Effects of Si addition on mechanical properties and superelasticity of Ti–7.5Nb–4Mo–2Sn shape memory alloy

• Fine Ti5Si3 particles precipitated in the Ti–7.5Nb–4Mo–2Sn alloy with Si additions.
• The strength of the alloy was raised due to Ti5Si3 precipitation.
• The additions of Si promoted the superelasticity of the alloy by increasing σSIM.

Effects of 0–2.1 at.% Si additions on microstructure and mechanical properties of a Ni-free biomedical superelastic β-Ti alloy, Ti–7.5 at.%Nb–4 at.%Mo–2 at.% Sn (Ti–7.5Nb–4Mo–2Sn), were investigated. The alloys after annealing at 973 K mainly contain β and α″. As the concentration of Si is higher than 1 at.%, Ti5Si3 particles can be found in the alloys, and the number density of the particles increases with the increasing of silicon’s concentration. The addition of Si promotes the strength of the Ti–7.5Nb–4Mo–2Sn due to the Si solid solution strengthening effect and fine Ti5Si3 precipitates. However, as the Si concentration reaches 2.1%, the alloy exhibits a brittle fracture. The 0.5–1.6 at.% Si additions improve the superelasticity of the Ti–7.5Nb–4Mo–2Sn alloy by increasing the critical stress for inducing martensite (σSIM).

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