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고액공존 Mg-Al-Zn 합금의 등온교반시 미세조직변화
김도향,유영호 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.4
The microstructural changes of Mg-Al-Zn-X(X=Si and Sr) alloys during semi-solid state processing has been investigated in the present study. The equiaxed α-Mg primary dendrites are broken into nearly spherical primary particles at the early stage of isothermal shearing, i.e. after isothermal shearing at f_s≒0.5 for ∼3-5 minutes. Once the non-dendritic structure has formed, the primary particle morphology and size distribution remain nearly unchanged for upto 40 minutes, due to the competing mechanisms of particle dissociation and restructuring. Microstructure and composition analysis shows that particle dissociation and restrucuring occur in various mechanisms such as recrystalization or fracture of dendritic structurers. Ostwald ripening and particle sintering due to isothermal shearing in semisolid state.
중력주조법에 의한 Al-Cu-Fe 준결정 입자 강화 Al 기 복합재료의 제조와 그 기계적 성질
김도향,김원태,이상목,Fleury, E . 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.7
An Al_(62)Cu_(26)Fe_(12) alloy was gas-atomized in a protective N₂ atmosphere to prepare powders containing the icosahedral quasicrystalline phase as reinforcing particles. Fabrication of composites was achieved by adding the Al_(62)Cu_(26)Fe_(12) powders into the pure Al molten metal as a matrix material, followed by a quick agitation during conventional casting. The composites showed a relatively good bonding between the particles and molten Al without the formation of any intermetallic compound, despite the partial dissolution of the small satellite particles. Mechanical properties evaluated through compression and non-destructive continuous indentation tests of the composites indicated a significant increase of the yield stress especially in the range up to 10% volume fraction of reinforcing particles within a reliable error range. Strengthening mechanisms were reviewed to estimate the role of the icosahedral and coexisting crystalline phases on the increase of the yield stress.
김도향 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.11
Recent studies show intermetallics with 5∼20 ㎚ grains show improved physical, chemical and mechanical properties. For example, intermetallics can have some amount of ductility due to ㎚ scale grains and increased portion of grainboundaries. The nanocrystalline intermetallics can be fabricated by using various techniques such as gas condensation, rapid solidification and mechanical attrition. The nanocrystalline intermetallics also have good thermal stability which is one of the important factors for successful consolidation, thus providing high performance bulk materials. Nanoscale crystallization and decomposition behavior of intermetallics have been reviewed with special emphasis on nanocrystalline FeAl, NiTi and NiAl intermetallics.