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Korean Journal of Metals and Materials > Volume 55(7); 2017 > Article
Korean Journal of Metals and Materials 2017;55(7): 453-459. doi: https://doi.org/10.3365/KJMM.2017.55.7.453
베타 타이타늄 합금의 슬립기구에 의한 준안정 상변태
최병학1, 장현수1, 이범규1, 임가람2, 나영상2, 현용택2, 김승언2, 김영욱3, 박찬성4
1강릉원주대학교 신소재금속공학과
2재료연구소 타이타늄연구실
3한양대학교 에리카공동기기원
4국립과학수사연구원 법안전과
Metastable Phase Transformation of Beta Titanium Alloys by Slip Mechanism
Byung Hak Choe1, Hyeon Su Jang1, Bum Kyu Lee1, Ka Ram Lim2, Young Sang Na2, Yong Taek Hyun2, Seung Eon Kim2, Young Uk Kim3, Chan Sung Park4
1Dept of Metal and Materials Engineering, Gangneung-Wonju National University, Gangneung 25457, Republic of Korea
2Light Metal Division, Korea Institute of Materials Science, Changwon 51508, Republic of Korea
3ERICA Analytical Instrumentation Center, Hanyang University, Ansan 15588, Republic of Korea
4Forensic Engineering Department, National Forensic Service, Wonju 26460, Republic of Korea
Correspondence  Byung Hak Choe ,Tel: +82-33-640-2365, Email: cbh@gwnu.ac.kr
Received: 30 August 2016;  Accepted: 3 January 2017.  Published online: 4 July 2017.
Extensive studies of the metastable structures in beta Ti alloys have investigated the ambiguity of the unstable phase. Their microstructural characteristics have been observed to have a modulated structure, and spot satellites of diffraction in TEM, however the formation mechanisms have not been successfully interpreted because of the resolution limit of the nano lattice structure. High resolution TEM was performed to observe the metastable nano structure and for analysis of the relationship between the nano lattice and spot satellites. A metastable structure was formed just before α precipitation by overlapping a new lattice onto the β matrix, inducing a modulated structure as a kind of Moire fringe. The new lattice structure of the 3a phase had 3 times the distance of the β lattice parameter and had lattice relationships with the β/ω/3a phases of β(112)/ω(1100)/3a[⅓(112)] and β(222)/ω(1101)/3a[⅓(222)]. It was unreasonable to interpret the 3a phase as a definite precipitation of the ω phase, because only the limited zone axes of <113> and <110> were present in the TEM diffraction results of the metastable structures. Other zone axes, such as <100> or <111> etc., were not able to break the distinct metastable features of the spot satellites. Rather than precipitation, the 3a phase was activated by the slip of <113>/(112) and <110>/(112) in the TEM diffraction. It exhibited 3 times the distance of the β lattice parameter, which could not be achieved by typical precipitation.
Keywords: metastable beta Ti, omega phase, spot satellite, 3a lattice parameter, slip, lattice relationship
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