Chromium depletion and microstructural effects on molten salt corrosion of wrought and wire-arc additively manufactured Hastelloy C276 alloys

The microstructure and high-temperature corrosion behavior of Hastelloy C276 fabricated by wrought processing and wire arc additive manufacturing (WAAM) were systematically investigated. The wrought alloy exhibited equiaxed grains with uniform elemental distribution, and sparse nanoscale grain boundary precipitates. In contrast, WAAM specimens taken from the top, middle, and bottom regions displayed a textured dendritic γ-Ni matrix with interdendritic Mo/Cr segregation and scattered second-phase particles. Rapid cooling near the substrate produced cellular structures in the bottom region, while limited heat transfer from subsequent layers led to finer and shorter dendrites in the top region. Corrosion testing in FLiNaK at 750 °C for 500 h resulted in average corrosion rates of 0.0935 mm/year (wrought) and 0.0979 mm/year (WAAM). Post-corrosion characterization and modeling identified chromium depletion as the primary degradation mechanism, driving vacancy formation, dynamic recrystallization, and localized pitting, particularly in defect-rich interdendritic and grain-boundary regions. A Cr-depletion-based damage factor was integrated into a corrosion model to predict mass loss and corrosion rate. Although Mo segregation and dynamically formed topologically close packed phases locally hindered Cr diffusion, their overall influence on corrosion depth was limited. The WAAM alloy exhibited slightly inferior corrosion resistance relative to wrought C276, attributable to its higher interdendritic area fraction, while the extent of corrosion remained governed by the Cr‑depletion‑controlled dissolution process. • WAAM C276 shows slightly inferior corrosion than wrought C276 in FLiNaK at 750 °C. • Corrosion is controlled by Cr depletion while microstructure governs where attack localizes. • Interdendritic Cr‑segregated regions in WAAM are the primary pit initiation sites. • The Cr depletion damage factor describes dissolution behavior and complements metal dissolution. • Mo segregation and TCP μ phase act as local diffusion barriers with only marginal influence on overall corrosion.