Wire-based directed energy deposition of NiTiTa shape memory alloys: Microstructure, phase transformation, electrochemistry, X-ray visibility and mechanical properties

TLDR

The study introduces a novel WAAM process to fabricate NiTiTa shape memory alloys and evaluates their microstructure, corrosion resistance, X‑ray visibility, and superelastic performance. Wire and arc additive manufacturing was employed using commercial NiTi wire and Ta foil feedstock to produce NiTiTa (2.5 at.% Ta) SMAs for the first time. Adding Ta raised transformation temperatures, produced a room‑temperature microstructure of B19′ martensite and B2 austenite with (Ti,Ta)₂Ni precipitates at grain boundaries, increased corrosion potential from –0.55 to –0.44 V, decreased corrosion current density.

Abstract

Wire and arc additive manufacturing (WAAM) technology was used for the fabrication of NiTiTa (2.5 at. % Ta) shape memory alloys (SMAs) for the first time, using commercialy available NiTi wire and Ta foil as the feedstock materials. The addition of Ta significantly increased the phase transformation temperatures, leading to a room-temperature microstructure composed of both B19′ martensite and B2 austenite, and (Ti,Ta)2Ni precipitates distributed at the grain boundaries. Compared with the WAAM fabricated NiTi counterpart, the corrosion potential (Ecorr) of the NiTiTa material increased from − 0.55 to − 0.44 V, while the corrosion current density (Icorr) decreased from 1.90 × 10−6 to 4.2 × 10−7 A/cm2. The X-ray brightness increased from 19.6 to 56.4 %. These results indicate that the addition of Ta can enhance the corrosion resistance and X-ray visibility of NiTiTa parts. Furthermore, the WAAM fabricated NiTiTa material was able to retain a stable superelastic response under 10 loading-unloading cycles, highlighting the great potential application value in the biomedical field. Our work provides an innovative method for additively manufacturing NiTi-based multi-component SMAs through WAAM.