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  • Title/Summary/Keyword: Grain refinement

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An Investigation on the Microstructure Evolution and Tensile Property in the Weld Heat-Affected Zone of Austenitic FeMnAlC Lightweight Steels (오스테나이트계 FeMnAlC 경량철강의 용접열영향부 미세조직 변화 및 인장특성에 관한 연구)

  • Moon, Joonoh;Park, Seong-Jun
    • Journal of Welding and Joining
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    • v.35 no.1
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    • pp.9-15
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    • 2017
  • IMicrostructure evolution and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-30Mn-9Al-0.9C lightweight steels were investigated. Five alloys with different V and Nb content were prepared by vacuum induction melting and hot rolling process. The HAZ samples were simulated by a Gleeble simulator with welding condition of 300kJ/cm heat input and HAZ peak temperatures of 1150C and 1250C. Microstructures of base steels and HAZ samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their mechanical properties were evaluated by tensile tests. The addition of V and Nb formed fine V and/or Nb-rich carbides, and these carbides increased tensile and yield strength of base steels by grain refinement and precipitation hardening. During thermal cycle for HAZ simulation, the grain growth occurred and the ordered carbide (κcarbide) formed in the HAZs. The yield strength of HAZ samples (HAZ 1) simulated in 1150C peak temperature was higher as compared to the base steel due to the formation of κcarbide, while the yield strength of the HAZ samples (HAZ 2) simulated in 1250C decreased as compared to HAZ 1 due to the excessive grain growth.

Fabrication of TiAl Alloys by Mechanical Milling and Spark Plasma Sintering (기계적 분쇄화 및 스파크 플라즈마 소결에 의한 TiAl 합금의 제조)

  • Kim, M.S.;Kim, J.S.;Hwang, S.J.;Hong, Y.H.;Oh, M.H.
    • Journal of the Korean Society for Heat Treatment
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    • v.17 no.1
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    • pp.17-22
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    • 2004
  • In the present study, newly developed spark plasma sintering(SPS) technique was introduced to refine the grain size of γ-based TiAl intermetallic compounds. Ti-46Al-1.5Mo and Ti-46Al-1.5Mo-0.2C(at%) prealloyed powders were produced by mechanical milling(MM) in high-energy attritor. The mechanically milled powders were characterized by XRD and SEM for the microstructural evolution as a function of milling time. And then, the MMed powders were sintered by both spark plasma sintering and hot pressing in vacuum (HP). After the sintering process, MM-SPSed specimens were heat-treated in a vacuum furnace (SPS-VHT) and in the SPS equipment(MM-SPS) for microstructural control. It was found from microstrutural observation that the microstructure consisting of equiaxed γ-TiAl with a few hundred nanometer in average size and α2Ti3Al particles were formed after both sintering processes. It was also revealed from hardness test and three-point bending test that the effect of grain refinement on the hardness and bending strength is much higher than that of carbon addition. The fully lamellar microstructures, which is less than 80μm in average grain size was obtained by SPS-VHT process, and the fully lamellar microstructure which is less than 100μm in average grain size was obtained by MM-SPS for a relatively shorter heat-treatment time.

Analysis of Densification Behavior during Powder Equal Channel Angular Pressing using Critical Relative Density Model (임계상대밀도 모델을 이용한 분말 등통로각압축 공정시 분말 치밀화 거동)

  • Bok, Cheon-Hee;Yoo, Ji-Hoon;Yoon, Seung-Chae;Kim, Taek-Soo;Chun, Byong-Sun;Kim, Hyoung-Seop
    • Journal of Powder Materials
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    • v.15 no.5
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    • pp.365-370
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    • 2008
  • In this study, bottom-up powder processing and top-down severe plastic deformation processing approaches were combined in order to achieve both full density and grain refinement with least grain growth. The numerical modeling of the powder process requires the appropriate constitutive model for densification of the powder materials. The present research investigates the effect of representative powder yield function of the Shima-Oyane model and the critical relative density model. It was found that the critical relative density model is better than the Shima-Oyane model for powder densification behavior, especially for initial stage.

Microstructure Evolution of 15Cr ODS Steel by a Simple Torsion Test (단순 전단변형에 의한 15Cr 산화물 분산강화 강의 미세조직 변화)

  • Jin, Hyun Ju;Kang, Suk Hoon;Kim, Tae Kyu
    • Journal of Powder Materials
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    • v.21 no.4
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    • pp.271-276
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    • 2014
  • 15Cr-1Mo base oxide dispersion strengthened (ODS) steel which is considered to be as a promising candidate for high- temperature components in nuclear fusion and fission systems because of its excellent high temperature strength, corrosion and radiation resistance was fabricated by using mechanical alloying, hot isostatic pressing and hot rolling. Torsion tests were performed at room temperature, leading to two different shear strain routes in the forward and reverse directions. In this study, microstructure evolution of the ODS steel during simple shearing was investigated. Fine grained microstructure and a cell structure of dislocation with low angle boundaries were characterized with shear strain in the shear deformed region by electron backscattered diffraction (EBSD). Grain refinement with shear strain resulted in an increase in hardness. After the forward-reverse torsion, the hardness value was measured to be higher than that of the forward torsion only with an identical shear strain amount, suggesting that new dislocation cell structures inside the grain were generated, thus resulting in a larger strengthening of the steel.

Comparative Study on the Fabrication of Single Grain YBCO Bulk Superconductors using Liquid Infiltration and Conventional Melt Growth Processes (단결정 YBCO 벌크 초전도체 제조에 대한 액상침투법과 고전적 용융공정의 비교연구)

  • Mahmood, Asif;Jun, Byung-Hyuk;Kim, Chan-Joong
    • Progress in Superconductivity
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    • v.11 no.1
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    • pp.42-46
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    • 2009
  • With an aim of comparison, single grain Y-Ba-Cu-O (YBCO) bulk superconductors were fabricated using a liquid infiltration growth (LIG) process and a conventional melt growth (MTG) process with top seeding. The MTG process uses an YBa2Cu3O7x(Y123) powder as a precursor, while the LIG process uses Y2BaCuO5(Y211)/Ba3Cu5O8(Y035) pre-forms. The growth of a single Y123 domain on the top seed was successful in the both processes. Different feature between the two processes is the interior microstructure regarding the critical current density (Jc). The LIG-processed YBCO sample showed a lower porosity, more uniform distribution of Y211 particles and the enhanced Y211 refinement compared to the conventional MTG process. The Jc improvement in the LIG process is attributed to the dispersion of finer Y211 particles as well as lower porosity within the Y123 superconducting matrix.

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A study on the Structure and Transformation Rate of Heat Treatment of Forged TAP Housing and Valve for Automotive Parts (단조용 자동차 부품 T/P Housing과 Valve의 열처리에 따른 조직 및 변형 속도에 관하여)

  • 유형종;이호진;이건영;최진일
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.4 no.3
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    • pp.155-158
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    • 2003
  • The effects of Mn, V addition on the behavior of structure and the effects of cooling rate of S20C steel for use of Tn housing and valve for automotive parts have been investigated. Transformation start temperature measured from inflection point of cooling curves has been found out to decrease with increasing cooling rate and to be more sensitive to Mn contents when cooling rate is fast. It was therefore shown that the grain was refined. If there is a big compacting pressure, it is indicated that hardness becomes much greater at surface than inside.

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Rolling of AZ31 Alloy and Microstructure of Rolled Plates (압연조건에 따른 AZ31 마그네슘합금판재의 변형거동 및 미세조직 변화)

  • Ha, T.K.;Jeong, H.T.;Sung, H.J.;Park, W.J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.63-66
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    • 2006
  • The effect of warm rolling under various conditions on the microstructure and mechanical property was investigated using an AZ31 Mg alloy sheet. Several processing parameters such as initial thickness, thickness reduction by a single pass rolling, rolling temperature, roll speed, and roll temperature were varied to elicit an optimum condition for the warm rolling process of AZ31 Mg alloy. Microstructure and mechanical properties were measured for specimens subjected to rolling experiments of various conditions. Warm rolling of 30% thickness reduction per pass was possible without any side-crack at temperatures as low as 200C under the roll speed of 30 m/min. The initial microstructure before rolling was the mixed one consisting of partially recrystallized and cast structures. Grain refinement was found to occur actively during the warm rolling, producing a very fine grain size of 7 mm after 50% reduction in single pass rolling at 200C. Yield strength of 204MPa, tensile strength of 330MPa and uniform elongation of 32% have been obtained in warm rolled sheets.

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The Effect of Nitride Coating on SiC Platelet in Al2O3/SiC Hybrid-Composite (Al2O3/SiC Hybrid-Composite에서 SiC에 질화물 코팅의 영향)

  • 이수영;임경호;전병세
    • Journal of the Korean Ceramic Society
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    • v.34 no.4
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    • pp.406-412
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    • 1997
  • Al2O3/SiC hybrid-composite has been fabricated by the conventional powder process. The addition of α-Al2O3 as seed particles in the transformation of γ-Al2O3 to α-Al2O3 provided a homogeneity of the microstructure. The grain growth of Al2O3 are significantly surpressed by the addition of nano-size SiC particles. Dislocation were produced due to the difference of thermal expansion coefficient between Al2O3 and SiC and piled up on SiC particles in Al2O3 matrix, resulting in transgranular fracture. The high fracture strength of the composite was contributed to the grain refinement and the transgranular fracture mode. The addition of SiC platelets to Al2O3/SiC nano-composite decreased the fracture strength, but increased the fracture toughness. Coated SiC platelets with nitrides such as BN and Si3N4 enhanced fracture toughness much more than non-coated SiC platelets by enhancing crack deflection.

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Effect of (Ti-B) and Sr Additives on Impact and Fatigue Properties of Recycled AC4A Aluminum Casting Alloy (재활용 AC4A 알루미늄 합금의 충격 및 피로 특성에 미치는 (Ti-B), Sr 첨가제의 영향)

  • Oh, Seung-Hwan;Kim, Heon-Joo
    • Journal of Korea Foundry Society
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    • v.39 no.4
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    • pp.61-74
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    • 2019
  • The effects of Sr and (Ti-B) additives on the impact and fatigue properties of recycled (35% scrap content) AC4A aluminum alloy are investigated here. The acicular morphology of the eutectic Si phase of as-cast specimens was converted to the fibrous one with Sr additives. The grain size of the α-solid solution decreased by the addition of (Ti-B) additives. The crack initiation energy (Ei) of the impact absorption energy decreased due to the incorporation of an oxide film and inclusions depending on the scrap used. The modification of the eutectic Si morphology by Sr additives is considered as the main factor of the increase of the average impact absorption energy (Et). The addition of (Ti-B) additives contributed to an increase in the occurrence of crack deflections due to the refining of α-Al grains, resulting in improved fatigue properties.

A Study on the Hydrogen treatment of It and Ti-pd Alloy (티타늄 및 티나늄-팔라듐 합금의 수소처리에 관한 연구)

  • Cha, Sung-Soo
    • Journal of Technologic Dentistry
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    • v.15 no.1
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    • pp.5-25
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    • 1993
  • Effects of hydrogenation on microstructure and mechanical properties of pure Ti and Ti-0.15Pd alloy have been studied by means of optical microscopy, differential scanning calorimeter(DSC), Xray diffraction and micro vicker's hardness test. Grain size of pure Ti and Ti-0.15Pd alloy decresed largely by hydrogenation finer than that of pure Ti and the grain size refinement was evedent in Ti-0.15Pd alloy than that in pure Ti. Ti-.015Pd alloy carried out solution treatment at 950C, the transformation of α' martensite was occured. The amount of Hydrogen absorption in Ti-.015Pd alloy was higher than that in pure Ti. Decomposition of hydride in pure titanium and Ti-0.15Pd alloy increased largely by hydrogenation, and micro vicker's hardness of Ti-.015Pd alloy was largely than that of pure Ti by 30% after hydrogenation. The micro vicker's hardness of Ti-0.15Pd alloy after solution treatment and dehydrogenation were higher at β phase ranger(950C) than that phase range(750C).

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