Kinetic analysis of Al 3 Ti intermetallic powder after mechanical treatment in hydrogen Emı ´lia Illekova ´ a, * , Peter S ˇ vec a , David Wexler b , Andrzej Calka b a Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava, Slovakia b Engineering Faculty, Wollongong University, NSW 2522 Wollongong, Australia Available online 27 March 2007 Abstract We present results of mechanochemical processing experiments performed on intermetallic powder, Al 3 Ti milled under hydrogen and helium atmospheres using a magnetically controlled Uniball device. Milling products were investigated by X-ray diffractometry (XRD), transmission electron microscopy (TEM) and advanced differential thermal analysis (DTA and DSC). Milling in both H 2 and in He resulted in breakdown of the intermetallic structure and, after extended milling, formation of nanostructural products comprising, pre- dominately, a solid solution of Ti in fcc Al, with some possible additional Al 1+x Ti 1x (x = 0.3) phase. Detailed kinetic analysis was pre- formed on the Al 3 Ti sample milled for 6 days in hydrogen. Under isothermal annealing, the crystallization of the Al 5 Ti 2 was found to follow the JMA kinetics, with constant activation energy E * and Avrami exponent n decreasing from 2.5 to 1.5. Ó 2007 Elsevier B.V. All rights reserved. PACS: 81.20.Ev; 65.80.+n; 64.70.Nd Keywords: Mechanical alloying; Crystallization; Nanocrystals; Electron diffraction/scattering; X-ray diffraction; TEM/STEM; Powders; Nanocrystals; Nanoparticles; Calorimetry 1. Introduction Mechanochemical processing of intermetallics under a hydrogen rich atmosphere can induce formation of a range of interesting and potentially useful reactions. These include e.g. formation of nanostructural alloy hydrides [1], hydrogen-induced amorphization of phases which are normally crystalline [2,3] and the formation of supersatu- rated solid solutions of one metallic element in another [4]. The compound Al 3 Ti is of interest due to its potential application as a low density oxidation resistant structural intermetallic. However, the stoichiometric phase possesses a D0 22 bct structure and has poor ductility. Recent research has concentrated on attempts to improve mechan- ical properties; particularly via minor alloy additions to promote formation Al 3 Ti based intermetallic with an ordered cubic structure (L1 2 ) structure [5]. Mechanical alloying of Al–Ti compounds with hydro- gen may be a useful tool for promotion of ultrafine grain hydrogen rich product for subsequent conversion to a use- ful monolithic material via hydrogen decomposition recombination processing (HDRP). In the current investi- gation we look at the breakdown and reaction of Al 3 Ti under controlled reactive ball milling (CRBM) in hydro- gen. In an attempt to understand reaction products and the reverse transformations occurring on reheating to remove the hydrogen a detailed structural and kinetic anal- ysis of the milling products is presented. 2. Experimental Alloy ingots were prepared from elemental ingredients (minimum 99.98% purity) mixed in stoichiometric propor- tions, Al:Ti 3:1, and arc melted under Ar, then chill cast 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.01.061 * Corresponding author. Tel.: +421 2 5941 0526. E-mail address: fyziille@savba.sk (E. Illekova ´). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 1970–1974