High-Temperature Applications of Intermetallic Compounds

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Abstract
One of the greatest challenges currently facing the materials community is the need to develop a new generation of materials to replace Ni-based superalloys in the hot sections of gas-turbine engines for aircraft-propulsion systems. The present alloys, which have a Ni-based solid-solution matrix surrounding Ni3Al-based precipitates, are currently used at temperatures exceeding 1100°C, which is over 80% of the absolute melting temperature. Since Ni3Al melts at 1395°C and Ni at 1453°C, it is clear that significantly higher operating temperatures, with the attendant improvements in efficiency and thrust-to-weight ratio, can only be attained by the development of an entirely new materials system. This problem is a primary reason for the current high level of interest in high-temperature intermetallic compounds.The development of such a material system has important implications for national defense and for spin-offs to civilian technology, as well as for the economy and balance of payments. Obviously it would be a boon to any economy to have these new materials developed domestically, as was the case in the United States for the currently used single-crystal technology applied to Ni-based superalloys. As an example, the aerospace industry is one area where the United States is still the undisputed world leader, with net exports of $29 billion in 1989, twice that of any other U.S. industry.