Residual stress in air-plasma-sprayed thermal barrier coatings under long-term high-temperature oxidation

Abstract

The accumulated residual stress in yttria-stabilized zirconia top coat (YSZ TC) and thermally grown oxide (TGO) is regarded as the key driving force for the delamination of air-plasma-sprayed thermal barrier coating system (APS-TBCs). In this study, the synchronous evolution of residual stress of both YSZ TC and TGO, as well as the TGO thickness, are characterized via the Raman spectroscopy (RS) and photoluminescence piezo-spectroscopy (PLPS) methods. For the APS-TBCs where one surface is coated with YSZ TC, while the other surface remains directly exposed to high temperature, the service life can be categorized into four distinct stages: the early stage with tensile stress state (0–40 h), the medium stage with reversal compressive stress state (40–100 h), the late stage with re-inverted tensile stress (100–140 h), and the final stage with compressive stress state (140–300 h). Such stress reversal phenomenon may be attributed to the competition between the growth of TGO and substrate oxide (SO). It is advisable to apply an oxidation-resistant coating on the inner wall of high-temperature blade cooling passages, to prevent the formation of SO and consequently avoid complex stress transitions during high-temperature service of the APS-TBC, ultimately preventing local stress concentration-induced cracking and delamination.