Claims
- 1. In a method for making a coated article of improved microstructural stability, to avoid detrimental formation of a Secondary Reaction Zone (SRZ) in alloy microstructure of the article under a coating at least partially diffused into the article surface portion after elevated temperature exposure, from a Ni base superalloy having a cast structure including dendrite cores and interdendritic regions, the superalloy having a gamma prime solvus temperature and including Re at greater than about 4 wt. %, the steps of:
- selecting for the superalloy a heat treatment, including solutioning temperature and time ranges above the gamma prime solvus of the superalloy, which results in a Re.DELTA. no greater than about 40%;
- the Re.DELTA. fraction being defined before conversion to percent, as: ##EQU2## and then, heating the superalloy according to the selected heat treatment to result in a Re.DELTA. no greater than about 40%.
- 2. The method of claim 1 in which selecting the heat treatment comprises the steps of:
- heating specimens of the superalloy at different combinations of solutioning temperatures above the gamma prime solvus temperature and solutioning times to result in different Re segregation levels in the dendrite cores and interdendritic regions within the cast structure;
- measuring the Re levels in the dendrite cores of the specimens;
- measuring the Re levels in the interdendritic regions of the specimens;
- determining the Re.DELTA. of the specimens; and then,
- selecting for the superalloy a heat treatment including solutioning temperature and time ranges which results in a Re.DELTA. of no greater than about 40%.
- 3. The method of claim 1 in which the coating of the coated article is a diffusion coating which includes Al.
- 4. The method of claim 3 in which the diffusion coating includes a combination of Al and Pt.
- 5. The method of claim 1 in which the superalloy includes Re in the range of greater than about 4 wt. % up to about 10 wt. %.
Parent Case Info
This is a divisional of patent application Ser. No. 08/528,273, filed Sep. 14, 1995, now U.S. Pat. No. 5,695,821, issue date Dec. 9, 1997.
US Referenced Citations (26)
Foreign Referenced Citations (1)
Number |
Date |
Country |
0 545 661 A2 |
Jun 1993 |
EPX |
Divisions (1)
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Number |
Date |
Country |
Parent |
528273 |
Sep 1995 |
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