• Korean Journal of Materials Research
• /
• v.25 no.11
• /
• pp.607-611
• /
• 2015

The microstructural evolution of Grade 91 tempered martensite ferritic steels heat treated at $760{\sim}1000^{\circ}C$ for two hours was investigated using scanning electron microscopy(SEM), energy disperse spectroscopy(EDS), electron backscattered diffraction (EBSD), and transmission electron microscopy(TEM); a microhardness tester was also employed, with a focus on the grain and precipitate evolution process as well as on the main hardening element. It was found that an evolution of tempered martensite to ferrite($760{\sim}850^{\circ}C$), and to fresh martensite($900{\sim}1000^{\circ}C$), occurred with the increase of temperature. Simultaneously, the parabolic evolution characteristics of the low angle grain boundary(LAGB) increased with the increase of the heating temperature(highest fraction of LAGB at $925^{\circ}C$), indicating grain recovery upon intercritical heating. The main precipitate, $M_{23}C_6$, was found to be coarsened slightly at $760{\sim}850^{\circ}C$; it then dissolved at $850{\sim}1000^{\circ}C$. Besides this, $M_3C$ cementite was formed at $900{\sim}1000^{\circ}C$. Finally, the experimental results show that the hardness of the steel depended largely on the matrix structure, rather than on the precipitates, with the fresh martensite showing the highest hardness value.

• Korean Journal of Materials Research
• /
• v.22 no.1
• /
• pp.16-23
• /
• 2012

Research into the development of high strength (1 GPa) and superior formability, such as total elongation (10%), and stretch-flangeability (50%) in hot-rolled steel was conducted with a thermomechanically controlled hot-rolling process. To improve the overall mechanical properties simultaneously, low-carbon steel using precipitation hardening of Ti-Nb-V multimicroalloying elements was employed. And, ideal microstructural characteristics for the realization of balanced mechanical properties were determined using SEM, EBSD, and TEM analyses. The developed steel, 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V), consisted of ferrite as the matrix phase and second phase of granular bainite with fine carbides (20-50 nm) in both phases. The significant factor of the microstructural characteristics that affect stretch-flangeability was found to be the microstructural homogeneity. The microstructural homogeneity, manifest in such characteristics as low localization of plastic strain and internally stored energy, was identified by grain average misorientation method, analyzed by electron backscattered diffraction (EBSD) and hardness deviation between the phases. In summar, a hot-rolled steel having a composition 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V) demonstrated a tensile strength of 998 MPa, a total elongation of 19%, and a hole expansion ratio of 65%. The most important factors to satisfy the mechanical property were the presence of fine carbides and the microstructural homogeneity, which provided low hardness deviation between the phases.

• Journal of Powder Materials
• /
• v.21 no.4
• /
• pp.271-276
• /
• 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.

• Korean Journal of Metals and Materials
• /
• v.47 no.5
• /
• pp.274-282
• /
• 2009

To investigate the evolution of deformation texture in dual phase (DP) steels during deep-drawing deformation, deep-drawing experiments were performed. Microtexture measurements were conducted using electron backscattered diffraction (EBSD) to analyze texture evolution. A rate-sensitive polycrystal model was used to predict texture evolution during deep-drawing deformation. In order to evaluate the strain path during deep-drawing deformation, a steady state was assumed in the flange part of a deep-drawn cup. A ratesensitive polycrystal model successfully predicted the texture evolution in DP steels during deep-drawing deformation. The final stable orientations were found to be strongly dependent on the initial location in the blank. Texture analysis revealed that the deep drawability of DP steels decreases as the true strain in the radial direction of the deep-drawn cup increases during deep-drawing deformation.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2016.11a
• /
• pp.139-139
• /
• 2016

반도체 다마신배선용 도금용 구리도금첨가제는 대표적으로 accelerator, suppressor 및 leveler 첨가제를 사용하여 다마신 패턴을 채우고 평탄화를 시킬 수 있다. Si 반도체 공정기술에 기반한 정확한 구조분석을 통해 각각의 첨가제의 기능이 비교적 체계적으로 연구되었으며, 최근에는 유속영향을 많이 받는 것으로 알려진 leveler 첨가제에 대한 연구가 활발히 진행되고 있다. 본 연구는 대표적 leveler 첨가제의 하나인 Janus Green B(JGB, $C_{30}H_{31}ClN_6$)를 0 ~ 1 mM을 첨가하여 Si 기판위에 증착된 Cu 씨드층 상의 도금후 표면상태 및 불순물의 농도를 분석하고, 이 박막층들의 결정립 성장 경향성을 electron backscattered diffraction(EBSD) 분석을 통해 진행하였다. C, H, N 등의 불순물이 JGB 농도와 선형적 관계를 가지고 증가하는 것을 알 수 있었으며, S와 O의 불순물도 JGB 농도 증가에 따라 증가하는 것을 알 수 있었다. 또한 0.1 mM 첨가한 경우에 60% 정도 결정립 성장이 진행된 것을 알 수 있었으며, 0.2 mM을 넣은 경우에는 결정립 성장이 일어나지 않은 것을 알 수 있었다. 흥미로운 점은 4 point probe를 통한 면저항 측정을 통해 EBSD를 통한 결정립성장이 관찰되지 않은 0.2 mM JGB를 첨가한 경우에 대해서도 면저항의 감소가 관찰되며, 오히려 JGB 농도가 높을수록 이러한 면저항의 감소가 빠르게 시작되는 것을 관찰할 수 있었다. 이는 JGB 농도 증가에 따라 박막층의 불순물의 농도가 증가하고 막내에 존재하는 불순물의 농도가 증가하면 내부응력장이 커짐으로 인해 더욱 빠른 속도로 불순물의 재배치가 일어난 것으로 보인다. 이러한 불순물이 결정립계면에 편석되는 경우에 pinning을 통해 결정립계면의 이동을 저하시킬 수 있으므로 결정립의 성장 억제가 가능해진 것으로 판단된다.

• Nuclear Engineering and Technology
• /
• v.53 no.8
• /
• pp.2629-2639
• /
• 2021

Within the frame of the EMPIrE test, four monolithic mini-plates were irradiated in the ATR reactor. In two of them, the monolithic U(Mo) foil had been PVD-coated with Zr before the plate manufacturing. Extensive microstructural characterizations were performed on a fresh archive mini-plate, using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectroscopy (EDS), Electron Backscattered Diffraction (EBSD) and Focused Ion Beam (FIB)/Transmission Electron Microscopy (TEM) with nano EDS. A particular attention was paid to the examination of the U(Mo) foil, the PVD coating, the cladding/Zr and Zr/U(Mo) interfaces. The Zr coating has a thickness around 15 ㎛. It has a columnar microstructure and appears dense. The cohesion of the cladding/Zr and Zr/U(Mo) interfaces seems to be satisfactory. An almost continuous layer with a thickness of the order of 100-300 nm is present at the cladding/Zr interface and corresponds to an oxidized part of the Zr coating. At the Zr/U(Mo) interface, a thin discontinuous layer is observed. It could correspond to locally oxidized U(Mo). This work provides a basis for interpreting the results of characterizations on EMPIrE irradiated plates.

• Journal of the Microelectronics and Packaging Society
• /
• v.25 no.3
• /
• pp.61-66
• /
• 2018

This research scrutinizes the self-annealing characteristics of copper used to metal interconnection for application of DRAM fabrication process. As the time goes after the copper deposited, the grain of copper is growing. It is called self-annealing. We use the electroplating method for copper deposition and estimate two kinds of electroplating chemicals having different organic additives. As the time of self-annealing is elapsed, sheet resistance decreases with logarithmic dependence of time and is finally saturated. The improvement of sheet resistance is approximately 20%. The saturation time of experimental sample is shorter than that of reference sample. We can find that self-annealing is highly efficient in grain growth of copper through the measurement of TEM analysis. The structure of copper grain is similar to the bamboo type useful for current flow. The results of thermal excursion characteristics show that the reliability of self-annealed sample is better than that of sample annealed at higher temperature. The self-annealed sample is not contained in hillock. The self-annealed samples grow until $2{\mu}m$ and develop in [100] direction more favorable for reliability.