Chromium-enriched diffused aluminide
A method of applying a protective coating to an article comprises the steps of a) depositing aluminum in a surface region of an article, and b) depositing chromium is the surface region of the article subsequent to step a), whereby at least a portion of the chromium replaces at least a portion of the aluminum. Another method and an article are also disclosed.
1. A method of applying a protective coating to an article, comprising the steps of:
a) depositing aluminum in a surface region of an article; and
b) depositing chromium in the surface region of the article with an activator subsequent to step a), whereby at least a portion of the chromium replaces at least a portion of the aluminum, wherein step b) results in a chromium layer having approximately 20-40% chromium by weight in an outer 30 to 60% of the coating thickness.
2. The method of claim 1 , wherein there is less aluminum in the surface region of the article subsequent to step b) than prior to step b).
3. The method of claim 1 , wherein at least one of the aluminum and the chromium are deposited by chemical vapor deposition.
4. The method of claim 3 , wherein the chemical vapor deposition is performed at a temperature of between approximately 1900° F. and 2100° F. (1037.78° C. and 1148.89° C.) for a time of between approximately 1 and 6 hours.
5. The method of claim 1 , wherein the activator is a halide activator.
6. The method of claim 1 , wherein step a) results in an aluminum layer between approximately 0.5 and 3.0 mils (0.01 to 0.08 mm) thick.
7. The method of claim 1 , wherein step b) results in a chromium layer substantially free of alpha chromium.
8. A method of applying a protective coating to an article, comprising the steps of:
a) vapor depositing aluminum in a surface region of an article formed of a low-chromium nickel-based alloy;
b) vapor depositing chromium in the surface region of the article while removing at least a portion of the aluminum using an activator; and
c) heating the article such that the chromium replaces at least a portion of the aluminum through action of the activator, wherein steps b) and c) result in a chromium layer having approximately 20-40% chromium by weight in an outer 30 to 60% of the coating thickness.
9. The method of claim 8 , wherein step c) is performed at a temperature of between approximately 1900° F. and 2100° F. (1037.78° C. and 1148.89° C.) for a time of between approximately 4 and 20 hours.
10. The method of claim 8 , wherein the activator is a halide activator.
11. The method of claim 8 , wherein the activator interacts with the aluminum such that chromium replaces the aluminum.
12. A method of applying a protective coating to an article, comprising the steps of:
a) depositing aluminum in a surface region of an article; and
b) depositing chromium in the surface region of the article with an activator subsequent to step a), whereby at least a portion of the chromium replaces at least a portion of the aluminum, wherein step b) results in a chromium layer substantially free of alpha chromium.
13. The method of claim 12 , wherein at least one of depositing the aluminum and depositing the chromium includes forming a slurry prior to the depositing.
14. The method of claim 12 , wherein there is less aluminum in the surface region of the article subsequent to step b) than prior to step b).
15. The method of claim 12 , wherein at least one of the aluminum and the chromium are deposited by chemical vapor deposition.
16. The method of claim 12 , wherein the activator is a halide activator.
17. The method of claim 12 , wherein depositing the chromium includes forming a slurry prior to the depositing.