Fracture behavior of Cr2Nb-based intermetallics

Microstructural evaluations and mechanical testing of Laves-phase alloys based on Cr₂Nb were examined in order to determine phase relationships with heat treating temperatures up to 1600°C. At ambient temperatures, single-phase Cr₂Nb alloys are very hard and brittle due to the complicated crystal structure (C-15). The following results were revealed through examination of the Cr-Cr₂Nb two-phase region: (a) with increasing amounts of the soft chromium-rich phase, the compression strength and hardness decrease; (b) the annealing treatments studied provided the best break-up of the brittle Laves-containing eutectic phase in the 94 at.% Cr - 6 at.% Nb (CN-7) alloy; (c) annealing for 1 hour at 1600°C + 4 hours at 1200°C drastically improved the room temperature strength and compressive ductility over previous annealing treatments. Previous studies have shown [1] that the introduction of a soft chromium phase has promising effects in improving the mechanical properties of brittle Cr₂Nb Laves-phase alloys.