Abstract
Vacancies in Fe(3)Al intermetallic alloys were investigated by positron annihilation spectroscopy combined with X-ray diffraction. Two complementary techniques of positron annihilation were employed: positron lifetime spectroscopy and coincidence Doppler broadening.
The experimental results were combined with ab initio theoretical calculations of positron characteristics. It was found that Fe(3)Al quenched from 1000 degrees C exhibits a mainly disordered A2 structure.
Defects in the as-quenched sample were identified as Fe vacancies on the A sub-lattice surrounded by A1 nearest neighbors. The concentration of quenched-in vacancies was determined from the positron lifetime results.
The samples were subsequently subjected to isochronal annealing which enabled an investigation of the recovery of quenched-in vacancies and the formation of thermal vacancies in B2 phase. It was found that recovery of quenched-in vacancies is accompanied by ordering to the D0(3) structure.
The enthalpy and entropy of formation were determined for vacancies in the B2 phase. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd.
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