Abstract
This study demonstrates a new surface treatment for thermal barrier coatings that combines ultrasonic vibration and laser remelting and assesses its effect on crack distribution, surface morphology, and grain refinement. YSZ coating samples were vibrated at 20 kHz at different power levels while being irradiated by a Nd:YAG pulsed laser operated at 5.2 J and 6 J. SEM examination revealed a uniform distribution of segmented network cracks in treated samples, which are shown to play an important role in relieving stress and increasing strain tolerance in topcoat layers, thus improving fracture toughness and thermal cycle life. Another important finding is that visible ribbon-like loops induced by variations in surface tension were eliminated as a result of improved surface convection facilitated by ultrasonic vibration. At a vibration power of 520 W, coating surfaces were uniform and flat, but at 1300 W, undulations and trough geometries were observed. The results of XRD analysis indicate that tetragonal to monoclinic phase transformations are prevented when ultrasonic vibration power is greater than 780 W.
