WEB Investigating the compatibility of high entropy alloys with aggressive Pb environments for energy related applicationWednesday (23.09.2020) 11:50 - 12:05 S: Structural Materials 2 Part of:
High entropy alloys (HEA) have attracted the worldwide attention due to their intriguing compositions, microstructures and engineering properties. Containing four or more principle elements (concentrations of each element: 5-35 at.%), they can form either single solid solution or solid solution plus intermetallic. By adding aluminum, the alloys are able to form thermodynamic stable alumina-rich scale in oxygen-containing condition. Recent studies of HEA exposed to harsh environments (e.g. high temperature, corrosion condition) have underlined their potential as structure materials for energy related applications .
Lead and lead-based alloys are under consideration as working fluids for energy production system, such as advanced nuclear reactors. However, the issue of the compatibility with structural steels, in terms of corrosion and mechanical resistance, causes considerable concerns. The results of a systematic study of the corrosion behaviour and microstructural stability of alumina-forming HEA, during exposure to oxygen-containing molten lead, are presented in this communication.
Eight HEA alloys have been designed based on the empirical parameters, including enthalpy of mixing, atomic size difference, parameter Omega and valance electron concentration. The designed alloys include three quaternary alloys with dual phase (FCC plus B2 or BCC), two quaternary alloys with single FCC phase, and three quinary alloys (single FCC, FCC+Laves and FCC+γ'-phase). Compatibility tests have been performed in 10-6 wt.% oxygen containing molten Pb at 600 °C for 1000-2000 h. Five samples are able to form protective oxide scale at both exposure time. Microstructure analysis of protected samples indicate the formation of an outer layer based on Cr2O3 or TiO2 (HEA alloyed with Ti), and an inner layer of Cr2O3-Al2O3. Moreover, samples with dual phases or secondary Laves (FCC+Laves) show their microstructure stability after 1000-2000 h exposure. The single phase HEA alloy has the B2-NiAl precipitates at the grain boundaries after the corrosion test. Sample with Ti addition exhibits phase transformations, namely FCC to sigma and γ'-phase to Eta-phase during 1000-2000 h exposure.
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