Fabrication of Ti–Nb alloys by powder metallurgy process and their shape memory characteristics

Abstract

Abstract Ti–Nb based shape memory alloys were fabricated by powder metallurgy (PM) process. The effects of ternary alloying additions of Ta, Al and Sn and cold working on the shape memory characteristics of the Ti–Nb based alloys were investigated. The mixed elemental powders at compositions of Ti–22 at%Nb and Ti–22 at%Nb–4 at%X (X = Ta, Al and Sn) sintered by a pulse-current sintering equipment. The solution-treatment was carried out to obtain homogeneous microstructure. As a result, the solution-treated Ti–22 at%Nb alloy consisted of α″ and β phases at 300 K. The martensitic transformation start temperature of the Ti–22 at%Nb alloy was lower than that of the wrought alloy of the same composition. The Ti–22 at%Nb–4 at%Al alloy indicated a superelastic-like behavior in the stress–strain curve, but the superelastic behavior could not be observed in the solution-treated alloys of other compositions. To improve the shape memory properties of the solution-treated Ti–22 at%Nb alloy, the alloys were cold-rolled at a reduction of 95% in thickness. The Ti–22 at%Nb alloy annealed after cold-rolling showed superelastic behavior due to formation of texture of β-phase. The alloy showed a two-way shape memory effect after isothermal tensile test.