JPH08104942A - High strength and high corrosion resistance material - Google Patents

Abstract

PURPOSE: To provide a material having higher strength at high temp. and higher corrosion resistance to a molten metal as compared with a conventional material obtd. by distributing ceramic particles in the grain boundaries of a high m.p. metallic material. CONSTITUTION: Oxide of a rare earth element is dispersed in the grain boundaries of a high m.p. metallic material and the amt. (wt.%) of P in the grain boundaries of the high m.p. metallic material is regulated to <=60% of that in the grain boundaries of the same pure high m.p. metallic material as the high m.p. metallic material to obtain the objective high strength and high corrosion resistance material. In other way, oxide of a rare earth element is dispersed in the grain boundaries of a high m.p. metallic material and multiple oxides of the rare earth element and the high m.p. metallic material and multiple oxides of the rare earth element and P as well as oxide of the rare earth element are allowed to exist in the grain boundaries of the high m.p. metallic material to obtain the objective high strength and high corrosion resistance material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material having high strength and high corrosion resistance.

[0002]

2. Description of the Related Art Generally, a container for melting a metal such as an active metal such as titanium (Ti) or zirconium (Zr) or a structural material has a high strength at a high temperature and a high corrosion resistance against a molten metal. Is required.

Conventionally, refractory metal materials such as tungsten (W) and molybdenum (Mo) have been used as such materials. These W and Mo are generally manufactured by powder metallurgy. That is, the raw material powder is molded,
After sintering, if necessary, plastic working such as rolling and forging is performed, and finally the product is processed into a desired shape.

Although the materials made of these high melting point metal materials have excellent heat resistance and thermal shock resistance, they are crystallized when used for a long time at a temperature higher than the recrystallization temperature of the high melting point metal material. There was a problem that the grains became coarse and became brittle.

Further, these refractory metal materials generally have T
Since the wettability with active metals such as i and Zr is good,
When used for melting an active metal, it reacts with the molten metal over a long period of time and corrodes the high-melting-point metal material, and the high-melting-point metal material itself mixes into the molten metal to improve the purity of the molten metal. There was a problem that it would cause a decrease.

For this reason, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2-73944 or Japanese Patent Application Laid-Open No. 4-99146, a technique for arranging ceramic particles at crystal grain boundaries of a refractory metal material has been studied.

By arranging the ceramic particles at the crystal grain boundaries of the high melting point metal material, a material having high strength and high corrosion resistance is obtained as compared with the case where a single high melting point metal material is used.

[0008]

However, in recent years, it has been desired to develop a material having higher strength and higher corrosion resistance, particularly excellent corrosion resistance against molten metal. In view of the above circumstances, it is an object of the present invention to provide a material having high strength at high temperature and high corrosion resistance against molten metal.

[0009]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies on conventional materials in which ceramic particles are arranged at the crystal grain boundaries of a refractory metal material, and as a result, Attention was paid to phosphorus (P) in the crystal grain boundaries of the melting point metal material.

That is, the amount of P in a refractory metal material which is generally said to be pure is 5 ppm or less, and P is contained as a trace impurity. However, when this refractory metal material is manufactured through a process such as sintering and plastic working by the powder metallurgy method, a trace amount of P segregates in the crystal grain boundaries of the refractory metal material, and the crystal grains A large amount of P of 20 atomic% or more exists in the field.

Due to P segregated at the grain boundaries,
The strength, plastic workability and corrosion resistance were adversely affected, and the effect of P could not be prevented even in the conventional high melting point metal material in which ceramic particles were arranged at the grain boundaries.

Therefore, the present inventors have found that the P of this grain boundary is
As a result of further studies on the reduction of the above, the present invention has been achieved. That is, first, the high-strength, high-corrosion-resistant material according to the first aspect of the present invention is obtained by dispersing an oxide of a rare earth element in a crystal grain boundary of a refractory metal material, The P content (atomic%) is 70% or less of the P content (atomic%) of the crystal grain boundary of the same pure refractory metal material as the refractory metal material.

Further, a high strength, which is the second invention of the present invention,
The high-corrosion resistant material is formed by dispersing an oxide of a rare earth element in a crystal grain boundary of the refractory metal material, and the rare earth element and the refractory metal material are included in the crystal grain boundary of the refractory metal material together with the oxide of the rare earth element. And a complex oxide of P and a rare earth element.

Here, the refractory metal material in the present invention means tungsten (W), molybdenum (Mo), rhenium (Re), hafnium (Hf), tantalum (Ta),
It refers to niobium (Nb) or zirconium (Zr).

The rare earth oxides referred to in the present invention include scandium (Sc), yttrium (Y),
Lanthanide elements such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (N)
d), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (H)
o), oxides of erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

The amount of the rare earth element oxide is 50% by volume or less, preferably 5 to 30% by volume, and more preferably 10 to 30% by volume. This is because within this range, the effect of reducing the segregation of P to the crystal grain boundaries is remarkable together with the improvement of the density, and the sintered body can be densified and a high-strength material can be obtained.

In the high-strength, high-corrosion resistant material according to the first aspect of the present invention, a high-melting-point metal material having the same amount of P at the crystal grain boundaries of the high-melting-point metal material of the present invention as the high-melting-point metal material is used. The amount of P at the crystal grain boundaries in the case of producing a pure pure refractory metal material is reduced.

Specifically, the P content (atomic%) of the crystal grain boundary of the refractory metal material of the present invention is the same as the P content of the crystal grain boundary of the pure refractory metal material (the same as the refractory metal material). Atomic%) of 70% or less, and by reducing P in the crystal grain boundary in this way, as compared with a conventional refractory metal material in which ceramic particles are arranged at the crystal grain boundary, it is It has become possible to provide a material that is strong and has high corrosion resistance against molten metal.

The P content (atomic%) of the crystal grain boundary of the refractory metal material of the present invention is the same as the P content (atomic%) of the crystal grain boundary of the same pure refractory metal material as the refractory metal material. The reason why the content is specified to be 70% or less is that if the P content is too large, the effect is not so different from the conventional material. More preferably, the P content of the present invention is 60% or less, and further preferably 50% or less of the P content (atomic%) of the crystal grain boundary of the same pure refractory metal material as the refractory metal material.

Here, the pure refractory metal material referred to in the present invention is in accordance with the method for defining the purity of W specified in JIS 9
It has a purity of 9.95% by weight or more and its P content is 5 pp.
Means less than or equal to m. For example, a sintered body manufactured by using W powder of WC1-20 (average particle size of about 2 μm) which is W powder manufactured by Toshiba Corporation can be used.

Further, the high strength which is the second invention of the present invention,
In the high corrosion resistance material, the refractory metal material of the present invention comprises a rare earth element oxide and a complex oxide of the rare earth element and the refractory metal material and a complex oxide of the rare earth element and P at the grain boundaries of the refractory metal material of the present invention. It is characterized by.

Here, the composite oxide of a rare earth element and a refractory metal material and the composite oxide of a rare earth element and P are, for example, when the rare earth element is A, the composite oxide of a rare earth element and W is A ₂ It is represented by (WO ₄ ) ₃ and the composite oxide of rare earth element and P is represented by AP ₅ O ₁₄ .

According to the present invention, the following reactions are carried out at the crystal grain boundaries of the refractory metal material. That is, an oxide of a rare earth element is added to the refractory metal material, and when the oxide is mixed, the mixing is performed more uniformly as compared with the conventional method, so that P in the refractory metal material is mixed in the sintering step.
₂ O ₅ and the oxide of the rare earth element are sufficiently reacted to form a complex oxide of P and the rare earth element. This complex oxide reacts with the refractory metal material to form another complex oxide. As the sintering process progresses, oxides of rare earth elements come to exist independently, and the above two types, specifically, the complex oxides of rare earth elements and refractory metal materials and the complex oxides of rare earth elements and P are included. The above two kinds of complex oxides, together with the oxide of the rare earth element, remain at the crystal grain boundaries of the refractory metal material.

It is assumed that the rare earth element oxide has an effect of absorbing impurities such as P. An example of the method for producing the high-strength, high-corrosion resistant material of the present invention is as follows.

First, a powder of a refractory metal material and a powder of an oxide of a rare earth element are mixed with a ball mill or the like. In this case, the amount of balls thrown into the ball mill is set to 4 times or more, preferably about 5 times as much as the conventional amount. The mixing time is also 5 times or more, and preferably about 5 to 7 times that of the conventional one. Uses a large amount of balls compared to this conventional mixing,
By mixing for a longer time, dissociation of the secondary particles of the refractory metal powder and refinement of the oxide particles of the rare earth element can be achieved, and it becomes possible to carry out the mixing more uniformly as compared with the conventional case, and it is intended in the present invention. It is possible to obtain an excellent effect of At the time of this mixing, more excellent mixing effect can be obtained by mixing with acetone or ethanol.

Next, in order to scatter acetone, ethanol, etc. in the obtained mixed powder, heating is performed in a non-oxidizing atmosphere. Then, if necessary, re-reduction is carried out by a conventional method.
For example, heating may be performed at 800 ° C. for 1 hour in a reducing atmosphere.

Next, the obtained mixed powder is made uniform in particle diameter by using a means such as a sieve. Next, it is molded into an arbitrary shape by a conventional method and is sintered to obtain a final product.

This is, for example, a cold isostatic press (CI
P) is used for molding, and for example, when W is used as the high melting point metal material, it is 1800 ° C. or higher, preferably 18
Sintering is performed at 00 to 2300 ° C.

The high-strength, high-corrosion resistant material of the present invention is used for applications requiring high-strength and high-corrosion resistance against molten metal at high temperature, and more preferably Ti, Zr. Suitable for containers and structural materials for melting active metals such as.

[0030]

Example: W powder having an average particle size of 2 μm (purity 99.95%
Above) and lanthanum oxide (La ₂ having an average particle size of 1 μm)
O ₃ ) was blended so that La ₂ O ₃ was 20% by volume.

Then, the compounded powder is ball milled.
Mixed with acetone. In that case, the amount of balls is 1
The mixing time was 0 kg, and the mixing time was 160 hours. The obtained mixed powder was heated in a hydrogen atmosphere to scatter the acetone used during the mixing.

Next, after re-reducing at 800 ° C. for 1 hour in a hydrogen atmosphere, it was sieved to obtain a mixed powder having a uniform particle size. The resulting mixed powder was cold isostatically pressed (CI
P), molding at 2ton / cm ² , bottom diameter 60c
The container was m, the height was 30 cm, and the thickness was 10 cm.

The obtained molded body was subjected to 2000 in a hydrogen atmosphere.
Sintering was performed at 8 ° C. for 8 hours to obtain a container as a final product. Density, W content at grain boundaries, P of the obtained product
Content, O content, corrosion resistance to molten metal, and high temperature strength were measured. The results are shown in Table 1 (Example 1).

Here, the amount of W at the grain boundary, P
The amount of oxygen and the amount of O were measured by Auger electron spectroscopy, and the measurement conditions were an acceleration voltage of 5 kV, a beam current of 80 mA, and a beam diameter of about 1 μm.

The corrosion resistance to molten metal was obtained by dissolving La in a container, and measuring how much W in the container was mixed in this La by measuring the content (% by weight) of W in the La.

The high temperature strength was measured by a 4-point bending test. The conditions were such that a fulcrum with a diameter of 6 mm was used, the distance between the fulcrums at the lower part was 30 mm, the distance between the fulcrum at the upper part was 10 mm, and the crosshead speed was 0.5 mm / min. Temperature is 700
The measurement was performed at ℃, 1000 ℃, 1300 ℃.

For comparison, W powder having an average particle size of 2 μm (purity of 99.95% or more) was subjected to CIP and sintering in the same manner as in Example 1 to obtain a similar final product container. The density, W content, P content, O content at the grain boundaries of the obtained product,
Corrosion resistance to molten metal and high temperature strength were measured. The results are also shown in Table 1 (Comparative Example 1).

As a further comparison, in the mixing by the ball mill, except that the amount of balls was 2 kg and the mixing time was 24 hours, the same process as in Example 1 was repeated to prepare a container as a final product. Obtained.

The density, W content, P content, O content at the grain boundaries, corrosion resistance to molten metal and high temperature strength of the obtained product were measured. The results are also shown in Table 1 (Comparative Example 2).

[0040]

[Table 1]

From the results shown in Table 1 above, the material of the present invention has a smaller amount of P in the crystal grain boundaries as compared with the pure W or the conventional W having the ceramic grains arranged in the crystal grain boundaries. As a result, excellent corrosion resistance against molten metal and strength at high temperature are obtained.

To describe further, P in the grain boundary of W
Since the amount of O ₂ increases with the decrease in the amount, P does not exist as a simple substance at the grain boundary, but LaP ₅ O.
_It can be understood that it exists in the complex oxide _{14 mentioned} above.

That is, since the free energy of formation of W oxide and P oxide is smaller in P oxide, it is more likely that P exists in the oxide (P ₂ O ₅ ), and P
₂ O ₅ forms LaP ₅ O ₁₄ together with La ₂ O ₃ . Note that La ₂ O ₃ and La ₂ (WO ₄ ) together with W
Generates ₃ .

[0044]

As described above, the high strength of the present invention,
High-corrosion resistance materials can provide materials that have high strength at high temperatures and high corrosion resistance to molten metal, as compared with conventional high-melting-point metal materials in which ceramic particles are arranged at crystal grain boundaries. .

Claims (2)

[Claims] 1. An oxide of a rare earth element is dispersed in a crystal grain boundary of the refractory metal material, and the phosphorus content (atomic%) of the crystal grain boundary of the refractory metal material is the same as that of the refractory metal material. 70% or less of the phosphorus content (atomic%) of the crystal grain boundaries of the pure refractory metal material of 1. 2. A rare earth element oxide is dispersed in a crystal grain boundary of the refractory metal material, and the rare earth element and the refractory metal material are present in the crystal grain boundary of the refractory metal material together with the oxide of the rare earth element. A high-strength, high-corrosion-resistant material, characterized by comprising the above complex oxide and the complex oxide of a rare earth element and phosphorus.