In this study, microstructural aspects and electrochemical properties of high-pressure torsion (HPT)-treated austenitic NiTi alloy were investigated. Microstructural characterizations were performed by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) analysis. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were used to evaluate the electrochemical properties in simulated body fluid (SBF) solution. It was found that HPT process increased the martensitic phase from 8.22 to 71.31 wt%. HRTEM results revealed a combination of amorphous/nanocrystalline austenitic and martensitic phases of NiTi after HPT. The lower value of corrosion current density of HPT-treated NiTi (2.5 × 10⁻⁶A/cm²) was observed compared with the untreated sample (7.6 × 10⁻⁶ A/cm²). EIS tests confirmed higher corrosion resistance of the HPT-treated sample. EIS analysis showed a decrease and increase in the impedance value of the specimens at different immersion times indicating the formation and degradation of oxide films over time on the specimens’ surface. However, the impedance value of the HPT-treated sample was more than that of the untreated sample. Localized corrosion is observed at the surface of the untreated specimen due to the absence of a dense oxide protective film but no evidence of localized and pitting corrosion on the surface of HPT-treated sample was observed.

在这项研究中，研究了高压扭转（HPT）处理的奥氏体NiTi合金的微观结构和电化学性能。通过高分辨率透射电子显微镜（HRTEM）和X射线衍射（XRD）分析进行了微观结构表征。电位动力极化和电化学阻抗谱（EIS）测试用于评估模拟体液（SBF）溶液中的电化学性能。发现HPT过程使马氏体相从8.22wt％增加到71.31wt％。HRTEM结果显示HPT后，NiTi的非晶/纳米晶奥氏体和马氏体相结合。HPT处理的NiTi的腐蚀电流密度的下限值（2.5×10 ^-6 A / cm ²与未处理的样品（7.6×10 ^-6 A / cm ²）相比，观察到）。EIS测试证实，经HPT处理的样品具有更高的耐腐蚀性。EIS分析表明，在不同的浸入时间下，样品的阻抗值减小和增加，表明随着时间的推移，在样品表面上氧化膜的形成和降解。但是，HPT处理过的样品的阻抗值比未处理过的样品大。由于没有致密的氧化物保护膜，未处理样品的表面出现了局部腐蚀，但没有观察到在HPT处理过的样品表面上出现局部腐蚀和点蚀的迹象。