Effects of grain size and surface condition on mechanical response, passivation behaviour and corrosion resistance of medical thin-walled NiTi tubes

Thin-walled NiTi alloy tubes are key raw materials for interventional stents and precision biomedical devices, whose performance depends strongly on microstructure and surface quality. This study systematically investigates the relationships among processing history, grain structure, surface condition, mechanical response, passive-film characteristics and electrochemical corrosion behavior in imported NiTi tubes (JK), domestic as-received tubes (GC-1) and process-optimized domestic tubes (GC-2). JK exhibits finer, more uniform grains (ASTM No. 11) and lower inner-surface roughness (R a = 0.115 μm) than GC-1, leading to the highest plateau stress (473 MPa), densest passivation film and lowest corrosion rate (0.37 μA/cm2). After multi-pass cold rolling and fine inner-surface polishing, GC-2 reaches ASTM No. 10 grain size and R a = 0.138 μm, the highest elongation (15.1%) and a 71% lower corrosion rate than GC-1. These findings provide guidance for developing high-performance domestic NiTi tubes.