Volumes 475-479

doi: 10.4028/

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Authors: Rui Long Zong, Ji Zhou, Shi Kao Shi, Long Tu Li
Abstract: We have improved an electrochemical process in which the alternate current (AC) electrodeposition combined with the etching of substrate to prepare transparent metallic nanoparticles and anodic alumina oxide (AAO) composite films. The new process greatly simplifies the direct current (DC) electrodeposition process to get transparent composite films. Moreover, the electrocrystallization mechanism has been analyzed. The Ag, Cu and Ag-Cu co-deposited nanoparticles/AAO films have distinct absorption peaks, which can be ascribed to the surface plasmon resonance (SPR) of these noble metal nanoparticles.
Authors: I. Kaplan-Ashiri, S.R. Cohen, K. Gartsman, R. Rosentsveig, V. Ivanovskaya, T. Heine, G. Seifert, H.D. Wagner, R. Tenne
Abstract: The Young’s modulus of WS2 nanotubes is an important property for various applications. Measurements of the mechanical properties of individual nanotubes are challenging because of the small size of the tubes. Lately, measurements of the Young’s modulus by buckling of an individual nanotube using an atomic force microscope1 resulted in an average value of 171GPa. Tensile tests of individual WS2 nanotubes were performed experimentally using a scanning electron microscope and simulated tensile tests of MoS2 nanotubes were performed by means of a densityfunctional tight-binding (DFTB) based molecular dynamics (MD) scheme. Preliminary results for WS2 nanotubes show Young’s modulus value of ca.162GPa, tensile strength value of ca. 13GPa and average elongation of ca. 12%. MD simulations resulted in elongation of 19% for zigzag and 17% for armchair MoS2 single wall nanotubes. Since MoS2 and WS2 nanotubes have similar structures the same behavior is expected for both, hence there is a good agreement regarding the elongation of WS2 nanotubes between experiment and simulation.
Authors: Soon Suk Yun, Young Won Chang
Authors: Jin Xu Li, Takahito Ohmura, Fu Gao Wei, Kaneaki Tsuzaki
Abstract: Nanoindentation technique was applied to evaluate nanohardness distribution in a submicron scale for two kinds of martensitic steels: Fe-0.4C binary steel and Fe-0.05C-0.22Ti steel with a stoichiometric composition of TiC. AFM images showed that Fe-C steel includes relatively coarse cementite particles with about 100~200 nm in diameter and a couple of hundreds nanometer in average spacing, while high-resolution TEM observation showed that the Fe-C-Ti steel has fine TiC precipitates with 5 nm in diameter and 15 nm for average spacing. Nanoindentation results revealed that the standard deviation was much higher for the Fe-C than that for the Fe-C-Ti. Since the typical indent size was a couple of hundreds nanometer, which was about two orders larger than the size of the TiC and comparable to the cementite size, the small distribution of nanohardness of the Fe-C-Ti was attributed to the homogeneous microstructure in sub-micron scale, while the inhomogeneity of cementite particles in the Fe-C steel leaded to large nanohardness.
Authors: Takahito Ohmura, Kaneaki Tsuzaki
Abstract: Nanoindentation measurements were performed for Fe-C based martensitic steels, and then the strengthening factors such as grain boundary effect were evaluated. Nanohardness of the matrix of the martensite is lower than that expected from macroscopic hardness, indicating that the grain boundary effect is significant for the macroscopic strength of the Fe-C martensite. A remarkable decrease of the grain boundary effect was found at the tempering temperature of 673 K, which is due to a disappearance of film-like carbides on grain boundaries. These results will be discussed in light of the interpretations of grain boundary strengthening.
Authors: C.S. Kim, S.I. Kwun
Abstract: Ultrasonic nondestructive evaluation (NDE) technique has been applied to investigate the cyclically deformed microstructures of a Cu and Cu-35Zn alloy. These materials, which had different stacking fault energies, were cyclically deformed in order to examine the ultrasonic reaction with different dislocation substructures. The observation of a dislocation structure using TEM and the measurement of the ultrasonic NDE parameters were performed after various fatigue deformation in order to clarify the relationship between them. The ultrasonic velocity was observed to decrease with increasing fatigue life fraction in both materials, which was attributed to the increasing dislocation density, resulted from the cyclic deformation. The increasing rate of ultrasonic attenuation in Cu with a cell structure that evolved during cyclic deformation was higher than that in the Cu-35Zn alloy, which had a planar array. This suggests that the dislocation cell structure is more sensitive to the change in the ultrasonic parameters than the planar array structure formed during cyclic deformation.
Authors: Hyun Chul Cho, In Sup Kim
Abstract: Tensile properties of SA508 Cl.3 reactor pressure vessel (RPV) steel were investigated at room temperature and at 288 °C before and after hydrogen charging by electrolysis. At room temperature, the charged hydrogen induced distinct hardening and ductility loss, where quasi-cleavage features were observed around inclusions. These results may be due to interactions between the dissolved hydrogen and dislocations and an increase of hydrogen concentration near the inclusions. On the other hand, at 288 °C, the charged hydrogen induced some softening, which was explained in terms of the hydrogen shielding effect, and of strain localization by dynamic strain aging (DSA). Further, at 288 °C, the fracture surfaces of the hydrogen-charged specimens showed brittle regions, where the hydrogen might have been trapped in microvoids, leading to internal pressurization.
Authors: Yo Sep Yang, S.Y. Park, Hyun Jo Jun, Chan Gyung Park, S.H. Lim, D.Y. Ban
Abstract: Effects of microstructural parameters on fatigue resistance (σFL) of the steel tire cords have been investigated experimentally from microscopic points of view. At first, microstructural parameters depending on carbon content have been identified by using transmission electron microscopy (TEM). The fatigue resistance of the steel tire cords depending on carbon content has been measured by using the Hunter rotating beam tester under the bending stress of 900 to 1500 MPa. The fatigue resistance was improved with increasing the carbon content from 0.7, 0.8 to 0.9 wt. % C, due to variations of microstructural parameters, such as lamellar spacing (λp), cementite thickness (tc), and volume fraction (Vc) of cementite. As the carbon content increased, the lamellar spacing and the cementite thickness decreased, while the volume fraction of cementites increased. The effects of microstructure on fatigue resistance have been discussed in terms of the microstructural parameters mentioned above.
Authors: J.H. Yoon, I.S. Kim, H.S. Kim, I.C. Hur, K.S. Son, Je Hyun Lee, H.S. Kim
Abstract: Mechanical and corrosion properties were evaluated in the nitrided and non-nitrided specimens of ASTM 355 and SUS422 steels. The oxides formed on the specimen were analyzed using by XRD and the weight change was measured after oxidation test at high temperature, high pressure, and steam conditions. The oxidation behaviors and rates between two alloys and nitrided/non-nitrided specimens were clearly different. XRD analysis showed that the nitrides formed on the nitrided specimen were composed of CrN, Fe4N, and Fe2-3N. Also, it was found that the hardness on the nitrided specimen at 283°C decreased from Hv 1150 of room temperature to Hv 425.
Authors: I.S. Kim, H.S. Kim, I.C. Hur, K.S. Son, Je Hyun Lee, J.H. Yoon, H.S. Kim
Abstract: ASTM A355, SUS422 and Nimonic 901 steel were nitrided and their wear characteristics such as the wear coefficient, amount of wear, shape and composition of wear debris were evaluated. Fe3N and Fe4N were observed in the nitrided layer of ASTM A355. Fe3N, Fe4N and CrN were appeared in the nitride of SUS422. However, only CrN phase was observed in the layer of Nimonic 901. The amount of wear and wear coefficient for the nitride specimen decreased remarkably compared with non-nitrided specimens. Also, the surface hardness and ductility increased and small debris was formed in the nitrided specimen.

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