Effect of Mo, Al and Si on the microstructure and mechanical properties of Cr–Cr2Ta based alloys

Highlights: ► The effect of Mo, Al and Si on Cr–Cr2Ta based alloys have been studied. ► Mo and Al partition to the Cr-rich solid solution while Si partitions to the Laves phase. ► Mo and Al additions increased hardness but reduced toughness compared to binary alloys. ► Si additions increase both hardness and toughness. - Abstract: A series of ternary alloys based on Cr–10 at% Ta with 5 and 10 at% of Mo, Al or Si have been studied. The microstructure of all the alloys following a primary annealing at 1000 °C for 72 h comprised of an A2 Cr-based solid solution and a C14 Cr2Ta Laves phase. Inhomogeneities observed in the microstructure of the alloys were attributed to melt undercooling as well as micro- and macrosegregation during solidification. The alloying elements were found to partition in different ways; both Mo and Al partitioned preferentially to the Cr-solid solution phase whilst Si partitioned to the Laves phase. The lattice parameters of the constituent phases were determined using X-ray diffraction and were found to be consistent with the partitioning behaviour of the alloying elements and their atomic radii. The hardness and room temperature fracture toughness of all the alloys were evaluated. The greatest hardening was observed in the Mo-containing alloys. However, this was accompanied by a significant loss of fracture toughness. Analogous results were observed with Al-bearing alloys. In contrast, Si-bearing alloys exhibited appreciable increases in both hardness and fracture toughness.