Experimental and Modeling Studies of Bond Coat Species Effect on Microstructure Evolution in EB-PVD Thermal Barrier Coatings in Cyclic Thermal Environments

Abstract

In this work, the effects of bond coat species on the thermal barrier coating (TBC) microstructure are investigated under thermal cyclic conditions. The TBC samples are prepared by electron beam-physical vapor deposition with two species of bond coats prepared by either air-plasma spray (APS) or high-velocity oxygen fuel (HVOF) methods. The TBC samples are evaluated in a variety of thermal cyclic conditions, including flame thermal fatigue (FTF), cyclic furnace thermal fatigue (CFTF), and thermal shock (TS) tests. In FTF test, the interface microstructures of TBC samples show a sound condition without any delamination or cracking. In CFTF and TS tests, the TBCs with the HVOF bond coat demonstrate better thermal durability than that by APS. In parallel with the experiments, a finite element (FE) model is developed. Using a transient thermal analysis, the high-temperature creep-fatigue behavior of the TBC samples is simulated similar to the conditions used in CFTF test. The FE simulation predicts a lower equivalent stress at the interface between the top coat and bond coat in bond coat prepared using HVOF compared with APS, suggesting a longer cyclic life of the coating with the HVOF bond coat, which is consistent with the experimental observation.

Review of Ceramic Composites in Aeronautics and Aerospace: A Multifunctional Approach for TPS, TBC and DBD Applications

“…Nonetheless, the TGO layer may increase the internal stress in the TBC system, hence potentially originating cracking at the interface between the bond and top coats. This phenomenon may eventually lead to the unwanted spallation or delamination of the top coat in service [46,47,53].…”

Thermal Stability of Rare Earth-PYSZ Thermal Barrier Coating with High-Resolution Transmission Electron Microscopy

“…Moreover, many processes have been employed to deposit bondcoat, such as APS, low-pressure plasma spray, and high-velocity oxygen fuel (HVOF) [27]. The APS technique is the most popular to form bondcoat due to its economic benefits; however, the HVOF process is more desirable to increase the working temperature and fuel performance in gas turbines and diesel engines [28,29]. According to Lu et al, more extended thermal durability was found in HVOF bondcoat than in the APS bondcoat due to lower equivalent stress at the TGO layer [28].…”

“…The APS technique is the most popular to form bondcoat due to its economic benefits; however, the HVOF process is more desirable to increase the working temperature and fuel performance in gas turbines and diesel engines [28,29]. According to Lu et al, more extended thermal durability was found in HVOF bondcoat than in the APS bondcoat due to lower equivalent stress at the TGO layer [28]. However, most HVOF bondcoating does not focus on the phase transformation of alumina in TGO and the stress-induced at the interface of topcoat and bondcoat simultaneously.…”