Microstructure, mechanical properties and corrosion behavior of AlxCrMoNbZr multiprincipal element alloy coatings for accident-tolerant fuel claddings: Effect of Al content

AlxCrMoNbZr (x = 0, 0.2, 0.4, 1.0, 2.7) multiprincipal element alloy (MPEA) coatings were prepared on Zircaloy-2 (Zr-2) substrates by radio frequency magnetron sputtering. The effects of Al content on the microstructure, mechanical properties and corrosion resistance of the coatings were systematically investigated. The amount of BCC nanocrystals in the as-deposited coatings was found to increase with the addition of Al, leading to an increase in hardness and elastic modulus. Al is found to be a promoting factor for weight gain and oxide layer thickening of the coatings during an autoclave test in static pure water at 360 °C and 18.7 MPa for 45 days, which is related to the vacancies introduced by rapid outward diffusion of Al and slow inward diffusion of O. However, these effects can be ignored when the Al content is low. All the coatings provide superior protection for the Zr-2 substrate due to the inner protective Cr-rich oxide layer adjacent to the coatings. These preliminary screening results provide a criterion and indication for the composition design of Al-containing MPEA coatings applied to accident-tolerant fuel (ATF) claddings.