Evaluation of microhardness, fracture toughness and residual stress in a thermal barrier coating system: A modified Vickers indentation technique

The evolution of microhardness, fracture toughness and residual stress of an air plasma-sprayed thermal barrier coating system under thermal cycles was investigated by a modified Vickers indentation instrument coupled with three kinds of indentation models. The results show that fracture toughness on the top coating surface after thermal cycles changes from 0.64 to 3.67 MPa m1/2, and the corresponding residual stress near the indented region varies from − 36.8 to − 243 MPa. For the interface region of coating and bond coat, fracture toughness in the coating close to interface ranges from 0.11 to 0.81 MPa m1/2, and residual stress varies from − 5 to − 30 MPa, which are consistent with available data. For the lateral region of coating, fracture toughness and residual stress display strong gradient characteristics along the thickness direction due to the special layered structure.

► We proposed a modified Vickers indentation instrument by re-designing load intervals.
► Microhardness, fracture toughness and residual stress of coating were measured.
► Mechanical properties display a strong gradient characteristics effect along the thickness direction.
► The method can be used to study the failure process of coating/film materials.