Pitting corrosion of intermetallic compound Ni3(Si,Ti) with 2 at% Mo in sodium chloride solutions

The pitting corrosion of Ni3(Si,Ti) with 2 at% Mo consisting of a single intermetallic compound Ni3(Si,Ti) phase of L12 structure and a two phase mixture of L12 and fcc nickel solid solution was investigated as functions of test temperature and chloride concentration in sodium chloride solutions by using a potential step method and compared with that of intermetallic compound, Ni3(Si,Ti). The pitting potential obtained for the Ni3(Si,Ti) with 2 at% Mo decreased with increasing chloride concentration and test temperature. A critical chloride concentration below which no pitting corrosion took place was found to exist and to decrease with increasing test temperature. The specific pitting potential at the critical chloride concentration also decreased with increasing test temperature. The pitting potential of Ni3(Si,Ti) with 2 at% Mo was higher than pure nickel, but lower than that of Ni3(Si,Ti). A critical chloride concentration was found to be lower than that of Ni3(Si,Ti), whereas the specific pitting potentials at the critical chloride concentration was found to be higher than that of Ni3(Si,Ti). Pitting corrosion occurred in the two phase mixture region.

► Pitting corrosion of Ni3(Si,Ti) with 2 at% Mo intermetallic compound in NaCl.
► Pitting potential decreased with increasing chloride concentration and test temperature.
► Pitting potential at constant chloride concentrations decreased with increasing test temperature.
► Pitting potential of Ni3(Si,Ti) with 2 at% Mo was higher than pure nickel, but lower than Ni3(Si,Ti).
► Pitting corrosion occurred in the two phase mixture region.