Alpha Al2O3 and Ti2O3 protective coatings on aluminide substrates

• US 20040009359A1
• Filed: 03/18/2003
• Published: 01/15/2004
• Est. Priority Date: 10/31/2000
• Status: Active Grant

• Current Assignee: Donald L. Alger
• Original Assignee: Donald L. Alger
• Inventors: Alger, Donald L.
• Granted Patent: US 6,933,053 B2
• Time in Patent Office: Days
• US Class Current: 428/472.2
• CPC Class Codes: C23C 8/02 Pretreatment of the material to be coated C23C8/04 takes precedence
• CPC Class Codes: C23C 8/16 using oxygen-containing compounds, e.g. water, carbon dioxide
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft
• CPC Class Codes: Y10S 428/938 Vapor deposition or gas diffusion

Abstract

In accordance with one aspect of the present invention, a process for forming a specific reactive element barrier on a titanium and aluminum containing substrate is provided. The process includes creating a dry air atmosphere with a concentration of water vapor below about 750 ppm at a temperature above about 550° C. contiguous to a surface of the substrate on which the barrier layer is to be formed. The temperature is maintained above 550° C. and the water vapor concentration is maintained below about 100 ppm while the water vapor in the dry air atmosphere is reacted with specific reactive elements at the substrate surface. The reaction forms a specific reactive element oxide barrier layer which is strongly bonded to the substrate surface. The barrier layer includes an aluminum oxide layer at the substrate/barrier layer interface and a second oxide layer at a barrier layer/atmosphere interface.

Claims

1. A process for forming a specific reactive element barrier on an aluminum containing substrate, the process comprising:

creating a dry air atmosphere with a concentration of water vapor below about 750 ppm at a temperature above about 550°

C. contiguous to a surface of the substrate on which the barrier layer is to be formed;

maintaining the temperature above 550°

C. and water vapor concentration below about 100 ppm;

reacting the water vapor in the dry air atmosphere with specific reactive elements at the substrate surface to form a specific reactive element oxide barrier layer which is strongly bonded to the substrate surface, said barrier layer including an aluminum oxide layer at the substrate/barrier layer interface.

2. The process of claim 1 wherein said barrier layer further includes a second oxide layer at a barrier layer/atmosphere interface.

3. The process of claim 2 wherein:

the aluminum oxide layer includes crystalline α

-Al₂O₃; and

the titanium oxide layer includes crystalline Ti₂O₃,

the crystalline α

-Al₂O₃ and the Ti₂O₃ having like lattice constants.

4. The process of claim 2 wherein the reacting step includes:

dissociating oxygen in said water vapor; and

reacting the dissociated oxygen with said specific reactive elements to form the aluminum and titanium oxide layers.

5. The process of claim 4 further including:

exposing the substrate to atmospheric air at a temperature greater than about 500°

C. to form crystalline fibers of TiO₂ titanium oxide.

6. The process of claim 5 wherein the reacting step is performed at a sub-atmospheric pressure.

7. The process of claim 6 wherein the pressure is between about 1×

10<sup>−

6</sup> to 1×

10<sup>−

2</sup> kPa.

8. The process of claim 6 wherein said high temperature is between 550 and 1100 C.

9. The process of claim 5 wherein the dry air atmosphere includes:

water vapor at a pressure between about 1×

10<sup>−

6</sup> and 1×

10<sup>−

2</sup> kPa.

10. The process of claim 5 wherein the dry air atmosphere is created free of hydrogen gas.

11. The process of claim 10 further including:

disassociating the water vapor into oxygen and hydrogen during the reacting step and reducing non-specific reactive elements on the surface of said substrate with the hydrogen/water vapor gas.

12. The process of claim 5 wherein the dry air is dried to a water vapor concentration in hydrogen of about 1 ppm and diluted to a concentration of 20-100 ppm.

13. The process of claim 2 wherein said titanium aluminide substrate includes at least 2% aluminum and at least 2% of titanium.

14. The process of claim 2 wherein said titanium aluminide substrate includes TiAl₃.

15. The process of claim 2 further including:

reacting sulfur at the substrate surface with hydrogen produced by dissociation of water vapor to form hydrogen sulfide gas; and

removing the hydrogen sulfide gas from the substrate surface.

16. The process of claim 2 wherein the dry air atmosphere includes 20-100 ppm of water vapor.

17. The product formed by the process of claim 2.

18. The product of claim 17 wherein:

the aluminum oxide layer is α

-Al₂O₃; and

the titanium oxide layer is Ti₂O₃.

19. The product of claim 18 wherein the oxide layers and the substrate adjacent the aluminum oxide layer are substantially free of sulfur.

20. The product of claim 18 wherein the Ti₂O₃ layer includes non-oxidized metals.

21. The product of claim 18 wherein a bond strength between layers is greater than 15,000 psi.

22. The product by the process of claim 5.

27. The product formed by the process of claim 1.

28. The product of claim 27 wherein said aluminum containing substrate is selected from the group consisting of nickel aluminide, iron-aluminum alloy, and Fe-6Al.

23. A process for forming a specific reactive element bilayer on a titanium aluminide substrate, the process comprising:

creating a gaseous/water vapor atmosphere with a concentration of water vapor below about 750 ppm at a temperature above about 550°

C. contiguous to a surface of the titanium aluminide substrate on which the barrier layer is to be formed;

while maintaining the temperature above about 550°

C. and water vapor concentration below about 750 ppm, reacting the oxygen of the water vapor with specific reactive elements at the titanium aluminide substrate surface until;

α

-Al₂O₃ is formed directly on the substrate surface in preference to titanium oxide to form a crystalline α

-Al₂O₃ layer at a substrate/barrier layer interface;

titanium atoms from titanium oxide are reduced with aluminum and the titanium atoms diffuse outward through the α

-Al₂O₃ layer;

oxidizing the titanium atoms that have diffused through the α

-Al₂O₃ layer to form a crystalline Ti₂O₃ layer at a barrier layer/gas interface the crystalline α

-Al₂O₃ and Ti₂O₃ have like lattice structures; and

exposing the substrate and the α

-Al₂O₃ and Ti₂O₃ layers to atmospheric air with a water vapor content above 750 ppm at a temperature greater than about 500°

C. to reach remaining titanium atoms to form TiO₂ fibers.

24. The process of claim 23 further including:

diffusing other metals in the substrate through the α

-Al₂O₃ layer into the Ti₂O₃ layer in non-oxidized state.

25. The process of claim 23 wherein the TiO₂ fibers are 1-5 micrometers in diameter.

26. A barrier layer protected titanium aluminide material substrate comprising;

a crystalline α

-Al₂O₃ layer bonded to a surface of the titanium aluminide substrate;

a crystalline Ti₂O₃ layer bonded to the α

-Al₂O₃ layer; and

crystalline TiO₂ fibers in the α

-Al₂O₃ and Ti₂O₃ layers.