Phase separation and nanocrystallization in Al₉₂Sm₈metallic glass

Recent Topics on the Structure and Crystallization of Al-based Glassy Alloys

“…In the primary crystallization, Al-based metallic glasses crystallize to an amorphous/nanocrystal composite, in which a high density of Al nanocrystals are embedded in an amorphous matrix. This process needs high nucleation frequency and low growth velocity 183 . The classical nucleation theory is difficult to explain such high nucleation density.…”

“…In the Al 92 Sm 8 and Al 91 Gd 9 metallic glasses, the nanoscrystals were observed to be formed inside the Al-rich regions 195 . Phase separation phenomenon prior to nanocrystallization is a mechanism triggering nanocrystallization 183,194,196 . The pure Al zone seems to catalyze the fcc-Al nucleation, which is responsible for the high nucleation frequency.…”

Small-angle X-ray scattering from phase-separating amorphous metallic alloys undergoing nanocrystallization

“…However in order to avoid ambiguity during interpretation of the SAXS data one must be careful in establishing the origin of the SAXS signal. In our previous works [2][3][4] we demonstrated the results of combined SAXS/WAXS (small-angle X-ray scattering/wide-angle X-ray scattering) study of nanocrystallization during annealing of binary Al-RE (RE = rare earth) melt-spun glassy alloys. The SAXS signal developing in the transformation progress exhibits a characteristic peak suggesting phase separation on nanometer scale occurring in the amorphous state.…”

Al-based amorphous alloys: Glass-forming ability, crystallization behavior and effects of minor alloying additions

“…However, the size and density of the phase-separated regions measured by the various methods are inconsistent, resulting in different mechanisms that have been proposed to explain how the phase-separated regions evolve into crystals. The Al-rich regions measured by the BF-TEM were about 50 nm in diameter for the Al-Gd-La-Ni amorphous alloy[38] while the SAXS/WAXS and EDS/EELS measurements yield a composition fluctuation size sale of about 10 nm in the Al 85 Ni 5 Y 6 Fe 2 Co 2 , Al 92 Sm 8 and Al 91 Gd 9 amorphous alloys[41,44,45]. With such large phase-separated regions, nanocrystals either start to nucleate on the surface[38] or from the center of the Al-rich amorphous phase[46] and the process is accomplished when all of the Al-rich phase regions undergo crystallization.…”

“…9,42,43], small-angle and wide angle X-ray scattering (SAXS/WAXS)[44][45][46] and high energy XRD (HEXRD) investigations[9]. For example, the X-ray diffraction pattern of the amorphous Al 87 Ni 8 La 5 alloy annealed at 150 ˚C (78 degrees lower than T x ) for 25 h shows two diffuse halos from the Al enriched and Al depleted amorphous regions[39].…”