| Title |
Localized Crack-Free Welding for DS 247LC Superalloy Correlated with Single-Mode Fiber Laser and CET Theory |
| Authors |
신민창(Min-Chang Shin) ; 천은준(Eun-Joon Chun) |
| DOI |
https://doi.org/10.3365/KJMM.2025.63.11.887 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
DS 247LC superalloy; Single-mode fiber laser welding; Solidification cracking; Epitaxial growth; Columnar-to-Equiaxed Transition (CET) theory |
| Abstract |
In this study, we systematically investigated the mechanisms enabling localized solidification
crack-free welding of directionally solidified (DS) 247LC superalloy using a single-mode fiber laser, with a
particular focus on the correlation with the columnar-to-equiaxed transition (CET) theory. Welding was
performed on a single DS grain under twelve conditions, varying heat input (1, 1.5, 2 J/mm), welding speed
(500, 750 mm/s), and energy density (7.1, 14.0 J/mm2). The weld bead geometry was found to depend on the
energy density, resulting in either heat conduction mode (7.1 J/mm2) or keyhole mode (14.0 J/mm2). In the
heat conduction mode, solidification cracking was completely suppressed across all conditions, while in the
keyhole mode, cracking was prevented under some conditions but appeared along the bead centerline under
specific high heat input conditions (C-3 and C-4). Crystallographic analysis revealed that reduced epitaxial
growth rates and increased high-angle grain boundaries were associated with crack formation in these cases.
CET maps were calculated using the Thermo-Calc Additive Manufacturing module to elucidate the
relationship between weld morphology and crack susceptibility, reflecting rapid solidification behavior under
laser welding conditions. The results showed that heat conduction mode welds remained within the columnar
growth region, while keyhole mode welds under higher heat input shifted towards the CET boundary or
equiaxed region, correlating strongly with crack formation. These findings demonstrate that the suppression
of CET and the promotion of epitaxial growth are critical for achieving crack-free welding in DS 247LC
superalloy using single-mode fiber lasers, providing practical guidelines for advanced manufacturing and
repair of turbine components under rapid solidification conditions. |