Primary crystallization process of amorphous Al_(88)Ni_6Sm_6 alloy investigated by differential scanning calorimetry and by electrical resistivity

摘要

The primary crystallization process of alpha-Al nanoparticles from the amorphous Al_(88)Ni_6Sm_6 ribbon was investigated by differential scanning calorimetry (DSC) under non-isothermal condition and by electrical resistivity (ER) measurements under both isothermal and non-isothermal conditions. The apparent activation energy, E_a, was measured to be 249.9 + - 12.5 kJ/mol by DSC and 245.7 + - 12.3 kJ/mol by ER. The local activation energy, E_c, was also evaluated and was observed to increase from 232.7 + - 4.7 to 268.5 + - 5.4 kj/mol during the whole crystallization process. A general model (GM) based on the JMA theory was used to analyze the primary crystallization kinetic taking into account the impingement effect. The non-linear fitting of the isothermal ER results with this GM model gave an apparent Avrami exponent, n_T, varying between 1.31 and 0.69 and an impingement factor lambda close to 3. The local Avrami exponent, n_(alpha), measured by non-isothermal DSC at 10 K/min was found to decrease from about 3.0 to near 0.5 as the transformed fraction increased from 0 to 0.9. The results indicate that the primary crystallization process is typically controlled by the diffusion but a relatively important impingement effect is observed.