T. Spassov et G. Tzolova, OXIDATION-KINETICS OF AMORPHOUS, POLYCRYSTALLINE, AND NANOCRYSTALLINECO33ZR67 ALLOYS, Crystal research and technology, 31(7), 1996, pp. 881-888
The oxidation kinetics of amorphous, polycrystalline, and nanocrystall
ine CoZr2 alloys have been studied under isothermal conditions in air
atmosphere with a microbalance. DSC and X-ray diffraction were used to
study the influence of oxidation on crystallization. The three alloys
under investigation which have the same composition but differ in the
microstructure showed noticeable differences in their oxidation behav
iour: the oxidation of the amorphous alloy is characterized by a very
fast initial oxygen absorption step, completed in less than 1-2 min, f
ollowed by a slow oxide growth obeying a logarithmic time law at 400 d
egrees C. The polycrystalline thermodynamically stable tetragonal allo
y absorbs small amounts of oxygen and obeys a parabolic rate law in th
e temperature range 500-800 degrees C. The activation energy of oxygen
diffusion in tetragonal CoZr2 was determined from the temperature dep
endence of the parabolic rate constant. The intermediate nanocrystalli
ne phase with a local structure more closely packed and ordered than t
hat of the precursor amorphous phase, shows an oxidation behaviour sim
ilar to that of the tetragonal phase, but with a different time expone
nt.