Recent Advances in Ordered Intermetallics
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RECENT ADVANCES IN ORDERED INTERMETALLICS C. T. LIU Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
ABSTRACT This paper briefly summarizes recent advances in intermetallic research and development. Ordered intermetallics based on aluminides and silicides possess attractive properties for structural applications at elevated temperatures in hostile environments; however, brittle fracture and poor fracture resistance limit their use as engineering materials in many cases. In recent years, considerable efforts have been devoted to the study of the brittle fracture behavior of intermetallic alloys; as a result, both intrinsic and extrinsic factors governing brittle fracture have been identified. Recent advances in first-principles calculations and atomistic simulations further help us in understanding atomic bonding, dislocation configuration, and alloying effects in intermetallics. The basic understanding has led to the development of nickel, iron, and titanium aluminide alloys with improved mechanical and metallurgical properties for structural use. Industrial interest in ductile intermetallic alloys is high, and several examples of industrial involvement are mentioned. INTRODUCTION Ordered intermetallics based on aluminides and silicides constitute a unique class of metallic materials for structural use at elevated temperatures in hostile environments. Their promising properties include excellent elevated-temperature strength, resistance to oxidation and corrosion, and relatively low density and high melting point [1-12]. However, most intermetallics exhibit brittle fracture and low ductility at ambient temperatures, and poor fracture resistance and limited fabricability restrict their use as engineering materials in many cases. The recent search for new high-temperature materials has stimulated a great deal of interest in development of ordered intermetallics for structural use. The progress made during the past 10 years has been recorded in several proceedings and books: 1. High-Temperature Ordered Intermetallic Alloys I. II. II. and IV, ed. Koch et al., 1985; Stoloff et al., 1987; Liu et al., 1989; and Johnson et al., 1991; respectively [1 -4]; 2. High Temperature Aluminides and Intermetallics, ed. Whang et al., 1990 and 1992 [5,6]; 3. Intermetallic Compounds - Structure and Mechanical Properties, ed. Izumi, 1991 [7]; 4. Ordered Intermetallics-Physical Metallurgy and Mechanical Behavior, ed. Liu et al., 1992 [8]; 5. Microstructure/Property Relationships in Titanium Aluminides and Alloys, ed. Kim and Boyer, 1991 [9]; 6. The Deformation Behavior of Intermetallic Superlattice Compounds, Yamaguchi and Umakoshi, 1990 [10]; 7. Ordered Intermetallics, Liu et al., 1990 [11]; and 8. Ordered Alloys, ed. Stoloff, 1984 [12]. At present, there is world-wide interest in ordered intermetallics; as a result, many new results have been generated each year. Because of page limitation, a systematic review of the recent progress on ordered intermetallics is not feasible in this brief paper. Cons
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