RESISTIVITY CHANGES OF SOME AMORPHOUS-ALLOYS UNDERGOING NANOCRYSTALLIZATION

The electrical resistivity of amorphous alloys with compositions: Fe73.5Nb3Cu1Si13.5B9, Fe86Zr7Cu1B6 and Co80Nb8B12 has been studied in the temperature range from 300 to 1100K, where crystallization occurs. The products of crystallization and the grain size have been studied by X-ray diffraction. In a first step, all the alloys crystallize with small grains of a few nanometers in diameter (nanocrystalline state), and the resistivity behavior at this process accounts for the difference between the amorphous and nanocrystalline phases. The nanocrystalline phases are: alpha-Fe-Si, alpha-Fe and fcc Co for the three compounds studied respectively. A second process, at which grain growth and precipitation of intermetallic compounds and borides takes place, has been found for all the alloys. The resistivity is sensitive, not only to the total transformed sample amount, but to the topological distribution of the crystalline phases, and therefore shows a more complex behavior than other well established techniques, as differential scanning calorimetry. This supplementary information given by the resistivity is also discussed.