DE2362469A1 - Joining sintered ceramic components - esp in the mfr of silicon nitride gas turbine impeller wheels - Google Patents

Abstract

One or more pre-sintered components are inserted in a hot die and a suitable sintering powder is then put in the die followed by hot-pressing to form a monolithic component. The pre-sintered parts are pref. made of silicon nitrile while the powder is silicon nitride contg. max. 10 wt. % of a sintering agent, e.g. MgO, which forms silicates with SiO2. Prior to hot pressing, the pre-sintered parts may be given an oxidn. treatment and/or coated with a sintering agent which forms silicates with SiO2. Used in the mfr. of impeller wheels for gas turbines where the rotor blades are the pre-sintered parts and the powder is used for hot-pressing the wheel. The finished prat will withstand high thermal-and mechanical stresses at high temp.

Description

Daimler-Benz Aktiengesellschaft Palm 9701A Stuttgart-Untertürkhexm } k. December 1973

"Process for connecting ceramic components"

The invention relates to a method for joining ceramic components. Such components, for example consist of aluminum oxide, can be according to known metallization and soldering processes, in which the surfaces to be connected by sintering or vapor deposition with coated with a metal layer and then soldered together. However, such compounds have only limited heat resistance. Workpieces exposed to high temperatures, such as the impellers of gas turbines, cannot be used. In the case of such highly stressed machine parts, however, it is advantageous to use components with different properties to combine with each other. This possibility does not apply to the previously known methods.

The invention is based on the object of eliminating this deficiency and specifying a method that allows ceramic To connect components to one another in such a way that the connection point is subject to high thermal and mechanical loads endures. This is done according to the invention in that one or more pre-sintered components in a hot press die are used, in which one or more components are then hot-pressed from a sinterable powder and thereby are simultaneously connected to the pre-sintered component or components to form a one-piece workpiece. With this one Process in which components are combined with other already finished components to form a workpiece during their manufacture.

509825/0568

- »- Paint 97OIA

be bound, despite different properties of its If the components form a unit, there are connection points that can withstand high thermal and mechanical loads.

Further advantageous embodiments of the invention are given in the description.

The drawing shows to explain an example of execution of the method according to the invention a hot press mold for the production of an impeller of a grass turbine composed of ceramic components.

The hot press mold consists of a bottom part 1 and a hollow cylindrical shell part 2, which together form the die 3, and a punch k. The bottom part 1 has a cylindrical extension 5 on its upper side, which engages in a step-shaped cylindrical recess 6 on the underside of the casing part 2 and thereby centers it the die 3 a lateral annular groove 7 for receiving presintered rotor blades 8 is formed. The end face 9 of the extension 5 of the bottom part 1 and the end face 10 of the stamp U have rotationally symmetrical shapes which correspond to the side surfaces of the wheel body 11, indicated by dash-dotted lines, of the turbine runner to be produced. 12 are the blade roots of the rotor blades 8, which adjoin the wheel body 11.

The turbine runner, its manufacturing and connection processes will be described below is, for example

S09825 / 0588

Palm 9701A

of rotor blades 8 made of reaction-sintered silicon nitride and a wheel body 11 composed of hot-pressed silicon nitride.

The production of the reaction-sintered rotor blades 8 can according to one of the known processes for the production of reaction-unified he tem silicon nitride. For example, silicon powder is made into the desired with a binder made of plastic Pressed blade shape. By subsequently heating the rotor blade 8 to temperatures between 1200 and 150 Degrees Celsius in a nitrogen-containing atmosphere, the silicon is nitrided and the plastic is expelled at the same time. When heated, a temperature of 13OO degrees Celsius is not exceeded, forms in a known manner predominantly still sinterable <X - silicon nitride *

The prefabricated reaction-sintered rotor blades 8 are inserted in the annular groove 7 of the die 3 according to their subsequent arrangement on the impeller. For this purpose, the punch k and the casing part 2 are removed and the rotor blades 8 are fixed on the base part 1. The undersides of the blade roots 12 form a closed ring wall that acts as part of the die 3. After the shell part 2 is centered on the base part 1 again, the amount of silicon nitride powder necessary for the formation of the wheel body 11 is poured into the die 3, to which about one to five percent magnesium oxide powder is added as a sintering aid. The punch _% k is then inserted into the jacket part 2 of the die 3.

During hot pressing, the powder mixture located in the die 3 becomes at a temperature of about 160 degrees Celsius

509825 / Q.S68

Palm 9701 A

Λ-

Formed and sintered under the pressure of the punch h to form the wheel body 11 and at the same time connected to the reaction-sintered rotor blades 8 arranged in the annular groove 7 to form a one-piece turbine impeller. The magnesium oxide used as a sintering aid has the task of combining with the silicon dioxide still present in the powder mixture in addition to the silicon nitride to form a silicate. The silicate particles melt when a temperature of 1500 degrees Celsius is exceeded and thus enable the silicon nitride particles to be sintered to form a well-compacted, pore-free wheel body 11 which is firmly connected to the rotor blades 8.

The impeller produced from various components by the connection method described combines in an advantageous manner Way the most favorable properties of both a reaction-sintered and a hot-pressed one Impeller in itself. The good shaping possibilities Reaction sintered components are used for an economical production of the complicated shape of the rotor blades 8 harnessed. The property of the reaction-sintered rotor blades 8, their strength, is particularly valuable Maintain even when heated to very high temperatures. This is due to the lack of sintering aids, the reaction products or their reaction products soften at higher temperatures and thus lose a considerable amount of strength. The one most exposed to centrifugal forces Wheel body 11 is produced by hot pressing, which gives the component high strength. A substantial · drop This strength falls below the permissible values at higher temperatures as a result of the sintering aids used in hot pressing does not occur because the wheel body 11 is in operation is not heated as much as the one exposed to the hot gas flow

509825/0568

- fr- Dft in the 9701/4

• Χ *

indirectly exposed blades 8. The simple shape of the wheel body 11 is very suitable for the hot pressing process, on the other hand, when producing intricate shapes is very complex and therefore expensive.

The integral impeller of a gas turbine manufactured according to the method described for connecting ceramic components is characterized by economical production and very good operating properties. Opposite to Impellers composed of different materials are, has the impeller made of one material according to the invention due to its uniform coefficient of thermal expansion the advantage that excessive thermal stresses are avoided.

According to a further embodiment of the method, the pre-sintered components can undergo an oxidation treatment before hot pressing, for example at a temperature of 130 degrees Celsius, received. This leads to a particularly good connection between the reaction-sintered component and the hot-pressed component Component. Tests have shown that if the mechanical load is increased to the point of rupture, the latter does not starts from the connecting layer of the components.

To further improve the sintering together of the components the reaction-sintered component, which may have been post-treated by oxidation, can also be treated with a sintering aid, e.g. by powdering. Compounds and elements that contain silicon dioxide are suitable for this purpose Form silicate «, e.g. magnesium oxide, boron trioxide, alurainura oxide, Lithium oxide and beryllium oxide.

The invention not only relates to the connection of

- 6 509825 / 0.56 «

Palm 9701A

reaction-sintered hot-pressed silicon uranium nitride, but can also be applied to other systems, e.g. recrystallized or reaction-sintered and hot-pressed silicon carbide, be transmitted. A prerequisite for good durability is that the ceramic to be joined Components have the same or approximately the same coefficient of thermal expansion to have.

50S825 / 0SG8

Claims (5)

Palm 9701/4 ^ k. December 1973 Expectations 1J method for joining ceramic components, thereby characterized in that one or more pre-sintered components (8) are inserted into a hot press die (3), in which one or more components (11) are then hot-pressed from a sinterable powder and thereby are simultaneously connected to the pre-sintered component (s) (8) to form a one-piece workpiece. 2. The method according to claim 1, characterized in that the presintered components (8) consist of reaction-sintered silicon nitride. 3. The method according to claim 1 or 2, characterized in that the sinterable powder consists of silicon nitride, to which up to ten percent of the weight of the powder sintering aids, e.g. magnesium oxide, are added, which with Silica form silicates. k. Method according to one or more of the preceding claims, characterized in that the presintered components (8) receive an oxidation treatment before hot pressing. 5. The method according to one or more of the preceding claims ·, characterized in that the presintered Components (8) are coated with sintering aids, which contain silicon dioxide silicates, before hot pressing form. S0982S / 0568 Daim 9701A Ceramic impeller produced according to the method according to one or more of the preceding claims for gas turbines, characterized in that the rotor blades (8) are pre-sintered and the wheel body (ii) is hot-pressed from a sinterable powder. 50Ö825 / 0S6Ö