Investigation of optimum materials selection in thermal spray coating for the corrosion protection of STS 304

Abstract

Various thermal spray methods were electrochemically investigated to optimize the anticorrosion protection for 304 stainless steel (STS 304) shafts used in small ships. In the presence of seawater, thermal spray coatings applied to STS 304 act as a sacrificial anode, allowing the coating to preferentially corrode over the stainless steel. For STS 304 alone and with the various coating materials tested, Tafel analysis indicated the following corrosion current densities: STS 304, 7x10-7 A/cm2; Zn, 2.4× 10 -5 A/cm2; Al, 7×10-6 A/cm2; and Zn+15%Al, 1×10-5 A/cm2. The corresponding corrosion potentials were STS 304, -0.1877 V; Zn, -1.1482 V; Al, -0.8119 V; and Zn+15%Al, -1.0108 V. Tafel current densities were the lowest for Al-coated specimens and highest for Zn-coated specimens. The corrosion protection characteristics and the lifetime of the thermal spray coating layers were also estimated. In general, the anticorrosion properties were excellent, exhibiting a noble potential and low corrosion current density.