간행물
한국재료학회지 KCI 등재 SCOPUS Korean Journal of Materials Research
- 발행기관 한국재료학회
- 자료유형 학술지
- 간기 월간
- ISSN 2799-8525 (Print)2799-8681 (Online)
- 수록기간 1991 ~ 2024
- 주제분류 공학 > 재료공학 공학 분류의 다른 간행물
- 십진분류KDC 530DDC 620
권호리스트/논문검색
제22권 제1호 (2012년 1월) 9건
1.
2012.01
구독 인증기관 무료, 개인회원 유료
Thin film electrode consisting purely of porous anodic tin oxide with well-defined nano-channeled structure was fabricated for the first time and its electrochemical properties were investigated for application to an anode in a rechargeable lithium battery. To prepare the thin film electrode, first, a bi-layer of porous anodic tin oxides with well-defined nano-channels and discrete nano-channels with lots of lateral micro-cracks was prepared by pulsed and continuous anodization processes, respectively. Subsequent to the Cu coating on the layer, well-defined nano-channeled tin oxide was mechanically separated from the specimen, leading to an electrode comprised of porous tin oxide and a Cu current collector. The porous tin oxide nearly maintained its initial nano-structured character in spite of there being a series of fabrication steps. The resulting tin oxide film electrode reacted reversibly with lithium as an anode in a rechargeable lithium battery. Moreover, the tin oxide showed far more enhanced cycling stability than that of powders obtained from anodic tin oxides, strongly indicating that this thin film electrode is mechanically more stable against cycling-induced internal stress. In spite of the enhanced cycling stability, however, the reduction in the initial irreversible capacity and additional improvement of cycling stability are still needed to allow for practical use.
4,000원
2.
2012.01
구독 인증기관 무료, 개인회원 유료
Silicon-based thin film was prepared at room temperature by an electrochemical deposition method and a feasibility study was conducted for its use as an anode material in a rechargeable lithium battery. The growth of the electrodeposits was mainly concentrated on the surface defects of the Cu substrate while that growth was trivial on the defect-free surface region. Intentional formation of random defects on the substrate by chemical etching led to uniform formation of deposits throughout the surface. The morphology of the electrodeposits reflected first the roughened surface of the substrate, but it became flattened as the deposition time increased, due primarily to the concentration of reduction current on the convex region of the deposits. The electrodeposits proved to be amorphous and to contain chlorine and carbon, together with silicon, indicating that the electrolyte is captured in the deposits during the fabrication process. The silicon in the deposits readily reacted with lithium, but thick deposits resulted in significant reaction overvoltage. The charge efficiency of oxidation (lithiation) to reduction (delithiation) was higher in the relatively thick deposit. This abnormal behavior needs to clarified in view of the thickness dependence of the internal residual stress and the relaxation tendency of the reaction-induced stress due to the porous structure of the deposits and the deposit components other than silicon.
4,000원
3.
2012.01
구독 인증기관 무료, 개인회원 유료
Research into the development of high strength (1 GPa) and superior formability, such as total elongation (10%), and stretch-flangeability (50%) in hot-rolled steel was conducted with a thermomechanically controlled hot-rolling process. To improve the overall mechanical properties simultaneously, low-carbon steel using precipitation hardening of Ti-Nb-V multimicroalloying elements was employed. And, ideal microstructural characteristics for the realization of balanced mechanical properties were determined using SEM, EBSD, and TEM analyses. The developed steel, 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V), consisted of ferrite as the matrix phase and second phase of granular bainite with fine carbides (20-50 nm) in both phases. The significant factor of the microstructural characteristics that affect stretch-flangeability was found to be the microstructural homogeneity. The microstructural homogeneity, manifest in such characteristics as low localization of plastic strain and internally stored energy, was identified by grain average misorientation method, analyzed by electron backscattered diffraction (EBSD) and hardness deviation between the phases. In summar, a hot-rolled steel having a composition 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V) demonstrated a tensile strength of 998 MPa, a total elongation of 19%, and a hole expansion ratio of 65%. The most important factors to satisfy the mechanical property were the presence of fine carbides and the microstructural homogeneity, which provided low hardness deviation between the phases.
4,000원
4.
2012.01
구독 인증기관 무료, 개인회원 유료
In2O3 films were deposited by RF magnetron sputtering on a glass substrate and then the effect of post depositionannealing in nitrogen atmosphere on the structural, optical and electrical properties of the films was investigated. Afterdeposition, the annealing process was conducted for 30 minutes at 200 and 400oC. XRD pattern analysis showed that the asdeposited films were amorphous. When the annealing temperature reached 200-400oC, the intensities of the In2O3 (222) majorpeak increased and the full width at half maximum (FWHM) of the In2O3 (222) peak decreased due to the crystallization. Thefilms annealed at 400oC showed a grain size of 28nm, which was larger than that of the as deposited amorphous films. Theoptical transmittance in the visible wavelength region also increased, while the electrical sheet resistance decreased. In this study,the films annealed at 400oC showed the highest optical transmittance of 76% and also showed the lowest sheet resistance of89Ω/□. The figure of merit reached a maximum of 7.2×10−4Ω−1 for the films annealed at 400oC. The effect of the annealingon the work-function of In2O3 films was considered. The work-function obtained from annealed films at 400oC was 7.0eV. Thus,the annealed In2O3 films are an alternative to ITO films for use as transparent anodes in OLEDs.
4,000원
5.
2012.01
구독 인증기관 무료, 개인회원 유료
The hydrogen embrittlement of high strength steel for automobiles was evaluated by small punch (SP) test. The test specimens were fabricated to be 5 series, having various chemical compositions according to the processes of heat treatment and working. Hydrogen charging was electrochemically conducted for each specimen with varying of current density and charging time. It was shown that the SP energy and the maximum load decreased with increasing hydrogen charging time in every specimen. SEM investigation results for the hydrogen containing samples showed that the fracture behavior was a mixed fracture mode having 50% dimples and 50% cleavages. However, the fracture mode of specimens with charging hydrogen changed gradually to the brittle fracture mode, compared to the mode of other materials. All sizes and numbers of dimples decreased with increasing hydrogen charging time. These results indicate that hydrogen embrittlement is the major cause of fracture for high strength steels for automobiles; also, it is shown that the small punch test is a valuable test method for hydrogen embrittlement of high strength sheet steels for automobiles.
4,000원
6.
2012.01
구독 인증기관 무료, 개인회원 유료
Presently, the most promising family of lead-free piezoelectric ceramics is based on K0.5Na0.5NbO3(KNN). Lithium, silver and antimony co-doped KNN ceramics show high piezoelectric properties at room temperature, but often suffer from abnormal grain growth. In the present work, the (Ba0.85Ca0.15)(Ti0.88Zr0.12)O3 component, which has relaxor ferroelectric characteristics, was doped to suppress the abnormal grain growth. To investigate this effect, Lead-Free 0.95(K0.5Na0.5)0.95Li0.05NbO3-(0.05-x)AgSbO3-x(Ba0.85Ca0.15)(Ti0.88Zr0.12)O3[KNLN-AS-xBCTZ] piezoelectric ceramics were synthesized by ball mill and nanosized-milling processes in lead-Free 0.95(K0.5Na0.5)0.95Li0.05NbO3-(0.05-x)AgSbO3 in order to suppress the abnormal grain growth. The nanosized milling process of calcined powders enhanced the sintering density. The phase structure, microstructure, and ferroelectric and piezoelectric properties of the KNLN-AS ceramics were systematically investigated. XRD patterns for the doped and undoped samples showed perovskite phase while tetragonality was increased with increasing BCZT content, which increase was closely related to the decrease of TO-T. Dense and uniform microstructures were observed for all of the doped BCZT ceramics. After the addition of BCTZ, the tetragonal-cubic and orthorhombic-tetragonal phase transitions shifted to lower temperatures compared to those for the pure KNNL-AS. A coexistence of the orthorhombic and tetragonal phases was hence formed in the ceramics with x = 0.02 mol at room temperature, leading to a significant enhancement of the piezoelectric properties. For the composition with x = 0.02 mol, the piezoelectric properties showed optimum values of: d33 = 185 pC/N, kp = 41%, Tc=325˚C, TO-T=-4˚C.
4,000원
7.
2012.01
구독 인증기관 무료, 개인회원 유료
The mechanical behavior and microstructural evolution during high temperature tensile deformation of recrystallizedNi3Al polycrystals doped with boron were investigated as functions of initial grain size, tensile strain rate and temperature. Inorder to obtain more precise information on the deformation mechanism, tensile specimens were rapidly quenched immediatelyafter deformation at a cooling rate of more than 2000Ks−1, and were then observed by transmission electron microscopy (TEM).Mechanical tests in the range of 923K to 1012K were carried out in a vacuum of less than 3×10−4 Pa using an Instron-typemachine with various but constant cross head speeds corresponding to the initial strain rates from 1.0×10−4 to 3.1×10−5s−1.After heating to deformation temperature, the specimen was kept for more than 1.8ks before testing. The following results wereobtained: (1) Flow behavior was affected by initial strain size; with decreasing initial grain size, the level of a stress peak inthe true stress-true strain curve decreased, the steady state region was enlarged and elongation increased. (2) On the basis ofTEM observation of rapidly quenched specimens, it was confirmed that dynamic recrystallization certainly occurred ondeformation of fine-grained (3.3µm) and intermediate-grained (5.0µm) specimens at an initial strain rate of 3.1×10−5s−1 andat 973K. (3) There were some dislocation-free grains among the new recrystallized grains. The obtained results suggest thatboth dynamic recrystallization and grain boundary sliding are operative during high temperature deformation.
3,000원
8.
2012.01
구독 인증기관 무료, 개인회원 유료
In this study, mechanical tests and microstructural analyses including TEM analyses with EDX of precipitates in modified 9Cr-1Mo steel were carried out to determine the cause of embrittlement observed after heat-treatment, which limits the usage of the alloy for power plants. Mod. 9Cr-1Mo steel specimens at austenite temperature were quenched to the molten salt baths at 760˚C and 700˚C, in which the specimens were kept for 10 min ~ 10 hr with subsequent air-cooling. Impact tests showed that the impact value dropped abruptly when the specimens were kept longer than 30 min at ~760˚C reaching to minima in about 1 hr, and then increasing at further retention. The tensile strength of the specimens reached the minimum value without much change afterward, whereas the values of elongation showed the same trend as that of the impact value. The isothermally heat-treated steel at 700˚C also showed a minimum impact value in about 1 hr. These results suggest that the isothermal heattreatment at 760 and 700˚C for about 1 hr induces temporal embrittlement in Mod. 9Cr-1Mo steel. The microstructural examination of all the specimens with extraction replica of the carbides revealed that the specimens with temporal embrittlement had Cr2C, indicating that the cause of the embrittlement was the precipitation of the Cr2C. In addition, TEM/EDX results showed that the Fe/Cr ratio was 0.033 to 0.055 for Cr2C, whereas it was 0.48 to 0.75 for Cr23C6, making the distinction of the Cr2C and Cr23C6 possible even without direct electron diffraction analyses.
4,000원
9.
2012.01
구독 인증기관 무료, 개인회원 유료
The particle size of MgO was examined as a function of the Na content in Mg(OH)2 powders and the calcination temperature. Mg(OH)2 suspension was obtained by dropwise precipitation of Mg(NO3)2·6H2O and NaOH solutions. The suspension was diluted by varying the dilution volume ratio of distilled water to Mg(OH)2 suspension to change the Na salt concentration in the suspension. Mg(OH)2 slurry was filtered and dried at 60˚C under vacuum, and then its Mg(OH)2 powder was calcined to produce MgO with different amount of Na content at 500~900˚C under air. Investigation of the physical and chemical properties of the various MgO powders with dilution ratio and calcination temperature variation was done by X-ray diffraction, transmission electron microscopy, BET specific surface area and thermal gravimetric analysis. It was observed that MgO particle size could depend on the condition of calcination temperature and dilution ratio of the Mg(OH)2 suspension. The particle size of the MgO depends on the Na content remaining in the Mg(OH)2 powder, which powder was prepared by changing the dilution ratio of the Mg(OH)2 suspension. This change increased as the calcination temperature increased and decreased as the dilution ratio increased. The growth of MgO particle size according to the increase of temperature was more effective when there was a relatively high content of Na. The increase of Na content lowered the temperature at which decomposition of Mg(OH)2 to MgO took place, thereby promoting the crystal growth of MgO.
4,000원
