T91 martensitic heat-resistant steel is a key structural material for generation IV lead–bismuth-cooled fast reactors; however, it suffers from severe oxidation corrosion in lead–bismuth eutectic (LBE) environments. To address this issue, FeNiCrAlTi high-entropy alloy (HEA) coatings were deposited on T91 steel using hot-filament-assisted magnetron sputtering with filament discharge currents of 0, 12, and 24 A. As the discharge current increased, the substrate bias current density increased, indicating higher ion bombardment energy during deposition. Therefore, the coating microstructure evolved from a loose, columnar to a highly dense morphology, accompanied by a phase transition from a single body-centered cubic (BCC) phase to stable face-centered cubic (FCC) + (BCC) dual-phases and considerable reduction in surface roughness. The 24 A discharge-current coating exhibited the highest corrosion potential (−0.3656 V), the lowest corrosion current density (1.186 × 10−6 A/cm2), and the largest charge-transfer resistance, indicating a barrier to Cl− ion diffusion. After immersion in oxygen-saturated LBE at 550 °C for 1000 h, the loose coating facilitated oxygen diffusion, leading to thick interfacial oxide layers. By contrast, the dense 24 A discharge-current coating formed a continuous and compact Cr2O3/Al2O3 surface oxide layer, and no oxide layer was observed at the coating–substrate interface. The dense HEA coating can effectively suppress inward oxygen diffusion and considerably enhance the oxidation-corrosion resistance of T91 steel in LBE environments.
Fu et al. (Tue,) studied this question.
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