Abstract
The recrystallization process in tungsten wire with different doping materials was studied under electron and optical microscopes. Drawn tungsten wires consist of long fibres, each of which is a bunch of sub-fibres 0.1 to 1μ in diameter. Before recrystallization takes place by heat treatment, the growth of sub-fibres starts. But when the doping effect is prominent, it does not allow sub-fibres to grow over 1μ in diameter, and the length of over several tens of microns remains, at 2, 400°K. At about 2, 800°K. a huge crystal grows directly out of sub-fibres and coexists with remaining sub-fibres and the boundary between the huge crystal and such remaining sub-fibres has steps here and there, height of the step being width of the sub-fibre.
In the meantime, another huge crystal grows into such remaining sub-fibres. After the recrystallization process is over, the very stable sub-fibre boundaries facing the former huge crystal form the boundary between the former and the latter huge crystals. In the resulting structure, therefore, large grains interpenetrate deep into the neighbouring grains in the axial direction of the wire. The wire having such a structure is suitable for practical uses, being non-sag at high temperatures and free from brittleness at room temperatures.
