Synthesis of ternary intermetallics by exothermic reaction

The manufacture of binary intermetallic compounds such as NiAl, TiAl, FeAl, Ni3Al, Ti3Al, etc, is possible, in principle, by reacting the elements bec ause of the exothermic nature of their reactions. In practice, however, sev eral factors must be optimized to produce a compound in a relatively pure f orm. Examples of the parameters that affect the production are the composit ion of the powder mix, the particle size, the efficiency of mixing and the synthesis temperature. A ternary intermetallic compound poses even greater production difficulties, since three elements have to be mixed intimately, instead of two, for the product to be uniform in chemical composition. Furt hermore, the three elements must react simultaneously to prevent binary int ermetallics forming by reaction between only two of the elements. This pape r presents some interesting results obtained in making a ternary Al-Fe-Si i ntermetallic by exothermic synthesis from its elements. The production meth od used is a conventional powder technique, i.e. ball milling, cold pressin g and heating in vacuum. It is shown that although the composition of the i nitial powder mix determines the product phase, some known ternary AlFeSi p hases cannot be produced even when the powder mix composition is stoichiome tric. The effect of particle size and ball milling speed are also investiga ted. It is concluded that only some of the known ternary phases could be pr oduced by this technique and that the particle size and milling parameters must be optimized to produce a pure ternary compound. (C) 2001 Elsevier Sci ence B.V. All rights reserved.