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준결정상을 포함한 Mg-Zn-Y 합금의 기계적 특성 및 부식 저항성
김도형 ( Do Hyung Kim ),김원태 ( Won Tae Kim ),김도향 ( Do Hyang Kim ),김영균 ( Young Kyun Kim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.2
Mechanical and property corrosion resistance of Mg-Zn-Y alloys with an atomic ratio of Zn/Y of 6.8 are investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, uniaxial tensile test and corrosion test with immersion and dynamic potentiometric tests. The alloys showed an in-situ composite microstructure consisting of α-Mg and icosahedral phase (I-phase) as a strengthening phase. As the volume fraction of the I-phase increases, the yield and tensile strengths of the alloys increase while maintaining large elongation (26~30%), indicating that I-phase is effective for strengthening and forms a stable interface with surrounding α-Mg matrix. The presence of I-phase having higher corrosion potential than α-Mg, decreased the corrosion rate of the cast alloy up to I-phase volume fraction of 3.7%. However further increase in the volume fraction of the I-phase deteriorates the corrosion resistance due to enhanced internal galvanic corrosion cell between α-Mg and I-phase.
최근섭,김도향,홍경태,Choi, Keun-Seob,Kim, Do-Hyang,Hong, Kyung-Tae 한국현미경학회 1997 Applied microscopy Vol.27 No.4
Disorder-order transformation of nanocrystalline FeAl have been investigated by a combination of electron and X-ray diffraction analysis including high resolution electron microscopy and differential scanning calorimetry. Fe-50at.%Al powders mechanically alloyed for 90 hours consist of $5\sim10$ nm size grains haying either disordered b.c.c. structure or amorphous structure. X-ray and electron diffraction of mechanically alloyed FeAl powders show that disorder-order transformation occurs at the temperature range of $300^{\circ}C\sim320^{\circ}C$. Such a low-temperature ordering behavior exhibiting an exothermic reaction is attributable to the nm-scale grain structure with a large amount of defects accumulated during mechanical alloying process.
고액공존 과공정 Al-Si 합금의 교반응고시 미세조직변화
유영호,김도향 ( Young Ho Ryoo,Do Hyang Kim ) 한국주조공학회 1995 한국주조공학회지 Vol.15 No.5
N/A The microstructural changes during semi-solid state processing of hypereutectic Al-Si alloy has been investigated in the present study. Stirring of semi-solid slurry results in the morphological changes of the primary Si particles, i.e. from angular rod shape to near-spherical shape. Besides the spherodization of primary Si particles, the average particle size increases, especially, at much higher rate in the final stage than that in the early stage of stirring. Various microstructure characterization techniques, such as anisotropic etching, SEM imaging and ECP analysis, reveal that the spherodization of primary Si particles occurs by the combinations of the mechanisms of coalescence, fracture, and wear of the individual particles. Isothermal shearing of hypereutectic Al-Si at 580℃ shows that spherical α-Al particles are formed by the dissociation of Al-Si eutectic structure at the early stage of isothermal shearing. The spherical α-Al particles gradually grow by the mechanisms of Ostwald ripening and coalescence of the particles.
고온자전 합성법에 의해 제조된 TiNiFe합금에서 Incommensurate 상의 형성
조재섭,김도향,김용석,Cho, Jae-Seob,Kim, Do-Hyang,Kim, Yong-Seog 한국현미경학회 1996 Applied microscopy Vol.26 No.3
Structure of premartensite in $Ti_{50}Ni_{49}Fe_1\;and\;Ti_{50}Ni_{50}$ prepared by self-propagating high temperature synthesis (SHS) method has been investigated by a detailed transmission electron microscopy. $Ti_{50}Ni_{49}Fe_1$ consists of microdomain area and needle type domain area. On the other hand, $Ti_{50}Ni_{50}$ consists of microdomain-free and microdomain area, and needle type domain area. Various types of extra superreflections, such as 1/2<100>, 1/2<110> and 1/4<210> type superreflection have been observed in the selected area electron diffractions from microdomain area. Such extra superreflections are due to transformation from B2 structure to distorted B2 structure or premartensite. The present study shows that incommensurate phase forms as an intermediate phase during martensitic transformation. Particularly, in Fe-free $Ti_{50}Ni_{50}$, two types of matrix phases have been observed, microdomain and microdomain-free area. Types of extra superreflections in $Ti_{50}Ni_{50}$ are different from those in $Ti_{50}Ni_{49}Fe_1$, i.e. 1/7<321> type superreflections have been observed, instead of 1/2<110>, 1/2<100>, 1/4<210> types in $Ti_{50}Ni_{49}Fe_1$.
김기배,김도향,이호인 ( Ki Bae Kim,Do Hyang Kim,Ho In Lee ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.2
N/A The wetting behaviour of SiC /Al-Li composite interface has been investigated by using an infiltration method. The critical pressure for melt infiltration into SiC particulate preform has been determined by measuring the melt infiltration distance changes with the variation of applied pressure. The threshold pressure of pure Al, Al-0.2wt%Li, Al-0.5wt%Li for melt infiltration are 3.94, 3.93> 3.75㎏/㎠ respectively, which implies a slight improvement in wettability of SiC /Al composite by addition of Li. The threshold pressure for melt infiltration also changes with the variation of other parameters such SiC particulate size, SiC particulate fraction and melt temperature.
중력주조 AM60 마그네슘 합금의 강화 거동에 미치는 Si 및 Ca 첨가영향
김재우,김도향,신광선 ( Jae Woo Kim,Do Hyang Kim,Kwang Seon Shin ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.4
N/A Effects of Si and Ca additions on the mechanical properties of AM60 based Mg alloys have been investigated. Hardness of the AM60 based Mg alloys reached a maximum value after aging for approximately 33 hours but the amount of hardness increase was negligible. The poor age hardening response of the alloys was due to low Al content, which implies that Al content must be >6 wt.% to observe age hardening effect. The tensile and yield strength increased with increasing AI, Si, and Ca content but elongation decreased with increasing Al and Si content. The best mechanical properties obtained in AM 40-2.5Si-0.2Ca alloy after T4 heat treatment were as follows; tensile strength 193.4 MPa, yield strength 79.2 MPa, and elongation 11.2%. High temperature property obtained from creep test was also improved by introducing Mg₂Si which has high hardness, high melting temperature and low thermal expansion coefficient. (Received February 6, 1998)