Distinctive test for tungsten wires with different splitting properties

Deformation is often localized into split induced Lüders bands upon the free-end torsion of heavily drawn and annealed doped tungsten at the ambient. The Lüders bands nucleate at very low true shear strains (γ < 0.01), when the samples are annealed below 1400 °C. This work reports on the Lüders band nucleation in primary recrystallized samples (annealed at 1800 °C) having an elongated homogeneous fine grained structure. The deformation without mechanical damage increased (0.09 < γ < 0.27) in this condition, when the material was slightly softer and the grain width was slightly larger. The diffuse Lüders bands contained macro-cracks having a continuous helical trace on the free surface in the quasi homogenous part of the band. In addition to the macro-cracks, also a great number of micro-cracks were formed connecting grain boundary triple lines along the width of the elongated primary recrystallized grains, although many grain boundary segments of this type remained micro-crack-free. The results may be taken as a hint for the importance of the orientation dependent grain boundary decohesion as well as for the effects of higher incompatibility stresses at the vicinity of triple lines, when they are sufficiently close to each other.