Comparison of the Phase Stability and Corrosion Resistance of the Ni-Based Alloys C-4 and C-276

A one-to-one correspondence is developed between the phase stability and corrosion resistance of the commercial (Ni-Cr-Mo)-based alloys C-276 and C-4. Alloy C-4 is shown to outperform alloy C-276 in acidic oxidizing media and approaches its resistance in acidic reducing media. Both alloys are found to have similar resistance to chloride-induced stress corrosion cracking in the annealed condition with short-range order. The aqueous corrosion resistance of both alloys is found to be improved by long-range order; however, they become highly susceptible to chloride-induced stress corrosion cracking. Alloy C-4 is distinguished by being stable toward precipitation of detrimental intermetallic compounds. However, alloy C-276 is shown to be prone to precipitation of mu phase which degrades its resistance to aqueous corrosion and chloride-induced stress corrosion cracking. It is concluded that the chemical composition of alloy C-4 is tailored to make it more versatile than alloy C-276 in acidic oxidizing media and the results are found to be consistent with the concept of atomic percent factor of each alloy.