Method of manufacturing products from tungsten/copper pseudoalloy

FIELD: powder metallurgy.

SUBSTANCE: parts of devices protecting against radioactive emission or electric contacts are proposed to be manufactured from tungsten/copper pseudoalloy. Tungsten powder is mixed with binder containing 0.5-1.5% colophony and 0.05-0.15% ammonium formate or citrate. Resulting mixture is compacted and resulting porous blanc is brought into contact with copper. The total is thermally treated by gradually raising temperature: first in vacuum to remove binder and to melt copper and then in argon atmosphere to 1360-1410оС.

EFFECT: increased wettability and uniformity of impregnation, and eliminated explosive risk due to excluded use of hydrogen.

3 cl, 1 tbl, 10 ex

 

The invention relates to the field of powder metallurgy, in particular, for the manufacture of parts of various devices protecting from the action of radiation, such as protective covers x-ray tubes, or electrical contacts electrocommunication apparatus of pseudoplane tungsten-copper.

Known methods for producing pseudoplane tungsten and copper, high-temperature liquid-phase sintering of pressed blanks from a mixture of their powders in a reducing atmosphere at a temperature close to 1200° With (see, for example, Uwide, Ihalainen. Vaidation. Liquid-phase sintering under pressure song tungsten-Nickel-copper. Powder metallurgy, 1977, No. 4, s.43-49). The disadvantage of these methods is the need for additional application of pressure during sintering, which significantly increases the cost of the process of obtaining products. In addition, this method is difficult to obtain products with a low content of low-melting component of the alloy - copper (less than 30 wt.%).

Known for cheaper ways of getting pseudoplane tungsten-copper, which are used relatively long and consist of capillary impregnation of a porous tungsten blanks liquid copper. These methods have a number of varieties. However, as a rule, they are conducted in a reducing atmosphere, stereodecoder.

So, there is a method of manufacturing contacts for electrical apparatus, in which products are produced by impregnation of the compacts of tungsten powder in contact with a compact copper, in an atmosphere of hydrogen or natural gas at a temperature of 1200° With (see A.S. the USSR # 213989, publ. 20.03.68, IPC B 22 F 3/26). However, working with hydrogen is explosive and requires additional costs for the provision of special conditions that increases the value of the products obtained.

Also known is a method of obtaining products on the basis of tungsten-copper impregnated blanks tungsten by bringing it in contact with copper when heated for 2 hours at 1250° C in an atmosphere of hydrogen (see U.S. patent No. 4710223, publ. 01.12.87, NCI 75/247), which is the closest to the number of matching characteristics to the method proposed by the authors, and used as a prototype. In this work the tungsten powder is pre-mixed with volatile ligament, containing palm oil, polyethylene and stearic acid taken in the quantity of 50 vol.%, then extruded and deleted a bunch of chemical dissolution with subsequent distillation in an argon atmosphere at 370° C. and then pressing was specaly and annealed in hydrogen atmosphere. The resulting product in accordance with the patented method have good qualitative and quantitative is e indicators (components, the density). The disadvantage of this method, as specified above, is that the end product is obtained in the environment of hydrogen, and all measures necessary to ensure the safety of equipment, labor, and fair in this case.

The task of the authors was to create a method of manufacturing products based pseudoplane tungsten-copper without the use of hydrogen, while maintaining the required quantitative and qualitative characteristics of the composition and density.

The problem is solved in that a method in which a mixed powder of tungsten with rosin, taken in an amount of 0.5-1.5 wt.%, when added to a mixture of citrate or ammonium formate in the amount of 0.05 to 0.15 wt.%, press the mixture to obtain a porous preform, and then the porous workpiece is brought into contact with the compacted copper, and perform heat treatment at a gradual heating of the first vacuum to remove organic ligaments and melting the copper, then in argon to 1360-1410° C. the heating in vacuum is carried out first at a residual pressure of not more than 1.10-1mm Hg to 800-900° With, then at 1.10-2mm Hg to a temperature of not more than 1200° C. the Heating is carried out in argon at a pressure of not less than 0.2 MPa with a holding time at the final temperature for 10-15 minutes

The difference between the proposed method and the known is the use of as ligaments, which is both a plasticizer and a blowing agent, rosin and citrate or ammonium formate, taken in the above quantities, as well as the implementation of heat treatment and impregnation in vacuum with subsequent replacement of vacuum in an inert atmosphere and operating conditions of the process.

From prior art it is known that the impregnated porous tungsten billet molten copper in a vacuum is difficult (see VII and other Influence of titanium and zirconium on the formation and properties of pseudoplane W-Cu. Powder metallurgy, 1975, No. 5, p.53-60). This is due to the presence of the powders of residual oxygen, most of which is related to surface oxides, the presence of which on the interfacial boundary of W-Cu dramatically increases the angle wettability of copper. Restoration of surface oxides in vacuum is only possible at temperatures above 1350° C. However, at these temperatures the evaporation of copper due to the high elasticity of vapor that affects the operational characteristics of the equipment and makes the impregnation process unprofitable. On the basis of numerous experimental studies, the authors found that the use of as bundles of rosin with the addition of ammonium salts of organic acids, in particular formate or ammonium citrate, enables to obtain a dense products on the basis of pseudoplane in Hram-copper without the use of hydrogen during heat treatment and impregnation. It is known that rosin is used as one component of the flux by mixing and pressing of metal powders (see, for example, Russia, application No. 99127935, publ. 20.09.01, MKI B 22 F 3/05). Also known from the field of chemistry that ammonium salts of organic acids, in particular formate, ammonium, can serve as a reducing agent (see, for example, Russia, application No. 96106007, MKI 22 In 11/00). However, by itself the reputation of individual characteristics could not solve the problem. Numerous experimental data have shown that the required quality of the product can be obtained only if the new set of features, which is declared by the authors. Beyond operating and process parameters, stated by the authors, does not lead to the desired result. The use of rosin as a bat ligament and pore-forming allowed the authors to carry out the basic process of impregnation of the porous preform tungsten molten copper in a vacuum at temperatures of ~ 1200° C. Rosin has a complex structure and consists of a series of resin acids with the General formula C20H30About2. In the process of distillation, and heating the gaseous decomposition products of rosin show reducing properties, freeing the inner surface of the tungsten billet from oxides, increasing its wettability and thereby the possibility propick is this billet copper. The amount of added rosin depends on the content of residual oxygen in the original powder. As a rule, industrial powder tungsten brand PVN contains from 0.02 to 0.2 wt.% the oxygen. The authors found that the introduction of a mixture of rosin in an amount less than 0.5 wt.% (with respect to the powder of tungsten) is inefficient, adding more than 1.5 wt.% it is impractical, because the volume occupied by the rosin may exceed the volume of voids to fill and obtain porous products, additionally, there are problems with Stripping ligament because of its large number and possible deterioration of the strength characteristics of tungsten billet. Introduction formate or ammonium citrate has allowed to increase reconstruction characteristics of rosin and effectively implement the impregnation when the claimed its concentrations regardless of the level of contamination of the tungsten powder with oxygen until the oxygen content of about 0.2 wt.%. However, the imposition of formate or ammonium citrate, as research has shown, in the amount of less than 0.05 wt.% (with respect to the original tungsten) is ineffective, and more than 0.15 wt.% it is impractical. The need for short-term heat treatment in the temperature range 1360-1410° under the excessive pressure of argon is explained as follows: when the heat treatment in vacuum up to temperatures of ~1200° With the possible presence of a certain amount of nedoustanovlennoy oxides. Basically they are distributed within the volume of the product and at 1200° will be completely surrounded by a filled copper areas, and, therefore, maintain the vacuum inside covered then when filling the system with argon. The increase of temperature from 1200° to 1360-1410° will result in the decomposition of the oxides in these areas and additional impregnation their copper, with a slight pressure of argon prevents evaporation of copper.

The proposed method is as follows. Mix the powder of tungsten with rosin, taken in an amount of 0.5-1.5 wt.% with respect to the tungsten. Rosin added to the alcohol solution at a ratio of rosin-alcohol equal to 1:10. Mixing is carried out in a ball mill to obtain a creamy mass. Then the mixture was added formate or ammonium citrate in the amount of 0.05 to 0.15 wt.% by weight of tungsten. The ammonium formate is introduced into the alcohol solution in the ratio 1:30, and citrate in the form of a suspension melhoramento powder in the same amount of alcohol. Mixing when this is carried out manually. Then the mixture is dried at 40-60° With, rubbed through a sieve (0.4 to 0.6 mm) to obtain a low charge and pressed at a pressure of 300 to 700 kN depending on the particle size distribution of the powder of tungsten, brand rosin and quantity of ammonium salts for billets with a diameter of 45.3 mm to a given the th density. The density of tungsten billet determines the volume of voids to fill with liquid copper, and is directly related to the amount of copper in the resulting product. For example, the concentration of copper 18±1 wt.% the density of the blanks can vary from 12,50 to 12.65 g/cm3. Porous tungsten pressing unit is placed in a graphite container in contact with the pressing of copper and covered with a graphite lid. The container was placed in a furnace, which vacuum to a residual pressure of not more than 1.10-1mm Hg and implement gradual heating at a rate of 100° C/hour up to 800-900° With removal of the ligament. The control option to remove the ligament is drop the pressure (increase of vacuum ovens. Then the furnace vacuum to a residual pressure of not more than 1.10-2mm Hg and increase the temperature up to 1200° C. At this temperature, putting in a furnace argon at a pressure of not less than 0.2 MPa and raise the temperature to 1360-1410° C. is maintained at the final temperature for 10-15 min and cooled in the furnace at a rate of ~ 250° C/hour. Product diameter 45,3 mm and a height of 51±1 mm had a density 15,40-15,55 g/cm3the porosity of 2-3% and 18±1 wt.% copper. Metallographic analysis showed that the structure of pseudoplane homogeneous. These products can be used for the manufacture of collimators x-ray tubes, and l is shallow gas-insulated circuit breaker.

In more detail the merits of the proposed method is disclosed using the following examples of specific performance.

Example 1.

For the implementation of the proposed method used a powder of tungsten brand PVN (TU-48-19-72-92) and copper powder electrolytic brand PMS-1 (GOST 4960-75). Tungsten powder with an average grain size (Fisher) of 5.4 μm in the amount of 1040 g was filled in a tungsten carbide ball mill. The powder was added pine rosin (GOST 19113-84) in the amount of 10.4 g (~1 wt.%) in the form of alcohol solution (ethyl alcohol according to GOST 5962-67) in the ratio of rosin-alcohol of 1:10. Then stirred the mixture in liquid form for about 3 hours in a ball mill rolls on. After stirring was separated through a sieve with cell diameter of 2-3 mm charge by the balls and was added to the mixture of 1 g (~0.1 wt.% with respect to tungsten) of ammonium formate (TU 6-09-11-2017-87) in the form of alcohol solution in a ratio of 1:30. The mixture was dried and rubbed sequentially through a sieve with cell sizes of 0.8 and 0.4 mm of the Prepared mixture was loaded into a mold and pressed by a hydraulic press, PI-2000 (GOST 28840-82) at a pressure of 420 kN. Pressed tungsten billet was a cylinder ⊘ 45,3 mm and a height of 51,85 mm hardness was 12,57 g/cm3. Copper in the amount of 245 g was compactional in the same mold and at the same pressure the AI with the receiving cylinder ⊘ 45,3 mm and height 22.5 mm Both blanks were placed in a graphite container with a lid, which was loaded into an electric furnace with a graphite heater. The furnace was evacuated to 1·10-1mm Hg and raising the temperature at a rate of ~100° C/hour up to 880° C. To this point, the ligament is completely removed from the workpiece (the vacuum was increased to 7·10-2mm Hg), after which the pumping installation was carried out paramanandam diffusion pump to a residual pressure of not higher than 1·10-2mm Hg Then raised the temperature to 1200° With (15-20 min) and fills the volume of the furnace with argon to excess pressure of 0.2 MPa, and then raised the temperature to 1400° With (15-20 min) dwell time at final temperature equal to 10 minutes Cooling installation was carried out at a speed of 250-50°With/hour.

The resulting product had the following geometrical dimensions: diameter - 45.1 mm; height - 51,65 mm, while the weight was 1280,3, Geometric density mattered 15,52 g/cm3the estimated composition represented 81.2 mass % of tungsten and 18.8 mass % of copper. Removing 2 mm in diameter and the ends on the lathe, and cutting the product into 3 equal parts to a height not identified visually on the microscope MBS violations of the uniformity of impregnation. On one part of the face has been cut, which showed the uniformity of impregnation in diameter and the absence of C is upitannyh then.

Examples 2-9 performed analogously to example 1, except for some moments, which are reflected in the table below. There are the main results of these examples in comparison with the prototype (example 10). Analysis of data on the density of the material made in accordance with a stated set of features, and prototype testify to the high quality of impregnation of the obtained products.

№№ p/pThe characteristics of initial powderThe structure of the ligamentThe temperature of the heat treatment at the end of the impregnation processThe calculated composition, wt.%The geometric density, g/cm3The density of theoretical, %Note
 The grain size (Fisher), micronsThe oxygen content, mass %NameNumber, mass% WolframCopper   
1234567891011
1of 5.4 0,04Pine rosin1,0140081,218.815,52of 98.2 
 The ammonium formate0,1      
2of 5.40,04Rosin tall1,0140081,418,615,5498,1 
 The ammonium formate0,1      
3of 5.40,04Pine rosin1,0140081,318,715,5097,9 
 The ammonium citrate0,1      
4of 5.40,04Pine rosin1,0140082,117,915,2995,8
5the 4.70,08Pine rosin1,01400----Copper is not soaked stocking
6the 4.70,08Pine rosin1,51400----Copper is not soaked stocking
7the 4.70,08Pine rosin1,01200 (vacuum)82,018,015,3496,1 
   The ammonium formate0,1      
8the 4.70,08Pine rosin1,0140081,418,715,48of 97.8 
   The ammonium formate0,1      
95,1 0,15Pine rosin1,0140081,418,615,4897,7 
   The ammonium formate0,1      
103-5-Palm oil. polyethylene, stearic acid, calcium50% vol125077+221+1-98According to U.S. patent No. 4710223

1. The method of manufacturing products based pseudoplane tungsten-copper, comprising mixing tungsten powder with a bunch, compressing the mixture, bringing the porous preform in contact with copper, heat treatment and impregnation, characterized in that as ligament use rosin and formate or ammonium citrate, taken respectively in the following amounts, wt.%:

Rosin 0.5 to 1.5

Formate or ammonium citrate 0,05-0,15

when this heat treatment is performed with a gradual rise in temperature initially in the vacuum before removing the ligaments and melting the copper, and then in argon to 1360-1410°C.

2. The method according to claim 1, characterized in that the heating in the Aquum carried out first at a residual pressure of not more than 1· 10-1mm Hg to 800-900°and then at a residual pressure of not more than 1·10-2mm RT. Art. to a temperature not higher than 1200°C.

3. The method according to claim 1, characterized in that the heating is carried out in argon at a pressure of not less than 0.2 MPa with a holding time at the final temperature for 10-15 minutes



 

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