MAGNETOTHERMAL ANALYSIS OF NANOCRYSTALLIZATION OF AMORPHOUS AND RELAXATIONS OF NANOCRYSTALLINE MATERIALS

For a few years it has been realized that nanocrystalline phases can b e formed during crystallization of amorphous alloys annealed isotherma lly below the crystallization temperature of usual heating experiments . Data of this transformation monitored by the measurement of magnetic susceptibility are presented. A method using a magnetic balance with electronic stabilisation and combined computer facilities is applied. Constant heating and cooling rates as well as isothermal heat treatmen ts are used. Magnetic measurements are able to detect the onset of the transformation of amorphous NI-P alloys much earlier than was possibl e with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl- Avrami equation. The kinetics of solid state reactions in the nanostru ctured material can be investigated similarly. Formation of a Ni-phase in a nanostructured Hf-Ni alloy could be detected in a very early sta ge, where calorimetric methods are not sensitive. Segregation phenomen a could be detected from the experiments even after long time. The sen sitivity of the applied method is not dependent on the heating rate as the sensitivity of scanning calorimetry is.