Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1995-03-09
1996-10-08
Zimmerman, John
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
428660, 428654, 148525, 148537, 416241R, B32B 1520, C22F 118
Patent
active
055629997
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a component made of an intermetallic compound consisting of titanium and aluminum or made of alloys of such intermetallic compounds with alloying additions so as to form the base material and with an aluminum diffusion coating on the base material.
This base material has interesting characteristics for the construction of engines. It has mechanical characteristics which are comparable to those of conventional titanium alloys while the specific weight is low, but can be used at significantly higher operating temperatures. However, the ductility of this base material at room temperature is lower and must therefore be improved by the use of alloying elements and heat treatment processes, as they are known from German Patent document DE 30 24 645.
While, in the case of conventional titanium alloys, an oxygen embrittlement in an oxidizing atmosphere begins at temperatures starting at 550.degree. C., in the case of intermetallic compounds made of titanium and aluminum, this temperature is at 700.degree. C. The oxygen embrittlement is disadvantageous because the already low ductility further deteriorates at room temperature and results in a brittleness which is known with respect to ceramic components.
In order to use this base material for components which are subjected to operating temperatures of 700.degree. C., as occur preferably in the case of components in the compressor and turbine range of engines, a closed and no-defect aluminum diffusion coating is required on the high-temperature-stressed component surfaces.
When conventional aluminum diffusion coatings are used on components made of the base material, no closed aluminum diffusion coating is achieved. Disadvantageously, coating defects occur. These coating defects include areas of extremely non-uniform coating thicknesses such as trough-shaped coating structures which have no coating on the bottom of the trough. When the coating is extremely thick, these troughs and defects can be covered with aluminum. However, when the component is stressed, these areas will disadvantageously break open and the aluminum covering will chip off.
It is an object of the present invention to provide a component of the above-mentioned type, and a process for its manufacture, in which no coating defects occur and which can be used at operating temperatures of 700.degree. C.
According to the present invention, this object is achieved in that, between the base material and the aluminum diffusion coating, the component has a closed zone which is close to the surface and has a recrystallization structure.
As determined in comprehensive development work, a closed aluminum diffusion coating grows in an undisturbed and uniform manner only on such a recrystallization structure of an intermetallic compound base material consisting of titanium and aluminum, or of alloys of such intermetallic compounds with or without alloying additions. The advantages of the invention are that the application range of such base materials is significantly expanded, and conventional technologies and processes which are suitable for mass production can be used for producing such components.
In the case of a preferred embodiment of the invention, the intermetallic compound is TiAl. In the case of this base material, it could be determined that crystallites with a high stacking fault density occur in the form of crystallographic twin planes in the crystallite. These crystallites exhibit a plate structure, as has not been observed in the case of conventional titanium alloys. In the case of conventional aluminum diffusion coatings, the twin planes remain uncoated. It is only after a zone is formed which is close to the surface and has a crystallization structure that components made from the base material could be represented with a closed aluminum diffusion coating.
A particularly high density of crystalline plate structures is exhibited by base materials made of alloys from intermetallic compounds with a constituent of TiAl of between 50 a
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Brungs Frank
Grunke Richard
Heinrich Walter
Peichl Lothar
Pillhoefer Horst
MTU Motoren-und Turbinen-Union Muenchen GmbH
Zimmerman John
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