High temperature properties of AlN coatings deposited by chemical vapor deposition for solar central receivers

• Published in: Surface & coatings technology 2019-11, Vol.377, p.124872, Article 124872
• Main Authors: Chen, D., Colas, J., Mercier, F., Boichot, R., Charpentier, L., Escape, C., Balat-Pichelin, M., Pons, M.
• Format: Article
• Language: English
• Subjects: Absorptivity; Accelerated tests; Aluminum nitride; Aluminum oxide; Chemical Sciences; Chemical vapor deposition; Coatings; Concentrated solar power plants; Cracks; Dispersion hardening alloys; Ferrous alloys; Gas turbine engines; Heat conductivity; Heat transfer; High temperature; Material chemistry; Optical properties; Organic chemistry; Oxidation; Oxidation tests; Oxide dispersion strengthening; Receivers; Solar furnaces; Substrates; Thermal conductivity; Thermal expansion
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2019.07.083

There is an increasing interest for tower concentrated solar power (CSP) systems which can work at temperatures higher than 1073 K to optimize the efficiency. One of the challenges is to design the receiver that will be heated at high temperatures in air. On the contrary to coatings in gas turbine engine, the coating/substrate system must have a high thermal conductivity to ensure a good heat transfer to the fluid. Aluminum nitride (AlN) coating, deposited by chemical vapor deposition at 1373 K at a growth rate of 10–50 μm h−1, is selected for its high thermal conductivity, low thermal expansion coefficient, high temperature stability and its ability to develop stable alumina scales above 1273 K. Cast and ODS (Oxide Dispersion Strengthened) FeCrAl alloys, also alumina-formers, are chosen as model substrates to reduce the influencing parameters in real-life receivers and to study the potential of these coatings. Accelerated cyclic oxidation tests and emissivity measurements allow the evaluation of AlN coatings as materials for high temperature CSP receivers. The multilayered systems show low degradation after hundreds of thermal cycles at 1073 K in air and can support higher temperatures (1373 K) for 100 to 500 h depending on the coating thickness. Nevertheless the fast cyclic oxidations in solar furnace generated cracks through the coatings. The measurement of the optical properties also revealed a decrease of the absorptivity after oxidation. •Thick AlN coatings (15-40 μm) were deposited on Fe-Cr-Al alloys by chemical vapor deposition.•Their microstructure can be controlled by the N/Al ratio of gaseous precursors.•Their oxidation in the 1073-1373 K temperature range showed that a porous alumina layer is growing.•Optical measurements reveal that the development of the alumina layer degrades the absorptivity of the initial layer.•The lifetime of 40 μm AlN coatings can be estimated to be several years in the 1073-1173 K temperature range.