Synthesis of ternary intermetallics by exothermic reaction

Abstract

The manufacture of binary intermetallic compounds such as NiAl, TiAl, FeAl, Ni 3Al, Ti 3Al, etc. is possible, in principle, by reacting the elements because of the exothermic nature of their reactions. In practice, however, several factors must be optimized to produce a compound in a relatively pure form. Examples of the parameters that affect the production are the composition 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. Furthermore, the three elements must react simultaneously to prevent binary intermetallics forming by reaction between only two of the elements. This paper presents some interesting results obtained in making a ternary Al–Fe–Si intermetallic by exothermic synthesis from its elements. The production method used is a conventional powder technique, i.e. ball milling, cold pressing and heating in vacuum. It is shown that although the composition of the initial powder mix determines the product phase, some known ternary AlFeSi phases cannot be produced even when the powder mix composition is stoichiometric. The effect of particle size and ball milling speed are also investigated. It is concluded that only some of the known ternary phases could be produced by this technique and that the particle size and milling parameters must be optimized to produce a pure ternary compound.