Recrystallization Process of Powder Metallurgy Tungsten Wires

Abstract

The time law of primary grain growth and the effect of doping agent, annealing temperature and heating rate on the shape of secondary recrystallized grains and the orientation distribution of the wire axis for them are investigated using sintered tungsten wires. The rate of primary grain growth is obtained from an increase in mean thickness of fibers, showing that the rate is fairly smaller in the doped wire than in the non-doped wire. Doping has another effect on retarding the start of secondary recrystallization from the surface and also its completion at the central part of the wire. The grains of the doped wire are much more elongated in a longitudinal direction than those of the non-doped wire after a complete secondary recrystallization. However, there is the tendency that the grains of both materials become more equiaxed in shape and are distributed near ⟨011⟩ in the wire axis as the annealing temperature and the rate of heating increase. It is concluded that the appearance of large elongated secondary recrystallized grains with a wire axis near ⟨011⟩-⟨135⟩ is directly due to the bubble effect and the large driving force of grain growth inherent in their orientations.