Investigation of crack growth on thermal barrier coating with various rare-earth elements in static condition application

Abstract

ABSTRACT Thermal barrier coating (TBC) has been applied to gas turbine components to increase exposure temperature beyond the turbine material limits. The modification in TBC by adding rare-earth elements, gadolinium (Gd) and lanthanum (La), may improve its properties. However, there are few studies on the performance limit of La–Gd–TBCs for crack propagation. Hence, a crack growth model for the modified TBC has been established in this study to evaluate its performance. Thermal oxidation test was conducted to determine the propagation of cracks with time at three different temperatures: 1200°C, 1300°C and 1400°C. The exhibited cracks were measured using a 3D measuring laser microscope and evaluated using scanning electron microscopy (SEM). The exhibitions of cracks are almost similar at 1200°C and 1300°. Some of the cracks were initiated from the topcoat and propagated towards the topcoat–thermally grown oxide (TGO) interface. The rest of the cracks were observed to initiate from the TGO itself. The crack growth model was established, and it was found that over time the crack growth rate reaches almost zero for temperatures 1200°C, 1300°C and 1400°C. Images of cracks captured under SEM were used to verify the measured cracks. Improvement in the reliability of the established model is suggested.