Strength and deformation mechanism of tungsten wires exposed to high temperature annealing: Impact of potassium doping

Recent efforts dedicated to the assessment of mechanical properties of tungsten wires, as means for fiber-reinforced composites, have shown that potassium (K) doping in the as-drawn state does not modify the mechanical properties of the wire. High temperature annealing (Ta up to 2300 °C) leads to the severe embrittlement of the wire associated with the loss of fracture strength. In this work, we assess the transition behavior of pure and K-doped W wires exposed to the annealing in the temperature range of 1000-2300 °C to identify and recommend temperatures suitable for operation and fabrication of the fiber-reinforced composites. The results of mechanical tests performed in the temperature range of RT-500 °C are reported and substantiated by the electron microscopy analysis. Room temperature tests demonstrate that pure W wires become fully brittle after annealing above 1300 °C, whereas K-doped wires loses ductility above 2100 °C. With raising the test temperature to 300-500 °C, it is found that the strength of pure W wire reduces by a factor of two at Ta = 1000 °C (as compared to non-annealed wire), and goes down to 100 MPa at Ta = 1900 °C. The K-doping suppresses the reduction of the fracture strength at least up to Ta = 1900 °C, thus offering a temperature gap of ~600 °C for the use as reinforcement.