Fracture toughness and microstructural characterization of polycrystalline rolled tungsten

Various fracture tests have been performed to determine the fracture toughness of sintered and rolled tungsten rods. The polycrystalline rods experienced a degree of deformation of about 65% after sintering and exhibited a pronounced fiber texture. Specimens with three different kinds of crack orientation were extracted and tested in the temperature range between − 150 °C and 950 C. The results confirm the strong influence of the anisotropic microstructure on the fracture behavior and on the brittle-to-ductile transition. To gain insight into the failure mechanisms, a close analysis of the microstructure was done by scanning electron microscopy and electron backscatter diffraction. Furthermore, in situ experiments were conducted at elevated temperatures in the transition regime to study crack initiation and fracture. Auger spectroscopy showed segregations of phosphorus and fluorine at intergranular fracture surfaces.