Effect of vacuum annealing on the adhesion strength of air plasma sprayed thermal barrier coatings

The thermal barrier coatings(TBCs) consisting of NiCoCrAlY/8YSZ were prepared by air plasma spraying(APS).Tensile testing process was conducted to observe the effect of vacuum annealing on the adhesion strength of the TBCs.Morphologies,microstructures and the chemical composition were investigated by using scanning electron microscope(SEM) with energy disperse spectroscopy(EDS).The result shows that the adhesion strength of the TBCs increases from 24.58 MPa to 30.60 MPa after vacuum annealing.The fracture site shifts from the bottom to the inner of the ceramic coating.Vacuum annealing promotes the element diffusion between the substrate and the coating,and also between the coatings,therefore,it can improve the metallurgical bonding of the coatings,and finally enhance the adhesion strength of the TBCs.