Method to produce powdered composite cu-cd/nb for electrocontact application

FIELD: metallurgy.

SUBSTANCE: from copper and niobium powders they prepare charge, cold pressing and sintering is carried out. Cadmium is added to a stock by diffusion saturation by means of its soaking in atmosphere, containing cadmium vapours. The sintered stock is exposed to deep treatment with pressure, which is combined with hot extrusion and subsequent cold rolling or drawing. Afterwards additional pressing and annealing is carried out.

EFFECT: reduced transition resistance in a contact pair, increased electric erosion resistance, higher durable mechanical strength in modes of multi-cycle impact loads and resistance against welding.

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The invention relates to the field of non-ferrous metallurgy, in particular the production of ceramic-metal electrical contact materials by powder metallurgy methods.

Due to scarcity, the high and growing cost of the main contact metal - silver, efforts continue its effective replacement for copper, with the necessary for such use electrical, thermal and physico-mechanical properties. The most difficult obstacle for widespread use is the tendency of copper to oxidation, which leads to uncontrolled growth of the transition positive opening operation resistance during operation. However, the developed formulations contact of composites, allows to overcome the mentioned difficulties and successfully use the contact elements on a copper basis in some applications. The highest level of performance provides a composite material, the electrical contact having heterogeneous, fine-grained microstructure, and also includes additives that promote extinguishing of the arc, reducing contact resistance and improving the resistance against welding [Ivanov V.V. Physico-chemical fundamentals of the technology and the science of powder contact composites / V.v.ivanov. - Krasnoyarsk: CPI KSTU, 2002. 234 S.].

Effective arc suppression additive in copper is the metal cadmium is already at small content ≥0,5% [SU # 939579, SS 9/00, SS 1/04, SS 1/10, NN 1/02, publ. 13.03.1978; RU №2038400, NN 1/02, publ. 27.06.1995; RU №2073736, SS 9/00, publ. 20.02.1997; RU №2131941, SS 9/00, NN 1/02, publ. 20.06.1999].

Adding refractory metal is niobium [SU # 1746416, NN 1/02, publ. 07.07.1992; RU №2009562, NN 1/02, SS 9/00, SS 32/00, publ. 15.03.1994], which has a very low solubility in copper, and the lower oxides with metallic conductivity, creates a heterogeneous structure of the contact material with a weak decrease in conductivity contributes to a decrease in contact resistance in the symmetric contact pairs. The simultaneous introduction of cadmium and niobium provides good erosion characteristics satisfactorily low for copper positive opening operation resistance, resistance welding contact pairs and mechanical strength in high-cycle modes of operation.

Known methods of obtaining the contact details for the electrical equipment of a composite material containing insoluble in each other refractory metal and copper [Powder metallurgy. Sintered and composite materials, Ed. VATTA. - M.: metallurgy, 1983. - 519 S.]. Do this using the methods of powder metallurgy, creating a porous skeleton of the refractory components, which the ZAT is impregnated with liquid copper, increase electrical and thermal conductivity of the material. Such composites have a high arcing, but the method requires a high content of refractory metal (up to 2/3 by volume). Therefore, their electrical and thermal conductivity is relatively low, the contact resistance is sufficiently high arc suppression ability is weak, which reduces their utility properties and narrows the scope.

A method of obtaining porous powder microcomposites copper-based [Bashilov, VA Composite superconducting materials of fibrous structure / Vasallo, Wasling, Iagency, Mar. - M.: Metallurgiya, 1986. - 136 C.]containing niobium or vanadium, and used in the manufacture of superconductors for cryogenic equipment. Materials get deep pressure treatment, which is formed by fine fibrous microstructure, completely removed porosity, compacted intergranular and interphase boundaries.

The material made by this method, contact the assignment is not used, although it has a number of required properties, along with high thermal and electrical conductivity, mechanical strength: good friction coefficient, wear resistance and contact resistance when the transfer current in the moving contact [Liu P., Bahadur, S., J.D. Verhoeven Eectrical sliding friction and wear behavior of Cu-Nb in situ composites // IEEE Trans. CPMT-17. Part A, 1994, No. 4, pp.616-624].

However, for electrical contact applications it has the major drawback is the absence in the composition of the arc quenching and hardening the copper matrix additives, which reduces erosion resistance as in arc mode, and when the sparks in sliding contacts. At the same time, the introduction of metallic cadmium on the stage of mixing the powder in this case is excluded because of the impossibility of further deep processing pressure of such material. Another well-known form is the addition of cadmium oxide, also in this material are unacceptable because of the lower thermodynamic strength of the oxide compared to the metal oxide supplements, which are in the process of heat treatment of oxidized, restoring CdO.

The closest technical solution, selected as a prototype, is a technical solution described in the patent [RU NO. 2122039, SS 9/00, NN 1/02, publ. 20.11.1998]. Powder composite electric contact materials for contact details of the electrical equipment on the basis of copper containing both insoluble in copper, refractory metals niobium and fusible cadmium, also produced by powder metallurgy, mixing together all of the original ingredients, taken in the form of powders, which are then pressed in a steel mold in the form of blanks of the desired shape and size is s, is sintered in an inert atmosphere, condense the finish pressing and annealed to relieve stress.

However, this method does not provide the porous composite (residual porosity is typically 2-3% or more) with black borders Cu/Cu and Cu/Nb, which negatively affects all functional properties of the material and, in particular, on health discontinuous contact elements under high shock loads. These contacts usually do not maintain the required number of cycles.

The objective of the invention is to improve the operational characteristics of electrical contact materials based on copper containing niobium and cadmium, in particular, the improvement of erosive characteristics and reduction of contact resistance on the basis of creating porous powder composite Cu-Cd/Nb with a fibrous microstructure.

Thus, the technical result obtained by use of the present invention is the reduction of contact resistance in the contact pair, the increase in spark erosion resistance, and increase long-term mechanical strength in high-cycle regimes shock loads and resistance welding.

The technical result is achieved in that in the method of manufacturing a powder of the composite Cu-Cd/Nb to contact the applications, including obtaining a mixture by mixing the powdered ingredients, cold pressing, sintering, seal the finish pressing and annealing, it is new that the charge is prepared from powders of copper and niobium sintered billet is subjected to deep pressure treatment, and deep pressure treatment combined with hot extrusion of sintered three-dimensional work pieces with subsequent cold rolling or hood, and the introduction of cadmium in the blanks exercise diffusion saturation, by exposure to an atmosphere containing vapor of cadmium.

The essence of the proposal is that the composite Cu-Cd/Nb for contact application, having a fine, fibrous microstructure (fiber niobium in the matrix of cadmium bronze) get deep pressure treatment (hot extrusion, drawing, rolling cadmium free powder composite of Cu/Nb, creating the desired microstructure - fiber niobium in the copper matrix, which is formed due to the proximity of the strength properties of these metals. Further, in the procurement of products injected cadmium by exposure to a gaseous environment containing pairs of this volatile component.

The presence of the refractory metal is niobium is necessary to reduce the electric arc and spark wear and contact resistance in the contact pair. The presence of ADME enhances arc suppression material properties and strengthens copper, which increases the resistance welding. Education fine fibrous structures after deep processing pressure enhances these properties and, in addition, a substantial increase long-term strength of the material under conditions of high shock loads during service contact products.

From the prototype of the proposed method differs in that

a mixture is prepared from powders of copper and niobium;

- sintered billet is subjected to deep processing pressure to create a fine, fibrous microstructure;

introduction cadmium in the blanks with the target microstructure is diffusion saturation, by exposure to an atmosphere containing vapor of cadmium.

These differences allow to draw a conclusion on the conformity of the proposed technical solution the criterion of "novelty". The features distinguishing the claimed method from the prototype, have been identified in other technical solutions in the study of this and related areas of chemistry, and, therefore, provide the claimed solution according to the criterion of "inventive step".

To implement the proposed method to obtain electrical contacts of the source powder components - copper and niobium, taken in the ratio of 9:1, is stirred in a mixer for one hour. Next, the mixture is subjected to double-sided pressing in was the Noah of the mold at a pressure of 300 MPa. The pressing is sintered at a temperature of 900°C for two hours in an argon atmosphere, resulting in a gain sintered billet with a diameter of about 60 mm Billet is subjected to hot extrusion to obtain the strip cross-section of 5×25 mm for the maximum reduction of residual porosity and formation of fibrous microstructure pseudoplane, and then cold rolling to a thickness of 2 mm, Then punching receive the contact details ⌀ 8-10×2 mm Introduction cadmium is conducted from the vapor phase at a temperature of 900°C to cadmium in ready contact details 1,0...1,2%. Some of the specimens not cadmium for comparative testing (table 1, they are denoted - X).

After completion of all operations, the density of the finished contact is 8.8...8,82 g/cm³, hardness HB=80-85, resistivity 3,2 3,4...µohm·see

For comparative tests were also made samples of material of the same composition as proposed, but with the use of the prototype method, i.e. not subjected to deep pressure treatment. Contact elements in symmetric pairs tested on a laboratory bench for switching durability for AC and transient voltage drop during its measurement. Test conditions: I=30 A, U=380 V, cosφ=0.8, number of cycles on/off - 10000. The voltage drop is the average of 15-30 measurements also Measured the hardness of materials Brinell. The results are given in table 1.

As shown by the measurement results, contact details, made according to the proposed method, have lower values electroerosive wear and contact resistance. Shows that importance to service its the STV has both composite fibrous microstructure, and the presence of arcing of the additive material. Higher hardness cadmium free material (X) caused by the lack of thermal annealing after forming.

The use of discontinuous and sliding electrical contacts are made by the proposed method will improve the reliability and durability of the respective switching nodes.

A method of manufacturing a powder of the composite Cu-Cd/Nb for electrical contacts, comprising obtaining a mixture by mixing powders, cold pressing, sintering, followed by sealing the workpiece finish pressing and annealing, characterized in that the mixture prepared from powders of copper and niobium sintered billet is subjected to deep pressure treatment, which combine with the hot extrusion of sintered three-dimensional work pieces with subsequent cold rolling or hood, and the introduction of cadmium in the blank exercise diffusion saturation by keeping in an atmosphere containing vapors of cadmium.