The Effect of the Amorphous and Crystalline States on Preferential Corrosion of Hf from a Cu₇₅Hf₂₀Dy₀₅ Alloy

Abstract

Amorphous solid-solution Cu₇₅Hf₂₀Dy₀₅, which undergoes devitrification without changing composition either locally or globally, was used to examine the effects of structural ordering on corrosion properties in the absence of any accompanying chemical partitioning. Melt spun amorphous Cu₇₅Hf₂₀Dy₀₅ undergoes single-phase devitrification to a Cu₅₁Hf₁₄ phase. The difference in corrosion behavior between these two structures was explored in hydrofluoric acid solutions where preferential dissolution of hafnium occurred. Preferential Hf dissolution occurred more readily in the amorphous alloy compared with its crystalline counterpart. Remaining copper reorganized to form a face-centered cubic (fcc) nanostructure in both conditions, but this process occurred quickly in the amorphous state and more slowly in the crystalline variant. A uniform, nanoporous Cu sponge structure, with a pore diameter of approximately 10 nm, formed after dissolution in the amorphous state. A less uniform, nanoporous structure developed more slowly when occurring from the crystalline state. These differences were traced to the effects of ordering on both dissolution and surface diffusion.