Effect of ternary alloying elements addition on atomic ordering characteristics of Fe–Al intermetallics

Abstract

The energetic and structural characteristics of atomic ordering processes in Fe 0.5(Al 1− n X n ) 0.5 intermetallics have been qualitatively analyzed based on the statistico-thermodynamical theory of ordering by means of a quasi-chemical method combined with electronic theory in the pseudopotential approximation. The effects of ternary impurities on order–disorder phase transformation temperature and the characteristics of atomic short-range order in Fe–Al type intermetallics have been calculated. Impurity elements in Fe 0.5(Al 1− n X n ) 0.5 where X=Ni, Co, Mn, Cr, Ti, Si, Zr, Hf, Nb, Ta, Re, Mo or W, are considered up to 1 at.% concentration. The results of the calculation indicate that the impurity elements, X, with regard to their lattice site occupancy characteristics (SRO) can be divided into two groups; X I=Ni, Co, Mn or Cr element atoms substitute mainly for Al sublattice sites, whereas X II=Ti, Si, Zr, Hf, Nb, Ta, Re, Mo or W element atoms substitute preferentially for Fe sublattice sites in Fe 0.5(Al 1− n X n ) 0.5 intermetallics. It has been found that the absolute values of partial ordering energies of the W Al–X( R 1) and W Fe–X( R 1) have a profound effect on the order–disorder transition temperature of Fe 0.5(Al 1− n X n ) 0.5 alloys that would either increase or remain unchanged depending on the type and content of the ternary substitutional alloying elements. The impurities X=Zr, Hf, Nb, Ta, Re, Mo or W which are preferentially distributed Fe sublattice sites are more effective in increasing order–disorder transition temperature in Fe–Al(B2) intermetallics. The results of the present calculation are in good qualitative agreement with experimental observation for most of the third component impurity elements X in Fe 0.5(Al 1− n X n ) 0.5 intermetallics.