CAVITATION IN TUNGSTEN FILAMENTS.

As a consequence of the porosity resulting from the KSiAl doping of tungsten produced by powder- metallurgy, the high temperature creep process of tungsten wires is accompanied by a characteristic cavitation, attributable to bubble movement and bubble growth. The present investigations show that microstructural changes connected with this phenomenon can also be detected in the tungsten filaments of lamp coils after long use. It may therefore be presumed that, in addition to the non-uniform vaporization of tungsten along the wire, the movement and growth of the bubbles may contribute to the deterioration of an incandescent filament and to the development of spots.