Oxidation and crystallization of an amorphous Zr₆₀Al₁₅Ni₂₅ alloy

The amorphous ternary metallic alloy Zr₆₀Al₁₅Ni₂₅ was oxidized in dry oxygen in the temperature range 310 °C to 410 °C. Rutherford backscattering (RBS) and cross-sectional transmission electron microscopy (TEM) studies suggest that during this treatment an amorphous layer of zirconium-aluminum-oxide is formed at the surface. Nickel was depleted in the oxide and enriched in the amorphous alloy near the interface. The oxide layer thickness grows parabolically with annealing duration, with a transport constant of 2.8 × 10⁻⁵ m²/s × exp(−1.7 eV/kT). The oxidation rate may be controlled by the diffusion of Ni in the amorphous alloy. At later stages of the oxidation process, precipitates of nanocrystalline ZrO₂ appear in the oxide near the interface. Finally, two intermetallic phases nucleate and grow simultaneously in the alloy, one at the interface and one within the alloy. An explanation involving preferential oxidation is proposed.