Strain analysis of plasma sprayed thermal barrier coatings under mechanical stress

The stiffness of air plasma sprayed (APS) thermal barrier coatings (TBCs) was determined from bending experiments combining strain analysis on a microstructural level with macroscopic mechanical parameters. Tests were performed with freestanding and attached TBCs, the latter either loaded in tension or in compression. Relationships are derived, which describe the TBC stiffness in a multilayer composite (attached TBC) and for a bimodular material that possess a lower stiffness in tension than in compression (stand-alone TBC). The increase of in-plane stiffness with increasing compressive stress emphasizes the importance of the spraying defects for the elastic response of the coating.