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Tensile deformation behavior and deformation twinning of an equimolar CoCrFeMnNi high-entropy alloy
Joo, S.-H.,Kato, H.,Jang, M.J.,Moon, J.,Tsai, C.W.,Yeh, J.W.,Kim, H.S. Elsevier 2017 Materials science & engineering. properties, micro Vol.689 No.-
<P><B>Abstract</B></P> <P>The tensile deformation and strain hardening behaviors of an equimolar CoCrFeMnNi high-entropy alloy (HEA) were investigated and compared with low and medium entropy equiatomic alloys (LEA and MEA). The HEA had a lower yield strength than the MEA because the addition of Mn weakens solid solution hardening in the HEA. However, deformation twinning induced the multiple stage strain hardening behavior of the HEA and enhanced strength and elongation. Using tensile-interrupted electron backscatter diffraction analysis, geometrically necessary dislocations were observed as plume-shaped features in grain interior, and a considerable texture was characterized, which is typical of face centered cubic metals. Moreover, the relationship between favorably oriented grains and twinning in the HEA bore a clear resemblance to the same tendency in TWIP steels. The thickness of the twin bundles was less than 100nm. A high density of stacking defects was found in the nanotwins. Nano twinning and stacking faults were found to contribute to the remarkable mechanical properties. Deformation induced twinning not only demonstrated the dynamic Hall-Petch effect but also changed dislocation cell substructures into microband structures.</P>
Correlation between Carbon Steel Corrosion and Atmospheric Factors in Taiwan
( C. M. Lo ),( L. H. Tsai ),( C. W. Hu ),( M. D. Lin ) 한국부식방식학회(구 한국부식학회) 2018 Corrosion Science and Technology Vol.17 No.2
Taiwan has a typical marine climate featuring perennial high-temperature and dampness. This climate, together with the emission of various industrial corrosive waste gases in recent years, contributes a lot to the corrosion of metal materials. In this study, samples of carbon steel exposed to various atmospheres in Taiwan were analyzed to investigate the impacts of atmospheric factors on carbon steel corrosion. Carbon steel samples were collected from 87 experimental stations between 2009 and 2012. Statistical analysis was employed to investigate the correlations between the carbon steel corrosion situations and the atmospheric factors such as concentrations of sulfur dioxide or chloride, exposure time, rainfall, etc. The results indicate that for samples from industrial areas, the sulfur dioxide concentration and exposure time during fall and winter are significantly correlated to the condition of the carbon steel corrosion. However, for samples from coastal zones, the significant correlated factors are chloride concentration and wetting time during winter. The results of this study are useful for the development of carbon steel corrosion prediction models.
Effect of Heat Treatment on the Pitting Corrosion Behavior of 347 SS Weld Overlay
Lo, I. H.,Lee, M. C.,Lin, K. Y.,Ho, W.,Yang, G. C. Y.,Tsai, W. T. 한국부식방식학회 2002 Corrosion Science and Technology Vol.31 No.5
The effect of heat treatment on the microstructural change and corrosion performance of 347 SS weld overlay has been investigated. The microstructure and phase changes of he as-weld and post weld heat-treated (PWHT) overlays were examined using optical microscropy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray analysis (EDS) was also used for intermetallic phase identification. The results showed that delta-ferrite transformation to sigma phase occurred for the as-weld overlay by PWHT at 690℃ for 8 hours. Pitting corrosion resistance of the weld with or without PWHT was evaluated by conducting potentiodynamic polarization tests in 3.5 % NaCl solution. The results showed that the presence of intermetallic phase greatly affected the pitting corrosion resistance of 347 SS weld overlay.