Mechanical properties and thermal cycling behavior of Ta2O5 doped La2Ce2O7 thermal barrier coatings prepared by atmospheric plasma spraying

Abstract

La2Ce2O7 (LC) is drawing increasing attention to be a new candidate material for thermal barrier coatings (TBCs) because of its higher phase stability, lower thermal conductivity and larger thermal expansion coefficient (TEC) than the traditional yttria partially-stabilized zirconia (YSZ). Unfortunately, the sudden TEC decrease at low temperatures greatly limits its application. In this study, Ta2O5 was added into LC to produce lanthanum-cerium-tantalum-oxide (LCT) solid solution, and LCT coatings were also newly developed by atmospheric plasma spraying (APS) using La2Ce1.7Ta0.3O7.15 powder. LCT coating exhibits excellent thermal stability between room temperature and 1573 K (up to 1000 h). The sudden TEC decrease is effectively suppressed due to the reduced oxygen vacancy concentration resulted from partial Ce4+ substitution by higher valence Ta5+, which is confirmed by Raman spectroscopy. Thermal cycling results showed that LCT TBC has relatively better thermal shock resistance than LC TBC, and spallation failure occurred within the ceramic top coat near the bond coat. It is considered that TEC mismatch stresses, low fracture toughness and coating composition deviation are primarily responsible for the poor thermal cycling performance. These findings provide valuable data for future technical optimization.