Determination of Degree of Thermal Barrier Coating Disbonding by Time-Resolved Infrared Radiometry (TRIR)

Abstract

IN1RODUCITONWe have previously described the time-resolved infrared radiometry (TRIR) technique and demonstrated how both measurement of coating thickness and detection of coating disbonding can be made within the same measurement [1]. We have also reponed indications of the sensitivity of the lRlR technique to differing degrees of coating disbonding [2]. In the present work we examine this question in detail and compare TRIR experimental results with both an analytical multilayer theory and a destructive analysis of the coating-substrate interface. While the material system studied in this work is a zirconia thermal barrier coating on a superalloy substrate, the methodology and analytical basis of the technique are applicable to a wide variety of materials and components including printed circuit boards and composite materials. The capability of the TRIR technique for characterization of these specific systems will depend on details of the thermal properties and layer thickness in these specimens. EXPERIMENTAL 1ECHNIQUEThe time-resolved infrared radiometry (1RIR) technique differs from many other pulsed radiometry techniques [3,4,5] in that we monitor the increase in specimen surface temperature during the application of a step heating pulse of specified duration rather than following the decay in temperature after application of a shon heating pulse. The experimental system consists of an infrared scanner (Mikron 6T61) used to monitor the time development of the surface temperature of the specimen. Synchronizing electronics and an acousto-optic modulator are used to gate a heating beam from an argon ion laser (Coherent Innova 90-5) at a fixed time with respect to the frame rate of the scanner. For most of the images presented here, a line heating source was employed. However a variety of heating beam patterns on the specimen can be produced by use of various lenses and an acousto-optic deflector. A positioning system (Burleigh CE-2000) is used to translate the specimen with respect to the line source. Operation of the infrared scanner, synchronizing electronics and positioning system is all under control of a microcomputer (Macintosh II) over the IEEE-488 bus.With this system it is possible to produce area maps of the time development of the surface temperature with a time resolution equivalent to the scan rate of the horizontal galvanometer (8.3 msec). The surface temperature along one horizontal line on the infrared scanner is monitored as the laser heating pulse is applied to the sample. A position-time temperature image is generated for this location on the sample. The sample is then translated venically so that the line heating source and the infrared viewing line have been shifted to a new horizontal line on the sample and a new position-time image is then recorded for the new location. After the desired number of positions on the sample have been recorded, a lRIR X-

Thermal Nondestructive Testing of Thermal-Barrier Coatings of Turbine Buckets

“…The analysis of one-, two-, and three-dimensional thermal testing models of coatings is beyond the limits of this study (see [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]). For further consideration, it is important that the suggested approach be based on a possibility of choosing a reference point belonging to the flawless area in a coating.…”

“…In many cases, such a compromise is achieved by using xenon flash lamps. The TT technique that does not require powerful heating is called Time-Resolved IR Radiometry (TRIR) and was proposed by Maclachlan et al [7]. This technique provides for continuous heating of a sample with a low-power laser beam with a wavelength beyond the spectral sensitivity of the used infrared imager, thus allowing avoidance of the effect of reflected radiation.…”

<title>Time-resolved infrared radiometry (TRIR) using a focal-plane array for characterization of hidden corrosion</title>

“…X=exp(-2L1/S1), I2÷I [2] Si 6 cii = , A1 = i+r2r23x2, A2 = x1(r2 +r'x2) ,c K In these definitions, S is the three-dimensional thermal diffusion length and is the one-dimensional thermal diffusion length. These values are different in each layer as identified by the subscript i.…”

“…In earlier work [1,2] we had shown that time-resolved infrared radiometry (TRIR) is an effective method for quantitatively detecting coating thickness variations and for characterizing the degree of coating disbonding for high temperature thermal barrier coatings on metals. Such hidden corrosion is expected to be the primary factor limiting the service life of military and civilian aircraft.…”