Improved fracture behavior and microstructural characterization of thin tungsten foils

• Main Authors: Vladica Nikolic, Stefan Wurster, Daniel Firneis, Reinhard Pippan
• Format: Article
• Language: English
• Published: Elsevier 2016-12-01
• Series: Nuclear Materials and Energy
• Subjects: Thin tungsten foil; Fracture toughness; High and low temperature fracture experiments; LEFM; EBSD analysis; SEM analysis
• Online Access: http://www.sciencedirect.com/science/article/pii/S2352179115301289

This study is focused towards the development of the technique for investigating the fracture behaviour of 100µm thick rolled tungsten foils, with a purity of 99.97%. Electron backscatter diffraction (EBSD) scans reveal that the grains are elongated along the rolling direction of the foil, which has a very strong {100}<011> texture. The test specimens were fabricated by electrical discharge machining (EDM) and cracks were initiated by consecutively using a diamond wire saw, a razor blade and a focused ion beam (FIB) workstation. Fracture experiments were performed at temperatures from −196°C to 800°C. The investigation of fracture appearance shows an improved behavior and significantly higher values of conditional fracture toughness Kq compared to bulk W-materials, which can be related to a higher degree of deformation during the production process. A high toughness at room temperature (RT) and 200°C, slowly decreases when approaching the highest testing temperature of 800°C. The most significant result reveals that the ductile to brittle transition temperature (DBTT) is around RT, which is an extraordinary result for any tungsten material. The fracture surfaces, investigated with a scanning electron microscope (SEM), show a transition from cleavage fracture at liquid nitrogen temperature, through pronounced delamination within the foil plane at ambient temperatures to ductile fracture at the highest testing temperatures.