Introduction of non-sag tungsten , also called doped tungsten, is a remarkable kind of dispersion strengthened material, which was the intentional simultaneous use of K-, Si-, and Al-compounds (AKS) as dope in order to obtain a well-defined internal interlocking structure. The term non-sag refers to the resistance of the wire against deformation under its own weight at working temperature.
Non-sag tungsten is a dispersion-strengthened micro alloy with elemental potassium, which is contained as microscopic bubbles in the tungsten lattice. Under working conditions in an incandescent lamp the potassium is a gas under high pressure. These gas bubbles essentially prevent the recrystallization of the tungsten wire and are responsible for the outstanding creep resistance of non-sag tungsten at the extremely high temperatures of a glowing lamp filament. More than 90% of non-sag tungsten is used for incandescent lamps. In addition, small amounts are used as defroster heating wires in automobile windshields and as heating wire coils for aluminium evaporation in metallization applications.