Mechanical properties, thermal shock resistance and stress evolution of plasma-sprayed 56 wt% Y2O3-stabilized ZrO2 thick thermal barrier coatings

The mechanical properties and thermal shock resistance of plasma-sprayed 56 wt% Y2O3-stabilized ZrO2 thick thermal barrier coatings (TTBCs) deposited with different critical plasma spraying parameter (CPSP) values and its stress evolution were investigated. With the CPSP value increased from 0.83 kW<middle dot>SLPM-1 to 1.17 kW<middle dot>SLPM-1, the porosity was decreased from 14.62 +/- 0.84 % to 7.00 +/- 0.38 % while the bonding strength was increased from 7.82 +/- 0.64 MPa to 9.95 +/- 0.30 MPa. As a result, the hardness of the coating obtained from the cross-section was increased from 2.16 +/- 0.61 GPa to 2.67 +/- 0.82 GPa, and the elastic modulus was also increased from 60.47 +/- 5.22 GPa to 71.93 +/- 6.91 GPa. During thermal cycling test at 1000 degrees C, thermal cycling lifespan presented a decrease from (83 +/- 3) cycles to (44 +/- 3) cycles, and coating failure was mainly attributed to the occurrence of partial or whole spallation of the top coat. According to the stress simulation result, residual stress in the coating was accumulated while thermal stress was released with the increase of thermal cycles, and the increasing residual stress was the main failure driver for the coating.