Application of Cr(3+)photoluminescence piezo-spectroscopy to plasma-sprayed thermal barrier coatings for residual stress measurement

Citation
Kw. Schlichting et al., Application of Cr(3+)photoluminescence piezo-spectroscopy to plasma-sprayed thermal barrier coatings for residual stress measurement, MAT SCI E A, 291(1-2), 2000, pp. 68-77
Citations number
30
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science","Material Science & Engineering
Journal title
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN journal
0921-5093 → ACNP
Volume
291
Issue
1-2
Year of publication
2000
Pages
68 - 77
Database
ISI
SICI code
0921-5093(20001031)291:1-2<68:AOCPTP>2.0.ZU;2-K
Abstract
Cr3+ photoluminescence piezo-spectroscopy (CPLPS) is being developed as a n on-destructive inspection technique for the measurement of residual stresse s within the thermally grown oxide (TGO; consisting of alpha-Al2O3 with Cr3 + solute) layer buried under Y2O3-stabilized ZrO2 (YSZ) thermal barrier coa tings (TBCs). In this study, CPLPS experiments were performed to measure re sidual stresses in TGOs buried under four different types of plasma-sprayed TBCs, as a function of TBC thickness (from 0 to full-thickness of 250 mu m ) using 'taper-polishing'. In one type of TBC, the CPLPS technique could be used to measure TGO residual stresses, but was limited to a TBC thickness of less than 170 mu m due to severe attenuation of the Cr3+ photoluminescen ce signal through the YSZ. In the other three types of TBCs, that thickness was limited to about 50 mu m. PIowever, non-TGO Cr3+ photoluminescence sig nals were obtained through thicker TBCs of these latter types. To identify the source of this non-TGO signal, chemical analyses and CPLPS of as-receiv ed and heat-treated plasma-spray feedstock powders were performed. It was f ound that these powders contained both Al and Cr, which upon hear-treatment created conditions for Cr3+ photoluminescence. To identify the sources of attenuation of the Cr3+ photoluminescence signal intensity in all types of TBCs, CPLPS was performed on a set of 'model coatings'. These 'model coatin gs' consisted of monolithic ceramics, where a polycrystalline alpha-Al2O3 s lab was placed underneath a variety of thin YSZ plates containing varying a mounts of porosities, pore sizes, Y2O3 contents, and grain boundaries. It w as found that porosity, grain boundaries, and most importantly splat bounda ries, were the key factors that obstructed the observation of CPLPS from al pha-Al2O3 through YSZ. In order to alleviate this signal attenuation by por es and microcracks, plasma-sprayed TBCs were vacuum-impregnated with high-r efractive-index materials (mineral oil or Stycast(TM) epoxy), allowing us t o measure, for the first time, TGO residual stresses through full-thickness plasma-sprayed TBCs using CPLPS. (C) 2000 Elsevier Science S.A. All rights reserved.