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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

# The Effect of Environment on Thermal Barrier Coating Lifetime

[+] Author and Article Information
Bruce A. Pint

Materials Science and Technology Division,
Oak Ridge National Laboratory,
Oak Ridge, TN 37831-6156
e-mail: pintba@ornl.gov

Kinga A. Unocic

Materials Science and Technology Division,
Oak Ridge National Laboratory,
Oak Ridge, TN 37831-6064

J. Allen Haynes

Materials Science and Technology Division,
Oak Ridge National Laboratory,
Oak Ridge, TN 37831-6063

Contributed by the Manufacturing Materials and Metallurgy Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 12, 2015; final manuscript received December 23, 2015; published online March 15, 2016. Editor: David Wisler.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

J. Eng. Gas Turbines Power 138(8), 082102 (Mar 15, 2016) (7 pages) Paper No: GTP-15-1524; doi: 10.1115/1.4032438 History: Received November 12, 2015; Revised December 23, 2015

## Abstract

While the water vapor content of the combustion gas in natural gas-fired land-based turbines is ∼10%, it can be 20–85% with coal-derived (syngas or H2) fuels or innovative turbine concepts for more efficient carbon capture. Additional concepts envisage working fluids with high CO2 contents to facilitate carbon capture and sequestration. To investigate the effects of changes in the gas composition on thermal barrier coating (TBC) lifetime, furnace cycling tests (1-h and 100-h cycles) were performed in air with 10, 50, and 90 vol. % water vapor and CO2-10% H2O and compared to prior results in dry air or O2. Two types of TBCs were investigated: (1) diffusion bond coatings (Pt-diffusion or Pt-modified aluminide) with commercial electron-beam physical vapor-deposited yttria-stabilized zirconia (YSZ) top coatings on second-generation superalloy N5 and N515 substrates and (2) high-velocity oxygen fuel (HVOF) sprayed MCrAlYHfSi bond coatings with air plasma-sprayed YSZ top coatings on superalloys X4, 1483, or 247 substrates. For both types of coatings exposed in 1-h cycles, the addition of water vapor resulted in a decrease in coating lifetime, except for Pt-diffusion coatings which were unaffected by the environment. In 100-h cycles, environment was less critical, perhaps because coating failure was chemical (i.e., due to interdiffusion) rather than mechanical. In both 1-h and 100-h cycles, CO2 did not appear to have any negative effect on coating lifetime.

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## Figures

Fig. 1

Average lifetimes (number of 1-h cycles to failure) for EB-PVD YSZ-coated superalloy specimens with two different Pt-containing diffusion bond coatings exposed at 1150 °C in several environments. The bars note a standard deviation for three specimens of each type. Data from Refs. [15,16,22,30,31,43].

Fig. 2

Light microscopy of polished cross sections of failed ((a) and (b)) N5 and ((c) and (d)) N515 substrates with EB-PVD YSZ top coated specimens after 1-h cycles at 1150 °C in ((a) and (b)) air + 10% H2O and ((c) and (d)) CO2-0.15% O2 + 10% H2O: (a) β-NiPtAl coating after 420 cycles, (b) γ–γ′ bond coating after 1377 cycles, (c) β-NiPtAl coating after 1320 1-h cycles, and (d) γ–γ′ bond coating after 2680 cycles

Fig. 3

Average coating lifetimes (number of 1-h cycles to failure) for APS YSZ-coated X4 and 1483 16 mm diameter superalloy coupons with HVOF NiCoCrAlYHfSi-type bond coatings with two different average roughness (Ra) values exposed at 1100 °C in dry and wet environments. Bars note a standard deviation for three specimens of each type. Data from Refs. [17,43].

Fig. 4

Light microscopy of polished cross sections of failed X4-coated specimens exposed in 10% H2O: (a) Ra = 5 μm after 440 cycles and (b) Ra = 8 μm after 380 cycles

Fig. 5

Electron microprobe line profile across a failed 1483 HVOF (Ra = 8 μm)/APS-coated specimen at 1100 °C after 240 1-hr cycles in air with 50% H2O. The gas interface is on the left and the substrate is on the right. Data from Ref. [43].

Fig. 6

Light microscopy of polished cross sections of failed HVOF (Ra = 8 μm)/APS-coated specimens exposed in 10% water vapor at 1100 °C: (a) X4 substrate after 340 1-h cycles and (b) 1483 substrate after 280 cycles

Fig. 7

Average coating lifetimes (number of 1-h cycles to failure) for APS YSZ-coated superalloy coupons with three batches of HVOF NiCoCrAlYHfSi-type bond coatings with two different average roughness (Ra) values and two different APS top coatings exposed at 1100 °C in air + 10% H2O. Bars note a standard deviation for three specimens of each type. Data from Ref. [48].

Fig. 8

Average coating lifetimes (h in 100-h cycles to failure) for APS YSZ-coated superalloy coupons with HVOF NiCoCrAlYHfSi-type bond coatings with two different average roughness (Ra) values exposed at 1100 °C in several different environments, data from Refs. [17,53]. Bars note a standard deviation for three specimens of X4 and five specimens of 1483.

Fig. 9

Light microscopy of polished cross sections of failed HVOF/APS-coated specimens exposed in 10% H2O at 1100 °C in 100-h cycles: (a) X4 substrate after 24 100-h cycles (Ra = 8 μm), (b) 1483 substrate after 14 100-h cycles (Ra = 8 μm), (c) X4 + RE substrate after 42 100-h cycles (Ra = 5 μm), and (d)1483 substrate after 13 100-h cycles (Ra = 8 μm)

Fig. 10

Electron microprobe line profiles across failed a 1483 HVOF (Ra = 8 μm)/APS-coated specimen at 1100 °C after 14 100-h cycles in air with 10% H2O. The gas interface is on the left and the substrate is on the right. Data from Ref. [53].

Fig. 11

Extrapolated TBC lifetimes from laboratory furnace cycle test data points. Data from Refs. [31], [51], and [53]. To achieve coating lifetimes over 10 kh, the bond coating metal temperature must be considerably lower, as indicated by the arrows in each case.

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