F. Carsughi

Followers

Following

Co-authors

Public Views

Interests

Uploads

Papers by F. Carsughi

Mechanical properties and microstructure of 800 MeV p-irradiated 304L and tantalum

Non-Destructive Analysis of the Gamma'Precipitation in a Udimet 720 Ni Superalloy Turbine Blade by SANS

Materials Science Forum, 1988

ABSTRACT An investigation on y'precipitation in a turbine blade consisting of UDIMET 720 Ni s... more

Non-destructive test of turbine blade by SANS

Physica B: Condensed Matter, 1989

... 3. P. Bianchi, F. Carsughi, D. D'Angelo, J. Kulda, A. Mengoni, P. Mikula and F. Rustichel... more

Radiation damage problems in high power spallation neutron sources

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1995

In planning the next generation of spallation sources with proton beam powers of several MW (as, ... more In planning the next generation of spallation sources with proton beam powers of several MW (as, for example, the European Spallation Source, ESS), it was soon recognized that materials&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; degradation by radiation damage will be the most problematic factor in determining the efficiency, lifetime and availability of high power spallation targets. This article gives a short introduction to the physics

The tensile properties of AISI 316L and OPTIFER in various conditions irradiated in a spallation environment

Journal of Nuclear Materials, 2005

Tensile specimens, prepared from AISI 316L austenitic stainless steel in three conditions (soluti... more Tensile specimens, prepared from AISI 316L austenitic stainless steel in three conditions (solution-annealed, coldworked and electron-beam welded) and from OPTIFER martensitic stainless steel in tempered condition, were irradiated in the Swiss spallation neutron source (SINQ) at 90-400°C to displacement doses from 3 dpa to 11 dpa. The mechanical properties were measured by tensile testing at room temperature and 250°C, respectively, and subsequent metallographic analysis was employed. The tensile results indicated that the strength of AISI 316L-SA is quite similar or a little higher than in 316L-EBW but elongation of SA 316L is somewhat larger than EBW for both unirradiated and irradiated samples. The cold-worked specimens revealed much higher strength but almost zero strain-to-necking after irradiation. The results from OPTIFER samples showed that irradiation hardening increases with dose, which is accompanied by a dramatic reduction of uniform elongation beginning at very low dose. The metallographic analysis showed that the samples of AISI 316L-EBW failed in the welded zone.

Download

Investigations on Inconel 718 irradiated with 800 MeV protons

Journal of Nuclear Materials, 1999

... c, APT Technical Project Office, Los Alamos National Laboratory, Los Alamos, USA. d, Facoltà ... more

Tensile properties and microstructure of martensitic steel DIN 1.4926 after 800 MeV proton irradiation

Journal of Nuclear Materials, 2000

A double-wall window of martensitic steel DIN 1.4926 (11% Cr) was irradiated with 800 MeV protons... more A double-wall window of martensitic steel DIN 1.4926 (11% Cr) was irradiated with 800 MeV protons in the LANSCE facility of the Los Alamos National Laboratory (LANL) to a total number of about 6X3 Â 10 22 protons (2.8 Ah) in a temperature range from 50°C to 230°C. Tensile tests show that irradiation hardening increases with¯uence up to the maximum attained dose of about 6.6 dpa. All irradiated specimens show signi®cant embrittlement, T 1X5% uniform elongation and 7.5±9% total elongation as compared to about 11% uniform elongation and 21% total elongation for the unirradiated specimens. SEM observations illustrate that the fracture of specimens changes gradually from ductile mode in unirradiated and low dose specimens to cleavage mode in specimens of high dose P 5X6 dpa. Intergranular brittle fracture mode has not been observed. Irradiation induced small defect clusters exist in all samples of irradiated material. Both of the size and the density of clusters increase with¯uence. At the highest dose of 6.6 dpa large dislocation loops of a size P 10 nm have been observed in addition to the clusters.

Download

Summary of the results from post-irradiation examination of spent targets at the FZ-Juelich

Journal of Nuclear Materials, 2003

The lifetime of structural components of spallation targets (beam window, liquid metal container,... more The lifetime of structural components of spallation targets (beam window, liquid metal container, return hull) is determined by the irradiation-induced changes of the mechanical properties of their materials. An extensive test program was initiated using specimens obtained from spent target components from operating spallation facilities (Los Alamos Neutron Science Center, LANSCE and the Spallation Neutron Source at Rutherford-Appleton Laboratory, ISIS). The investigated materials include a nickel-based alloy (IN 718), an austenitic stainless steel (AISI 304L), a martensitic stainless steel (DIN 1.4926) and a refractory metal (tantalum). The materials experienced 800 MeV proton irradiation to maximum fluences of >10 25 p/m 2. The mechanical property changes were investigated by microhardness measurements, three-point bending tests and tensile tests at temperatures ranging from room temperature (RT) to 250°C. Subsequent scanning electron microscopy was employed to investigate the fracture surfaces. Generally, irradiation hardening and a decrease in ductility with increasing proton fluence was observed. Nevertheless, all materials except IN 718 tested at RT, retained some ductility up to the maximum doses explored. The transmission electron microscopy investigation showed that a high density of Ôblack dotsÕ and dislocation loops appeared in all materials. No effect of long-range radiation-induced segregation at grain boundaries was detected by energy dispersive X-ray investigation on AISI 304L and IN718 which failed by intergranular fracture.

format_quoteProton fluence of 1.6 x 10^26 p/m² leads to around 60 dpa and significant helium buildup in steels; impacts material longevity.format_quote

Download

Coarsening of helium bubbles in CrNi measured by small angle neutron scattering

Journal of Nuclear Materials, 1992

Abstract A 100 μm thick specimen of Fe-15% Cr-15% Ni (serving as a model alloy for austenitic sta... more Abstract A 100 μm thick specimen of Fe-15% Cr-15% Ni (serving as a model alloy for austenitic stainless steels) has been homogeneously implanted with 1200 appm He and then isothermally annealed at 973 K for periods between 0.25 and 2780 h. After each annealing step the size distribution and the density of helium bubbles have been determined by small angle neutron scattering (SANS). After the last annealing step the bubble structure was also measured by TEM and good agreement with SANS results was found. The observed changes of the mean bubble radius and the bubble density with annealing time can be described by power laws. The corresponding exponents of 0.14 and −0.37, respectively, indicate bubble migration and coalescence as the dominating coarsening mechanism. It is further concluded that the gas pressure in the bubbles is significantly higher than the thermal equilibrium value, in agreement with earlier results on pure nickel.

Study of the enzyme ascorbate oxidase by small angle neutron scattering

Journal of Molecular Structure, 1996

We report a study of the large scale structure of the “blue” copper enzyme ascorbate oxidase by s... more We report a study of the large scale structure of the “blue” copper enzyme ascorbate oxidase by small angle neutron scattering. The enzyme has been extracted from zucchini and studied in solutions of two different preparations. Contrast variation method was used by performing the measurements in water, heavy water and mixtures of H2OD2O. Our data show that, at least at

Sample geometry effects on incoherent small-angle scattering of light water

Journal of Applied Crystallography, 2000

Light water is frequently used as a standard for calibrating small-angle neutron scattering (SANS... more Light water is frequently used as a standard for calibrating small-angle neutron scattering (SANS) data. The intensities collected for 1 and 2 mm of light water in standard quartz cells may differ by up to about 50% due to the presence of multiple and inelastic scattering [Rennie & Heenan (1993).Proceedings of ISSI Meeting, Dubna,pp. 254–260, Report E3-93-65; Teixeira (1992).Structure and Dynamics of Strongly Interacting Colloids and Supramolecular Aggregates in Solution, edited by S. H. Chen, pp. 625–658. Dordrecht: Kluwer Academic Publishers]. Multiple scattering increases with the thickness of the sample. The use of only elastically scattered neutrons may lead to an absolute intensity of the SANS data of about a factor of 2 higher than that obtained by taking into account all of the neutrons on the detector [Ghosh & Rennie (1990).Inst. Phys. Conf. Ser.107, 233–244]. However, it is shown here that the scattering intensities collected with different ratios of sample-to-beam dimensi...

format_quoteCalibration using light water resulted in cross-sections values approximately 25% lower due to inelastic effects being neglected.format_quote

Download

A simple method for background determination in small angle scattering experiments

Le Journal de Physique IV, 1993

Contribution of the copper ions in the dinuclear active site to the stability of Carcinus aestuarii hemocyanin

Archives of Biochemistry and Biophysics, 2005

We have investigated the effect of copper binding on the structural properties of hemocyanin (Hc)... more We have investigated the effect of copper binding on the structural properties of hemocyanin (Hc). To this aim, we have studied the holo-and apo-form of the protein, both in the hexameric and in the monomeric state (CaeSS2 subunit), with experimental approaches that report on the protein aggregation and conformational stability. The results of gel-filtration chromatography and small angle X-ray scattering (SAXS) provide evidence that the hydrodynamic and gyration radius (R g) of Hc in the hexameric form only slightly increase upon copper removal, whereas a remarkable enhancement in the R g value is observed for the CaeSS2 monomer. CD measurements in the far-and near-UV region indicate that removal of copper only marginally affects the conformation of the hexameric Hc. Instead, copper depletion in the CaeSS2 strongly alters the tertiary structure of the monomer (near-UV CD), even though it is almost inconsequential on the secondary structure content (far-UV CD). These findings are fully consistent with the results of limited proteolysis experiments showing that the hexameric Hc is similarly resistant to proteolysis by trypsin both in the holo-and apo-form. Conversely, the apo-form of CaeSS2 monomer is much more susceptible to proteolytic attack by trypsin than the holo-form. Based on SAXS measurements, the concentration-dependent oligomerization process for apo-CaeSS2 has been analyzed on the basis of a thermodynamic model involving a concentration-dependent equilibrium between a monomer in a nativelike and an hexameric aggregate of monomers.

Download

Small angle neutron scattering from helium bubbles in metals

Bulletin of Materials Science, 1997

Small angle neutron scattering (SANS) has been widely used in investigating defects in metals, an... more Small angle neutron scattering (SANS) has been widely used in investigating defects in metals, and in particular, to characterize the helium bubble population in implanted materials. The main advantage in using SANS is the non-destructive feature of the tests and the quantitative results obtained by averaging over a large sample volume, SANS is a powerful technique, very sensitive to microstructural changes and its use was of fundamental importance to show the bimodal distribution of the bubble population: in the vicinity of grain boundaries and free surface and inside grains, respectively. Here the most important applications of the SANS technique to the study of the helium bubbles in implanted materials are reviewed. Most of the work has been done on nickel samples, but also a ternary alloy Fe-Ni 15%wt-Cr 15%wt and a steel (MANET) with a more complicated structure have been successfully investigated. Different annealing treatments, isothermal and isochronal, were in-cestigated in order io determine the active mechanisms of the bubble coarsening and their activation energies. From the SANS data the bubble size distributions have been determined, from which parameters such as mean radius and density of the bubble population have been calculated. The gas pressure inside the bubbles was also determined by the contrast variation technique in SANS and by a computational procedure, and an excellent agreement was found between the results. These results show a marked overpressure inside the bubbles as compared to thetmodynamical equilibrium values of about 3 GPa. A comparison with results obtained by other techniques confirms the validity of SANS, which has to be considered as a complementary technique for its indirect image of the sample.

Download

Nanoscale Hardening Precipitiation in AlMgSi Alloys: A Transmission Electron Microscopy and Small-Angle Neutron Scattering Study

Journal of Applied Crystallography, 1998

Transmission electron microscopy (TEM) and smallangle neutron scattering (SANS) have been used to... more Transmission electron microscopy (TEM) and smallangle neutron scattering (SANS) have been used to study hardening precipitation in a 6056 A1-Mg-Cu-Si alloy at peak ageing. TEM observations revealed that the precipitates adopt rod and lath morphologies. A TEM image analysis, using group-symmetry properties, revealed that the precipitates belong to the orthorhombic (2/m 2/m 2/m) point group. The SANS data analysis, based on a log-normal model, yields the distribution and mean size of the rod precipitates.

Download

SAS from inhomogeneous particles with more than one domain of scattering density and arbitrary shape

Journal of Applied Crystallography, 2000

The Small Angle Scattering from inhomogeneous particles is very important in the investigation of... more The Small Angle Scattering from inhomogeneous particles is very important in the investigation of biological systems, where the scattering objects might be formed by many domains. For these systems, the scattering intensity, as well as its Fourier transform, are written as a sum of different contributions. In this work, for the simple case of two domains, the form factors of different scattering particle shapes, such as the oblate, prolate and biaxial ellipsoids, spherocylinder and disks were calculated by using a Monte Carlo method. Finally, SAS data of sodium lauryl sulfate micelles in water were analysed by using a model that accounts for polydispersity and micelles of different shape.

Download

Transition from itinerant to polaronic conduction in La 1 − x Sr x CoO 3 perovskites

Europhysics Letters (EPL), 1999

Neutron diffraction and small-angle scattering on La1−xSrxCoO3 (0 < x ≤ 0.30) show that for x = 0... more Neutron diffraction and small-angle scattering on La1−xSrxCoO3 (0 < x ≤ 0.30) show that for x = 0.3 the system is near a two-phase percolation threshold and undergoes a transition from itinerant to polaronic conduction at the Curie temperature TC. The stabilization of superparamagnetic clusters on warming through TC is revealed by an anomalous thermal expansion of the volume and a deviation of the paramagnetic susceptibility from the Curie-Weiss law. The development of a temperature-dependent small-angle-scattering signal confirms that regions of short-range ferromagnetic order are present above TC.

Download

Structural Characterization of the pH-Denatured States of Ferricytochrome-c by Synchrotron Small Angle X-Ray Scattering

Biophysical Journal, 2001

The ferricytochrome-c (cyt-c) shows a complex unfolding pathway characterized by a series of stab... more The ferricytochrome-c (cyt-c) shows a complex unfolding pathway characterized by a series of stable partially folded states. When titrated with HCl at low ionic strength, two transitions are detected. At pH 2, cyt-c assumes the U 1 unfolded state, whereas the successive addition of Cl Ϫ ion from either HCl or NaCl induces the recompaction to a molten globule conformation (A 1 and A 2 states, respectively). A second unfolded state (U 2) is also observed at pH 12. Recent data evidence different features for the local structure of the heme in the different states. To derive relationships between local and overall conformations, we analyzed the structural characteristics of the different states by synchrotron small angle x-ray scattering. The results show that in the acidic-unfolded U 1 form the protein assumes a worm-like conformation, whereas in the alkaline-unfolded U 2 state, the cyt-c is globular. Moreover, the molten globule states induced by adding HCl or NaCl to U 1 appear structurally different: in the A 1 state cyt-c is dimeric and less compact, whereas in the A 2 form the protein reverts to a globular-like conformation. According to the local heme structure, a molecular model for the different forms is derived.

Download

Ligand-Induced Conformational Changes in Tissue Transglutaminase: Monte Carlo Analysis of Small-Angle Scattering Data

Biophysical Journal, 2000

Small-angle neutron and x-ray scattering experiments have been performed on type 2 tissular trans... more Small-angle neutron and x-ray scattering experiments have been performed on type 2 tissular transglutaminase to characterize the conformational changes that bring about Ca 2ϩ activation and guanosine triphosphate (GTP) inhibition. The native and a proteolyzed form of the enzyme, in the presence and in the absence of the two effectors, were considered. To describe the shape of transglutaminase in the different conformations, a Monte Carlo method for calculating small-angle neutron scattering profiles was developed by taking into account the computer-designed structure of the native transglutaminase, the results of the Guinier analysis, and the essential role played by the solvent-exposed peptide loop for the conformational changes of the protein after activation. Although the range of the neutron scattering data is rather limited, by using the Monte Carlo analysis, and because the structure of the native protein is available, the distribution of the protein conformations after ligand interaction was obtained. Calcium activation promotes a rotation of the C-terminal with respect to the N-terminal domain around the solvent-exposed peptide loop that connects the two regions. The angle between the longest axes of the two pairs of domains is found to be above 50°, larger than the value of 35°calculated for the native transglutaminase. On the other hand, the addition of GTP makes possible conformations characterized by angles lower than 34°. These results are in good agreement with the proposed enzyme activity regulation: in the presence of GTP, the catalytic site is shielded by the more compact protein structure, while the conformational changes induced by Ca 2ϩ make the active site accessible to the substrate.

format_quoteGTP induces compact conformations in TG-ase, shielding the catalytic site from substrates, while Ca2+ enhances accessibility.format_quote

Download

MnAs: magnetic-field-induced structural phase transformation and associated magnetoresistance

MnAs, a commercially available material first studied a century ago, exhibits a first-order phase... more MnAs, a commercially available material first studied a century ago, exhibits a first-order phase transition from a ferromagnetic, high-spin metal NiAs-type hexagonal phase to a paramagnetic, lower-spin insulator MnP-type orthorhombic phase at T_C= 313 K. We report the results of neutron diffraction experiments showing that an external magnetic field, B, stabilizes the hexagonal metallic phase above T_C. The phase transformation is reversible and constitutes the first demonstration of a bond-breking transition induced by a magnetic field. At 322 K the hexagonal structure is restored for B > 4 tesla. The field-induced phase transition is accompanied by an enhanced magnetoresistance of about 17 % at 310 K. We discuss the origig of this phenomenon, which appears to be similar to that of the colossal magnetoresistance response observed in some members of the manganese perovskite family.

F. Carsughi

Uploads

Papers by F. Carsughi

Log In