Microstructural change and delamination resistance of the thermal barrier coatings with cold sprayed ce-content bond coats

Abstract

Thermal barrier coatings (TBC) are widely used in gas turbine engines as protective coatings. TBC systems usually consist of a ceramic top coating (TC) and an intermediate metallic bond coating (BC) on a Ni-based superalloy substrate. Thermally grown oxide (TGO), however, forms at the interface between the TC and BC during high-temperature operation. A delamination can occur at the interface because of the TGO formation and growth. Previous studies had successfully improved delamination resistant properties drastically, due to a wedge-like TGO formation in a high-temperature environment, by adding Cerium (Ce) to a conventional CoNiCrAlY bond coat material. However, relationship between the microstructural variation of the wedge-like TGO and the delamination resistance with increasing high-temperature exposure time have not been clarified. In this work, Ce-content BC was formed by a cold spray technique. Following the high-temperature exposure process at 1100°C, wedge-like TGO generation was confirmed in the TBC with the Ce-content BC. The wedge-like TGO shows an increase in growth with an increase in the high-temperature exposure time, and it was confirmed to grow throughout the BC at 100 h. The delamination resistance of the high-temperature exposed TC specimens at 1100oC were evaluated at various times by using static four-point bending tests. From the results of four-point bending tests, the Ce-content BC indicated high delamination resistance. The residual strain in the TGO was calculated from the Raman peak shift change of Al2O3. The residual strain of the Ce-content BC is relatively small compared to the TBC with convention bond coat. It is expected to be due to the stress dispersed by the generation of the wedge-like TGO. This effect contributes to the improvement of delamination resistance.