Effects of Cr, Mo and B on corrosion behavior of Fe3Al intermetallic compounds

Effects of Cr, Mo and B on the corrosion behavior of Fe3Al intermetallic compounds in H2SO4, H2SO4+KSCN and HCl solutions were investigated using electrochemical tests. The corrosion morphologies and the corrosion products were analyzed by utilizing scanning electron microscopy (SEM) and electron probe micro analysis (EPMA). Addition of Cr and Mo to the Fe3Al intermetallic compound increased corrosion potential, pitting potential and repassivation potential. Active current density, passive current density and reactivation current density decreased as Cr and Mo were added. In the case of Mo addition, the passive current density was slightly higher in the H2SO4 solution than in the solutions containing SCN- and Cl-. When B was added, the corrosion potential and repassivation potential decreased, whereas the active current density, passive current density, reactivation current density and pitting potential increased. Fe3Al intermetallic compounds containing Mo and Cr showed remarkably improved resistance against intergranular and pitting corrosion in SCN- and Cl- solutions. On the other hand, boron-addition accelerated both general and intergranular corrosion by precipitation of borides.