RU2535419C1 - High-temperature antifriction material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: antifriction material contains the following, wt %: molybdenum disulphide not more than 10, ceramic compounds of monocrystal molybdenum - the rest. Its porousness is 5-35%.

EFFECT: possibility of use under radiation emission and high temperatures in places of hard access for repair without replacement and maintenance due to better wear-resistance, heat resistance, hardness and low plasticity.

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Description

The invention relates to the production of antifriction materials for use in high-temperature zones of industrial equipment, in particular at nuclear power plants.

The relevance of the problem to be solved is based on the specific requirements imposed on the operating conditions of the developed antifriction materials in the core of a nuclear transport reactor at temperatures up to 1500 ° C without replacement and maintenance during the entire lifetime of the installation under intense neutron irradiation, constant contact with the material of the shell of the absorbing element ), inability to use greases, inaccessibility for maintenance or replacement of a failed assembly.

Antifriction material is known from the prior art (RF patent No. 2132364, IPC СМ 125/02, publ. 06/27/1999), containing molybdenum disulfide (5-10 wt.%.), Epoxy-diane resin, coke and graphite.

An analogue of the proposed high-temperature antifriction material is high-temperature antifriction material (patent No. 2220219, IPC С22С 19/03, publ. 12/27/2003), containing aluminum, nickel, calcium fluoride, which is applied as a coating to the protected parts.

The prototype of the proposed high-temperature antifriction material is high-temperature antifriction material (from patent No. 02461534, IPC С04В 41/80, publ. 09/20/2012), containing a heat-resistant ceramic matrix, a solid lubricant - boron nitride, which is applied as a coating to the protected parts.

The disadvantages of analogues and prototype include the inability to use it in conditions of exposure to radiation and high temperatures (over 1500 ° C).

The task of the authors of the invention is to develop a high-temperature antifriction material for use in the inaccessible for repair of the active zone of a gas-cooled transport nuclear reactor at an operating temperature of up to 1500 ° C without replacement and maintenance during the entire life of the installation.

A new technical result when using the proposed invention is to enable its use in conditions of exposure to radiation and high temperatures (above 1500 ° C) in places that are difficult to repair without replacement and maintenance due to increased wear resistance, heat resistance, hardness and low ductility.

These tasks and a new technical result are ensured by the fact that in the known antifriction material, including a heat-resistant matrix, solid lubricant, according to the invention, it contains ceramic compounds of polycrystalline molybdenum as a heat-resistant matrix, molybdenum disulfide as a solid lubricant, in the following ratio of ingredients, wt .%:

- molybdenum disulfide no more than 10, - ceramic compounds of polycrystalline molybdenum rest

while its porosity is characterized by a value in the range of 5-35%.

The proposed high temperature antifriction material is illustrated as follows.

The operating conditions of the developed material are characterized by the presence of intense neutron irradiation, constant contact with the material of the shell of the absorbing element (PEL) - molybdenum (Mo), the inability to use lubricants, the inaccessibility to service or replace dictate the introduction of restrictions and specific requirements for it.

In addition, the following factors are taken into account:

- due to constant contact with the metal shell of the absorbing rod under high temperature conditions, the interaction of the shell and bearing with the destruction of the shell and depressurization of the PEL is possible;

- constant intense neutron radiation will have a high damaging effect on the crystal lattice of the material.

It should be noted that the nuclei of some isotopes can absorb neutrons with further nuclear reactions, which will lead to the release of a significant amount of heat in the material, a change in its chemical composition and additional radiation damage in the crystal structure

Refractory metals traditionally used as antifriction materials with a melting point significantly higher than 1500 ° C, or alloys based on them (in brackets, melting points): Hf (2150 ° C), Nb (2468 ° C), Ta (2996 ° C ), Mo (2610 ° C), W (3380 ° C), Re (3180 ° C), Ru (2250 ° C), Os (3027 ° C), Ir (2410 ° C), along with high heat resistance, have a number of significant disadvantages: at high temperatures, they have a fairly high chemical activity. In addition, many metals have several polymorphic modifications; rearrangement of the crystal lattice during heating to operating temperature, as a rule, leads to a sharp loss of mechanical strength and even to destruction of the material (with a significant difference in the densities of low- and high-temperature modifications). Technically pure metals, due to the good diffusion mobility of atoms, quickly soften when heated.

The presence of constant contact with the molybdenum shell, the high temperature of the bearing assembly and the long time the PEL is in a “rest” state (most PELs are used to completely stop the reactor or in case of emergency) can lead to diffusion welding between the metal matrix of the bearing and the shell.

Of refractory metals, the neutron capture cross section has a high (in parentheses is the absorption cross section of thermal neutrons, × 10 ^-28 m ² ): Hf (105), Ta (21), Re (86), Ir (440) and boron. In addition, the products of nuclear reactions with are gases (helium, tritium) or lithium, an extremely active alkali metal. For this reason, the use of borides, including boron nitride BN, in the composition of the developed material is impractical.

The use of carbon in the form of graphite as a lubricating component is also fraught with a number of difficulties: all refractory metals, including the material of the shell of the rod - Mo, at high temperature will actively interact with carbon to form carbides (solid materials with abrasive properties), which will lead to a decrease or complete loss of antifriction qualities.

Refractory metal compounds: oxides, carbides, borides, silicides, having good heat resistance and high (with respect to their own melting temperature) heat resistance, as a rule, have high hardness and low ductility, which leads to difficulties in machining.

In connection with the above considerations, ceramic compounds have the advantage in these conditions as the basis of high-temperature antifriction material.

As “solid lubricants” introduced into the antifriction material in the form of powders at the stage of preparation of the powder mixture, graphite, molybdenum disulfide, boron nitride, and certain metal selenides powders are traditionally used. Taking into account the requirements for ensuring a maximum operating temperature of ≈1500 ° C, in fact, three substances remain: graphite (C), molybdenum disulfide (MoS ₂ ), and hexagonal boron nitride (BN).

Taking into account the above considerations and experimental results, the most promising material is a material based on molybdenum ceramic compounds, optimally, MoSi ₂ molybdenum disilicide in combination with MoS ₂ molybdenum disulfide as a solid lubricant. Such a choice of components allows minimizing the possible interaction between the matrix (MoSi ₂ ), solid lubricant (MoS ₂ ) and the PEL sheath material (Mo). The MoSi ₂ compound is electrically conductive, which will positively affect the workability of the obtained material by EDM. The amount of lubricant is about 10 wt.%.

Figure 1 shows a photo of the structure of the obtained material (MoSi ₂ + 10% MoS ₂ ), obtained by metallographic examination with an Axiovert 200 mat optical microscope. Sections were prepared according to the generally accepted technique; the study was carried out without etching at an image magnification × 1000 times.

The optimal lubricant is molybdenum disulfide (MoS ₂ ). It is non-toxic, has a melting point above 1500 ° C and is commercially available. Powder MoS ₂ grade DM-1 according to TU 48-19-133-90 has an average particle size of 7 μm, the total content of impurities (Si, Fe, Al, Ca, MoO ₃ ) is less than 1 wt.% And well meets the requirements for the lubricating component anti-friction material.

Thus, the proposed high-temperature antifriction material makes it possible to use it under conditions of radiation and high temperatures (above 1500 ° C) in places that are difficult to repair without replacement and maintenance due to increased wear resistance, heat resistance, hardness and low ductility.

The possibility of industrial use of the proposed high-temperature antifriction material is confirmed by the following example.

Example 1

The proposed high temperature antifriction material was obtained in laboratory conditions.

In laboratory experiments, the preparation of powder mixtures for high-temperature antifriction material was carried out by grinding in a planetary centrifugal mill (PCM) from powders (based on single-crystal molybdenum) molybdenum disilicide MoSi ₂ and molybdenum disulfide MoS ₂ grade DM-1. The following processing conditions for grinding powders were experimentally established: Pulverisette 6 planetary mill, rotational speed of the drum - 150 min ^-1 , drum with lining of “hard alloy” VK15, steel balls (ШХ15), processing time - 10 min. In this example, a mixture of the composition was prepared: 90% MoSi ₂ + 10% MoS ₂ . In Example 2, under the same conditions, a composition of 95% MoSi ₂ + 5% MoS _{2 was} obtained _.

For the manufacture of prototypes of high-temperature antifriction material, the installation was pressed with an upper press arrangement. Powder compounds MoSi ₂ was obtained by direct synthesis from individual starting elements.

After pressing, prototypes with a density of 4.71 g / cm ³ were obtained, the estimated relative porosity of about 20% (porosity from 5 to 35% for high-temperature antifriction materials is necessary: wear products accumulate in the pores, which improves the tribological characteristics of the material).

Example 2

Under the conditions of Example 1, a composition of 95% MoSi ₂ + 5% MoS _{2 was} obtained to obtain a high temperature antifriction material.

As the examples showed, the proposed high-temperature antifriction material makes it possible to use it under conditions of radiation and high temperatures (above 1500 ° C) in places that are difficult to repair without replacement and maintenance due to increased wear resistance, heat resistance, hardness and low ductility.

Table 1 Implementation example The main ingredients, their ratio wt.%. Wear resistance, heat resistance, Hardness, ductility Porosity,%
Density g / cm ³ Prototype Ceramic Matrix, Boron Nitride 1000 ° C There is no data There is no data Proposed Material Example 1 MoSi ₂ 90 1500 ° C 5-35 MoS ₂ 10 4.71 Example 2 MoSi ₂ 95 1500 ° C 5-35 MoS ₂ 5 4,50

Claims (1)

High-temperature antifriction material, including powdery heat-resistant matrix and solid lubricant, characterized in that it contains ceramic compounds of single-crystal molybdenum as a heat-resistant matrix, and molybdenum disulfide as a solid lubricant, in the following ratio, wt.%:
molybdenum disulfide no more than 10
ceramic compounds
single crystal molybdenum rest
while the porosity of the material is characterized by a value in the range of 5-35%.

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