Materials Science and Engineering A361 (2003) 23–28 Combination of mechanochemical activation and self-propagating behaviour for the synthesis of Ti aluminides E. Medda a , F. Delogu a,b,∗ , G. Cao a,b a Dipartimento di Ingegneria Chimica e Materiali, Università di Cagliari, Centro Studi sulle Reazioni Autopropaganti (CESRA) and Unità di Ricerca del Consorzio InteruniversitarioNazionale di Scienza e Tecnologia dei Materiali (INSTM), piazza d’Armi, 09123 Cagliari, Italy b Consorzio PROMEA Scarl, c/o Dipartimento di Fisica, Cittadella Universitaria di Monserrato, SS 554, bivio per Sestu, 09042 Monserrato, Italy Received 14 August 2002; received in revised form 27 March 2003 Abstract The synthesis of TiAl 3 is not easy, since conventional techniques based on thermal treatments provide mixtures of intermetallics, due to the particular thermodynamic stability of the TiAl and Ti 3 Al phases. The synthesis of the aluminium-rich intermetallic TiAl 3 becomes, however, feasible when non-equilibrium processing techniques are properly combined. The methodology we set up for the preparation of the TiAl 3 consists of two different stages. During the first stage, reactant powders at the correct composition undergo mechanochemical activation inside a ball mill under inert atmosphere. A self-propagating high-temperature reaction is then induced on the pre-treated powders through thermal ignition. At the end of the reaction, the TiAl 3 equilibrium compound is obtained with impurities below 5 wt.%. © 2003 Elsevier B.V. All rights reserved. Keywords: Ball milling; Self-propagating high-temperature synthesis; Intermetallics; Aluminides 1. Introduction The synthesis of materials suitably developed for specific high-tech applications is one of the most important research goals in Materials Science. Much work has been done in the last years along this direction and several classes of materi- als with tailored properties have been correspondingly syn- thesised [1]. Due to their characteristic mechanical strength and refractoriness, the so-called intermetallic compounds are currently regarded as the most promising materials for var- ious future technological applications [2]. Among the others, titanium aluminides, TiAl 3 in par- ticular, have attracted considerable attention since their physical, chemical and mechanical properties together with their lightness make them ideal candidates as structural ma- terials in the aerospace industry [3]. Their application on industrial scale is, however, hindered by difficulties of vari- ous nature. The most important one is probably connected with their synthesis. Indeed, conventional techniques, ba- sically consisting of prolonged thermal treatments [4], do ∗ Corresponding author. Tel.: +39-070-675-50-73; fax: +39-070-675-50-67. E-mail address: delogu@visnu.dicm.unica.it (F. Delogu). not permit the production of homogeneous intermetallic phases. This is quite often prevented by the contemporary nucleation and growth of the most thermodynamically sta- ble TiAl and Ti 3 Al phases [5]. Such a behaviour is clearly demonstrated when synthesising the TiAl 3 equilibrium com- pound, since a mixture of the three aluminides is generally obtained. In the present work, we describe a process which allows one to avoid the difficulties mentioned above and therefore synthesise a pure TiAl 3 intermetallic phase. The method- ology consists of the combination of two non-equilibrium processing techniques, namely the mechanical alloying (MA) by ball milling (BM) and the self-propagating high-temperature synthesis (SHS). Such techniques are characterised by seemingly different behaviour. In the for- mer one, powder particles are repeatedly trapped between colliding surfaces and undergo mechanical deformation to- gether with cold-welding and fracturing events inducing a significant enhancement of chemical reactivity and the ap- pearance of far-from-equilibrium reactive behaviours [6,7]. In the later case, instead, the technique takes advantage of the self-propagation capability, under suitable conditions, of high-temperature reaction fronts characteristic of highly exothermic chemical reactions [8–10]. 0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0921-5093(03)00566-5