Rev.Adv.Mater.Sci. (RAMS)
No 5, Vol. 18, 2008, pages 454-458

EARLY STAGES OF PHASE SEPARATION AND NANOCRYSTALLIZATION IN Al-RARE EARTH METALLIC
GLASSES STUDIED USING SAXS/WAXS AND HRTEM METHODS

Jerzy Antonowicz, Elzbieta Jezierska, Marcin Kedzierski, Alain Reza Yavari,
Lindsay Greer, Pierre Panine and Michael Sztucki

Abstract

Early stages of nanocrystallization in Al92Sm8 and Al19Gd9 glassy melt-spun alloys were investigated in-situ using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS). The measurements were performed during isothermal annealing at temperatures below crystallization point. The results are supported by high resolution transmission electron microscopy (HRTEM). In both alloys a continuous SAXS signal increase was observed during annealing while WAXS revealed fully amorphous structure. After the initial transient, the Bragg peaks of the fcc-Al nanocrystalline phase start to appear on the halo diffraction pattern. HRTEM images of the annealed samples show presence of nanometer-size crystalline grains embedded in the amorphous matrix. Within the experimental conditions a minimal detectable crystalline volume fraction was estimated to be 0.05%. The results indicate that amorphous phase separation prior to crystallization occurs in investigated systems.

A presence of a characteristic signal maximum in a small-angle region suggests that glassy phase separation proceeds by a spinodal mechanism. It is concluded that nanocrystallization in aluminium-rare earth metallic glasses is triggered and controlled by the phase separation process.

full paper (pdf, 368 Kb)