Evolution of Nanoporous Surface Layers on Gas-Atomized Ti₆₀Cu₃₉Au₁ Powders during Dealloying

Nanoporous golf ball-shaped powders with a surface porous layer consisting of fcc Cu and Cu₃Au phases have been fabricated by selectively dissolving gas-atomized Ti₆₀Cu₃₉Au₁ powders in 0.13 M HF solution. The distribution profiles of the Ti₂Cu and TiCu intermetallic phases and powder size play an important role of the propagation of the selective corrosion frontiers. The final nanoporous structure has a bimodal characteristic with a finer nanoporous structure at the ridges, and rougher structure at the shallow pits. The powders with a size of 18⁻75 m dealloy faster due to their high crystallinity and larger powder size, and these with a powder size of smaller than 18 m tend to deepen uniformly. The formation of the Cu₃Au intermetallic phases and the finer nanoporous structure at the ridges proves that minor Au addition inhibits the fast diffusion of Cu adatoms and decreases surface diffusion by more than two orders. The evolution of the surface nanoporous structure with negative tree-like structures is considered to be controlled by a percolation dissolution mechanism.