Pavel Strunz

General formula for determination of cross-section from measured SANS intensities

A detailed derivation of the formula connecting measured SANS intensity with the smeared cross-section (raw-data treatment) is presented. The derivation is carried out considering also a possible high probability of the coherent small-angle scattering. The information content of the so-called transmission measurement is analyzed. The individual effects which contribute to the primary-beam attenuation as well as the different modes of the transmission measurement are described. Multiple scattering contribution to the excess of the forward scattering of the water calibration standard is discussed.

Lattice misfit measurement in Inconel 706 containing coherent γ′ and γ″ precipitates

Abstract Lattice misfit is an important parameter in Ni–Fe based alloy IN706 as coherency strain influences the strength of the alloy and the stability of the microstructure. X-ray and synchrotron measurements were performed on bulk samples with precipitates in constrained lattice. Lattice parameters of different phases and the lattice misfit could be determined even though the peaks were completely overlapped.

Double-Bent-Crystal Small-Angle Neutron Scattering Setting and its Applications

Theoretical relations for optimum adjustments of two arrangements of a double-bent-crystal (DBC) small-angle neutron scattering (SANS) diffractometer are discussed. Results of several experiments demonstrate the applicability of DBC SANS in the investigation of some technologically important materials in the range of scattering-vector sizes 0.0002-0.02 A -1. Formulas derived for data analysis, which describe the transformation of the SANS cross section to the measured intensity, indicate that water calibration is not required and that the indirect method of data evaluation is the most appropriate.

Evaluation of anisotropic small-angle neutron scattering data; a faster approach

An improvement of the anisotropic small-angle neutron scattering (SANS) data evaluation program is presented. The program is particularly suited for treatment of data from dense precipitate systems like those appearing in single crystal Ni-base superalloys. A new model of the precipitate microstructure was implemented allowing for a significant shortening of the evaluation time which is necessary mainly for in-situ studies. The change concerns the mode in which the size distribution is calculated. The local random smearing of the size as well as the distance of particles was introduced, too, which leads to a more realistic look of the microstructure model. The form of individual cuboidal particle was changed as well. The characteristics of the new microstructure model with respect to the SANS data modeling are tested on several measured as well as simulated data.

High temperature stability of Cr-carbides in an experimental Co–Re-based alloy

Abstract The stability of the microstructure at high temperatures was studied in an experimental Co–Re-based alloy. The experimental alloy is mainly strengthened by Cr-carbides, particularly by those in the form of thin lamellar plates. Electron microscopic investigation on samples exposed for up to 1 000 h to temperatures of 1 000 and 1 200 °C showed that Cr23C6 type carbides present in the alloy in different morphologies are unstable at these temperatures. It was also observed that the alloy hardness dropped after exposing the samples to elevated temperatures and much of this loss occurred within the first 100 h. In-situ diffraction measurements with synchrotron radiation showed that carbide dissolution started as early as 3 h of holding at 1 000 °C. Moreover, in-situ small angle neutron scattering results indicated that the carbides at the grain boundaries and the blocky carbides dissolve first and then the thin lamellar carbides. Further, the enrichment of Cr in the Co-matrix phase, which took place due to the dissolution of Cr-carbides, stabilized a Cr–Re-rich σ phase. Although the dissolution of lamellar carbides results in a significant loss of strength, the formation of σ phase with extremely high hardness partly compensated the for loss. The σ phase is stable even at 1 200 °C.

Measurement of γ′ precipitate morphology by small angle neutron scattering

Modern Ni-base superalloys contain large volume fraction of ordered Ni{sub 3} (Al, Ti) precipitates ({gamma}{prime} phase) which are coherently embedded in a Ni-Al solid solution ({gamma} phase). Superalloys are strengthened by the {gamma}{prime} precipitates and it is known that the precipitate morphology, their distribution in the matrix and their volume fraction strongly influence the strength of the alloys. In this paper the authors results from the measurements by small angle neutron scattering (SANS) and use special data analysis procedures to quantify various {gamma}{prime} morphological parameters. The authors use complementary measurements by scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) to verify and augment the results of SANS. They find SANS is a very useful tool for these kind of measurements as it measures over a large volume of specimen. Further, the 3-Dimensional microstructural parameters could be obtained quantitatively from measurements on a single specimen with the help of a cradle used to in-situ align the specimen with respect to the neutron beam.

Double bent crystal diffractometer for SANS experiments

Abstract The medium resolution SANS diffractometer equipped with a pair of bent perfect crystals set in symmetric Bragg reflection geometry has been employed in NPI Řeẑ in the last decade. The technical realization of a new version of the diffractometer with fully asymmetric diffraction geometry of the analyzer in combination with linear PSD was finished recently. The present paper provides a methodological comparison of both concepts as well as an example of medium resolution SANS experiment on a Vycor glass.

Austenite content and dislocation density in electron-beam welds of a stainless maraging steel

Abstract The volume fraction of austenite and dislocation density in electron beam weld joints of a martensitic-austenitic age-hardenable CrNiMoTiAl stainless steel were investigated using neutron diffraction. Experiments were performed on a high-resolution diffractometer which resolved microstrains of the order of 10 −4 . The effect of post-weld heat treatment on austenite content and dislocation density was investigated. As in other maraging steels, the maximum volume fraction of austenite was obtained after quenching and intercritical annealing. Dislocation densities computed on the base of mean-square microstrain values were about 10 11 cm −2 . These densities were systematically higher in martensite than in austenite, with very small differences between the weld metal and base metal.

Neutron and synchrotron probes in the development of Co-Re-based alloys for next generation gas turbines with an emphasis on the influence of boron additives

Nickel-based superalloys are the materials of choice in the hot section of current gas turbines, but they are reaching temperature limits constrained by their melting temperature range. Co–Re alloy development was prompted by a search for new materials for future gas turbines, where the temperature of application will be considerably higher. Addition of the very high melting point refractory metal Re to Co can increase the melting range of Co alloys to much higher temperatures than the commercial Co alloys in use today. The alloy development strategy is first discussed very briefly. In this program, model ternary and quaternary compositions were studied in order to develop a basic understanding of the alloy system. In situ neutron and synchrotron measurements (small and wide angle) at high temperatures were extensively used for this purpose and some selected results from the in situ measurements are presented. In particular, the effect of boron doping in Co–Re–Cr alloys and the stability of the TaC precipitates at high temperatures were investigated. A fine dispersion of TaC precipitates strengthens some Co–Re alloys, and their stability at the application temperature is critical for the long-term creep properties.

Determination of γ' solution temperature in Re-rich Ni-base superalloy by small-angle neutron scattering

A harmful segregation of heavy elements (e.g. W, Mo, Re) during solidification of Ni-base superalloys can only be eliminated by using a homogenizing heat treatment, which needs to be carried out in the single-phase (γ) field above the γ′ solvus temperature but below the solidus temperature. Small-angle neutron scattering (SANS) was employed for in situ observation of the dissolution of precipitates in an Re-rich superalloy. The temperature dependence of the relative volume fraction and the size distribution of smaller γ′ precipitates, and the specific surface of large inhomogeneities as well as some other parameters were determined from the two-dimensional scattering curves measured for as-cast and heat-treated samples. Overlap of the incipient melting region with the region where a certain amount of precipitates remained undissolved was observed, thus complicating a determination of the temperature at which all γ′ precipitates are already dissolved. Nevertheless, conclusions about the temperature at which the precipitates dissolve and about the temperature at which the incipient melting starts could be formulated. The total scattering probability is suggested as the measure of the overall homogeneity of the distribution of elements in the sample. The temperature dependence of this parameter indicates the optimum solution procedure.