Component covered with a layer and method of producing such...

Details Component covered with a layer and method of producing such... Component covered with a layer and method of producing such...

2002-04-12

2004-04-20

Mai, Ngoclan T. (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

C148S281000, C148S284000, C427S295000, C427S372200, C427S532000

Reexamination Certificate

active

06723176

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a component covered with a layer, particularly a component consisting of titanium, a titanium alloy and an intermetallic phase on the basis of titanium and to a method of producing such a layer.
Titanium, titanium alloys and intermetallic phases on the basis of titanium have high mechanical strength and, at the same time, a relatively low density. Titanium components are therefore used where a small weight and high-density based strength is required. Such components are particularly airplane and jet engine components, rotating parts in stationary gas turbines, and moving parts such as valves in internal combustion engines.
In comparison with the most important lightweight construction material, which is aluminum, titanium, titanium alloys and intermetallic phases on the basis of titanium have substantially greater strength at high temperatures. As a result, these materials are used, depending on the respective alloy composition, as construction materials for components having operating temperatures of up to about 800° C., whereas aluminum and aluminum alloys can be used only for operating temperatures below about 400° C.
It is, however, an important disadvantage of titanium, titanium alloys and intermetallic phases on the basis of titanium that, at high operating temperatures, their oxidation resistance is insufficient. On contact with oxygen, the components form already at relatively low temperatures rapidly growing surface layers on TiO
2
basis so that the operating temperatures for titanium are limited to about 500° C. and the operating temperatures for titanium alloys are limited to about 550° C. The operating temperatures of most intermetallic phases on the basis of titanium (not of some titanium silizides) are limited to 600 to 650° C. By certain alloying procedures, the oxidation resistance can be somewhat improved, but the mechanical properties are detrimentally affected thereby to such a degree that the improved oxidation resistance generally does not result in a larger application range of the components mentioned.
The use of protective layers to avoid the oxidation-based deterioration of components of the groups of materials mentioned is very limited. Conventional protective layers on the basis of NiCoCrAl have an insufficient compatibility with titanium, titanium alloys and intermetallic phases on the basis of titanium. The reason herefor is the difference in the thermal expansion behavior and the formation of brittle phases as a result of diffusion phenomena at the interphase base material/protection layer.
The formation of brittle phases is also the reason that conventional aliting layers are generally not suitable for the protection of the components mentioned from oxidation. Commercial systems, which are based on chromium oxide cover layers are not suitable as protective layers since titanium oxides are thermodynamically more stable than chromium oxide.
It is the object of the present invention to provide a component with a surface layer, which provides for good oxidation and corrosion protection of the component in the temperature range of 500 to 1000° C. It is further the object of the invention to provide a method of producing such a layer on the surface of a component.
SUMMARY OF THE INVENTION
In a method of producing on the surface of a component which consists of a titanium alloy or an intermetallic phase on the basis of titanium, a protective layer (according to the formula Ti
5.0−x
Ag
x+y
Al
3.0−y
O
2
), a mixture of Ti powder and TiO
2
powder, which has been sintered, is applied to the surfaces of the component or, if the titanium alloy includes 40-60 at % Al, a coating of silver is applied to the component and the component is then heat treated at 500 to 900° C. to form the protective layer on its surfaces.
The layer on the surface of the component is an alloy on the basis of Ti
5
Al
3
O
2
. It includes small amounts of silver that is amounts of 0.5 to 10 at % particularly in the area of 2 to 5 at %, which partially replaces the titanium. Consequently, the layer is based on a (Ti,Ag)
5
Al
3
O
2
alloy, wherein the replacement of titanium by silver does not occur necessarily stoichiometrically. The oxygen content in this phase may vary between 10 and 22 at % depending on the instant partial oxygen pressure.
Particularly suitable component materials are titanium, titanium alloys, or intermetallic phases on the basis of titanium since, with these materials, the physical and chemical compatibility between the material and the protective layer is very good. However, steel components generally may also be used. The layer according to the invention on the surface of a component forms at temperatures of 500 to 1000° C. a slowly growing cover layer on the basis of Al
2
O
3
when exposed to oxygen and forms in this way an effective oxidation or, respectively, corrosion protection for the component. The almost gas tight Al
2
O
3
cover layer prevents the further diffusion of metal or oxygen ions into the layer and/or the component.
In contrast to other Ti containing protection layers in which in air as well as in nitrogen-containing gases conversions to TiAl will often occur (see N. Zheng et al. “Scripta Metallurgica et materialia Vpl. 33(1), 1995, pages 47-53, the layer according to the invention including silver is particularly long-term stable.
The present patent application discloses a method of providing a surface layer on the basis of a Ti
5
Al
3
O
2
compound. The layer has a silver content of 0.5 to 10 at % (atomic percent) particularly a content of 2 to 5 at % which partially replaces the titanium and partially the aluminum.
At % (atomic %) must not be confused with the indices in the sum formula. The basic sum formula Ti
5
Al
3
O
2
indicates 5 atoms Ti, 3 atoms Al and 2 atoms O resulting in the sum of 10 atoms in the compound. This compound however represents 100 at %, that is, all of the atoms of the compound. Therefore the index 5 for titanium (half of the 10 atoms) represents 50 at %. The index 3 for the Al represents 30 at % and the index 2 for the O represents 20 at % in the particular compound.
The disclosed silver content of 0.5 to 10 at % on the basis of the sum formula index is therefore 0.05 to 1.0 (Ag 0.05-1.0) and consequently the indices sum (x+y) is 0.05<(x+y)<1.0.
In connection with the invention, it has been found that chromium further improves the oxidation resistance of the layer. In a particular embodiment of the invention, the layer therefore consists of a composition on the basis of a (Ti, Ag, Cr)
5
Al
3
O
2
alloy. This means that in a Ti—Al oxide compound, titanium is partially replaced not only by Ag, but also by chromium.
Preferably, the chromium content of the layer is in the area of 0.5 to 15 at %, however, particularly in the range of 5 to 10 at %.
These chromium additions affect the oxidation rates in a positive way and provide for a protective layer, which is further improved.
In the listings of the alloy compositions for the layer, typical alloy additives are not represented. Alloy additives are, among others, Nb, Ta, Cr, Mn or Si. These elements may be present in amounts of 1 to 3 at % each.
The method for the manufacture of the layer according to the invention is explained on the basis of examples in connection with the figures. The layers mentioned may be manufactured for example by the following three procedures. (The component to be protected which consists of titanium of a titanium alloy or of an intermetallic phase on the basis of titanium or another component is designated as “base material”).
For the manufacture of a layer consisting of a ternary phase on the basis of a (Ti, Ag, Cr)
5
Al
3
O
2
alloy or a layer layer with a chromium content of 0.5-15 at %, additional chromium materials were used in an analog manner.
In principle, the methods already known such as laser alloying, plasma spraying, spattering are suitable for applying the layer according to the invention on the respective components as well as the PVD process (

Affiliated with

Also associated with

Rating

Component covered with a layer and method of producing such... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Component covered with a layer and method of producing such..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Component covered with a layer and method of producing such... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3201730