Inhomogeneous deformation substructure and its effect on the recrystallization behavior of yttria dispersion-strengthened tungsten plate

Abstract

Tungsten materials have been chosen for use in critical parts (i.e., as the armor of plasma-facing material) in fusion reactors. Deformed tungsten will undergo recrystallization at a high-temperature service environment, and recrystallized tungsten exhibits brittleness, which reduces mechanical properties, thermal shock resistance and service lifetime. The deformation heterogeneity may result in an inhomogeneous microstructure, affecting its recrystallization behavior. The main aim of the present work is to qualitatively and quantitatively characterize the heterogeneity in the through-thickness deformed microstructure of an yttria dispersion-strengthened tungsten plate warm-rolled to 50 % thickness reduction ratio and study the effect of heterogeneous microstructure on recrystallization behavior. For this, topological maps of the surface, quarter and center region are measured on the deformed state and annealed state utilizing electron backscatter diffraction (EBSD). Distributions of grain size, geometrically necessary dislocations (GND) energy, potential nuclei density and texture have been analyzed in detail. The results revealed that the deformed microstructure of tungsten plate along full-thickness has no apparent heterogeneity gradient of grain size and texture, but the center layer has a larger subgrain size and more potential recrystallized nuclei compared to the surface layer. The larger subgrain is more conducive to static recrystallization nucleation, while the existing potential recrystallized nuclei can grow rapidly without incubation time during subsequent high-temperature annealing, thereby recrystallization preferentially undergoes in the center layer of the tungsten plate.

Keywords

• Tungsten
• Rolling
• Inhomogeneous microstructure
• Recrystallization
• Texture