JPH06346171A - Oxide-dispersed-type alloy and its production - Google Patents

Abstract

PURPOSE:To produce an oxide-dispersed-type alloy consisting of a rare-earth- containing refractory metal, where oxides are uniformly contained even in the inner part and which is free from dispersion in characteristics and has uniform quality. CONSTITUTION:In this oxide-dispersed-type alloy, a refractory metal, such as W, Mo, and alloy containing W and/or Mo, is used as master alloy and rare earth oxides, such as cerium oxide and samarium oxide, are uniformly dispersed in the inner part of this master alloy. This oxide-dispersed-type alloy can be produced by subjecting a refractory metal powder containing rare earth oxides to compacting at (4 to 5)tons/cm<2> and then to four-stage sintering containing at least four-stage temp.-keeping stages including temporary sintering for strength improvement.

Description

Detailed Description of the Invention

[0001]

The present invention relates to tungsten (W),
Regarding oxide-dispersion-type alloys in which oxides are dispersed in refractory metals such as molybdenum (Mo) and alloys containing these, in detail, oxide dispersion used in electrode wires for wire electric discharge machining (hereinafter referred to as cut wires) A mold alloy and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a refractory metal to which a rare earth oxide such as cerium oxide is added is used as a cut wire, for example, a tungsten alloy (W alloy). For example, W
In the case of 1, the powder to which the rare earth oxide is added is pressed by the usual method of powder metallurgy and then sintered by the direct current method.

A method of dispersing a rare earth oxide by a direct current heating method in order to impart recrystallized structure control and electron emission characteristics while utilizing the characteristics of refractory metals such as W and molybdenum (Mo). Being tried.

[0004]

However, in the tungsten alloy sintered body produced by the direct current heating method, the cerium oxide moves toward the outer periphery during sintering, so that the cerium oxide is not present in the center of the cross section of the sintered body. It was found that the number was small and the number was large in the outer peripheral portion. As a result, it was also found that unevenness in structure occurs in the cross-sectional direction of the sintered body, causing surface cracks during rolling and disconnection during electrical discharge machining.
Here, when the direct current heating sintering method is used, the melting point of the added rare earth oxide is lower than the sintering temperature (so-called temperature gradient is simply steep). It moves to a certain outer circumference, and there is a concentration difference that there is less oxide in the center and more oxide in the outer circumference. Due to this difference in concentration, a phenomenon was observed in which the crystal grains of the sintered body differed in size, such as being large in the center and small in the outer periphery. The reverse phenomenon may also occur depending on the sintering conditions.

If the center of the former sintered body has a small amount of oxide and a large amount of oxide in the outer peripheral portion, the workability of the outer peripheral portion becomes worse than that of the inside, causing surface cracks during rolling. Furthermore, when not only the electrical discharge characteristics but also the tensile strength at high temperature during electrical discharge machining are required as in the case of a cut wire, the unevenness of the structure between the inside and the outside due to the difference in concentration becomes a great harm.

On the other hand, when the latter sintered body has a large amount of oxide in the center and a small amount in the outer peripheral portion, the amount of oxide in the outer peripheral portion is small, so that the purpose of improving discharge characteristics cannot be sufficiently achieved. or,
When the purpose of the oxide addition is to control the recrystallized structure, whether the former or the latter, the difference in concentration appears as a nonuniformity of the recrystallized structure and has an adverse effect.

Therefore, the technical problem of the present invention is to provide an oxide-dispersed alloy capable of reducing surface cracks caused by uneven distribution of rare earth oxides, especially cerium oxide, and disconnection during electric discharge machining, and a method for producing the same. To do.

Further, another technical problem of the present invention is to provide an oxide-dispersed alloy containing a rare-earth-containing high-melting-point metal that contains an oxide evenly inside and has little variation in characteristics, and therefore has uniform quality. It is to provide the manufacturing method.

[0009]

Means for Solving the Problems The present inventor has found that a rare earth oxide added to a sintered body obtained by pressing and sintering a powder obtained by adding a rare earth oxide to W, Mo or the like according to a conventional method of powder metallurgy. The present invention has been accomplished by finding an alloy sintered body in which is distributed almost uniformly inside the sintered body and a manufacturing method thereof.

According to the present invention, there can be obtained an oxide-dispersed alloy characterized in that a refractory metal is used as a master alloy and rare earth oxides are uniformly dispersed in the master alloy.

According to the present invention, a refractory metal powder containing a rare earth oxide is pressed and compressed at 4 to 5 ton / cm ² , and at least four temperature maintaining steps including pre-sintering for improving strength are performed. A method for producing an oxide-dispersed alloy is obtained, which comprises performing four-step sintering having

Here, in the present invention, the refractory metal preferably contains at least one of W and Mo. Further, in the present invention, the rare earth oxide is preferably at least one of cerium oxide and samarium oxide.

The present invention will be described in more detail. W, M
In the production of an alloy sintered body in which a rare earth oxide is added to o or the like, the heated rare earth oxide is uniformly added to the compacted body that is pressed and compressed, which includes at least four temperature maintaining steps. Obtain a distributed alloy sintered body.

For example, W powder and rare earth oxide powder are mixed using a crusher and a V-type mixer to prepare a powder in which oxide is uniformly dispersed. This powder is pressed at 4 to 5 ton / cm ² to obtain a rectangular rod-shaped molded body. In order to provide the molded body with strength that can be used in the subsequent sintering step, heat pre-sintering is performed in hydrogen and a vacuum atmosphere as the first step of the four-step sintering. Next, the main sintering process starts. First, the second of the four-stage sintering
As a step, in order to remove impurities other than the added oxide contained in the molded body and to densify the molded body, the temperature is raised to a temperature not higher than the melting point of the oxide and insufficient for sintering, and kept for several minutes. Next, as the third step of the four-step sintering, in order to proceed the sintering without moving the oxide, it is heated to a temperature lower than the melting point of the oxide and higher than the second step for a few minutes to a dozen minutes. Hold. At this stage, sintering proceeds considerably, but the oxide is maintained in a uniformly dispersed state. Further, as a fourth step, in order to complete the sintering, it is heated to a temperature equal to or higher than the melting point of the oxide and kept for a few minutes to a few dozen minutes to obtain a predetermined sintered body. The density of the thus obtained sintered body is 90% or more of the theoretical value, and the added oxide is present in the sintered body in a substantially uniformly dispersed state. Similar effects were obtained with Mo.

[0015]

EXAMPLES Examples of the present invention will be described below.

A purity of 99.9% or more and an average particle diameter of 2.5 μm
W powder of 99.99% purity, 7 by BET particle size measurement method
m ² / g cerium oxide powder (melting point 2600 ° C.) 0.1
wt%, 0.7 wt%, and 1.0 wt% were added and mixed for 3 hours in total using a crusher and a V-type mixer, to prepare a mixed powder in which cerium oxide was uniformly dispersed. These powders were pressed at a pressure of 5 ton / cm ² to prepare a rectangular rod-shaped molded body. In order to give strength to this molded body, the first step of the four-step sintering was 3
Pre-sintering was performed by heating for 0 minutes. Next, the pre-sintered body was further heat-sintered in three steps in a hydrogen atmosphere.

First, as the second step of the four-step sintering, the temperature was raised to 1850 ° C. in 1 minute and maintained at this temperature for 3 minutes after the completion of the temperature increase. Since this temperature is much lower than the melting point of the oxide, no melt migration of the oxide occurs, so that impurities other than the added oxide can be extracted as a melt or gas to the outside of the sintered body and the compacted body can be densified. is there.

Further, as a third step, 185 is spent for 1 minute.
The temperature was raised from 0 ° C to 2300 ° C, and the temperature was maintained at this temperature for 10 minutes after the completion of the temperature increase. At this stage, the melting point of cerium oxide is 2
By sintering at a temperature lower than 600 ° C. and higher than the temperature of the above-mentioned second stage, the sintering proceeds while suppressing the melt transfer of cerium oxide.

After holding for 10 minutes, 2800 for 1 minute
The temperature was raised to 0 ° C., and the temperature was maintained for 15 minutes after the temperature was completed. In order to complete the sintering in the fourth stage, the sintering is performed at a temperature higher than the melting point of cerium oxide, but since the sintering has already progressed considerably, the grain boundary migration of the molten oxide is hardly performed. The density of the sintered body thus obtained was 93.3% of the theoretical value.

Next, the dispersion state of cerium oxide in the sintered body obtained by the above method was inspected.

As shown in FIG. 1, first, a sample to be inspected is taken from the sintered body. The results of analyzing the CeO ₂ in the analysis sample by cutting the square bar-shaped tungsten alloy after sintering and further dividing it into 9 parts as shown in FIG. 2 are shown in Tables 1 to 3 below. Further, FIG. 3 is a map of the dispersion of cerium by EPMA for the cross section of the slag after sintering. Similar results were obtained for other rare earth oxides.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3] From the examples of Tables 1 to 3 and FIG. 3, it was found from the distribution of cerium in the cross section of the sintered body that the dispersion remained almost uniformly.

In the case of Mo, the temperature of each step is set to the first step 1
250 ° C, 2nd stage 1450 ° C, 3rd stage 2100 ° C,
In the fourth step, the temperature was set to 2300 ° C., and the same result as in the case of W was obtained.

As a rare earth oxide having the same effect, samarium oxide (Sm ₂ O ₃ , melting point 2300 ° C.)
Can be illustrated.

On the other hand, the second stage is 1700 ° C. × 5 minutes, the third stage
The result of the cerium oxide-tungsten system was the same as the above-described embodiment except that the treatment was performed at 1900 ° C. for 30 minutes, and the density was 89% of the theoretical density, and the variation was as shown in the comparative example of Table 2 above, and the cut wire Also did not reach the desired level.

FIG. 3 is a map of the dispersion of Ce by an electron probe microanalyzer (EPMA) as a scale for measuring the distribution of CeO ₂ in the alloy with respect to the cross section of slag after sintering. The alloy according to Example (1) and (b) show the alloy according to Comparative Example (1). As shown in FIG. 3, it was confirmed that Ce was more uniformly dispersed in the oxide-dispersed alloy according to the example of the present invention than in the oxide-dispersed alloy according to the comparative example.

[0029]

As described above, since the rare earth oxide is uniformly dispersed in the sintered body according to the present invention, the crystal grains are also substantially uniform. As a result, processing irregularities and surface cracks are less likely to occur during rolling processing, and it has a great effect on the control of the recrystallization structure, which is the purpose of addition. However, since not only a cut wire having a general wire diameter but also an ultrafine wire (φ50 μm) is used as the cut wire, there is no unevenness in the fiber structure, so that there are few breaks and no step is formed on the cut surface. Therefore, it greatly contributes to the improvement of cutting efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of collecting an oxide-dispersed alloy sample according to an example of the present invention.

FIG. 2 is a diagram showing a method of manufacturing a sample obtained by dividing the sample of FIG. 1 into nine parts.

FIG. 3 (a) is an image image of Ce by EPMA showing a particle structure of an oxide-dispersed alloy according to Example (1) of the present invention. (B) EPM showing the grain structure of the alloy according to Comparative Example (1)
It is an image image of Ce by A.

Claims (7)

[Claims] 1. An oxide-dispersed alloy characterized in that a refractory metal is used as a master alloy, and rare earth oxides are uniformly dispersed in the master alloy. 2. The oxide dispersion type alloy according to claim 1, wherein the master alloy contains at least one of W and Mo. 3. The oxide dispersion type alloy according to claim 1, wherein the rare earth oxide is at least one of cerium oxide and samarium oxide. 4. A high melting point metal powder containing a rare earth oxide
Compressed at ~ 5 ton / cm ² and has at least 4 temperature maintenance steps including pre-sintering to improve strength 4
A method for producing an oxide-dispersed alloy, which comprises performing stepwise sintering. 5. The method for producing an oxide-dispersed alloy according to claim 4, wherein the four-step sintering includes performing preliminary sintering for providing strength enough to cope with a main sintering process. A first step, a second step including holding for a few minutes at a temperature not higher than the melting point of the rare earth oxide and not sufficiently sintered, and at a temperature not higher than the melting point of the rare earth oxide and higher than the second step. A method for producing an oxide-dispersed alloy, comprising: a third step including heating; and a fourth step including holding at a temperature equal to or higher than the melting point of the oxide for several minutes. 6. The method for producing an oxide-dispersed alloy according to claim 4, wherein the refractory metal is W or Mo.
A method for producing an oxide dispersion type alloy, comprising at least one of the above. 7. The oxide dispersion type alloy according to claim 4 or 5, wherein the rare earth oxide is at least one of cerium oxide and samarium oxide. Manufacturing method.