Influences of additional alloying elements (V, Ni, Cu, Sn, B) on structure and mechanical properties of high-strength hypereutectic Ti-Fe-Co bulk alloys

High-strength nonequilibrium hypereutectic bulk alloys were obtained recently in the Ti-Fe and Ti-Fe-Co systems by arc-melting. Following these results, the influences of the additional alloying elements (V, Ni, Cu, Sn, B) on high strength hypereutectic Ti-Fe-Co bulk alloys are studied and analyzed in the present work. The structure of the hypereutectic quaternary Ti ₆₇Fe₁₄Co₁₄Sn₅, Ti ₆₇Fe₁₄Co₁₄V₅, Ti₇₀Fe ₁₇Co₇Cu₆, Ti₇₀Fe₁₇Co ₇Ni₆, and Ti_69.4Fe_14.8Co _14.8B₁ alloys obtained in the form of arc-melted ingots of about 20-30 mm diameter and 10-15 mm height was studied by X-ray diffractometry and scanning electron microscopy. The mechanical properties were tested by an Instron-type machine. Ti₆₇Fe₁₄Co ₁₄Sn₅ alloy exhibits a high ultimate compressive strength of 1830 MPa and a large plastic strain of 24% which exceeds the ductility values obtained for Ti-Fe and Ti-Fe-Co alloys. The addition of Sn causes formation of a relatively rough eutectic structure which is preferable for the high strength hypereutectic alloys. Rough primary dendrites and eutectic rods of the cP2 intermetallic phase act as efficient barriers for shear strain and cracks propagation while fine eutectic rods of submicron size are quite effortlessly cut by deformation bands and cracks.