High-temperature oxidation behavior of HiPIMS as-deposited Cr–Al–C and annealed Cr2AlC coatings on Zr-based alloy

Abstract

Protective coatings of Zr-based claddings have been proposed for the development of Accident Tolerant nuclear Fuel (ATF). Coatings forming stable oxides at high temperature such as MAX phases are attractive candidates for these applications. In this study Cr–Al–C coatings were deposited on coupons of Zr-based alloy (Zr702) by High Power Impulse Magnetron Sputtering (HiPIMS). Cr2AlC coatings were then obtained by annealing of the as-deposited films at a temperature below metallurgical degradation of Zr alloys. The behavior of as-deposited Cr–Al–C and annealed Cr2AlC coatings with respect to high-temperature oxidation slightly differ for short oxidation times but converge for longer durations. Oxidized coatings are made of (i) an external dense, covering, adherent and thin scale of aluminum and chromium oxides, (ii) an intermediate thicker, porous layer of chromium carbide and (iii) an interdiffusion layer. Both coatings are protective in dry and wet air (up to 1473 K for 2 h in air-28% H2O for an initial thickness of 7 μm), and are thermal shock-resistant. Self-healing capability is observed for submicronic defects. The top oxide scale acts as a barrier against oxygen diffusion, thus efficiently protecting the Zr702 substrate from extended oxidation except near coupon edges. The results indicate that Cr–Al–C thin films grown by HiPIMS process and annealed Cr2AlC coatings are both promising candidates for ATF cladding coatings.