α-Al2O3 and Ti2O3 protective coatings on aluminide substrates
First Claim
1. A process for forming a specific reactive element bilayer barrier on a titanium aluminide substrate, the process comprising:
- creating a hydrogen atmosphere with a concentration of water vapor below 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;
maintaining the temperature above 550°
C. and water vapor concentration below 750 ppm; and
reacting the gaseous hydrogen/water vapor atmosphere with specific reactive elements at the titanium aluminide substrate surface and with oxygen to form a specific reactive element oxide barrier layer which is strongly bonded to the substrate surface, said barrier layer having an aluminum oxide layer at a substrate/barrier layer interface and a titanium oxide layer at a barrier layer/gas interface.
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Abstract
A titanium aluminide substrate (4) is vulnerable to air oxidation, limiting the use of this substrate in a variety of industrial applications, including the aircraft and aerospace industries. A bilayer reactive barrier (2) is formed on a titanium aluminide substrate. The barrier layer includes an α-Al2O3 layer (6) from the reaction of oxygen from the disassociation of water with alumina in a gaseous and water vapor atmosphere at high temperatures and low oxygen concentration. During the process, titanium migrates through the α-Al2O3 to a gas/barrier layer surface (14) and is oxidized to form a Ti2O3 layer (8). A surface of the Ti2O3 layer is subsequently oxidized to form a TiO2 layer (12). In this manner, a triple layer barrier is formed in which the immersible TiO2 and α-Al2O3 are separated by Ti2O3. The three layers are bonded to each with a bond strength greater than 4500 kPa.
12 Citations
29 Claims
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1. A process for forming a specific reactive element bilayer barrier on a titanium aluminide substrate, the process comprising:
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creating a hydrogen atmosphere with a concentration of water vapor below 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;
maintaining the temperature above 550°
C. and water vapor concentration below 750 ppm; and
reacting the gaseous hydrogen/water vapor atmosphere with specific reactive elements at the titanium aluminide substrate surface and with oxygen to form a specific reactive element oxide barrier layer which is strongly bonded to the substrate surface, said barrier layer having an aluminum oxide layer at a substrate/barrier layer interface and a titanium oxide layer at a barrier layer/gas interface. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
disassociating oxygen in said water vapor; and
reacting the disassociated oxygen with said specific reactive elements to form the aluminum and titanium oxide layers.
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4. The process of claim 3 wherein the reacting step is performed at a subatmospheric pressure.
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5. The process of claim 4 wherein the pressure is between about 1×
- 10−
6 to 1×
10−
2 kPa.
- 10−
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6. The process of claim 1 wherein the temperature is between 550 and 1100°
- C.
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7. The process of claim 1 wherein the gaseous atmosphere comprises:
hydrogen at atmospheric pressure that contains less than 750 ppm of water vapor.
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8. The process of claim 1 wherein the gaseous atmosphere comprises:
an inert gas at atmospheric pressure that contains less than 750 ppm of water vapor.
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9. The process of claim 1 wherein the gaseous atmosphere comprises:
water vapor at a pressure between about 1×
10−
6 and 1×
10−
2 kPa.
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10. The process of claim 1 wherein the atmosphere creating step includes:
heating a region of the substrate surface with a pulsed laser.
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11. The process of claim 10 further including:
controlling an intensity of the laser to hold the substrate below an ablation temperature.
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12. The process of claim 11 wherein the laser intensity is below 1011 Joules/sec2.
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13. The process of claim 10 wherein a heated region of the substrate is bordered by substrate surfaces coated with the aluminum oxide layer and the titanium oxide layer.
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14. The process of claim 1 further including:
reducing non-specific reactive elements on the surface of said substrate with the hydrogen gas.
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15. The process of claim 1 wherein said water vapor in hydrogen is at a concentration of between about 1 and 500 ppm.
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16. The process of claim 1 wherein said titanium aluminide substrate comprises at least 2% aluminum.
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17. The process of claim 1 wherein said titanium aluminide substrate comprises TiAl3.
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18. The product formed by the process of claim 1.
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19. The product of claim 18 wherein:
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the aluminum oxide layer includes α
-Al2O3; and
the titanium oxide layer includes Ti2O3.
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20. The product of claim 19 further including:
a TiO2 layer formed on the Ti2O3 layer.
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21. The product of claim 19 wherein the oxide layers and the substrate adjacent the aluminum oxide layer are substantially free of sulfur.
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22. The product of claim 19 wherein the Ti2O3 layer includes non-oxidized metals.
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23. The product of claim 19 wherein a bond strength between layers is greater than 69,000 kPa.
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24. A process for forming a specific reactive element bilayer barrier on a titanium aluminide substrate, the process comprising:
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creating a gaseous hydrogen/water vapor atmosphere with a concentration of water vapor below 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 750 ppm, reacting the gaseous hydrogen/water vapor atmosphere with specific reactive elements at the titanium aluminide substrate surface and with until;
α
-Al2O3 is formed directly on the substrate surface in preference to titanium oxide to form an α
-Al2O3 layer at a substrate/barrier layer interface;
titanium atoms from titanium oxide are reduced with aluminum and the titanium atoms difuse outward through the α
-Al2O3 layer; and
the titanium atoms that have diffused through the α
-Al2O3 layer are oxidized to form a Ti2O3 layer at a barrier layer/gas interface.- View Dependent Claims (25, 26, 27)
diffusing other metals in the substrate through the α
-Al2O3 layer into the Ti2O3 layer in non-oxidized state.
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26. The process of claim 24 further including:
oxidizing Ti2O3 at a gas/barrier layer interface surface of the Ti2O3 layer to form a TiO2 layer on the Ti2O3 layer such that immiscible layers of TiO2 and α
-Al2O3 are separated by Ti2O3.
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27. The process of claim 24 further including:
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reacting sulfur at the substrate surface with the hydrogen to form hydrogen sulfide gas; and
removing the hydrogen sulfide gas from the substrate surface.
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28. A barrier layer protected titanium aluminide material comprising:
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a titanium aluminide substrate;
an α
-Al2O3 layer bonded to a surface of the titanium aluminide substrate;
a Ti2O3 layer bonded to the α
-Al2O3 layer.- View Dependent Claims (29)
a TiO2 layer bonded to the Ti2O3 layer.
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Specification