Mechanical and chemical properties of PVD and cold spray Cr-coatings on Zircaloy-4

• Published in: Journal of nuclear materials Vol. 541; no. C; p. 152420
• Main Authors: Umretiya, Rajnikant V., Elward, Barret, Lee, Donghwi, Anderson, Mark, Rebak, Raul B., Rojas, Jessika V.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.2020; Elsevier BV; Elsevier
• Subjects: Accident tolerant fuel; Accidents; Atomic force microscopy; Chemical properties; Chromium; Cladding; Coating effects; Coatings; Cold spray; Contact angle; Cr-coated Zircaloy-4; Critical heat flux; Fuels; Heat flux; Hydrophobicity; Mechanical properties; Nuclear engineering; Nuclear fuels; Nuclear safety; Oxides; Photoelectron spectroscopy; Photoelectrons; Physical vapor deposition; Protective coatings; Reactors; Substrates; Surface chemistry; Surface roughness; Thickness; Wettability; Zircaloys (trademark); Zirconium; Zirconium alloys; Zirconium base alloys; Wettability; Accident tolerant fuel; Cold spray; Surface chemistry; Physical vapor deposition; Critical heat flux; Cr-coated Zircaloy-4
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2020.152420

Accident-tolerant fuel (ATF) cladding materials aim to improve fuel reliability and safety during accident scenarios in water-cooled reactors. These ATF cladding should also perform comparable or better than the current zirconium alloy cladding under reactor normal operating conditions. Surface-modified Zircaloy-4 was produced by depositing a protective coating of chromium by two different coating techniques, Physical Vapor Deposition (PVD) and Cold Spray (CS). The coating thickness, structure, composition, and mechanical properties of the coated Zircaloy were assessed with advanced materials characterization techniques. Results showed a strengthening effect of the Cr-coating, along with ∼83% higher hardness compared to that of the Zircaloy-4 substrate. Surface topography and surface chemistry of the Cr-coated Zircaloy-4 were assessed with contact profilometry, atomic force microscopy, contact angle goniometry, and X-ray photoelectron spectroscopy. Deposited Cr-coating significantly improved surface wettability compared to the substrate Zircaloy-4. The formation of surface oxides on the coatings by prolonged exposure to ambient air showed a further increase in the hydrophobic behavior. Surface parameters and surface chemistry after flow boiling critical heat flux tests, conducted at atmospheric pressure, evidenced a slight increase in surface roughness with notable changes in wettability associated with the formation of surface oxides.