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

Abstract

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. 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 , was 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, were 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 allowed the evaluation of AlN coatings as materials for high temperature CSP receivers. The multilayered systems showed 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.

Modeling multilayer coating systems in solar receivers

“…The AlN/TZM system appears to be a potentially ideal system for solar receivers thanks to the exceptional elevated temperature strength of TZM. Also, AlN has a reasonable oxidation resistance [8] and has a thermal expansion coefficient close to the one of TZM. Therefore, such multilayer system is used for the following discussion, Figure 3(a).…”

“…40-µm-thick AlN coatings are deposited on all faces of the pre-oxidised substrate by chemical vapor deposition. Details on deposition conditions are given in [8]. Briefly, in-situ produced AlCl 3 (from reaction between Al and Cl 2 at 800 K) reacts with NH 3 to form AlN at 1200°C.…”

“…The growth of scales is accompanied by the generation of a large residual stress due to the intrinsic oxide growth strain in the lateral direction, resulting in the redistribution of the stress field in the system. Based on our previous study, we assume a linear oxidation behavior for AlN [8] When the oxidation is controlled by a surface reaction, the oxide scale grows linearly. We assumed that in this analysis the lateral growth strain in the oxide, , , is constant when oxidation follows linear kinetics, with a value of , =0.001 deduced from our experiments.…”

Overview of the Enablers and Barriers for a Wider Deployment of CSP Tower Technology in Europe

“…Aluminum nitride (AlN) as a protective coating in extreme environments could be used in its polycrystalline form because R&D projects have demonstrated its low fabrication cost [51]. The infiltration of SiC matrix lattices through high-temperature chemical vapor deposition is an innovation oriented towards all those applications in high-temperature conditions (transfer knowledge to pressure/temperature sensors market) [52].…”

Coupling powder bed additive manufacturing and vapor phase deposition methods for elaboration of coated 3D Ti-6Al-4V architectures with enhanced surface properties

“…Corrosion prevention at temperatures from 600 to 900°C can be achieved. To our knowledge, aluminium nitride (AlN) coating has never been reported on Ti-6Al-4V despite its high oxidation resistance at temperature below 800°C [22,23] and its high temperature stability.…”