Materials Science and Engineering A304–306 (2001) 574–578 Phase selection in Al–TM–RE alloys: nanocrystalline Al versus intermetallics P. Rizzi ∗ , M. Baricco, S. Borace, L. Battezzati Dipartimento di Chimica IFM and Unità INFM, Università di Torino, Via Pietro Giuria 9, 10125, Torino, Italy Abstract Al–TM–RE (TM: transition metal, RE: rare earth metal) and Al–RE alloys were analysed with the aim of studying phase selection under various processing conditions. The metastable phases formed in binary Al-rich systems (notably Al–Sm) are revised for a unified interpretation of the literature. Two groups of alloys had different behaviour as for phase selection. In Al 88 Fe 9 Nd 3 and Al 87 Ni 10 Ce 3 stable intermetallic compounds form as primary phases during solidification. Nanocrystalline Al is formed at high undercooling. This may occur directly in rapid solidification or when fully amorphous materials are suitably annealed. In Al 90 Sm 8 Ni 2 and Al 90 Sm 8 Fe 2 metastable intermetallics form during rapid solidification together with a fraction of amorphous phase, whereas nanocrystalline Al forms on annealing the amorphous phase. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Phase selection; Al–TM–RE alloys; Nanocrystalline Al forms 1. Introduction Amorphous Al alloys containing rare earths (RE) and transition metals (TM) have good mechanical properties [1,2]. Work on these materials has found further stimu- lus from the finding that partially crystallised alloys, also termed nanocomposites since they contain crystals of small size, may display outstanding mechanical strength [3] and promising wear [4] and corrosion [5] resistance. High cooling rates are needed for amorphisation of Al rich alloys due to the tendency to nucleation of crystal phases, specifically Al. This can be exploited for obtaining partially crystallised materials directly from melt quenching [6]. Al- ternatively the glass is annealed to induce devitrification. Both during the quench and during annealing intermetallic phases may form. Complex phase selection behaviour has been reported in devitrification [7–10]. This paper aims at clarifying the sequence of phases pro- duced in ternary Al–RE–TM alloys. To this goal use will be made of transformation schemes newly derived for binary Al–RE alloys either during melt quenching and on glass annealing. 2. Experimental Master alloys were prepared by arc melting suitable quantities of the pure elements. The alloys were rapidly ∗ Corresponding author. Tel.: +39-11-6707-569; fax: +39-11-6707-855. E-mail address: rizzi@ch.unito.it (P. Rizzi). solidified by melt spinning under protective atmosphere. The alloy phases were studied by X-ray diffraction (XRD) with Co K radiation. The microstructure was examined by scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (EDX). High temperature thermal analysis was performed with a high temperature differential scanning calorimeter (HTDSC) using lumps of alloy embedded in alumina powder and contained in alumina crucibles under flowing He. A con- ventional differential scanning calorimeter (DSC) was used under flowing Ar for anneals up to selected temperatures at the heating rate of 20 ◦ C/min. The selected temperature generally corresponds to the end of a thermal event. 3. Results 3.1. The Al–Sm binary We reported previously the devitrification behaviour of Al–Sm alloys [7,11] showing that a phase mixture (primary Al nanocrystals + amorphous) can be obtained for Al 92 Sm 8 both by rapid quenching from the melt and by annealing the glass. Alloys with higher Sm content, from 10 to 14 at.%, can also be amorphised. They devitrify via step processes involving several intermetallic phases, mostly metastable. This behaviour was confirmed later [9] with differences con- cerning phases formed and transformation sequences. We reconsider now the Al–Sm system to provide a unified view of the results appeared in the literature. 0921-5093/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0921-5093(00)01537-9