레이저 급속 표면용융에 따른 일방향응고 247LC 초내열합금의 에피택셜 성장 및 응고균열 억제 방안

• Published in: 대한금속재료학회지 Vol. 61; no. 4; pp. 252 - 260
• Main Authors: 김경민, Kyeong-min Kim, 천은준, Eun-joon Chun
• Format: Journal Article
• Language: Korean
• Published: 대한금속재료학회 05.04.2023
• Subjects: 247LC superalloy; directional solidification; epitaxial growth; laser surface melting; solidification cracking
• ISSN: 1738-8228

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)