Xiao Yude

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

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, EIso and EKis and growth activation energies Eg 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, EIso, EKis and Eg 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.

Second phases of rapidly solidified AlFeCrZrVSi alloy and their thermal stabilities

The rapidly solidified powder of AlFeCrZrVSi aluminum alloy was prepared using multi-stage atomization and consolidated by hot-extrusion, the evolution of microstructure of the extruded materials during thermal exposure was studied with optical microscope, X-ray diffraction and transmission electron microscope (TEM). The results show that the majority of dispersions present in the as-extruded alloy are metastable Al12 (Fe, Cr, V)3Si, which has excellent thermal-dynamical stability and coarsening resistance; the coarsening rate-controlling process of the Al12 (Fe, Cr, V)3Si phase is considered to be diffusion of Fe atom along grain boundaries instead of bulk diffusion of Fe atom.