JPH10212157A - Aluminous sintered compact and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aluminous sintered compact having high toughness and high strength well as superior strength in the temp. range from room temp. to a high temp. of 1,200 deg.C. SOLUTION: A compact based on Al2 O3 and contg. 0.1-5wt.% (expressed in terms of TiO2 ) Ti, 0.5-2wt.% (expressed in terms of MgO) Mg and 0.01-2wt.% (expressed in terms of SiO2 ) Si is subjected to solid soln. formation and deposition treatment by heating to obtain the objective sintered compact of. >=20vol% play Al2 O3 crystals having an aspect ratio of >=5 and <=20μm average major axis size with. a Ti- or Mg-contg. oxide dispersed as crystal grains having <=0.3μm average grain diameter in the grains and grain boundaries of Al2 O3 crystals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina sintered body having excellent strength and toughness, and particularly to an alumina sintered body useful as a high-temperature structural material used for wear-resistant parts, engine parts and the like. The present invention relates to a binder and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, alumina-based sintered bodies have attracted attention as structural members because of their excellent heat resistance, environmental resistance, and strength. Further, in order to further improve the strength, and particularly to improve the fracture toughness, various composites have been attempted. For example, for alumina, SiC, Zr
Composite materials in which O ₂ and La-containing β-Al ₂ O ₃ are dispersed are known (JP-A-61-122164, JP-A-61-122164).
3-139044, JP-A-63-134551),
It has been reported that such a composite material can improve strength and toughness as compared with a general alumina-based sintered body.

On the other hand, there has been proposed an attempt to improve the fracture toughness of a sintered body by making plate-like alumina crystals having shape anisotropy exist in the alumina-based sintered body. Such a structure is formed by adding an oxide-based auxiliary agent capable of forming a liquid phase to alumina and calcining (for example, J. Amer. Cer. Soc., 73 (1990) ) 20
77-85 and J. Mat. Sci., 28 (1993) 5953-56).

[0004]

However, as a method for strengthening the above-mentioned alumina-based sintered body, there has been a problem that, when SiC is dispersed, when it is used in a high-temperature oxidizing atmosphere, it lacks chemical stability. . Further, the sintered body in which ZrO ₂ is dispersed has a problem that the strength characteristics are rapidly lowered at a temperature of 900 ° C. or higher. Furthermore, La-based β-A
The alumina sintered body in which l ₂ O ₃ is dispersed has high strength and toughness, and a small decrease in strength at high temperatures.
_{Since the 2} O ₃ phase has a low Young's modulus, if it is contained at 20% by volume or more, there are problems such as a decrease in hardness of the sintered body and a decrease in wear resistance.

On the other hand, in a sintered body in which plate-like alumina is grown and dispersed, usually, a total of 1 mol% or less of SiO ₂ —MgO, CaO—SiO ₂ , Na ₂
Although addition of O-SiO ₂ or the like has been studied, particles grow abnormally during the growth process of plate-like alumina, and a liquid phase forming aid remains at the grain boundaries in the sintered body. And the strength at high temperatures was significantly reduced.

Therefore, the present invention solves the above-mentioned problems,
It is an object of the present invention to provide an alumina-based sintered body having excellent strength at high temperatures from room temperature to 1200 ° C. and high toughness, and a method for producing the same.

[0007]

Means for Solving the Problems The present inventors have repeatedly studied a method of obtaining plate-like alumina crystals having a high aspect ratio and improving strength characteristics by dispersing fine particles in order to improve fracture toughness. , For alumina, T
When iO ₂ , MgO and SiO ₂ are blended at a predetermined ratio, the interaction of these components exerts an effect of promoting the formation of a liquid phase in the sintering process, whereby alumina crystals are partially formed into a plate shape, and Ti and / or Alternatively, Mg is dissolved in the alumina crystal and the solid solution is subjected to T
An oxide containing i or Mg precipitates from the alumina crystal,
The present inventors have found that a high-strength and high-toughness alumina-based ceramics sintered body can be obtained by forming a finely dispersed structure in alumina grains and in grain boundaries, and have accomplished the present invention.

That is, the alumina-based sintered body of the present invention is made of Al
Mainly ₂ O ₃ , Ti is 0.1 to 5% by weight in terms of TiO ₂ , Mg is 0.05 to ₂ % by weight in terms of MgO, and Si is 0.01 to ₂ % by weight in terms of SiO _2. A sintered body containing 20% by volume or more of Al ₂ O ₃ crystals having an aspect ratio of 5 or more and an average major axis of 20 μm or less, and an oxide containing Ti and / or Mg. It is characterized by being dispersed as crystal particles having an average particle size of 0.3 μm or less.

According to the method for producing an alumina-based sintered body of the present invention, Al ₂ O ₃ is mainly used, Ti is 0.1 to 5% by weight in terms of TiO ₂ , and Mg is 0.05 to 0.05% in terms of MgO. ~
A molded body containing ₂ % by weight and Si in an amount of 0.01 to 2% by weight in terms of SiO ₂ was prepared by mixing A with Ti and / or Mg.
After heat-treating under the condition that the amount of solid solution in l ₂ O ₃ crystal becomes large to produce an Al ₂ O ₃ solid solution in which Ti and Mg are dissolved, the Ti and / or Mg are introduced into Al ₂ O ₃ crystal. Is heat-treated under the condition that the solid solution amount of the Al ₂ O ₃ crystal is reduced to an aspect ratio of 5 or more and an average major diameter of 20 μm or less.
Volume% or more, and Ti and / or
Alternatively, an oxide containing Mg is precipitated and dispersed as crystal particles having an average particle diameter of 0.3 μm or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The alumina-based sintered body of the present invention contains alumina as a main component. As another component, Ti is 0.1 to 5% by weight in terms of TiO ₂ , especially 0.1 to 5% by weight.
5 to 3% by weight, Mg is 0.05 to ₂ % by weight, especially 0.3 to ₂ % by weight in terms of MgO, and Si is 0.01 to ₂ % by weight, particularly 0.03 to 1% in terms of SiO2. %.

Ti is less than 6% by weight in terms of TiO ₂ in a reducing atmosphere, and the same atomic ratio of T
i and Mg can form a solid solution in the alumina crystal lattice at a ratio of 5% by weight or less in terms of TiO ₂ and MgO. Such ions having a high solid solubility are 001 of the alumina crystal.
The effect of suppressing the growth in the direction is great, and the highly anisotropic growth of crystals can be promoted. Therefore, the addition of Ti alone or the simultaneous addition of Ti and Mg is effective in promoting the growth of plate-like alumina crystals. However, when Ti alone is added, the crystal grain size tends to grow coarsely. Therefore, when Ti is added simultaneously with Mg, an effect of suppressing grain growth is exhibited.

On the other hand, plate-like growth of alumina crystals requires the presence of a liquid phase having an appropriate amount and an appropriate viscosity. In order to satisfy this condition, it is effective to mix an appropriate amount of SiO ₂ in addition to the above-described Ti component and Mg component. Also, the amount of Si slightly larger than necessary to form a liquid phase
When O ₂ is blended, a small amount of mullite is generated by the reaction with alumina, whereby the grain growth of alumina can be effectively suppressed.

Therefore, if the addition amount of any one of the above Ti, Mg, and Si is less than the composition range of the present invention, the above effects cannot be exerted. The strength and toughness of the sintered body are reduced by suppressing the growth of the crystallites and generating a coarse grain boundary reaction phase.

In addition, the sintered body of the present invention contains 20% by volume or more, particularly 30 to 90% by volume or more of the total amount of plate-like alumina crystals having an aspect ratio of 5 or more, along with controlling the above compositional components. By including such a plate-like alumina crystal in the above-mentioned predetermined amount, the toughness of the sintered body can be increased by the deflection of crack propagation. Also, this plate-like alumina crystal,
It is also important that the average major axis is not more than 20 μm, especially not more than 14 μm. If the average major axis of the plate-like alumina crystal exceeds 20 μm, the plate-like alumina crystal serves as a fracture source and lowers the strength of the sintered body. Especially,
It is desirable that no crystal having a major axis exceeding 30 μm is present, or even if it is present, it is 2% by volume or less. The alumina crystal particles other than the plate-like alumina crystal had an average major axis of 3 μm.
It is desirable that the particles exist as fine particles of m or less in order to increase the strength.

Further, according to the present invention, in such a sintered body, crystal particles of an oxide containing Ti or Mg are formed as fine crystal particles having an average particle diameter of 0.3 μm or less, particularly 0.2 μm or less. It is important to improve the strength of the sintered body if it is present in the crystal grains or dispersed in the grain boundaries. Here, the oxide containing Ti or Mg refers to Al ₂ Ti
O ₅ , TiO ₂ , MgAl ₂ O ₄ and the like. Due to the presence of such fine crystal grains, a stress field is generated around the dispersed crystal grains, thereby contributing to an improvement in the strength of the sintered body. It is particularly preferable that the average particle size of the crystal particles is 0.1 μm or less, in order to exert a strengthening mechanism more greatly.

To produce the alumina sintered body of the present invention, first, a Ti-containing compound, a Mg-containing compound and a Si-containing compound are added to alumina powder. The compound may be any of oxide powder, metal powder, organic salts, inorganic salts and a solution thereof.

The amount of these additives is the total amount including impurities contained in the alumina powder, and is equivalent to 0.1% of Ti in terms of TiO ₂ .
1 to 5% by weight, especially 0.5 to 3% by weight, Mg is 0.05 to 2% by weight in terms of MgO, particularly 0.3 to 2% by weight, Si
From 0.01 to ₂ % by weight, particularly from 0.03 to
It is prepared to contain 1% by weight.

The mixture weighed and mixed as described above is formed into an arbitrary shape by desired molding means, for example, a die press, a cold isostatic press, injection molding, extrusion molding, cast molding, sheet-like molding, or the like. Molding.

Next, the molded body is subjected to a known sintering method, for example, a hot pressing method, a normal pressure sintering method, a gas pressure sintering method, a microwave heating sintering method, and a hot isostatic pressure treatment after sintering. HIP) treatment and after glass sealing (HI
P) by sintering by various sintering methods such as treatment to have an alumina structure of a predetermined aspect ratio and particle size, and
A dense body having a solid solution of i and / or Mg and a theoretical density of 95% or more is obtained.

According to the present invention, in this sintering process, first,
An alumina solid solution in which Ti and Mg are dissolved in alumina crystals is prepared. In the production of this solid solution, Ti can be mainly dissolved in alumina by sintering the molded body in a reducing atmosphere such as hydrogen, but when sintering in an oxidizing atmosphere such as air, Ti and Mg are It can be dissolved in alumina crystals at almost the same atomic ratio. Also,
The firing temperature during the solid solution treatment can be appropriately adjusted depending on the amounts of the raw materials and the additives, but a range of 1350 to 1650 ° C. is particularly preferable.

Next, following the above solid solution treatment, T
A precipitation treatment of fine crystal particles of an oxide containing i or Mg is performed. This precipitation treatment is performed by using the Ti and / or M
Heat treatment is performed under the condition that the amount of g dissolved in the Al ₂ O ₃ crystal becomes small. In this precipitation treatment, it is possible to heat at a temperature lower than the temperature at the time of the solid solution treatment. Al ₂ TiO
₅ and TiO ₂ can be precipitated, and when a sintered body in which Ti and Mg are dissolved in an equal amount is treated in a reducing atmosphere, MgA
l ₂ O ₄ can be precipitated. Further, the temperature during the precipitation treatment is 1000 ° C. to 165 ° C. from the viewpoint of suppressing the deposition rate and the grain growth of the precipitated particles and the alumina crystal which is the parent phase.
A range of 0 ° C. is preferred.

By such a precipitation treatment, solid solution Ti or Mg can be precipitated as fine oxide crystal particles from the alumina crystal and dispersed in the alumina crystal grains or at the grain boundaries.

[0023]

EXAMPLE Alumina powder having an average particle size of 0.5 μm, titanium oxide (TiO ₂ ) powder having an average particle size of 0.7 μm, and magnesium hydroxide (Mg (O
H) ₂ ) and further using tetraethyl silicate as a SiO ₂ source, and weighed and mixed such that the total amount of Ti, Mg and Si (including impurities) had the composition shown in Table 1 to obtain a mixed powder. Then, this mixed powder was subjected to die molding at a pressure of 1 t / cm ² , and further subjected to hydrostatic pressure treatment at a pressure of 3 t / cm ² to produce a molded body. Then, the formed body was heat-treated at 1500 ° C. for 2 hours in the atmosphere shown in Table 1 to form a solid solution, and then subjected to a precipitation treatment in the atmosphere shown in Table 1 at the temperature, time and atmosphere shown in Table 1.

X-ray diffraction measurement was performed on each of the obtained sintered bodies to identify a crystal phase. Table 2 shows crystal phases other than Al ₂ O ₃ . Also, the sintered body section is mirror-finished,
Image analysis was performed on the electron micrograph after etching, and the area ratio with respect to the whole alumina crystal having an aspect ratio of 5 or more was determined, and this was regarded as the volume ratio.
Further, the observed average major axis of the plate-like alumina crystals and the particle diameter of the fine crystal particles precipitated in the alumina crystal grains or at the grain boundaries were obtained from electron micrographs, and the results are shown in Table 2.

Further, as mechanical properties, JISR160
The four-point bending strength at room temperature and 1200 ° C. based on No. 1 was measured. Also, measure the Vickers hardness of the sintered body mirror surface,
The fracture toughness was calculated by the indentation method. Table 2 also shows the results of these characteristic measurements.

[0026]

[Table 1]

[0027]

[Table 2]

According to Tables 1 and 2, the sintered body obtained according to the present invention has a room temperature bending strength of 560 MPa or more,
0 ° C strength of 430 MPa or more, fracture toughness of 4.7 MPa · m
It exhibited excellent properties of ^1/2 or more and Vickers hardness of 17 GPa or more.

On the other hand, Sample No. 1 having a small amount of Ti
In Samples Nos. 4 and 15 which were not subjected to the precipitation treatment, no precipitation phase was observed, and the mechanical properties were lower than those of the sintered body of the present invention.

In addition, Sample No. 9 and T
Sample No. 11 having an i content of more than 5% by weight has low mechanical properties due to a large amount of aluminum titanate having an average particle size exceeding 0.3 μm.

In Sample No. 12 in which the Mg content was less than 0.05% by weight, grain growth was observed, and the average major axis of the plate-like alumina crystal exceeded 20 μm, and all of the strength, toughness, and hardness were low. Even in Sample No. 17 in which the Mg content exceeded 2% by weight, the ratio of plate-like alumina crystals was small and the toughness was low.

Furthermore, SiO ₂ amount is less than 0.01 wt% the sample No.18, also in Sample No.22 SiO ₂ amount exceeds 2 wt%, produced less toughness of both the plate-like alumina crystals Was low.

Particularly, the product of the present invention has a Ti content of 0.5 to 3% by weight in terms of TiO ₂ and a Mg content of 0.3 to _{2 in} terms of MgO.
% By weight, the amount of Si in terms of SiO ₂ is 0.03 to 1% by weight, the volume fraction of plate-like Al ₂ O ₃ crystals is 30 to 90% by volume, and the fine precipitated crystal particle diameter is 0.2 μm or less. Is room temperature strength of 570 MPa or more, 1200 ° C. strength of 440 MPa
As described above, fracture toughness of 5.0 MPa · m ^1/2 or more and Vickers hardness of 17.5 GPa or more were achieved.

[0034]

As described above in detail, the present invention not only produces plate-like alumina crystals having a high aspect ratio but also removes fine oxide crystal particles containing Ti or Mg within the alumina crystals or at the grain boundaries. By dispersing, a sintered body having high strength and toughness from room temperature to high temperature can be obtained.

Claims (2)

[Claims] (1) Mainly composed of Al ₂ O ₃ , Ti is 0.1 to 5% by weight in terms of TiO ₂ , and Mg is 0.05 to 5% in terms of MgO.
A sintered body containing ₂ % by weight and Si in a ratio of 0.01 to 2% by weight in terms of SiO ₂ , wherein 20% by volume or more of the sintered body has an aspect ratio of 5 or more and an average major axis of 20 μm or less. It is composed of Al ₂ O ₃ crystal and has Ti and / or
Alternatively, an alumina-based sintered body characterized in that an oxide containing Mg is dispersed as crystal particles having an average particle size of 0.3 μm or less. 2. A composition mainly comprising Al ₂ O ₃ , Ti being 0.1 to 5% by weight in terms of TiO ₂ , and Mg being 0.05 to 5% in terms of MgO.
A molded body containing ₂ % by weight and Si in an amount of 0.01 to 2% by weight in terms of SiO ₂ was prepared by mixing A with Ti and / or Mg.
After heat-treating under the condition that the amount of solid solution in l ₂ O ₃ crystal becomes large to produce an Al ₂ O ₃ solid solution in which Ti and Mg are dissolved, the Ti and / or Mg are introduced into Al ₂ O ₃ crystal. Is heat-treated under the condition that the solid solution amount of the Al ₂ O ₃ crystal is reduced to an aspect ratio of 5 or more and an average major diameter of 20 μm or less.
Volume% or more, and Ti and / or
Alternatively, a method for producing an alumina-based sintered body, wherein an oxide containing Mg is precipitated and dispersed as crystal particles having an average particle size of 0.3 μm or less.