Evolution of oxide nanoparticles during thermomechanical processing and its influence on mechanical properties of a 12Cr ODS alloy

Abstract

A Fe-12Cr-2W-0.2Zr-0.1Ti-0.35Y₂O₃ ODS ferritic alloy was prepared by ball milling, hot isostatic pressing (HIP) and thermomechanical processing herein. The evolution of oxide nanoparticles (ONPs) with different intermediate annealing temperatures of thermomechanical processing and its effect on microstructure and mechanical properties of the ODS alloy were investigated. The result shows that the intermediate annealing temperatures played a decisive role in the size, morphology and structure of nanoparticles in the final alloy since this was attributed to the fact that fine particles were dissolved through dislocation shearing during cold deformation and then re-precipitated during subsequent heat treatment. The high intermediate annealing temperature promotes the growth of the near-spherical ONPs, while the ellipsoidal nanoparticles are developed at relatively low temperature. Meanwhile, the structural change of the ONPs was also facilitated by the dissolution-reprecipitation behavior. The predominant Y₂(Zr_yTi_1−y)₂O₇ with cubic pyrochlore phase in as-HIPed alloy can be transformed into Y₄Zr₃O₁₂ particles with rhombohedral structure during the thermomechanical treatment. However, compared with the change in size of ONPs, the change in morphology and structure of ONPs has no obvious influence on the mechanical strength. Different intermediate annealing temperatures play a different role in the coarsening of ONPs during thermomechanical treatment, which makes the alloy annealed at low temperature exhibiting more uniform distribution of ONPs and better mechanical properties.