Improved mechanical properties of porous nitinol by aluminum alloying

Abstract

Aluminum alloying effects (up to 2 at %) on the macrostructure, microstructure, and mechanical properties of porous nitinol (NiTi) obtained by self-propagating high-temperature synthesis (SHS) were studied. It has been established that Ni and Ti interactions with liquid Al (0.5–1 at % Al) in the SHS process significantly change macrostructure, decrease the size of the interpore bridges, and increase their number, resulting in a larger effective cross-sectional area. An increase in the aluminum content above 1 at % leads to larger interpore bridges in the SHS product. The microhardness of TiNi(Al) increases from 305 HV 50 g to 422 HV 50 g with aluminum concentration, while the fraction of the TiNi(Al) (B2 + B19′) phases decreases from 75% to 50%. The Ti 2 Ni(Al) phase fraction increases from 25% to 50% with Al concentration. The 64 MPa tensile strength and 2.9% fracture strain of porous Ti 50 Ni 49 Al 1 alloy are higher than without Al. The increase in strength is due to the formation of a more homogeneous macrostructure and solid solution strengthening of the alloy-forming phases. Porous NiTi with 0–2 at % Al was obtained by self-propagating high-temperature synthesisNiTiAl macro and microstructure are optimal at 1 at %Al, along with mechanical properties. • Porous NiTi with 0–2 % Al was obtained by self-propagating high-temperature synthesis. • Al doping changed macrostructure and decreased interpore bridge size. • The TiNi(Al) phases fraction decreased from 75 % to 50 % with more Al. • Vickers hardness increased with Al concentration. • The optimal Al content is 0.5–1 % for improved structure and mechanical properties.