Papers by Keyword: In Situ Observation

Abstract: In-situ diffraction measurements were carried out on a tensile specimen of SUS304 stainless steel using a small autoclave at BL22XU at SPring-8. The temperature of circulating water in the autoclave was changed from room temperature to 561 K under ambient pressure and also under a pressure of 8.8 MPa. Tensile stress of 260 MPa was applied to the specimen at 561 K under 8.8 MPa, and a two dimensional strain distribution was obtained by calculation based on measured lattice spacings of the γ-Fe311 plane under various conditions. The interior region of the specimen showed higher strain compared with that on the surface region. After the tensile deformation in the autoclave, CT images of cross sections of the specimen were taken. Void-like images with about 50 μm in size were observed.

Abstract: Up to date very few organic substances have been reported that show a non-faceted/non-faceted (nf/nf) peritectic phase diagram in a temperature range suitable for direct observation in a micro Bridgman furnace setup. Sturz et al. [1] and Barrio et al. [2] studied the peritectic phase diagram for the organic model alloy TRIS (Tris(hydroxymenthyl)aminomethane) - NPG (Neopentylglycol). The phase diagram is based on thermal analysis by means of DSC measurements [1, 2] and evaluation of lattice parameters measured with x-ray diffractometry [2]. In the current work we present investigations on the system TRIS – NPG that have been obtained by optical investigations of directional solidification in a micro Bridgman-furnace with various initial alloy concentrations and pulling rates in a fixed temperature gradient. The phase diagram [1, 2] was confirmed by direct comparison of DSC measurements and optical investigations. Furthermore we present in situ observations of solidification in the peritectic region. They show a solidification behavior that was clearly distinguishable from the solidification in hyper- and hypoperitectic regions of the phase diagram.

Abstract: Since the liquid / liquid separation occurs in hypermonotectic alloys and the liquid / liquid interface agitates mass transfer around solidifying front, it is rather difficult to achieve the aligned-rod structure. The high magnetic filed such as 10T achieved the aligned-rod structure in the Al-10at%In alloys. The in-situ observations of the monotectic solidification in the Al-10at%In alloys were performed using synchrotron radiation X-ray. Coarse and fine In rods coexisted during the unidirectional solidification without magnetic field. The local melt flow induced by the In-rich liquid / Al-rich liquid interface enhanced the mass transfer and consequently the coarse rods could continuously grow. The suppression of the local melt flow of which scale was several 10 m by the high static magnetic field resulted in the aligned-rod structure.

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.

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.

Abstract: A kind of in-situ crystal growth observation system for solution temperature reduction method was designed. The growth surface morphology of KDP crystal was observed by this system. Dislocation hillocks with elliptical shape were clearly distinguished on the {100} face. The dynamics process of morphology evolvement on growth surface of KDP crystals was recorded and analyzed. The growth velocity of the step trains generated from dislocation hillocks was about ~10-4.

Abstract: Unidirectional solidification for low-carbon steel weld metal was characterized by using Time-Resolved X-Ray Diffraction (TRXRD) system. Solid-state phase transformation was also insitu observed in reciprocal lattice space. It was shown that TRXRD analysis had a potential as a comprehensive characterization technique for solidification and phase transformation process in welding. It made for the growth behavior of dendrites in unidirectional solidification and α γ δ − − phase transformation in steel weld metal to be characterized.

Abstract: To study the fatigue microcrack initiation and propagation behaviors of cast magnesium alloys, the small fatigue crack propagation tests were carried out using the in-situ observation with scanning electron microscope (SEM). All initiations and propagations of fatigue small cracks focused on effects of the interaction of artificial two small holes, which there are the different distances and alignments of two small holes. The results indicate that the fatigue small cracks of cast magnesium alloys occurred mainly at the defects or root of notch but the early stage crack propagations were influenced on the distance and alignment between two small holes. For cast AM50 and AM60B alloys, the fatigue small cracking prior to occurred at the weak dendrite boundary and had some concomitances such as the plastic deformation on surface of α-Mg phase. For AZ91 alloy, the fatigue cracking characterization depended mainly on the brittle properties of β-Mg17Al12 phase, which the multi cracks occurred at the boundaries of β-Mg17Al12 phase. The effect of notch on the fatigue cracking behavior becomes weaker when the radius of notch is over 3-4 times than that of average α-Mg grain size. The fatigue crack propagation behaviors varied with the different arrangements of two small holes. The effects of distance and alignment of two small holes on the fatigue crack propagation behaviors are also obvious.

Abstract: The dynamic process of crack initiation and propagation in a SiC/BN-Al2O3 laminated composite was observed in situ by scanning electron microscopy. During a bending test with a single-edge notched-beam specimen, an interfacial crack first initiated in the interlayer near the notch tip, after which a through-thickness crack formed in the matrix layer at the notch tip. After the through-thickness crack had grown across the first matrix layer, it was deflected by the next interlayer and again became an interfacial crack. Interfacial cracks and through-thickness cracks were generated alternately until the composite failed. The load-displacement plot of the laminated composite exhibited several peaks, each caused by one propagation of a through-thickness crack. The toughening mechanisms of the laminated composite included crack deflection, interfacial cracking, and through-thickness branch cracking.

Abstract: The plasticity of a copper (Cu) nano-component is experimentally evaluated by a cantilever specimen with multi-layered structure. The cantilever is monotonically loaded by a diamond tip and the deflection at the free-end is precisely measured by a transmission electron microscope (TEM). The plastic deformation of the Cu nano-component is successfully monitored through the non-linear behavior of applied load, P, and cantilever deflection, δ. The plastic constitutive quation of the Cu component is inversely analyzed by finite element method (FEM) assuming that the component obeys the Ramberg-Osgood law. The parameters in the R-O law (σ0, n and α) are optimally fitted to reproduce the experimentally evaluated P-δ relation. The resultant parameter set is derived as (σ0, n, α) = (345 MPa, 3.2, 1.25). The Cu nano-component has a much higher yield stress and a hardening rate compared with the ones in a bulk Cu.