Fossil energy applications of intermetallic alloys

This paper presents the history and results of the US Department of Energy, Office of Fossil Energy (FE), development effort on iron aluminide alloys and the status of research and development on ultrahigh temperature (well above 1000°C) intermetallic alloys. The outstanding (perhaps unequaled) sulfidation resistance of iron aluminide alloys, based on the Fe3Al composition, was the basis for initiation of an exploratory project to determine whether improvement in mechanical properties of iron aluminide alloys could be achieved. This was a high-risk venture but with significant payoff if successful, because sulfidation was a critical problem for applications of alloys in coal gasification systems. The exploratory project, which was conducted at Oak Ridge National Laborator (ORNL), was successful, and the program was expanded in both scope and participation. Several other national laboratories, industrial research organizations, and universities were involved. Iron aluminide development is now quite mature. Some of the research has transferred to line programs leading to product that will be used in advanced fossil energy systems. The first product to be commercialized for fossil energ applications was a porous metal filter developed jointly by ORNL and Pall Corporation. In addition to th coal gasification application, these filters are also being used in combustion systems. Several other commercial products are being pursued. Additional exploratory projects on intermetallic alloys have been initiated. These are also high risk activities, but, as with the iron aluminides, the payoff potential is great. The intermetallic alloys presently being investigated include a Cr2Ta-strengthened chromium alloy and a boron-modified molybdenum silicid based on Mo5Si3. The challenges with these alloys are to modify them to provide acceptable mechanical properties, including ductility and toughness, and corrosion resistance to allow them to be used in structure applications such as gas turbines.