Softening processes in single-crystal tungsten ribbons

Recovery processes in rolling-deformed (001)[110] tungsten single crystals having various degrees of purity are investigated. It is shown that the dislocation structure formed in the plastic deformation of tungsten single crystals is transformed in subsequent high-temperature anneals to a system of dislocation subboundaries; only polygonization, which preserves the single-crystal structure, takes place in samples heated to a temperature close to the melting point. The formation of subboundaries proceeds in two stages with subsequent transformation of the unstable structure to a configuration having an energy minimum. The decisive factor affecting the polygonization rate is the stacking fault energy; the presence of impurities also has a significant influence.