The effect of Ta segregation on the corrosion resistance of the Fe₃₀Ni₃₀Cr₃₀Al_10-xTa_x high entropy alloys in lead-bismuth eutectic at 800 °C

Abstract

Lead-bismuth eutectic (LBE)-cooled reactors were considered promising candidates for Generation IV nuclear reactor systems due to the favorable physical properties and exceptional safety performance of LBE. This study investigated the role of Ta in enhancing the corrosion resistance of Fe30Ni30Cr30Al10-xTax high-entropy alloys (HEAs) exposed to static LBE at 800 degrees C. Multiscale characterization revealed that Ta-free HEA (0Ta-HEA) formed an outer FeCr2O4 spinel layer, which permitted significant LBE penetration and inward diffusion of oxygen within the first 48h. In contrast, the 2 at.% (in atomic percent) Ta HEA (2Ta-HEA) exhibited superior corrosion resistance, with corrosion depth reduced by similar to 40 %. The low solubility of Ta in LBE led to its rapid saturation and local precipitation, which, in turn, formed protective phases comprising a mixed layer of Al2O3, Cr-rich phase, and FeCr phase. After 168 h of exposure, the competitive mechanism between dissolution and oxidation dominated in the 2Ta-HEA. The mixed layer formed during the initial stage of corrosion gradually evolved into a double-layered scale, consisting of an outer Ta-rich LBE layer and an inner layer of Cr2O3 and FeCr2O4. The discontinuous Al2O3 only inhibited the penetration of LBE at the initial stage of corrosion. These findings highlighted Ta as a strategic alloying element for mitigating LBE corrosion in nuclear applications, stabilizing interfaces, and minimizing elemental loss.