Papers by Keyword: Dislocation Structure

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Authors: Yoshihiro Sugawara, Y. Yao, Yukari Ishikawa, Katsunori Danno, Hiroshi Suzuki, Takeshi Bessho, Yoichiro Kawai, Yuichi Ikuhara
Abstract: We developed the transmission electron microscopy (TEM) sample preparation technique for the low dislocation density of 4H-SiC by combining the KOH+Na2O2 (KN) etching and the focused ion beam (FIB) microsampling technique. The dislocation under sea-shell pit was then characterized by large-angle convergent-beam electron diffraction (LACBED). It is demonstrated that this method is powerful for evaluating Burgers vectors of dislocations. Burgers vector of the measured basal plane dislocation (BPD) is determined to be b=1/3[-12-10]. Two-beam bright-field (TBBF) imaging identified the rotating direction of the threading screw dislocation (TSD) is counter-clockwise.
Authors: Jenő Gubicza, Iuliana C. Dragomir, Gábor Ribárik, Yuntian T. Zhu, Ruslan Valiev, Tamás Ungár
Authors: Milan Heczko, Philippe Spätig, Hans Peter Seifert, Tomáš Kruml
Abstract: Load-controlled experiments were conducted to study the influence of mean stress on the fatigue behavior of 316L austenitic stainless steel at the temperature of 288°C in air and light water reactor (LWR) conditions. Water environment was characterized by high-purity, neutral water with 150 ppb dissolved hydrogen. The internal dislocation structures of the material were investigated by means of transmission electron microscopy (TEM). The formation of dislocation structures for different loading conditions and different mean stresses was assessed and discussed in relation to the cyclic stress-strain response of the material as well as the effects of non-zero mean stress conditions. All findings were considered to discuss the fatigue softening/hardening behavior and the influence of mean stress on the fatigue life of material in the LWR environment.
Authors: Yoko Yamabe-Mitarai, Hiroshi Harada
Authors: Toshiyuki Fujii, Shizuma Uju, Chihiro Watanabe, Susumu Onaka, Masaharu Kato
Abstract: Fully reversed tension-compression fatigue tests were performed on solid-solutioned Al-0.7mass%Mg single crystals with a single slip orientation under constant plastic-strain amplitudes. Dislocation microstructures were quantitatively examined by transmission electron microscopy. The cyclic stress–strain curve (CSSC) exhibited three distinct regions with a short plateau region in the intermediate plastic-strain amplitude range, and the plateau stress was 26MPa. Characteristic microstructures were developed corresponding to the three regions in the CSSC. Vein structure was observed at the low strain-amplitude region. In the plateau regime, the persistent slip bands (PSBs) were observed. Labyrinth structure was also observed at the higher strain-amplitude region. The plateau stress, the cyclic flow stress of PSBs, can be explained by considering not only the Orowan bowing stress and the dipole passing stress of screw dislocations but also solid-solution hardening by Mg atoms.
Authors: Keizo Hashimoto, Rieko Matsumoto
Abstract: In this study, Nb doped γ-TiAl is designed and examined their tensile properties at elevated temperatures. Small compositional changes cause drastic changes of the mechanical properties at 1273K. In order to clarify the deformation mechanism at elevated temperatures, dislocation structures have been observed using transmission electron microscope (TEM). All of the specimens observed by TEM show that at least two slip systems are operating in each grain. The specimen having relatively lower strength and higher tensile elongations shows more than four operating slip systems in the grains. The specimen having a medium strength shows many super-dislocations and their dissociations that block the other dislocation motions. The specimen having the highest strength shows many deformation twins. These observations suggest that deformation twins become the strong obstacles against moving dislocations at elevated temperatures. The relationships between observed dislocation structures and mechanical properties of γ-TiAl are discussed.
Authors: Jung B. Singh, Apu Sarkar, Garima Sharma, V. Basavaraj, J.K. Chakravartty
Abstract: Development of microstructure and texture in alloy Al5052 deformed at room and cryogenic temperatures in an equal channel angular pressing (ECAP) die has been investigated. Billets were deformed using the Bc route up to 14 passes. Billets pressed at room temperature showed almost a 4 fold increase in the yield strength, which increased to about 320 MPa from about 90 MPa, while it increased to about 230 MPa in billets deformed at cryogenic temperature. At two deformation temperatures, grains were refined at more or less similar size reduction rate as a function of number of passes. However, for a given amount of strain, billets pressed at the two temperatures showed subtle differences in their microstructures and texture.
Authors: Yoko Yamabe-Mitarai, Y. Ro, Shizuo Nakazawa, Tomohiro Maruko, Hiroshi Harada
Authors: Martin Petrenec, Karel Obrtlík, Jaroslav Polák, Jiří Man
Abstract: Dislocations structures were studied using transmission electron microscopy in specimens of cast polycrystalline nickel based superalloy Inconel 792-5A cyclically strained up to failure with constant total strain amplitudes at temperatures 23 and 700 °C. Spatial arrangement of dislocations in individual grains was determined using the technique of oriented foils. Planar dislocation arrangements in the form of bands parallel to the {111} planes were observed in specimens cycled at both temperatures. The bands showed up as thin slabs of high dislocation density cutting both the γ channels and γ´ precipitates. They correspond to areas of cyclic slip localization. Experimental results concerning the dislocation structure are used to discuss the effect of temperature on the cyclic stress-strain response and fatigue life.
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