RU2087575C1 - Sintered composite material - Google Patents

Abstract

FIELD: powder metallurgy, particular, sintered composite material applicable in manufacture, for instance, of contacts of electrical apparatuses or antifriction products. SUBSTANCE: the offered sintered material containing metallic matrix of one or several noncarbide- forming metals and graphite, additionally contains nanofibers and/or fullerens with the following quantities of components, mas.%: graphite 1-20; nanofibers and/or fullerens 0.1-20; the balance, metallic matrix. EFFECT: higher mechanical properties as compared with known industrial composite material, that prolongs service life, for instance, of electrical contracts; higher efficiency. 2 tbl

Description

 The invention relates to powder metallurgy, in particular to sintered composite materials used, for example, for the manufacture of contacts of electrical apparatus or anti-friction products.

 Composite materials are known that are used to make contacts of electrical apparatuses, containing silver and its alloys with graphite additives (TU 16-685.020-85), copper and its alloys with graphite additives (TU 16-538.272-75) as a basis.

 Known composite materials are characterized by low welding resistance, low arc resistance, low wear resistance, mechanical strength and hardness, which reduces their useful life.

 The closest analogue of them is an industrial composite material containing a copper-nickel matrix and graphite. (The reference book p / r GG Gnesina "Sintered materials for electrical engineering and electronics" M. Metallurgy, 1981, p. 195).

 The essence of the present invention lies in the fact that the proposed sintered composite material containing a metal matrix of one or more non-carbide-forming metals and graphite additionally contains nanofibers and / or fullerenes in the following ratio of components, wt.

graphite 1 20;
nanofibers and / or fullerenes 0.1 to 20;
metal matrix rest
The introduced nanofibers and / or fullerenes are new spatial carbon compounds in the form of spherical or tube-shaped shapes with dimensions of the order of a nanometer in diameter and a length (for nanofibers) of a fraction of micrometers. These new solid state phases of carbon are obtained by vaporization of graphite in an electric arc in an inert gas atmosphere, as well as by laser or electron beam evaporation in vacuum or by some other method (W. Kratschmer et al, Nature, 347, 354, 1990; S. Jijima , Nature, 354, 56, 1991).

 The use of graphite in composite materials is determined by its ability as a solid lubricant to reduce the coefficient of friction and wear in friction pairs (surfaces) due to the formation of a thin graphite film between them during the operation of the materials. On the other hand, graphite, while not greatly degrading the electrical properties of electrical contact materials, increases their resistance to welding and increases their arc resistance, that is, reduces wear caused by the thermal and electrodynamic effects of the arc that occurs in electrical switching processes.

 The upper limit of the graphite content (20 wt.) Is determined by the fact that a larger amount does not affect the decrease in the coefficient of friction, reaching the level of the coefficient of friction of pure graphite, regardless of the composition of the matrix. The lower boundary of the graphite content (1 wt.) Is determined by the minimum amount necessary for the formation of a thin graphite film between the rubbing couples, and, accordingly, quite effectively reducing the friction coefficient and reducing the adhesion or weldability of the two products.

 Fullerenes and nanofibers in the composition of the composite material perform several functions. Due to their small size (of the order of nanometers), being present as separate particles (spherical or tube-shaped clusters) in the deep layers of the material, they act as dispersed hardeners, being effective stoppers for the movement of dislocations, and thereby increase the strength of the material.

On the other hand, it is known that carbon nanofiber films with a thickness of 0.5 μm have a microhardness of 40,000 MPa, significantly superior in microhardness to the T15K6 hard alloy, which has H _M 25,000 MPa (Z.Ya. Kosakovskaya, L.A. Chernozatonsky, E.A. . Fedorov Letters in JETP, 1992, Volume 56, Issue 1, p. 26). Due to the high natural hardness of nanofibers and fullerenes, they increase the overall hardness of the composite material and thereby, to a certain extent, its wear resistance.

 Given the spatial structure of the new solid-state phases of carbon, spherical in fullerenes and tube-like in nanofibers, van der Waals, the nature of the interaction between them and their small size and high hardness, the presence of these clusters in the surface and surface layers at the interface of two working pairs leads to a change nature of friction and, as a consequence, a decrease in the coefficient of friction and a decrease in wear of the material.

 High conductive properties of fullerenes and nanofibers contribute to an increase in the current density of electrical contacts when introducing clusters into the composition of composite materials.

 The upper limit of the content of nanofibers and / or fullerenes (20 wt.), As in the case of graphite, is determined by the fact that a larger number of them does not affect a further decrease in the coefficient of friction and wear regardless of the composition of the matrix. The lower limit of the content of nanofibers and / or fullerenes (0.1 wt.), Is determined by the minimum amount, by analogy with graphite, starting from which there is a decrease in friction and wear of the material.

 Example 1

 To obtain a composite material, powders of copper and graphite with a particle size of not more than 200 μm are used as the initial charge, a powder mixture of nanofibers and / or fullerenes and graphite obtained in the known process of synthesis of fullerenes by burning graphite in an electric arc in a helium atmosphere is added to them. The particle size of the added mixture also does not exceed 200 microns.

The powders are mixed together in a predetermined ratio in dry form, then pressed in the form of washers with a diameter of 20 mm Pressing pressure from 1 to 5 t / cm ² . The compacts are then sintered in a vacuum of 10 ^-3 Pa or in a protective atmosphere at temperatures of 700 to 1000 ^o C for 2 to 10 hours. Sintered materials determine the density, electrical resistivity and microhardness. Next, the sintered billets are rolled with various degrees of deformation and at various temperatures. On rolled billets, density, electrical resistivity and microhardness are measured.

 The above properties of the proposed material and the well-known composite material KMK B!) (TU 16 538.272 75, see "Sintered materials for electrical engineering and electronics". Handbook edited by GG Gnesin. -M. Metallurgy, 1981, p. 195) are given in table 1.

 As can be seen from table 1, the use of the inventive composite material can increase after sintering the microhardness by about 1.5 times compared with the known industrial composite material with the same and even slightly lower level of electrical resistivity and about the same material density. The use of rolling in the processes of technological redistribution allows to increase the microhardness of the proposed material by 1.3 times in comparison with the known material, which should lead to an increase in the wear resistance of the material and the extension of its service life. Note that the proposed material has a higher technological ductility.

 In addition, the proposed material has a lower electrical resistivity, which makes it possible to use it at high current densities.

 Example 2

 To obtain a composite material, powders of copper (90 wt.), Tin (5 wt.) And graphite (5 wt.) With a particle size of not more than 200 microns are used as the initial charge. This composition is taken as a prototype. The initial charge of the proposed material consists of the following components: copper powders (90 wt.), Tin (5 wt.) And a mixture of nanofibers and / or fullerenes (1 wt.) And graphite (4 wt.) With a particle size of not more than 200 microns.

 All further technological operations with the selected prototype and the proposed material are carried out in parallel and under the same conditions.

The powders are mixed together in a predetermined ratio in dry form, and then pressed in the form of washers with a diameter of 20 mm Pressing pressure from 1 to 5 t / cm ² . The compacts are then sintered in a vacuum of 10 ^-3 Pa or in a protective atmosphere at temperatures of 700 to 1000 ^o C for 2 to 10 hours. On sintered materials determine the density and microhardness. Further, the obtained billets are rolled with various degrees of deformation and at various temperatures. Density, electrical resistivity and microhardness are measured on rolled samples.

 The above properties of the selected prototype and the proposed material are shown in table 2.

 As can be seen from table 2, the proposed material has about 1.5 times greater microhardness than the selected prototype, with a slightly lower density and greater electrical conductivity.

 The proposed sintered composite material has higher mechanical properties than the known industrial composite material, which should lead to an increase in the service life of, for example, electrical contacts.

Claims (1)

 Sintered composite material containing a metal matrix of one or more non-carbide-forming metals and graphite, characterized in that it additionally contains nanofibers and / or fullerenes in the following ratio of components, wt. Graphite 1 20
Nanofibers and / or fullerenes 0.1 20
Metal Matrix

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