• Title/Summary/Keyword: metallic phase

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On the distribution of temperature and metallic structures in quenching process considering latent heat of phase transformation (변태잠열을 고려한 담금시편의 온도 및 조직분포에 대하여)

  • 민수홍;구본권
    • Journal of the korean Society of Automotive Engineers
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    • v.6 no.4
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    • pp.46-53
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    • 1984
  • The analysis of temperature distribution and change of metallic structures during water quench were presented by finite element method. In temperature calculation the equation of unsteady state hear conduction problem considering latent heat due to phase transformation was applied to finite solid cylinder, SM 45C of 40mm diameter and 40mm height. In metallic structure analysis iso-thermal transformation curve and the equations of evolution in pearlite-martensite transformation were applied. The calculated results upon temperature and metallic structures were agreed with those of experimental observations.

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Nanoscopic Understanding of Phase Transition of Epitaxial VO2 Thin Films (에피택셜 VO2 박막의 상전이에 대한 미시적 이해)

  • Kim, Dong-Wook;Sohn, Ahrum
    • Journal of the Korean institute of surface engineering
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    • v.50 no.3
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    • pp.141-146
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    • 2017
  • We investigated configuration of metallic and insulating domains in $VO_2$ thin films, while spanning metal-insulator phase transition. Kelvin probe force microscopy, of which spatial resolution is less than 100 nm, enables us to measure local work function (WF) at the sample surface. The WF of $VO_2$ thin films decreased (increased) as increasing (decreasing) the sample temperature, during the phase transition. The higher and lower WF regions corresponded to the insulating and metallic domains, respectively. The metallic fraction, estimated from the WF maps, well explained the temperature-dependent resistivity based on the percolation model. The WF mapping also showed us how the structural defects affected the phase transition behaviors.

Micro-deformation behavior of Brittle Hf-based Metallic Glass during Mechanical Milling (기계적 합금화 공정에 의한 Hf계 비정질 분말의 미세변형거동 관찰)

  • Kim, Song-Yi;Lee, A-Young;Cha, Eun-Ji;Kwon, Do-Hun;Hong, Sung-Uk;Lee, Min-Woo;Kim, Hwi-Jun;Lee, Min-Ha
    • Journal of Powder Materials
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    • v.25 no.3
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    • pp.246-250
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    • 2018
  • In this study, we investigate the deformation behavior of $Hf_{44.5}Cu_{27}Ni_{13.5}Nb_5Al_{10}$ metallic glass powder under repeated compressive strain during mechanical milling. High-density (11.0 g/cc) Hf-based metallic glass powders are prepared using a gas atomization process. The relationship between the mechanical alloying time and microstructural change under phase transformation is evaluated for crystallization of the amorphous phase. Planetary mechanical milling is performed for 0, 40, or 90 h at 100 rpm. The amorphous structure of the Hf-based metallic glass powders during mechanical milling is analyzed using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Microstructural analysis of the Hf-based metallic glass powder deformed using mechanical milling reveals a layered structure with vein patterns at the fracture surface, which is observed in the fracture of bulk metallic glasses. We also study the crystallization behavior and the phase and microstructure transformations under isothermal heat treatment of the Hf-based metallic glass.

Time-Resolved Photoexcitation Dynamics of Electrical Conductivity of Magnetic Organic Superconductor λ-(BETS)2Fe0.45Ga0.55Cl4

  • Sabeth, Farzana;Islam, Md. Serajul;Endo, Tadashi;Ohta, Nobuhiro
    • Rapid Communication in Photoscience
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    • v.4 no.1
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    • pp.25-28
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    • 2015
  • The time-resolved photoexcitation dynamics of electrical conductivity of the magnetic organic superconductor ${\lambda}-(BETS)_2Fe_{0.45}Ga_{0.55}Cl_4$ has been studied with a nanosecond visible laser pulse at its three different phases, i. e., metallic phase, superconducting phase and insulating phase. A transient increase of the resistance is induced by photoirradiation at all the temperatures measured for all three phases, but the decay profile shows a significant temperature dependence. The relaxation rate in the metallic and insulating phase are different from each other, and the decay time is relatively faster and almost constant in the metallic phase. However, a prolongation of the relaxation time is observed at temperature just around the narrow superconducting phase. Nonbolometric (nonthermal) origin of the observed photoresponse of the electrical conductivity is confirmed in the superconducting phase.

Fabrication of Metallic Glass/metallic Glass Composites by Spark Plasma Sintering (방전플라즈마 소결법에 의한 비정질/비정질 복합재의 제조)

  • Lee, Jin-Kyu
    • Journal of Powder Materials
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    • v.14 no.6
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    • pp.405-409
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    • 2007
  • The Cu-based bulk metallic glass (BMG) composites containing Zr-based metallic glass phase have been consolidated by spark plasma sintering using the mixture of Cu-based and Zr-based metallic glass powders in their overlapped supercooled liquid region. The Zr-based metallic glass phases are well distributed homogeneously in the Cu-based metallic glass matrix after consolidation process. The successful consolidation of BMG composites with dual amorphous phases was corresponding to the sound viscous flow of the two kinds of metallic glass powders in their overlapped supercooled liquid region.

Fabrication and Mechanical Properties of Nanoquasicrystalline Phase Reinforced Ti-based Bulk Metallic Glass Matrix Composites (나노 준결정상으로 강화된 Ti계 벌크 비정질기지 복합재의 제조 및 기계적 특성 고찰)

  • Park, Jin-Man;Lim, Ka-Ram;Kim, Tae-Eung;Sohn, Sung-Woo;Kim, Do-Hyang
    • Journal of Korea Foundry Society
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    • v.28 no.6
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    • pp.261-267
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    • 2008
  • In-situ quasicrystalline icosahedral (I) phase reinforced Ti-based bulk metallic glass (BMG) matrix composites have been successfully fabricated by using two distinct thermal histories for BMG forming alloy. The BMG composite containing micron-scale Iphase has been introduced by controlling cooling rate during solidification, whereas nano-scale I-phase reinforced BMG composite has been produced by partial crystallization of BMG. For mechanical properties, micron-scale I-phase distributed BMG composite exhibited lower strength and plasticity compared to the monolithic BMG. On the other hand, nano-scale icosahedral phase embedded BMG composite showed enhanced strength and plasticity. These improved mechanical properties were attributed to the multiplication of shear bands and blocking of the shear band propagation in terms of isolation and homogeneous distribution of nanosize icosahdral phases in the glassy matrix, followed by stabilizing the mechanical and deformation instabilities.

Synthesis of Ni-based Bulk Metallic Glass Composites (Ni계 벌크 비정질 복합재의 제조)

  • Lee, Jin-Kyu
    • Journal of Powder Materials
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    • v.15 no.4
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    • pp.297-301
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    • 2008
  • The Ni-based bulk metallic glass matrix composites were fabricated by spark plasma sintering of mixture of gas-atomized metallic glass powders and ductile brass powders. The successful consolidation of metallic glass matrix composite was achieved by strong bonding between metallic glass powders due to viscous flow deformation and lower stress of ductile brass powders in the supercooled liquid state during spark plasma sintering. The composite shows some macroscopic plasticity after yielding, which was obtained by introducing a ductile second brass phase in the Ni-based metallic glass matrix.

Phase Transformation and Work-hardening Behavior of Ti-based Bulk Metallic Glass Composite

  • Hong, Sung Hwan;Kim, Jeong Tae;Park, Hae Jin;Kim, Young Seok;Park, Jin Man;Suh, Jin Yoo;Na, Young Sang;Lim, Ka Ram;Kim, Ki Buem
    • Applied Microscopy
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    • v.45 no.2
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    • pp.37-43
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    • 2015
  • In present work, work-hardening behavior of TiCu-based bulk metallic glass composite with B2 particles has been studied by systemic structural and mechanical investigations. After yield, pronounced work-hardening of the alloy was clearly exhibited, which was mainly related to the martensitic transformation as well as the deformation twinning in B2 particles during deformation. At the early plastic deformation stage (work-hardening stage), the stress-induced martensitic transformation from B2 phase to B19' phase and deformation-induced twinning of B19' phase was preferentially occurred in the around interface areas between B2 phase and amorphous matrix by stress concentration. The higher hardness value was observed in vicinity of interface within the B2 particles which are probably connected with martensitic transformation and deformation twinning. This reveals that the work-hardening phenomenon of this bulk metallic glass composite is a result of the hardening of B2 particles embedded in amorphous matrix.

Modelling Strength and Ductility of Nanocrystalline Metallic Materials

  • Kim, Hyoung-Seop
    • Journal of Powder Materials
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    • v.8 no.3
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    • pp.168-173
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    • 2001
  • The effect of grain refinement of the strength and ductility of metallic materials is investigated. A model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanisms: dislocation glide and mass transfer by diffusion. The model was exemplified by simulating uniaxial tensile deformation of Cu down to the nanometer grain size. The results confirm the observed strain hardening behaviour and a trend for reduction of ductility with decreasing grain size at room temperature.

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Crystallization behavior of Cu-base bulk metallic glass in supercooled liquid region during compression and tension (과냉각 액상구간에서 압축.인장시 Cu기 비정질 합금의 결정화 거동)

  • Park, E.S.;Kim, S.H.;Huh, M.Y.;Kim, H.W.;Bae, J.C.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.10a
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    • pp.215-217
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    • 2008
  • Crystallization behavior of the bulk metallic glass (BMG) during compression and tension was studied in the supercooled liquid region (SLR). Rod samples of the BMG alloy were produced by consolidating gas atomized powders of $Cu_{54}Zr_{22}Ti_{18}Ni_6$ using spark plasma sintering. The crystallization behavior in these samples was examined by tackling changes in thermal property during heating the samples in DSC. The present BMG alloy was firstly decomposed and then crystallized during annealing in the SLR. The phase decomposition from the original amorphous phase was retarded by the compressive stress, while it was accelerated by the tensile stress.

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