Optimization of mechanical properties and thermal shock resistance of LaPO4/8YSZ thick composite coatings via plasma spraying

The aim of the current study was to optimize the mechanical properties and thermal shock resistance of plasma-sprayed LaPO ₄ /8YSZ coatings with thickness of 1 mm based on a modified Vickers indentation method. As the LaPO ₄ content increased from 1 wt% to 30 wt%, the increasing porosity of the composite coatings led to the decrease of bonding strength of the coatings from 8.43 ± 0.29 MPa to 6.08 ± 0.12 MPa, while residual stress and fracture toughness of the composite coatings exhibited an increased tendency. Although the bonding strength of LaPO ₄/8YSZ coatings was lower than that of 8YSZ coating (11.49 ± 0.19 MPa), the minimum residual stress of -(51.83 ± 3.38) MPa for the coating with LaPO ₄ content of 1 wt% was obtained, further resulting in the maximum thermal cycling lifetime of 5340 ± 49 cycles during thermal shock test at 900 °C. Correspondingly, thermal shock resistance was strongly dependent on the microstructure and mechanical properties of LaPO ₄/8YSZ coatings with the addition of nano-LaPO ₄ particles.