Ultrastrong nanocrystalline oxide-dispersion-strengthened ferritic alloy with exceptional thermal stability

Abstract

As structural materials candidates of advanced fission and future fusion reactors, oxide-dispersion-strengthened (ODS) alloys, which are often ultrafine-grained (with a grain size between 100 and 1000 nm), have attracted widespread interest in past decades. However, fabrication of fully dense bulk nanocrystalline ODS alloys has rarely been reported. In this work, a novel Zr-doped nanocrystalline 14YWTZ ferritic ODS alloy (Fe–14Cr–3W-0.4Ti-0.8Zr-0.3Y2O3) was prepared by mechanical alloying and high-pressure consolidation techniques. The high consolidation pressure (4 GPa) endows the bulk nanocrystalline 14YWTZ alloy with a nearly full relative density (~99.5%) and a reasonable tensile elongation. The consolidated nanocrystalline 14YWTZ alloy with an average grain size of ~50 nm shows an ultra-high compressive yield strength of ~2641 MPa. Besides, the alloy exhibits an exceptional thermal stability, i.e., limited grain growth occurs after annealing at a high temperature of 1000 °C. After hot rolling, the alloy retains nanocrystalline microstructures and exhibits an unprecedented tensile yield strength of 2730 MPa, far exceeding those of previous reported ferritic ODS alloys. The high thermal stability of the annealed nanocrystalline 14YWTZ alloys can be ascribed to the combined effects of the thermodynamic multicomponent co-segregation to grain boundaries and strong kinetic Zener pinning by high-density Zr–Ti–Y–O-enriched nanoparticles with an average particle size of ~3.18 nm and a high number density of ~3 × 1024 m−3. The outstanding strength of the present nanocrystalline 14YWTZ alloys primarily originates from the Hall-Petch strengthening of the nanocrystalline matrix, distinguishing them from conventional ODS alloys strengthened by dislocation forest and/or dispersed oxide nanoparticles.