SOFTENING PROCESSES IN SINGLE-CRYSTAL TUNGSTEN RIBBONS

Recovery processes In rolling-deformed (001)[110] tungsten single crys tals having various degrees of purity are investigated, It is shown th at the dislocation structure formed in the plastic deformation of tung sten single crystals is transformed in subsequent high-temperature ann eals to a system of dislocation sudboundaries; only polygonization, wh ich preserves the single-crystal structure, takes place in samples hea ted to a temperature close to the melting point. The formation of subb oundaries proceeds in two stages with subsequent transformation of the unstable structure to a configuration having an energy minimum. The d ecisive factor affecting the polygonization rate is the stacking fault energy; the presence of impurities also has a significant influence. (C) 1998 American Institute of Physics. [S1063-7834(98)02003-6].