Crystallization Kinetics of Misch Metal Based Bulk Metallic Glasses

Abstract

The crystallization kinetics of Mm 55Al 25Cu 10Ni 5Co 5 bulk metallic glass (BMG) was investigated by means of differential scanning calorimetry (DSC) in the mode of continuous heating or isothermal annealing. It was found that the apparent activation energy E g, E x and E p of the BMG calculated by Kissinger's method were 189.58, 170.68 and 170.41 kJ·mol −1, respectively, which was bigger than those of La 55Al 25Cu 10Ni 5Co 5 BMG indicating that thermal stability of the former was higher than that of the latter. The local activation energy obtained using Ozawa equation decreased as crystallization proceeded except for the initial stage. The Avrami exponents were calculated to be in the range of 3.26 ∼ 5.23 for different crystallization stages and isothermal temperatures. This implied that crystallization of Mm 55 Al 25Cu 10Ni 5Co 5 BMG was governed by diffusion-controlled three-dimensional growth with either reduced or increased nucleation rate, depending on isothermal temperature. Inconsistency of thermal stability with glass-forming ability for Mm(La)-Al-Cu-Ni-Co BMGs was discussed.