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

This paper provides a comprehensive review of the recent research on the ph ase stability, point defects, and fracture toughness of AB(2) Laves phases, and on the alloy design of dual-phase alloys based on a soft Cr solid solu tion 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 si de of ZrCo2. Only thermal vacancies were detected in the Laves phase alloys quenched from high temperatures. The room-temperature fracture toughness c annot be effectively improved by increasing thermal vacancy or reducing sta cking fault energy through control of phase stability. Microstructures, mec hanical properties, and oxidation resistance of dual-phase alloys based on Cr-NbCr2, Cr-TaCr2, and Cr-ZrCr2 were studied as functions of heat treatmen t and test temperature at temperatures to 1200 degreesC. Among the three al loy systems, Cr-TaCr2 alloys possess the best combination of mechanical and metallurgical properties for structural use at elevated temperatures. (C) 2000 Published by Elsevier Science Ltd.