Because of its high melting point, tungsten has a great potential as a structural material for the use in power generation applications, such as in nuclear fusion components. The material’s macroscopic brittleness and its high brittle-to-ductile transition temperature, though, represent major difficulties to an application, even more so as these properties are strongly influenced by the material microstructure.
In this study, experiments with microscale, non-standard specimens were conducted and accompanied by finite element simulations with the goal to separate the contributions of plasticity and cracking to the fracture process.
The experiments were performed using two different free-standing, single-crystalline microscale cantilever geometries at different crystal orientations to test different crack systems. The specimens’ width and length were 40 µm and 160 µm, and 15 µm and 80 µm, respectively. The micro cantilevers were fabricated using micro-electro-discharge machining and focused ion beam (FIB) milling. FIB was also used to introduce a Chevron Notch as crack initiation. The cantilevers were then loaded using a nanoindenter. Finite element simulations were closely matched with the experiments. To describe the anisotropic plastic behavior of the single crystalline beams, crystal plasticity was used while cohesive zone elements were implemented to handle crack initiation and crack growth.
In both, the numerical simulation and the experiments, the load deflection curves of the notched cantilever beams were determined for different crystal orientations. Based on these curves, we will show that the fracture toughness values of microscale specimens can be determined despite the occurrence of plastic deformation. The influence of sample dimensions will be discussed.