Microstructure and mechanical properties of Laves-phase alloys based on Cr 2Nb

Abstract

Mechanical properties of Laves-phase alloys based on Cr 2Nb at temperatures up to 1000°C were examined and correlated with microstructures and phase relationships. Single-phase Cr 2Nb alloys are very hard and brittle at ambient temperatures, indicating the difficulty in generation and glide of dislocations due to the complicated crystal structure (C-15). Examination of the CrCr 2Nb two-phase region revealed the following: (a) the hardness decreases with increasing amounts of the soft chromium-rich phase; (b) the eutectic composition has a niobium concentration of 17 at.%, instead of 12 at.% as reported in the currently existing phase diagram; (c) heat treatments produce uniform dispersion of fine Laves-phase precipitates in primary chromium-rich patches for the hypoeutectic alloys, and these particles are very stable even at temperatures above 1000°C; (d) the soft particles are very effective in preventing crack propagation originating in the brittle Laves-phase matrix, which results in a high yield strength with moderate ductility up to 1000°C. These results demonstrate that the introduction of a soft chromium phase has promising effects in improving the mechanical properties of brittle Cr 2Nb Laves-phase alloys.