As-deposited mixed zone in thermally grown oxide beneath a thermal barrier coating

K. S. Murphy; K. L. More; M. J. Lance

doi:10.1016/S0257-8972(01)01371-8

As-deposited mixed zone in thermally grown oxide beneath a thermal barrier coating

K. S. Murphy, K. L. More, M. J. Lance

Research output: Contribution to journal › Article › peer-review

68 Scopus citations

Abstract

Gas turbine designers are increasingly using electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBC) to meet the challenge of higher efficiency gas turbine engine requirements. A key feature for expanding the use of TBCs is increased spallation life and reduced spallation life variability. Such a coating system comprises a substrate (Ni-based single crystal alloy), a bond coat (diffusion aluminide or MCrAIY), a ceramic (7 wt.% yttria stabilized zirconia), and a thin thermally grown oxide (TGO) between the bond coat and the ceramic. The TGO is intended to be α-alumina, but evidence reported by other researchers suggests that in some cases the as-deposited TGO may not be entirely α-alumina. The thin nature of the TGO in as-deposited TBCs ( <0.5 μm) makes analysis of the phases present and morphology difficult. Advancements in transmission electron microscopy (TEM) sample preparation and photo-stimulated luminescence spectroscopy (PSLS) have allowed higher quality and easier characterization of the TGO. In this study, EB-PVD TBCs were applied to platinum-aluminide bond coats on a Ni-based superalloy. Three types of coatings were produced by changing one PVD process variable. The as-processed TGO layer was characterized utilizing scanning transmission electron microscopy (STEM) and PSLS for each of the three coating process variables used. Results of this work found that the TGO comprised two sublayers; (1) a continuous layer of υ-Al₂O₃ between the mixed oxide zone and the bond coat; and (2) a mixed oxide zone between the continuous υ-Al₂O₃ and the TBC layer. An explanation for the creation of the mixed oxide zone found in these TGO morphologies is presented.

Original language	English
Pages (from-to)	152-161
Number of pages	10
Journal	Surface and Coatings Technology
Volume	146-147
DOIs	https://doi.org/10.1016/S0257-8972(01)01371-8
State	Published - Sep 2001

Funding

The authors gratefully acknowledge the supportive work by K.S. Trent, D.W. Coffey and T.S. Geer at ORNL for preparing the TEM specimens and performing the SEM imaging. We also thank Professors Meier and Clarke and Dr. Tolpygo for technical discussions regarding this work. This research was also sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the US Department of Energy under contract number DE-AC05-00OR22725. M.J. Lance supported in part by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, Department of Energy.

Keywords

Electron beam evaporation
Pack diffusion coatings
Phase transitions
Thermally grown oxide
Transmission electron microscopy
Zirconium oxide

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10.1016/S0257-8972(01)01371-8

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title = "As-deposited mixed zone in thermally grown oxide beneath a thermal barrier coating",

abstract = "Gas turbine designers are increasingly using electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBC) to meet the challenge of higher efficiency gas turbine engine requirements. A key feature for expanding the use of TBCs is increased spallation life and reduced spallation life variability. Such a coating system comprises a substrate (Ni-based single crystal alloy), a bond coat (diffusion aluminide or MCrAIY), a ceramic (7 wt.% yttria stabilized zirconia), and a thin thermally grown oxide (TGO) between the bond coat and the ceramic. The TGO is intended to be α-alumina, but evidence reported by other researchers suggests that in some cases the as-deposited TGO may not be entirely α-alumina. The thin nature of the TGO in as-deposited TBCs ( <0.5 μm) makes analysis of the phases present and morphology difficult. Advancements in transmission electron microscopy (TEM) sample preparation and photo-stimulated luminescence spectroscopy (PSLS) have allowed higher quality and easier characterization of the TGO. In this study, EB-PVD TBCs were applied to platinum-aluminide bond coats on a Ni-based superalloy. Three types of coatings were produced by changing one PVD process variable. The as-processed TGO layer was characterized utilizing scanning transmission electron microscopy (STEM) and PSLS for each of the three coating process variables used. Results of this work found that the TGO comprised two sublayers; (1) a continuous layer of υ-Al2O3 between the mixed oxide zone and the bond coat; and (2) a mixed oxide zone between the continuous υ-Al2O3 and the TBC layer. An explanation for the creation of the mixed oxide zone found in these TGO morphologies is presented.",

keywords = "Electron beam evaporation, Pack diffusion coatings, Phase transitions, Thermally grown oxide, Transmission electron microscopy, Zirconium oxide",

author = "Murphy, {K. S.} and More, {K. L.} and Lance, {M. J.}",

year = "2001",

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doi = "10.1016/S0257-8972(01)01371-8",

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T1 - As-deposited mixed zone in thermally grown oxide beneath a thermal barrier coating

AU - Murphy, K. S.

AU - More, K. L.

AU - Lance, M. J.

PY - 2001/9

Y1 - 2001/9

N2 - Gas turbine designers are increasingly using electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBC) to meet the challenge of higher efficiency gas turbine engine requirements. A key feature for expanding the use of TBCs is increased spallation life and reduced spallation life variability. Such a coating system comprises a substrate (Ni-based single crystal alloy), a bond coat (diffusion aluminide or MCrAIY), a ceramic (7 wt.% yttria stabilized zirconia), and a thin thermally grown oxide (TGO) between the bond coat and the ceramic. The TGO is intended to be α-alumina, but evidence reported by other researchers suggests that in some cases the as-deposited TGO may not be entirely α-alumina. The thin nature of the TGO in as-deposited TBCs ( <0.5 μm) makes analysis of the phases present and morphology difficult. Advancements in transmission electron microscopy (TEM) sample preparation and photo-stimulated luminescence spectroscopy (PSLS) have allowed higher quality and easier characterization of the TGO. In this study, EB-PVD TBCs were applied to platinum-aluminide bond coats on a Ni-based superalloy. Three types of coatings were produced by changing one PVD process variable. The as-processed TGO layer was characterized utilizing scanning transmission electron microscopy (STEM) and PSLS for each of the three coating process variables used. Results of this work found that the TGO comprised two sublayers; (1) a continuous layer of υ-Al2O3 between the mixed oxide zone and the bond coat; and (2) a mixed oxide zone between the continuous υ-Al2O3 and the TBC layer. An explanation for the creation of the mixed oxide zone found in these TGO morphologies is presented.

AB - Gas turbine designers are increasingly using electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBC) to meet the challenge of higher efficiency gas turbine engine requirements. A key feature for expanding the use of TBCs is increased spallation life and reduced spallation life variability. Such a coating system comprises a substrate (Ni-based single crystal alloy), a bond coat (diffusion aluminide or MCrAIY), a ceramic (7 wt.% yttria stabilized zirconia), and a thin thermally grown oxide (TGO) between the bond coat and the ceramic. The TGO is intended to be α-alumina, but evidence reported by other researchers suggests that in some cases the as-deposited TGO may not be entirely α-alumina. The thin nature of the TGO in as-deposited TBCs ( <0.5 μm) makes analysis of the phases present and morphology difficult. Advancements in transmission electron microscopy (TEM) sample preparation and photo-stimulated luminescence spectroscopy (PSLS) have allowed higher quality and easier characterization of the TGO. In this study, EB-PVD TBCs were applied to platinum-aluminide bond coats on a Ni-based superalloy. Three types of coatings were produced by changing one PVD process variable. The as-processed TGO layer was characterized utilizing scanning transmission electron microscopy (STEM) and PSLS for each of the three coating process variables used. Results of this work found that the TGO comprised two sublayers; (1) a continuous layer of υ-Al2O3 between the mixed oxide zone and the bond coat; and (2) a mixed oxide zone between the continuous υ-Al2O3 and the TBC layer. An explanation for the creation of the mixed oxide zone found in these TGO morphologies is presented.

KW - Electron beam evaporation

KW - Pack diffusion coatings

KW - Phase transitions

KW - Thermally grown oxide

KW - Transmission electron microscopy

KW - Zirconium oxide

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SN - 0257-8972

VL - 146-147

SP - 152

EP - 161

JO - Surface and Coatings Technology

JF - Surface and Coatings Technology

ER -

As-deposited mixed zone in thermally grown oxide beneath a thermal barrier coating

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