An Investigation of Pitting Behavior of Iron-Molybdenum Binary Alloys

An investigation of the iron-molybdenum binary system was undertaken to determine the effects of molybdenum on pitting and passive film behavior. Polarization curves, galvanostatically determined pitting potentials, and AES and ESCA surface analysis were employed to investigate binaries in the composition range of 5 to 95% Mo. Passive films, which were formed in a borate buffer solution, were depleted in molybdenum and were in general less protective than that on Fe. Alloying up to 15% Mo increased the resistance to pitting in a borate buffer solution +0.1 N KCl solution, but with less effect than observed for stainless steels. Also, the pitting resistance was observed to decrease with increasing temperature for each binary. Precipitated material identified as FeMoO₄ was found in the pits and along the flow paths establishing the existence of a salt film containing molybdenum as a factor in the pitting behavior of molybdenum containing alloys.