• Title, Summary, Keyword: microstructure

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A Study of Mechanical Properties and Microstructure of ZrO2-Ag Depending on the Composite Route (ZrO2-Ag의 복합화 공정에 따른 기계적 특성 및 미세조직 평가)

  • Yeo, In-Chul;Han, Jae-Kil;Kang, In-Cheol
    • Journal of Korean Powder Metallurgy Institute
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    • v.19 no.6
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    • pp.416-423
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    • 2012
  • This paper introduces an effect of a preparing $ZrO_2$-Ag composite on its mechanical properties and microstructure. In present study, $ZrO_2$-Ag was prepared by reduction-deposition route and wetting dispersive milling method, respectively. Two type of Ag powders (nano Ag and micron Ag size, respectively) were dispersed into $ZrO_2$ powder during wetting dispersive milling in D.I. water. Each sample was sintered at $1450^{\circ}C$ for 2hr in atmosphere, and then several mechanical tests and analysis of microstructure were carried out by bending test, hardness, fracture toughness and fracture surface microstructure. As for microstructure, the Ag coated $ZrO_2$ showed homogeneously dispersed Ag in $ZrO_2$ in where pore defect did not appear. However, $ZrO_2$-nano Ag and $ZrO_2$-micro Ag composite appeared Ag aggregation and its pore defect, which carried out low mechanical property and wide error function value.

Microstructure and Magnetic Properties of Nanocomposite Sm2Fe15Ga2Cx/α-Fe Permanent Magnets

  • Cheng, Zhao-hua
    • Journal of Magnetics
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    • v.8 no.1
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    • pp.18-23
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    • 2003
  • In our previous work, microstructure and magnetic properties of two-phase exchange-coupled $Sm_2Fe_{15}Ga_2C_{x}$/$\alpha$-Fe nanocomposites have been investigated by means of x-ray diffraction, transmission electron microscopy and magnetization measurement. It was found the exchange coupling between the magnetically hard phase $Sm_2Fe_{15}Ga_2C_{x}$ and the magnetically soft one ${\alpha}$-Fe results in an enhancement of the remanence. The sizes of crystallites of both phases are, however much larger than the Block domain-wall width of the magnetically hard phase. This microstructure gives rise to a concave demagnetization curve and consequently reduces the maximum energy Product. In order to improve their magnetic properties, a few Percent of Zr, which may be effective to refine the microstructure through rapid quenching, was introduced into the nanocomposites. The addition of Zr was found to improve the magnetic properties significantly, Under optimum heat-treatment conditions, the remanence, coercivity and maximum energy Product increase from 0.65 T, 0.48 T and 50 kJ/$m^{3}$ for the Zr-free sample to 0.72 T, 0.77 T and 71.6 kJ/$m^{3}$ for the 1 at.% Zr-containing one, respectively, The improvements of magnetic properties are due to the refinement of microstructure by the addition of Zr.

The Fretting Fatigue Behavior of Ti-6Al-4V Alloy on Change of Microstructure (Ti-6Al-4V 합금의 조직 변화에 따른 프레팅 피로거동)

  • Bae Yong Tak;Choi Sung long;Kwon Jae Bo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.4
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    • pp.584-590
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    • 2005
  • The effect of microstructure on mechanical behavior for Ti-6Al-4V alloy was studied. Two different kinds of specimens are prepared using heat treatments (rolled plate, $1050^{\circ}C)$ in order to Produce different microstructures. Various kinds of mechanical tests such as hardness, tensile, fatigue and fretting fatigue tests are performed for evaluation of mechanical properties with the changes of microstructures. Through these tests, the following conclusions are observed: 1) Microstructures are observed as equiaxed and $widmanst{\ddot{a}}ten$ microstructures respectively. 2) Impact absorbed energy is superior for the equiaxed microstructure, and the hardness and tensile strength are superior for the $widmanst{\ddot{a}}ten$ microstructure. 3) The fatigue endurance of $widmanst{\ddot{a}}ten$ microstritcture shows higher value than that of the equiaxed microstructure. 4) The fatigue endurance in fretting condition was reduced about $50{\%}$ from that of the non-fretting condition.

Microstructure and Mechanical Properties of Continuous Cast Ductile Iron (연속주조한 구상흑연주철의 미세조직과 기계적 성질)

  • Choe, Kyeong-Hwan;Cho, Gue-Serb;Lee, Kyong-Whoan;Kim, Ki-Yeong
    • Journal of Korea Foundry Society
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    • v.24 no.1
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    • pp.52-59
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    • 2004
  • Microstructure and mechanical properties of ductile cast iron were investigated in terms of diameter change of samples that gives rise to modify the microstructure due to different cooling rate in the continuous casting process. The chemical composition used in this study was GCD 400 grade. From the microstructural observation, we have found a large number of graphite with small size in diameter which is comparable to the microstructure of the sample produced by conventional sand casting. The major reason of this would he due to high cooling rate. In the sample with 26 mm in diameter, the microstructure was composed of pearlite, iron carbide, and graphite. In the samples with 60 and 100 mm in diameter, however, we have observed a dissimilar microstructure that consisting of ferrite and graphite. Concerning the mechanical property, the sample with 26 mm in diameter showed higher hardness and strength compared to those samples with 60 and 100 mm in diameter. The result obtained for ductility appeared a reversal. Much more works such as inoculation, process design and chemical composition would be required in order to have a sound product even in a small diameter of samples.

Effect of Si on Mechanical and Anti-oxidation Properties of Ti-Si-N Coating (Si가 Ti-Si-N 코팅막의 기계적 성밀 및 내산화특성에 미치는 영향)

  • 박범희;김정애;이종영;김광호
    • Journal of the Korean Ceramic Society
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    • v.37 no.1
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    • pp.96-101
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    • 2000
  • Comparative studies on microstructure, and mechanical and anti-oxidation properties between TiN and Ti-Si-N films were performed. The Ti-Si-N films were deposited on high-speed steel and silicon wafer substrates by plasma-assisted chemcial vapor deposition(PACVD) technique. The Si addition to TiN film caused to change the microstructure such as grain size refinement, randomly multi-oriented microstructure, and nano-sized codeposition of silicon nitride in the TiN matrix. The Ti-Si-N film, contains Si content of ∼7 at.%, showed the micro-hardness value of ∼3400 HK, which was higher than the pure TiN film whose hardness was ∼1500HK. The Ti-Si(7 at.%)-N film also showed much improved anti-oxidation properties compared with those of the pure TiN film. These properties were also related to the microstructure of Ti-Si(7 at.%)-N film was formed and retarded further oxidation of the nitridelayer. These properties were also related to the microstructure of Ti-Si(7 at.%)-N film which was characterized by nano-sized precipitates of silicon nitride phase in the TiN matrix and randomly oriented grains.

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Microstructure Characteristics and Identification of Low-Carbon Steels Fabricated by Controlled Rolling and Accelerated Cooling Processes (제어 압연과 가속 냉각에 의해 저탄소강에서 형성되는 미세조직의 특징과 구분)

  • Lee, Sang-In;Hong, Tae-Woon;Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.27 no.11
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    • pp.636-642
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    • 2017
  • In the present study the microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes was characterized and identified based on various microstructure analysis methods including optical and scanning electron microscopy, and electron backscatter diffraction(EBSD). Although low-carbon steels are usually composed of ${\alpha}-ferrite$ and cementite($Fe_3C$) phases, they can have complex microstructures consisting of ferrites with different size, morphology, and dislocation density, and secondary phases dependent on rolling and accelerated cooling conditions. The microstructure of low-carbon steels investigated in this study was basically classified into polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite based on the inverse pole figure, image quality, grain boundary, kernel average misorientation(KAM), and grain orientation spread(GOS) maps, obtained from EBSD analysis. From these results, it can be said that the EBSD analysis provides a valuable tool to identify and quantify the complex microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes.

Design of Microstructure by Evaluating the Effect of Thermal Barrier Coating's Microstructure on TGO Interface Stress (열차폐코팅의 미세구조가 TGO 계면 응력에 미치는 영향 평가를 통한 미세구조 형상 설계)

  • Kim, Damhyun;Park, Kibum;Wee, SungUk;Kim, Keekeun;Park, Soo;Seok, Chang-Sung
    • Journal of the Korea Institute of Military Science and Technology
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    • v.23 no.5
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    • pp.435-443
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    • 2020
  • Thermal barrier coating(TBC) applied to fighter and turbine engines is a technology that improves the durability of core parts by lowering the surface temperature of base material. The thermal stress caused by mis-match of the coefficient of thermal expansion between the top coating and the TGO interface is the main cause of TBC breakage. Since the thermal stress is dependent on the microstructure of the TBC, designing microstructure of TBC can improve the durability as well as lower the thermal stress. In this study, the effect of coating thickness, volume of porosity and vertical cracking on the thermal stress was analyzed through finite element analysis. Through the analysis results, a design range of a microstructure that can improve the durability of thermal barrier coating by lowering thermal stress is proposed.

Static analysis of cutout microstructures incorporating the microstructure and surface effects

  • Alazwari, Mashhour A.;Abdelrahman, Alaa A.;Wagih, Ahmed;Eltaher, Mohamed A.;Abd-El-Mottaleb, Hanaa E.
    • Steel and Composite Structures
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    • v.38 no.5
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    • pp.583-597
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    • 2021
  • This article develops a nonclassical model to analyze bending response of squared perforated microbeams considering the coupled effect of microstructure and surface stress under different loading and boundary conditions, those are not be studied before. The corresponding material and geometrical characteristics of regularly squared perforated beams relative to fully filled beam are obtained analytically. The modified couple stress and the modified Gurtin-Murdoch surface elasticity models are adopted to incorporate the microstructure as well as the surface energy effects. The differential equations of equilibrium including the Poisson's effect are derived based on minimum potential energy. Exact closed form solution is obtained for bending behavior of the proposed model considering the classical and nonclassical boundary conditions for both uniformly distributed and concentrated loads. The proposed model is verified with results available in the literature. Influences of the microstructure length scale parameter, surface energy, beam thickness, boundary and loading conditions on the bending behavior of perforated microbeams are investigated. It is observed that microstructure and surface parameters are vital in investigation of the bending behavior of perforated microbeams. The obtained results are supportive for the design, analysis and manufacturing of perforated nanobeams that commonly used in nanoactuators, nanoswitches, MEMS and NEMS systems.

Analysis of Microstructure Evolution using Different Powder Metallurgy Process in Ti-X Alloy System (Ti-X계 합금의 분말야금 공정 차이에 따른 미세조직변화 분석)

  • Kwon, Hyeok-Gon;Kim, Doo-Hyeon;Gang, Min;Park, Ji-Hwan;Oh, Myung-Hoon
    • Journal of the Korean Society for Heat Treatment
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    • v.34 no.1
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    • pp.17-24
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    • 2021
  • In this study, Ti-X (X=Mn, Fe, Mo) powder alloys were designed and manufactured by both powder metallurgy (PM) and metal powder injection molding (MIM) process to improve strength and formability compared to CP-Ti powder materials. It was found that the lamellar microstructure consisted of α and β phases was formed in PM-processed alloys. However, MIM-processed alloys showed not the lamellar microstucture but the equiaxed α + β microstructure. It was also revealed that the contents of X component and feedstock were not affected to microstructure evolution. The reason why different microstructure was appeared between PM-processed and MIM-processed alloys is not clear yet, but supposed to be the effect of intersticial elements such as C, H and N derived from feedstock during debinding process of MIM.

Tensile Properties and Thermal Conductivities of Mg-Al alloy with As-Cast and Discontinuous Precipitates Microstructures (주조 및 불연속 석출물 미세조직을 가지는 Mg-Al 합금의 인장 특성 및 열전도도)

  • Jun, Joong-Hwan
    • Journal of the Korean Society for Heat Treatment
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    • v.33 no.5
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    • pp.219-225
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    • 2020
  • The objective of this study was to investigate the tensile properties and thermal conductivities of Mg9.3%Al alloy in as-cast state and heat-treated state consisting of fully discontinuous precipitates (DPs), respectively. The fully DPs microstructure was obtained by solution treatment at 405℃ for 24 h, followed by furnace cooling to RT. The as-cast alloy showed a partially divorced eutectic β(Mg17Al12) phase particles formed along the α-(Mg) cell boundaries. The DPs had various apparent (α+β) interlamellar spacings, which is related to different transformation temperatures during the furnace cooling. The DPs microstructure exhibited better tensile strength than the as-cast one, resulting from the higher value of elongation in response to its more homogeneous microstructure. It is noticeable that the DPs microstructure had 12.4% higher thermal conductivity in average than the as-cast one between RT and 200℃. The XRD analyses revealed that the lower Al concentration in the α-(Mg) matrix may well be responsible for the better thermal conductivity of the DPs microstructure.