Versprödung von Metallen bei hohen Temperaturen (T ≤\leq 0.45 TM_{M}) durch Helium

High temperature helium embrittlement, swelling and irradiation creep are the main technical problem of $\underline{fusion}$ $\underline{reactor}$ $\underline{materials}$. The expected helium production will be very high. The helium produced by (n, $\alpha$)-processes precipitates into heliumbubbles because its solubility in solid metals is very low. Under continuous helium production at high temperature and stress the helium bubbles grow and lead to intergranular early failure. Solution annealed foil specimens of austenitic stainless steel AISI 316 were implanted with a-particles: (1) during creep tests at 1023 K ("in-beam" test) (2) before the creep tests at high temperature (1023 K). The creep tests have been performed within large ranges of test parameter, e. g. applied stress, temperature, helium implantation rate and helium concentration. After the creep tests the microstructure was investigated using scanning (SEM) and transmission (TEM) electron microscopy. All the helium implanted specimens showed high temperature helium embrittlement, i. e. reduction of rupture time t$_{R}$ and ductility $\epsilon$$_{R}$ and evidence of intergranular brittle fracture. The "in-beam" creep tests showed greater reduction of rupture time t$_{R}$ and ductility than the preimplanted creep tests. The comparison of this experimentally obtained data with various theoretical models of high temperature helium embrittlement showed that within the investigated parameter ranges the mechanism controlling the life time of the samples is probably the gas driven stable growth of the helium bubbles within the grain boundaries

Post-operational characterization of solid oxide fuel cell stacks-1

Progress in solid oxide fuel cell (SOFC) cell and stack development depends strongly on improvements stimulated by post-operational characterizations. Although highly motivated by the analysis of unintended interruptions or stack failures, detailed characterization of SOFC stacks after operation provides information on the behaviour of advanced materials and optimized microstructures as well as interactions during start-up, operation, and shut-down, hence, also with respect to manufacturing quality control and stack structural integrity and its relationship to manufacturing, design, dimensions and tolerances. This work summarized the experience of more than 300 post-test analyses that have been carried out in the past 15 years, their careful dissection, photography, and subsequent detailed characterization that included numerous detailed examinations of all stack components. Particular analyses' concerning the different stack components are highlighted, exemplifying useful analytical methods. Finally, conclusions are presented with respect to ongoing R&D work and future directions

Post-test characterization of an SOFC short stack after 17,000 hours of steady operation

The characterization of operated SOFC stacks is one important possibility to i) develop novel materials, ii) to optimize cell microstructures, iii) to understand interactions during start-up, operation and shut-down, iv) to analyse unwanted interruptions or stack failure, v) to control manufacturing quality and vi) to characterize stack structural integrity with respect to the engineering drawings, manufacturing admeasurements and tolerances. In the past 10 years approximately 150 stacks were, after operation, carefully dissected, photographed, characterized and follow-up examinations from all stack components performed. This chapter deals with the description of the course of action and highlights various analyses, including the analytical methods, concerning different stack parts. Finally some conclusions based on the post-test characterization for ongoing R&amp;D were presented.</jats:p