Microstructure characterization and mechanical properties of a Laves-phase alloy based on Cr2Nb

Microstructure and mechanical properties of a binary Cr2Nb-based alloy containing the Laves phase Cr2Nb and Cr phase have been studied in the arc-melted condition. Microstructure consisting of fully coupled eutectic was firstly observed in this hypereutectic alloy. The Cr2Nb primary phase experienced a faceted to nonfaceted transition as the solidification distance increased. Based on the maximum interface growth temperature criteria, the microstructure evolutions in this alloy were explained successfully by means of the competitive growth between the β-Cr2Nb phase and eutectic. Meanwhile, the yield strength and fracture toughness of the samples taken from the bottom of the ingot attained 1986 MPa and 4.3MPa⋅m1/2 respectively, which were considerably enhanced over the monolithic Cr2Nb. The enhancements were explained in terms of the second Cr phase toughening and grain boundary toughening mechanisms. Furthermore, the variation of mechanical properties in different position of arc-melted ingot was proven to result in different eutectic fracture mechanisms.

► The cooling rate of the arc-melted ingot was in the range of 0.022 m/s–0.32 m/s.
► Fully coupled eutectic was observed in the bottom of Cr–20% Nb ingot.
► The Cr2Nb primary dendrite experienced a faceted to nonfaceted transition.
► Different eutectic fracture mechanisms were observed in different position.