The influence of SRB on corrosion behavior of Cu-based medium-entropy alloy coating sprayed by HVOF

In this study, a novel Cu-based (Cu55Al20Ni12Ti8Si5, at.%) medium-entropy alloy (MEA) coating was prepared by high-velocity oxygen-fuel (HVOF) spraying technology. Thermo-Calc was employed to simulate the phase diagram of the alloy system. Phase composition and microstructure of the as-sprayed coating were characterized by means of XRD, FESEM, TEM and STEM/EDX. The effect of sulfate-reducing bacteria (SRB) on the corrosion behavior of the coating and the as-cast Ni-Al bronze (NAB) was investigated using electrochemical measurements and surface characterization. The Thermo-Cala simulation results showed that the alloy system presented a single BCC solid solution phase, while the detailed characterization of microstructure indicated that a few NiTi-rich B2-ordered precipitates could be also found in the as-sprayed coating other than the Cu-rich BCC matrix. Electrochemical studies illustrated that the coating exhibited superior corrosion resistance than the NAB in SRB medium, the corrosion acceleration efficiency induced by SRB of the NAB (95.3 %) was more severe than that of the coating (63.8 %). Surface analysis results demonstrated the occurrence of pitting corrosion and the formation of Cu2S on the coating surface after corroded in SRB medium. Corrosive metabolite HS- induced microbiologically influenced corrosion was considered as the main corrosion acceleration mechanism caused by SRB.