The corrosion behavior of intermetallic compounds Ni 3(Si,Ti) and Ni 3(Si,Ti) + 2Mo in acidic solutions

Abstract

The corrosion behavior of the intermetallic compounds homogenized, Ni 3(Si,Ti) (L1 2: single phase) and Ni 3(Si,Ti) + 2Mo (L1 2 and (L1 2 + Ni ss) mixture region), has been investigated using an immersion test, electrochemical method and surface analytical method (SEM; scanning electron microscope and EPMA: electron probe microanalysis) in 0.5 kmol/m 3 H 2SO 4 and 0.5 kmol/m 3 HCl solutions at 303 K. In addition, the corrosion behavior of a solution annealed austenitic stainless steel type 304 was studied under the same experimental conditions as a reference. It was found that the intergranular attack was observed for Ni 3(Si,Ti) at an initial stage of the immersion test, but not Ni 3(Si,Ti) + 2Mo, while Ni 3(Si,Ti) + 2Mo had the preferential dissolution of L1 2 with a lower Mo concentration compared to (L1 2 + Ni ss) mixture region. From the immersion test and polarization curves, Ni 3(Si,Ti) + 2Mo showed the lowest corrosion resistance in both solutions and Ni 3(Si,Ti) had the highest corrosion resistance in the HCl solution, but not in the H 2SO 4 solution. For instance, it was found that unlike type 304 stainless steel, these intermetallic compounds were difficult to form a stable passive film in the H 2SO 4 solution. The results obtained were explained in terms of boron segregation at grain boundaries, Mo enrichment and film stability (or strength).