Papers by Keyword: In Situ Observation

Abstract: In this paper, we present our new setup and technique for obtaining a real-time 3-D volume shape of the SiC crystal using X-ray computed tomography (CT). Hence, it is possible to determine in-situ the shape of the growth interface with high precision at growth temperatures above 2000 °C in a conventional 3" physical vapor transport (PVT) growth system. We show that the size and shape of a facet can be monitored at different stages during growth and furthermore the crystals face boundary can be determined with high precision throughout the whole growth process.

Abstract: The consolidation effect of vacuum combined with fill surcharge preloading always influenced by many factors including vacuum pressure, vertical load pressure and vertical drainage depth. As the way to improve the reliability of the method, based on the soil consolidation mechanisms and actual data getting from the laboratory test and in-situ test, the main indexes of the method were studied in this paper. The test results show that the ratio of the vacuum pressure and vertical load pressure can cause difference soil settlement-deformation, if the ratio close to 1 the consolidation effect of the foundation can be gradually advanced. The soil outside the embankment always has displacement to reinforcement region in the upper depth of the foundation soil when the vacuum pressure equals to the vertical load pressure.

Abstract: The δ-phase growth process of Fe-0.2%C-0.6%Mn steel during solidification was in-situ observed using Confocal Scanning Laser Microscope (CSLM). The effects of shape of solid/liquid interface on the growth rate were investigated. The results indicate the growth rate of concave-shaped solid/liquid interface is faster than that of convex-shaped solid/liquid interface at the beginning of δ-phase growth. The two kinds of growth rates decreased both and approached to the same gradually as the solidification continues. The intrinsic reasons were discussed in detail.

Abstract: The Ti-10Nb-5Sn alloy was heated and cooled repeatedly in a heater system located in transmission electron microscope chamber. The phase and morphology transformation was in situ observed to analyze the transformation mechanism from austenite β to martensite phase. The results reveal that he Ti-10Nb-5Sn alloy has round trip shape memory function.

Abstract: Close observation with a transmission electron microscope (TEM) and a scanning electron microscope (SEM) was performed for the growth process of tin (Sn) whiskers on lead (Pb)-free Sn-plating. Whiskers were formed on a Sn layer plated on Cu/polyimide flexible substrate. The whisker was found to be of a single crystal and have a characteristic "Y"-shaped grain boundary structure at its root. The growth process of a curling whisker was successfully observed in a continuous way in SEM. TEM observation revealed that the curling whisker had a single crystallographic orientation irrespective with its external shape. these microstructures indicate that the rearrangement of dislocations plays an important role in the growth process of whiskers.

Abstract: An in situ observation experiment of faceted cellular growth was carried out using transparent organic alloy, salol - t-butyl alcohol, in microgravity conditions on the International Space Station. The temperature and solute concentration fields in the vicinity of the solid-liquid and the growth rate were simultaneously measured by microscopic interferometers.

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.

Abstract: A novel set-up developed to continuously observe and measure stress driven grain boundary migration is presented. A commercially available tensile/compression SEM unit was utilized for in-situ observations of mechanically loaded samples at elevated temperatures up to 850°C by recording orientation contrast images of bicrystal surfaces. Two sample holders for application of a shear stress to the boundary in bicrystals of different geometry were designed and fabricated. The results of first measurements are presented.

Abstract: In this paper, in situ observation of fracture process of short carbon fibers/epoxy (SCF/EP) composites was researched. The samples were prepared firstly. And then, in order to get high quality reconstruction images of carbon fiber–epoxy composites, experiments of in situ static observation of SCF/EP composites were carried out. As results, static 2D and 3D reconstruction images of fiber-epoxy composites were obtained. At last, a special small tensile testing device which can be used to apply extraneous force to small samples was designed. Based on the above work, in situ observation of fracture process of composites will be realized most probably in the next work.

Abstract: X-ray microtomography (XMT) has been utilized for the in-situ observation of various structural materials under external disturbance such as loading. In-situ XMT provides a unique possibility to access the three-dimensional (3D) character of internal microstructure and its time evolution behaviours non-destructively, thereby enabling advanced techniques for measuring local strain distribution. Local strain mapping is readily enabled by processing such high-resolution tomographic images either by the particle tracking technique or the digital image correlation technique. Procedures for tracking microstructural features which have been developed by the authors, have been applied to analyse localised deformation and damage evolution in a material. Typically several tens of thousands of microstructural features, such as particles and pores, are tracked in a tomographic specimen (0.2 - 0.3 mm³ in volume). When a sufficient number of microstructural features is dispersed in 3D space, the Delaunay tessellation algorithm is used to obtain local strain distribution. With these techniques, 3D strain fields can be measured with reasonable accuracy. Even local crack driving forces, such as local variations in the stress intensity factor, crack tip opening displacement and J integral along a crack front line, can be measured from discrete crack tip displacement fields.