| Title |
Method of Suppressing Solidification Cracking by Laser Surface Melting and Epitaxial Growth Behavior for Directionally Solidified 247LC Superalloy |
| Authors |
김경민(Kyeong-min Kim); 천은준(Eun-joon Chun) |
| DOI |
https://doi.org/10.3365/KJMM.2023.61.4.252 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
directional solidification; 247LC superalloy; laser surface melting; epitaxial growth; solidification cracking |
| Abstract |
In this study, the relationship between solidification cracking and epitaxial growth behavior with the high-speed laser surface melting of a directionally solidified 247LC superalloys was fundamentally and metallurgically investigated, to develop a successful welding procedure for the next generation of gas turbine blades. Under typical laser surface melting conditions (scan speed: 50 mm/s, heat input: 40 J/mm), severe solidification cracking phenomena occurs. The key metallurgical factors of solidification cracking have been identified as solidification segregation-assisted pipeline diffusion behavior at the solidification grain boundary, and in the randomly formed polycrystalline melting zone microstructure. In addition, under extremely low heat input and high-speed laser beam scan conditions (scan speed: 1000 mm/s, heat input: 2 J/mm), an effective surface melting zone can be obtained within a single directionally solidified grain under a relatively high-energy beam density (65 J/mm2) using the characteristics of single-mode fiber lasers. Results reveal that the laser melting zone successfully shows a 99.9% epitaxial growth achievement ratio. Because of the superior epitaxial growth ratio within the laser surface melting zone, and the rapid solidification phenomena, formation of a solidification grain boundary and solidification segregation-assisted pipeline diffusion behavior can be suppressed. Finally, a solidification crack-free laser melting zone can thus be achieved.(Received 9 December, 2022; Accepted 28 December, 2022) |