Growth kinetics of icosahedral phase and formation of banded structure in Al50Cu45Ti5 alloy during solid state transformation

Abstract

X-ray diffraction and transmission electron microscopy investigation were carried out to study the transformation from amorphous to icosahedral/crystalline phases on the rapidly quenched Al45+xCu45Ti10−x (for x = 0, 2, 4, 5 and 6) alloys. Various composition of Al–Cu–Ti alloys namely Al45+xCu45Ti10−x (for x = 0, 2, 4, 5 and 6) have been synthesized to investigate the influence of electron concentration per atom (e/a) and atomic size on the stabilization of amorphous and icosahedral phases. All these alloys exhibit amorphous phase. However, only in case of Al50Cu45Ti5 alloy, amorphous to icosahedral phase transformation has been observed. In the beginning, amorphous phase transforms to icosahedral and α-Al phases. A parabolic growth behaviour of icosahedral phase has been found at isothermal annealing temperatures 280 °C, 310 °C, 320 °C, 330 °C and 350 °C. The activation energy associated with the growth of icosahedral phase has been found to be ≈110 ± 20 KJ/mole. A novel micorstructure has been found in the form of banded structures surrounding the icosahedral grains originating at the later stage of transformation. It has been suggested that the banded structure is originating due to cellular precipitation in solute rich α-Al region which surrounds the icosahedral phase. Stability of icosahedral phase in Al50Cu45Ti5 alloy has also been compared with the other alloys of Al–Cu–TM (where TM = transition metals) series of alloys. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)