Microstructural Evolution and Corrosion Behavior of W-Coated Zr-4 Alloy Deposited by DC Sputtering at Different Voltages
DOI:
https://doi.org/10.55981/urania.2026.16104Keywords:
DC sputtering, tungsten coating, Zircaloy-4, corrosion, nuclear claddingAbstract
Zirconium (Zr) alloys are widely used as nuclear fuel cladding materials due to their low neutron absorption, high mechanical properties, and good corrosion resistance in high temperature aqueous environments. However, their performance might degrade under severe accident conditions. Tungsten (W), a refractory metal with high thermal stability and irradiation resistance, is a promising candidate material for protective coating. Nevertheless, the tungsten oxide film is not as stable in aqueous environments as the passive ZrO2 film. The effect of DC sputtering voltage on the microstructure, mechanical properties and corrosion behavior of W-coated Zr-4 substrates for nuclear applications was studied. To investigate the effect of deposition energy on coating characteristics, W coatings were deposited at 4, 5 and 6 kV. XRF and SEM-EDS analysis confirmed successful W deposition, with the sample at 5 kV having the most uniform coating coverage. SEM observations and cross-sectional analyses show that the coating microstructure and thickness are strongly dependent on the sputtering voltage. The coating thickness increased from ~4.8 to 7.8 µm at 4 and 5 kV and decreased to 5.2 µm at 6 kV. The coating density increased with increasing sputtering voltage, and at 6 kV the higher ion energy caused partial resputtering and, hence, a reduction in coating thickness. XRD results revealed the formation of nanocrystalline BCC (body-centered cubic) tungsten with crystallite sizes decreasing from 8.98 to 5.56 nm with increasing voltage. The hardness of Zr-4 substrate was only 187.63 ± 5.06 HV, while the coated sample reached 480-620 HV due to grain refinement and densification. The potentiodynamic polarization tests showed that the corrosion potential (Ecorr) shifted from −3.05 × 10⁻¹ V for the uncoated substrate to −3.12 × 10⁻¹ V for the 5 kV-coated sample, while the corrosion current density (Icorr) increased from 1.44 × 10⁻⁷ A/cm² to 4.86 × 10⁻⁷ A/cm². The results show lower corrosion resistance after coating deposition under the conditions explored. Nevertheless, the 5 kV coating showed the best compromise between mechanical enhancement and corrosion performance due to its compact microstructure and high hardness, suggesting the trade-off between the hardness enhancement and corrosion behavior. The increase in the corrosion current density is likely due to coating defects and the lower stability of tungsten oxide films compared with the protective ZrO₂ layer on uncoated Zr-4.
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Copyright (c) 2026 Suminar Setiati Achmadi, Agus Jamaludin, Wulan Tri Wahyuni, Syaiful Bakhri, Yusuf Gigih Wicaksono, Maman Kartaman Ajiriyanto, Usman Sudjadi
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