Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-11-29
2001-11-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S472000, C428S633000, C428S701000, C428S702000, C501S001000, C501S103000, C501S134000
Reexamination Certificate
active
06322897
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a metal-ceramic gradient material, a product made from a metal-ceramic gradient material, in particular a thermal shield or a gas turbine blade, and a process for producing a metal-ceramic gradient material.
In order to provide heat-resistance for a component which is exposed to extremely high temperatures, for example a thermal shield or a gas turbine blade, it is known, for example from U.S. Pat. No. 4,321,311, to produce the component from a metal base body and to coat the metal base body with a ceramic thermal barrier layer of ZrO
2
. The ceramic thermal carrier layer is bonded-on through a metallic adhesion promoter layer formed of an alloy of the type MCrAlY. Since the ceramic thermal barrier layer is generally a good conductor of oxygen ions, the adhesion promoter layer becomes oxidized during the course of operational use of the component. As a result, the thermal barrier layer can become detached from the metal base body. That results in the duration of use of a component of that kind being limited. That is the case in particular in the event of frequent temperature changes, which occur when a gas turbine is started up and run down.
An article entitled “Keramische Gradientenwerkstoffe fur Komponenten in Verbrennungsmotoren” [Ceramic Gradient Materials for Components in Internal Combustion Engines] by W. Henning et al. in Metall, Vol. 46, Issue 5, May 1992, pp. 436-439, discusses a fiber ceramic body with a density gradient for the purpose of improving the resistance of piston heads to temperature changes. That fiber ceramic body is composed of four layers of different layer thicknesses and different ceramic fractions. The difference in the ceramic fraction resides in the fact that the ratio of fibers (short Al
2
O
3
fibers) to ceramic particles of Al
2
TiO
5
differs distinctly in the four layers. As a result, the porosity of the four layers also differs considerably with respect to one another. The high porosity of the layers, lying between 40% and 79%, is used to introduce molten metal into the cavities in the fiber ceramic body through the use of squeeze casting, so as to produce a defect-free composite. As a result, it is possible to produce a piston head which has a gradient of metal and ceramic that changes considerably and suddenly. Due to the low thermal conductivity of the ceramic fractions, a thermal barrier is formed, so that the piston is insulated. In addition, the fiber ceramic reinforces the piston and therefore improves the resistance of the piston to thermal shocks.
An article entitled “Projected Research on High Efficiency Energy Conversion Materials”, by M. Niino and M. Koizumi in FGM 94, Proc. of the 3
rd
Int. Symposium on Functional Gradient Materials, ed. B. Ilschner and N. Cherradi, pp. 601-605, 1994, has described composite materials, in connection with the development of materials for a space shuttle, which are referred to as Functional Gradient Material (FGM). The essential feature of FGM is a continuous composition gradient and/or microstructure gradient, which is intended to lead to a continuous gradient of the relevant functions, e.g. the strength, thermal conductivity, ductility, inter alia.
The intention is to increase the load-bearing capacity and efficiency of the material by avoiding abrupt changes in properties. FGMs are therefore intended to combine the positive properties of laminated composites and lump composites in a single material.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a metal-ceramic gradient material for use at high temperatures over a long period of time, a product for a high operating temperature made from a metal-ceramic gradient material and a process for producing a metal-ceramic gradient material, which overcome the hereinafore-mentioned disadvantages of the heretofore-known materials, products and processes of this is general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a metal-ceramic gradient material, in particular for a thermal shield or a gas turbine blade, comprising a metal base material; a ceramic; a metal-rich zone, a ceramic-rich zone; an additive for high-temperature oxidation protection; the metal base material having a concentration decreasing from the metal-rich zone into the ceramic-rich zone; the additive having a concentration with a concentration gradient; and the concentration of the additive having a maximum.
With the objects of the invention in view, there is also provided a product, in particular a gas turbine blade or a heat-protection element of a gas turbine, comprising a gradient material including a metal base material; a ceramic; a metal-rich zone; a ceramic-rich zone; an additive for high-temperature oxidation protection; the metal base material having a concentration decreasing from the metal-rich zone into the ceramic-rich zone; the additive having a concentration with a concentration gradient; and the concentration of the additive having a maximum.
With the objects of the invention in view, there is additionally provided a process for producing a gradient material, which comprises pouring powders having different mixtures of at least one of a metal base material, a ceramic and an additive for high-temperature oxidation protection over one another to form a packed bed; and then compacting and sintering the packed bed to form a gradient material; the metal base material having a concentration decreasing from a metal-rich zone into a ceramic-rich zone, the additive having a concentration with a concentration gradient, and the concentration of the additive having a maximum.
In accordance with another feature of the invention, the concentration gradient of the additive has an essentially continuous maximum. In accordance with a further feature of the invention, the concentration gradient of the additive extends from the ceramic-rich zone as far as into the metal-rich zone.
In accordance with an added feature of the invention, there is provided a metal-free zone, the maximum lying between the metal-free zone and the ceramic-rich zone.
In accordance with an additional feature of the invention, the concentration of the additive increases from approximately 5% by volume in the metal-rich zone to approximately 30% by volume and falls to approximately 5% by volume in the ceramic-rich zone.
In accordance with yet another feature of the invention, the concentration of the additive has a plurality of maximums.
In accordance with yet a further feature of the invention, the additive has a bimodal grain size distribution, in particular a fine-grain fraction with grain diameters of less than 10 &mgr;m and a coarse-grain fraction with grain diameters of greater than 100 &mgr;m.
In accordance with yet an added feature of the invention, the additive forms pores, in particular with a diameter of between 0.1 &mgr;m and 5 &mgr;m and preferably between 1.0 &mgr;m and 2.0 &mgr;m.
In accordance with yet an additional feature of the invention, the metal base material is a nickel-chromium alloy and the ceramic includes zirconium oxide.
In accordance with a concomitant feature of the invention, the additive includes zirconium silicate.
The invention is based on the concept of refining a Functional Gradient Material (FGM) with regard to the oxidation-resistance function. In the case of a ceramic-metallic FGM, the gradient of the composition may extend over the function-performing cross-section of a component from 100% ceramic to 100% metal, although it is also possible to use gradients of other limit concentrations, or “partial gradients”, for certain purposes. Furthermore, in addition to a continuous gradient, for certain components symmetrical gradients are also possible, e.g. ceramic-metal-ceramic or combinations of the composition gradients.
An FGM can also be regarded as a link between conventional layer systems and typical ceramic-matrix systems with 2D or 3D reinforcing elements. In that case, in the microstructure between
Borchert Ralph
Willert-Porada Monika
Greenberg Laurence A.
Jones Deborah
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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