IN939W 합금에서 다양한 냉각속도 및 공정에 따른 응고조직 형성거동 및 분석

다국어 초록 (Multilingual Abstract)

The nickel-based superalloy IN939W is an alloy designed to
provide excellent weldability through the control of trace
elements and is currently used in the repair and refurbishment of
aircraft engine components. In this study, unidirectional
solidification and TIG, DED, and L-PBF welds of IN939W were
analyzed to investigate the solidification behavior of low- and
high-speed solidified microstructures, contributing to the
optimization of welding processes. During directional
solidification, the solid–liquid interface transitioned from planar to
cellular and dendritic with increasing solidification rate, and both
PDAS and SDAS decreased accordingly. Dendritic structures
were observed in all welds, with finer dendrites in the order of
L-PBF, DED, and TIG; the same trend was seen in PDAS and
SDAS. Using the Goldak flux model, the temperature distributions
were numerically analyzed to calculate cooling rate, temperature
gradient, and solidification rate for each process, which were
found to be fastest in the order of L-PBF, DED, and TIG,
attributed to differences in heat input and welding speed.
Thermodynamic calculations of the equilibrium phase diagram
and physical properties of IN939W were used to determine
changes in solidus and liquidus temperatures, tip temperatures of
the solid–liquid interface, and the critical transition velocity
governing interface morphology transitions. When the
temperature gradient and solidification rate obtained from the
directional solidification experiment and the TIG, DED, and LPBF
welds were plotted on a solidification interface map, the
theoretical interface morphologies were found to be consistent
with the experimentally observed ones.

목차 (Table of Contents)

• 목 차
• I.   서 론
• II.   이론적 고찰
• 1. Ni기 초내열합금
• 2. IN939W 합금의 특징
• 3. 적층 제조
• 4. 항공우주 산업의 적층 제조 적용
• 5. 합금의 응고
• 5.1 고상/액상계면 형상 및 형태
• 5.2 조성적 과냉
• 5.3 고상/액상 계면의 천이
• 5.4 일방향 응고
• III.   실험방법
• 1. TIG/DED/L-PBF 용접 시험편 제작
• 2. 일방향응고 실험
• 3. 일방향응고 온도 구배 측정
• 4. 일방향응고/용접부 미세조직 관찰
• 5. 응고수치 해석
• 6. 응고 거동 예측
• IV.   결과 및 고찰
• 1. 일방향응고 미세조직 분석
• 2. 입열량에 따른 TIG/DED/L-PBF 용접부 형상 분석
• 3. 용접속도에 따른 TIG/DED/L-PBF 용접부 형상 분석
• 4. 입열량에 따른 TIG/DED/L-PBF 용접부 미세조직 분석
• 5. 용접속도에 따른 TIG/DED/L-PBF 용접부 미세조직 분석
• 6. 용접부 내 온도분포 해석
• 7. 저속/고속 응고조직 이론적 해석
• V.   결론
• 참고문헌
• List of figures
• List of tables
• abstract