Zr alloy protection against high-temperature oxidation: Coating by a double-layered structure with active and passive functional properties

In this work, a new concept of metal surface protection against degradation caused by high-temperature oxidation in water environment is presented. We were the first to create a double-layered coating consisting of an active and passive part to protect Zr alloy surface against high-temperature oxidation in a hot water environment. We investigated the hot steam corrosion of ZIRLO fuel cladding coated with a double layer consisting of 500 nm nanocrystalline diamond (NCD) as the bottom layer and 2 m chromium-aluminum-silicon nitride (CrAlSiN) as the upper layer. Coated and noncoated ZIRLO samples were exposed for 4 days at 400 °C in an autoclave (working water-cooled nuclear reactor temperature) and for 60 minutes at 1000 °C (nuclear reactor accident temperature) in a hot steam furnace. We have shown that the NCD coating protects the Zr alloy surface against oxidation in an active way: carbon from NCD layer enters the Zr alloy surface and, by changing the physical and chemical properties of the Zr cladding tube surface, limits the Zr oxidation process. In contrast, the passive CrAlSiN coating prevents the Zr cladding tube surface from coming into physical contact with the hot steam. The advantages of the double layer were demonstrated, particularly in terms of hot (accident-temperature) oxidation kinetics: in the initial stage, CrAlSiN layer with low number of defects acts as an impermeable barrier. But after a longer time (more than 20 minutes) the protection by more cracked CrAlSiN decreases. At the same time, the carbon from NCD strongly penetrates the Zr cladding surface and worsen conditions for Zr oxidation. For the double-layer coating, the underlying NCD layer mitigates thermal expansion, reducing cracks and defects in upper layer CrAlSiN

Properties of boron-doped (113) oriented homoepitaxial diamond layers

Although significant efforts have been dedicated to optimize the quality of epitaxial diamond layers, reported properties of diamond based electronic devices do not yet approach expected theoretical values. Recent works indicate that boron-doped and phosphorous-doped diamond can be grown on atomically stepped (113) surfaces (A. Tallaire et al., 2016; M.-A. Pinault-Thaury et al., 2019), however the electrical properties of these layers have not been studied in detail. In this work, we report on structural and electrical properties of boron-doped epitaxial diamond layers grown on (113) substrates. Properties of the diamond layers have been investigated by means of scanning electron microscopy, atomic force microscopy, Hall effect, secondary ion mass spectrometry and Raman spectroscopy. Our results show that boron-doped diamond layers can be grown on (113) substrates at high deposition rates with atomically flat surfaces, excellent electrical properties and high boron incorporation efficiency