Ternary atom site location in L12-structured intermetallic compounds

Abstract

Ternary sublattice site occupancy in two L1₂-structured intermetallic compounds were evaluated by a transmission electron microscope technique called ALCHEMI, or atom site location by channeling enhanced microanalysis, and by x-ray diffractometry, through measuring the relative integrated intensity of fundamental and superlattice x-ray diffraction peaks. The x-ray diffractometry showed that in nickel-rich Ni₃Al + Hf hafnium was found to occupy preferentially the aluminum sublattice, and in a multiphase alloy an L1₂-structured phase with the composition Al_74.2Ti₁₉Ni_6.8 nickel atoms showed a strong preference for the titanium sublattice. The ALCHEMI data broadly agreed with the x-ray results for Ni₃Al but gave completely the opposite result, i.e., a preference of nickel for the titanium sublattice, for Al₃Ti. The methods of ALCHEMI and x-ray diffractometry are compared, and it is concluded that ALCHEMI data may be easily convoluted by peak overlap and delocalization effects.