Liquid metal embrittlement sensitivity by LBE of Face-Centered Cubic austenitic steels and Complex Concentrated Alloys
Résumé
One of the challenges in the development of Lead Fast Reactors (LFR) or Accelerator
Driven Systems is the reliability of the structural materials in contact with the coolant,
so the lead or the Lead-Bismuth Eutectic (LBE) and in temperature. In addition of
damage due to irradiation, one of the major damages to structural materials could be
due to corrosion by liquid metal. Additionally, under stress (mechanical stress or stress
caused by temperature fluctuations), structural materials can be susceptible to liquid
metal embrittlement (LME), i.e. partial or total loss of ductility in the presence of liquid
metal and therefore an earlier fracture. Because of the LME sensibility of the Body Centered Cubic alloys, the most ductile Face-Centered Cubic (FCC) alloys could be
preferred because of their low LME sensitivity below 450 °C and despite the corrosion
observed, in particular the selective dissolution of Ni and possible LME sensitivity at
high temperature (500 °C and more). The objective of the presentation is the study of
the LME sensibility of 5 different FCC alloys (15-15Ti steel, two alumina forming
austenitic (AFA) steels and two Complex Concentrated Alloys (CCA) of the family of
the FeCrNiMn alloys, susceptible to be used in presence of LBE and Pb. Small Punch
Tests were performed in air and in LBE saturated in oxygen at different temperatures
between 200 °C and 500 °C. Then, the fracture surfaces and cracking were observed
by Scanning Electron Microscopy. The influences of a lower strain rate and the
composition of the liquid metal (tests in Pb, Bi) were investigated too. All the materials
present ductile behavior and ductile fracture in air. The steels are less susceptible to
LME by LBE that the studied CCAs. In case of LME occurrence, intergranular cracks
were observed. The LME occurrence is discussed taking into account the
microstructure, the hardness and the composition of the alloys. The study was
supported by the GEMMA and INNUMAT projects (Euratom research and training
programme: respectively 2014-2018 - grant agreement No 755269, and 2021-2022 -
grant agreement 101061241).