Synthesis of nanocrystalline NbAl3 by mechanical and field activation

The mechanically-activated, field-activated, and pressure-assisted synthesis (MAFAPAS) process, which combines the simultaneous synthesis and densification of nanophase materials, was utilized to produce nanocrystalline NbAl3 material from Nb+3Al mechanically activated powders. Nb+3Al elemental powders were co-milled for a short time in a specially designed planetary ball mill to obtain nanoscale distributed reactants but to avoid the formation of any product phases. These were then subjected to high AC currents (1500-1650 A) and uniaxial pressures (56-84 MPa). Under these conditions, a reaction is initiated by field activation and completed within a short period of tithe (3-6 min). Using XRD analyses, the MAFAPAS end-product was identified as NbAl3. Back-scattered electron SEM observations coupled with EDXS analyses showed the presence of small amounts of alumina precipitates together with unreacted niobium in the NbAl3 matrix. The end-product relative density ranged from 85 to 96%. The NbAl3 crystallite size, determined by XRD line-broadening analysis using the Langford method, was in the range of 57-150 um. (C) 2001 Elsevier Science Ltd. All rights reserved.