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김동익,Abbaschian, Reza 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.9
The effect of cooling rate on the metastable liquid phase separation(MLPS) in Cu-Fe binary and Cu-Fe-Co ternary alloys was investigated using an electromagnetic levitation technique. The cooling rate during phase separation was controlled by dropping the specimens to copper substrate which was in 15 ㎝ apart from levitation coil. The cooling rate in levitation state was 5-20 K/sec, and those of free falling and after splash were 130 K/sec and 2300 K/sec respectively. In the specimen solidified at medium cooling rate(about 130 K/sec), secondary phase separation was observed in both L1(Fe- or Fe, Co-rich phase) and L2(Cu-rich phase) phases that have been formed by primary phase separation. In this case the phase separation occured by nucleation and growth. Spinodal decomposition is considered as a dominent phase separation mechanism in L1 droplets solidified at fast cooling rate (about 2300 K/sec). There was no evidence of spinodal decomposition in L2 phase.
Cu-Co-Fe 3 원계 합금의 준안정 액상 상분리 및 응고조직
김동익,Abbaschian, Reza 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.2
Metastable liquid phase separation(MLPS) in Cu-Co-Fe ternary system was investigated using an electromagnetic levitation technique. The temperature of the metastable liquid phase separation(Tsep) was measured directly from the time-temperature profile during the cooling in levitated state. The metastable liquid miscibility boundary of the Cu-Co-Fe ternary was determined using the measured Tsep and the compositional analysis of the separated phases. Metastable liquid phase separated structures of Cu-Co-Fe system were found to be consistent with (Co, Fe)-Cu quasi binary phase diagram. In Cu-rich alloys, phase separation generally appeared as dispersed L1(Co, Fe rich phase) droplets in a L2(Cu rich phase) matrix, whereas for alloys containing Cu less than 45-47 wt%(depending on the alloy composition), L2 droplets formed in a L1 matrix. Secondary metastable liquid phase separation were observed in specimens which were cooled rapidly against a copper substrate.
Cu-Co 2 원계 합금에서 준안정 액상의 상분리와 미세조직
김동익,Abbaschian, Reza 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.1
Metastable liquid phase separation(MLPS) in Cu-Co binary system was investigated using an electromagnetic levitation technique. In Co-rich alloys, Phase separation generally appeared as dispersed L2(Cu-rich) droplets in a L1(Co-rich) matrix, whereas for alloys containing Co less than 55 wt%, L1 droplets formed in a L2 matrix. Secondary MLPS was occurred in the primary separated L1 droplets by increasing the cooling rate during phase separation. The effect of undercooling and cooling rate on the microstructure of L1 phase was investigated. The microstructure of L1 phase was found to fall into three categories of dendrite, spherical and mixed (dendritic plus spherical) morphology. As the undercooling and/or cooling rate was increased the spherical morphology became a dominent structure.
김동익,Abbaschian, Reza 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.12
Metastable liquid phase separation(MLPS) in Cu-Fe binary system was investigated using an electromagnetic levitation technique. The temperature of the MLPS(Tsep) was measured directly from the time-temperature profile during cooling in the levitated state. The metastable liquid miscibility boundary of Cu-Fe binary system was illustrated using these measured Tsep. In Fe-rich alloys, phase separation generally appeared as dispersed L2(Cu-rich) droplets in a L1(Fe-rich) matrix, whereas for alloys containing Fe less than 53 wt%, L1 droplets formed in a L2 matrix. Secondary MLPS was occured in the primary separated L1 droplets by increasing the cooling rate during phase separation.
$MoSi_2$/W 복합재료의 합성과 성질에 관한 연구
장대규,Jang, Dae-Kyu,Abbaschian, R. 한국재료학회 1998 한국재료학회지 Vol.8 No.10
$MoSi_2$에 W분말을 첨가하여 $MoSi_2$/W 복합재료를 $1600^{\circ}C$에서 3시간 동안 유지하면서 30MPa의 조건하에서 고온진공 가압기를 이용하여 제조하였으며, 텅스텐 분말의 첨가량이 $(Mo)Si_2$의 미세조직과 기계적 성질에 미치는 영향을 조사하였다. 텅스텐은 몰리브덴과 치환하면서 고용체 합금을 이루었으며, 입자의 크기는 텅스텐 분말의 첨가량이 증가할수록 감소하였다. 비커스경도는 텅스텐 분말의 첨가량이 증가할수록 향상되었으나, 반면에 압흔파단 강도는 오히려 감소되었다. 10%정도의 텅스텐 분말을 첨가하였을 때, 압흔파단 강도가 $4.5MPa$\sqrt{m}$로서 순수 $MoSi_2$의 $2.7MPa\sqrt{m}$에 비하여 향상되었음을 알 수 있었다. $MoSi_2$/W composites were fabricated by vacuum hot press at $1600^{\circ}C$ under 30MPa for 3 hrs. The effects of the amount of tungsten in the composites was explained in terms of the microstructure and mechanical properties. Although tungsten was mainly substituted to Mo atoms forming a complete solid solution of (Mo.W).Si, (x= 1, 5, y=2, 3). the grain size of composites became smaller with the increase of tungsten added. Vickers hardness was increased with the increase of tungsten content due to the solid-solution hardening. On the other hand, toughness of composites decreased sharply by increasing the amount of tungsten. Optimum tungsten amount was determined to be a 10 vol% of composite. Indentation fracture toughness was calculated to be 4.5MPa\sqrt{m}$ in this composites, compared with $2.7MPa\sqrt{m}$ in pure $MoSi_2$.
A Study on Synthesis of (Mo.W)$\textrm{Si}_2$ Composites
장대규,Jang, Dae-Gyu,Abbaschian, R. Materials Research Society of Korea 1999 한국재료학회지 Vol.9 No.1
(Mo.W)Si$_2$ composites were fabricated by vacuum hot-pressing elemental Mo, W and Si powders at various temperatures. Elemental Mo, W and Si powders were alloyed in the proper proportions to form solid solutions. The microstructure and properties of these materials was characterized by using x-ray diffraction, optical microscopy, energy dispersive x-ray spectroscopy and Vicker's technique. It was found that tungsten was mainly substituted for Mo atoms, and made a completed solid solution of (Mo.W)Si$_2$ over 1$600^{\circ}C$. The lattice parameters and Vickers hardness increased largely with increasing reaction temperature by the most soluble elements, due to the solid-solution hardening.
On the control of structural/compositional ratio of coherent order-disorder interfaces
Forghani, Farsad,Han, Jong Chan,Moon, Jongun,Abbaschian, Reza,Park, Chan Gyung,Kim, Hyoung Seop,Nili-Ahmadabadi, Mahmoud Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.777 No.-
<P><B>Abstract</B></P> <P>Order-disorder coherent interfaces determine the microstructure and mechanical properties of precipitation-hardened high-temperature alloys. The characteristics of these interfaces can be defined by a compositional width, δ, and structural width, δ′. The latter, which can be considered as the width of the ordered part of the interface, can play an important role in high-temperature mechanical behavior of precipitation-hardened alloys. This is due to the fact that diffusion in the ordered part of the interface is generally much slower than diffusion in the disordered phase, thus hindering the solid-state diffusion-based phenomena. Here, we investigate the order-disorder interface in a Ni-19Al (at.%) alloy as a model alloy for Ni-based superalloys using atomic-resolution scanning transmission electron microscopy and three-dimensional atom probe tomography. Then, we employ thermodynamic modeling to describe the interplay between the structural and compositional interface widths in binary Ni-Al and in ternary Ni-Al-Cr and Co-Al-W systems. We introduce the δ′/δ ratio as a critical parameter that varies significantly in different alloys. Our findings offer a general pathway to control the δ′/δ ratio of interfaces, which in turn affect the high-temperature properties of precipitation-hardened alloys.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Characterization of the order-disorder coherent interface in a Ni-19Al model alloy. </LI> <LI> Describing the dual nature of order-disorder coherent interfaces. </LI> <LI> Prediction of the structural interface width δ′ based on the thermodynamic modeling. </LI> <LI> Introducing the δ′/δ ratio as a critical parameter that varies in different alloys. </LI> </UL> </P>