PHYSICAL METALLURGY AND MECHANICAL PROPERTIES OF DUCTILE ORDERED ALLOYS (Fe, Co, Ni)//3V.

Ordered crystal structures in (Fe, Co, Ni)//3V alloys are characterized by sequences of stacked close-packed ordered layers, and their stacking character can be altered systematically by controlling the electron concentration (e/a). Partial substitution of Fe for Co and Ni lowers e/a, thus stabilizing the L1//2-type cubic ordered structure. Alloys with the cubic ordered structure are ductile. Mechanical behavior is reviewed with emphasis on deformation at high temperatures. Yield strengths increase with temperature, peaking around the critical ordering temperature T//c (650-950 degree C). This anomalous temperature dependence is caused by a thermally activated process. Creep behavior can be described by a power-law rate equation. Other metallurgical and mechanical properties are also discussed, including workability, fatigue behavior, hydrogen embrittlement, oxidation and corrosion, irradiation effects, and microstructural features. Potential development as new structural materials for high-temperature applications is also discussed.