Three-dimensional Imaging Of Thermal Barrier Coatings By Nano-CT

Thermal barrier coatings(TBCs)is one of the key technologies of turbine blades in high thrust-weight aero-engine,it has typical layered structure characteristics.The three-dimensional structure of TBCs has a very important influence on its performance,which directly affect the service life of the coatings.It is very important to evaluate the three-dimensional characterization of the layered structure of TBCs and the quality of the morphology,composition,thickness,pores and porosity of the coatings.In this paper,the double-layer structure TBCs prepared by plasma spraying method is considered as research object,and the following research is listed below:(1)The surface microstructure of TBCs was analyzed by metallographic microscopy and scanning electron microscopy(SEM),and layer structure of TBCs was observed.The thickness of the TBCs was measured by SEM,the thickness of the thermal barrier coatings was 211.0?m,wherein the thickness of the ceramic topcoat is114.5?m and the thickness of the bond coat is 96.5?m.The energy spectrum analysis of ceramic topcoat,bond coat and substrate was carried out by energy dispersive spectrometer,the element distribution and percentage content of different structures were determined,and the X-ray linear attenuation coefficient of TBCs was calculated theoretically.(2)The TBCs samples was researched by Nano-CT with the resolution of 1.57?m and 0.99?m respectively,and the tomographic images of TBCs were obtained after the projection images were reconstructed.The structure,characteristic defect and interface morphology of the thermal barrier coatings were analyzed in tomographic images.The segmentation and extraction of ceramic topcoat,bond coat and substrate are realized by image processing method.The three-dimensional reconstruction of TBCs was obtained,and the three-dimensional morphology of the structure of TBCs was obtained respectively.the surface morphology of TBCs can be described by surface roughness,The surface roughness of outer surface on ceramic topcoat layer,the interface between ceramic topcoat and bond coat,the interface between bond coat and substrate were calculated respectively.The three surface roughness are 9.30?m,5.76?m and 4.69?m when the resolution is 1.57?m.The three surface roughness are9.37?m,6.09?m and 4.07?m respectively when the resolution is 0.99?m.(3)On the basis of three-dimensional segmentation,the thickness of TBCs,ceramic topcoat and bond coat were measured by the number of pixels along thickness direction.The thickness of each layer is 227.08?m,126.21?m and 100.87?m when the resolution is 1.57?m.The thickness of each layer is 229.98?m,124.96?m and105.02?m when the resolution is 0.99?m.The thickness uniformity of ceramic topcoat and bond coat can be characterized by variance of thickness,and the thickness distribution of bond coat was uniform.(4)The volume porosity of TBCs,ceramic topcoat and bond coat under different resolutions were calculated respectively by gray threshold segmentation.The porosity of each layer is 3.13%,3.10% and 3.18% respectively when the resolution is 1.57?m.The porosity of each layer is 3.41%,3.38% and 3.45% respectively when the resolution is 0.99?m.The three-dimensional distribution of the pores in TBCs was displayed by 3D visualization.Finally,the pore characteristics were quantitatively characterized by pore volume and pore diameter.The results show that nano-CT can be used to quantitatively analyze the three-dimensional morphology,thickness,porosity and porosity of TBCs in turbine blade.