Resumen:
The strengthening mechanism observed during ageing at temperatures of 435 and 475 degrees C in the oxide dispersion strengthened (ODS) Fe-Cr-Al-Ti system has been investigated. Atom probe tomography (APT) and high-resolution transmission electron microscopy (HRTEM) analyses determined that the alloy undergoes simultaneous precipitation of Cr-rich (alpha' phase) and nanoscale precipitation of TiAl-rich intermetallic particles (beta' phase). APT indicated that the composition of the intermetallic beta' phase is Fe2AlTi0.6Cr0.4, and the evolving composition of alpha' phase with ageing time was also determined. The results obtained from HRTEM analyses allow us to confirm that the beta' precipitates exhibit a cubic structure and hence their crystallography is related to the Heusler-type Fe2AlTi (L2(1)) structure. The strengthening could be explained on the basis of two hardening effects that occur simultaneously: the first is due to the alpha-alpha' phase separation through the modulus effect, and the second mechanism is due to the interaction of nanoscale beta' particles with dislocations. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
