Surface-Condition-Dependent Corrosion of Wire-Laser DED MoNiCr in FLiBe at 750 °C: Effects of As-Built Topography, Wire EDM, and Hot Isostatic Pressing

A Hastelloy N-like MoNiCr alloy produced by wire-laser directed energy deposition (W-DED) was exposed to eutectic LiF–BeF₂ (FLiBe) at 750 °C for 1000 h to assess the effects of manufacturing-generated surface states on corrosion response. Surface-skin coupons were extracted from as-built (AB) and hot-isostatically pressed (HIP) portions of a W-DED cube while preserving either the deposited surface or a wire electrical-discharge-machined (wire-EDM) surface. High-purity LiF and BeF₂ powders were mixed to the eutectic composition (66 mol% LiF–34 mol% BeF₂), melted at 700 °C under nitrogen, and the salt was subsequently remelted and poured over specimens in individual graphite crucibles before hermetic enclosure in laser-welded AISI 304 capsules. Optical profilometry compared exposed coupons with adjacent unexposed reference regions; metallography, SEM, and EDS evaluated microstructure and near-surface chemistry. Preserved deposited surfaces largely retained their orientation-dependent topography, whereas exposed wire-EDM surfaces had lower height-related roughness parameters than the unexposed references and developed a more uniform chromium-depleted region. HIP altered internal microstructure more strongly than macroscopic surface morphology. Because redox potential and a complete material balance were not measured, the results are interpreted as comparative static-screening data for MSR service. Mean chromium-depletion depth was approximately 8 ± 2 µm for preserved W-DED surfaces and 11 ± 1 µm for wire-EDM surfaces.