Wall Forum 2017

The elemental mapping of large areas using ion beam techniques is a desirable capability of several scientific communities, involved on topics ranging from geoscience to cultural heritage. Usually, the constraints for large-area mapping are not met in setups employing micro- and nano-probes implemented all over the world. In this sense, a novel setup for mapping large sized samples in an external beam was recently built at the University of São Paulo employing a broad MeV-proton probe with sub-millimeter dimension, coupled to a high-precision large range XYZ robotic stage (60 cm range in all axis and precision of 5 um ensured by optical sensors). An important issue on large area mapping is how to deal with the irregularities of the sample's surface, that may introduce artifacts in the images due to the variation of the measuring conditions. In our setup, we implemented an automatic system based on machine vision to correct the position of the sample to compensate for its surface irregularities. As an additional benefit, a 3D digital reconstruction of the scanned surface is also obtained. [mehr]

Oxide dispersion strengthened (ODS) steels are promising structural material candidates for both generation four (GEN-IV) fission reactors and breeding blanket material in future fusion power plants. Within the framework of FP7 project MatISSE (Material's innovations for safe and sustainable nuclear energy in Europe), characterization and mechanical testing of several Fe-Cr alloys was undertaken. One of the alloys under investigation is a tempered martensitic 9Cr-ODS steel. The microstructure typically consists of a high density of hierarchically organized internal interfaces such as prior austenitic grain, packet or block boundaries, lath boundaries and sub-grains with high dislocation density. Coarse non-regular M23C6 carbides decorate different boundaries and are rich in Fe, Cr, and W. The complex nano-sized Y-Ti-O particles were observed embedded in the matrix. Tensile tests at various temperatures showed a good compromise between strength and ductility. However, for application, the behavior of ODS steels under cyclic loading is of decisive importance.The fully reversed strain-controlled low-cycle fatigue tests at elevated temperatures revealed a distinctive cyclic response. Apart from the higher cyclic stress levels, the steel manifests complex cyclic softening which is significantly lower in comparison to that observed for similar non-ODS steels. The presence of nano-sized particles was found beneficial in terms of mitigating the well-known cyclic softening in non-ODS steels. Testing includes creep-fatigue investigations by introducing a hold-time at the peak tensile strain. Such a hold period simulates the loading of a component under stationary operation. Introducing creep into the fatigue loading results in lower fatigue life. The tests are accompanied by microstructural investigations for the identification of main deformation and damage mechanisms. [mehr]

The H diffusion in intact model MOS structures is probed by H depth profiling via resonant 15N-H nuclear reaction analysis (NRA) combined with a variety of surface-sensitive spectroscopies. It is discovered that a specific oxynitride layer observed on the near-surface region of nitride films is able to function as a potential H diffusion barrier. This ultra-thin layers are desirable in the integrated circuit processing of silicon transistors. [mehr]