Effects of supersonic fine particles bombarding on thermal barrier coatings after isothermal oxidation

This work was attempted to modify the current technology for thermal barrier coatings (TBCs) by adding an additional step of surface modification, namely, supersonic fine particles bombarding (SFPB) process, on bond coat before applying the topcoat. After isothermal oxidation at 1000 °C for different time, the surface state of the bond coat and its phase transformation were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and Cr3+ luminescence spectroscopy. The dislocation density significantly increases after SFPB process, which can generate a large number of diffusion channels in the area of the surface of the bond coat. At the initial stage of isothermal oxidation, the diffusion velocity of Al in the bond coat significantly increases, leading to the formation of a layer of stable α-Al2O3 phase. A great number of Cr3+ positive ions can diffuse via diffusion channels during the transient state of isothermal oxidation, which can lead to the presence of (Al0.9Cr0.1)2O3 phase and accelerate the γ→θ→α phase transformation. Cr3+ luminescence spectroscopy measurement shows that the residual stress increases at the initial stage of isothermal oxidation and then decreases. The residual stress after isothermal oxidation for 310 h reduces to 0.63 GPa compared with 0.93 GPa after isothermal oxidation for 26 h. In order to prolong the lifespan of TBCs, a layer of continuous, dense and pure α-Al2O3 with high oxidation resistance at the interface between topcoat and bond coat can be obtained due to additional SFPB process.