Buckling and interface strength analyses of thermal barrier coatings combining Laser Shock Adhesion Test to thermal cycling

Abstract

Laser Shock Adhesion Test (LASAT) is a non-contacting technique that can be applied to evaluate the interfacial adherence of ceramic layer on metallic substrate. This study aims at combining the laser-induced delamination and blistering when applied to a conventional EB-PVD TBC submitted to thermal cycling. Besides, the use of white spot diagnostic as a NDT technique and 3D profilometer measurement along thermal cycling were fully consistent. The LASAT analysis of as-deposited samples with various initial substrate roughness is discussed regarding the corresponding life to top-coat spallation under air thermal cycling. Mixing thermal cycling with LASAT has enabled to show that the adherence was sensitive to process condition consistently with the performance measured by conventional thermal cycling tests. Moreover, the evolution of the adherence has also been be assessed by LASAT applied to TBC samples with different interrupted thermal cycling conditions. According to this methodology, LASAT could also be used to introduce an interfacial defect known in location, size of debonded area, height of the blister and number of cycles. After further interrupted thermal cycling, the crack propagation and the buckling were monitored. Such measurements allowed to derive the interfacial toughness corresponding to these various aging conditions.