Method of removing casting defects

1. A method of removing a casting defect which is not usually visible on the casting without the aid of grain etching or fluorescent penetrant inspection from a single crystal or directionally solidified article with an oriented microstructure, comprising:

locating at least one casting defect by applying a grain etch and/or fluorescent penetrant inspection technique to the article;

melting the casting defect locally by a heat source to a depth at least as great as the casting defect itself; and

solidifying the molten material epitaxially with respect to the surrounding oriented microstructure of the article that is substantially free of a casting defect whereby the ratio G n /V s (with G=temperature gradient at the melting point, n=material constant and V s =solidification speed) is kept above a material dependent threshold value.

2. The method of claim 1 , wherein during melting, the casting defect is locally melted along the length of the casting defect by moving the heat source.

3. The method of claim 1 , further comprising:

re-melting the solidified portion of the material using a reduced energy density of the heat source as compared to the energy density employed during the first melting; and

solidifying the re-melted material epitaxially with respect to adjacent defect free microstructure.

4. The method of claim 1 , wherein the molten material solidifies epitaxially with respect to the surrounding oriented micro structure of the article in a way that the solidified area is restored substantially to a volume equal to the volume of the area when it included the casting defect.

5. The method of claim 1 , further comprising:

preparing the article for a repair operation after locating the at least one casting defect.

6. The method of claim 1 , wherein the at least one casting defect includes at least one of the following: a freckle, a sliver, an equiaxed grain, a recrystallized grain, a linear crack, a surface micro-crack, a chain of pores, a linear dross inclusion, and a linear cluster of inclusions.

7. The method of claim 1 , further comprising:

removing a portion of the casting defect by machining before solidifying begins.

8. The method of claim 1 , further comprising:

adding additional material before melting or to the locally melted area during or after melting.

9. The method of claim 8 , wherein the additional material added before melting includes one of a preform solid, a powder compress, a paste, and a slurry.

10. The method of claim 8 , wherein the additional material added to the locally melted area includes substantially the same composition as the article.

11. The method of claim 8 , further comprising:

machining excess material away after solidification of the molten material.

12. The method of claim 1 , further comprising:

melting a portion of the solidified material a second time while this time adding additional material.

13. The method of claim 12 , further comprising:

machining excess material away after solidification of the molten material.

14. The method of claim 1 , further comprising:

using a vision system to locate the at least one casting defect and to guide the heat source for melting the at least one casting defect.

15. The method of claim 1 , further comprising:

pre-heating the article to a temperature in the range of 500–1000° C. prior to the melting of the casting defect.

16. The method of claim 1 , wherein melting includes using at least one laser as the heat source to locally melt the casting defect.

17. The method of claim 16 , wherein the melting of the casting defect is carried out under an inert gas atmosphere, with inert gas shielding, or under vacuum.

18. The method of claim 1 , wherein the heat source used in melting includes at least one of Plasma Transfer Arc, Micro Plasma, Tungsten Inert Gas, and Electron Beam.

19. The method of claim 18 , wherein the melting of the casting defect is carried out under an inert gas atmosphere, with inert gas shielding, or under vacuum.

20. The method according to claim 1 , wherein the article is a gas turbine component made from a nickel or cobalt base super alloy.