CCS and Power Systems
Crosscutting Research - University Training and Research
Multi-Scale Computational Design and Synthesis of Protective Smart Coatings for Refractory Metal Alloys
Performer: University of Wisconsin System
Project No: FE0007377
Improving the energy efficiency and emissions performance of advanced fossil fueled generation systems requires overcoming the physical limitations of currently used alloys so that they can be used in aggressive environments at temperatures beyond 1400 degrees Celsius (°C). The current state-of-the-art nickel (Ni)-based superalloys have shown remarkable performance at operating temperatures near their melting point; however, the need for higher energy efficiency demands a higher operating temperature than is possible with Ni-based alloys. The University of Wisconsin is enabling the full integration of a new high-temperature protective coating technology into advanced combustion systems for fossil-fuel energy generation that provides both environmental and thermal protection and a 200 to 400 ˚C increase in material operating temperature beyond that of current Ni-based superalloys.
Refractory metal-based alloys provide a unique solution to temperature constraints due to their very high melting points. While alloys such as those based on molybdenum (Mo) and niobium (Nb) offer a unique set of favorable materials properties (i.e., higher melting temperatures and superior high-temperature strength), the main limiting factor to their use remains their poor corrosion/oxidation resistance. The oxidation protection of Mo-rich Mo-silicon (Si)-boron (B) alloys is based on the formation of a self passivating boron-doped silica layer facilitated by the boron reservoir from the ternary-based Mo5SiB2 phase, but these alloys have limited use at temperatures beyond 1300 °C as a consequence of the lower viscosity borosilica surface layer. A similar temperature limitation for oxidation resistance holds for Nb-rich alloys with significant Si content. Coatings that enhance oxidation resistance are essential to achieve the high-temperature operation potential of refractory metal-based alloys.
The enabling technology underlying this advance is based on the computational design of a novel, multifunctional integrated coating strategy that will provide both environmental and thermal protection to advanced combustion systems. The design of a borosilicide smart coating presents a novel advancement and a key enabling coating technology that the coal industry can use meet the demand for high efficiency and reliable operation of advanced combustion systems in aggressive environments. The coating will provide not only essential protection against aggressive oxidation environments, but a thermal blanket to reduce the temperature of the underlying coating structure and assist in corrosion resistance.