• Journal of Powder Materials
• /
• v.11 no.1
• /
• pp.69-73
• /
• 2004

The sintering characteristics of commercial 7xxx series Al-Zn-Mg-Cu alloy have been investigated. Sintering system of this blended elemental powder has aspects of both transient and supersolidus liquid phase sintering. Transient liquids occur when the constitution point during sintering lies in a solid phase region but where the sintering temperature is greater than either the melting point of one of the constituent or a eutectic temperature. Supersolidus liquid phase sintering occurs when a preblended powder is heated to a temperature between the solidus and liquids. However, these reaction were restrained their inter diffusion due to the appearance of the oxide film. Thus, 7xxx series Al alloy is extremely sensitive to process variables, including particle size, holding time and sintering temperature. Therefore, above phenomenons were observed formation and behaviour of the liquid by using SEM and DSC.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.327-330
• /
• 2001

Phase intergrowth in BSCCO thin films have been investigated. It turned out from XRD analyses of these phases that molar fraction of each constituent phase in the intergrowth thin film can be exhibited as a function of substrate temperature and ozone pressure. Superconducting behavior of the intergrowth thin film is also discussed.

• Journal of the Korean Society for Heat Treatment
• /
• v.16 no.2
• /
• pp.78-82
• /
• 2003

Nitrided compound layer and diffusion layer structure were observed by SEM. The compound layer and the constituent of nitrided surface of STS 304, STS 316, STS 410 and SACM 645 steel were analysed using EMPA and XRD respectively. The depth of nitriding layer that is obtained from similar nitriding condition decrease in the order of SACM 645 > STS 410 > STS 316 > STS 304. Result of phase transformation of the nitrided at $550^{\circ}C$ by XRD analysis were as follows; The austenitic stainless steel was mainly consist of $Cr_2N$ accompanying with $Fe_4N$ and $Fe_{2-3}N$ phase and martensitic stainless steel was mainly consist of present $Fe_{2-3}N+Cr_2N$ phase, but SACM 645 steel was $Fe_{2-3}N$ phase present only.

• Smart Structures and Systems
• /
• v.25 no.6
• /
• pp.707-717
• /
• 2020

In this paper, analysis of thermal post-buckling behaviors of sandwich nanobeams with two layers of multi-phase magneto-electro-thermo-elastic (METE) composites have been presented considering geometric imperfection effects. Multi-phase METE material is composed form piezoelectric and piezo-magnetic constituents for which the material properties can be controlled based on the percentages of the constituents. Nonlinear governing equations of sandwich nanobeam are derived based on nonlocal elasticity theory together with classic thin beam model and an analytical solution is provided. It will be shown that post-buckling behaviors of sandwich nanobeam in thermo-electro-magnetic field depend on the constituent's percentages. Buckling temperature of sandwich nanobeam is also affected by nonlocal scale factor, magnetic field intensity and electrical voltage.

• Coupled systems mechanics
• /
• v.6 no.1
• /
• pp.29-40
• /
• 2017

This work employed density functional theory to investigate the structural and ferroelectric properties of the Ruddlesden-Popper (RP) phase of lead titanate, $Pb_2TiO_4$, as well as its phase transitions with epitaxial strain. A wealth of novel structural instabilities, which are absent in the host $PbTiO_3$ material, were identified in the RP phase through phonon soft-mode analysis. Our calculations showed that the ground state of $Pb_2TiO_4$ is antiferroelectric, distinct from the dominant ferroelectric phase in the corresponding host material. In addition, applied epitaxial strain was found to play a key role in the interactions among the instabilities. The induction of a sequence of antiferroelectric and antiferrodistortive (AFD) phase transitions by epitaxial strain was demonstrated, in which the ferroic instability and AFD distortion were cooperative rather than competitive, as is the case in the host $PbTiO_3$. The RP phase in conjunction with strain engineering thus represents a new approach to creating ferroic orders and modifying the interplay among structural instabilities in the same constituent materials, enabling us to tailor the functionality of perovskite oxides for novel device applications.

• Korean Journal of Materials Research
• /
• v.27 no.1
• /
• pp.8-11
• /
• 2017

Binary Ti-Al alloys containing 50 to 60 atomic percent aluminum are rapidly solidified by hammer anvil method under an argon atmosphere. Constituent phases in each alloy are identified by X-ray diffractometry and microstructures of the alloys are investigated using a transmission electron microscope. In alloys with aluminum content between 50 and 54 percent, a second phase exists besides TiAl(${\gamma}$); this second phase is identified as $Ti_3Al$(${\alpha}2$). The ${\alpha}2$ phase is observed in two types of morphology. One is as fine lamellar alternating with ${\gamma}$ and the other is as a particle. It is concluded that the existence of a metastable phase with the morphologies stated above should arise from a higher quenching rate attained by the hammer anvil method as compared to the conventional roll or splat-quench method. Implications of the above observation are discussed with respect to the phase relations in the Ti-Al binary system; these implications are still controversial in many respects.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.334-336
• /
• 2009

An elastic-plasticity model during the austenitic decomposition was derived and implemented to incorporate the two important deformation behaviors observed during the phase transformations: the volumetric strain and transformation induced plasticity due to the temperature change and phase transformation. To obtain transformed phase volume fractions during cooling, the fourth order Runge-Kutta method was used to solve the Kirkaldy's phase kinetics model which is function of temperature, austenitic grain size and chemical composition. The volumetric strain was calculated by considering the densities of constituent phases, while the transformation induced plasticity was based on the micro-plasticity due to the volume mismatch between soft austenitic phase and other harder phases. The constitutive equations were implemented into the implicit finite element software and a simple boundary value problem was chosen as a model problem to validate the effect of transformation plasticity on the deformation behavior of steel under cooling from high temperature. It was preliminary concluded that the transformation plasticity plays a critical role in relaxing the developed stress during forming and thus reducing the magnitude of springback.

• Progress in Superconductivity
• /
• v.1 no.1
• /
• pp.56-60
• /
• 1999

Ultra fine MgO particles added BSCCO tapes were fabricated by tape casting using Doctor Blade Method and enclosed by silver foil for different starting compositions (that is, 2223 major, 2212 major). In order to obtain optimum microstructure, thermomechanical treatment was done. Microstructure and phase were analyzed by XRD, SEM and DTA. The critical current density was measured under magnetic field at 77K. The tapes fabricated from the precursor powder with BSCCO-2223 phase (>90%) result in a microstructure with a larger grain size and higher transport critical current density value under magnetic field at given thermomechanical treatment conditions.

• Journal of Powder Materials
• /
• v.2 no.1
• /
• pp.53-62
• /
• 1995

TLP(Transient-Liquid-Phase) bonding of Fe-base MA956 ODS alloy was performed. As insert metal a commercially available Ni-base alloy(MBF50) and an MA956 alloy with additive elements of 7wt% Si and 1wt% B were used. To confirm the idea that a concurrent use of MA956 powder with Insert metals can enhance the homogenization of constituent elements and thereby reduce the thickness of joint interface, MA956 powder was also inserted In a form of sheet. SEM observation and EDS analysis revealed that Cr-rich phase was formed in the bonded interface in initial stage of isothermal solidification during the bonding process, irrespective of kind of insert metals. Measurement of hardeness in the region of bonded interface and EDS analysis showed that a complete homogenization of composition could not be obtained especially in case of MBF50. Joints using either BSi insert metals only or BSi insert together with MA956 powder interlayer showed, however, a remarkable improvement in a compositional homogenization, even though a rapid grain growth in the bonded interface could not be hindered.

• Bulletin of the Korean Chemical Society
• /
• v.11 no.2
• /
• pp.118-123
• /
• 1990

X-ray photoelectron spectra have been obtained and comparisons have been made for 1-2-3 and 2-1-1 phases of YBaCuO compounds. The photoelectron binding energies of all the constituent elements are consistently larger for the 2-1-1 phase than for the 1-2-3 phase. The peak intensities reflect different stoichiometries of the two phases. For the superconducting 1-2-3 phase, its degradation in air and interaction with water and carbon dioxide were examined by taking core level spectra of all the elements. It appears that yttrium is the most affected by exposure to air, since it undergoes a rapid change to carbonate when water and subsequently carbon dioxide are introduced.