Effect of Long Range Order on the Stress Corrosion Susceptibility of a Nickel-33 at% Chromium Alloy

Fracture mechanics based stress corrosion testing in high-temperature, high purity water was conducted on a Ni-33 at% Cr (30.7 wt%) binary alloy heat treated to produce different degrees of strength via long range order. The as-fabricated and 475°C/200 h aged samples did not exhibit stress corrosion cracking (SCC) at the test conditions (338°C, K_I = 33 MPa√m, and 12 SCC H₂/kg H₂O), but the 475°C/2,000 h aged sample was susceptible. Similar to the effect of “cold work,” the increased hardness, higher strength, and decreased ductility associated with the development of the long range ordered Ni₂Cr phase is detrimental to SCC resistance.