Thermal vacancy formation and D0(3) ordering in nanocrystalline intermetallic (Fe3Si)(95)Nb-5 - art. no. 134114

The correlation between thermal vacancy characteristics and D0(3) ordering in ball-milled nanocrystalline (Fe3Si)(95)Nb-5 was studied by combined meas urements of x-ray diffraction and positron annihilation. Structural stabili zation due to grain boundary segregation of Nb enables high-temperature pos itron lifetime measurements up to 1023 K from which vacancy formation param eters identical to those in single-crystalline D0(3) Fe3Si are deduced. Mea surements of coincidence Doppler broadening show that prior to the onset of thermal defect formation in the nanocrystallites, positrons are annihilate d in Nb-enriched grain boundaries. The D0(3) ordering of the initially diso rdered Fe3Si nanocrystallites is discussed on the basis of the thermal vaca ncy characteristics and self-diffusion behavior.