Nondestructive Evaluation of Coatings Delamination Using Microwave Time Domain Reflectometry Technique

• Published in: IEEE access Vol. 8; pp. 114833 - 114841
• Main Authors: Akbar, Muhammad Firdaus, Jawad, Ghassan Nihad, Rashid, Laith Danoon, Sloan, Robin
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Catastrophic failure analysis; Ceramic coatings; Ceramics; Coating delamination; Coatings; Defects; Delamination; Destructive testing; Engine components; Fourier analysis; Frequency analysis; Frequency domain analysis; Gas turbine engines; High temperature; Industrial applications; Inspection; Insulation; Maintenance management; Metal surfaces; Microwave imaging; Microwave measurement; microwave NDT; Microwave theory and techniques; Nondestructive testing; open-ended rectangular waveguide; Predictive maintenance; Rectangular waveguides; Reflectometry; Schedules; Substrates; Thermal barrier coatings; Time domain analysis; Time Domain Reflectometry
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2020.3003829

Ceramic based coatings such as Thermal Barrier Coatings (TBCs) are widely deposited onto gas turbine engine components to protect their metal substrate against high temperature. However, improper adhesive application, thermal stress and moisture penetration through the insulation materials can cause defects such as delamination to grow between the insulation and the metal surface. Such defects could lead to catastrophic failure if not immediately detected and repaired. Hence, it is imperative to non-destructively inspect these interfaces for delamination to avoid such an event. In this paper, a novel microwave non-destructive testing technique for ceramic-based coatings is proposed. This technique is based on scanning the surface of the coating with an open-ended rectangular waveguide and analyzing the reflections in the time domain. The proposed time-domain technique appears to reveal more about the depth of any existing delamination than any other microwave non-destructive testing (NDT) technique. Here, a ceramic sample with machined delamination is scanned using rectangular waveguides operating from 26.5 to 40 GHz. After applying Fourier analysis to the frequency domain waveguide reflections, time-domain results showed the delamination with significantly better depth resolution compared to frequency domain analysis. The results reported in this paper prove the advantages of the time-domain technique to forecast the relative delamination depth, which is important for many industrial applications. The depth information of delamination can be used in a condition-based predictive maintenance schedule to plan the inspection intervals efficiently, minimize the unnecessary replacements and provide practical guidance for future design.