In previous work, it was shown that CaSO 4 -induced corrosion can cause significant internal oxidation in single-crystal Ni-based superalloys similar to that observed in field-exposed components when subjected to a bi-thermal exposure (8 h at 1150 °C → 60 h at 871 °C) in air + 30% steam. In this work, the influence of (1) 1150 °C initiation stage temperature, (2) propagation stage temperature, and (3) CaSO 4 deposit mass on the mechanism of CaSO 4 -induced corrosion were investigated further. The results of these experiments showed that subsurface depletion of Al and Cr caused by rapid Ca 4 Al 6 O 16 S, CaAl 2 O 4 , and CrS formation due to CaSO 4 corrosion is required for internal oxidation to occur in N5 and N500, but that these alloys can “heal” when held for long durations at 1150 °C due to the enhanced diffusion of Al within the alloy at elevated temperatures.

Thermochemical processing of sustainable biomassBiomass paired with carbon captureCarbon capture and storage has the potential to provide 1/7th of the emission mitigations necessary for the world to meet net-zero targets by 2050 while also providing carbon-negative fuel, electricity, and economic development. This work has developed coating solutions to mitigate the hot corrosion that occurs when biomassBiomass is processed in boilers, gasifiers, and other thermal conversion equipment, in addition to coating solutions to mitigate solid particle erosion that occurs when steam turbines are used for aggressive load following. Analysis of 66 hot corrosion coatings and 75 solid particle erosion coatings reveals unique mechanisms that enable significantly improved performance relative to conventional coatings used today without increasing material costCost. Implications of this work to fuel flexibility, process efficiencyEfficiency, and lessons learned utilizing ICME will also be discussed. This material is based upon work supported by the Department of EnergyEnergy under Award Number DE-FE0031911.

The goal of this research project was to provide a fundamental understanding of CaO-and CaSO4-induced corrosion in second-generation Ni-based single-crystal superalloys and to develop a lab-scale test procedure, which accurately replicates corrosion observed in field-exposed components. Secondary and transmission electron microanalyses were used to characterize the corrosion of field-exposed components taken from commercial aviation turbines. It was found that the field-exposed components had been attacked by internal oxidation-sulfidation. Isothermal laboratory-scale experiments at 900 and 1150 °C in air were conducted on superalloy coupons deposited with either CaO or CaSO4 to assess the extents and modes of solid-state corrosion caused by either deposit. A novel bi-thermal test procedure was then developed which effectively replicated the internal oxidation-sulfidation found in the field-exposed components. It was determined that compositional and microstructural changes to the alloy subsurface caused by CaSO4-induced corrosion at elevated temperatures made the alloy susceptible to internal oxidation at lower temperatures.