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박은수,옥재범,김원태,김도향,Park, Eun-Soo,Ok, Jae-Bum,Kim, Won-Tae,Kim, Do-Hyang 한국현미경학회 2002 Applied microscopy Vol.32 No.1
As-cast microstructure of Mg-rich $Mg_{68}Zn_{28}Y_4$ has been investigated by a detailed transmission electron microscopy. The as-cast $Mg_{68}Zn_{28}Y_4$ alloy consisted of three different types of phases: $10{\sim}20{\mu}m$ size primary solidification phase, dendritic phase grown from the primary phase and a eutectic structure formed at the later stage of solidification. The primary solidification phase has an icosahedral structure with a large degree of phason strain. 1/1 rhombohedral approximant phase with lattice parameters: $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$ is first observed in Mg-Zn-Y system. The rhombohedral structure can be obtained by introducing phason strain in the six dimensional face centered hyper-cubic lattice. The decagonal phase nucleates with orientation relationship with the icosahedral phase, and $Mg_4Zn_7$ nucleates with orientation relationship with the decagonal phase, indicating a close structural similarity between the three phases. Gradual depletion of Y during solidification plays an important role in heterogeneous nucleation of decagonal and $Mg_4Zn_7$ phases from icosahedral and decagonal phases respectively. [ $Mg_{68}Zn_{28}Y_4$ ] 합금의 응고 조직은 primary solidification phase, primary solidification phase로부터 성장된 ${\alpha}-Mg$ dendrite, 그리고 응고 말기에 형성된 eutectic structure의 세 가지형태 조직으로 구성되어져 있다. Primary solidification phase에는 매우 큰 정도의 phason strain이 존재하고 있으며, $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$의 격자상수를 갖는 1/1 rhombohedral approximant가 존재한다. 이와 같은 rhombohedral approximant의 구조는 six dimensional face centered hyper-cubic lattice에 phason strain을 도입함에 의해 얻어질 수 있다. Decagonal phase는 icosahedral phase로부터 방위 관계를 가지며 형성되며, $Mg_4Zn_7$는 decagonal phase로부터 방위관계를 가지며 성장한다. 이는 세 상간에 구조적 유사성이 존재하고 있음을 의미하며, 응고시 용질원자의 분배에 의해 이들 세 상이 순서대로 형성되어진다.
Mg-Cu-TM-Y (TM = Ag, Ni, Zn) 합금의 비정질 형성능
김원태,박은수,김도향 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.11
Effect of Transtion Metal (TM = Ag, Ni, Zn), as a substitution for Cu, on the glass forming ability was examined in Mg_(65)Cu_(25-x)TM_xY_(10) (x = 0, 5, 10, 15, 20, 25) alloys by using thermal analysis and X-ray diffractometry. Partial substitution of Cu with less than 15 at% Ag and 5 at% Ni in Mg_(65)Cu_(25)Y_(10) alloy enhanced the glass-forming ability. Maximum diameter for single amorphous phase formation in Mg_(65)Cu_(15)Ag_(10)Y_(10) alloy by injection casting was 6 ㎜. Both amorphous alloys prepared by melt spinning and injection casting showed similar crystallization process during continuous heating in DSC. Also in this section as composition changes, co-relationship between variation of critical diameter for formation of an amorphous phase and that of parameters suggested to reflect glass-forming ability was examined.
Mg-Cu-Ag-Y 합금의 벌크 비정질 제조에 관한 연구
김원태,박은수,강형구,김도향 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.7
We have studied the effect of Ag as a substituting element for Cu on class forming ability in Mg_(65)Cu_(25-x)Ag_xY_(10) alloy and the possibility of manufacturing new bulk Mg-based glass material with maximum thickness by the squeeze casting process. Ag was selected as a candidate element due to following reasons : 1) Atomic size difference between Ag and constituting elements is more than 10%; 2) Mixing enthalpies between Ag-Mg and Ag-Y are large; and 3) Ag and Cu belong to a same family in periodic table and number of valence electron of Ag is same as that of Cu. Mg_(65)Cu_(15)Ag_(10)Y_(10) alloy has improved glass forming ability, by partially substituting Cu with Ag in Mg_(65)Cu_(25)Y_(10) alloy. Injection casting produced bulk metallic glass of Mg_965)Cu_(15)Ag_(10)Y_(10) alloy having diameter up to 6 ㎜, which is larger than the maximum diameter of 4 ㎜ in Mg_(65)Cu_(25)Y_(10) alloy. Squeeze casting enabled to produce larger bulk metallic glass with Mg_(65)Cu_(15)Ag_(10)Y_(10) alloy up to 10 ㎜ in diameter due to rapid heat extraction and undercooling of the liquid alloy by applying pressure during solidification.
Cu47Ti33Zr11(Ni,M)8Si1 (M = Co, In, Sn) 합금의 비정질 형성능
장혜정,김원태,박은수,김도향 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.6
The effect of the sixth element(M = Co, In, Sn), as a substitution for Ni in Cu_(47)Ti_(33)Zr_(11)(Ni, M)_8Si₁ alloys, on the glass forming ability was examined using thermal analysis, X-ray diffractometry and TEM. Partial substitution of Ni with 2 at% In and Sn in Cu_(47)Ti_(33)Zr_(11)Ni_8Si₁ alloy enhanced the glass-forming ability. The maximum diameter for single amorphous phase formation in Cu_(47)Ti_(33)Zr_(11)Ni_8Sn₂Si₁ alloy by injection casting was 6 ㎜. Both amorphous alloys prepared by melt spinning and injection casting showed similar crystallization process during continuous heating in DSC. Co-relationship between variation of critical diameter for formation of an amorphous phase and that of parameters suggested to reflect glass-forming ability such as ΔT^*_m, T_(rg), ΔT_x, T_m-T_x, K parameter was examined.