Determination of UO2 thin films mechanical properties under heavy ion irradiation using nanoindentation and finite element modeling

Uranium Oxide (UO2)

ElBakhshwan, Mohamed

关键词: Uranium Oxide (UO2);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/46802/Mohamed_ElBakhshwan.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The mechanical response of UO2 to irradiation is becoming increasingly important due to the shift to higher burn-up rates in the next generation of reactors. In the current study, thin films of UO2 were deposited on YSZ substrates using reactive-gas magnetron sputtering. Nanoindentation was used to measure the mechanical properties of the as-grown and irradiated films. Finite element modeling was used to account for the substrate effect on the measurements.Two sets of experiments were designed to study the effect of radiation damage on UO2 films. First, study the effect of displacement cascades accompanying fission gas bubbles by irradiating 4600/5000Å UO2 films with 600 keV Kr+ ions at 25°C and 600°C. These irradiation conditions were used to confine radiation damage effects within the film. Second, study the effect of displacement cascades alone by irradiating 2000Å thin films with 1.8 MeV Ar+ ions. The film thickness and irradiation conditions were optimized to assure no gas bubbles formed into the film and only damage cascades exist.Both experiments showed an increase in the film hardness. However, irradiation at 25°C with either with 600 keV Kr+ or 1.8 MeV Ar+ ions, resulted in saturation of the film mechanical property response as a function of dose. The change in hardness and elastic modulus is attributed to the introduction of gas bubbles, displacement cascade damage, and point defect production by irradiation. The saturation of mechanical properties with dose is attributed to the high density of dislocations in the as-grown films.Irradiation at 600°C resulted in a decrease in the hardness and elastic modulus after irradiation using 600 keV Kr+ at a dose of 1E14 ions/cm2. Then both hardness and elastic modulus increased with dose. This behavior is attributed to recrystallization during irradiation at 600°C. Film microstructure using TEM showed 2 to 3 nm nanocrystals with density increases with dose. The calculation of the CRSS demonstrated that nanocrystals are the primary effect for film hardening based on the Orowan hardening mechanism.