WO2013045308A1 - Laser soldering of silicon carbide-based materials - Google Patents

Abstract

Disclosed is a method for repairing critical flaws in silicon carbide-based materials, wherein a laser or two combined laser sources are used for reactively soldering in a bonding manner by feeding silicon carbide powder or a mixture of silicon, carbon and silicon carbide powder.

Description

 Laser beam needs of silicon carbide based materials

The invention relates to a method for laser beam soldering for the correction of critical defects of silicon carbide based materials.

The technical field of the invention can be referred to as reactive soldering, that is to say that temperatures of more than 1200 ° C. are used, which makes it possible to use the composite produced where the

Temperatures, for example, exceed 900 ° C and go up to 1600 ° C or even beyond.

Due to the high temperatures - for example around 1000 ° C - which may be exposed to ceramics such as SiSiC, the elimination of critical defects of silicon carbide based materials by adhesion with organic products is excluded.

The state of the art is to process SiSiC ceramics by means of laser cutting. Thermal ablation with laser beams is defined as separation of material particles by heat processes, whereby heat is converted by energy conversion during the heat treatment

Occurrence of a laser beam on the workpiece arises. With lasers, a treatment is possible regardless of the material hardness, with no wear on the material. The focus of laser applications in the machining of

Ceramics is in the separating processing of plate-shaped or thin-walled curved workpieces. In addition to this separating processing, the

Laser treatment the possibility of material removal from the surface without complete cutting of the workpiece.

Since silicon carbide does not form its own melting phase, the classic

Bonding techniques that work with or without welding consumables (TIG, electron or laser welding) and imply a partial melting of the parts to be joined, not usable for the removal of critical defects of silicon carbide based materials because a ceramic substrate or part can not be melted can and in particular the SiC decomposes before melting. Therefore, a cohesive joining method as in the oxide ceramics, in which the parts to be joined are locally melted in the seam area, not possible.

As a result, solid-phase diffusion bonding, sintered bonding, and reactive soldering are currently the most common techniques for refractory bonding of ceramics.

Diffusion bonding in the solid phase as well as the sintered joining technique have the disadvantage of being problematic in terms of their performance.

In the course of the production of, for example, Si-SiC ceramics by means of the LSI process (liquid silicon infiltration), cracks in the component arise as a result of thermal stresses in the cooling phase of the thermal treatment. On the other hand, for example, the LSI process is characterized by short process times and low

Production costs.

It is therefore particularly important in the realization of a connection between ceramics to limit the residual stresses that develop in the cooling due to different thermal expansion coefficients of the parts to be joined, if they are of different types, but also between the ceramic and the solder, if the both ceramics are of the same type. For this reason, the thermal expansion coefficient of the solder must be very close to that of

Corresponding ceramic parts correspond.

It is therefore the task of finding a new method for cohesive soldering of cracks in components. It should have a mechanically strong, corrosion and high temperature resistant compound of similar or identical material from the solder to the surrounding structure with a localized energy input

be guaranteed. This object is achieved by reactive soldering with a laser or two combined laser sources cohesively with supply of silicon carbide powder or a mixture of silicon, carbon and silicon carbide powder.

In order for the coefficient of thermal expansion of the solder to be almost equal to but slightly higher than that of the silicon carbide-based material, the content of silicon should as far as possible not exceed 97%, expressed as atomic percentage. One

Method using solders whose atomic percentages are within the above range is easy to use because these

Compositions have very good wetting and adhesion properties towards SiC. The solder composition itself is not expensive, since no expensive elements are included. In the case of reactive brazing, preference is given to using nitrogen, compressed air or a protective gas as inert gas, for example argon or helium.

It is particularly preferred that the laser employed are Nd: YAG lasers, CO2 lasers or a combination of the two laser sources. Preferably, a short-pulse laser with a pulse duration of less than 10 ps and a focus diameter of 20 μm is used as the laser for influencing the area to be soldered, or a continuous laser or a combination of short-pulse and continuous lasers of different wavelengths.

Furthermore, the path energy should be varied depending on the gap size to get the best possible soldering result.

The laser beam soldering is preferably carried out at a temperature of 1200 ° C to 1850 ° C.

It is preferable that pretreatment (for example, metallization) of the silicon carbide-based material does not occur. However, this should not preclude mechanical pretreatment of the cracks with mechanical tools, for example degreasing or dedusting. As preferred Lotzusannnnensetzung one with the constituents contained in the ceramic base material of compounds or elements SiC and / or Si and / or C is used.

The solder composition consists of SiC and / or C and / or Si in an amount of 5 to 95 wt .-% SiC and / or C and / or Si, based on the weight of the solder composition and is in a form consisting of a powder

different grain sizes, textile fabrics or a foam can exist.

Preferably, a powder of a solder composition is formed, worked up this powder with an organic binder in pasty form or as a suspension and the sections or parts or joining gaps of the molded body to be soldered coated over the entire surface with the resulting paste or suspension or inserted into the joint gap.

Preferably, the powder of a solder composition is processed into compacts and the compacts are locally melted on the portions or parts or joining gaps of the parts to be soldered by the action of a laser or lasers.

In reactive soldering, a temperature of at least 1200 ° C. is preferably achieved by the laser light at the section edges and in the joint gap.

The silicon carbide-based materials whose critical defects are to be corrected by laser beam soldering are preferably selected from silicon carbide ("PLS-SiC") silicon-infiltrated silicon carbide ("SiSiC" or "RBSC"), porous recrystallized silicon carbide ("RSiC"). ); Graphite silicon ("C-SiC"), which consists of graphite and is coated with a layer of SiC; the SiC / SiC composites, for example with fibers or whiskers, the C / SiC composites, for example with fibers or Carbon and SiC whiskers, the SiC single crystals, the SiC composites with another ceramic, for example SiC / Si3N and SiC / TiN composites. It is preferable that the silicon carbide based materials have a

Have silicon carbide content greater than or equal to 80 wt .-%.

The inventive method is preferably used for the production of ceramic moldings for the automotive industry, the construction of air and

Spacecraft as well as for furnace construction.

example

SiSiC component with a crack

The crack is milled along the crack course with a hand mill to a depth, depending on crack depth and size, from 1 -2 mm. In this milling groove, the solder is carefully filled to avoid blistering. The component is placed in an evacuated chamber and the solder pressed by briefly applying vacuum and pressure in the gap. Then the crack course is filled up to 1 mm supernatant with the solder. After drying, ₂ laser of wavelength 10.6 μιτι is under a protective gas atmosphere, and a maximum power of 700 W the crack path traced by means of a CO. The laser light reaches a temperature> 1420 ° C in the plate edges and in the gap and it comes to the melting of the silicon, the simultaneous onset of reaction of silicon with carbon in an exothermic reaction to form SiC. Due to the additional heat that is formed by the reaction, a heating also takes place in the depth of the gap and the plate edges. The crack is then

closed and the component strength is restored.

Claims

claims 1 . Method for eliminating critical defects of silicon carbide-based materials, characterized in that it is reactively soldered with one laser or two combined laser sources in a materially bonded manner with supply of silicon carbide powder or a mixture of silicon, carbon and silicon carbide powder. 2. A method for the removal of critical defects of silicon carbide based materials according to claim 1, characterized in that in the reactive soldering as purge nitrogen, compressed air or inert gas as a noble gas is used. 3. A method for eliminating critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that are used as the laser Nd: YAG laser, CO ₂ laser or a combination of the two laser sources. 4. A method for eliminating critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that as a laser for influencing the area to be soldered a short-pulse laser with a pulse time less than 10 ps and a Focusing diameter of 20 μιτι is used or a continuous laser, or a combination of short-pulse and continuous lasers of different wavelengths is used. 5. A method for eliminating critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that the laser beam soldering takes place at a temperature of 1200 ° C to 1850 ° C. 6. A method for the removal of critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that no pretreatment of the material Silicicarbarbidbasis takes place, apart from a mechanical pretreatment of the cracks. 7. A method for eliminating critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that a solder composition is used with components contained in the ceramic base material of compounds or elements SiC and / or Si and / or C. 8. A method for eliminating critical defects of silicon carbide-based materials according to one or more of the preceding claims, characterized in that the solder composition of SiC and / or C and / or Si in an amount of 5 to 95 wt .-% SiC and / or C and / or Si, based on the weight of the solder composition and in a form which may consist of a powder of different particle sizes, textile fabrics or a foam. 9. A method for eliminating critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that a powder of a solder composition is formed, this powder with an organic binder in pasty form or as Worked up the suspension and the sections or parts or joining gaps of the molded body to be soldered coated over the entire surface with the resulting paste or suspension or inserted into the joint gap. 10. A method for eliminating critical defects of silicon carbide-based materials, characterized in that the powder of a Solder composition is processed into compacts and the compacts are locally melted on the sections or parts or joining gaps of the parts to be soldered by the action of a laser or lasers. 1 1. Method for eliminating critical defects of silicon carbide-based materials according to one or more of the preceding claims, characterized in that during reactive soldering a temperature of at least 1200 ° C is achieved by the laser light at Abschhnittskanten and in the joint gap. 12. A method for eliminating critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that the silicon carbide based materials whose critical defects are to be corrected by laser beam soldering are selected from unpressurised silicon carbide ("PLS-SiC"). ); silicon-infiltrated Silicon carbide ("SiSiC" or "RBSC"); porous recrystallized silicon carbide ("RSiC"), graphite silicon ("C-SiC"), which consists of graphite and is coated with a layer of SiC; the SiC / SiC composites, for example with fibers or whiskers; the C / SiC composites, for example with fibers or whiskers of carbon and with a SiC matrix; the SiC single crystals; SiC composites with another ceramic, such as SiC / Si3N and SiC / TiN composites. 13. A method for eliminating critical defects of silicon carbide based materials according to one or more of the preceding claims, characterized in that the silicon carbide based materials Have silicon carbide content greater than or equal to 80 wt .-%. 14. Use of the method for the removal of critical defects of silicon carbide based materials according to claim 1 for the production of Ceramic moldings for the automotive industry, the construction of air and Spacecraft as well as for furnace construction.