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논문 : 기계적 성질 ; 2 상 Ti-6Al-4V 합금의 크리프및 초소성 변형에 대한 미세조직학적 고찰
김지식 ( J. S. Kim ),김진홍 ( J. H. Kim ),박찬경 ( C. G. Park ),이종수 ( C. S. Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 1998 대한금속·재료학회지 Vol.36 No.7
A study has been made to investigate the microstructural aspects of phase/grain boundary sliding and its accommodation mechanism/mode during superplastic deformation in a two phase Ti-6Al-4V alloy. Tensile tests have been carried out at 600℃ and 900℃ using specimens of 3.2 and 10.6 μm grain sizes. Deformed microstructures have been analysed by transmission electron microscopy to understand the deformation mode, accommodation mechanism, and relative sliding rate of the phase boundary and grain boundaries, In the fine grain (3.2 μm) microstructure deformed at 600℃ and 900℃, dislocations were homogeneously distributed in the α-phase with low density implying that deformation mode follows an iso-stress model. However, the coarse-grain specimens (10.6 μm) reveal the planar slip behavior in the α-phase which indicates that the deformation mode is of a mixed type between iso-stress and iso strain rate mode. It is also considered that accommodation for phase/grain boundary sliding in the α and β phase mainly results from a dislocation activated process, The generation of boundary dislocations is more concentrated along α/β phase boundaries than the α/α grain boundaries, which confirms the sliding resistance of α/β < α/ α.
조대 연신 결정립을 가지는 Al5083합금의 부풀림 성형 특성 연구
이상수(S. S. Lee),김지식(J.S.Kim),이영선(Y.S.Lee),권용남(Y- N. Kwon) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
Blow forming process has been used produce complex shapes with superplastic materials in the aerospace industry. Among superplastic materials, a series of 5000 series aluminum alloys with fine grains have been studied for superplastic blow forming. However, coarse grained has never been tried for the blow forming process. The blow forming characteristics of Al 5083 alloy with the coarse elongated grains were studied in the present study. As the forming pressure gets lowered, more uniform thickness of formed part was attained.
김지식,장영원,이종수,김낙준 국립경상대학교 공과대학 부설 첨단소재연구소 1995 尖端素材 Vol.5 No.-
Superplastic forming (SPF) has become an attractive manufacturing technique in the aerospace industry due to its advantages of weight and cost savings for producing the complicated airframe structures. Combined with the diffusion bonding (DB), the design flexibility to produce complex multisheet structures can be further enhanced. In this paper, a brief review has been made as to the application of superplasticity to the fabrication of aircraft components, the various forming methods, the analytical and numerical simulation methods for predicting and optimizing both the design and production of superplastically formed parts. Finally, current status and future directions for SPF/DB technology in Korea have also been descibed.
金知植,李在祥,周雄龍 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.4
A study has been made to investigate the effects of various oxide particles on the nucleation and growth during strain induced dynamic transformation(SIDT) in Ti and Mg added steels. Compression tests have been carried out for steels with fine(20 ㎛), medium(90 ㎛) and coarse austenite(200 ㎛) microstructures at 750, 700 and 650℃ at a strain rate of 1s^-1. After the tests, specimens were water quenched and analyzed by OM, SEM and TEM. The results showed that the ferrite nucleation during SIDT was enhanced by Ti and Mg oxide particles as well as prior austenite boundaries via providing nucleation sites. On the other hand, the growth rate of ferrite formed by SIDT seemed to be more closely related with carbon in steel.