Modifications of the phase selection during the crystallization of amorphous Al-Y-Fe
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Modifications of the phase selection during the crystallization of amorphous Al-Y-Fe N. Boucharat, H. Rösner, R.J. Hebert, J.H. Perepezko1 and G. Wilde Forschungszentrum Karlsruhe, Institute of Nanotechnology, P.O. Box 3640, 76021 Karlsruhe, Germany 1 University of Wisconsin-Madison, Department of Materials Science and Engineering, Madison, WI 53706, USA ABSTRACT The effect of thermal treatments, plastic deformation and inoculation of quenched Al88Y7Fe5 glasses with immiscible Pb and In on their crystallization behavior has been studied based on calorimetric and microstructural analyses. The results demonstrate the effect of the plastic deformation and of the inoculants to promote nanocrystallization. Moreover, the formation of a pronounced concentration gradient at the growing nanocrystal interface provides for the kinetic stability of the nanostructure and the modification of the phase evolution sequence of the crystallization reactions. INTRODUCTION New aspects of devitrification behavior have attracted extensive attention in terms of both fundamental understanding and opportunities for materials in structural applications with the discovery of new glass forming alloys. The stability of Al-based glasses is often discussed in terms of their thermal stability against crystallization since upon heating an extremely high number density of nanoscale Al crystallites (1021 – 1023 m-3 [1]) can develop in an amorphous matrix that results in a remarkably high tensile strength [2]. Although the initial stage of the formation of the Al-nanocrystallites is still under active investigation, recent experimental and kinetics analyses [3, 4, 5] have provided new evidence that nuclei form during quenching and serve as precursors for the development of Al-nanocrystals. However, the large disparity between the component diffusivities [5] involves concentration gradients at the interface of growing Al-nanocrystals that limit the growth and that can affect the nucleation conditions for different phases [6, 7]. While several investigations of the thermally-induced crystallization process have been performed, relatively few studies have addressed the effect of plastic deformation and incorporated immiscible elements, e.g. Pb and In on the crystallization behavior. The present results indicate that the processing pathways influence strongly the microstructure and the phase formation sequence of Al-Y-Fe alloys that represents new opportunities to achieve specific structures. EXPERIMENTAL PROCEDURES Al88Y7Fe5, Al87Y7Fe5Pb1 and Al87Y7Fe5In1 alloys were melt-spun on a single-roller melt spinner yielding ribbons with an approximate thickness of 40 µm. Energy dispersive X-ray analysis (EDX) in a scanning electron microscope (SEM, Leo 1530) have confirmed that the sample compositions correspond to the nominal starting compositions. As-spun ribbons were
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examined by X-ray diffraction (STOE and Philips X´Pert) using Cu-Kα radiation and by transmission electron microscopy (TEM, Philips CM 30 ST and Philips CM200) coupled with se
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