Preliminary experimental study on simultaneous polishing and shape setting of Nitinol wire

Abstract

Separate processes for shape setting and polishing of Nitinol workpieces are well investigated in scientific literature and adopted industrially. However, a simultaneous process for shape setting and polishing of Nitinol has not yet been reported. In this study, preliminary results of such process are presented, providing insights and directions for further research on post-processing shape memory materials. For this purpose, Nitinol wire samples with phase transformation temperatures A_f = 4.5 °C, A_f = 31 °C and A_f = 61 °C were plasma electrolytic polished (PEP) while fitted in a specially designed sample holder at three electrolyte temperatures t_e = 50 °C, t_e = 65 °C and t_e = 80 °C. The PEP process duration was τ_PEP = 60 s, τ_PEP = 180 s and τ_PEP = 300 s. After the PEP processes, the samples were investigated for the shape memory effect (SME). The training effect, known to be present in shape memory alloys (SMA), was taken into account. The surface roughness of the investigated wires was measured before and after the PEP process. The obtained results demonstrate that both a phase transformation temperature and an electrolyte temperature have a strong effect on polishing and shape setting results.

Article highlights

Plasma electrolytic polishing enables coupling the shape setting step of Nitinol with simultaneous polishing;

Austenitic and martensitic Nitinol responds differently to the same PEP conditions;

Partial shape memory effect was observed in NiTi samples that underwent the shape setting step coupled with the PEP process.