KR910008029B1 - The making method of w-cu fusion alloy - Google Patents

Abstract

An infiltrated W-Cu alloy is produced by adding 0.3-1 wt.% Ni-P alloy to W powder of 1-10μ particle size by the electroless plating to form a mixed powder, molding the mixed powder to form a green compact, and infiltrating the green compact with Cu in the furnace of hydrogen or ammonia gas stream at 1100-1200 deg.C for 20min or less. The W-Cu alloy is useful as a very high pressure electric contact material.

Description

Manufacturing Method of Tungsten Copper (W-Cu) Infiltration Alloy

1 is a schematic view of a general tungsten-copper infiltration alloy manufacturing method of the prior art.

2 is a schematic view of a tungsten-copper infiltration alloy manufacturing method of the present invention.

3 is a scanning electron micrograph of a tungsten powder green compact skeleton structure heated and cooled to a temperature of 1150 ° C. at a rate of 150 ° C./min in a hydrogen atmosphere,

3a is a skeleton structure of a tungsten powder green compact in which a nickel-phosphorus (Ni-P) alloy is added by an electroless plating method according to the present invention;

3b is a skeletal structure of a prior art tungsten powder compact without addition of a nickel-phosphorus (Ni-P) alloy.

4 is a scanning electron micrograph of the tungsten-copper infiltration alloy microstructure,

Figure 4a is a infiltration alloy microstructure prepared according to the present invention,

Figure 4b is an infiltration alloy microstructure prepared according to the prior art.

5 is a graph showing the electrical contact characteristics (change in contact resistance according to contact opening and closing frequency) of a tungsten-copper infiltration alloy to which a nickel-phosphorus alloy is added and a prior art infiltration alloy according to the present invention.

The present invention provides an improved method for producing a tungsten-copper (W-Cu) -based infiltration alloy, which is useful as an ultra-high pressure electrical contact material, and more specifically, a tungsten in which a small amount of nickel-phosphorus (Ni-P) alloy is added by electroless plating. It relates to a method for producing a winter infiltration alloy.

Tungsten-copper infiltration alloys are very useful as ultra-high pressure electrical contact materials, and are prepared by infiltration of copper in tungsten powder compacts (sintered compacts) using powder metallurgical infiltration. A typical tungsten-copper infiltration alloy in the prior art is a sintered compact after primary sintering of a tungsten powder obtained by compression molding a tungsten powder having an average particle of about 5 microns as outlined in FIG. It is composed of a two-step process by placing molten copper (Cu) on the top and heat treatment again to allow molten copper to penetrate into the micropores in the tungsten sintered framework.

In this case, general heat treatment conditions are performed for about 1 hour at 1200-1250 ° C. under decomposition ammonia or hydrogen gas in both the primary sintering treatment and the secondary heat treatment. The primary reason for the primary sintering of tungsten green compacts is to ensure that the tungsten green compacts (skeleton) have sufficient strength for handling. However, it is difficult to obtain a satisfactory strength at a temperature of 1200-1250 ° C. used in a general manufacturing method, and in particular, due to the low sintering temperature, the pore structure of the resulting sintered tungsten skeleton keeps the polygonal structure before sintering almost intact. The powder structure gives a rough and irregular shape (see also 3b). That is, as shown in the tissue photograph of FIG. 3b, the tungsten powder particles sintered by adding a trace amount (about 0.3 wt%) of Ni according to the prior art are very irregular in size and are sluggishly angled particles (white part in the picture). The structure of the powder skeleton is thus formed. Therefore, the pore structure (black part in the photo) existing between these tungsten particles also maintains the shape corresponding to the skeletal structure, resulting in a pore passage having a very irregular diameter size and a jagged surface. Done. Therefore, the subsequent agitation process may also proceed undesirably.

On the other hand, if the sintered tungsten powder is sintered at a high temperature of 1600 ° C. or more, sufficient sintering strength can be obtained, but in this case, a special equipment for ultra-high temperature treatment is required, and the process is complicated and economically unreasonable. It is difficult to put it to practical use. On the other hand, the heat treatment condition of the copper infiltration step is also treated for 1 hour at 1200-1250 ° C., which is the same as the primary sintering treatment condition, which is higher than necessary in consideration of the copper melting temperature (1083 ° C.). As such, sufficient heat treatment conditions are given to overcome the drawbacks of the primary sintering treatment and the inhibitory effects on the infiltration process.

The present invention is to solve the problems of the prior art manufacturing method, to provide a new and improved method for producing a tungsten-copper infiltration alloy with improved physical properties by heat treatment for a short time at a relatively low heat treatment temperature. In particular, the present invention aims to provide a manufacturing method capable of simultaneously performing excellent sintering and infiltration of a tungsten-copper alloy by heat treatment only once at a low temperature for a short time.

According to the present invention, a small amount of nickel-phosphorus alloy is added to and mixed with tungsten powder by an electroless plating method to form a green compact, and then the melt is applied to the green compact, which is short within 20 minutes at a temperature of 1100-1200 ° C. By heating for a time, a method for producing a tungsten-copper infiltration alloy having excellent physical properties is provided. As outlined in FIG. 2, the manufacturing method of the present invention not only shortens the heat treatment process performed in the conventional two-step process to one-step process but also considerably improves the heat treatment temperature and time through the addition of nickel-phosphorus alloy. Has characteristics. That is, in the conventional method, the heat treatment was performed for 1 hour at 1200-1250 ° C. for 1 hour and the second step, respectively, but in the method of the present invention, it is sufficient by heat treatment only once within 20 minutes at about 1100-1200 ° C., rather, the resultant tungsten. -The physical properties of the winter infiltration alloy is also improved.

In more detail, the preparation method of the present invention is an alloy of nickel- (7-12 wt%) in tungsten powder having a particle size of 1-10 microns and an average particle size of about 5 microns [Ni- (7-12 wt%). ) P alloy] is added in an amount of 2% by weight or less by electroless plating to form a nickel-phosphorous tungsten mixed powder, which is formed into a green compact. Here, in the nickel-phosphorous alloy added to tungsten, too small phosphorus content can lead to improved tungsten skeletal structure change at a lower temperature than when nickel alone is used, and when too large, no further effect can be expected and strength is increased. 7-12% by weight is preferred, with 10-11% by weight being particularly preferred as it may adversely affect. In addition, when the amount of nickel-phosphorus alloy added to tungsten is 0.1% by weight or less, the desired tungsten skeleton structure change cannot be satisfactorily induced, and when 2.0% by weight or more, no further effect can be expected and the final W-Cu-based It may adversely affect the alloy electrical contact characteristics. Preferred amounts of addition are from 0.3% by weight to about 1% by weight. Electroless plating of nickel-phosphorus alloy can be carried out by various known techniques and is not specific. The pretreatment step in electroless plating can also be done by well known prior art. A typical method is to heat tungsten powder in hydrogen gas at 800 ℃ for about 1 hour to remove impurities and contaminating film of tungsten powder, and then immerse for several minutes in dilute hydrochloric acid solution at about 65-75 ℃ for activation of powder surface. And wash with distilled water.

On the other hand, as is widely known in the prior art, the porosity of the green compact depends on the amount of copper to be infiltrated, and the desired porosity can be achieved by controlling the green compacting pressure. For example, when the urine oscillation content is 20wt%, the desired porosity is about 37% and the molding pressure for this is about 2ton / cm ² .

As described above, a tungsten-copper infiltration alloy having excellent physical properties is obtained by forming a nickel-phosphorus-containing tungsten green compact, followed by application of a melt-precipitation and heat treatment at a temperature of about 1100-1200 ° C. under a hydrogen or decomposition ammonia atmosphere for less than 20 minutes. In this case, the heat treatment is preferably carried out by increasing the temperature to 1100-1200 ℃ at a rate of about 120-150 ℃ / min and maintained at that temperature for about 10 minutes.

Meanwhile, the copper content range applied in the copper infiltration step is about 10-40 wt%, preferably about 18-25 wt%, depending on the use, as in the general tungsten-copper infiltration alloy.

In the production method of the present invention, due to the addition of the nickel-phosphorus alloy, the powder sintering in the nickel-phosphorous tungsten green compact is rapidly activated in a short temperature rising step within about 10 minutes before the copper infiltration is started. The interbonding is strengthened and the powder form is smoothly changed so that the green compact (sintered body) forms a pore structure (see also 3a) advantageous for copper infiltration. As a result, the copper infiltration behavior in the nickel-phosphorus-containing tungsten sintered body having such a skeletal structure is performed very well even at a relatively low temperature and a short time.

The present invention will now be described by way of examples.

Example 1

A nickel-phosphorus alloy was added to a tungsten powder having a particle size in the range of 1-10 microns and an average particle size of about 5 microns by the following electroless plating method.

As a pretreatment for electroless plating, the tungsten powder is heated in 800 ° C hydrogen gas for about 1 hour to remove impurities and contaminant coating of the tungsten powder, followed by 2-3 to 5% hydrochloric acid solution at 71 ° C for activation of the powder surface. It was deposited for a minute and washed with distilled water. As the electroless plating bath, a mixed aqueous solution of nickel chloride hexahydrate (NiC1 ₂ · 6H ₂ O), sodium phosphate (NaH ₂ PO ₄ ), and sodium acetate trihydrate (CH ₃ COONa · 3H ₂ O) was used. 21 g of nickel chloride hexahydrate, 24 g of sodium phosphate, and 10 g of sodium acetate oxide were added and mixed in 1 L of distilled water to maintain the pH and temperature of the plating solution at 5.4 and 90 ° C., respectively, followed by mixing 250 g of the pretreated tungsten powder. Electroless plating was performed by stirring the powder in a state where iron pieces were soaked as a reaction initiation accelerator. The plated tungsten powder was washed 2-3 times with water and dehydrated and vacuum dried at 55 ° C. for 6 hours. As a result of chemical analysis, 0.3 wt% of nickel-phosphorus alloy was coated on the tungsten powder after 3 minutes of plating time, and the composition of the plated alloy was nickel-11.2 wt%.

100 g of plated nickel-phosphorous tungsten powder was pressurized and molded at a molding pressure of about 2 ton / cm 2 to prepare a green compact having a porosity of about 37%, and 25 g of a molten metal was applied to the top of the furnace. Charged. In the hydrogen atmosphere, the furnace temperature was raised to a temperature of 1150 ° C. at a rate of 150 ° C./min, and then maintained at that temperature for 9 minutes to complete the infiltration. As a result, a tungsten-copper infiltration alloy having a copper content of 20 wt% was calculated.

On the other hand, for the purpose of comparison, according to the general method of the prior art, a tungsten powder (average particle: 5 microns) was formed into a green compact having a porosity of about 37%, and then, at a rate of 150 ° C./min in a hydrogen atmosphere. The furnace was heated to a temperature of 1250 ° C. and maintained for 1 hour. After cooling, the resultant tungsten sintered body was applied to the resulting tungsten sintered body, and again heated to a temperature of 1200 ° C. at a rate of 150 ° C./min. A tungsten-copper infiltration alloy having a content of 20% by weight was calculated.

The microstructures of the tungsten-copper immersion alloy of the present invention prepared as described above and the tungsten-copper immersion alloy of the prior art were observed with a scanning electron microscope and the photograph is shown in FIG.

As shown in FIG. 4, the infiltration alloy 4a of the present invention has a dense and homogeneous microstructure by uniformly distributing copper between tungsten skeletons forming a strong bonding structure, while the infiltration alloy 4b of the prior art is The tungsten skeleton retained the initial polygonal powder structure, resulting in uneven distribution of copper and less dense texture.

On the other hand, the ultra-high voltage electrical contact material was manufactured from each infiltration alloy, and its electrical characteristics were measured and evaluated as follows. That is, the contact force 500g, the opening force 300g, the switching speed 2cm / sec and the switching frequency 1 / sec. Shown in

As shown in the figure, according to the present invention, the tungsten-copper contact material added with nickel-phosphorus exhibited a very low increase in contact resistance compared to the contact material according to the prior art. In addition, the tungsten-copper contact material of the present invention was 12 mg, whereas the tungsten-copper contact material of the present invention was 12 mg even in the arc consumption measured after 12,000 opening and closing tests. It can be seen that the infiltration alloy has superior electrical contact characteristics compared to the pure tungsten-copper infiltration alloy according to the prior art.

Example 2-5

As shown in the following table, tungsten-copper infiltration alloys were prepared according to the method of Example 1, by varying the nickel-phosphorus alloy composition and addition amount, tungsten compact porosity, infiltration content and infiltration conditions.

On the other hand, in the infiltration conditions, the heating rate of heating up to the infiltration temperature was performed at about 120-150 ° C / min.

As a result of analyzing and analyzing the microstructure and electrical contact characteristics of the resulting tungsten copper-based infiltrating metals, the microstructure and electrical contact characteristics were almost the same as those of the infiltration alloy prepared in Example 1.

TABLE 1

(Note) In the above%, the porosity is% by volume, the rest are% by weight.

As described above, the present invention provides a relatively low temperature without ancillary primary sintering treatment by electroless plating of a small amount of nickel-phosphorus alloy to the tungsten powder before sintering (annealing) heat treatment in the production of tungsten copper-based infiltration alloy. It is to provide a very economical and improved method for producing a tungsten copper-based infiltration alloy, which has a metallurgical property and an electrical contact property, which is superior to the conventional tungsten-copper infiltration alloy, in a one step infiltration process for a short time.

Claims (6)

In the production of tungsten copper-based infiltration alloy, nickel-phosphorus alloy is added to fine tungsten powder in an amount of 0.1-2wt% by electroless plating to form a nickel-phosphorus-containing tungsten mixed powder, which is press-molded as a green compact. After that, the molten metal is applied to the resulting green compact and heat-treated for 20 minutes at a temperature of 1100-1200 ° C. in a furnace under hydrogen or decomposition ammonia. The method according to claim 1, wherein the nickel-phosphorus alloy has a composition of Ni- (7-12wt%) P. The method according to claim 2, wherein the nickel-phosphorus alloy has a composition of Ni- (10-11 wt%) P. The method of claim 1 wherein the nickel-phosphorus alloy is added in an amount of 0.1-1.0 wt%. The method of claim 4 wherein the nickel-phosphorus alloy is added in an amount of 0.1-0.5 wt%. The method according to claim 1, wherein the heat treatment is performed by raising the temperature to 1100-1200 ° C at a heating rate of 120-150 ° C / min and then maintaining the temperature for 8-12 minutes.

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