Tensile behaviour of drawn tungsten wire used in tungsten fibre-reinforced tungsten composites

In tungsten fibre-reinforced tungsten composites (W-f/W) the brittleness problem of tungsten is solved by utilizing extrinsic toughening mechanisms. The properties of the composite are very much related to the properties of the drawn tungsten wire used as fibre reinforcements. Its high strength and capability of ductile deformation are ideal properties facilitating toughening of W-f/W. Tensile tests have been used for determining mechanical properties and study the deformation and the fracture behaviour of the wire. Tests of as-fabricated and straightened drawn wires with a diameter between 16 and 150 mu m as well as wire electrochemically thinned to a diameter of 5 mu m have been performed. Engineering stress-strain curves and a microscopic analysis are presented with the focus on the ultimate strength. All fibres show a comparable stress-strain behaviour comprising necking followed by a ductile fracture. A reduction of the diameter by drawing leads to an increase of strength up to 4500 MPa as a consequence of a grain boundary hardening mechanism. Heat treatment during straightening decreases the strength whereas electrochemical thinning has no significant impact on the mechanical behaviour.