STATISTICAL THEORY OF LONG- AND SHORT-RANGE ORDERING IN TERNARY SOLID SOLUTIONS OF SUBSTITUTION

Abstract

The statistical theory of atomic ordering, long- and short-range, in ternary substitutional solid solutions AB 3 + C with fcc crystal lattice L1 2 of the Cu 3 Au type has been elaborated within the quasi-chemical approximation on the assumption that C atoms are located in the sites of both types, legal for A and B atoms. On the basis of molecular-kinetic concepts using some simplifying assumptions the free energy of the fcc substitutional alloy in dependence on the composition, temperature, correlation parameters and energetic constants has been found as a result of the calculations. The quasichemical method, the approximation of pair-interaction of the nearest neighboring atoms have been used in calculations taking into account short-range ordering. The correlation parameters has been calculated depending on the temperature, alloy composition, degree of long-range order and energy constants, their functional dependences have been elucidated, the plots have been constructed. The calculation results have been compared with the published experimental data for these alloys. The performed study of the correlation parameters in ternary substitutional solid solutions has showed that the addition of a third component C to the alloy АВ 3 can substantially affect the degree of short-range order in the atoms arrangement and, therefore, lead to changes in its physical properties. The knowledge from independent experiments of energetic parameters of atomic interaction in the alloy can allow by the use of derived formulae to calculate the required amount of impurity of the certain type necessary to produce alloy with the predetermined degree of short- and long-range order.