• Title/Summary/Keyword: microstructure

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Effects of Surface Treatment using Oxide-Dispersion-Strengthening on the Mechanical Properties of Zr-based Fuel Cladding Tubes (산화물 분산강화 표면처리에 따른 지르코늄 피복관의 기계적 강도)

  • Jung, Yang-Il;Kim, Il-Hyun;Kim, Hyun-Gil;Jang, Hun;Lee, Seung-Jae
    • Korean Journal of Materials Research
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    • v.29 no.4
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    • pp.271-276
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    • 2019
  • Oxide-dispersion-strengthened (ODS) alloy has been developed to increase the mechanical strength of metallic materials; such an improvement can be realized by distributing fine oxide particles within the material matrix. In this study, the ODS layer was formed in the surface region of Zr-based alloy tubes by laser beam treatment. Two kinds of Zr-based alloys with different alloying elements and microstructures were used: KNF-M (recrystallized) and HANA-6 (partial recrystallized). To form the ODS layer, $Y_2O_3$-coated tubes were scanned by a laser beam, which induced penetration of $Y_2O_3$ particles into the substrates. The thickness of the ODS layer varied from 20 to $55{\mu}m$ depending on the laser beam conditions. A heat affected zone developed below the ODS layer; its thickness was larger in the KNF-M alloy than in the HANA-6 alloy. The ring tensile strengths of the KNF-M and HANA-6 alloy samples increased more than two times and 20-50%, respectively. This procedure was effective to increase the strength while maintaining the ductility in the case of the HANA-6 alloy samples; however, an abrupt brittle facture was observed in the KNF-M alloy samples. It is considered that the initial microstructure of the materials affects the formation of ODS and the mechanical behavior.

Analysis of Attrition Rate of 50μm Size Y2O3 Stabilized Zirconia Beads with Different Microstructure and Test Conditions (50μm급 이트리아 안정화 지르코니아 비드의 미세구조 및 마모 조건에 따른 마모율 분석)

  • Kim, Jung-Hwan;Yoon, Sae-Jung;Hahn, Byung-Dong;Ahn, Cheol-Woo;Yoon, Woon-Ha;Choi, Jong-Jin
    • Korean Journal of Materials Research
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    • v.29 no.4
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    • pp.233-240
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    • 2019
  • This study analyzes the mechanical properties, including the attrition rate, of $50{\mu}m$ size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grain-boundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of $50{\mu}m$ YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than $BaTiO_3$ powder (Hv ~315).

Interfacial Properties of Friction-Welded TiAl and SCM440 Alloys with Cu as Insert Metal (삽입금속 Cu를 이용한 TiAl 합금과 SCM440의 마찰용접 계면 특성)

  • Park, Sung-Hyun;Kim, Ki-Young;Park, Jong-Moon;Choi, In-Chul;Ito, Kazuhiro;Oh, Myung-Hoon
    • Korean Journal of Materials Research
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    • v.29 no.4
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    • pp.258-263
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    • 2019
  • Since the directly bonded interface between TiAl alloy and SCM440 includes lots of cracks and generated intermetallic compounds(IMCs) such as TiC, FeTi, and $Fe_2Ti$, the interfacial strength can be significantly reduced. Therefore, in this study, Cu is selected as an insert metal to improve the lower tensile strength of the joint between TiAl alloy and SCM440 during friction welding. As a result, newly formed IMCs, such as $Cu_2TiAl$, CuTiAl, and $TiCu_2$, are found at the interface between TiAl alloy and Cu layer and the thickness of IMCs layers is found to vary with friction time. In addition, to determine the relationship between the thickness of the IMCs and the strength of the welded interfaces, a tensile test was performed using sub-size specimens obtained from the center to the peripheral region of the friction-welded interface. The results are discussed in terms of changes in the IMCs and the underlying deformation mechanism. Finally, it is found that the friction welding process needs to be idealized because IMCs generated between TiAl alloy and Cu act to not only increase the bonding strength but also form an easy path of fracture propagation.

Crack growth and cracking behavior of Alloy 600/182 and Alloy 690/152 welds in simulated PWR primary water

  • Lim, Yun Soo;Kim, Dong Jin;Kim, Sung Woo;Kim, Hong Pyo
    • Nuclear Engineering and Technology
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    • v.51 no.1
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    • pp.228-237
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    • 2019
  • The crack growth responses of as-received and as-welded Alloy 600/182 and Alloy 690/152 welds to constant loading were measured by a direct current potential drop method using compact tension specimens in primary water at $325^{\circ}C$ simulating the normal operating conditions of a nuclear power plant. The as-received Alloy 600 showed crack growth rates (CGRs) between $9.6{\times}10^{-9}mm/s$ and $3.8{\times}10^{-8}mm/s$, and the as-welded Alloy 182 had CGRs between $7.9{\times}10^{-8}mm/s$ and $7.5{\times}10^{-7}mm/s$ within the range of the applied loadings. These results indicate that Alloys 600 and 182 are susceptible to cracking. The average CGR of the as-welded Alloy 152 was found to be $2.8{\times}10^{-9}mm/s$. Therefore, Alloy 152 was proven to be highly resistant to cracking. The as-received Alloy 690 showed no crack growth even with an inhomogeneous banded microstructure. The cracking mode of Alloys 600 and 182 was an intergranular cracking; however, Alloy 152 was revealed to have a mixed (intergranular + transgranular) cracking mode. It appears that the Cr concentration and the microstructural features significantly affect the cracking resistance and the cracking behavior of Ni-base alloys in PWR primary water.

A Study on the Mechanical Properties and Moisture Control Performance of Diatomite filled Olefin Foams (규조토를 함유한 올레핀계 폼의 기계적 물성 및 수분 제어 성능에 관한 연구)

  • Kim, Jae Yang;Lee, Ji Eun;Seong, Dong Gi
    • Journal of Adhesion and Interface
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    • v.22 no.1
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    • pp.22-28
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    • 2021
  • Products using diatomaceous earth, which are used in various fields, are optimized for moisture absorption, but have problems such as high hardness, powder flying, and rough surface feel. To improve this, an olefin-based foam having low hardness and high elasticity was prepared by adding an excessive amount of inorganic material using EVA (Ethylene vinyl acetate) having low hardness and excellent elasticity. Diatomaceous earth was added to impart moisture absorption characteristics of the foam, and the moisture absorption/drying characteristics showed a moisture absorption rate of about 10 to 15% and a moisture drying rate of 10 to 70% depending on the content of the diatomaceous earth. Through this study, it was possible to manufacture a water-absorbing olefin-based foam with diatomaceous earth added, and it was confirmed that the diatomaceous earth added to the foam had a great influence on water absorption and dissipation due to its microstructure and characteristics.

Influence of Milling Conditions on the Microstructural Characteristics and Mechanical Properties of Non-equiatomic High Entropy Alloy (밀링 조건이 고엔트로피 합금의 미세조직 및 기계적 특성에 미치는 영향)

  • Seo, Namhyuk;Jeon, Junhyub;Kim, Gwanghoon;Park, Jungbin;Son, Seung Bae;Lee, Seok-Jae
    • Journal of Powder Materials
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    • v.28 no.2
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    • pp.103-109
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    • 2021
  • High-entropy alloys have excellent mechanical properties under extreme environments, rendering them promising candidates for next-generation structural materials. It is desirable to develop non-equiatomic high-entropy alloys that do not require many expensive or heavy elements, contrary to the requirements of typical high-entropy alloys. In this study, a non-equiatomic high-entropy alloy powder Fe49.5Mn30Co10Cr10C0.5 (at.%) is prepared by high energy ball milling and fabricated by spark plasma sintering. By combining different ball milling times and ball-to-powder ratios, we attempt to find a proper mechanical alloying condition to achieve improved mechanical properties. The milled powder and sintered specimens are examined using X-ray diffraction to investigate the progress of mechanical alloying and microstructural changes. A miniature tensile specimen after sintering is used to investigate the mechanical properties. Furthermore, quantitative analysis of the microstructure is performed using electron backscatter diffraction.

Electrochemical Characteristics of Synthesized Nb2O5-Li3VO4 Composites as Li Storage Materials

  • Yang, Youngmo;Seo, Hyungeun;Kim, Jae-Hun
    • Corrosion Science and Technology
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    • v.20 no.4
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    • pp.183-188
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    • 2021
  • The increasing demand for energy storage in mobile electronic devices and electric vehicles has emphasized the importance of electrochemical energy storage devices such as Li-ion batteries (LIBs) and supercapacitors. For reversible Li storage, alternative anode materials are actively being developed. In this study, we designed and fabricated an Nb2O5-Li3VO4 composite for use as an anode material in LIBs and hybrid supercapacitors. Nb2O5 powders were dissolved into a solution and the precursors were precipitated onto Li3VO4 through a simple, low-temperature hydrothermal reaction. The annealing process yielded an Nb2O5-Li3VO4 composite that was characterized by X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy. Electrochemical tests revealed that the Nb2O5-Li3VO4 composite electrode demonstrated increased capacities of approximately 350 and 140 mAh g-1 at 0.1 and 5 C, respectively, were maintained up to 1000 cycles. The reversible capacity and rate capability of the composite electrode were enhanced compared to those of pure Nb2O5-based electrodes. These results can be attributed to the microstructure design of the synthesized composite material.

Austenite Stability and Mechanical Properties of Nanocrystalline FeNiCrMoMnSiC Alloy Fabricated by Spark Plasma Sintering (방전플라즈마소결로 제조된 나노결정 FeNiCrMoMnSiC 합금의 오스테나이트 안정성과 기계적 특성)

  • Park, Jungbin;Jeon, Junhyub;Seo, Namhyuk;Kim, Gwanghun;Son, Seung Bae;Lee, Seok-Jae
    • Journal of Powder Materials
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    • v.28 no.4
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    • pp.336-341
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    • 2021
  • In this study, a nanocrystalline FeNiCrMoMnSiC alloy was fabricated, and its austenite stability, microstructure, and mechanical properties were investigated. A sintered FeNiCrMoMnSiC alloy sample with nanosized crystal was obtained by high-energy ball milling and spark plasma sintering. The sintering behavior was investigated by measuring the displacement according to the temperature of the sintered body. Through microstructural analysis, it was confirmed that a compact sintered body with few pores was produced, and cementite was formed. The stability of the austenite phase in the sintered samples was evaluated by X-ray diffraction analysis and electron backscatter diffraction. Results revealed a measured value of 51.6% and that the alloy had seven times more austenite stability than AISI 4340 wrought steel. The hardness of the sintered alloy was 60.4 HRC, which was up to 2.4 times higher than that of wrought steel.

Fabrication and Magnetic Properties of Mg and BaFe12O19 Ferromagnetic Composite Powders by Mechanical Alloying (기계적합금화법에 의한 Mg-BaFe12O19 계 강자성 복합분말의 제조 및 자기특성)

  • Lee, Chung-Hyo
    • Korean Journal of Materials Research
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    • v.31 no.2
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    • pp.61-67
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    • 2021
  • Fabrication of a ferromagnetic composite powder for the magnesium and BaFe12O19 system by mechanical alloying (MA) is investigated at room temperature. Mixtures of Mg and BaFe12O19 powders with a weight ratio of Mg:BaFe12O19 = 4:1, 3:2, 2:3 and 1:4 are used. Optimal MA conditions to obtain a ferromagnetic composite with fine microstructure are investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that Mg-BaFe12O19 composite powders in which BaFe12O19 is dispersed in Mg matrix are successfully produced by MA of BaFe12O19 with Mg for 80 min. for all compositions. Magnetization of Mg-BaFe12O19 composite powders gradually increases with increasing the amounts of BaFe12O19, whereas coercive force of MA powders gradually decreases due to the refinement of BaFe12O19 powders with MA time for all compositions. However, it can be seen that the coercivity of Mg-BaFe12O19 MA composite powders with a weight ratio of Mg:BaFe12O19=4:1 and 3:2 for MA 80 min. are still high, with values of 1260 Oe and 1320 Oe compared to that of Mg:BaFe12O19=1:4. This clearly suggests that the refinement of BaFe12O19 powders during MA process for Mg:BaFe12O19=4:1 and 3:2 tends to be suppressed due to ductile Mg powders.

Effect of Heat Treatment on Microstructure, Mechanical Property and Corrosion Behavior of STS 440C Martensitic Stainless Steel (STS 440C 마르텐사이트계 스테인리스 강의 열처리에 따른 미세조직, 기계적 특성 및 부식 거동)

  • Kim, Mingu;Lee, Kwangmin
    • Korean Journal of Materials Research
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    • v.31 no.1
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    • pp.29-37
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    • 2021
  • Martensitic stainless steel is commonly used in the medical implant instrument. The alloy has drawbacks in terms of strength and wear properties when applied to instruments with sharp parts. 440C STS alloy, with improved durability, is an alternative to replace 420 J2 STS. In the present study, the carbide precipitation, and mechanical and corrosion properties of STS 440C alloy are studied as a function of different heat treatments. The STS 440C alloy is first austenitized at different temperatures; this is immediately followed by oil quenching and sub-zero treatment. After sub-zero treatment, the alloy is tempered at low temperatures. The microstructures of the heat treated STS 440C alloy consist of martensite and retained austenite and carbides. Using EDX and SADP with a TEM, the precipitated carbides are identified as a Cr23C6 carbide with a size of 1 to 2 ㎛. The hardness of STS 440C alloy is improved by austenitization at 1,100 ℃ with sub-zero treatment and tempering at 200 ℃. The values of Ecorr and Icorr for STS 440C increase with austenitization temperature. Results can be explained by the dissolution of Cr-carbide and the increase in the retained austenite. Sub-zero treatment followed by tempering shows a little difference in the properties of potentiodynamic polarizations.