From cast to wire-arc DED: An investigation on NAB alloy MIC resistance

Abstract

This paper presents a comparison of the microbiologically influenced corrosion (MIC) of the cast and multi-pass wire-arc directed energy deposition (DED) nickel-aluminum bronze (NAB) alloys in sulfate-reducing bacteria (SRB) solution. The corrosion of the alloys is concentrated in the large-sized κ phase and the residual β phase. Owing to the complete suppression of the precipitation of the large-size κ_Ⅰ phase and the reduction in the size of the remaining κ phase, the corrosion resistance of the wire-arc DED NAB alloys is higher than that of the cast alloys. The precipitated phases in the pre-deposition layer of the wire-arc DED NAB alloy in the lap zone are almost entirely converted to κ_Ⅲ and κ_Ⅳ phases, and the grain size of 6.7 μm is smaller than that of the substrate (12.6 μm). Thus, the corrosion sensitivity of the lap zone is higher, and the MIC resistance is lower than that of the substrate, the R_ct value after 30 d is 1.60 × 10⁵ Ω·cm² which is smaller than that of the substrate (1.96 ×10⁵ Ω·cm²).