Claims
- 1. A method for applying a diffusion aluminide coating to a metal substrate comprising the steps of:
providing a metal substrate; cleaning the substrate of foreign material; coating the metal substrate with a layer of aluminum containing paint, said paint comprising substantially aluminum, solvents, and binders; drying the substrate; baking the layer of aluminum containing paint to a first temperature for a first period of time sufficient to volatilize solvents remaining in the layer of aluminum-based paint; baking the layer of aluminum containing paint to a second temperature for a second preselected period of time sufficient to remove the binders in the layer of aluminum containing paint without oxidizing the aluminum, the remaining layer comprising substantially aluminum of sufficient thickness; heating the metal substrate having a substantially continuous layer of aluminum to a third temperature for a third period of time sufficient to diffuse the aluminum into the substrate to form a diffusion aluminide layer; and heating the diffusion aluminide layer to a fourth temperature for a fourth period of time to form a continuous, tightly adherent alumina scale over the diffusion aluminide coating; cooling the substrate.
- 2. The method of claim 1 wherein the paint is selected from the group consisting of KRYLON® No. 1404, aluminum-based paint and combinations thereof.
- 3. The method of claim 1 further comprising the step of applying an outer coating over the diffusion metal layer after cooling the substrate, the alumina scale forming a diffusion barrier between the applied outer layer and the substrate underlying the alumina scale.
- 4. The method of claim 1 wherein the paint contains aluminum particles about 0.5 microns in thickness.
- 5. The method of claim 4 wherein the aluminum particles have an aspect ratio in the range of about 100:1 to about 10:1.
- 6. The method of claim 5 wherein the aluminum particles have an aspect ratio of about 20:1.
- 7. The method of claim 3 wherein the paint contains aluminum particles about 0.5 microns in thickness.
- 8. The method of claim 7 wherein the aluminum particles have an aspect ratio in the range of about 100:1 to about 10:1.
- 9. The method of claim 8 wherein the aluminum particles have an aspect ratio of about 20:1.
- 10. The method of claim 1 wherein the first temperature is in the range of about 300° F. to about 485° F., the first time is in the range of about one hour to about three hours, the second temperature is in the range of about 750° F. to about 930° F., the second time is in the range of about one hour to about three hours, the third temperature is in the range of about 1100° F. to about 2000° F., the third time is in the range of about one hour to about fifty hours, the fourth temperature is in the range of about 1200° F. to about 1800° F. and the fourth temperature is in the range of about two hours to about four hours.
- 11. The method of claim 1 wherein the first temperature is about 400° F., the first time is about two hours, the second temperature is about 750° F. and the second time is about two hours, the third temperature is about 1800° F., the third time is about 2 hours, the fourth temperature is about 1380° F. and the fourth time is about three hours.
- 12. The method of claim 2 wherein the first temperature is in the range of about 300° F. to about 485° F., the first time is in the range of about one hour to about three hours, the second temperature is in the range of about 750° F. to about 930° F., the second time is in the range of about one hour to about three hours, the third temperature is in the range of about 1100° F. to about 2000° F., the third time is in the range of about one hour to about fifty hours, the fourth temperature is in the range of about 1200° F. to about 1800° F. and the fourth temperature is in the range of about two hours to about four hours.
- 13. The method of claim 2 wherein the first temperature is about 400° F., the first time is about two hours, the second temperature is about 750° F. and the second time is about two hours, the third temperature is about 1800° F., the third time is about 2 hours, the fourth temperature is about 1380° F. and the fourth time is about three hours.
- 14. The method of claim 3 wherein the first temperature is in the range of about 300° F. to about 485° F., the first time is in the range of about one hour to about three hours, the second temperature is in the range of about 750° F. to about 930° F., the second time is in the range of about one hour to about three hours, the third temperature is in the range of about 1100° F. to about 2000° F., the third time is in the range of about one hour to about fifty hours, the fourth temperature is in the range of about 1200° F. to about 1800° F. and the fourth temperature is in the range of about two hours to about four hours.
- 15. The method of claim 3 wherein the first temperature is about 400° F., the first time is about two hours, the second temperature is about 750° F. and the second time is about two hours, the third temperature is about 1800° F., the third time is about 2 hours, the fourth temperature is about 1380° F. and the fourth time is about three hours.
- 16. The method of claim 4 wherein the first temperature is in the range of about 300° F. to about 485° F., the first time is in the range of about one hour to about three hours, the second temperature is in the range of about 750° F. to about 930° F., the second time is in the range of about one hour to about three hours, the third temperature is in the range of about 1100° F. to about 2000° F., the third time is in the range of about one hour to about fifty hours, the fourth temperature is in the range of about 1200° F. to about 1800° F. and the fourth temperature is in the range of about two hours to about four hours.
- 17. The method of claim 4 wherein the first temperature is about 400° F., the first time is about two hours, the second temperature is about 750° F. and the second time is about two hours, the third temperature is about 1800° F., the third time is about 2 hours, the fourth temperature is about 1380° F. and the fourth time is about three hours.
- 18. The method of claim 5 wherein the first temperature is in the range of about 300° F. to about 485° F., the first time is in the range of about one hour to about three hours, the second temperature is in the range of about 750° F. to about 930° F., the second time is in the range of about one hour to about three hours, the third temperature is in the range of about 1100° F. to about 2000° F., the third time is in the range of about one hour to about fifty hours, the fourth temperature is in the range of about 1200° F. to about 1800° F. and the fourth temperature is in the range of about two hours to about four hours.
- 19. A gas turbine blade coated with a diffusion barrier coating using the method of claim 1.
- 20. A gas turbine nozzle coated with a diffusion barrier coating using the method of claim 1.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is related to application Ser. No. ______, Attorney Docket No. 13DV-14153 filed contemporaneously with this Application on Dec. 27, 2002, entitled “LOW COST CHROME AND CHROME/ALUMINIDE PROCESS FOR MODERATE TEMPERATURE APPLICATIONS” assigned to the assignee of the present invention, and which is incorporated herein by reference.