• ageing
• austenitic steels
• electron microscopy
• Generation IV

This Master’s Thesis is the result of an experimental work conducted at University of Illinois of Urbana-Champaign and, in part, at Argonne National Laboratory.
The aim of the study is the investigation of an austenitic stainless steel, called DS4, developed to be deployed as structural material for generation IV reactor. In particular, microstructural characteristics have been analyzed by means of electron microscopy and X-ray diffraction, to understand the response of the material to high temperature environment and heavy-ions irradiation.
The evolution of the steel microstructure in a nuclear reactor severely influences the change of macroscopic mechanical properties, for example the on-set of cavities nucleation results in the change of volume of a nuclear component, such as the cladding.
Moreover, this is intended to verify the effect caused by the variation of material composition of DS4, provided by ENEA-Brasimone Research Center, with respect to the previous version of the alloy. The main hazard of a non-optimized composition is the nucleation of brittle phases, able to promote fracture without plasticization.
In addition, an in-situ TEM analysis has been carried out to assess the performance of the material under heavy-ions bombardment.
Experimental data revealed that the steel is stable at high temperature (ageing at 550°C and 750°C) and that the ductility is so preserved. On the other hand, the performance at 5 dpa and 500°C is totally unsatisfactory, since, at the end of the test, cracks appear along grain boundaries.