• 제목/요약/키워드: microstructure

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고속도강롤의 미세조직, 고온마모특성, 표면조도에 미치는 탄소, 텅스텐, 바나듐의 영향 (Effects of Carbon, Tungsten, and Vanadium on the Microstructure, High-Temperature Wear Properties, and Surface Roughness of High Speed Steel Rolls)

  • 하대진;성효경;박준욱;이성학
    • 대한금속재료학회지
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    • 제47권7호
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    • pp.406-415
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    • 2009
  • A study was conducted on the effects of carbon, tungsten, and vanadium on the wear properties and surface roughness of four High Speed Steel (HSS) rolls manufactured by the centrifugal casting method. Hot-rolling simulation tests were carried out using a high-temperature wear tester capable of controlling speed, load, and temperature. HSS rolls contained a large amount (up to 25 vol.%) of carbides such as MC, $M_{2}C$, $M_{7}C_{3}$, and $M_{6}C$ carbides formed in the tempered martensite matrix. The matrix consisted mainly of lath tempered martensite when the carbon content in the matrix was small, and contained a considerable amount of plate tempered martensite when the carbon content increased. The high-temperature wear test results indicated that the wear properties and surface roughness of the rolls improved when the amount of hard MC carbides formed inside solidification cells increased. The rolls distribution was also homogeneous. The best wear properties and surface roughness were obtained from a roll where a large amount of MC carbides was homogeneously distributed in the lath tempered martensite matrix. The proper contents of carbon equivalent, tungsten equivalent, and vanadium were 2.0~2.3%, 9~10%, and 5~6%, respectively.

Change of Crystalline Properties of Poly(ethylene-co-vinyl acetate) according to the Microstructures

  • Choi, Sung-Seen;Chung, Yu Yeon
    • Elastomers and Composites
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    • 제56권2호
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    • pp.92-99
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    • 2021
  • Microstructure-dependent changes in the crystalline properties of poly(ethylene-co-vinyl acetate) (EVA) was investigated using various EVAs at different VA contents via X-ray diffraction (XRD). The parameters analyzed herein were percentage crystallinity (Xc), interplanar crystal spacing (dhkl), crystal stack size (Dhkl), and the number of crystal plane piles (Nhkl). The Xcs of [110] and [200] crystals were 21.0-4.1 and 6.7-1.4%, respectively, and they decreased by approximately 2.3 and 0.7% for every mol% of the VA content, respectively. The Xc ratios of the [110] and [200] crystals were approximately 3. The d110s and d200s values were 0.41-0.42 and 0.37-0.38 nm, respectively. The D110s and D200s values were 9.56 -21.92 and 7.00-16.42 nm, respectively. The dhkls increased with an increase in the VA content, whereas the Dhkls decreased. The N110s and N200s were 22.7-51.3 and 18.3-43.2, respectively, and they decreased by increasing the VA content. EVA with the same VA content showed different crystalline properties as per the suppliers, and some EVAs deviated from the average trends. This could be explained by the difference in their microstructures such as the sizes and distribution uniformity of the ethylene sequences in EVA chains.

양성자 조사가 316 스테인리스강의 미세조직과 표면산화 특성에 미치는 영향 (Effects of Proton Irradiation on the Microstructure and Surface Oxidation Characteristics of Type 316 Stainless Steel)

  • 임연수;김동진;황성식;최민재;조성환
    • Corrosion Science and Technology
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    • 제20권3호
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    • pp.158-168
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    • 2021
  • Austenitic 316 stainless steel was irradiated with protons accelerated by an energy of 2 MeV at 360 ℃, the various defects induced by this proton irradiation were characterized with microscopic equipment. In our observations irradiation defects such as dislocations and micro-voids were clearly revealed. The typical irradiation defects observed differed according to depth, indicating the evolution of irradiation defects follows the characteristics of radiation damage profiles that depend on depth. Surface oxidation tests were conducted under the simulated primary water conditions of a pressurized water reactor (PWR) to understand the role irradiation defects play in surface oxidation behavior and also to investigate the resultant irradiation assisted stress corrosion cracking (IASCC) susceptibility that occurs after exposure to PWR primary water. We found that Cr and Fe became depleted while Ni was enriched at the grain boundary beneath the surface oxidation layer both in the non-irradiated and proton-irradiated specimens. However, the degree of Cr/Fe depletion and Ni enrichment was much higher in the proton-irradiated sample than in the non-irradiated one owing to radiation-induced segregation and the irradiation defects. The microstructural and microchemical changes induced by proton irradiation all appear to significantly increase the susceptibility of austenitic 316 stainless steel to IASCC.

고온 압축 공정에서 금형과 알루미늄 빌렛의 접촉 열전달 계수 도출에 관한 연구 (A Study on Derivation of Contact Heat Transfer Coefficient Between Die and Aluminum Billet in High Temperature Compression Process)

  • 전효원;서창희;오상균;권태하;강경필;육형섭
    • 소성∙가공
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    • 제30권3호
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    • pp.142-148
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    • 2021
  • In hot forging analysis, the interfacial heat transfer coefficient (IHTC) is a very important factor defining the heat flow between the die and the material. In particular, in the hot forging analysis of aluminum 6xxx series alloy, which are used in automobile parts, differences in load and microstructure occur due to changes in surface temperature according to the IHTC. This IHTC is not a constant value but changes depends on pressure. This study derived the IHTC under low load using aluminum 6082 alloy. An experiment was performed by fabricating a compression die, and a heat transfer analysis was performed based on the experimental data. The heat transfer analysis used DEFORM-2D, a commercial finite element analysis program. To derive the IHTC, heat transfer analysis was performed for the IHTC in the range of 10 to 50 kW/m2℃ at intervals of 10kW/m2℃. The heat transfer analysis results according to the IHTC and the actual experimental values were compared to derive the IHTC of the aluminum 6082 alloy under low load.

슈퍼 듀플렉스 스테인리스강(UNS S32506) 레이저 조관용접 튜브의 용접 후 열처리에 따른 부식거동 (Corrosion Behaviors of Laser-welded Super Duplex Stainless Steel(UNS S32506) Tube with Post-Weld Heat Treatment Conditions)

  • 조동민;박진성;홍승갑;황중기;김성진
    • 한국표면공학회지
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    • 제54권3호
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    • pp.102-111
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    • 2021
  • The corrosion behaviors of laser-welded super duplex stainless steel tubes with post-weld heat treatment(PWHT) conditions(950, 1000, 1050, 1100 ℃ for 5 and 30 min) were evaluated by electrochemical potentiodynamic polarization and critical pitting temperature measurements. This study showed that the critical metallurgical factors affecting the degradation of corrosion resistance of a steel tube in as-welded condition were the unbalanced phase fraction(ferrite:austenite = 94:4), Cr2N precipitation, and phase transformation from the austenite phase to ɛ-martensite(via stress-induced phase transformation). The improvement in the corrosion resistance of the welded specimen depends greatly on the PWHT conditions. The specimens after PWHT conducted below 1000 ℃ showed inferior corrosion resistance, caused by precipitation of the sigma phase enriched with Cr and Mo. At 1100 ℃ for a longer duration in PWHT, the ferrite phase grows, and its fraction increases, leading to an unbalanced phase fraction in the microstructure. As a result, pitting can be initiated primarily at the interface between the ferrite/austenite phase, particularly in base metal.

방전플라즈마 소결 공정을 이용한 WC-Co-Mo2C 소재의 기계적 특성평가 (Mechanical Property Evaluation of WC-Co-Mo2C Hard Materials by a Spark Plasma Sintering Process)

  • 김주훈;박현국
    • 한국재료학회지
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    • 제31권7호
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    • pp.392-396
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    • 2021
  • Expensive PCBN or ceramic cutting tools are used for processing of difficult-to-cut materials such as Ti and Ni alloy materials. These tools have the problem of breaking easily due to their high hardness but low fracture toughness. To solve these problems, cutting tools that form various coating layers are used in low-cost WC-Co hard material tools, and research on various tool materials is being conducted. In this study, binderless-WC, WC-6 wt%Co, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co-2.5 wt% Mo2C hard materials are densified using horizontal ball milled WC-Co, WC-Co-Mo2C powders, and spark plasma sintering process (SPS process). Each SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co-2.5 wt% Mo2C hard materials are almost completely dense, with relative density of up to 99.5 % after the simultaneous application of pressure of 60 MPa and almost no significant change in grain size. The average grain sizes of WC for Binderless-WC, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co-2.5 wt% Mo2C hard materials are about 0.37, 0.6, 0.54, and 0.43 ㎛, respectively. Mechanical properties, microstructure, and phase analysis of SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co-2.5 wt% Mo2C hard materials are investigated.

CAS glass와 Yb2O3를 이용한 2차상의 형상 제어가 AlN 세라믹의 열전도도 및 기계적 특성에 미치는 영향 (Effect of Morphological Control of Secondary Phase using Yb2O3 and Ca-Al-Si-O-based Glass on Thermal and Mechanical Properties of AlN)

  • 최동규;김시연;여동훈;신효순;정대용
    • 한국분말재료학회지
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    • 제27권6호
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    • pp.498-502
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    • 2020
  • We investigate the effects of Yb2O3 and calcium aluminosilicate (CAS) glass as sintering additives on the sintering behavior of AlN. The AlN specimens are sintered at temperatures between 1700℃ and 1900℃ for 2 h in a nitrogen atmosphere. When the Yb2O3 content is low (within 3 wt.%), an isolated shape of secondary phase is observed at the AlN grain boundary. In contrast, when 3 wt.% Yb2O3 and 1 wt.% CAS glass are added, a continuous secondary phase is formed at the AlN grain boundary. The thermal conductivity decreases when the CAS glass is added, but the sintering density does not decrease. In particular, when 10 wt.% Yb2O3 and 1 wt.% CAS glass are added to AlN, the flexural strength is the highest, at 463 MPa. These results are considered to be influenced by changes in the microstructure of the secondary phase of AlN.

내산화성 Cr-Si-Al합금의 주조상태 및 고온가열 후의 미세조직 특성 (Microstructural Characteristics of Oxidation Resistant Cr-Si-Al alloys in Cast State and after High Temperature Heating)

  • 김정민;김채영;양원철;박준식
    • 한국재료학회지
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    • 제31권3호
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    • pp.156-161
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    • 2021
  • Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 ℃, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.

The nano scale buckling properties of isolated protein microtubules based on modified strain gradient theory and a new single variable trigonometric beam theory

  • Alwabli, Afaf S.;Kaci, Abdelhakim;Bellifa, Hichem;Bousahla, Abdelmoumen Anis;Tounsi, Abdelouahed;Alzahrani, Dhafer A.;Abulfaraj, Aala A.;Bourada, Fouad;Benrahou, Kouider Halim;Tounsi, Abdeldjebbar;Mahmoud, S.R.;Hussain, Muzamal
    • Advances in nano research
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    • 제10권1호
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    • pp.15-24
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    • 2021
  • Microtubules (MTs) are the main part of the cytoskeleton in living eukaryotic cells. In this article, a mechanical model of MT buckling, considering the modified strain gradient theory, is analytically examined. The MT is assumed as a cylindrical beam and a new single variable trigonometric beam theory is developed in conjunction with a modified strain gradient model. The main benefit of the present formulation is shown in its new kinematic where we found only one unknown as the Euler-Bernoulli beam model, which is even less than the Timoshenko beam model. The governing equations are deduced by considering virtual work principle. The effectiveness of the present method is checked by comparing the obtained results with those reported by other higher shear deformation beam theory involving a higher number of unknowns. It is shown that microstructure-dependent response is more important when material length scale parameters are closer to the outer diameter of MTs. Also, it can be confirmed that influences of shear deformation become more considerable for smaller shear modulus and aspect ratios.

소수성 증진을 위한 PMHS 유액 혼입 시멘트 복합체의 미세구조 분석 (Microstructure Analysis of Cement Composite containing PMHS Emulsion to Improve Hydrophobic)

  • 김영환;오홍섭
    • 한국구조물진단유지관리공학회 논문집
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    • 제25권1호
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    • pp.25-32
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    • 2021
  • 고내구성 친환경 콘크리트를 개발하기 위하여 폴리메틸 하이드로실록산과 폴리비닐알코올을 교반, 혼합하여 발수 및 소수성화합물을 제조하였다. 시멘트페이스트에 혼합물을 첨가한 후 BSE와 EDS 분석을 통하여 수화반응 특성과 화학조성의 변화 정도를 분석하였으며, MIP 분석에 의해 미세공극을 평가하였다. PMHS 유액을 혼입한 시멘트는 수화반응성이 높아지고 모세공극률이 낮아지는 것으로 분석되었으나, 시멘트 페이스트내에서의 유액의 분산 정도에 따라 공극률의 편차가 발생하는 것으로 나타났다. 메타카올린을 혼입한 유액의 경우에는 PMHS 유액만을 사용한 경우와 수화도와 공극률에서 거의 차이가 없는 것으로 나타났다. 그러나 시멘트 표면을 PMHS 유액으로 도포한 경우의 접촉각은 OPC와 비교하여 크게 증가하는 것으로 나타났으며, 특히 PVA 섬유를 같이 사용한 경우에는 과소수성 표면으로 변화되는 것으로 분석되었다.