Mg6Ni formation in rapidly quenched amorphous Mg–Ni alloys

Abstract

The crystallization behavior of two Mg-rich near eutectic Mg–Ni amorphous alloys (Mg88Ni12 and Mg87Ni12Y1) was compared. The influence of Y substitution for Mg and quenching rate on the crystallization process was studied. Formation of the metastable nanocrystalline Mg∼6Ni phase as well as its decomposition were mostly studied and compared to the crystallization behavior of the recently investigated Mg83Ni17 glass with a composition corresponding to the Mg∼6Ni intermetallic compound [T. Spassov, P. Solsona, S. Surinach, M.D. Baro, J. Alloys Compd. 345 (2002) 123–129, T. Spassov, S. Todorova, V. Petkov, J. Non-Cryst. Solids, submitted for publication]. The metastable compound decomposes in a large temperature interval with a very broad exothermic effect for both alloys. Due to the very low rate of transformation its DSC peak and the associated enthalpy change can be detected only at high heating rates (>40 K/min). The isothermal crystallization kinetics analysis revealed a three-dimensional linear growth of existing nuclei mechanism for the Mg∼6Ni formation in both Mg87Ni12Y1 and Mg88Ni12 glasses, appearing as a second crystallization reaction after the primary αMg formation. The activation energies of Mg∼6Ni nanocrystallization in both glasses were determined and compared with that in Mg83Ni17.