EP0513685B1 - Method for impregnating porous, fibrous or pulverulent materials with a melt of a metal or an alloy - Google Patents

Description

The invention relates to a method for impregnating porous, fibrous or powdery materials in a previously degassed infiltration space with the melt of a metal or an alloy from a feed area, the melt being pressed into the infiltration space under pressure.

Such processes are used in particular for the production of metal objects reinforced with fibers, particles or the like, or of preforms which have porous cavities impregnated with metal, such as are e.g. can be used for highly stressed components.

Methods according to the preamble of claim 1 are known from DE-B-24 15 868 and DE-C-35 04 118.

The difficulties with the known methods and devices lie in particular in the application and maintenance of the pressure at the necessary high temperatures during the infiltration and in the introduction of the molten metal into the spaces between the fillers.

These difficulties are overcome with a method as defined in claim 1.

With such a procedure it is possible that the metal to be infiltrated only by a few degrees, e.g. 10 ° to 20 ° C above its melting point or solidus point and the necessary infiltration pressure is reached, but at the same time the possibility of a reaction between the molten metal and the filling material is largely limited.

Since the melting parameters (change in volume, thermal expansion of the containers, metals, etc.) are known or can be calculated easily and can be selected accordingly, the method according to the invention does not cause any great difficulties.

In particular for sealing the melt space or feed area and the receiving volume (infiltration space) it can be provided that only a portion of the metal (alloy) that is close to the receiving volume, in particular the lower portion, is melted and between the partial volume that receives the molten metal (alloy) a temperature difference is set or maintained in the task area and the partial volume of the feed area that receives the unmelted metal (alloy) and / or a pressure body, so that melted metal (alloy) penetrating into the colder partial volume is solidified again and as the unmelted metal (alloy) and / or at least one pressure body or solidified sealing material adhering to the boundary walls forms and maintains a seal between the two partial volumes. In the partial volume that holds the unmelted metal, instead of or in addition to the unmelted metal (s), a pressure body can also be provided, which e.g. from a higher melting metal or from another material, e.g. Ceramic, can exist; it is essential that between the molten metal and the residual metal or the pressure body a metal layer can melt and solidify again, which lies tightly against the metal to be melted or on the pressure body and the container wall or connects to this or this or adheres to it and, due to the seal, allows pressure to build up when the remaining metal to be melted is melted. The pressure built up pushes the molten metal into the infiltration room. The formation of a sealing zone formed by solidified, molten metal is supported by a temperature gradient between the molten metal and the non-molten metal or the pressure body, e.g. a temperature gradient is created by appropriate heating and cooling of the container.

Suitable metals and alloys to be melted are, for example, aluminum, magnesium or Cu and their alloys which are infiltrated into porous substances or infiltrated into a receiving volume which is made of metallic, with reinforcing elements, for example fibers, particles, whiskers or the like. mineral, ceramic, graphitic or other materials are filled as densely as possible or in a predetermined density. It is particularly advantageous if the length of the fibers introduced extends through the entire infiltration space.

A device for carrying out the method is characterized in that the part of the pressure chamber close to the pressure vessel and the pressure vessel, preferably over the entire length of the infiltration path, can be heated with a heating device, preferably an induction heater.

In this way, the infiltration takes place in porous materials or preforms of metallic, ceramic, graphitic or mineral nature or in cavities which are filled with particles, whiskers, short and / or long fibers, with or without a binder, with a metallic melt and with the pressure that arises from the increase in volume when one or more initially solid metal bodies (s) melt in the closed container. The inner volume of the container or the pressure space closed by it, the volume of the metal body (s) and the volume of the infiltrate space in the preform, the thermal expansion coefficients of the container and the pressure vessel, the metal (alloy) of the fibers are matched to one another, that the evacuated infiltration space (preform) is preferably completely infiltrated with metallic melt either during the melting process or in the course of a further increase in temperature of the molten metal. The temperature of the melt in the infiltration room is e.g. adjusted by appropriate heating of the pressure vessel or the infiltration space itself or the melting area such that the entire or at least the main part of the infiltration pressure is created by the liquefaction of the melt. By regulating the temperature to values just above the melting point, a reaction between the melt and the filling or reinforcing materials can be minimized.

The restriction of the melt area to a partial area of the pressure space provided for the pressure build-up in the feed area or in the pressure space is achieved by sealing the partial volume with the expanding melt with the aid of at least one pressure body which consists of foreign metal, another material and / or the metal to be melted can, on which the solidifying melt can attach again and seal the melt area. For this reason, the area in which the sealing takes place is at a temperature level below the melting temperature; this temperature is set by heat dissipation, for example radiation or external cooling.

Advantageous embodiments of the invention can be found in the following description, the drawing and the subclaims.

The invention is explained in more detail below with reference to an embodiment shown in the drawing. 1 shows a schematic section through a device and FIG. 2 shows a detailed section.

1 shows a schematic section through a device for pressure infiltration of molten metal into a pressure vessel 2 with an infiltration space 8 filled with filling material 7. The pressure vessel is optionally connected in one piece to a pressure-resistant container 1. In operation, the pressure chamber 6 of the container 1 is divided into two partial volumes, namely a lower partial volume in which the metal (alloy metal) is melted and in an upward subsequent partial volume in which the metal 9 to be melted is kept in solid form in order to To act pressure or sealing body; alternatively or additionally, a pressure or sealing body 9 made of another material can be provided in the application area. A possibly common heating device 11 is assigned to the pressure vessel 2 and the container 1; the upper region of the container 1 is surrounded by a cooling device 12 in order to create a temperature gradient in the container 1. The setting of the temperature gradient can also be achieved by thermal radiation, in that the heating device 11 surrounds the container 1 only over a certain partial area. By depositing the molten metal in the area 14 on metal that has not yet melted or on a pressure body and on the wall of the container 1, the melt area is sealed off from the container closure 3; at the same time the size of the melting volume can be adjusted. The container 1 is connected with a connection 4 to a vacuum pump. The metal 10 melted in the melting volume by the heating device 11 solidifies on the colder pressure part 9 or on the colder wall surrounding it and penetrates into the gap between the pressure part 9 and the wall of the pressure vessel 1 in a certain way until it solidifies . This solidifying metal (14) prevents further penetration of the molten metal 10, as a result of which a pressure space is created which is only open towards the pressure vessel 2 or against the infiltration space 8 to be filled.

In the same way, it is possible to seal the end of the infiltration space 8, as is shown in detail in FIG. In the area of Closure 5 of the infiltration space 8, a body made of metal to be melted or a pressure body 13 made of another material is introduced and a temperature gradient or temperature gradient is set by a cooling device 15, so that infiltrated, molten metal in the infiltration space 8 upon contact with the pressure body 13 or of the wall area surrounding it solidifies and seals the gap between the pressure body 13 and the wall of the pressure vessel 2. In this way, the closures 3 and 5 do not require a specially designed seal that is resistant to liquid metal; they are only to be interpreted in such a way that the pressure and the temperatures occurring are resisted.

It is also possible that the metal body 9 inserted into the pressure chamber 6 or the metal body 13 inserted into the infiltration chamber 8, due to its thermal expansion, bring about a seal between itself and the respective walls of the container 1 or pressure vessel 6 , which largely prevents the penetration of molten metal. This measure can be carried out in addition or as an alternative to sealing with the aid of a temperature gradient to form a sealing layer 14 made of solidifying metal.

The cross sections of the pressure chamber 6 or of the infiltration chamber 8 can be any, since the shape of the sealing body 9 or 13 can also be selected as desired or can be adapted to the clear width of the rooms.

The method is particularly advantageously suitable for the infiltration of aluminum, magnesium or other metals or their alloys, since these metals expand considerably during melting; e.g. When melting aluminum increases its volume by 6%, and it is for the introduction of aluminum and / or magnesium or their alloys in preforms or infiltration volumes 8, or the like with particles and / or fibers made of silicon carbide, aluminum oxide, carbon, boron nitride. are filled, only short infiltration times are necessary, which largely preclude a reaction of the fibers (formation of metal carbides, nitrides, etc.) with the introduced metals.

Before melting or after filling the infiltration space 8 with the fibers 7 or the pressure space 6 with the metal to be melted, the device is evacuated, which evacuation can continue until the seal 14 is formed between the melted metal and the pressure body 9.

It is essential that only a very small space (e.g. a few tenths of a millimeter) is maintained between the pressure bodies 9 and 13 and the wall of the pressure vessel 2 and the container 1 in order to prevent the solidified metal 14 from breaking through with liquid metal; for this reason, the pressure bodies 9 and 13 are adapted as precisely as possible to the inside width of the container or pressure vessels 2. This is particularly easy if the pressure body consists of solid metal to be melted, since the extent of the empty spaces to be taken into account when calculating and regulating the infiltration pressure is then minimized.

To determine the temperature and / or the pressure in the pressure chamber 6, temperature and / or pressure measuring devices 16, 17 are expediently provided, by means of which the heating device (s) 11 and / or cooling device 12 can be controlled.

In principle, it is also possible to arrange the container shown in Figure 1 horizontally; however, the infiltration from the pressure chamber 6 into an infiltration chamber 8 lying below it is preferably carried out.

A possible reaction between the infiltrated metal and the filling material 7 can be minimized if the container 2 is cooled immediately after the infiltration metal has penetrated, e.g. quenched by immersion in water or hot oil.

Claims (8)

1. Method for impregnating porous, fibrous or pulverulent materials in a previously degassed infiltration chamber (8) with the melt of a metal or of an alloy from a charging zone (6), the melt being forced under pressure into the infiltration chamber (8), characterized in that, by controlled melting of the solid metal or of the solid alloy, present in the charging zone, and by the resulting increase in volume, the hydrostatic pressure of the melt is increased and the latter is forced into the infiltration chamber (8).
2. Method according to Claim 1, characterized in that the metal which is to be melted is arranged in the charging zone (6), at least largely filling the cross-section thereof, and is then melted only in a part volume, adjoining the infiltration chamber (8), of the charging zone.
3. Method according to Claim 2, characterized in that the distance of the metal from the walls, determining the cross-section, of the charging zone is selected to be of the order of magnitude from 0.1 to 0.5 mm.
4. Method according to one of the preceding claims, characterized in that the metal to be melted is heated to at most 20 K above the solidus point.
5. Method according to one of Claims 2 to 4, characterized in that the part volume, in which melting should not take place, is cooled.
6. Method according to one of the preceding claims, characterized in that the metals used are aluminium, magnesium, lead, tin or alloys thereof.
7. Method according to one of the preceding claims, characterized in that a fibrous material is impregnated whose fibres extend through the infiltration chamber (8) over the length thereof.
8. Method according to one of Claims 2 to 7, characterized in that the infiltration chamber (8) and a part volume, adjoining the infiltration chamber, of the charging zone (6) are heated by an inductive heater (11).

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