Unveiling the influence of zirconium on the corrosion behavior of Fe-36Ni Invar alloy

The influence of zirconium (Zr) on the corrosion resistance of Fe-36Ni Invar alloy in a 3.5 wt% NaCl solution was systematically investigated. Results indicated that adding Zr promoted the formation of Zr-bearing intermetallic compounds (Ni7Zr2 and Ni2Zr). The phases suppressed the grain growth and numerous dislocations were enriched around the Ni-Zr phases. Unfortunately, the incorporation of Zr into Fe-36Ni Invar alloy impaired corrosion resistance. The marked disparity in Volta potential between the Ni-Zr phases and the matrix signified the existence of micro-galvanic coupling, which caused the matrix to dissolve preferentially. Furthermore, the matrix around the Ni-Zr phases possessed high dislocation density, promoting the emergence of local galvanic corrosion. The introduction of Zr also decreased the protectiveness of the passive film, which was ascribed to the reduction of the thickness of the passive film and the beneficial oxide content in the passive film.