Three-dimensional Structural Analysis Of Turbine Blades Thermal Barrier Coating Based On Micro Computed Tomography Technology

Thermal barrier coating is one of the key technologies of high temperature protection which protecting the aviation turbine engine blades. The typical two-layer structure thermal barrier coating consists ceramic insulation surface(TBC) and bond coat,which protecting the blades from high temperature oxidation and hot corrosion,structure of the thermal barrier coating conditions its function.As some problems such as internal defects,pore and porosity,nonuniform coating thickness and sureface morphology always exist when the preparation and use process of the thermal barrier coating,the nondestructive examination assessment of the quality of thermal barrier coating is essential.This article performs a micro CT experiment on thermal barrier coating of turbine blades:(1)This article performs SEM and EDS analysis of two samples from the thermal barrier coating of turbine blades. The distinguish between TBC, bond coat and substrate alloy is observed through SEM clearly, A lot of pores are observed in the TBC of the samples. The average thickness of the two ceramic surfaces are 123.90μm and 111.80μm through calculation of SEM.(2)Micro CT scan and rebuilt experiment is performed in the two samples.Defects such as inner pores and lamination inside the thermal barrier coating is analyzed in three different positions. The distinguish between TBC,bond coat and substrate alloy of the samples is observed,but the density differences between bond coat and substrate alloy is small,resulting in lower contrast between them.(3)Based on CT rebuilt image, the density of the TBC has significant differences with other area,the TBC is separated from the thermal barrier coating by image segmentation. Though the separation of bond coat and substrate alloy is hard,but the interface between bond coat and substrate alloy has a lot of pores,Bond coat is separated by the interface which has the most pores.Based on the 3D segmentation,The average thickness of TBC of the two samples are respectively121.83μm and 117.55μm. The error of-1.7% and 5.1% is observed between this method and SEM. The internal pores of TBC are separated by image thresholding,Theporosity of the TBC are respectively 28.75% and 23.13%. The inner pores are 3-D visualized.Based on the 3D segmentation,propose the method of the surface morphology extract,the three surface are two of TBC and underneath(which is next to TBC) of bond coat,Calculate the surface roughnesses of two sureface of TBC and the underneath sureface of bond coat.The surface roughnesses of No. 1 sample are 5.6μm, 5.7μm, 10.1μm while those of No. 2 sample are 6.3μm, 5.5μm, 14.1μm.Finally the TBC and the thermal barrier coating of the samples are 3-D visualized.The results illustrate that micro CT is able to assess the quality of heat barrier coating.