Protective Cr Coatings with ZrO2/Cr Multilayers for Zirconium Fuel Claddings

Abstract

This article described the protective properties of Cr coatings with a barrier layer composed of ZrO2/Cr multilayers deposited onto E110 zirconium alloy. The coatings with a ZrO2/Cr multilayer thickness of 100, 250, and 750 nm and single-layer (1.5 µm) ZrO2 barrier were obtained by multi-cathode magnetron sputtering in Ar + O2 atmosphere. Then, cracking resistance and oxidation behavior were studied under conditions of thermal cycling (1000 °C) in air and high-temperature oxidation at 1200–1400 °C in a water steam. The role of the ZrO2/Cr multilayers and multilayer thickness on cracking resistance of the experimental coatings and oxidation resistance of the coated E110 alloy was discussed. It was shown that the coatings with more quantity of the ZrO2/Cr multilayers have higher cracking resistance, but such types of samples have a large amount of coating spallation under thermal cycling. The high-temperature steam oxidation (1200–1400 °C) demonstrated that interfaces of the ZrO2/Cr multilayers can act as a source of cavities formed by the Kirkendall mechanism that results in accelerating Cr–Zr interdiffusion for Cr-coated E110 alloy.

Aspects of Applied Chemistry Related to Future Goals of Safety and Efficiency in Materials Development for Nuclear Energy

“…or Si. Table 2 summarizes the main candidate materials as coatings for nuclear fuel cladding [ 35 , 37 , 47 , 55 , 56 , 57 , 58 , 59 , 60 , 61 ].…”

High-Temperature Steam Oxidation of Accident-Tolerant Cr/Mo-Coated Zr Alloy at 1200–1400 °C

“…The SEM image also shows blisters at the ZrO 2 /α-Zr(O) interface. The formation of these blisters is most probably associated with a displacement of the eutectic Cr-Zr-Mo layer on the surface region due to the "capillary" effect of the Cr-Zr liquid phase and then local swelling caused by solid-to-liquid volume changes [28]. Thus, the use of a Mo barrier sublayer (3 µm thick) between the protective Cr coating (8.5 µm-thick) and the Zr alloy during LOCA oxidation in a water steam at 1400 • C cannot effectively suppress the Cr-Zr interdiffusion for 120 s. Molybdenum actively diffuses into the zirconium alloy at the specified temperature, resulting in loss of its barrier properties.…”

“…The residual Cr and Mo as well as Mo and Zr can be mutually diffused between each other to form corresponding Cr-Mo and Mo-Zr interdiffusion layers (as observed in the case of oxidation at lower (1200-1330 • C) temperatures). The voids at the Cr 2 O 3 /Cr, Cr-Mo/Mo, and Mo/Mo-Zr interfaces can be produced by the Kirkendall mechanism due to the difference between the diffusion coefficients of different atoms, which causes the formation of vacancies and voids [28]. The Kirkendall voids can grow in size due to their coalescence.…”

“…As a result, oxidation of the zirconium alloy is significantly accelerated, resulting in the cracking and degradation of the protective coating [26]. Therefore, different barrier sublayers are considered to suppress the Cr-Zr interdiffusion [27][28][29][30][31].…”

“…It was found that the ZrO 2 sublayer can suppresses oxygen diffusion up to 1100 • C. However, the oxidation behavior of the protective coating at higher temperatures has not been established. In addition, an approach using ZrO 2 -based multilayer barrier coatings has been proposed [28]. It was found that steam oxidation at higher temperatures (1200-1400 • C) accelerated the mutual diffusion of Cr-Zr due to the formation of cavities at the interface of the ZrO 2 /Cr multilayers.…”