Search

The Laue lens is an emerging technology that uses crystal diffraction to concentrate gamma-rays. The Darwin model describes diffraction in mosaic crystals at high energies (>50 keV) and is the basis for assessing the throughput of a Laue lens. While the Darwin model has been used successfully to describe binary alloys, it has shown inconsistencies when applied to diffraction with pure-metal crystals. This paper presents a systematic study of diffraction in pure-metal silver mosaic crystals and the performance of the Darwin model when applied to the data. Two cut silver crystals were tested at the Institute Laue–Langevin facility at three gamma-ray energies and at three different crystallographic orientations. The rocking curves were fitted using the Darwin model. A single Gaussian for the distribution of crystallite orientations leads to poor quality fits. A crystallite distribution that is the sum of two Gaussians gives improved fits. However, for each crystal, the Darwin model gives mosaicities and crystallite sizes that are not consistent with one another as a function either of energy or of crystallographic orientation, despite these being physical properties of the materials. Without an adequate model to describe diffraction in pure-metal crystals, either a Laue lens design must severely limit its catalogue of usable materials or each crystal in the design must be tested at the exact energy at which it is to be used. A more general theory to describe hard X-ray diffraction using pure-metal mosaic crystals, possibly involving a distribution of crystallite sizes, is therefore required.

The development of a Laue lens to focus soft gamma rays appears today as the only solution to improve significantly telescopes’ sensitivity and angular resolution in the 100 keV – 1 MeV domain. A Laue lens makes use of diffraction in the volume of a large number of crystal tiles carefully orientated to concentrate incident radiations from a large collecting area in a small focal spot. Various type of crystal have been measured and show excellent results, with angular spread of diffracting planes in the range 15-45 arcsec, and reflectivities up to 31 % at 600 keV. Precision of orientation of crystals is demanding because of the long focal length involved by small angles of diffraction. A prototype currently being built by a French collaboration including the CESR, the CNES and Thales Alenia Space aims to achieve 10 arcsec of tolerance.

We present a computer inexpensive method to calculate the profile of the high resolution diffraction pattern of a single crystal superalloy. The displacement field is taken as the sum of the individual fields of cuboidal inclusions with uniform eigenstrains. Early simulations are compared to experimental data.

The shape of the diffraction peaks of a single crystal superalloy measured by Three Crystal Diffractometry changes during a creep test. We show that these variations are directly linked to the strain and dislocation density within the γ’ phase.

A germanium crystal was bent through a grid of superficial grooves, manufactured on the sample surface. The resulting diffraction planes were bent thanks to quasi-mosaicity, which is an effect of mechanical anisotropy in crystals. High integrated diffraction efficiency was achieved in symmetric Laue geometry with a monochromatic X-ray beam set at 150 and 300 keV. It is demonstrated that the sample is capable of efficiently focusing X-rays. Such crystals can be used as optical components to focalize X- and γ-rays in a high-resolution Laue lens.

A method to acquire three dimensional diffraction data and orientation mapping with the 2D imaging setup of Hasylab beamline G3 is presented. The method has been successfully applied to undeformed large grains extracted from ice samples and extended to the 2D determination of lattice misorientation and lattice orientation distribution within deformed grains.

One of the major ingredients of modelling the mechanical behaviour of superalloys is the knowledge of dislocation densities and strain distribution. Both can be measured using post mortem BF TEM and CBED, but such methods do not allow following their variations during a test. The aim of the present work is to investigate the usefulness of in situ X-Ray Three Crystal Diffractometry (TCD) to measure the density and distribution of dislocations within a rafted superalloy, i.e. during stage II of high temperature creep. As the instrument contribution is very low, the two-peaked experimental profiles are representative of the lattice parameter distribution within the material. The profiles were measured within bulk specimens at the BW5 high energy beamline Hasylab (DESY), during high temperature (1050°C to 1180°C) tests under loads between 0 MPa and 300 MPa. The peak shapes were observed to change with varying experimental conditions. The peak width follows different patterns under low and high stress, i.e. with low and high strain rates. The distribution of elastic strains was calculated by assuming two main contributions: dislocation segments trapped at the γ/γ’ interfaces in a more or less regular network, and dislocations moving within the γ’ rafts. A comparison between experimental and simulated peaks shows that several features of their behaviour can be explained: the absolute magnitude of the peak width, the observed decrease of the peak width under low loads with increasing interfacial dislocation densities. The larger increase in the width of the γ’ peak under high load (and strain rate) may be attributed to a dislocation density within the 1013 m-2 range within the rafts. The present results are presently being cross-checked by post mortem TEM observations.

The combination of high temperature (1050°C -1150°C) testing and in situ high energy X-Ray diffraction measurements using synchrotron Three Crystal Diffractometry may give various insights into the mechanical behaviour of superalloys: measurement of the lattice mismatch, order within the ' phase, elastic constants, and dynamic response to changes in the experimental conditions. Several examples are given on the rafted AM1 superalloy, resulting from experiments at the ID15A (ESRF) and BW5 (DESY) high energy beamlines.

Nuclear astrophysics presents an extraordinary scientific potential for the study of the most powerful sources and the most violent events in the Universe. But in order to take full advantage of this potential, telescopes should be at least an order of magnitude more sensitive than present technologies. Today, Laue lenses have demonstrated their capability of focusing gamma-rays in the 100 keV–1 MeV domain, enabling the possibility of building a new generation of instruments for which sensitive area is decoupled from collecting area. Thus we have now the opportunity of dramatically increase the signal/background ratio and hence improve significantly the sensitivity. With a lens, the best detector is no longer the largest possible within a mission envelope. The point spread function of a Laue lens measures a few centimeters in diameter, but the field of view is limited by the detector size. Requirements for a focal plane instrument are presented in the context of the Gamma-Ray Imager mission (proposed to European Space Agency, ESA in the framework of the first Cosmic Vision AO): a 15–20 cm a side finely pixellated detector capable of Compton events reconstruction seems to be optimal, giving polarization and background rejection capabilities and 30 arcsec of angular resolution within a field of view of 5 arc min.

Crystals are the elementary constituents of Laue lenses, an emerging technology which could allow the realization of a space-borne telescope 10–100 times more sensitive than existing ones, in the 100 keV–1.5 MeV energy range. This paper addresses the development of efficient crystals for the realization of a Laue lens. In the theoretical part, 35 candidate crystals, both pure and two-component crystals, are considered. Their peak reflectivity at 100, 500 keV and 1 MeV is calculated assuming they are mosaic crystals. It is found that, by careful selection of crystals, it is possible to achieve a reflectivity above 30% over the whole energy range, and even up to 40% in the lower part of the energy range. In the experimental part, three different materials (Si1−xGexwith a gradient of composition, mosaic Cu and Au) have been measured at both ESRF and ILL using highly monochromatic beams ranging from 300 to 816 keV. The aim was to check their homogeneity, quality and angular spread (mosaicity). These crystals have shown outstanding performance, such as reflectivity up to 31% at ∼600 keV (Au) or 60% at 300 keV (SiGe) and angular spread as low as 15 arcsec for Cu, fulfilling very well the requirements for a Laue lens application. An unexpected finding is that there are important discrepancies with Darwin's model when a crystal is measured using various energies.

Uniaxial plastic strain along [0 0 1] is introduced in three types of matrix domains in γ−γ′ nickel superalloys: uniformly in the γ matrix, the horizontal matrix channels normal to [0 0 1] and the vertical channels normal to [1 0 0] and [0 1 0]. Using a mean field method, an elastic energy change due to the introduction of plastic strain (elongation or compression) in the three types of domains is calculated. It is also shown that the particle shape change from a cuboid to a disk, parallel to {0 0 1}, due to the elastic energy decrease, occurs only when the precipitate misfit is present. If there is no plastic strain in the matrix, these disks can be formed with random orientations, parallel to three types of {0 0 1} planes. It is only when there is a plastic strain in the matrix in addition to a precipitate misfit that the alignment of disks occurs on particular types of {0 0 1}. The choice of the alignment plane depends on the sign of the ratio of the plastic strain to the precipitate misfit strain.

Rafting of the γ′ particles in the fourth-generation single-crystal nickel-based superalloy MC-NG was investigated in situ using small-angle neutron scattering. Rafting was induced by high-temperature annealing of a predeformed sample in the absence of applied stress. The use of extended Porod’s approximation allowed the investigation of the specific area evolution during the microstructure change. By comparison with a first-generation alloy, it is found that the alloy composition does not seem to influence the kinetics of rafting.

The elastic strain of both phases of a superalloy are measured by high-resolution in situ diffraction experiments done at 1070 °C, under variable stress from 0 to 300 MPa, on a specimen with a raft microstructure. The Young modulus can be evaluated, and the stresses and strain rates of both phases can then be calculated with a good precision. Between the pre-strain stress and the maximum stress, the effective stress within the γ phase remains at a constant level, just enough to allow dislocation glide within the rafts.

Quasicrystals are long-range-ordered materials that lack translational invariance, so the study of their physical properties remains a challenging problem. Here, we have carried out inelastic-X-ray- and neutron-scattering experiments on single-grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of a pseudo-Brillouin-zone in the quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results. This paves the way for a detailed understanding of the physics of quasicrystals.

Rafting in Ni-based superalloys is investigated by examining the dependence of elastic energy on the shape and orientation of γ′ particles. The precipitation misfit strain and the plastic strain occurring in the matrix are taken into account. The elastic energies associated with spherical or disc-shaped particles with different orientations are evaluated for some combinations of transformation strain and matrix plastic strain. The anisotropy in elastic constants as well as the difference in elastic constant between the particles and matrix are taken into account. It is found that the elastic energy becomes minimum when γ′ particles adopt a certain shape and direction with respect to the elongation axis 〈0 0 1〉. These results are in agreement with the rafted morphologies observed in crept superalloys. The onset of the shearing of rafted γ′ particles, leading to accelerated creep of the alloy, is also discussed by examining the stress state of rafted γ′ particles.

The strain distribution in a new generation nickel-based single crystal superalloy has been determined in the temperature range 293 K– 1598 K. Measurements have been performed using diffraction of high energy synchrotron radiation (150 keV, λ = 0.008 nm) to determine the variations with temperature of the γ/γ′ lattice mismatch and of the γ′ volume fraction. The chemical segregation at the dendrite scale and the internal stress induce a large range of values for the lattice mismatch. The measurements of the γ′ volume fraction determined by X-ray diffraction are in agreement with those obtained by atom probe tomography, image analysis or computation.

Large single crystals of copper with an uniform and very narrow mosaic spread between 25 seconds and 1 minute of arc are now available at I.L.L. This result is of great interest in the construction of a Laue lens for astrophysical applications for which such quality copper single crystals may be used. The X-ray diffraction properties of copper single crystals produced at I.L.L. were studied for x-ray energies ranging from 100 keV to 400 keV. Several monocrystalline plates with different thicknesses and mosaic distributions were then prepared from the as-grown crystals in order to measure their diffraction efficiency as a function of energy. As expected, the value of the peak reflectivity depends on the crystal thickness. Reflectivity measurements show the excellent properties of copper crystals for gamma-ray diffraction. A peak reflectivity of 24% was measured at 220 keV from a copper single crystal of 3.75 mm thickness having a mosaic spread of 1.5 minutes of arc. Some technical aspects on the preparation of copper single crystal plates are also discussed.

Bulk crystals of Ge 1 - x Si x solid solutions grown by modified Czochralski (CZ) technique were used for the production of the diffraction optics elements of the high-energy γ -ray telescope. The mosaic crystals were grown to improve the diffraction efficiency of the crystal lens. For developing growth methods for such crystals, the shape of the growth interface, the striation pattern of the distribution of the components and the mosaic structure must be known. Applying the lateral photovoltage scanning (LPS) method and optical microscopy their mosaic structure and shapes of the growth interface have been determined. In this paper, the first attempt was made to find the correlation between crystal structure, mosaicity and diffraction efficiency of Ge 1 - x Si x -based γ -ray optical elements.

The Institut Laue-Langevin hard X ray diffraction technique has been used to study natural quartz crystals from the Alps and Madagascar. The results are consistent with the known descriptions of these types of crystals. This technique presents the advantage to be directly related to the structural properties of the samples. These measurements show the interest of this non destructive technique, which allows global bulk analysis of centimeter size samples, in the field of mineralogy and geosciences. It completes information given by usual methods.

Hard X-ray diffraction experiments were performed on ice single crystals deformed in pure torsion. The torsion strain appears to be totally accommodated by geometrically necessary basal screw dislocations. Dislocation slip is concentrated on macroscopic basal slip bands, which are clearly seen on the prismatic diffraction lines. The slip band spacing is decreasing with the increase of the finite torsion strain. The deformation appears to result from the increase of the number of slip bands and not from the accumulation of dislocations within these bands. The elastic interaction between dislocations located in neighbouring slip bands is weak since they all have the same sign and move in the same direction.

La caracterisation en volume de materiaux cristallins de forte epaisseur (plusieurs cm) n'est possible que par l'utilisation de sources de rayonnement X de forte energie (diffractometres gamma, lignes haute energie du rayonnement synchrotron) ou encore par l'utilisation de faisceau de neutrons. L'Institut Laue Langevin a developpe et construit, en cooperation avec le Laboratoire de Spectrometrie Physique, un nouveau type d'instrument utilisant le spectre continu rayons X a tres haute energie (typiquement 100 a 400 keV) emis par un generateur rayons X a foyer fin utilise pour des radiographies. Ce diffractometre permet la caracterisation rapide, precise et en volume d'echantillons de forte epaisseur. Outre des applications variees dans differents domaines (structure cristalline, mesure de parametre de maille, contraintes, textures,...), il est possible de caracteriser completement des echantillons cristallins a partir d'une serie de mesures en diffraction. Il est en particulier possible de visualiser (localiser) les desorientations du reseau cristallin au sein d'un echantillon (topographie en transmission). Il est egalement possible de visualiser les volumes diffractants dans une section de l'echantillon en utilisant une reconstruction de type tomographique a partir d'une serie d'acquisitions en diffraction. Ces nouvelles possibilites s'averent etre particulierement utiles pour le controle non destructif de materiaux cristallins.

The objective of the RD the astrophysical target was a “standard candle”, the Crab nebula. CLAIRE’s first light consists of ∼33 diffracted photons from the Crab, corresponding to a 3σ detection. The performance of the gamma-ray lens during the balloon flight has been confirmed by ground data obtained at a 200 m long test range. Based on the diffraction efficiencies measured with CLAIRE, the mission concept of a space borne gamma-ray lens is proposed, and its potential for nuclear astrophysics is outlined.

Hard X-ray diffraction experiments were performed on ice single crystals deformed in torsion. This work shows the relationship between the density of geometrically necessary dislocations and strain gradients. The torsion strain appears to be totally accommodated by geometrically necessary basal screw dislocations.

Hard X-ray diffraction experiments have been carried out on ice monocrystals taken from the 3623 m long Vostok core (Antarctica). Strain gradients associated with the storage of geometrically necessary dislocations appear to be a general feature of the deformation microstructure of ice. The observed lattice distortion is related to the bending of the basal plane and the torsion of the lattice around the c-axis. The lattice distortion is shown to be compatible with the basal dislocations generally observed in ice crystals, supporting the assumption of deformation modes governed by basal slip and accommodated by recrystallization processes. The dependence of the ice viscosity on grain size in ice sheets appears to be compatible with these accommodation modes.

The origin of the opalescence observed at the α–β transition of quartz remains an open question. This intense light scattering occurs during the coexistence, at the first order transition, of the α and incommensurate (inc) phases, in the vicinity of the phase interface. New hard x-ray diffraction experiment shows that the large angle light scattering is mainly in the α-phase region of the crystal and reveals the existence of an intermediate structure between the α-phase and the 3q inc phase.

The lattice mismatch between the fcc γ matrix and the ordered γ ′ cuboidal precipitates in superalloys induces large internal stresses within the material. These stresses have a major effect on its mechanical behaviour and on the anisotropic evolution of the microstructure (rafting…) during its lifetime. The evolution of the effective lattice mismatch of the AM1 and MCNG superalloys was measured continuously during high temperature creep tests (1100 °C, 150 MPa) at the ID 15 (high energy) beamline of the ESRF. The bulk profiles of the 200 reflection (parallel to the tensile axis) were recorded using the triple crystal diffractometer. Both materials have a negative mismatch, and exhibit a transition between the initial wide γ ′ peak to a two peaks profile during stage I of the creep curve, as rafting takes place. During stage II, the 200 mismatch decreases in magnitude. During stage III, as a microstructural transition (coalescence) occurs and the strain rate increases, the mismatch changes in the same direction, but at a faster rate, while the thickness of both peaks increases. Evolution of the MCNG specimen was the same as AM1 ones, but rafting and transition to stage II take place at a different rate.

The grooving technique was employed for manufacturing a self-standing curved Ge crystal. The crystal focuses hard X-rays with high efficiency by diffraction in Laue geometry through asymmetric bent planes. The sample was tested at the Institut Laue–Langevin (Grenoble, France), undergoing two types of characterization. A monochromatic and low-divergence γ-ray beam was used to test the curvature of asymmetric planes, showing a diffraction performance better than for any mosaic crystal under equal conditions. Then, the focusing capability of the crystal was probed through a polychromatic and fine-focus hard X-ray beam. Asymmetric (220) planes were chosen for analysis because of the impossibility of obtaining a curvature along this family of planesviaany symmetric configuration in focusing crystals. A method for calculating the curvatures induced in any family of lattice planes is also presented.

The lattice mismatch between the γ matrix and the γ′ precipitates in the AM1 superalloy was measured in situ during a creep experiment up to fracture (150 MPa, 1050 and 1080 °C) by high energy XRD at the ID 15 beamline of the ESRF. The results are coherent with experiments done post mortem on specimens just annealed, and a specimen strained at 1050 °C, 150 MPa up to 1.03%. From the evolution of the mismatch, it is proposed that the elastic interfacial energy varies strongly during a creep test, and might put a limit on the high temperature ductility of superalloys.

X-ray diffraction experiments were carried out on large ice crystals from accreted ice above Lake Vostok, a subglacial lake lying beneath the East Antarctic ice sheet. Results indicate a surprisingly very low lattice distortion. This crystalline quality does not seem to be affected by impurities. Abnormal grain growth should occur and could explain both the large grain size and the low lattice distortion. Accreted ice is therefore supposed to be non-plastically deforming. These results should be taken into account for further studies of the permeability of accreted ice to drilling fluid present in the borehole.

The diffraction properties of a crystalline silicon plate of which one face was mechanically indented have been studied. This treatment induced a permanent curvature in the sample, which allowed a diffraction efficiency of 88% for 150 keV photons,i.e.a reflectivity of 64% including the absorption. This efficiency is constant over 14 arcseconds and is very close to the theoretical expectation, meaning that the curvature is highly homogeneous. The technique enables the fabrication, in a very reproducible fashion, of crystals for the realization of an astronomical hard X-ray concentrator (Laue lens).

L'appareillage dedie a la mise en oeuvre de la methode de Laue refocalisee a haute energie, installe a l'Institut Laue Langevin, a ete equipe d'un systeme de detection permettant l'analyse en energie des faisceaux diffractes. Apres une rapide description du dispositif, de ses caracteristiques et de sa resolution, nous montrerons l'interet de cette mesure pour, par exemple, aider a l'indexation des diagrammes de Laue, separer les ordres de diffraction successifs, acceder aux raies de surstructure et determiner les variations des parametres de maille. Des resultats obtenus sur differents materiaux illustreront les nouveaux champs d'application ouverts par l'analyse en energie.

The CLAIRE collaboration is presently preparing the first astronomical observation of a gamma-ray lens. In June 2000, the instrument is to be flown on a stratospheric balloon by the French Space Agency CNES. CLAIRE features a Laue diffraction lens, a detector module with a 3×3 germanium array, and a balloon gondola stabilized to 15″ pointing accuracy. The instruments lens focuses gamma-ray photons from its 526 cm 2 area onto a small solid-state detector, with only 18 cm 3 equivalent volume for background noise. Hence, for the first time in gamma-ray astronomy, the statistics will be dominated by the signal. Besides its excellent sensitivity, the telescope has outstanding angular and spectral resolution. The primary objective for the first balloon flight of CLAIRE is to detect the Crab nebula and measure its extend at 170 keV with an angular resolution of about 1 arcmin. Scientific objectives for further flights include collapsed objects, SNRs, and broad class annihilators.

Grâce a une machine d'essais mecaniques a haute temperature developpee a Nancy et aux caracteristiques de la ligne a haute energie de l'ESRF, nous avons mesure in situ l'evolution du desaccord parametrique du superalliage monocristallin AM1 au cours d'une deformation en fluage conduite jusqu'a la rupture. Ces mesures montrent une forte correlation entre cette evolution et les stades caracteristiques de la courbe de fluage. De plus, on observe que, durant le stade II qui correspond a la phase d'utilisation du materiau, le desaccord parametrique evolue de facon continue et monotone. Sa mesure permet donc de caracteriser l'etat d'endommagement de l'eprouvette et d'estimer sa duree de vie restante. La possibilite d'utiliser ce type de mesures comme methode de controle non destructif de l'endommagement est suggeree.

Single crystal nickel base superalloys are used for the high-temperature parts of aircraft engines like turbine blades. Their good mechanical properties at high temperature are related to the precipitation of an ordered {gamma}{prime} phase which induces a structural hardening of the material. The {gamma}{prime} phase has an ordered L1{sub 2} structure while the {gamma} matrix is disordered and has a FCC structure. The volume fraction of f{gamma}{prime} of the {gamma}{prime} phase evolves with the temperature and a complete solutionizing occurs above 1,280 C in the AM1 superalloy. The {gamma}{prime} phase of Ni based superalloys is usually analyzed through its prototype Ni{sub 3}Al. As the Ni{sub 3}Al structure remains totally ordered up to temperature very close to the melting point, it is commonly assumed in superalloys that the {gamma}{prime} phase precipitates are fully ordered up to their solutionizing and that the volume fraction of the precipitates is equivalent to the volume fraction of the ordered phase. However, in superalloys, it is difficult to separate experimentally the effects related to the solutionizing of the precipitates from those due to a possible partial disordering of the {gamma}{prime} phase and this assumption has not been verified yet. The aim of this paper is tomore » study the structural order in the {gamma}{prime} phase of a superalloy.« less

Diffraction profiles of single crystal Ni-based superalloy samples with different microstructures were measured in situ up to the complete solutionizing of the {gamma}{prime} phase, using a high resolution triple crystal diffactometer and high energy synchrotron radiation (150 keV, {lambda} = 0.08 {angstrom}). A comparison between an undeformed sample and creep-deformed specimens with various resultant microstructures evidenced a relation between the lattice parameter distribution, the {gamma}{prime} precipitate microstructure and the sign of the connectivity. It was shown that a deformation induces a change in the relative volume cell of {gamma} and {gamma}{prime} phases. Moreover, the high resolution of the experimental set-up allows in many cases the {gamma}{prime} phase volume fraction to be measured with a good accuracy.

In order to characterize the microstructure of crystalline and polycrystalline thick materials, the Bragg diffraction pattern associated with the diffracted energy analysis allows texture determination, strain analysis, crystalline phase identification and grain size evaluation. This work describes an innovative application of a hard x-ray diffractometer, employed for the first time to obtain, in a non-destructive way, interesting microstructural information related to the production processes of archaeological finds. Two ancient bronze artefacts of different historical periods were selected to demonstrate an application of the method, which could be implemented at a museum. In fact drastically different structural characteristics were observed.

The combination of in situ high resolution diffraction experiments with synchrotron radiation and mechanical and diffraction modelling is used to investigate the microstructure and mechanical state of single crystal superalloys during high temperature tests: a very high temperature annealing without external load and a creep test.

Crystals with curved diffracting planes have been investigated as high-efficiency optical components for the realization of a Laue lens for satellite-borne experiments in astrophysics. Curved crystals implementing the quasi-mosaic effect, namely an effect of crystalline anisotropy, are able to focus an X-ray beam to a size far smaller than that of the diffracting element, in turn increasing the focusing power of a Laue lens. This work provides first results about the feasibility of a self-standing stack composed of quasi-mosaic crystals. Stacking of crystalline lamellae is a solution to overcome the thickness limitation in existing self-standing quasi-mosaic crystals. Ten thin silicon crystalline lamellae were stacked, and then the planes affected by the quasi-mosaic effect were tested by polychromatic X-ray diffraction. The multicrystal behaved as one diffracting element, yielding a broad and smooth diffraction profile. The effective realization of a quasi-mosaic multicrystal opens up the prospective of building a Laue lens with a large integrated reflectivity, which leads to a high sensitivity, a necessary condition for the observation of celestial X-ray sources via a Laue lens.

Due to its importance for industrial applications, the microstructural behavior of single crystal nickel base superalloys as a function of the thermo-mechanical history of the material is the subject of many studies. However, some controversies remain concerning parameters which are driving the coarsening of {gamma}{prime} precipitates. In particular the role of the lattice parameter mismatch between the {gamma} and {gamma}{prime} phases (usually defined as {Delta}d/d = (a{gamma}{prime} {minus} a{gamma})/ where a{gamma}{prime} and a{gamma} represent respectively the lattice parameter value of the {gamma}{prime} and {gamma} phases) and of the internal stresses at the interfaces has to be clarified. An experiment was performed on a creep deformed sample using high energy synchrotron radiation and a Triple Crystal Diffractometer set-up (TCD) which allow nondestructive measurements and probe the bulk of the sample. With this method the superstructure reflection (100) was measured with a good accuracy and a reasonable statistics.

High-energy X-ray synchrotron radiation was used to measure internal strains inside the bulk of creep deformed AM1 single crystal superalloy specimen. A sample creep deformed at 1050 °C with γ′ raft-like precipitates was studied ‘in situ’ in temperature. The superstructure reflections (100) and (001) as well as fundamental reflections (200) and (002) were measured up to the temperature of deformation using a high-resolution triple crystal diffractometer. The lattice parameter distribution which is related to internal stress distribution was determined for each phase in parallel and perpendicularly to the rafts. It was shown that these parameters depend strongly on the thermomechanical history of the analysed material and on the temperature at which measurement is performed.

Using the small angle neutron scattering technique, we have observed rafting in nickel based single crystal superalloys. Kinetics of morphological evolution of the precipitates have been studied in situ. Therefore we used a special furnace designed for the ageing of prestrained specimens under a neutron beam. The evolution of both the precipitate aspect ratio and the distance between precipitates confirms the importance of strain in the directional coarsening process. Results are presented and discussed regarding kinetics and microstructural aspects. In such conditions, rafts seem to be different from those obtained after a creep test.

The purpose of the present work is to introduce a technique of investigation based on the diffraction of high energy synchrotron radiation which appears to be very well adapted to the microstructural analysis of single crystal superalloys. In comparison with previous synchrotron measurements made on superalloys, the use of high energy radiation permits to keep the advantage of neutron experiments, measurement on bulk sample in a furnace and a much better resolution (of about one order of magnitude) is reached with a Triple Crystal Diffractometer (TCD) set-up. In particular, the contribution of the mosaicity and of the lattice parameter distribution can be separated and measured in the same experiment. Furthermore the high flux available at the European Synchrotron Radiation Facility (ESRF) reduces the acquisition time and/or allows to analyze a relatively small volume of the sample (few mm{sup 3}). Very small values of the lattice parameter mismatch usually defined as {Delta}d/d = (a{gamma}{prime}-a{gamma})/ where a{gamma}{prime} and a{gamma} are the lattice parameter of the {gamma}{prime} and {gamma} phases respectively, can be measured. Then, as shown in this study, the evolution of the lattice parameters during the first creep stage when the microstructure evolves very fast can be analyzed.

We report on the status of the Laue lens development effort led by UC Berkeley, where a dedicated X-ray beamline and a Laue lens assembly station were built. This allowed the realization of a first lens prototype in June 2012. Based on this achievement, and thanks to a new NASA APRA grant, we are moving forward to enable Laue lenses. Several parallel activities are in progress. Firstly, we are refining the method to glue quickly and accurately crystals on a lens substrate. Secondly, we are conducting a study of high-Z crystals to diffract energies up to 900 keV efficiently. And thirdly, we are exploring new concepts of Si-based lenses that could further improve the focusing capabilities, and thus the sensitivity of Laue lenses.

International audience; The high temperature effective (constrained) gamma/gamma' lattice mismatch of a Ni-based single crystal superalloy has been measured in a wide temperature range [930 degrees C-1125 degrees C] using three different techniques: in-situ X-ray diffraction under synchrotron radiation, and post-mortem gamma/gamma' interfacial dislocation network mesh size measurements using Transmission Electron Microscopy (TEM) or high resolution Scanning Electron Microscopy (SEM). It is shown that all three techniques are complementary considering precision and spatial distribution of lattice mismatches in the analyzed volume and that they provide a very similar average value of the gamma/gamma' lattice mismatch. Since isothermal creep experiments were performed under variable applied stress, it is deduced that the post-mortem lattice misfit measurements using both TEM and SEM are representative of the very last loading step of the experiments, even if dislocation networks are out of an equilibrium configuration. Contrary to the unconstrained gamma/gamma' lattice mismatch, it is shown that the effective lattice mismatch is a function of the temperature, applied stress and accumulated plastic strain, i.e. of the thermomechanical histories of the samples.

Modeling of the mechanical behavior of a two-phased material, even with a simple microstructure such as a single crystal superalloy remains a difficult task, for lack of phase specific experimental data. The combination of Three Crystal Diffractometry with high energy synchrotron radiation and in situ experiments can give access to such data in real time. A few examples are given on load transfer between phases, dislocation densities, and the stress – strain behavior of a phase.