Erosion-corrosion behavior of high-speed steel (HSS) and titanium aluminum nitride (TiAlN) coating were investigated under different flow conditions in simulated seawater. On the front side (facing toward the direction of water flow), there was a negligible failure of the TiAlN coating, but clear marks of erosion-corrosion on the HSS. Notwithstanding, unexpected failure features were identified on the back side (back against the direction of water flow) on both specimens because the high-velocity water flow was localized at the edge and the center was high in turbulence. For the HSS, there was dominant corrosion in the center and dominant erosion at the edge. For the TiAlN/HSS coating, the dense and layered structure retards the propagation of surface cracks as the major failure into the bulk and instead promotes layer-by-layer spallation. Additionally, visible “flow marks” were observed on both specimens and can be explained by the flow-accelerated-corrosion.

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