RU2840950C1 - Reactor for combination of metallothermy and self-propagating high-temperature synthesis - Google Patents

Abstract

FIELD: powder metallurgy.

SUBSTANCE: invention relates to powder metallurgy, in particular to a device for producing blanks from ceramic-metal composite materials by self-propagating high-temperature synthesis (SHS) followed by spontaneous impregnation with liquid metal. Reactor comprises an upper chamber for housing the thermite mixture, made in the form of a thick-walled graphite cylinder, a protective graphite cover with a hole in the centre for ignition of the thermite mixture, lower chamber for arrangement of mixture of initial powders for SHS, made in the form of thick-walled graphite cylinder with casting slope, and base of lower chamber, made in the form of graphite circle with protruding wall. Upper and lower chambers are separated by a washer-adaptor, in which a through hole is made in the centre, which provides free flow of the metal melt from the upper chamber to the lower one, and slot for installation of steel plate closing said hole from above. Lower chamber is equipped with two openings located in upper part of the chamber, which are intended for free discharge of gas released during SHS reaction and for preliminary ignition of mixture of initial elementary powders.

EFFECT: improving energy efficiency due to excluding the use of complex process equipment and obtaining composite materials with high tribotechnical and mechanical properties.

1 cl, 1 dwg

Description

Field of technology to which the invention relates

The invention relates to the field of metallurgy, and specifically to a device for producing ceramic-metal composite materials (cermets).

State of the art

A device for producing cermets is known, including a closed reactor / Patent US 4988645A - Cermet materials prepared by combustion synthesis and metal infiltration /.

The reasons that prevent the achievement of the technical result specified below when using the known device include the fact that the closed reactor limits the size of the cermets obtained and complicates the possibility of supplying the metal melt in the required volume, allowing the entire pore space of the porous ceramics to be filled.

A device for producing cermet is known, including a centrifuge, in which the action of centrifugal forces in the centrifuge is used for forced impregnation of the metal melt obtained by metallothermy / Patent CN 1309855 C - Method for preparing cermet using powder stock /.

The reasons preventing the achievement of the technical result specified below when using the known device include the complexity of the production technology and the high cost of composite materials obtained with its help.

The closest in terms of the set of features to the claimed invention is a device that includes an electric furnace for preparing a metal melt for the purpose of infiltrating it into porous ceramics / Patent RU 2733524 C1 - Method for producing ceramic-metal composite materials /, adopted as a prototype.

The reasons that prevent the achievement of the technical result specified below when using the known device include the high cost of obtaining cermets and the complexity of the process of their production.

Disclosure of the essence of the invention

The essence of the invention consists in creating a simple device for obtaining cermets containing interpenetrating ceramic and metallic phases using self-propagating high-temperature synthesis (SHS) of a refractory ceramic framework in the combustion mode of the initial powder mixture (SHS charge) with its subsequent spontaneous impregnation with liquid metal obtained as a result of a high-temperature metallothermic combustion reaction of another powder mixture (metalothermic charge), without applying external pressure or centrifugal forces and additional sources and energy costs, which makes it possible to improve the physical and mechanical properties of cermets.

The technical result of the invention is spontaneous infiltration of molten metal into a refractory ceramic frame without applying external pressure, without using centrifugal forces and additional energy sources, ensuring increased energy efficiency and simplification of the technology for producing cermets by reducing energy costs and decreasing the duration of the production cycle, as well as increasing the physical and mechanical properties of cermets.

The technical result is achieved in that the reactor for combining metallothermy and self-propagating high-temperature synthesis is made in the form of a graphite structure, including two thick-walled cylinders representing an upper chamber for a thermite mixture and a lower chamber - a crucible for a mixture of initial elemental powders, which are separated by a washer-adapter with a through hole in the center, ensuring free flow of molten metal under the action of gravity from the upper chamber to the lower one, a protective cover with an opening for igniting the thermite mixture, a base with a protruding wall to impart stability and eliminate the possibility of tipping over the crucible with the molten metal during the synthesis process, wherein the lower chamber is made with a casting slope and is provided with two windows located in the upper part of the chamber, intended for the free discharge of gas released during the SHS reaction, as well as for preliminary ignition of the mixture of initial elemental powders; the washer-adapter has a groove for installing a steel plate, closing its through hole from above.

Brief description of the drawings

The drawing shows a reactor for combining metallothermy and SHS, where the following are shown: graphite cover - 1, upper chamber - 2, adapter washer - 3, lower chamber - 4, crucible base - 5, steel plate - 6. View A - windows of the lower reactor chamber, intended for the release of gases formed during the synthesis process, providing for the possibility of preliminary ignition of the SHS charge and the implementation of impregnation of the already formed SHS frame.

The reactor is a graphite structure, which includes: two thick-walled cylinders representing the upper chamber 2 and the lower chamber 4 - the crucible, a washer-adapter 3 with a through hole connecting the upper and lower chambers of the reactor and ensuring the free flow of molten metal under the action of gravity from the upper chamber 2 to the lower chamber 4, the base of the crucible 5 in the form of a graphite circle with a protruding wall to provide stability and eliminate the possibility of tipping over the crucible with molten metal during the synthesis process, a graphite cover 1, with a hole in the center for igniting the thermite mixture.

The graphite cover 1 performs a protective role and prevents the active release of the thermite mixture during the reaction.

The upper chamber 2 is a thick-walled graphite cylinder in which the ignition of the thermite mixture, the formation of a copper melt and the phase separation process occur.

The lower chamber 4 is also a thick-walled graphite cylinder with a casting slope (according to GOST R 53465-2009) to ensure easier extraction of the obtained composite and to minimize its damage during the extraction process. There are also two windows, for example, 10x10 mm in size, located in the upper part of the lower chamber, designed for the free removal of gas released during the SHS reaction. In addition, these windows provide the possibility of preliminary ignition of the SHS charge and the implementation of impregnation of the already formed SHS framework.

The adapter washer 3 separates the volumes of the upper and lower chambers of the reactor and provides in its design a groove for the tight-fitting installation of a steel plate 6, which closes the through hole in the adapter washer 3, connecting the upper and lower chambers of the reactor and ensuring the free flow of molten metal.

Steel plate 6 with a thickness of 0.1 to 0.5 mm, installed tightly into the groove of adapter washer 3, prevents the powder of copper thermite mixture from spilling out of the upper chamber 2 onto the SHS charge in the lower chamber 4 of the reactor, and also retains the metal melt, ensuring the phase separation process.

The SHS charge is installed in the lower chamber 4 - a mixture of the initial elemental powders in bulk or pressed form. Inert powders of elements are added to the initial powders in the lower chamber 4 of the reactor, providing an increase in the strength of the porous ceramics and/or improving its wettability with liquid metal. Powders of metals and/or alloys for alloying the metal melt are added to the thermite mixture in the upper chamber 2 of the reactor.

To form porous ceramics, the ceramic phase is not taken in a finished form, but synthesized from the initial powder components - reagents in the process of manufacturing cermet in the lower chamber 4 of the reactor, for which the initial elemental powders are mixed in a stoichiometric ratio corresponding to the target ceramic compound, and placed in the lower chamber 4 of the reactor in bulk form, after which combustion is initiated from contact with the metal melt, synthesizing porous ceramics, which are sintered ceramic particles of the target ceramic compound with a high temperature, which is simultaneously impregnated with the incoming metal melt. The metal melt is obtained in the upper chamber 2 of the reactor from a mixture of powder reagents (for example, CuO + Al) due to the metallothermic reaction, which is initiated by local heating with a heating coil or an ignition mixture. Inert powders of elements that increase the strength of the porous ceramics and/or improve its wettability with liquid metal are added to the initial powders in the lower chamber 4 of the reactor. Powders of metals and/or alloys for alloying the metal melt are added to the thermite mixture in the upper chamber 2 of the reactor.

Porous ceramics are sintered ceramic particles of the target ceramic compound obtained by the method of self-propagating high-temperature synthesis (SHS) and having, immediately after synthesis, a temperature significantly exceeding the temperature of the liquid metal, which ensures spontaneous impregnation of the porous ceramics with the liquid metal due to improved wettability. The initial elemental powders are mixed to obtain an exothermic mixture (SHS charge) in a stoichiometric ratio that ensures independent combustion and obtaining the target ceramic phase, and the resulting powder mixture in bulk form is placed in the lower chamber 4 of the reactor. A thermite mixture in bulk form is placed in the upper chamber 2 of the reactor, in which a thermite reaction is triggered by local heating, as a result of which a metal melt (for example, copper) is formed, which, melting a thin steel plate 6 separating the upper and lower chambers of the reactor, falls into the lower chamber 4 of the reactor under the action of gravity. Contact with the metal melt in the exothermic mixture (SHS charge) initiates a combustion reaction, resulting in the formation of porous ceramics with a high temperature (up to 1200-3000°C), which is spontaneously impregnated with the metal melt coming from the upper chamber 2 of the reactor. Then the porous ceramics impregnated with the metal cools down, the metal hardens, thus forming cermet.

The SHS reaction in the lower chamber of the reactor is started before the thermite reaction in the upper chamber of the reactor by initiating the SHS with a heating coil, due to which the liquid thermite metal from the upper chamber of the reactor enters the already synthesized porous ceramics and spontaneously impregnates it.

The positive effect of using the proposed device is expressed in the fact that it provides a simple and energy-efficient production of porous ceramics by the SHS method with a strength significantly exceeding the strength of porous ceramics sintered by the traditional powder metallurgy method from the corresponding ceramic powders. Very high temperatures of liquid thermite metal and refractory ceramic framework synthesized during combustion of powder reagents, fresh and clean, not contaminated with adsorbed substances and moisture surface of porous ceramics contribute to better wettability and adhesion with liquid metal, which ensures spontaneous impregnation of liquid thermite metal into porous ceramics, ultimately, increases such physical and mechanical properties of cermets as strength, hardness, wear resistance, impact toughness, electrical conductivity.

Energy efficiency in the production of cermets is ensured by using the internal heat released during combustion of powder reagents, rather than from external energy sources. Firstly, by releasing the heat of the SHS reaction to obtain a product - a refractory ceramic framework, self-heated as a result of SHS to a high temperature of 1200-3000 ° C, with simultaneous provision of spontaneous impregnation of the framework pores with liquid thermite metal, without the need to use equipment to create excess pressure or centrifugal forces. Secondly, the energy efficiency of obtaining a metal melt is ensured by using a thermite reaction, which does not require an external energy source to melt the metal. Thus, this does not require external energy for the synthesis of a refractory ceramic framework and its heating, ensuring good wettability with a metal melt, and does not require external energy to obtain a metal melt. An increase in the hardness and wear resistance of cermets is ensured by the presence of a refractory ceramic framework. High impact toughness and electrical conductivity of cermets are provided by the metal matrix, which is distributed in the open pore space of the porous ceramics. Strength is provided by good wettability of the porous ceramics by liquid metal at very high combustion temperatures, as well as due to the absence of impurities on the clean fresh surface of the porous ceramics immediately after SHS.

The rapidity of the processes of impregnation of porous ceramics with liquid metal and cooling of the impregnated porous ceramics makes it possible to obtain cermets with mutually reacting ceramics and metal with a minimum content of side compounds that arise during the interaction of liquid metal and porous ceramics at high temperatures.

Implementation of the invention

Information confirming the possibility of implementing the invention with the achievement of the above-mentioned technical result is as follows.

First, a steel plate was tightly installed into the groove of the adapter washer, which separates the volumes of the upper and lower chambers of the reactor, closing the through hole of the adapter washer.

To obtain the SHS charge, the following grades of initial powder components were used: titanium grades PTS, TPP-7; technical carbon grade P 701 (soot), graphite grades C-1, C-2; aluminum grade PA-4, silicon grade Kr0. The initial elemental powders were mixed for 1 hour in a 1-liter ball mill at a ratio of balls to initial powder components of 3:1. The dosage of the initial powder components was carried out with an accuracy of 0.1 g. The molar composition of the initial powder components is selected based on the atomic ratio of elements in the target ceramic compound, for example, Ti + C = TiC. The resulting powder mixture (SHS charge) was placed in bulk form in the lower chamber of the reactor. The metal melt for impregnating the porous ceramics was obtained in the upper chamber of the reactor by carrying out a thermite reaction in a mixture of powders (for example, CuO + Al). The thermite reaction was started by local ignition of the heating coil or ignition mixture. As a result of the thermite reaction, liquid metal was formed, which melted a thin steel plate separating the upper and lower chambers of the reactor and fell into the lower chamber of the reactor under the action of gravity. Contact with liquid metal in the SHS charge started a combustion reaction, as a result of which porous ceramics were formed, which were simultaneously impregnated with liquid metal coming from the upper chamber of the reactor. After 30-40 seconds, the porous ceramics impregnated with metal cooled, the metal hardened, thus forming cermet.

The proposed device allows to simplify the technology of cermet production and increase its energy efficiency due to the absence of the need for external energy sources and forced infiltration and the use of appropriate complex technological equipment, including a melting furnace, press or centrifuge.

Claims (1)

A reactor for simultaneously carrying out self-propagating high-temperature synthesis (SHS) and metallothermy for producing a ceramic-metal composite, comprising a chamber for placing a mixture of initial powders for SHS, characterized in that it comprises an upper chamber for placing a thermite mixture, made in the form of a thick-walled graphite cylinder, a protective graphite cover with an opening in the center for igniting the thermite mixture, a chamber for placing a mixture of initial powders for SHS, which is a lower chamber and is made in the form of a thick-walled graphite cylinder with a casting slope, and a base of the lower chamber, made in the form of a graphite circle with a protruding wall to impart stability and prevent the said chamber from tipping over during the synthesis process, wherein the upper and lower chambers are separated by an adapter washer, in which a through opening is made in the center, ensuring the free flow of molten metal from the upper chamber to the lower one, and a groove for installing a steel plate, closing the said opening from above, and The lower chamber is equipped with two windows located in the upper part of the chamber, designed for the free removal of gas released during the SHS reaction and for the preliminary ignition of the mixture of the initial elemental powders.