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조용덕,Xue Li,조동민,최병상 조선대학교 공학기술연구원 2019 공학기술논문지 Vol.12 No.2
An investigation of microstructure changes in a new, in situ-fabricated, three-dimensionally interconnected graphene-networked Cu composite was performed in relation to the heat treatment temperature in H2 and in air. Heat-treated in H2 revealed that recrystallization commenced at ~ 300 ℃ and the crystal grew afterward. However, the crystal growth was constrained within the initial Cu grains and inhibited due to Cu grains being wrapped by the stable graphene, even at 1000 ℃. This resulted in similar or narrower grain-size distribution. Meanwhile heat treatment in air resulted in the oxidation of carbon, instability of graphene, and crystal growth over the grain boundaries, which resulted in a wider grain-size distribution. Increases in tensile and plastic deformation (30% and 144%, respectively) were observed due to the grain size refinement and the strong interfacial bonds between graphene and the Cu matrix. The result was greater load bearing and toleration of a substantial load during plastic deformation.
Soft Nano Optics Using Plasmonics-High Index Dielectric Hybrid Metalmolecules
조용덕,이승우 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.1
나노광학에 있어 빛과 물질간의 서브 파장영역(subwavelength)에서 상호작용을 극대화하기 위해 다양한 나노물질들이 연구되어 왔다. 특히, 고 굴절률 유전 물질과 함께 메탈을 이용한 플라즈모닉스 연구는 각각의 장점을 이용하여 많은 발전을 해왔다. 고 굴절 유전물질은 높은 Q 인자값을 이용하는 한편 플라즈모닉스는 작은 모드 체적을 이용한 연구들을 진행하여 왔으며 각각 이에 맞는 응용분야들이 발전해 왔다. 하지만, 최근 이 두 물질의 광학적 특성을 동시에 갖는 새로운 연구분야가 각광을 받게 되었고 고굴절률 유전물질과 메탈의 하이브리드 형태인 나노 구조체 합성을 통하여 이러한 광학적 특성 연구들이 진행되었다. 이에 본 연구는 이러한 하이브리드 형태의 나노 구조체를 실제 합성적으로 구현하고 이들의 광학적 특성인 높은 Q 인자와 낮은 모드 체적을 이용하여 다양한 응용분야(directional scattering, fano resonance, SERS)등을 분석하고 보고하고자 한다.
고강도 냉간압조용 중탄소 Cr-Mo 합금강의 고온변형특성 및 동적재결정 거동 평가
조용덕,이희주,남성실,강현우,장병록 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.6
The hot deformation behavior of medium-carbon Cr-Mo alloy, which has been developed for high strength cold-heading quality wire rod, was investigated to evaluate its hot workability. A flow curve was derived using the hot torsion test, under conditions with temperatures of 1173-1273 K and strain rates of 0.1- 1.0 s-1. At lower deformation temperature and higher strain rate, the overall stress of the flow curve increased, and the flow curve showed a three-stage variation related to the offset of dynamic recrystallization and dynamic recovery. First, as the strain increased, the stress also increased due to work hardening, and reached peak stress. After that, the stress decreased due to softening of the dynamic recrystallization. And when the effect of the dynamic recrystallization and the dynamic recovery reached equilibrium, the stress became steady state. In this paper, the constitutive equation of the peak stress was established using a form of a hyperbolic sine function, and here the thermal activation energy for deformation of the specimen was 244.90 kJ/mol. The peak stresses calculated from the constitutive equation were in good agreement with the experimental results. The dynamic-recrystallized grains were observed using electron backscatter diffraction (EBSD). It showed that the volume fraction of dynamic recrystallization increased as the strain increased under hot deformation. Based on the Avrami kinetic equation, a dynamic recrystallization kinetic model was established. The volume fraction of dynamic recrystallization was predicted from the kinetic model, and can be applied at arbitrary deformation temperatures and strain rates.