JPH1068001A - Intermetallic-compound consumable electrode for rotational electrode process and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrode for a rotational electrode process having an optional composition by mixing raw powders having a specified grain diameter into a target composition, press-forming a mixture, heating a compact to a specified temp. in a nonoxidizing atmosphere to bring about an exothermic reaction and then heat-treating a compact. SOLUTION: The raw powders having <=150μm grain diameter and one of which consists of Al are mixed into a target composition, a mixture is press- formed, and a compact is heated to >=873K in a nonoxidizing atmosphere to bring about an exothermic reaction. The compact is heat-treated at >=1273K to obtain the intermetallic-compd. consumable electrode for a rotational electrode process contg. <=1000ppm oxygen and Al.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a powder.
A consumable electrode for use in producing a spherical powder of an intermetallic compound containing Al using a rotating electrode method as a seed,
The present invention relates to the manufacturing method.

[0002]

2. Description of the Related Art TiAl and NbAl intermetallic compounds are being developed as high-temperature structural materials. Since these materials are brittle and have poor ductility, attempts have been made to improve the structure of the material from a molten cast material to a workable material as a structural material by high-temperature forging or high-temperature heat treatment, and considerable prospects have been obtained on an experimental scale.

On the other hand, since these intermetallic compounds are difficult-to-process materials, they need to be formed into members by applying powder metallurgy in practical use. Further, in the development of composite materials, the use of powder has been considered. In response to such needs for powders, some powders and their production techniques have been introduced. One of them is an application of a mechanical alloying method in which a mixture of raw metal powders having a target composition is kneaded for a long time using a ball mill or an attritor. Many studies have proved that an intermetallic compound can be synthesized by this method. However, this method requires a long time of several hundred hours, a non-uniform kneading effect due to the sticking of the raw material powder in the manufacturing apparatus or the mixing of impurities due to abrasion powder of the equipment material, and an increase in the amount of oxygen in particular. Under these circumstances, the current situation is that the ratio is excessively increased to nearly 1%, so that it is still necessary to overcome these drawbacks for use in the production of practical parts.

[0004] As another production method, there is a method of igniting a blended powder, causing a self-heating reaction, and then pulverizing the powder to produce a powder, which has been studied as a combustion synthesis method. However, the powder produced by this method has a problem that the amount of oxygen increases mainly to about 4000 ppm in the pulverization step and becomes excessive. Even if these intermetallic compounds are formed from powder even in the powder metallurgy method aimed at by the present invention, it is desirable to secure a ductility at room temperature of several percent or more in processing as a structural material. It is necessary that the oxygen amount is at least 1000 ppm or less. Therefore, it can be said that the rotating electrode method is an effective powder manufacturing method as a method in which the amount of oxygen does not increase in the powdering step. In this method, since the amount of oxygen does not increase, it is necessary to obtain a low acid material in the electrode material used.

Heretofore, for this purpose, a melt-cast ingot has been used after being processed into an electrode material. However, in TiAl, the melting point difference between the raw material Ti and Al is about 1,160K,
bAl has a temperature of about 1755K, and has been able to overcome component segregation by repeated dissolution. Here, as a further new problem to be used as an electrode material, the intermetallic compound in the melted ingot includes one having a particle size larger than the powder particle size to be produced by the rotating electrode method, and melting of the surrounding phase having a lower melting point. Fluid, not fully fused,
It scatters as non-spherical powder and is mixed in the powder. Therefore, in the past, cast ingots were heat-treated to have a uniform lamellar structure, or small-scale melting was used to produce and use ingots that suppressed grain growth by casting one electrode and one electrode. Not only was it out of the field of traditional techniques, but it was also a detour to return to powder and reach the ingot, as compared to the method of material production starting from casting.

[0006]

Problems to be Solved by the Invention The use of powders ultimately involves making bulk materials by hot pressing or HIP, but the oxygen content is related to the ductility at room temperature,
Even with 4000 ppm of the powder produced by combustion synthesis, the tensile elongation of the bulk material due to it is about 1%. Since the amount of oxygen does not increase in the process of hot pressing or HIP, it is necessary to reduce the amount of oxygen in the powder itself. If the rotating electrode method is used as the powder production method, there is an advantage that the amount of oxygen does not increase in the process. Therefore, it is necessary to reduce the amount of oxygen in the electrode material, and one of the aims of the present invention is in this respect.

Next, a method of using an ingot obtained by melting and casting as an electrode material has been conventionally used as a low oxygen electrode.
In this case, a melting method for avoiding oxygen pick-up from the melting furnace material has been adopted, and a melting operation has been repeatedly performed so as not to cause melting segregation due to differences in physical property values of constituent materials. However, in the rotating electrode method, when a melt is formed on the electrode surface, it flows immediately by centrifugal force and scatters as a droplet from the electrode end, so that an intermetallic compound as the object of the present invention is Since the materials are composed of compounds with different melting points, if they are unevenly distributed in the electrode material, compounds that do not fuse in the melt on the electrode surface will remain, and apparently mixed as non-spherical powder in the powder I do. This point is a point to be noted when the electrode material is produced by melting and casting, and if only this is mentioned, the method of mechanical alloying or combustion synthesis is suitable for the production method of the electrode material. The present invention has been made to prevent such segregation from the electrode material into the powder based on the characteristics of the powder generation phenomenon in the rotating electrode method.

[0008]

SUMMARY OF THE INVENTION The first aspect of the present invention is to provide a digital camera having a 150
An intermetallic compound consumable electrode for a rotary electrode method in which a constituent element or compound having a particle size of μm or less is dispersed and an oxygen content is 1000 ppm or less, and the diameter is more than 30 mm and less than 80 mm. The second aspect of the present invention is that the particle size is 150 μm.
The smaller raw material powder is blended with the target composition of the intermetallic compound to be prepared and mixed and press-formed, and then gradually heated from 873K in a non-oxidizing atmosphere to cause a self-heating reaction. Then, a diffusion heat treatment is performed at a temperature of 1273K or more, which is
This is a method for producing an intermetallic compound consumable electrode for a rotating electrode by processing the rod into a round bar of less than m.

The technical constitution is that the particle size of the raw material powder is limited in relation to the subsequent diffusion heat treatment and in terms of the uniform dissolution in the rotating electrode method, and the self-heating reaction synthesis is performed after press molding to complete the reaction. The electrode material was used as it was without a pulverizing process that could increase the amount of oxygen at the same time, and the reaction synthesis stopped the furnace temperature raising operation there to prevent damage to the furnace due to reaction heat. In addition, the diffusion of the components and the homogenization of the structure were achieved by further high-temperature heat treatment, and the uniform fusion of the melt on the melting surface was achieved by limiting the electrode diameter from the melting phenomenon of the rotating electrode method. It is in.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The production of an electrode according to the present invention is as follows.
A mixed powder of raw material powders having a size of 50 μm or less is used, and includes self-heating reaction synthesis. Many experimental results have shown that the synthesis reaction starts near the melting point of Al during the temperature raising process, but if the particle size of the high melting point material other than Al is large, it remains in the end reaction. The limit is 150 μm or more, and in the present invention, it is limited to 150 μm or less at which a complete reaction occurs.

The value of 150 μm is also a limit value of the homogenizing fusion at the time of melting the rotating electrode by the method of the present invention. The mixing of the raw material powders is performed in an inert gas, and a method of mixing materials having a large difference in density is sufficient. Press molding may be a uniaxial press depending on the shape of the raw material powder,
It is desirable to use cold isostatic pressurization (CIP), which has a small variation in the molding density, and to obtain a final electrode shape. For the raw material under the conditions of the present invention, 340 MPa is sufficient. As a result, thermoconductivity in the subsequent reaction synthesis is obtained, and the reaction proceeds sufficiently.

The synthesis reaction is started by heating to 873K or higher. In order to prevent damage to the furnace because the furnace temperature rises due to the reaction heat, the end of the reaction is determined by controlling the furnace temperature, and then the temperature is raised to the high-temperature heat treatment temperature. A method of causing a synthetic reaction of a CIP molded product in an inert gas atmosphere by using pseudo-HIP has an effect of suppressing volume expansion due to reaction synthesis. This is one embodiment included in the invention. Reaction-synthesized electrodes contain different types of intermetallic compounds,
The tissue is heterogeneous. Add this to another 12
A high-temperature heat treatment at 73 K or more is performed to homogenize the structure and diffuse components. The diffusion of the component elements progresses in a relationship between temperature and time, and it takes much longer at 1273K or less. In practice, the diffusion is performed at a temperature of 1273K or more and less than the melting point depending on the material. The intermetallic compound in the electrode material thus obtained does not exceed 150 μm and is characteristically different from the cast electrode.

[0013] An electrode made from a powder material without melting as in the present invention has some pores and exhibits a dissolution phenomenon different from that of a cast electrode in rotating electrode melting. And is limited to less than 80 mm. If the thickness is less than 30 mm, it is difficult to hold the melt on the dissolving surface of the electrode, and it becomes a liquid on the electrode surface and immediately flies away. On the other hand, if it is 80 mm or more, the melt on the melting surface partially solidifies due to thermal diffusion to the solid portion of the electrode, making it impossible to hold the melt properly and the droplets are not scattered smoothly. The means to solve this point does not simply increase the power of the heat source, but requires the arrangement of the heat source in consideration of the flow of the melt on the electrode surface and the generation of droplets at the end of the electrode in the rotating electrode method. This requires another technique different from the rotating electrode method.

The constituent structure of the intermetallic compound includes a structure having a large melting point difference. If a large amount of segregation of the structure remains in the electrode material, the pre-dissolution of the low melting point structure portion occurs, and the flow of the melt on the electrode surface is caused. Begins, and the specific composition compound is mixed as a non-spherical powder in the powder while being separated. In order to eliminate this, in addition to improving the structure by heat treatment of the electrode material, it is effective to maintain the melt layer on the electrode surface by taking a slightly concave shape on the dissolution surface of the electrode. The diameter of the electrode from which it can be removed is more than 30 mm and less than 80 mm.

[0015]

[Embodiment] As for the raw material powder, the amount of oxygen obtained by dehydrogenating titanium hydride through grinding in an inert gas is 8
As for Nb, the one having an oxygen amount of 590 ppm produced through chemical purification was used, and for Al, the one having an oxygen amount produced by argon gas atomization of 900 ppm was used for Al.

These are sieved in an argon gas atmosphere using a glove box, and those having respective particle diameters are similarly weighed in the glove box with respect to Ti and Al in a weight ratio of 67:33 for Nb and Al. Was combined in a weight ratio of 94: 6. These were sealed and sealed in cylindrical containers, respectively, taken out of the glove box, mounted on a three-dimensional swinging mixer, and operated for 30 minutes. One hour after the operation, the mixed powder was taken out, degassed and sealed in a neoprene cylindrical container, and then 340MP using a CIP machine.
A round bar was formed by the water pressure of a.

The molded round bar is buried in zirconia powder and placed in a vacuum furnace. At a pressure of 5 × 10 ⁻³ Pa or less, the temperature is first raised to 873 K, and the temperature is gradually increased while watching the furnace thermometer.
When the self-heating reaction started, the temperature of the furnace was stopped and the reaction was completed. When the furnace temperature settled down, the temperature was raised again to perform a high temperature treatment. The oxygen content of the electrode was 840 ppm for No. 3 TiAl and 6% for No. 14 NbAl.
It was 10 ppm.

The round bar that has been subjected to the high-temperature heat treatment is finished into electrodes of various sizes by machining, and is rotated using a rotating electrode device.
A powder was produced. The table summarizes the electrode diameter, operating conditions of the plasma rotating electrode, and the shape of the obtained powder.

[0019]

[Table 1]

[0020]

According to the method of the present invention, an electrode for a rotating electrode method having an arbitrary composition can be prepared by selecting a raw material powder and a compounding ratio thereof. The amount of oxygen can be made lower than that of the powder obtained by any of the above methods. The present invention can provide a powder having sufficient performance to overcome the difficult-to-workability of an intermetallic compound containing Al, which will be a future material, by powder metallurgy.

Claims (2)

[Claims] Claims: 1. An Al element containing a constituent element or compound having a particle size of 150 μm or less dispersed therein and having an oxygen content of 1000 ppm or less.
A consumable intermetallic compound electrode for a rotating electrode method having a diameter of more than 30 mm and less than 80 mm in a contained intermetallic compound. 2. Among the raw material powders having a particle size smaller than 150 μm, one of them is Al, and these are blended to a target composition, and the mixture is press-molded, and once subjected to 873K or more in a non-oxidizing atmosphere. A self-exothermic reaction, followed by a heat treatment at a temperature of 1273 K or more, to produce a consumable electrode for a rotating electrode method.