Microstructure and Mechanical Properties of Two-Phase Cr-Cr2Ta Alloys

The microstructure and fracture toughness values of a series of binary Cr-Cr2Ta alloys have been studied in the as-cast condition and after long-term annealing of up to 500 hours at 1573 K (1300 A degrees C). With increasing annealing time, both the Cr(Ta) solid solution and the Cr2Ta Laves phases progressively approached equilibrium compositions. This observation was accompanied by the transformation of the Laves phase from the hexagonal C14 to the cubic C15 polytype, along with a small fraction of an intermediate hexagonal polytype. The overall hardness values of the alloys increased with the Laves phase fraction, which was accompanied by a decrease in the room-temperature fracture toughness values. The fracture surface of the three-point bend specimens revealed brittle cleavage-type fracture in all the alloys.