Nondestructive measurements of residual stress in air plasma‐sprayed thermal barrier coatings. Issue 3 (20th November 2020)

• Record Type: Journal Article
• Authors: Jiang, Peng; Yang, Liuyu; Sun, Yongle; Li, Dingjun; Wang, Tiejun
• Is Part Of: Journal of the American Ceramic Society. Volume 104:Issue 3(2021)
• Page Start: 1455
• Page End: 1464
• Publication Date: 2020-11-20
• Subjects: debonding -- photoluminescence piezo‐spectroscopy -- residual stress -- thermal barrier coating -- x‐ray computed tomography; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.17550
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract: Premature spallation of thermal barrier coatings (TBCs) is a critical issue during the service of gas turbines, and nondestructive evaluation is crucial to address this problem. Herein, a novel approach that indicates delamination by measuring the residual stress evolution of thermally grown oxide (TGO) for air plasma spraying (APS) TBCs is proposed and verified via the combination of photoluminescence piezo‐spectroscopy (PLPS) and X‐ray computed tomography. A mineral‐oil‐impregnating approach and a cold‐mount low‐shrinkage epoxy‐mounting approach are used to alleviate the signal attenuation by pores and microcracks in APS TBCs, improving the detectable PLPS signal and X‐ray transmission for stress measurement and delamination characterization, respectively. We have nondestructively measured the TGO residual stress mapping in APS TBCs and its evolution with oxidation. Furthermore, the evolution of TGO morphology and critical microcracks are obtained by X‐ray computed tomography. The synchronous evolution of TGO residual stress, TGO thickness, and critical microcracks as a function of oxidation time is obtained and correlated. The transition point, as experimentally identified, at which the TGO stress starts to drop, agrees well with the critical moment of microcrack coalescence. This directly verifies that the TBC delamination can be effectively indicated by residual stress evolution of TGO in APS TBCs. Abstract : Delamination in APS‐TBCs is indicated by measuring the TGO residual stress.