Assessment of the chemical compatibility between EUROFER and ceramic breeder with respect to fatigue lifetime

In advanced designs of DEMO breeding blankets with ceramic breeder, the structural material EUROFER is in direct contact with the pebbles of the ceramic breeder (Li4SiO4 + Li2TiO3) that results in a loss of constituent elements in the ceramic and the formation of a corrosion layer on EUROFER under operation relevant condi-tions. The impact of this corrosion attack on damage mechanisms which are significantly influenced by microstructural changes at the surface, in particular fatigue, needs to be considered in the design of affected components and is therefore investigated within the work reported here. Fatigue specimens made out of EUROFER in unconstrained contact to ceramic breeder pebbles were exposed to purge gas conditions for different durations. The chemical surface attack observed after the exposure is characterized by round stains, partly even round dimples, consisting of concentric diffusion zones which meet in case of the long exposure time forming an almost closed corrosion multi-layer. The impact of this attack on the fatigue behavior was subsequently investigated by performing strain-controlled low cycle fatigue (LCF) tests at 550 degrees C. To cover the scatter expected for the fatigue lifetime, a sufficient number of LCF experiments were conducted. The results show significant reduction of the fatigue lifetime, which quantitatively depends on the level of the attack/exposure time as well as the level of the applied load/strain amplitude.