Effects of Mo additions on the potentiostatic corrosion behaviour of multiphase 316L SS-based alloys

ABSTRACT A set of cast alloys was made by alloying 316L stainless steel powder with 5, 10, and 15 wt-% Mo to study the effects of the Mo content on the microstructures and corrosion behaviours. Sigma phases formed in all alloys and Laves phases co-precipitated in alloys with Mo additions of 10 and 15 wt-%. Alloys with higher Mo concentrations had greater volume fractions of both intermetallic phases, which contained higher Mo but lower Ni levels than the austenite. Potentiodynamic and potentiostatic tests were performed in pH 4 solution containing 10 mM NaCl to provide an aggressive chemical environment. All cast alloys had higher corrosion resistance than 316L SS. Electrochemical impedance spectroscopy showed the Mo content had a significant beneficial effect on the electrical properties of the passivating layers under highly oxidising conditions, but only a minor effect under moderately oxidising redox conditions.