Evaluation of fracture toughness and residual stress for both single GYbZ and double layered GYbZ/8YSZ coatings by modified indentation tests

Single (Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ) and double layered GYbZ/yttria partially stabilized zirconia coatings were prepared with supersonic plasma sprayed technique. The microstructure and texture of the two coatings were analyzed by scanning electron microscope and X-ray diffraction. The elastic modulus, hardness, fracture toughness and residual stress of both coating systems were measured in indentation tests. The influence of residual stress on fracture toughness measurements was discussed with different indentation models. It is interesting to find that the absolute value of residual stress on the cross section of the coating becomes smaller, while the corresponding fracture toughness gets larger when the indented point gradually moves to the interface. The present results would be helpful for understanding the design optimization and failure mechanisms of advanced ceramic coatings.