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Development of a Portable System for Detection of Thermally Grown Oxide Layer in Thermal Barrier Coating
Author(s) -
FUKUCHI TETSUO,
OKADA MITSUTOSHI,
FUJII TOMOHARU
Publication year - 2017
Publication title -
electronics and communications in japan
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.131
H-Index - 13
eISSN - 1942-9541
pISSN - 1942-9533
DOI - 10.1002/ecj.11937
Subject(s) - coating , thermal barrier coating , oxide , layer (electronics) , materials science , barrier layer , thermal , composite material , physics , metallurgy , thermodynamics
SUMMARY Thermal barrier coating (TBC) is applied to high temperature components in gas turbines. The thermally grown oxide (TGO) layer, which forms at the interface between the topcoat and the bondcoat, is an origin of topcoat damage, which can lead to delamination of the topcoat. In order to detect the TGO layer in in‐service components, a portable detection system based on photoluminescence was developed. The system consists of a compact, continuous wave Nd:YAG laser of wavelength 532 nm to excite Cr 3+ included as an impurity in Al 2 O 3 and a compact spectrometer with a two‐dimensional CCD array for enhanced sensitivity to detect the photoluminescence from Cr 3+ at 694.3 nm (R 1 ) and 692.9 nm (R 2 ). An optical probe is used to illuminate the specimen with laser light and to collect the photoluminescence. The probing region is a circle of diameter 5 mm. The optical probe is coupled to the main body by an optical fiber, which allows flexibility to match specimens with curved surfaces or complex structures. The system performance was tested using TBC specimens heated at 1000 °C and 1100 °C, and an as‐sprayed, unheated TBC specimen. Photoluminescence (R 1 and R 2 ) was observed from heated specimens and was not observed from the unheated specimen, and agreed with previous measurement results. This system can be used for screening test of topcoat delamination inspection, since delamination is likely to occur at locations where the TGO layer has grown.