Papers by Keyword: In Situ Observation

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Authors: Hidenori Terasaki, Zhang Shouyuan, Yu Ichi Komizo
Abstract: A hybrid in-situ observation system has been developed to study the phase transformation behaviour simultaneously in both real and reciprocal lattice space. This paper presents the development of the observation system. Furthermore, as an example of the application of our developed system, martensitic transformation of Cr–Ni steel along a designed thermal cycle was in-situ tracked with the developed system. As a result of analysing the time-resolved X-ray diffraction data for the observed target, our system could directly detect the effect of transformation strain on austenite during martensitic transformation.
1255
Authors: Hiroshi Fukushima, Masanobu Azuma, Yukihiro Kanechika
Abstract: A high temperature HRTEM holder equipped with a W-coil heater was used to make insitu observation of high temperature behavior of Al2O3 very thin (about 1 nm in thickness) protective film on AlN particles. The film was used to prevent AlN particles from damages by moisture. Rapid melting and rapid solidification of very small Al2O3 particles of about 2 nm in diameter were found within about 0.2 seconds. Therefore we concluded that the Al2O3 protective film worked as the sintering additives in the high temperature heating process. In the present study, very small Al2O3 particles were identified by the space between observed lattice fringe images. It was found that a tilt boundary was instantaneously formed and annihilated in an Al2O3 particle. There was also evidence that showed the formation and annihilation of edge dislocations within seven seconds during sintering.
123
Authors: Christoph Günster, Dmitri A. Molodov, Günter Gottstein
Abstract: The results of investigations of magnetically driven grain boundary migration in high purity (99.995%) zinc bicrystals are presented. In-situ measurements were conducted by means of a specially designed and fabricated polarization microscopy probe. The migration of planar tilt grain boundaries with various misorientation angles in the range between 60° and 90° was studied. The absolute grain boundary mobility and its temperature dependence was measured in the regime between 330°C and 415°C and the corresponding migration activation parameters were determined. The results revealed that there is a pronounced misorientation dependence of grain boundary mobility in the investigated angular range. The migration activation enthalpy was found to vary between 1.18 eV and 2.15 eV. The obtained activation parameters comply with the compensation law, i.e. the migration activation enthalpy changes linearly with the logarithm of the pre-exponential factor.
467
Authors: Tsuyoshi Furushima, Tetsuro Masuda, Kenichi Manabe
Abstract: To understand the free surface roughening phenomena of polycrystalline metals, the surface roughening behaviors of three kinds of metal sheets were investigated under uniaxial tension. The materials used were AZ31 magnesium alloy, SPFC 590Y steel, and A5052-O aluminum alloy. In the in-situ observation of surface roughening for AZ31 magnesium alloy, it seemed that the surface of each grain roughened independently and the roughness increases with increasing plastic strain. In contrast to A5052-O and SPFC, the anisotropy of free surface roughening was observed for AZ31 magnesium alloy. Compared with planar anisotropy , the microscopic anisotropy of surface roughening is not related to . In AZ31 magnesium alloy, the anisotropy of surface roughening arises and, instead of the r-value, another parameter is needed to evaluate the anisotropy of free surface roughening.
450
Authors: Alisa Boonyapookana, Yoshiharu Mutoh, Kohsoku Nagata
Abstract: In-situ observation of fatigue crack growth of epoxy resin composite reinforced with crushed silica particle was carried out. The test was performed under constant ΔK condition. Based on the results, the crack propagation mechanism was discussed. The in-situ observation revealed that in front of the main crack, a microcrack was nucleated at the interface of matrix/particle and then coalesced with the main crack. At the same time, new microcracking occurred ahead of the crack tip and the crack propagated by repeating these processes. Retardation of crack growth rate was found to result from crack bridging induced by microcracking at silica particles and crack deflection.
753
Authors: Yan Wang, Noriyuki Hirota, Hidehiko Okada, Tie Liu, Qiang Wang, Yoshio Sakka
Abstract: The effect of high magnetic field on diamagnetic fluid flow has been studied by in-situ optical observation. The Schlieren optics utilizable under high magnetic fields was developed to carry out in-situ observation of the behavior of feeble magnetic fluids. Using a crystal of the diamagnetic aluminum potassium sulfate dodecahydrate, the behavior of the downward flow of high concentration solution in the sample dissolution process was observed. It was found that the direction of diamagnetic fluid flow was changed under spatially varied magnetic field. This phenomenon was understood qualitatively by considering the magnetic force acting on the high concentration solution and the surrounding solution.
188
Authors: Yasuhiro Yogo, Kouji Tanaka, Koukichi Nakanishi
Abstract: An in-situ observation method for structures at high temperature is developed. The new observation device can reveal grain boundaries at high temperature and enables dynamic observation of these boundaries. Grain growth while maintaining microstructure at high temperature is observed by the new observation device with only one specimen for the entire observation, and grain sizes are quantified. The quantifying process reveals two advantages particular to the use of the new observation device: (1) the ability to quantify grain sizes of specified sizes and (2) the results of average grain size for many grains have significantly less errors because the initial structure is the same for the entire observation and the quantifying process. The new observation device has the function to deform a specimen while observing structures at high temperature, so that enables it to observe dynamic recrystallization of steel. The possibility to observe recrystallization is also shown.
1077
Authors: Xu Dong Yue, Guang Can Jin, Shu Ying Chen, Guo Wei Chang
Abstract: In situ observation of growth process of high temperature phase in 0.15% C carbon steel during solidification concerned with using Confocal Scanning Laser Microscope (CSLM), the growth rate of -phase has been measured. The results indicate that high temperature -phase grows at cell crystal way when the cooling speed reaches 2°C/min in 0.15% C carbon steel. The -phase of round or oval cross-sectional shaped may grow stably. The growth rate of -phase is gradually getting slow along with increasing of curvature radius. The variation of growth speed tends to be similar with different solid-liquid interface shapes of -phase. The growth rate of concave solid-liquid interface is faster than that of convex solid-liquid interface for phase. The smaller radius of curvature of phase is, the faster the growth rate reaches.
341
Authors: Rui Zhang, Shan Wu Yang, Chao Sun, Xin Lai He
Abstract: The dominant microstructures in low carbon bainite steels such as bainitic ferrite are non-equilibrium phases, which will tend to evolve into equilibrium phases when the steels are subjected to thermal disturbance. In-situ observation by optical and scanning electron microscopy was carried out in this investigation to track the evolution when the steels were isothermally held below A1 temperature. It is found that the primary polygonal ferrite grows slowly during isothermal holding, while bainitic ferrite changes rapidly into polygonal ferrite. Self-tempered bainitic ferrite would recover further and recrystallize. The lower the concentration product of carbon and niobium, the faster is the evolution.
126
Authors: Arne Kromm, Thomas Kannengiesser, Jens Gibmeier
Abstract: Tensile residual stresses introduced by conventional welding processes diminish the crack resistance and the fatigue lifetime of welded components. In order to generate beneficial compressive residual stresses at the surface of a welded component, various post-weld treatment procedures are available, like shot peening, hammering, etc. These post-weld treatments are, however time and cost extensive. An attractive alternative is to generate compressive stresses over the complete weld joint in the course of the welding procedure by means of so-called Low Transformation Temperature (LTT) filler materials. The volume change induced by the transformation affects the residual stresses in the weld and its vicinity. LTT fillers exhibit a relatively low transformation temperature and a positive volume change, resulting in compressive residual stresses in the weld area. In-situ measurements of diffraction profiles during real welding experiments using Gas Tungsten Arc (GTA)-welding process were realized successfully for the first time. Transformation temperatures during heating and subsequent cooling of LTT welding material could be assessed by means of energy dispersive diffraction using high energy synchrotron radiation. The results show that the temperature of martensite start (Ms) is strongly dependent on the content of alloying elements. In addition the results indicate that different phase transformation temperatures are present depending on the welding depth. Additional determination of residual stresses allowed it to pull together time and temperature resolved phase transformations and the resulting phase specific residual stresses. It was shown, that for the evaluation of the residual stress state of LTT welds the coexisting martensitic and austenitic phases have to be taken into account when describing the global stress condition of the respective material in detail.
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