13423 Melt Infiltrated SiCSiC with Environmental Barrier Coating

The third example of NDE data detecting a delamination concerns a MI SiC/SiC cylinder used as a combustor liner in a 4.5-MW gas turbine [56]. The annular combustor of the engine—see Fig. 13.33—consists of an outer liner 75 cm in diameter and an inner liner 33.5 cm in diameter. In this case, both liner components had been coated with a protective environmental barrier coating (EBC) [57]. Prior to insertion of the components into the engine, which was a full-size field test engine, both thermal diffusivity imaging and air-coupled ultrasonic imaging NDE data were obtained. Figure 13.34a shows the NDE thermal image data, which suggested a delaminated region. Figures 13.34b and c show the occurrence of a spallation of the coating. Figure 13.34b is after 357 h of operation

FIGURE 13.33 Diagram of gas turbine engine and photograph of annular combustor liner set made of SiC/SiC ceramic matrix composite.

NONDESTRUCTIVE EVALUATION OF STRUCTURAL CERAMICS t-Circumference = 105 cm -

20 cm j^Prorgresion of coating spall

Low diffusivity

High diffusivity

Low diffusivity

High diffusivity

FIGURE 13.34 Use of thermal image NDE data to predict spall regions of EBC on MI SiC/SiC gas turbine combustor inner 33.5-cm-diameter liner as shown in Fig. 13.32.

and Fig. 13.34c is after 1573 h of operation. This demonstrates the ability of NDE data to accurately predict spall locations.

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