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In this work, synchrotron radiation rocking curve imaging (RCI) is used to visualize and characterize dislocations and second‐phase defects in a highly perfect and absorbing CdTe(Zn) crystal. This technique requires recording a series of Bragg diffracted images along the rocking curve to produce maps of the 'local' integrated intensity, full width at half‐maximum and peak position. The diffraction conditions of the reported experiment are such that anomalous transmission (Borrmann effect) is a crucial ingredient for the formation of the image of the defects. The images recorded and maps produced allow the investigation of a series of topics that, to the authors' knowledge, have not been previously studied. The first of these topics is the variation of the position and width of the Borrmann image of a defect when sitting on the peak and on the flanks of the diffraction curve. The second topic is the way Borrmann images show up on the usual RCI maps. The final topic is the combination of Borrmann and weak‐beam images to infer the depth of the defect within the crystal. [ABSTRACT FROM AUTHOR]

Basal slip of dislocations, the easiest deformation mechanism of ice crystals, does not allow a response to any strain state. The first steps of another mechanism, with a moving subgrain boundary precursor region, which permits accommodating the effect of an applied load, is investigated on an ice single crystal, mainly using synchrotron radiation Bragg diffraction imaging. During this process, the evolution of the local integrated intensity shows that there is both a general multiplication of dislocations within the crystal and a movement of basal dislocations towards the surface. The `subgrain boundary precursor' region evolves towards a classical grain boundary when further deformed. [ABSTRACT FROM AUTHOR]

Abstract: Directional solidification of multicrystalline silicon for photovoltaic applications is investigated by means of synchrotron X-ray imaging techniques at the European Synchrotron Radiation Facility. Our experimental device combines two complementary modes: X-ray radiography imaging giving information on the dynamical evolution of the solid/liquid interface and X-ray topography giving information on the grain structure and phenomena occurring during the solidification process such as strains and twinning. In this paper, we report on the experimental details of the developed device and on some preliminary results obtained by using both imaging techniques. [Copyright &y& Elsevier]

Hard x rays from a synchrotron source are used in this implementation of computed laminography for three-dimensional (3D) imaging of flat, laterally extended objects. Due to outstanding properties of synchrotron light, high spatial resolution down to the micrometer scale can be attained, even for specimens having lateral dimensions of several decimeters. Operating either with a monochromatic or with a white synchrotron beam, the method can be optimized to attain high sensitivity or considerable inspection throughput in synchrotron user and small-batch industrial experiments. The article describes the details of experimental setups, alignment procedures, and the underlying reconstruction principles. Imaging of interconnections in flip-chip and wire-bonded devices illustrates the peculiarities of the method compared to its alternatives and demonstrates the wide application potential for the 3D inspection and quality assessment in microsystem technology. [ABSTRACT FROM AUTHOR]

The analysis of gas release modes from irradiated materials during out-of-pile temperature transients and of the related microstructure evolution provides fundamental evidence for developing and validating models of the behaviour of gases in solids. Gas atoms are uniformly generated by nuclear reactions in the lattice. If temperature and/or gas concentration increase, gas atoms diffuse and precipitate into bubbles, then bubbles grow and coalesce until they form at grain boundaries porosity networks connected to the free surface. The formation of such percolation paths is related to the appearance of release bursts where most part of the gas inventory escapes. The morphology of percolation patterns determines the porosity limit necessary to start the percolation stage and finally affects the performance of the material in engineering applications.The gas percolation stage in a weakly irradiated beryllium sample, a 2 mm diameter pebble, has been examined by computer aided microtomography based on synchrotron radiation, with the aim to identify and qualitatively characterise the 3D morphology and topology of open porosity networks. [Copyright &y& Elsevier]

A furnace covering the temperature range from 298 to 1300 K has been designed and constructed to study in situ the structural evolution of materials by using synchrotron X-ray microtomography. The furnace has cylindrical symmetry, compatible with the required 180° rotation, small dimensions and low absorption. It can also be used for other scattering methods, such as diffraction. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a comparison between the in situ and real time observation of a directional solidification experiment carried out at the European Synchrotron Radiation Facility and a direct simulation of grain structure formation in the sample using a two-dimensional cellular automaton–finite element (CA-FE) model. In situ characterization of the columnar-to-equiaxed transition in a refined Al–3.5wt.% Ni alloy is achieved by synchrotron X-ray radiography. Two main characteristics are derived from the radiographs for each nucleated grain, namely the nucleation position in the sample and the orientation of the main trunk relative to the vertical temperature gradient. These data are then used as input for the CA-FE simulations. The CA-FE model takes into account the effects of macroscopic transport of heat, liquid momentum and solute mass on the development of the dendritic grain structure and vice versa. The influence of convection on macroscopic shape of the growth front, the grain structure, the microstructure distribution and macro-segregation is determined by a comparison between the experimental observations and results from the numerical simulations with and without fluid flow. Good qualitative agreement is obtained and limitations that are linked to the two-dimensional approximation and the need for direct tracking of the eutectic grain structure are pointed out. [Copyright &y& Elsevier]

Abstract: This paper addresses dendritic equiaxed growth during grain structure formation in alloy solidification, and focuses on the growth and interaction of primary dendrite arms, which drive and limit grain development, respectively. Dedicated solidification experiments on Al–10wt.% Cu alloy were carried out at the European Synchrotron Radiation Facility, enabling live observation by in situ and real-time synchrotron X-ray radiography. Equiaxed solidification was achieved by cooling nearly isothermal samples, and the growth of the grains was continuously monitored from the very early stages of solidification up to a state where changes in grain structure were no longer visible to the observer’s naked eye. The time evolution of individual equiaxed grains is analysed through measurements of the lengths and tip velocities of the primary dendrite arms driving grain growth. It is found that equiaxed dendrite propagation is characterized by two growth regimes. The first regime, in which a gradual increase in the tip growth rate is observed, corresponds to free dendritic growth, when the relative distance between grains is large enough to consider a grain as isolated. During this regime, the far-field liquid concentration ahead of the advancing dendrite tip remains constant, equal to the initial alloy composition, and the driving force for growth is the undercooling applied by cooling of the sample, in agreement with three-dimensional models of free dendritic growth. The second regime shows a decrease in the tip velocity towards zero and is attributed to grain interaction when the solute diffusion field in front of the advancing dendrite tip under consideration overlaps with the solute field associated with the growth of the grain(s) facing it. Solute concentration profiles are measured in the extra dendritic liquid ahead of dendrite tips interacting with neighbour grains, from which the far-field solute concentration and neighbour–interaction distance are deduced. These measurements confirm that impingement of the solute boundary layers is the main cause of dendrite growth being slowed down and stopped. [Copyright &y& Elsevier]

Abstract: In situ monitoring of the initial transient of directional solidification was carried out by means of synchrotron X-ray radiography. Experiments with Al–4wt.% Cu alloy samples were performed on beamline ID19 of the European Synchrotron Radiation Facility (ESRF) in a dedicated Bridgman-type furnace. X-ray radiography enabled a detailed analysis of the evolution over time of the solid–liquid interface macroscopic shape in interaction with convection in the melt. Lateral solute segregation induced by fluid flow resulted in a significant deformation of the solid–liquid interface. The time-dependent velocity of the solidification front was determined at different abscissa values along the curved interface during the solidification process, from the growth phase with a smooth interface to the onset of morphological instability. Further, using a novel quantitative image analysis technique we were able to measure longitudinal solute profiles in the melt during the initial transient. Solutal length was then deduced as well as concentration in the melt, both at the interface and far away from it. The influence of convection on growth velocity and the characteristic parameters of the solute boundary layer are discussed, and a comparison with the Warren and Langer model is also presented. [Copyright &y& Elsevier]

Abstract: The phenomena involved during equiaxed growth, which is the most common growth morphology in metal casting, are dynamic. Therefore, in situ investigation is necessary to fully analyse the microstructure formation. Synchrotron X-ray radiography has become a major tool for in situ characterization of solidification in metallic systems. This paper reports on dedicated equiaxed solidification experiments carried out at the European Synchrotron Radiation Facility (ESRF) in Grenoble-France on Al–10wt.% Cu alloy. The analysis is based on the recorded images obtained through absorption radiography. Equiaxed growth is achieved in nearly isothermal conditions and observed continuously in real time from the early stages of solidification to the final state. The evolution of the dendrite arm lengths and the corresponding growth rates are analysed for two couples of grains in relation with their environment. This analysis suggests that the solutal interaction is dominant between equiaxed grains. [Copyright &y& Elsevier]

Abstract: The three-dimensional (3D) distribution of defects was investigated in several crystals by synchrotron radiation diffraction tomography. This experimental procedure combines white-beam synchrotron radiation section topography with electronic image recording and computer data processing. A scan involving many section topographs is performed with the same Bragg reflection, resulting in a stack of section topographs containing the 3D information. [Copyright &y& Elsevier]

Abstract: Among solidification processes, the columnar to equiaxed transition (CET) and equiaxed growth are still raising issues both from the metallurgical point of view and for the understanding of the fundamental related physical phenomena. The phenomena involved are complex and most of the time intimately related to the dynamical events happening during the solidification. Bridgman solidification of Al–Ni alloys is performed at the ID19 beamline of the European Synchrotron Radiation Facility (ESRF) in Grenoble. The use of a third generation synchrotron X-ray source allows for in situ and real-time observation of the solid–liquid interface, in particular at the CET. To provoke the CET, refined alloys are used and the pulling rate is increased following several profiles. The experiments give direct access to specific behaviours and enable the measurement of several key parameters during the CET and equiaxed growth, which can be discussed. [Copyright &y& Elsevier]

Abstract: The porosity was studied using coherent synchrotron X-ray radiography, firstly in several bulky icosahedral Al–Pd–Mn quasicrystals, grown in different laboratories by various techniques (Bridgman, Czochralski, Flux) and then in quasicrystal grains of many other alloys and structures (Part II). In this part I, we report a quantitative analysis which has been carried out in order to find some correlation of this porosity with some growth or after-growth cooling parameters (growth parameters). The size distribution of pores was observed to change drastically among samples grown with different growth parameters as well as in those extracted from the same ingot and no mode values were evidenced when we plotted the distribution of pores in all investigated as-grown samples. These changes point out the influence of the solidification process on the occurrence of porosity, especially the influence of the vacancy migration. These results are used to discuss the two main current hypotheses on the origin of porosity. [Copyright &y& Elsevier]