Abstract
Thermal barrier coatings (TBCs) are usually subjected to the combined action of compressive stress, tensile stress, and bending shear stress, resulting in the interfacial delamination of TBCs, and finally causing the ceramic top coat to peel off. Hence, it is vital to detect the early-stage subcritical delamination cracks. In this study, a novel hybrid artificial neural network combined with the terahertz nondestructive technology was presented to predict the thickness of interface delamination in the early stage. The finite difference time domain (FDTD) algorithm was used to obtain the raw terahertz time-domain signals of 32 TBCs samples with various thicknesses of interface delamination, not only that, the influence of roughness and the thickness of the ceramic top layer were considered comprehensively when modeling. The stationary wavelet transform (SWT) and principal component analysis (PCA) methods were employed to extract the signal features and reduce the data dimensions before modeling, to make the cumulative contribution rate reach 100%, the first 31 components of the SWT detail data was used as the input data during modeling. Finally, a back propagation (BP) neural network method optimized by the genetic algorithm (GA-BP) was proposed to set up the interface delamination thickness prediction model. As a result, the root correlation coefficient R2 reached over 0.95, the various errors—including the mean square error, mean squared percentage error, and mean absolute percentage error—were less than or equal to 0.53. All these indicators proved that the trained hybrid SWT-PCA-GA-BP model had excellent prediction performance and high accuracy. Finally, this work proposed a novel and convenient interface delamination evaluation method that could also be potentially utilized to evaluate the structural integrity of TBCs.
Highlights
Aero-engine technology is known as the jewel in the industrial crown and is the focus technology that countries all over the world are pursuing
Interface delamination generates under repeated high-temperature thermal shock cycles, owing to the crack propagation along the bottom of Thermal barrier coatings (TBCs), and the interface delamination will induce the ceramic top coat to peel off and fail
Terahertz non-destructive evaluation technology has been applied in various fields, mainly including human security, integrated circuits, biopharmaceuticals, glass fiber reinforced plastic materials and thermal barrier coatings, of which the research in thermal barrier coatings non-destructive evaluation mainly focuses on the detection and characterization of ceramic layer thickness [13,14], interface thermally grown oxide layer (TGO) [15,16], ceramic top coat microstructure features [17,18,19], and erosion morphology [20]
Summary
Aero-engine technology is known as the jewel in the industrial crown and is the focus technology that countries all over the world are pursuing. Thermal barrier coatings (TBCs) have been widely used as a protective material for hot-end components of aero-engines, owing to their excellent high-temperature resistance, low thermal conductivity, and anti-wear and anti-corrosion properties, which can effectively improve. Terahertz non-destructive evaluation technology has been applied in various fields, mainly including human security, integrated circuits, biopharmaceuticals, glass fiber reinforced plastic materials and thermal barrier coatings, of which the research in thermal barrier coatings non-destructive evaluation mainly focuses on the detection and characterization of ceramic layer thickness [13,14], interface TGO [15,16], ceramic top coat microstructure features [17,18,19], and erosion morphology [20]. There are few reports about the terahertz nondestructive research on interface delamination evaluation of thermal barrier coatings
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