Microstructures, thermophysical properties and thermal cycling behavior of LaZnAl11O19 thermal barrier coatings deposited by atmospheric plasma spraying†
Magnetoplumbite-type LaMgAl11O19 with high thermal stability and excellent sintering resistance has been proposed as a promising thermal barrier coating (TBC) material for next generation gas turbines. However, LaMgAl11O19 shows poor stability at 1500 °C in humid environments caused by H+/Mg2+ ionic exchange. In this work, a LaZnAl11O19 coating which is supposed to possess enhanced anti-deliquescent property was produced by plasma spraying and its properties as a potential TBC were comprehensively investigated. The results show that the thermal conductivity of the as-sprayed LaZnAl11O19 coating ranges from 1.24 W m−1 K−1 to 1.46 W m−1 K−1 and the average thermal expansion coefficient is less than 6.0 × 10−6 K−1 due to the presence of an amorphous phase in the as-sprayed coating. During exposure to 1300 °C, a total porosity of ∼10.5% can be maintained even after 1000 h aging, indicating a high sintering resistance. Besides, nano-sized grains recrystallized from the molten lamellae give the LaZnAl11O19 coating enhanced mechanical properties. In 1100 °C furnace cyclic testing, the LaZnAl11O19/YSZ double-ceramic-layer TBC exhibits a thermal cycling lifetime of ∼669 cycles, which is about 1.7 and 1.16 times as long as the conventional YSZ coating and the LaMgAl11O19/YSZ TBC, respectively. The results indicate that LaZnAl11O19 might be a promising candidate for advanced TBC applications.