Abstract:

 A super-saturated solution of Fe-50Cu nanocrystalline coating was prepared using magnetron sputtering， and thermogravimetric analysis was performed at 800℃ in air both for the coating and as-cast Fe-50Cu alloy， in order to study the effect of grain size changes on the oxidation behavior of the two-phase alloys. The results showed that a complex external scale containing the oxides of iron and copper and their double oxides had been formed in the as-cast alloy， combined with an internal oxidation of iron. However， an exclusive external oxidation of iron took place for the coating after a short time， while an internal oxidation of iron was present again in the matrix once the coating degraded completely. The transition mechanism of the above oxidation modes was attributed to an enlarged solubility of iron in copper provided by the grain size reduction in the coating， and also to the presence of high density of grain boundaries both in the coating and in the oxide layer， which could act as short-circuit diffusion paths and therefore resulted in the changes of the microstructure of the initial oxide scale. 

Key words: Fe-Cu, Nanocrystallization, Oxidation mode