Stress Corrosion Cracking of Zirconium in Hot Nitric Acid

Zirconium (Zr) has excellent general corrosion resistance in nitric acid. However, stress corrosion cracking (SCC) has been reported in concentrated nitric acid. The purpose of this work is to evaluate the SCC susceptibility of Zr as a function of HNO3 concentration, from 6 to 94%, and temperature. The SCC mechanism was also investigated in relation to the electrochemical behavior. The slow strain rate test technique, under constant potential conditions, was mainly adopted for SCC testing. SCC did not occur in the boiling HNO3 at concentrations less than 70% unless an anodic potential was applied. The critical SCC potential, which coincides with the transient potential from passive to transpassive behavior in the polarization curve, decreased with an increase in HNO₃ concentration. In boiling 94% HNO₃, Zr exhibited SCC even under open-circuit potential conditions.