Infrared Radiation and Thermal Cyclic Performance of a High-Entropy Rare-Earth Hexaaluminate Coating Prepared by Atmospheric Plasma Spraying

In this study, a high-entropy RMgAl11O19 (HE-RMA, R = La, Pr, Nd, Sm, Gd) and LaMgAl11O19 (LMA) coatings were fabricated by atmospheric plasma spraying. The phase composition, microstructure, thermal stability, infrared emissivity performance and shock resistance were comparatively characterized. The results showed that doping multiple rare-earth cations could be conductive to enhance the infrared emissivity. The as-sprayed HERMA coating exhibited the highest infrared emissivity, which reached up to 0.971 at 1000 degrees C. The reason for the improvement of the infrared emissivity was attributed to introduced impurity energy level resulting from doping cations, which could reduce the forbidden bandwidth and increase probability of electronic transition. Meanwhile, HE-RMA coating exhibited better shock resistance at 1100 degrees C due to superior fracture toughness (1.84 +/- 0.41 MPa.m(1/2)) during thermal cycling test at 1100 degrees C. In addition, HE-RMA coating still exhibited high infrared emissivity (0.932 at 1000 degrees C) at 1100 degrees C annealing for 100 h with only a slight reduction.