DE102011083865A1 - Laser beam brazing of silicon carbide based materials for the manufacture of ceramic components - Google Patents

Abstract

A method for producing a component from ceramic workpieces comprising the steps of: a) depositing plate-shaped ceramic materials in defined positions in one or more crucibles or in defined positions on one or more racks, wherein the edges are placed against each other so that a defined gap between b) full-surface coating of the gap with a solder and subsequent drying, d) reactive soldering with a defined beam diameter, wherein both the gap and the region of the edges of the plate-shaped ceramic materials is evenly painted over.

Description

The invention relates to a method for laser beam soldering for the production of ceramic components.

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

Due to the high temperatures - for example, around 1000 ° C - which may be exposed to ceramics such as SiSiC, the production of ceramic components 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 generated by energy conversion when a laser beam appears on the workpiece. With lasers, a treatment is possible regardless of the material hardness, with no wear on the material. The focus of laser applications in the processing of ceramics lies in the separating processing of plate-shaped or thin-walled curved workpieces. In addition to this separating treatment, the laser treatment offers the possibility of material removal from the surface without complete cutting of the workpiece.

Since silicon carbide does not form its own molten phase, the classical joining techniques that work with or without welding consumables (TIG, electron or laser welding) and imply a partial melting of the parts to be joined are not usable for the removal of critical defects of silicon carbide based materials, since a substrate or a part made of ceramic can not be melted 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 contrast, the LSI process (Liquid Silicon Infiltration) is characterized by short process times and low production costs.

In the realization of a connection between ceramics, it is particularly important to limit the residual stresses that develop during cooling due to different coefficients of thermal expansion of the parts to be joined, if they are of different types, but also between the ceramics and the solder, if the two ceramics of of the same kind. For this reason, the coefficient of thermal expansion of the solder must correspond very closely to that of the ceramic parts to be joined.

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

• a) Ablegen von plattenförmigen keramischen Werkstoffen in definierten Positionen in einen oder mehrere Tiegel oder in definierten Positionen auf ein oder mehrere Gestelle, wobei die Kanten so aneinander gelegt werden, dass ein definierter Spalt (Länge, Breite, Tiefe) zwischen den Platten entsteht,
• b) Vollflächiges Überziehen des Spalts mit einem Lot und anschließende Trocknung,
• d) Reaktives Löten mit einem definierten Strahlendurchmesser, wobei sowohl der Spalt als auch der Bereich der Kanten der plattenförmigen keramischen Werkstoffe gleichmäßig mit Lot bedeckt sind.

This object is achieved by a method for producing a component from ceramic workpieces with the following steps:

• a) placing plate-shaped ceramic materials in defined positions in one or more crucibles or in defined positions on one or more racks, wherein the edges are placed against each other so that a defined gap (length, width, depth) is formed between the plates,
• b) full-surface coating of the gap with a solder and subsequent drying,
• d) reactive soldering with a defined beam diameter, wherein both the gap and the region of the edges of the plate-shaped ceramic materials are uniformly covered with solder.

The reactive soldering takes place cohesively with supply of silicon carbide powder or a mixture of Si, C and SiC powder. In order for the coefficient of thermal expansion of the solder to be almost equal but slightly higher than that of the silicon carbide, the silicon content must not exceed the value of 97%, expressed as atomic percentage. A method that uses solders whose atomic percentages are within the above range is easy to use because these compositions have very good wetting and adhesion properties to SiC. The Lotzusammensetzung itself is not expensive, because it contains no expensive elements. The soldering is preferably carried out with the laser in the free atmosphere or, if necessary, in a protective gas atmosphere.

Preferably, the plate-shaped workpieces have a thickness of 3 to 15 mm.

The surface of the crucible facing the plates is preferably coated with a BN suspension prior to laying down the plate-shaped ceramic materials.

Preferably, the crucible or frame (s) are made of graphite. The gap between the plates preferably has a distance of 0.1 mm to 1 mm.

Preferably, a continuous or a pulsed laser for reactive soldering or a combination of the two laser modes is used.

It is preferable that a CO ₂ laser or a Nd: YAG laser or a combination of the two laser sources is used for reactive soldering.

Preferably, the soldering is performed with a laser in a free atmosphere or in a protective gas atmosphere.

The laser used is preferably a short-pulse laser with a pulse time of less than 10 ps and a focus diameter of 20 μm.

Preferably, the defined beam diameter is 1 to 10 mm.

Preference is given to no pretreatment of the ceramic material, except for mechanical preparation of the joining surfaces, for example degreasing or dedusting of the ceramic material.

The solder composition used is preferably a compound or elements such as SiC and / or Si and / or C contained in the ceramic base material.

The solder composition preferably consists of SiC and / or C and / or Si in an amount of from 5 to 95% by weight of SiC and / or C and / or Si, based on the weight of the solder composition, and is in a form consisting of a powder, grains, pieces, particles, a woven fabric, a nonwoven, a felt or a foam.

Preferably, a powder of a solder composition is formed, this powder is treated with an organic binder in suspension or pasty form and the sections or edges of the molded body to be soldered are coated with the resulting suspension.

The powder of the solder composition is preferably processed into compacts and locally melted by the action of lasers on the parts to be soldered.

In reactive soldering, preference is given to using nitrogen or compressed air as purge gas or inert gas such as argon or helium as protective gas.

Preferably, in reactive soldering, a temperature of at least 1200 ° C is achieved by the laser light at the plate edges and in the gap.

Preferably, the soldered parts are detachable again.

Particularly preferably, the plates are firmly bonded by reactive soldering with a SiSiC layer.

It is preferable that the silicon carbide-based materials are selected from non-pressure sintered silicon carbide ("PLS-SiC"); silicon-infiltrated silicon carbide ("SiSiC" or "RBSC"); porous recrystallized silicon carbide ("RSiC"); Graphite silicon ("C-SiC") made of graphite and 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; the SiC composites with another ceramic, for example, SiC / Si ₃ N ₄ and SiC / TiN composites.

Preferably, the silicon carbide-based materials have a silicon carbide content greater than or equal to 80% by weight.

The silicon carbide-based materials are preferably used for the production of ceramic moldings for the automotive industry, the construction of aircraft and spacecraft and for furnace construction.

example 1

Preparation of the mixture of the solder

In an Eirich intensive mixer, 400 g of Si powder (average particle size 100 μm) 300 g of SiC powder of grain size F 360 (particle size d 50: 22.8 ± 1.0 μm), 200 g of powder of grain size F 600 (particle size d 50: 9 , 3 ± 1.0 μm) and 240 g of powder of grain size F 1200 (particle size d 50: 3.0 ± 0.5 μm), and 50 g of a graphite powder of average grain size 30 μm and the mixture at a swirling speed 200 U / min for 5 min and then homogenized at 1200 rev / min with the addition of 300 ml of ethanol and 10 ml of paraffin oil. The thereby forming plastic ethanol wet mass is transferred to a container with a lid.

Example 2

Connection of the ceramic workpieces

The prepared and degreased plate-shaped ceramic workpieces of a thickness of 15 mm are placed in a crucible made of graphite. The surface of the crucible facing the plates was previously coated with BN suspension to prevent subsequent sticking by molten silicon. The cleaned edges are put together so that there is a gap of 1 mm between the plates. In this gap, the produced solder is now filled layer by layer. It is important to ensure that no air bubbles are included. The gap is covered by approx. 1mm and then dried at RT in air. Using a CO ₂ laser of wavelength 10.6 microns is under a protective gas atmosphere and a maximum power of 700 W is aligned with a beam diameter of 3mm so that it covers both the gap and the area of the edges of the plates evenly with one millimeter. 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 which is formed by the reaction, heating also takes place in the depth of the gap and the plate edges. This reactive soldering bonds the plates together with a SiSiC layer.

Claims (21)

Method for producing a component from ceramic workpieces with the steps: a) placing plate-shaped ceramic materials in defined positions in one or more crucibles or in defined positions on one or more racks, the edges are laid together so that a defined gap is created between the plates, b) full-surface coating of the gap with a solder and subsequent drying, d) reactive soldering with a defined beam diameter, wherein both the gap and the region of the edges of the plate-shaped ceramic materials is uniformly painted over. A method for producing a component from ceramic workpieces according to claim 1, characterized in that the plate-shaped workpieces have a thickness of 3 to 15 mm. A method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that the surface of the crucible, which faces the plates, is coated with a BN suspension before laying down the plate-shaped ceramic materials. Method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that the crucible or frame (s) consist of graphite. Method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that the gap between the plates has a spacing of 0.1 mm to 1 mm. Method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that a continuous or a pulsed laser or a combination of the two laser modes is used. Method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that a CO ₂ laser or an Nd: YAG laser is used for reactive soldering. Method according to one or more of the preceding claims, characterized in that a short-pulse laser with a pulse time of less than 10 ps and a focus diameter of 20 μm is used as the laser. Method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that the defined beam diameter is 1 to 10 mm. Method for producing a component from ceramic workpieces according to one or more of more of the preceding claims, characterized in that no pretreatment takes place to mechanical processing of the joining surfaces or degreasing or dedusting of the ceramic material. Method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that a solder composition with additives contained in the ceramic base material SiC and / or Si and / or C is used. A method for producing a component from ceramic workpieces 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, fabrics or a foam. A method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that a powder of a defined Löt composition is formed, this powder is treated with an organic binder in suspension or pasty form and the sections or edges of the molded body to be soldered be coated with the resulting suspension. Method according to one or more of the preceding claims, characterized in that the powder of a solder composition is processed into compacts and locally melted by the action of lasers on the parts to be soldered. A method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that the reactive soldering as purge gas nitrogen or compressed air or inert gas is used as inert gas. Method for producing a component from ceramic workpieces 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 the plate edges and in the gap. Method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that the soldered parts are detachable again. A method for producing a component from ceramic workpieces according to one or more of the preceding claims, characterized in that the plates are fixedly connected by the reactive soldering with a SiSiC layer. A method of manufacturing a component according to one or more of the preceding claims, characterized in that the silicon carbide-based materials are selected from unpressurised silicon carbide ("PLS-SiC"); silicon-infiltrated silicon carbide ("SiSiC" or "RBSC"); porous recrystallized silicon carbide ("RSiC"); Graphite silicon ("C-SiC") made of graphite and 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; the SiC composites with another ceramic, for example, SiC / Si ₃ N ₄ and SiC / TiN composites. Method for producing a component according to one or more of the preceding claims, characterized in that the silicon carbide-based materials have a silicon carbide content greater than or equal to 80% by weight. Use of the silicon carbide-based materials treated according to claim 1 for the production of ceramic moldings for the automotive industry, the construction of aircraft and spacecraft and for furnace construction.