CCS and Power Systems
Advanced Energy Systems - Hydrogen Turbines
Coating Issues in Coal-Derived Synthesis Gas/Hydrogen-Fired Turbines
Performer: ORNL - Oak Ridge National Laboratory
Project No: FWP-FEAA070
- Laboratory evaluations at ORNL are focusing on evaluating TBC specimens in different environments containing water vapor and CO2 to determine their effect on performance.
- A CO2-10 percent water vapor environment was not detrimental to TBC lifetime for diffusion bond coatings tested at 1150 °C. Thus, the lower CO2 levels found in conventional or syngas-fired turbines are not likely to impact TBC performance.
- The effect of as-sprayed coating surface roughness on thermally-sprayed (metal) MCrAlYHfSi coatings was evaluated at 1100 °C. Rougher coatings (Ra~8) showed similar TBC lifetimes in 1-hour cycles in air with 10 percent water vapor as coatings with Ra~5. The performance in 100-hour cycles is now being evaluated.
- The TBC test matrix has included lower cost single-crystal superalloy substrates being implemented in current turbines including low-Rhenium (Re) second-generation alloys (N515) and Re-free first-generation alloys (1483). The higher Hf con-tent in N515 resulted in longer TBC lifetimes, while the lower Al content in 1483 may have reduced their performance com-pared to conventional 3% second-generation alloys X4 and N5.
- Current alloy development is evaluating cast MCrAlYX compositions before fabricating coatings. Recent work has shown that combinations of Y and Hf or La and Hf result in improved oxidation resistance with less internal oxidation and no detrimental effect of Ti additions was identified.
- High-resolution analytical electron microscopy has been used to study the segregation behavior of Y, La, Hf and Ti as well as study the minor effects of water vapor on the thermally-grown alumina on the surface of coatings and model alloys.
- A characterization methodology was developed where the same 500 by 670 μm area was characterized as a function of exposure time to determine changes in the surface roughness and residual stress in the thermally-grown alumina scale. The technique was also used to track the location of transient metastable alumina phases on aluminide bond coatings and these phases did not appear to contribute to increased oxide thickness or higher stress levels.