The Effect of Environment on TBC Lifetime

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 and 100h 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 TBC’s 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 1h 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 100h cycles, environment was less critical, perhaps because coating failure was chemical (i.e. due to interdiffusion) rather than mechanical. In both 1h and 100h cycles, CO2 did not appear to have any negative effect on coating lifetime.