DISORDERING OF FeAl BY MECHANICAL MILLING

Point defect concentrations in milled samples of stoichiometric FeAl were obtained by Mšssbauer measurements. Mšssbauer spectra consisted of a single absorption dip with broadening attributed to unresolved hyperfine interactions. A local environment model was used to analyze spectra that allowed for defect-induced changes in monopole interactions at Fe probe atoms due to elementary defects in the two nearest atomic shells. It was found that pre-existing vacancies on the Fe sublattice disappear rapidly in the first five minutes of milling, with a corresponding rapid increase in the concentration of antisite-atom pairs. This behavior is very different to that observed in this laboratory for PdIn, using PAC, where vacancies are the principal defect produced. The difference is attributed to a lower energy of ordering for FeAl. A stationary state was observed after 10 minutes of milling, in which the mole fraction of antisite atoms, the average lattice parameter, and the monopole interactions of defect-free probes all ceased to change further. The mole fraction was observed to become stationary at about 10 atomic percent.