Microstructure and mechanical behavior in liquid lead-bismuth eutectic and liquid lead of some materials design to limit corrosion by liquid metal : Alumina-Forming Austenitic (AFA) steels and the 15-15 Ti steel with and without aluminium-based coating
Résumé
The corrosion resistance and the mechanical behaviour assessment of structural alloys is crucial for the durability and the safety of the lead cooled Fast Reactor (LFR) and accelerated driven systems (ADS). Moreover, it is well-known that the presence of a liquid metal may compromise the good performances of a metallic alloy due to liquid metal corrosion or liquid metal assisted mechanical damage. Though tough and ductile metallic alloys are selected, they may become brittle when stressed in liquid metal exhibiting thus the so called Liquid Metal Embrittlement (LME). Furthermore, at low oxygen content in liquid metal, dissolution of the metallic alloy or of one element of the alloy can be observed according to the temperature.To avoid LME sensitivity and to increase corrosion resistance of some steels in contact with lead or LBE, different materials were selected, developed and then tested in contact with Pb or LBE. One of the solutions is the presence of aluminium at the surface of the materials in order to allow the formation of an oxide layer, permanently and whatever the content of oxygen present in the liquid metal. This oxide layer aims at avoiding the contact between the steel and the liquid metal, limiting all steel / liquid metal interactions and therefore reducing the corrosion phenomena.The results presented in this communication concern two types of materials: 2 Alumina-Forming Austenitic (AFA) steels and the 15-15 Ti steel coated by aluminium-based material. For the considered steels (for the 15-15Ti steel: with and without coating – for the AFA steels : according to an aging at 650°C for 1000 to 5000 hours), the influence of the presence of the liquid metal was investigated by performing monotonic tests (Small Punch Tests and tensile tests) in air and in liquid LBE or/and liquid lead. After tests, cracking and fracture surfaces were analysed by SEM (scanning electron microscopy), EDX-SEM (energy dispersive X-ray) to characterize and understand the effect of the liquid metal. The effect of the presence of liquid metal (Pb or LBE) will be discussed according to the microstructure of the steels as well as to the strain rate and the temperature (between 350°C and 500°C).The results presented in this paper is a part of the contribution obtained in our lab, for the GEMMA (Generation IV Materials Maturity) H2020 program.