Devitrification behaviour of rapidly solidified Al₈₇Ni₇Cu₃Nd₃ amorphous alloy prepared by melt spinning method

Abstract

Rapidly solidified Al₈₇Ni₇Cu₃Nd₃ amorphous alloy was prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter in a continuous or isothermal heating mode. phase transformation was investigated, with a special interest in primary crystallization, by using an in-situ examination of X-ray diffractometry (XRD) and high resolution transmission electron microscopy (HRTEM). The results show that, the whole devitrification of rapidly solidified Al₈₇Ni₇Cu₃Nd₃ amorphous alloy involves two main processes of primary crystallization and secondary crystallization that consist mainly of two reactions. For primary crystallization, the apparent activation energies, E_Iso and E_Kis and growth activation energies E_g are about 153, 166 and 288 kJ/mol, respectively. The interdiffusion of Al atoms is a rate-controlled step of formation of the α(Al) particles, but slow diffusion of Ni and Nd atoms plays a significant role in retarding growth of the α(Al) particles. For secondary crystallization, E_Iso, E_Kis and E_g of the first reaction are about 291, 208 and 290 kJ/mol, and those of the second reaction are about 367, 269 and 372 kJ/mol. The two reactions of secondary crystallization are controlled mainly in an interface-controlled three-dimensional mode, depending mainly on slow diffusion of Ni and Nd atoms.

Keywords

rapid solidification / Al-rich amorphous alloy / crystallization / nucleation and growth