has properties very similar to zirconium oxide, as is well known, and therefore, part or all of zirconium oxide may be replaced with hafnium oxide. Moreover, you may form the solid solution of both.

The toughening phase may include MgO and Ca as required.
Stabilizers such as O, Y ₂ O ₃ and CeO ₂ can be included. This prevents the strength from being reduced due to the bonding of microcracks due to excessive monoclinic crystal formation, and the type and content of the preferred stabilizer may be selected depending on the composition of the sintered body, the particle size, and the like. . Particularly, in the case of a cutting tool sintered body, Y ₂ O ₃ is preferable because a sintered body of high strength can be obtained. The content of Y ₂ O ₃ is preferably 5 mol% or less of the whole oxide forming the toughening phase.

The content of the toughening phase is in the range of 5 to 40% by weight of the sintered body including the stabilizer, if the stabilizer is present. If it is less than 5% by weight, the desired strength and toughness cannot be obtained. On the contrary, if it exceeds 40% by weight, the thermal shock resistance is remarkably lowered, and the hardness is remarkably lowered, so that the wear resistance is lowered.

In the sintered body of the present invention, zirconium silicate has the effect of improving strength at high temperature, plastic deformation resistance and thermal shock resistance, and particularly the effect of improving thermal shock resistance, as in the case of mullite described later. . This is because the coefficient of thermal expansion of zirconium silicate is smaller than that of mullite.

The content of zirconium silicate is 1 to 30% by weight, preferably 5 to 20% by weight of the sintered body. If it is less than 1% by weight, the above-mentioned effect is insufficient, and if it exceeds 30% by weight, the decrease in strength at room temperature becomes remarkable.

In the sintered body of the present invention, mullite has an effect of improving strength at high temperature, plastic deformation resistance and thermal shock resistance.

The content of mullite is 1 to 20% by weight, preferably 5 to 15% by weight of the sintered body. This is because if the amount is less than 1% by weight, the above-mentioned effect is insufficient, and if the amount exceeds 20% by weight, the wear resistance and the strength at room temperature are significantly reduced.

In the sintered body of the present invention, spinel has the functions of suppressing the growth of alumina particles and improving the sinterability. The content of spinel may be selected according to the shape and application of the sintered body. For example, when it is used as a tool for high-speed cutting of steel, it is preferably 10% by weight or less so as not to deteriorate wear resistance.

The alumina-based sintered body of the present invention comprises a toughening phase forming powder composed of at least one of zirconium oxide and hafnium oxide, alumina or alumina containing magnesia, zirconium silicate and a starting material containing silicon dioxide powder. After mixing, molding and heat-sintering, it can be manufactured by performing hot isostatic treatment under conditions of a pressure of 1,000 atm or higher and a temperature of 1,300 ° C or higher.

Although mullite powder may be used as a starting material for mullite, it is preferably added as silicon dioxide powder or zirconium silicate powder and produced by the following reaction during sintering. This is because the sinterability is improved, and the bond between the alumina-mullite particles is strong when the silicon dioxide powder is used, and the bond between the alumina-mullite-zirconium oxide particles is strong when the zirconium silicate powder is used. This is because a dense sintered body is formed and the fracture resistance is further improved.

[0022]

[Chemical 1]

The spinel, which constitutes a matrix together with alumina, can be produced by the following reaction between alumina and magnesia during sintering.

[0024]

[Chemical 2]

In the production method of the present invention, the amounts of zirconium oxide, hafnium oxide, stabilizer, alumina, magnesia, zirconium silicate, mullite and silicon dioxide used are contained in the sintered body obtained by the above chemical reaction. Zirconium oxide, hafnium oxide,
It may be calculated from the amounts of stabilizer, zirconium silicate, mullite and alumina.

The sintered body of the present invention can be manufactured by a conventional powder metallurgy method, but by subjecting it to hot isostatic pressing (HIP) treatment, a sintered body having higher strength and excellent reliability can be obtained. Obtainable. That is, various starting materials are mixed in required amounts, and are uniformly mixed and pulverized by, for example, a ball mill. A molding aid such as paraffin is added to the above raw material powder mixture, granulated, and then press-molded into a predetermined shape. Then, the molded body is sintered at a temperature of 1,350 to 1,650 ° C. in an atmospheric pressure atmosphere, for example, to obtain the sintered body of the present invention. Furthermore, HIP processing can be performed as needed. As an HIP treatment condition, an inert gas such as Ar or N ₂ is used as an atmosphere gas, but a gas atmosphere containing oxygen is more preferable. In particular, when CeO ₂ is contained as a stabilizer, it is preferable to perform HIP treatment in an oxygen atmosphere. The gas pressure needs to be 1,000 atm or higher, and the treatment temperature is preferably 1,300 to 1,600 ° C. Gas pressure less than 1,000 atm or 1,300 ℃
If the temperature is lower than this, the effect of improving the strength and reliability by the HIP treatment is not sufficient.

[0027]

Example As starting materials, alumina powder having an average particle size of 0.1 μm, magnesia powder, mullite powder, zirconium silicate powder having an average particle size of 0.2 μm, and a primary particle size of 3
Zirconium oxide powder of 00Å, zirconium oxide powder containing 3 mol% of yttrium oxide, and hafnium oxide powder having an average particle diameter of 0.8 μm were used. These were weighed so as to have the composition shown in Table 1, and were mixed and pulverized by a ball mill for 48 hours using a methanol solvent and alumina balls to obtain a slurry. After drying the obtained slurry, 5% by weight of paraffin wax was added and granulated. The granules thus obtained were molded by a die press at a pressure of 1 ton / cm ² and sintered in the air at 1,500 ° C. for 1 hour. Further, HIP treatment is performed at 1,500 ° C. for 1 hour under the condition of Ar gas of 1,500 atm, whereby the sintered bodies 1 to 9 and the comparative product sintered bodies 1 to 4 according to the present invention are processed.
Got

[0028]

[Table 1]

Regarding the sintered body thus obtained,
The composition was analyzed by X-ray diffraction, and the bending strength at room temperature and the high temperature bending strength at 1,200 ° C. in Ar atmosphere were measured. Further, a thermal shock test was carried out by an underwater quenching method to measure a critical temperature difference ΔTc at which strength reduction occurs. The results are shown in Table 2.

[0030]

[Table 2]

Further, the products of the present invention 1 to 9 and the comparative products 1 to 4
Was used to perform a dry continuous turning test under the conditions (A) and (B) shown in Table 3 and a milling cutting test under the condition (C). The results are shown in Table 4.

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

INDUSTRIAL APPLICABILITY The sintered body of the present invention has bending strength, especially bending strength at high temperature, a critical temperature difference due to an underwater quenching method, as compared with a conventional alumina-based sintered body containing mullite and zirconium oxide. The wear resistance and fracture resistance in the cutting test are remarkably excellent.

Therefore, the sintered body of the present invention can be used not only for conventional alumina-based sintered bodies but also for various cutting tools including high-speed cutting tools for steel and cast iron.
Further, it is an industrially useful material that can be applied to wear-resistant tools and machine parts such as slitters, balls, sleeves, nozzles, plungers, scissors, and knives.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Toshiyuki Mori 1-18-7 Fujisaki, Tsuchiura City, Ibaraki Prefecture (72) Inventor Hiroshi Yamamura 460-35 Kamihirooka, Tsukuba City, Ibaraki Prefecture

Claims (3)

[Claims] 1. An alumina-based sintered body comprising the following components (1) to (4): (1) Toughening phase 5 to 40 containing at least one of zirconium oxide, hafnium oxide and mutual solid solutions thereof
% By weight; (2) 1-30% by weight of zirconium silicate; (3) 1-20% by weight of mullite; and (4) Alumina or a matrix containing alumina and spinel. 2. The alumina-based sintered body according to claim 1, wherein the toughening phase is zirconium oxide containing yttrium oxide as a stabilizer. 3. A starting material comprising a toughening phase forming powder comprising at least one of zirconium oxide and hafnium oxide, alumina or alumina containing magnesia, zirconium silicate and silicon dioxide powder, mixed, molded and heat-sintered. Later, over 1,000 atmospheres, 1,300
The method for producing an alumina-based sintered body according to claim 1, wherein the hot isostatic treatment is performed at a temperature of not less than ° C.