Ultra-miniaturised fracture toughness testing of nanostructured tungsten films in the context of nuclear fusion
(2024) EMMC19 - 19th European Mechanics of Materials Conference — Location: Madrid, Spain (29.May.2024)
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- Abstract
- In the context of Euro fusion structural integrity assessment of the fusion materials, the mode I fracture toughness of nanostructured freestanding tungsten thin films is investigated using the ultra-miniaturized crack-on-chip (COC) method. A MEMS-based process has followed to create on-chip test structures involving an actuator undergoing large tensile stresses and a notched specimen beam. Upon release from the substrate, the actuator applies a pulling force to the specimen. A crack initiates, propagates and arrests. Tungsten films with a 370 nm thickness were deposited using the DC magnetron sputtering under different deposition conditions. The films were characterised using grazing Incidence X-ray diffraction (GIXRD), surface curvature measurements, scanning electron microscope (SEM), and nano-indentation. The microstructure evolution, phase development, residual stress, and mechanical properties were explored to confirm the BCC α-phase similar to the bulk tungsten. Subsequent annealing was also applied to reduce the internal stresses of the selected W films in order to enhance the mechanical stability with respect to the cracking test method. The fracture toughness of the W thin films was assessed on-chip using a combination of scanning electron microscope (SEM) observations to measure the arrest crack length and finite element modelling (FEM) to extract the critical stress intensity factor KIc. The analysis was conducted on 90 successful test structures, resulting in an average fracture toughness value of 3.03 ± 0.64 MPa √m. This value is about 50 % of the fracture toughness of bulk tungsten recorded at room temperature, despite the film having a submicron thickness. This indicates the potential of this approach to provide valuable information about the fracture toughness of tungsten under irradiation.
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Naceri, S. E., Jaddi, S., Coulombier, M., Rusinowicz, M., Delannay, L., Tumanov, N., & Pardoen, T. (2024). Ultra-miniaturised fracture toughness testing of nanostructured tungsten films in the context of nuclear fusion. EMMC19 - 19th European Mechanics of Materials Conference, Madrid, Spain.