Acoustic emission characteristics for diagnosis of TBC damaged by high-temperature thermal fatigue

Acoustic emission (AE) technology was adopted to the damage diagnosis of thermal barrier coating (TBC) by plasma spray process. These samples were composed of CoNiCrAlY bond layer made by vacuum plasma spray and ZrO2-8 wt.%Y2O3 ceramic layer made by air plasma spray on Inconel-718 substrate. To investigate the thermal fatigue damage by high-temperature, the AE signal was measured during four-point bending test followed by cyclic thermal test. The AE monitoring system was composed of PICO type sensor, a wide band pre-amplifier and a DSP board. The AE events, amplitude, cumulative energy, and count were evaluated according to the cycles of thermal fatigue. By AE test, it is shown that AE sources is caused from the stress of thermally grown oxide layer and micro-crack.