Effect of Pb-16Li long term exposure on mechanical properties of ceramic materials

The Dual Coolant Lithium Lead (DCLL) Breeding Blanket (BB) concept is based on the use of liquid metal Pb–16Li. In the current design of the DCLL BB, Pb-16Li circuit is enclosed inside a box made of ceramic material. In the presented design, the ceramic material is directly in contact with Pb-16Li at elevated temperature that may lead to formation of high stresses caused by thermal gradients. In order to prevent premature failures of ceramic box due to demanding operation at elevated temperatures, assessment of the mechanical properties of ceramic material exposed to Pb-16Li is of primary interest.Pristine ZrO2 with 3 mol. % Y2O3 (PSZ) and SiC samples were subjected to three-point bending at room temperature and at 650 °C in argon. The flexural strength of PSZ decreased with increased temperature. SiC material exhibited the similar flexural strengths regardless of the testing temperature. To assess the potential effect of mechanical strength degradation caused by Pb-16Li, some samples were exposed to Pb-16Li at 650 °C for 1000 h prior to mechanical testing in Pb-16Li at 650 °C. Testing of the exposed PSZ and SiC samples showed the similar flexural strengths to the unexposed samples, meaning no significant effect of liquid Pb-16Li was observed.Closer inspection of the polished cross-sections produced from the exposed PSZ samples revealed formation of the two layered structure near the sample surface. Micro-/nano- indentation technique was adopted to assess the difference between the developed surface layers and inner material in terms of hardness. In addition to hardness evaluation, fracture toughness of the material was evaluated from the length of the cracks developed after micro-indentation testing. Chemical composition of the surface layers was investigated by means SEM/EDS. The analysis showed thin surface layer depleted in Zr and Y.Additionally, hardness and fracture toughness were also studied and evaluated for SiC material. In contrast to PSZ, exposed SiC material to Pb-16Li did not exhibit changes in microstructure when compared to material in its as-received state.