• Transactions of Materials Processing
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• v.13 no.8
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• pp.704-709
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• 2004

The effect of annealing temperature on microstructures and mechanical properties of the 5052 Al sheets rolled 88% reduction at cryogenic temperature was investigated for the annealing temperature of 150 ~ $300^{\circ}C$, in comparison with those rolled at room temperature. The presence of equiaxed grains, whose size is about 200nm in a diameter, was observed in the alloy deformed 88% and annealed $200^{\circ}C$ for an hour. When compared with the deformation at room temperature, the deformation at cryogenic temperature showed the higher strengths and equivalent elongation after annealing at the annealing temperature below $200^{\circ}C$. However, for annealing above $250^{\circ}C$ materials deformed at cryogenic temperature showed the lower strength than those deformed at room temperature. This behavior might be attributed to the higher rate of recrystallization and growth in materials deformed at cryogenic temperature during annealing, due to the lager density of dislocations accumulated during the deformation.

• Journal of Korea Foundry Society
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• v.26 no.4
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• pp.191-196
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• 2006

The effects of Bi and Te on the anti-galling behaviors of Ni base alloy were investigated by SEM, galling test and wear test. Anti-galling characteristics depended on the structure of matrix and distribution of Bi-rich phase which was precipitated at grain boundary. The addition of 5 wt% Bi markably enhanced anti-galling properties. The addition of Te caused Bi-rich precipitates to disperse finely and casting structure to form equiaxed type. From the above tests, the concentration of 5 wt% Bi and 1 wt% Te was selected to optimize in this alloy.

• Journal of the Korean institute of surface engineering
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• v.34 no.4
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• pp.303-312
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• 2001

Composition and microstructure of the tin-zinc alloys electroplated in gluconate bath were studied according to pulse current parameters. The cathode current efficiency increased with both the mean current density and the off-time decrease. Zinc content of the alloy deposits increased with increasing mean current density, while it decreased noticebly with increasing the off-time from 10-30ms to 100-150ms. The preferred orientation of the alloy deposits changed with the increase of peak current density in the sequence of (220)longrightarrow(220)+(420) or (220)+(420)+(321) mixed structure. The equiaxed grain size of the alloy increased with the increase of off-time and the decrease of mean current density.

• Korean Journal of Materials Research
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• v.22 no.8
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• pp.403-408
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• 2012

A sample of ultra low carbon IF steel was processed by six-layer stack accumulative roll-bonding (ARB) and annealed. The ARB was conducted at ambient temperature after deforming the as-received material to a thickness of 0.5 mm by 50% cold rolling. The ARB was performed for a six-layer stacked, i.e. a 3 mm thick sheet, up to 3 cycles (an equivalent strain of ~7.0). In each ARB cycle, the stacked sheets were, first, deformed to 1.5 mm thickness by 50% rolling and then reduced to 0.5 mm thickness, as the starting thickness, by multi-pass rolling without lubrication. The specimen after 3 cycles was then annealed for 0.5 h at various temperatures ranging from 673 to 973 K. The microstructural evolution with the annealing temperature for the 3-cycle ARB processed IF steel was investigated in detail by transmission electron microscopy observation. The ARB processed IF steel exhibited mainly a dislocation cell lamella structure with relatively high dislocation density in which the subgrains were partially observed. The selected area diffraction (SAD) patterns suggested that the misorientation between neighboring cells or subgrains was very small. The thickness of the grains increased in a gradual way up to 873 K, but above 898 K it increased drastically. As a result, the grains came to have an equiaxed morphology at 898 K, in which the width and the thickness of the grains were almost identical. The grain growth occurred actively at temperatures above 923 K.

• Korean Journal of Materials Research
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• v.8 no.4
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• pp.368-374
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• 1998

The corrosion characteristics of zirconium alloys have been investigated in various aqueous solutions of LiOH. NaOH, KOH, RbOH. and CsOH at 3S$0^{\circ}C$. The concentrations of solutions were set to 4.3 mmol and 32.Smmol with equimolar $M^+$ and OH . The oxide characterization was performed using TEM on the samples corroded in 32. Smmol LiOH, NaOH, and KOH solution. The samples were prepared to have the same oxide thickness for the pretransition and post- transition regimes. Considering the trend of experimental data, the cation would playa major role in the corrosion process of Zr alloys in alkali hydroxide solutions. The microstructures of the oxides formed in various solutions were quite different. In LiOH solution the oxides grown in pre-transition as well as post-transition had the equiaxed structures with many pores and open grain boundaries. The oxides grown in NaOH solution had the protective columnar structures in pre-transition and the equiaxed structures with many open grain boundaries in post- transition. On the other hand. in KOH solution the columnar structure was maintained from pre- transition to post- transition. It was considered that the cation incorporation into zirconium oxide controlled the oxide characteristics and the corrosion acceleration in alkali hydroxide solutions.

• Composites Research
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• v.18 no.3
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• pp.21-30
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• 2005

Vacuum hot pressing has been used for the development of titanium metal matrix composites using foil-fiber-foil method. Heterogeneous microstructures prior to and following consolidation have been quantified, and the relations to densification behavior investigated. As shown by the results, dramatic variations of the microstructures including equiaxed $\alpha$, transformed $\beta$ and $ Widmanst\ddot{a}tten$ $\alpha$ are obtained during the process according to the fiber distributions. The dependence of microstructures on the consolidation then has been explained in terms of the change in mechanisms such as grain growth and recrystallization that occur with changing levels of inhomogeneity of deformation. Further, micro-mechanics based constitutive model enabling the evolution of density over time together with the evolutions of microstructure to be predicted has been developed. The mode developed is then implemented into finite element scheme so that practical process simulation has been carried out.

• Korean Journal of Materials Research
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• v.4 no.7
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• pp.828-836
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• 1994

In order to investigate the high temperature deformation characteristics in YBaiCu307-, oxide superconductor, the compression test was performed at temperatures from $890^{\circ}C$ to $930^{\circ}C$ at initial strain rate between $1.0 x 10^{-5}s^{-1}\; and \; 1.0^{-4}s^{-1}$. As the temperature increased and the initial strain rate decreased, the flow stress decreased. The strain rate sensitivity exponent measured as 0.41-0.46, supporting occurence of a superplastic deformation. The activation energy for superplastic deformation was calculated as 500-580KJ/mol, which decreased with increasing Ag content. Microstructure of the superplastically-deformed specimens showed that a grain growth occurred during deformation, and it appeared to be considerable when Ag content increased, but most grains still remained equiaxed after deformation. In this study, the deformation mechanism of YBCO superconductor was the grain boundary sliding with the diffusional accommodation and the contribution of the gram boundary sliding to the total strain was estimated to be 65%.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.4
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• pp.492-500
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• 2019

Equal channel angular pressing(ECAP) is a severe plastic deformation technique capable of introducing large shear strain in bulk metal materials. However, if an ECAPed material has an inhomogeneous microstructure and anisotropic mechanical properties, this material is difficult to apply as structural components subjected to multi-axial stress during use. In this study, extruded oxygen-free copper(OFC) rods with a large diameter of 42 mm are extruded through ECAP by route Bc up to 12 passes. The variations in the microstructure, hardness, tensile properties, and microstructural and mechanical homogeneity of the ECAPed samples are systematically analyzed. High-strength OFC rods with a homogeneous and equiaxed-ultrafine grain structure are obtained by the repeated application of ECAP up to 8 and 12 passes. ECAPed samples with 4 and 8 passes exhibit much smaller differences in terms of the average grain sizes on the cross-sectional area and the tensile strengths along the axial and circumferential directions, as compared to the samples with 1 and 2 passes. Therefore, it is considered that the OFC materials, which are fabricated via the ECAP process with pass numbers of a multiple of 4, are suitable to be applied as high-strength structural parts used under multi-axial stress conditions.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.1
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• pp.124-133
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• 2003

Ti-25Al-xNb (x=0, 3, 7, 11, 13 at. %) alloys and 18 vol. % TiB/(Ti-25Al-11Nb) metal matrix composite were fabricated by spark plasma sintering process at 900-120$0^{\circ}C$. Microstructural characteristics of the sintered bodies were identified by SEM, EDX analysis, X-ray diffraction, and differential scanning calorimeterric method. $Ti_3Al$ alloy was consisted of equiaxed $\alpha_2$ phase. $Ti_3Al-Nb$ alloys and the matix of TiB/(Ti-25Al-11Nb) metal matrix composite had the morphology that O phase was precipitated at the grain boundary of $\alpha_2$phase. Volume fraction of O phase and hardness were depended on the concentration of Nb in $Ti_3Al-Nb$ alloy, Rule of mixing could be applied to hardness and Young's modulus of 18 vol. % TiB/(Ti-25Al-11Nb) metal matrix composite.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.2
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• pp.101-105
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• 2004

After extrusion, cold rolling and T-6 treatment, texture development of 7x1x Al-alloy with 0.1% Sc is studied. During extrusion the very strong <111>+weak <100> fiber texture is developed, which is Influenced on the formation of rolling texture. The texture after 80% cold rolling can be described by strong{112}<111>(Cu)+{123}<634>(S) component in the cross section of the extruded rod, the strong -fiber+weak{110}<001>(Goss) components in the longitudinal section, and the strong {110}<112>(Bs)+weak{001}<100>(Cube) components in the transverse section. The components of rolling texture are remained after T-6 treatment, but the maximum density of ODF is higher. The calculated mean r-values and the planar anisotropy are relatively high, which are dependent on the texture. After T-6 treatment, recrystallized equiaxed grains with average grain size of $1{\sim}2{\mu}m$ are obtained.