A. Wiedenmann

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.

Creep Deformation and Microstructural Examination of a Prior Thermally Exposed Nickel Base Superalloy

When exposed for long time at elevated temperatures of 430°C and 650°C the nickelbase superalloy EI 698 VD can experience a significant decrease in the creep. The cause of the creep degradation of nickel-base superalloy has never been unequivocally explained, but it has generally attributed to the microstructural instability at prolonged high temperature exposure. The creep lifetime decrease was more expressive as time of thermal exposure was extended up to 52 000 hours. In this article, the creep life data, generated on prior long thermally exposed wrought nickelbase superalloy were related to the microstructural changes observed using SEM and TEM analysing techniques. Qualitative and quantitative structure analyses provided supporting evidence concerning changes associated with grain boundary carbide precipitation and with volume fraction changes of gamma prime the exposure time prolonged. In order to clarify the role of gamma prime distribution modification in thermally exposed superalloy on creep degradation the SANS (Small Angle Neutron Scattering) diffraction experiment was employed in the characterization of the gamma prime morphology and the size distribution with respect to the period of thermal exposure.

SANS study and a model for partially ordering during decomposition in bulk amorphous Zr41Ti14Cu12.5Ni10Be22.5 amorphous alloys

Abstract Small-angle neutron-scattering experiments have revealed information about the decomposition behaviour of Zr41Ti14Cu12.5Ni10Be22.5 bulk amorphous alloys. In the undercooled liquid range, a microstructure consisting of precipitates of an amorphous phase was observed. Experimental results showed that all scattering curves have a characteristic maximum. In wide intervals of annealing temperature and annealing time the curves obey a universal scaling law. This behaviour is reproduced by a model consisting of a hard-core arrangement of spherical particles with constant scattering length density in the core and a diffusion profile in a surrounding shell. The model is treated analytically at volume fractions below 12.5% and by computer simulation otherwise.

Small-Angle Neutron Scattering Investigation of Precipitation in Single-Crystal Nickel-Based Superalloy ZS26

The influence of different heat treatments on the microstructure of ordered cuboidal γ′ precipitates in the ZS26 superalloy (wt%: Ni 64, W 11, Co 9, Al 6, Cr 5, Nb 1.5, Ti 1, Mo 1, V 1) was studied by small-angle neutron scattering. The average shape and size of the precipitates were determined by modelling the scattering curves and by fitting them to the measured 2D data. The volume fraction of the precipitates was deduced from the fitted parameters under the assumption of a homogeneous distribution of particles inside the sample.

Analysis of SANS-data with models of stochastic geometry

Abstract Variable random and partially disordered germ-grain models are generated both by analytical mathematical methods and by computer simulations. The small-angle scattering intensities of the models are calculated and the experimental SANS data obtained from Si3N4-ceramics and from bulk amorphous metallic alloys are interpreted in terms of the models.