Physical metallurgy and mechanical properties of transition-metal Laves phase alloys

This paper provides a comprehensive review of the recent research on the phase stability, point defects, and fracture toughness of AB2 Laves phases, and on the alloy design of dual-phase alloys based on a soft Cr solid solution reinforced with hard XCr2 second phases (where X=Nb, Ta and Zr). Anti-site defects were detected on both sides of the stoichiometric composition of NbCr2, NbCo2, and NbFe2, while they were observed only on the Co-rich side of ZrCo2. Only thermal vacancies were detected in the Laves phase alloys quenched from high temperatures. The room-temperature fracture toughness cannot be effectively improved by increasing thermal vacancy or reducing stacking fault energy through control of phase stability. Microstructures, mechanical properties, and oxidation resistance of dual-phase alloys based on Cr–NbCr2, Cr–TaCr2, and Cr–ZrCr2 were studied as functions of heat treatment and test temperature at temperatures to 1200°C. Among the three alloy systems, Cr–TaCr2 alloys possess the best combination of mechanical and metallurgical properties for structural use at elevated temperatures.