Properties evolution of plasma-sprayed La₂Zr₂O₇ coating induced by pore structure evolution during thermal exposure

To study the inter-lamellar pores evolution under thermal exposure and how it affects the coating properties, free standing atmospheric plasma sprayed (APS) La₂Zr₂O₇ (LZO) coating was subjected to thermal exposure at the temperatures of 1200 °C and 1300 °C for different durations. It was found that APS LZO coating experiences a rapid sintering during the early 5–20 h of thermal exposure. Such microstructure evolution behavior was attributed to the presence of the lamellar structure, which contains most 2D pores with a small inter-lamellar spacing. As a result, the density, inter-lamellar bonding ratio, mechanical properties and thermal conductivity of the LZO coating remarkably increase in about 20 h of thermal exposure. It was revealed that the evolution of the properties of the APS LZO coating during high temperature exposure is mainly ascribed to the shape change of the inter-lamellar pores for the formation of grain bridging in inter-lamellar pores.