Crosscutting Research Technology Manager
National Energy Technology Laboratory
3610 Collins Ferry Road
P.O. Box 880 PO3D
Morgantown, WV 26507-0880
Vito Cedro III
National Energy Technology Laboratory
626 Cochrans Mill Road
P.O. Box 10940
Pittsburgh, PA 15236-0940
Iowa State University
Ames, IA 50011-3020
DOE Share: $575,000.00
Performer Share: $0.00
Total Award Value: $575,000.00
Performer website: Ames National Laboratory - http://www.ameslab.gov
This project will develop a tool to rapidly assess materials to find candidate high-temperature, oxidation-resistant alloys capable of meeting the requirements of high-temperature gas turbine components. The basis for this method is that materials can be compared using formation enthalpy data, which shows the heat released or absorbed in their formation. Using this tool will allow researchers to narrow down possible alloy formulations from tens of thousands to a manageable number of combinations that are most likely to succeed.
Project researchers will investigate potential alloy formulations using progressively more accurate thermodynamic methods; conduct critical experiments to test the accuracy of the calculations; and evaluate each alloy’s key mechanical, thermal, and oxidation properties. Those alloys showing the greatest potential for high performance will be further screened for thermochemical stability using state-of-the-art thermal analysis, high-temperature X-ray diffraction analysis, and microstructural evaluation with electron microscopy.
Program Background and Project Benefits
The need for fossil-fueled power plants to run cleaner and more efficiently leads toward ever-higher operating temperatures and pressures. Gas turbines, which can be fueled by natural gas, synthetic gas (syngas), or a high-hydrogen stream derived from coal, are critical components in this development. High-temperature operation of turbines is generally achieved by using nickel-chrome superalloys with coatings to improve thermal characteristics and resistance to oxidation and corrosion. The maximum temperature capability of current commercial coatings is limited to about 1,150 °C. Next-generation gas turbine technologies will require alloys that can function at about 1,350 °C in corrosive environments. Hence, design of ultra-high temperature alloys is a major task in gas turbine development.
To this end, the Department of Energy (DOE) National Technology Energy Laboratory (NETL) is partnering with Ames Laboratory to develop a method for finding novel materials capable of performing well at very high temperatures required by advanced coal-fired power systems. Further experimental screening will yield promising candidate alloys for further development.
The method developed by this project will improve the materials selection process for continued alloy design for the construction of components of advanced power systems. The alloys developed during this project for performance in high-temperature, high-pressure, corrosive environments will improve power plant operation. This will reduce emissions of greenhouse gases and pollutants for better environmental management. Higher process efficiencies will reduce costs and conserve energy resources.
Goals and Objectives
The goal of this project is to develop high-temperature, oxidation-resistant alloys capable of meeting the requirements of high-temperature gas turbine components. Specific project objectives include (1) developing an extended Miedema model for a rapid estimation of formation enthalpies of multicomponent alloys; (2) screening potential high-temperature alloys using the extended Miedema model, and conduct experimental studies on scale-forming ability of select alloys; (3) performing a more rigorous thermodynamic modeling of promising alloy systems, with the aims of tailoring alloy compositions and of feeding results back into the extended Miedema model; (4) developing databases, both experimentally and computationally, to supplement thermodynamic modeling; (5) conducting experimental studies on oxidation kinetics, microstructural characterization of oxide scale, and diffusion behavior of the tailored alloy compositions; and (6) conducting experimental studies on microstructure development.
Researchers have determined that a 20 percent molybdenum (Mo)- balance nickel aluminum (NiAl) alloy has promising characteristics with respect to high temperature oxidation resistance. Mo-Ni-Al alloy compositions made via drop casting showed better oxidation resistance than alloys made by liquid phase sintering. Nodular microstructures showed best resistance to cyclic air oxidation exposure. Researchers have also identified which mix of platinum group metals provides best high temperature oxidation resistance in air. Hafnium doped NiAl plus 6-9 percent iridium provided best oxidation resistance at 1150 – 1300 °C compared to other NiAl plus platinum-group metal alloy compositions tested. Additions of iridium and rhodium to NiAl base alloy increased the melting point of the alloy, as predicted by theoretical calculations.
The alloy system design identified based on previous laboratory-scale tests are directionally solidified NiAl-Mo alloy with columnar Mo grains for mechanical strength plus a coating with platinum-group metal additions for high temperature oxidation resistance. Directional solidification and coating experiments were started. These experiments showed that the high temperature (1150-1250 °C) air oxidation resistance of the coating alloy could be improved by decreasing its grain size.