Restoration kinetics and microstructural evolution of moderately warm-rolled yttria dispersion-strengthened tungsten plate during annealing at high temperatures

Abstract

The thermal stability of an yttria particle dispersion strengthening tungsten (W-2vol%Y2O3) plate with 67 % rolling thickness reduction (WY67) fabricated by powder metallurgy and warm rolling is investigated through isochronous annealing and isothermal annealing. Hardness testing of annealed specimens allows tracking the degradation of the mechanical properties and electron backscatter diffraction (EBSD) was used to characterize the corresponding microstructure. Isochronous annealing for 1 hour between 1150 °C and 1450 °C indicates that the recrystallization temperature of WY67 is about 1400 °C. Herein, the recovery kinetics, recrystallization kinetics, and the evolution of microstructure and texture of WY67 during isothermal annealing at temperatures ranging from 1300 ℃ to 1450 ℃ were investigated in detail. The effect of both the heterogeneity of the deformed microstructure and the yttria particles on the recovery and recrystallization was further studied. The results show that the stored energy of the deformed grains of yttria dispersion strengthened tungsten is texture-dependent and the grain with γ-fiber (normal direction // <111>) texture has the largest stored energy of 546 KJ/m3. The grains with higher stored energy are conducive to recrystallized nucleus/grain growth rather than nucleation during subsequent annealing. The recrystallized texture inherits the deformed texture and is mainly composed of γ-fiber texture. There are more pre-existing potential recrystallization nuclei in the elongated grains with larger deformation in the as-rolled microstructure. Micron-sized yttria particles can stimulate the formation of recrystallization nuclei through particle-stimulated nucleation mechanism, nevertheless, this is not the dominant nucleation mode for WY67 during recrystallization in this study. Fine (submicron) yttria particles hinder the recovery and recrystallization processes through the Smith–Zener pinning effect.