OXIDATION AND CRYSTALLIZATION OF AN AMORPHOUS ZR60AL15NI25 ALLOY

The amorphous ternary metallic alloy Zr60Al15Ni25 was oxidized in dry oxygen in the temperature range 310 degrees C to 410 degrees C, Ruther ford backscattering (RES) and cross-sectional transmission electron mi croscopy (TEM) studies suggest that during this treatment an amorphous layer of zirconium-aluminum-oxide is formed at the surface, Nickel wa s depleted in the oxide and enriched in the amorphous alloy near the i nterface. The oxide layer thickness grows parabolically with annealing duration, with a transport constant of 2.8 x 10(-5) m(2)/s x exp(-1.7 eV/kT). The oxidation rate may be controlled by the diffusion of Ni i n the amorphous alloy. At later stages of the oxidation process, preci pitates of nanocrystalline ZrO2 appear in the oxide near the interface . Finally, two intermetallic phases nucleate and grow simultaneously i n the alloy, one at the interface and one within the alloy. An explana tion involving preferential oxidation is proposed.