Development and testing of a high-chromium, Ni-based filler metal resistant to ductility dip cracking and solidification cracking

Abstract

Ni-based filler metals for repair and construction of nuclear reactor components require 30 wt% Cr to insure resistance to primary water stress corrosion cracking (PWSCC). Current generation alloys can be susceptible to solidification cracking and ductility dip cracking, depending on Nb content and the amount of eutectic that forms during weld solidification. Computational thermodynamic modeling was used to identify alternative eutectic-forming elements to Nb, such as Hf and Ta. Previous work has utilized a design of experiment methodology (DOE) in conjunction with computational and experimental techniques to optimize a new filler metal composition that should be resistant to weld cracking. In this paper, the optimized compositions were subjected to further weldability testing, namely the cast pin tear test (CPTT) and the strain-to-fracture (STF) test. An optimized Ta-bearing composition was found to be crack resistant, while an optimized Hf-bearing composition was highly susceptible to solidification cracking. Differences may be related to the nature of the eutectic constituents that form at the end of solidification. The Hf-bearing composition did not form Laves phase as its final eutectic constituent, while Laves is present in both the Nb- and Ta-bearing systems.