National Energy Technology Laboratory
3610 Collins Ferry Road
P.O. Box 880
Morgantown, WV 26507-0880
National Energy Technology Laboratory
626 Cochrans Mill Road
P.O. Box 10940
Pittsburgh, PA 15236-0940
University of Wisconsin
1509 University Avenue
Madison, WI 53706
DOE Share: $300,000.00
Performer Share: $0.00
Total Award Value: $300,000.00
Performer website: University of Wisconsin System - http://www.engr.wisc.edu
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.
Program Background and Project Benefits
The goal of the University Coal Research (UCR) Program within the Department of Energy (DOE) National Energy Technology Laboratory (NETL) is to further the understanding of coal utilization. Since the program’s inception in 1979, its primary objectives have been to (1) improve understanding of the chemical and physical processes involved in the conversion and utilization of coal so it can be used in an environmentally acceptable manner, (2) maintain and upgrade the coal research capabilities of and facilities at U.S. colleges and universities, and (3) support the education of students in the area of coal science.
The National Energy Technology Laboratory’s Office of Coal and Power Systems supports the development of innovative, cost-effective technologies for improving the efficiency and environmental performance of advanced coal and power systems. One current focus area facilitates research on the development of computational tools and simulations to reliably predict properties of materials in advance of fabrication and the development of new materials with high performance potential for fossil-energy systems.
The National Energy Technology Laboratory has partnered with the University of Wisconsin to facilitate the multi-scale computational design and synthesis of protective smart coatings for refractory metal alloys.
This project, through the modification of refractory metal-based alloys, will deliver the key enabling coating technology to produce an increase of 200 °C to 400 °C in the operating temperature of refractory alloy. These improvements, when implemented, should deliver an increase in power efficiency.
Goal and Objectives
The goal of this project is to employ a new smart coating concept for refractory metal-borosilicide and -aluminide systems in order to provide a 200 °C to 400 °C increase in temperature resistance beyond that of current Ni-based superalloys in materials that comprise advanced fossil fueled generation systems.
Niobium samples were coated with different ratios of Si-B and Mo-Si-B before undergoing oxidation testing. The presence of Nb2O5 was identified in the mixed oxides of samples at all ratios. Given the same Si:B ratios, the Mo-Si-B coating imparted enhanced oxidation protection to the Nb samples compared to the samples coated with Si-B only. These empirical results, along with computer modeling results, will be used to develop and test new refractory alloy coatings with the goal of increasing their useful operating temperatures.