Ti–Nb–Si-based surface alloy fabricated on TiNi SMA substrate through additive electron beam method: structure and perspectives

Here, we report the ongoing research dedicated to the surface alloy fabrication on TiNi substrate by means of a low-energy high-current electron beam. Glassy crystalline Ti–Nb–Si-based surface alloy of 1.5-μm thickness was synthesized by pulsed electron beam melting and liquid-phase mixing of «Ti60Nb30Si10 film/TiNi substrate» system. Conventional X-ray diffraction and electron microscopic studies revealed a composite structure consisting of dendritic (βTi,Nb) crystals, nano-precipitates of Ti2Ni, (αTi,Nb) phases and bubbles embedded into glassy matrix. Electrochemical behavior of Ti–Nb–Si-based surface alloy is characterized by a higher corrosion rate in comparison with a reference electro-polished Ti–Ni sample. The modified surface layers of 1.0-μm thickness show gradient decrease of Young’s modulus (from ~ 100 GPa near the surface to ~ 70 GPa) and increased hardness. The plasticity characteristic is below 55% within the subsurface layer of ~ 500 nm thickness and retains a nearly constant (~ 60%) at a higher depth of the analyzed layer. Complete recovery of 6% torsional strain occurs without accumulation of plastic deformation or delamination of the synthesized surface alloy. The issues of proposed method for development of drug delivery systems relying on the processed (Nb, Si)-bearing Ti–Ni-shaped memory alloy are discussed.