Split-induced Lüders bands in non-sag tungsten wires during torsion

Commercial K-Si-Al-doped tungsten wires, selected by different splitting properties, are investigated by torsion. During deformation the as-drawn wires deform in visible Lüders bands (LBs), while no LBs appear after stress-relieve annealing (at 1700 K). This change in the properties corresponds to a transition annealing temperature of T 1200 K, which can hardly be seen in wires with splits or latent splits. The first LB usually appears at low surface strains (γ &le 0.04) and coincides with the yield point phenomenon. At higher strains new LBs appear and propagate axially till they all meet at γ 0.7 to 1. In some respect axially split wires resemble to a cable, represented now by a stranded copper cable (10 mm × 0.1 mm).