Self-ion irradiation effects on mechanical properties of nanocrystalline zirconium films
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Self-ion irradiation effects on mechanical properties of nanocrystalline zirconium films Baoming Wang and M. A. Haque, Mechanical and Nuclear Engineering, Penn State University, University Park, PA 16802, USA Vikas Tomar, School of Aeronautics & Astronautics, Purdue University, West Lafayette, IN 47907, USA Khalid Hattar, Sandia National Laboratories, PO Box 5800, Albuquerque, NM 87185, USA Address all correspondence to M. A. Haque at [email protected] (Received 16 May 2017; accepted 23 June 2017)
Abstract Zirconium thin films were irradiated at room temperature with an 800 keV Zr+ beam using a 6 MV HVE Tandem accelerator to 1.36 displacement per atom damage. Freestanding tensile specimens, 100 nm thick and 10 nm grain size, were tested in situ inside a transmission electron microscope. Significant grain growth (>300%), texture evolution, and displacement damage defects were observed. Stress–strain profiles were mostly linear elastic below 20 nm grain size, but above this limit, the samples demonstrated yielding and strain hardening. Experimental results support the hypothesis that grain boundaries in nanocrystalline metals act as very effective defect sinks.
Introduction Radiation in nuclear applications adversely influences the microstructure of the fuel, cladding, and other component materials. Depending on the radiation fluence, flux, temperature, and other environmental conditions, such influence on grain size, shape, texture, and dislocation density may inflict anisotropic dimensional change, hardening, and even amorphization.[1,2]. This is manifested with the loss of ductility and plastic instability that is known to degrade the structural performance of these materials.[3] Zirconium and its alloys have been historically popular as cladding materials because of their low-thermal neutron capture cross-section, high temperature, corrosion resistance, and satisfactory mechanical properties. Post-irradiation, mechanical behavior of zirconium and Zr alloys is characterized by an increase of yield strength and hardness,[4,5] which comes at the cost of reduced ductility and fracture toughness.[1] This study is motivated by the application potentials of nanocrystalline materials, which are hypothesized to exhibit better resistance to irradiation by reducing irradiation-induced dislocation and cavity density.[6] It is postulated that grain boundaries in nanocrystalline systems are effective sinks for radiation-induced defects. Since the volume fraction of grain boundary increases exponentially at
