Anomalous ultra-small-angle x-ray scattering from evolving mcrostructures during tensile creep

摘要

Ultra-small-angle X-ray scattering provides quantitative and statistically significant information on the size distribution of electron density inhomogeneities with dimensions between approx apprhx 100 A and approx approx 5 mu m. All sizes are sampled simultaneously with a single experient, removing the possibility of observational bias. In a material such as commercial silicon nitride, where the inhomogeneities are due to populations of intergranular secondary phases and viods of similar dimensions, the scattering contains contributions from each individual population. A single USAXS scan cannot separate overapping populations of scatterers due to the different contrasts of the microstructural components. Anomalous USAXS (A-USAXS) is an element-populations contrast variation method to vary the scattering contribution from one of the opopulations while holding that of the other populations fixed. To follow the size evolution under tensile creep of both the cavities and the Yb disilicate secondary phases, A-USAXS data was measured near the Yb L_(III) absorption edge. Creep cavity and dislicate size distributions were each determined as a function of deformation.