Effect of minor boron on mechanical properties of Ti-Fe-Cu-Sn-Nb alloys

Based on grain refinement and secondary phase strengthening, minor boron (B) was added to near β-Ti alloy to strengthen the alloys. Ti85Fe6Cu5Sn2Nb2 alloys with various B contents were designed, prepared by using a non-consumable vacuum arc melting furnace, and hot rolled at 800℃followed by quenching. The effects of minor B addition on the microstructure and mechanical properties of Ti85Fe6Cu5Sn2Nb2 alloy were investigated through microstructure observation, tensile mechanical test, fracture observation and transmit electron microscopy. The results reveal that minor B addition can refine the grains, improve the strength whereas the plasticity of the alloy is decreased. The alloy containing 0.15% (mass fraction)B possesses the better comprehensive mechanical properties(σ0.2=1105 MPa, δb=4.5%).With the increase of B content, the strength of the alloy is increased and reaches up to 1156 MPa. Orthorhombic TiB compounds are formed in the alloy, distributed in the β-Tialloy matrix. Upon deformation, the fracture of TiB phases, cutting and debonding of TiB phases to the alloy matrix, formed the fracture source, resulted in the decrease of the alloy plasticity