J. M. Vitek, S. S. Babu, S. A. David, Oak Ridge National Laboratory, Oak Ridge, TN

Summary:

Repair technologies for single crystal nickel-based superalloy components are desired because of the very high intrinsic cost of these components. However, repairs often lead to diminished performance due to compromises that must be made. For example, to avoid cracking during weld repair, alternative filler metals are used that have reduced levels of the strengthening gamma prime phase. In addition, the optimum single crystal grain structure is destroyed during current repair practices. This paper addresses the issue of stray grain formation during weld repair. Extensive research has led to an in-depth understanding of the mechanism of stray grain formation and the means for avoiding them during repair. This work identifies promising new methods for weld repair that avoid stray grain formation. The absence of stray grains has two desirable consequences: it maintains the original single crystal microstructure (and thereby, high strength) and it helps to avoid cracking along high-angle grain boundaries. The research also shows that alternative, inferior filler metal compositions are not necessary, so that the high gamma prime content can be maintained. Finally, the work shows that successful weld repairs may be possible for a wide range of geometries, so repairs could be applied to single crystal components regardless of the location of the repair.

This research was sponsored by the Office of Fossil Energy, U.S. Department of Energy, National Energy Technology Laboratory, and the Division of Materials Sciences and Engineering, U. S. Department of Energy, under Contract DE-AC05-00OR22725 with UT-Battelle, LLC.