Evolution of microstructural and mechanical properties of lanthanum zirconate thermal barrier coatings at high temperature

• Thick lanthanum zirconate TBCs were deposited by APS.
• Thermal aging of as-sprayed samples promoted partial sintering of microstructure.
• The TBCs were characterized by four-point bending tests from RT to 1500 °C.
• High-temperature microcracking and stress relaxation enhanced mechanical properties.
• The Cp decreased after thermal aging at 1350 °C, while the CTE slightly changed.

Ceramic thermal barrier coatings (TBCs) are advanced systems for more efficient turbine engines. In this work, thick lanthanum zirconate TBCs were fabricated by Air Plasma Spraying (APS). The coatings showed a lamellar microstructure containing splat boundaries, pores and microcracks. After thermal exposure at 1200 and 1350 °C the partial sintering of the porous microstructure occurred.High-temperature evolution of the mechanical properties was investigated by arranging specific bending tests up to 1500 °C using SiC testing assembly which allowed to calculate the strain by means of curvature measurement. The mechanical properties improved with increasing the testing temperature, due to the inelastic deformation and stress relaxation which counteracted the sintering effects.The elastic modulus increased after thermal aging, but decreased for the aged coatings tested at higher temperature.The thermal expansion coefficient of as-sprayed coatings slightly increased after thermal aging, while a reduction of specific heat capacity was noticed.