Transmission electron microscopic studies of rapidly solidified Al–Cu–Gd alloys

We report the results of the synthesis and structural explorations of the rapidly solidified Al–Cu–Gd alloys. Interesting structural phases have been observed for Al33.3Cu33.3Gd33.3, Al25Cu25Gd50, Al30Cu30Gd40, Al65Cu20Gd15 and Al42Cu50Gd8. For the Gd-rich compositions Al33.3Cu33.3Gd33.3, Al30Cu30Gd40 and Al25Cu25Gd50 the observed phases have been found to be dominantly amorphous and glassy. The metallic-glass nature of these phases has been confirmed through the occurrence of glass-transition observed in differential thermal analysis measurements. On the other hand, the Al65Cu20Gd15 and Al42Cu50Gd8 alloys exhibit some ordered crystalline phases. The Al65Cu20Gd15 alloy exhibits a tetragonal phase (a=6.2±0.1 Å and c=10.1±0.1 Å) and a monoclinic phase (a=6.499±0.002 Å, b=5.028±0.002 Å, c=4.372±0.002 Å and β=108.43±0.01°). After preliminary analysis of electron diffraction patterns it appears that these phases may correspond to the vacancy ordered phases based on CsCl-type structure. In the case of Al42Cu50Gd8 alloy, we have observed a cubic phase (a=8.742±0.005 Å) which is a τ3 modulated phase based on the CsCl-type structure.