The correlation between thermal vacancy characteristics, and D03 ordering, in ball-milled nanocrystalline samples of (Fe3Si)95Nb5 was studied by means of X-ray diffraction and positron annihilation. A structural stabilization, due to Nb grain boundary segregation, permitted positron lifetime measurements to be performed at up to 1023K. Vacancy formation parameters were deduced which were identical to those for monocrystalline D03 Fe3Si. Measurements of coincidence Doppler broadening showed that, before the onset of thermal defect formation in the nanocrystallites, positrons were annihilated in the Nb-enriched grain boundaries. The D03-ordering of initially disordered Fe3Si nanocrystallites was considered on the basis of the thermal vacancy characteristics and self-diffusion behavior.

Thermal Vacancy Formation and D03 Ordering in Nanocrystalline Intermetallic (Fe3Si)95Nb5. L.Pasquini, A.A.Rempel, R.Würschum, K.Reimann, M.A.Müller, B.Fultz, H.E.Schaefer: Physical Review B, 2001, 63[13], 134114 (7pp)