The Electrochemical Behavior of P- and C-Doped Ni-16Cr-9Fe⁽¹⁾ Available to Purchase

High purity Ni-16Cr-9Fe alloys with controlled additions of P and C were annealed and heat- treated to produce all combinations of chromium carbide precipitation, chromium depletion, and phosphorus segregation at the grain boundary. Each alloy heat treatment was subjected to potentiodynamic polarization and electrochemical potentiokinetic reactivation. Polarization scans showed little difference between alloy heat treatments; the most pronounced was a higher critical current density in P-doped alloys. An electrochemical potentiokinetic reactivation (EPR) test solution and method were developed to discriminate between varying degrees of chromium depletion while eliminating the problem of intragranular pitting. The total charge transferred during a reverse scan is not highly sensitive to the variation in Cr in the depleted zone. Dissolution models that are independent of and proportional to the Cr gradient in the depleted zone indicate that the threshold level of Cr below which grain boundaries are attacked is 14 and 15%, respectively. Evidence of a combined effect of P segregation and Cr depletion on intergranular attack (IGA) was found.