Effect of combined PM and aging treatment on the microstructural evolution and corrosion resistance of NiTi alloys

Nickel–titanium alloys produced through powder metallurgy were subjected to controlled aging treatments to examine how thermal exposure influences microstructural evolution, oxide formation, and corrosion performance. Aging at 600 °C for 1–3 h progressively reduced porosity and promoted the development of intermetallic phases such as Ni 3 Ti, Ni 4 Ti3, and Ti 2 Ni, along with increasingly uniform TiO 2 surface layers. SEM, EDS, and XRD analyses confirmed enhanced oxide coverage and phase redistribution with longer aging durations. Electrochemical testing revealed a consistent improvement in corrosion resistance, with the 3 h-aged alloy exhibiting the lowest corrosion rate and highest charge-transfer resistance. These results demonstrate that aging-induced TiO 2 formation significantly stabilizes the surface and improves biocorrosion behavior, offering an effective strategy for optimizing PM-processed NiTi alloys for biomedical applications.