Enhancing the Corrosion Resistance of Near-Stoichiometric Ni₄Mo Alloy by Doping with Yttrium

It is shown that doping with yttrium can significantly improve the corrosion resistance of near-stoichiometric Ni₄Mo alloy, which is otherwise susceptible to severe intergranular attack in the ordered condition. A one-to-one correspondence is found to exist between corrosion resistance and morphology of ordered Ni₄Mo. The susceptibility to intergranular corrosion is correlated with a discontinuous grain boundary reaction resulting from self-generated recrystallization to accommodate the strain associated with continued growth of the ordered crystals. Doping with Y is found to maintain an ultrafine ordered microstructure suppressing the occurrence of self-generated recrystallization and, therefore, improving the corrosion resistance.