Deformation behavior of high strength metastable hypereutectic Ti–Fe–Co alloys

The high strength metastable Ti–Fe–Co alloys were produced by arc-melting in the shape of nearly semi-spherical ingots. The structure of the hypereutectic Ti–Fe–Co alloys (with equiatomic Fe and Co contents) is found to consist of the primary dendrites of an ordered cP2 Ti(Fe,Co) compound and an eutectic consisting of the cP2 Ti(Fe,Co) compound and a disordered BCC cI2 β-Ti solid solution. Hypereutectic Ti–Fe–Co alloys exhibit a high mechanical strength exceeding 2000 MPa and a plastic deformation of 16%. The deformation behavior and the fractography of Ti–Fe–Co alloys are studied in detail. The β-Ti solid solution phase exhibits a dislocation-type deformation mechanism, while no dislocations but only shear bands were found in the cP2 IM Ti(Fe,Co) phase. This phase deforms by localized shear deformation and also undergoes accommodation deformation likely by intergranular sliding. The formation of partially ordered structure may enhance plasticity of Ti–Fe–Co compared to Ti–Fe alloys. Moreover a good crystal lattice correspondence between cP2 and cI2 phases was found. Rough primary dendrites and eutectic rods of the cP2 intermetallic phase act as efficient barriers for shear strain and crack propagation.