• Journal of Welding and Joining
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• 제34권3호
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• pp.61-68
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• 2016

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.

• Elastomers and Composites
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• 제47권3호
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• pp.238-245
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• 2012

천연 흑연으로부터 Graphene oxide(GO)를 합성한 후 diisocyanatodicyclohexylmethane($H_{12}MDI$)를 이용하여 GO의 표면을 기능화하였고, hydrazine monohydrate에 의한 환원을 통해 isocyanate-graphene sheet(i-RGO)를 얻었다. 폴리우레탄과 적합한 나노복합체를 형성하기 위하여 GO, i-RGO, 천연흑연 및 열적환원된 graphene을 서로 비교분석하였으며, i-RGO가 가장 적합한 나노충전제로 선정되었다. 선정된 i-RGO의 함량에 따른 폴리우레탄의 물성 향상을 확인하기 위하여 충전제의 함량을 다르게 하여 PU/i-RGO 나노복합체를 합성하였다. 물성 평가에서, i-RGO의 함량이 증가할수록 열적 안정성, 경도 및 접촉각(발수력)이 향상되었는데, 이는 i-RGO의 물성 특성 및 가교점 작용에 기인한 것으로 판단되었다. 다만, 인장강도와 신장률의 경우 함량이 4 wt%를 넘어갈 경우 오히려 물성이 감소하는 것을 확인할 수 있었는데, 이는 과량의 가교점 형성이 원인인 것으로 해석되었다.

• 대한금속재료학회지
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• 제47권4호
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• pp.209-216
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• 2009

It was evaluated that the microstructural and mechanical properties of Ta-bearing 9Cr-0.5Mo-2W ferritic/martensitic experimental steels. All the experimental steels showed the tempered martensitic microstructures, and $M_{23}C_6$ carbides, whose sizes were ranged from 200 to 300 nm, were easily observed at both boundaries of the prior austenite grain and the martensite lath. In addition, a relatively large Nb-rich MX carbonitrides were intermittently detected at the prior austenite grain boundaries, whereas a lot of Vrich MX carbonitrides, whose mean diameter was less than 50 nm, were observed randomly at both boundaries. Ta was mainly incorporated into the V-rich MX carbonitrides rather than the Nb-rich ones and their content was spanned from 5 to 20 at.%. Ta contents within the MX precipitates also increased as the content of Ta increased. Because the Ta addition into the steels would be attributed to the precipitation strengthening, solid solution strengthening and lath width reduction, it was shown that the mechanical properties, including hardness, tensile strength and creep rate of the 9%Cr-0.5Mo-2W steels were improved by the increase of Ta content. Especially, 9Cr-0.5Mo-2W-0.3V-0.05Nb-0.14Ta steel was revealed to be relatively excellent in the application for the SFR fuel cladding.

• 공업화학
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• 제9권1호
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• pp.58-65
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• 1998

에폭시계 분체도료에 사용되고 있는 경화제로는 치환 dicyandiamide(Sub-DICY), 촉진 dicyandiamide(Acc-DICY), trimellitic anhydride(TMA), pyromellitic dianhydride(PMDA), Phenolic curing agent(Ph.C.A.)등이 사용되고 있다. 본 연구는 상기 5가지의 에폭시 경화제를 사용해서 제조한 에폭시 분체도료를 적합한 경화조건에서 완전히 경화시킨 뒤 여러 가지 실험기기 및 분석기기를 이용해서 경화된 도막 $T_g$, 인장강도, 파단신율, 경도, 내마모성등의 기계적 물성을 측정하였다. 그리고 흡수율, 내산성, 내알카리성등의 화학적물성, 전기적특성, 방식성등을 측정함으로써 경화제의 종류에 따른 에폭시 도막의 화학구조가 도막의 물성에 미치는 영향을 비교하였다. 그 결과 Phenolic curing agent는 toughness가 우수하지만 온도에 따른 색상 변화가 크고 산무수물 경화제는 전기절연성과 온도에 따른 색상안정성이 우수하지만 toughness와 부착성이 부족하고 DICY계는 흡수율과 온도에 따른 색상변화가 큰 특성을 나타내었다.

• 한국재료학회지
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• 제21권5호
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• pp.263-267
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• 2011

The present study was carried out to evaluate the microstructural and mechanical properties of cross-roll rolled pure copper sheets, and the results were compared with those obtained for conventionally rolled sheets. For this work, pure copper (99.99 mass%) sheets with thickness of 5 mm were prepared as the starting material. The sheets were cold rolled to 90% thickness reduction and subsequently annealed at $400^{\circ}C$ for 30 min. Also, to analyze the grain boundary character distributions (GBCDs) on the materials, the electron back-scattered diffraction (EBSD) technique was introduced. The resulting cold-rolled and annealed sheets had considerably finer grains than the initial sheets with an average size of 100 ${\mu}M$. In particular, the average grain size became smaller by cross-roll rolling (6.5 ${\mu}M$) than by conventional rolling (9.8 ${\mu}M$). These grain refinements directly led to enhanced mechanical properties such as Vickers micro-hardness and tensile strength, and thus the values showed greater increases upon cross-roll rolling process than after conventional rolling. Furthermore, the texture development of <112>//ND in the cross-roll rolling processed material provided greater enhancement of mechanical properties relative to the case of the conventional rolling processed material. In the present study, we systematically discuss the enhancement of mechanical properties in terms of grain refinement and texture distribution developed by the different rolling processes.

• 한국수산과학회지
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• 제20권3호
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• pp.208-212
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• 1987

인스탄트 면제품의 영양강화와 고기풀의 이용도 증대를 위하여 인스탄트면제품 가공시 고기풀 $10\%,\;20\%,\;30\%$를 각각 첨가하여 그 품질을 조사하였다. 그 결과를 요약하먼 다음과 같다. 제품의 단백질 함량은 고기풀 $10\%$ 첨가시에는 $1.5\%,\;30\%$를 첨가한 때는 $4.4\%$까지 단백질 량을 증대시킬 수 있었다. 특히 밀가루에 부족한 lysine은 명태 냉동고기풀을 $20\%$ 첨가하여 무첨가 면제품에 비해 $333.2mg\%$가 증가하여 2.5배 정도 강화 효과가 있었다. 조리후 면의 중량과 부피 및 경도는 고기풀의 첨가량이 많을수록 증가하는 경향을 보였고 국물의 탁도와 면발의 인장력은 반대로 감소하는 경향을 보였다. 관능검사 결과 고기풀의 첨가량이 증가할수록 향미와 색택은 무첨가 제품에 비해 높은 기호도를 보였고 조직감에 있어서는 고기풀 $10\%$ 첨가수준에서 기호도가 가장 높았다.

• Elastomers and Composites
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• 제33권3호
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• pp.193-200
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• 1998

고무소재는 다양한 종류별로 구조에 따라 다른 물성을 갖는 것으로 알려져 있다. 일반적으로 EPDM 고무는 내후성과 내오존성이 뛰어나고 열이나 냉기, 습기의 노출에도 잘 견디는 것으로 밝혀진 바 있다. 한편 crosslinked IIR은 물과 기체투과에 대한 저항성이 큰 것으로 알려져 두가지 성분의 장점을 갖도록 EPDM/crosslinked IIR의 블렌드를 새로운 형태의 소재로 추천할 수 있다. 따라서 본 실험에서는 EPDM과 crosslinked IIR의 블렌드비를 변화시키면서 가교시간과 블렌드후 물리/화학적 특성의 개선을 목표로 하였다. 결과적으로 30wt.%의 crosslinked IIR 조성을 갖는 블렌드소재가 내후성, 내오존성 및 내기체투과 특성이 뛰어나, O-링이나 전기관련 제품에 상업적으로 응용가능한 것으로 판단되었다.

• 한국분말재료학회지
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• 제20권6호
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• pp.467-473
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• 2013

This research presents a preparation method of dental components by metal injection molding process (MIM process) using titanium scrap. About $20{\mu}m$ sized spherical titanium powders for MIM process were successfully prepared by a novel dehydrogenation and spheroidization method using in-situ radio frequency thermal plasma treatment. The effects of MIM process parameters on the mechanical and biological properties of dental components were investigated and the optimum condition was obtained. After sintering at $1250^{\circ}C$ for 1 hour in vacuum, the hardness and the tensile strength of MIMed titanium components were 289 Hv and 584 MPa, respectively. Prepared titanium dental components were not cytotoxic and they showed a good cell proliferation property.

• 한국재료학회지
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• 제23권11호
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• pp.607-612
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• 2013

A powder in sheath rolling method was applied to the fabrication of a carbon nano tube (CNT) reinforced aluminum composite. A 6061 aluminum alloy tube with outer diameter of 31 mm and wall thickness of 2 mm was used as a sheath material. A mixture of pure aluminum powder and CNTs with a volume content of 5% was filled in the tube by tap filling and then processed to an 85% reduction using multi-pass rolling after heating for 0.5 h at $400^{\circ}C$. The specimen was then further processed at $400^{\circ}C$ by multi-pass hot rolling. The specimen was then annealed for 1 h at various temperatures that ranged from 100 to $500^{\circ}C$. The relative density of the 5vol%CNT/Al composite fabricated using powder in sheath rolling increased with increasing of the rolling reduction, becoming about 97% after hot rolling under 96 % total reduction. The relative density of the composite hardly changed regardless of the increasing of the annealing temperature. The average hardness also had only slight dependence on the annealing temperature. However, the tensile strength of the composite containing the 6061 aluminum sheath decreased and the fracture elongation increased with increasing of the annealing temperature. It is concluded that the powder in sheath rolling method is an effective process for fabrication of CNT reinforced Al matrix composites.

• Elastomers and Composites
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• 제51권2호
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• pp.113-121
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• 2016

Magneto-rheological elastomer (MRE) is a material which shows reversible and various modulus under magnetic field. Comparing to conventional rubber vibration isolator, MREs are able to absorb broader frequency range of vibration. These characteristic phenomena result from the orientation of magnetic particle (i.e., chain-like formation) in rubber matrix. In this study, silicone rubber was used as a matrix of MREs. Carbonyl iron particle (CIP) was used to give magnetic field reactive modulus of MRE. The surface of the CIP was modified with chemical reactants such as silane coupling agent and poly(glycidyl methacrylate), to improve interfacial adhesion between matrix and CIP. The mechanical properties of MREs were measured without the application of magnetic field. The results showed that the tensile strength was decreased while the hardness was increased with the addition of CIP. Also, surface modification of CIP resulted in the improvement of physical properties of MRE, but the degree of orientation of CIP became decreased. The analysis of MR effect was carried out using electromagnetic equipment with various magnetic flux. As the addition of CIP and magnetic flux increased, increment of MR effect was observed. Even though the surface modification of CIP gave positive effect on the mechanical properties of MRE, MR effect was decreased with the surface modification of CIP due to decrease of CIP orientation. Throughout this study, it was found that the loading amounts of CIP affected the mechanical properties of MRE, and surface property of CIP was an important factor on MR effect of MRE.