Method for applying a barrier layer to a silicon based substrate

• US 6,254,935 B1
• Filed: 04/15/1999
• Issued: 07/03/2001
• Est. Priority Date: 04/15/1999
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Eaton, Harry E., Lawton, Thomas H.
• Primary Examiner(s): Beck, Shrive
• Assistant Examiner(s): BARR, MICHAEL E
• Application Number:
  US09/292,351
• Time in Patent Office: 810 Days
• Field of Search: 427/452, 427/453, 427/454, 427/290, 427/309, 427/376.2, 427/379, 427/397.7, 427/374.2, 427/398.1, 427/419.2, 427/419.3
• US Class Current: 427/376.2
• CPC Class Codes: C04B 35/565 based on silicon carbide
• CPC Class Codes: C04B 35/584 based on silicon nitride
• CPC Class Codes: C04B 35/597 based on silicon oxynitride, e.g. SIALONS
• CPC Class Codes: C04B 35/806 The matrix of the ceramic products consisting of non-oxides only
• CPC Class Codes: C04B 41/0072 Heat treatment
• CPC Class Codes: C04B 41/009 characterised by the material treated
• CPC Class Codes: C04B 41/4523 applied from the molten state vitreous materials C04B41/5022; Thermal spraying, e.g. plasma spraying
• CPC Class Codes: C04B 41/4527 Plasma spraying deposition from the gas phase using plasma C04B41/4533
• CPC Class Codes: C04B 41/5024 Silicates C04B41/5022 takes precedence; silico-fluorides C04B41/5018
• CPC Class Codes: C04B 41/5037 Clay, Kaolin
• CPC Class Codes: C04B 41/5096 Silicon C04B35/573 takes precedence
• CPC Class Codes: C04B 41/52 Multiple coating or impregnating multiple coating or impregnating with the same composition or with compositions only differing in the concentration of the constituents, is classified as single coating or impregnation
• CPC Class Codes: C04B 41/522 Multiple coatings, for one of the coatings of which at least one alternative is described
• CPC Class Codes: C04B 41/53 involving the removal of at least part of the materials of the treated article, e.g. etching, drying of hardened concrete C04B41/0036 - C04B41/0054 take precedence
• CPC Class Codes: C04B 41/85 with inorganic materials
• CPC Class Codes: C04B 41/89 for obtaining at least two superposed coatings having different compositions
• CPC Class Codes: C23C 28/042 including a refractory ceramic layer, e.g. refractory metal oxides, ZrO2, rare earth oxides
• CPC Class Codes: C23C 4/02 Pretreatment of the material to be coated, e.g. for coating on selected surface areas
• CPC Class Codes: C23C 4/11 Oxides
• CPC Class Codes: C23C 4/18 After-treatment
• CPC Class Codes: F01D 5/288 : Protective coatings for blades
• CPC Class Codes: F05D 2230/90 : Coating; Surface treatment manufacture with deposition of material F05D2230/30
• CPC Class Codes: F05D 2300/611 : Coating

Abstract

A method for applying a barrier layer which comprises a barium-strontium aluminosilicate to a silicon containing substrate which inhibits the formation of cracks.

Claims

1. A method of preparing an article comprising the steps of:

(a) providing a substrate comprising silicon;

(b) heating the silicon containing substrate to a temperature T of greater than or equal to about 1100°

C.;

(c) applying a barrier layer comprising barium-strontium aluminosilicate to the silicon containing substrate at the temperature T to provide a coated substrate;

(d) thereafter holding the coated substrate at the temperature T for a time period of greater than or equal to about 15 minutes; and

(e) cooling the coated substrate wherein the cooled coated substrate, prior to a subsequent heat treating, has a barrier layer having a crystalline structure of at least about 80% by volume.

2. A method according to claim 1 further including the step of heat treating the cooled, coated substrate.

3. A method according to claim 1 wherein the crystalline structure comprises celsian and hexacelsian phases.

4. A method according to claim 1 wherein the coated substrate is held for a time period of greater than or equal to 30 minutes.

5. A method according to claim 1 wherein the temperature T is greater than 1200°

C.

6. A method according to claim 2 including the step of heat treating the article at a temperature of about 1250°

C. for about 24 hours.

7. A method according to claim 1 wherein the barrier layer comprises from about 0.10 mole to about 0.90 mole BaO and from about 0.10 mole to about 0.90 mole SrO.

8. A method according to claim 1 wherein the barrier layer comprises from about 0.25 mole to about 0.75 mole BaO and from about 0.25 mole to about 0.75 mole SrO.

9. A method according to claim 1 wherein the barrier layer comprises about 0.75 mole BaO and about 0.25 mole SrO.

10. A method according to claim 1 wherein the coefficient of thermal expansion of the barrier layer is within ±

3.0 ppm/°

C. the coefficient of thermal expansion of the substrate.

11. A method according to claim 1 wherein the coefficient of thermal expansion of the barrier layer is within ±

0.5 ppm/°

C. the coefficient of thermal expansion of the substrate.

12. A method according to claim 1 further including the step of grit blasting the substrate prior to applying the barrier layer.

13. A method according to claim 12 including grit blast with alumina particles having a particle size of ≦

30 microns.

14. A method according to claim 13 including grit blasting at a velocity of about 150 m/sec to about 200 m/sec.

15. A method according to claim 1 including applying the barrier layer by thermal spraying.

16. A method according to claim 1 including the step of applying at least one intermediate layer prior to steps (b) through (e).

17. A method according to claim 16 wherein the at least one intermediate layer comprises a bond layer of Si.

18. A method according to claim 17 including applying the bond layer by heating the substrate to a temperature of at least about 800°

C., applying an Si layer of a thickness of 3 to 6 mils and cooling the substrate to room temperature.

19. A method according to claim 16 wherein the at least one intermediate layer is selected from the group consisting of mullite and mullite-barium strontium aluminosilicate.

20. A method according to claim 19 including applying the intermediate layer by heating the substrate to a temperature of at least about 1100°

C., applying the intermediate layer at the temperature T, thereafter holding the substrate at the temperature T for at least 15 minutes, and cooling the substrate to room temperature.

21. A method according to claim 16 including applying two intermediate layers.

22. A method according to claim 21 including applying a bond layer of Si to the substrate and thereafter applying an intermediate layer selected from the group consisting of mullite and mullite-barium strontium aluminosilicate prior to steps (b) through (e).

23. A method according to claim 22 including applying the intermediate layer by heating the substrate to a temperature of at least about 1100°

C., applying the intermediate layer at the temperature T, thereafter holding the substrate at the temperature T for at least 15 minutes, and cooling the substrate to room temperature.

24. A method according to claim 23 including after step (e) heat treating the cooled, coated substrate.

25. A method according to claim 24 including the step of heat treating the article at a temperature of about 1250°

C. for about 24 hours.

26. A method according to claim 23 wherein the crystalline structure comprises celsian and hexacelsian phases.