DE4116865C2 - Process for the production of composite bodies coated with silicon carbide and solder material - Google Patents

Description

The invention relates to a method for producing silicon carbide coated composite body, the base body (individual parts) preferably made of Silicon carbide coated graphite or ceramic carrier materials exist, wherein the base bodies are connected using silicon.

Carrier or base materials coated with pure silicon carbide (SiC) layers silicon made from graphite or coated with SiC layers carbide or silicon-silicon dispersion materials coated with SiC layers Carbide (Si-SiC) are becoming increasingly important with regard to their technical-industrial Application. The advantage of surface coating with an SiC layer is that that this layer has a uniform structure, is gas-tight and in addition to good mecha nical and thermal properties a high resistance to corrosive media including oxygen.  

Widely used have SiC-coated graphite moldings with relatively simple Geometry z. B. as susceptors in the doping of silicon wafers in the semiconductor industry found.

Today, composite bodies coated with SiC layers are very complicated Geometry and internal cavities, e.g. B. cooling channels for the production of Laser mirrors, mirrors for X-rays as well as high thermal loads compact heat exchanger, in the foreground. In particular, laser mirrors and X-ray mirrors have extremely high dimensional accuracy requirements or mechanical and geometric stability.

Such mirrors require plan for the reflective surface in terms of roughness parallelism or desired radii of curvature accuracies in the nanometer range rich or below. At the same time, such mirrors have to be filigree warmth shear with the lowest possible coefficient of thermal expansion, so that no distortions in the reflecting surface and in the whole system occur due to temperature inhomogeneities.

Even the internal cavities or cooling channels or cooling caverns must be included a thick SiC layer so that no cooling liquid or vapors or gases can penetrate into the carrier material, which leads to an un would build up pressure and thus lead to distortions in the mirror.

It is easy to see that such requirements with metallic materials due to their mechanical-physical properties are no longer met can.

The difficulty in producing such composite bodies is that they are not made of a block or a compact piece made by mechanical processing can be and on the other hand a SiC coating of cavities or Kühlka channels or curved cooling channels with a continuous length of several  meters and a cross-section of one to a few square millimeters is more possible.

For this reason, such bodies must be made from individual parts (basic bodies) a composite technology.

In the DE-AS 17 96 276 to be removed and generic method are basic bodies made of graphitic material, which were previously covered with a mixture have been drawn from an organic polymer as a binder, fine ver shared free carbon and finely divided silicon carbide, with others Basic bodies made of carbon connected by the basic bodies in the presence of a - based on the amount of carbon in the mixture - excess of ge molten silicon for a period of 30 to 60 seconds to one Temperature from 1,649 ° C to 2,204.4 ° C can be heated. The excess is on Silicon was previously placed in the furnace. Because of the excess of silicon a silicon-silicon carbide structure is created. This creates a connection between the basic bodies, which consist entirely of silicon-silicon carbide.

A disadvantage of this method is u. a. that on the one hand a very high temperature is required and on the other hand obviously a silicon melt pool in the furnace Must be available to connect the base body.

The invention is based on the problem, for graphite and ceramic reasons form temperature-resistant composites true to size at the lowest possible temperature to manufacture fittings.

This object is achieved in that the basic bodies at least in their ver bonding areas are coated gas-tight with a silicon carbide (SiC) layer and that the base body by using solid elemental silicon or  free silicon-containing solid silicon-silicon carbide (Si-SiC) dispersion material to be soldered as solder material.

Surprisingly, it has been shown that elemental silicon has certain Conditions is extremely suitable, a solder joint between several with one Silicon carbide (SiC) layer coated base bodies, i.e. to produce individual parts. The silicon used as solder material may only have a low content Have oxygen or silicon oxide so that those to be connected are coated with SiC Parts are well wettable, so to make a secure solder connection. At the However, a higher oxygen content in the silicon could hinder the soldering process and the Strength of the solder joint can be reduced.

But not only elementary pure silicon, but also free silicon containing Silicon-silicon carbide dispersion material is suitable for coating with silicon carbide  to connect basic bodies by soldering.

In a further embodiment of the invention it is provided that the temperature at Soldering process has to be slightly above the melting point of the silicon, whereby however, a temperature of 1698 K must be specified as the upper limit. Through this Supplementary conditions ensure that the boundary layers between the soldered parts forms a uniform diffusion zone with a uniform structure.

According to a further proposal of the invention it is provided that the application of the Solder material on a base body of the later composite body or a part of a base body by the extensive melting of solder material plates or Foils and / or by spot or line melting of solder material Plates or foils are preferably made using laser technology. Procedural are the applied plates or platelets before the actual soldering process initially ground flat, preferably a flat grinding down to a thickness of 120 µm.

After another, allow a particularly simple soldering of the base body the proposal provides that between those to be connected with silicon carbide coated base body thin disks or thin foils of the solder material be placed, then soldering at the required temperatures alone to support that during the soldering process on the areas to be connected che the base body acts on a force caused by the gravity of the upper base body is caused. If necessary, however, an additional mechanical Force are introduced, but do not lead to mechanical deformation of the connecting basic body may lead.

According to a further, particularly elegant process, the Si solder layer can still pass through Deposition from the gas phase, e.g. B. with the help of a CVD process or by Evaporation of elemental silicon can be applied.  

Suitable materials are those whose materials are made of graphite or silicon carbide or consist of such ceramic materials that neither with the applied Silicon carbide layer also react with a phase change during soldering go through accompanying volume change.

A solder material for the production of composite bodies consisting of basic bodies is characterized in that in the case of composite bodies coated with silicon carbide Elemental silicon solder material or silicon silicon card containing free silicon bid is dispersion material. The solder material is preferably in the form of plates or foils formed.

Further details, advantages and features of the invention do not only result from the claims the features to be found in this - for themselves and / or in Combination, but also from the following description of execution play.

example 1

In a first example, a graphite base body 18 cm long, 5 cm wide and 2 cm thick was provided with 13 grooves running parallel to the longitudinal edge. The groove width was 2 mm, the groove depth was also 2 mm and the web width between the grooves was 1.5 mm. This base body was coated on all sides - ie also the grooves and webs - with a 150 µm thick SiC layer using the CVD (chemical vapor deposition) process. This body is referred to below as section A ₁ .

In parallel, a graphite plate 18 cm long, 5 cm wide, but only 2.5 mm Coated on all sides with a 150 µm thick SiC layer. This coated Plate is referred to as section B. In preparation for the soldering process First, silicon wafers with a thickness of 0.4 mm were placed on one side of section B. and melted them briefly so that the silicon covered the surface of the section B  completely wetted. The silicon that acts as a solder was then applied a layer thickness of 120 µm is ground flat.

On this so pretreated section B, section A _{1 was placed} so that its webs were in contact with the silicon layer of part B.

This arrangement was carried out in a furnace in a graphite holding device at a Argon pressure of 10 mbar brought to a temperature of 1692 K and for 5 minutes kept at this temperature. Then the furnace was under the same argon pressure cooled down.

As a result, the following could be stated:

A firmly bonded composite body was obtained macroscopically, which had no ver throwing showed. The plane parallelism of the cover plate was preserved.

After cutting the body and microscopic examination of the boundary layers, it was found that there was a clean solder joint at all examined points. The thickness of the boundary layer between the Si solder layer and the two SiC views of the sections A ₁ and B was approximately 1 μm. This boundary layer showed a uniform appearance, with Si and SiC coexisting.

Example 2

A graphitic base body corresponding to Example 1 was provided with grooves and coated on all sides with an SiC layer 150 μm thick (section A ₂ ). In parallel, a plate made of sintered silicon carbide 18 cm long, 5 cm wide and 3 mm thick was coated with a 150 µm thick SiC layer (section C). Analogously to example 1 Si plates of 0.4 mm thickness were placed on this section C and melted. Thereafter, the Si solder layer melted in this way was ground plane-parallel to a thickness of 120 μm.

Section A ₂ and C were placed one on top of the other in accordance with Example 1 and soldered in accordance with Example 1.

As a result, a composite body made of a SiC coated silicon car bidplatte and a SiC coated graphite body obtained.

In this case too, the microscopic examinations showed a perfect connection of the sections A ₂ and C.

Example 3

2 plane-parallel ground graphite plates 10 cm long, 5 cm wide and 0.5 cm Thicknesses were separately coated on all sides with a 150 µm thick SiC layer. Between these plates was a plane-parallel plate made of Si-SiC dispersion material with a free Si content of 10% of 10 cm in length, 5 cm in width and 0.3 mm in thickness placed.

This arrangement was according to Examples 1 and 2 in a holding or Spannvor direction of graphite at an argon pressure of 10 mbar for five minutes on one Temperature held at 1692 K.

After cooling, a solid sandwich composite consisting of the layers:
with SiC-coated graphite "Si-SiC" with SiC-coated graphite
receive.

The microscopic examination shows that the soldering process in each case from the free Si of the dispersion material had run out.  

Example 4

Two hexagonal plane parallel ground graphite plates with a width across flats of 240 mm and a thickness of 4 mm were separated on all sides with a thickness of 150 µm SiC layer coated. The Si solder was then passed through on one side of the plate Deposition of the same from the gas phase by decomposing dichlorosilane applied.

The plates were placed on top of one another in such a way that the Si solder layer of one plate and SiC layer of the second plate was in contact.

The soldering process was carried out analogously to Example 1.

In this example, too, the two plates were bonded perfectly.

Claims (14)

1. A method for producing silicon carbide-coated composite bodies, the base body (parts) preferably consist of graphite's or ceramic carrier materials coated with silicon carbide, the base bodies being connected using silicon, characterized in that the base bodies are connected at least in their Areas are gas-tightly coated with a silicon carbide (SiC) layer and the base bodies are soldered as solder material by using solid elemental silicon or free silicon-containing solid silicon-silicon carbide (Si-SiC) dispersion material. 2. The method according to claim 1, characterized, that in a first step, the solder material on the with the Silizi carbide layer coated area at least one of the base body is brought and that the soldering of the base body to the composite body in a second step.   3. The method according to claim 1 and 2, characterized, that the application of the solder material on at least one of the base bodies of the later composite body, or a part of this, by areal Melting plate or foil-shaped solder material and / or through point or line melting of plate or foil Solder material is carried out using preferably laser technology. 4. The method according to claim 3, characterized, that the plate or foil-shaped solder material after its application at least one area of the base body is ground flat. 5. The method according to claim 4, characterized, that the plate or foil-shaped solder material to a thickness of preferred as 120 µm is ground. 6. The method according to claim 1 and 2, characterized, that the application of the solder material to at least one base body of the later composite body by depositing Si from the gas phase, for. B. by a CVD process using dichlorosilane and hydrogen or by vapor deposition or sputtering of elemental Si. 7. The method according to claim 1 and 2, characterized, that between the base body to be coated with silicon carbide with thin slices or foils of the solder material and put on finally the base bodies are soldered.   8. The method according to at least one of the preceding claims, characterized, that soldering at a few degrees above the melting point of the silicon lying temperature T takes place, where T is 1698 K. 9. The method according to at least one of the preceding claims, characterized, that the thickness of the preferably applied or interposed solder material is smaller than the sum of the silicon carbide layer thicknesses of the base body in the areas to be soldered directly to one another. 10. The method according to at least one of the preceding claims, characterized, that the soldering is carried out in the absence of oxygen and nitrogen. 11. The method according to at least one of the preceding claims, characterized, that the base body to be soldered during soldering by own heavy force or by additional mechanical forces. 12. The method according to at least claim 1, characterized, that as the base body graphite, silicon carbide or such ceramic Substances are used that do not react with the applied silicon carbide layer during the soldering phase change with accompanying Go through volume change. 13. Solder material for the production of basic bodies (sections) Composite bodies, characterized, that in the case of base bodies coated with silicon carbide, the solder material elemen  tares silicon or silicon-silicon carbide disper containing free silicon sionsmaterial is. 14. solder material according to claim 13, characterized, that the solder material has a plate or foil shape.