Thermal conductivity of self-ion irradiated nanocrystalline zirconium thin films

- A micro-electro-mechanical system was setup for thin film thermal conductivity study.
- 100 nm thick zirconium thin films (10 nm grain size) were self-ion irradiated.
- For 2.1 displacement per atom damage level, thermal conductivity decreased 32%.
- Thermal conductivity decreased with irradiation induced defects and oxidation.

Thermomechanical stability and high thermal conductivity are important for nuclear cladding material performance and reliability, which degrade over time under irradiation. The literature suggests nanocrystalline materials as radiation tolerant, but little or no evidence is present from thermal transport perspective. In this study, we irradiated 10 nm grain size zirconium thin films with 800 keV Zr+ beam from a 6 MV HVE Tandem accelerator to achieve various doses of 3 × 1010 to 3.26 × 1014 ions/cm2, corresponding to displacement per atom (dpa) of 2.1 × 10− 4 to 2.28. Transmission electron microscopy showed significant grain growth, texture evolution and oxidation in addition to the creation of displacement defects due to the irradiation. The specimens were co-fabricated with micro-heaters to establish thermal gradients that were mapped using infrared thermometry. An energy balance approach was used to estimate the thermal conductivity of the specimens, as function of irradiation dosage. Up to 32% reduction of thermal conductivity was measured for the sample exposed to a dose of 2.1 dpa (3 × 1014 ions/cm2).