Thermal cycling damage monitoring of thermal barrier coating assisted with LASAT (LAser Shock Adhesion Test)

Abstract

One of the major challenges for thermal barrier coating (TBC) system is to determine the time to failure of ceramic layer during aging. The aim of this paper is to propose new methodologies for experimental assessment of adhesion and for analysing its link to lifetime to spallation. Recently, the use of LAser Shock Adhesion Test (LASAT) with multi-shock experiments have shown its capability for both ranking different coating solutions in terms of adhesion and evaluating its evolution with aging. The methodology developed in this study is based on single shock experiments using the same laser parameters in order to measure non destructively and compare directly the resulting crack sizes and corresponding interface strength levels during interrupted thermal cycling. This cycle-by-cycle non destructive methodology was also enriched by the assessment of the evolution of the interfacial damages that were first initiated by LASAT and further propagated during subsequent thermal cycling. The evolution of interfacial damage during thermal cycling was shown to be consistent with interfacial delamination measured post-mortem by cross-sectioning. Besides, the influence of dwell time at high temperature has been clearly established, confirming that short dwell time was more detrimental as compared to longer and conventional dwell used for thermal cycling tests at high temperature.