Structural Studies of Dispersoids in Fe-15 wt% Y2O3-5 wt% Ti Model ODS Alloys During Milling and Subsequent Annealing

Abstract

Oxide dispersion strengthened (ODS) steels have very high thermal stability and creep resistance due to reinforcement of hard and stable nano-sized ceramic dispersoids in metallic matrix which act as barriers to dislocation motion. This study established the role of Ti in the structural evolution of yttria during mechanical milling and subsequent annealing in a Fe-15 wt% Y2O3-5 wt% Ti model ODS alloy, using electron microscopy and XRD techniques. The alloy was synthesized in a high energy planetary ball mill in Ar atmosphere by varying the milling durations in the range of 0 (un-milled) to 60 h. The XRD result revealed amorphisation of Y2O3/Ti during milling and evolution of YTiO3 complex oxide upon annealing at 1273 K for 1 h. The electron microscopy studies revealed the refinement of alloy powders from similar to 50 mu m to few nanometers during milling. Electron diffraction analysis and high resolution transmission electron microscopy of 60 h milled as well as and annealed powder showed formation of different types of Y-Ti-O complex oxides such as Y2Ti2O7, Y2TiO5 and YTiO3.