ELECTRODISCHARGE CONSOLIDATION OF NANOCRYSTALLINE NB-AL POWDERS PRODUCED BY MECHANICAL ALLOYING

Nanocrystalline powders of a 77 at % Nb-Al system prepared by mechanic al alloying were subjected to external pressures of up to 450 MPa in a ceramic die, producing a green density between 75% and 85% of theoret ical. These powders were consolidated into a solid bulk with a relativ e density of up to 99% by discharging a high-voltage, high-density cur rent pulse (discharge time <500 mu s and input energy of 0.5-1.0 kJ g( -1)). The consolidated bulk was still a mixture of two nanocrystalline intermetallic phases of Nb2Al and Nb3Al. The resultant grain sizes ra nged from 13-33 nm. A negative Hall-Petch relation between Vickers mic rohardness and grain size was clearly observed, indicating that grain- size softening occurs.