Metallography and mechanical parameters of plasma-exposed plasma-facing materials and components

Abstract

The performance of materials in a fusion environment is strongly dependent on the loading history, potentially leading to material modification due to thermal and particle (charged and neutral) loads. One clear indication of material modification by thermal loads is the modification of the microstructure by recrystallization, which is assessed by metallographic means as well as hardness measurements. Thereby, the recrystallization behaviour of a material strongly depends on its manufacturing route, the impurity level and on plasma impact, i.e. processes related to plasma–wall interactions. In this study, surface roughness and morphology as well as metallographic examinations and investigation by indentation techniques of components coming from different joint European torus (JET) experimental campaigns were performed for the first time on tritium-containing and therefore radioactive materials and components. This comprises on the one hand standard, marker and dedicated melt tungsten lamellae obtained from the divertor. On the other hand, beryllium components covered by nickel/beryllium marker coatings from the inner wall of JET, i.e. the inner wall guard limiter, wide poloidal limiter and dump plate were investigated. These have undergone various loading conditions and temperature excursions leading to surface modifications like material erosion, deposition and melting, and have also been assessed by scanning electron microscopy and energy-dispersive x-ray spectroscopy in view of the influence of the marker layers.