COLLOQUE DE PHYSIQUE Colloque C4, suppl6ment au n014, Tome 51, 15 juillet 1990 ON THE AMORPHISATION REACTIONS OF CuTi BY MECHANICAL ALLOYING G. COCCO, I. SOLETTA, S. ENZO*, M. MAGINI"* and N. COWLAM*'* Fipartimento di Chimica, Via Vienna 2. I-07100 Sassari, Italy Dipartimento di Chimica Fisica, 0.0.2137, I-30123 Venezia, Italy "'ENEA Tib, CRE-Casaccia, Roma, Italy **t Department of Physics, University of Scheffield, GB-Scheffield S1 350, Great-Britain Resume Les alliages des poudres de Cu et de Ti ont bte realise au moyen d'un moulin a bille. Dans un intervalle de concentration 45< Cu at% 575 la phase amorphe se dkveloppe directement B partir des Blements d'origine, alors qu'a basse concentration, cette meme phase se verifie avec l'apparition d'un composk cristallin de CuTiz et CuTi. Si le processus mecanique se prolonge, on aboutit a une transformation presque complete des composes cristallins en phase amorphe. On observe un mkcanisme d'amorphisation different lorsqufonarrive a un refroidissement a 253 K. Abstract Crystalline powders of Cu and Ti were mechanically alloyed by a ball-mill apparatus. For 45< Cu at% 575 amorphous phases form directly from starting elements, whereas CuTiz and CuTi interrnetallics develop concurrent with an amorphous fraction in the lower Cu content range. Further milling causes the transformation of the intermediate compounds into an almost complete amorphous condition. A different amorphisation mechanism is operative when the milling tool vial is cooled to 253 K. 1 - INTRODUCTION While neither a great deal of experimental results nor an increasing theoretical effort have yielded a definitive explanation of the Mechanical Alloying (MA) process, there is a firm basis for the belief that its mechanism can be successfully described in terms of thermodynamic quantities and kinetics constraints /l-2/. It was argued that To curves, which define the thermodynamic limits for polymorphous transformation, can also be used as a useful guide to identify possible glass forming regions when the amorphous phase is treated as an undercooled liquid, provided that single phase compound formations are supressed. Thus, To and glass transition temperature curves define a temperature composition range where the formation of an amorphous phase is accessible via solid state reaction. A wealth of essentially consistent experimental data supports the val- idity of To criterion. The CuTi system, however, constitutes a noticeable exception. Actually, To curves calculated by Schwarz et a1 /2/ by making use of different models, intersect above the experimental glass transition temperature thus predicting no glass formation for this system. Similar behaviours have been reported by Murray /3/ and Massalski and Woychik /4/. In contrast, Politis and Johnson /5/, found by MA an exceptional wide glass forming region extending from 0.10 to 0.87 Cu at%. This discrepancy was also underlined by Hellstern and Schultz /6/ who discussed the problem in terms of excess free entalpy partially stored in the highly defective crystalline lattice of the reactant elements. Weeber and Bakker /7/, by an extension of Miedema8s semiempirical model /8/, presented recently an entalphy diagram for metastable CuTi predicting an amorphisable region extending from 0.28 < xcu < 0.75, smaller than the experimental one. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990422