Ti-6Al-4V 합금의 고온 변형 후 기계적 물성 변화에 관한 연구

다국어 초록 (Multilingual Abstract)

The mechanical properties of Ti-6Al-4V alloys were investigated in the superplastic forming process(SPF) according to cooling rate and strain. In order to simulate the SPF, the mill-annealed Ti-6Al-4V alloy was heated at different cooling rate. The α-case thickness varied depending on the cooling rate, and α-case generated by the high temperature exposure was removed to understand the effect on the mechanical properties. Also, considering the high temperature forming conditions of Ti-6Al-4V alloy, preliminary specimens were prepared and hot deformed.
High temperature exposure time was 60 min, temperature was 875~925 oC, strain was 0~50 %. The effects of temperature and strain on mechanical properties were investigated by microstructure observation, tensile test and fatigue test. As the temperature and strain increased, the thickness of the α-case tended to increase. The presence of α-case has a negative effect on tensile strength, elongation and fatigue strength. The tensile strength, elongation and fatigue strength of the specimens with α-case removed were recovered.

목차 (Table of Contents)

• Ⅰ. 서 론 1
• Ⅱ. 이론적 배경 6
• 1. 초소성과 초소성 성형 6
• 2. 초소성 재료의 특성 13
• 3. 결정립 크기와 결정립 성장 22
• 4. 산화와 표면 산화층(α-case) 25
• Ⅲ. 실 험 28
• 1. 냉각방법에 따른 미세조직과 인장특성 28
• 2. 고온 변형 후 변형률에 따른 기계적 특성 변화 32
• Ⅳ. 결과 및 고찰 38
• 1. 냉각방법에 따른 미세조직 인장특성 분석 38
• 1.1 미세조직 관찰 38
• 1.2 인장시험 및 파면관찰 42
• 2. 고온 변형 후 변형률에 따른 기계적 특성 분석 52
• 2.1 미세조직 및 EBSD 관찰 52
• 2.2 인장시험 및 파면관찰 63
• 2.3 피로시험 및 파면관찰 70
• Ⅴ. 결론 77
• References 79