Corrosion resistance tests on NiTi shape memory alloy

Area of Science:

• Biomaterials Science
• Materials Science
• Corrosion Engineering

Background:

• Nickel-titanium (NiTi) shape memory alloys (SMAs) are increasingly used in medical implants due to their unique properties.
• Evaluating the long-term corrosion performance and biocompatibility of NiTi SMAs in physiological environments is crucial for patient safety.

Purpose of the Study:

• To compare the corrosion behavior of NiTi SMAs with other common implant materials (Ti6Al4V, austenitic stainless steels) in simulated body fluid.
• To assess the integrity and protective capacity of the passive film formed on NiTi under various corrosive conditions.

Main Methods:

• Potentiostatic polarization tests to measure passivity current density as an indicator of ion release.
• Potentiodynamic scans to evaluate resistance to localized corrosion (pitting).
• Potentiostatic scratch tests and modified ASTM F746 to assess passive film durability after mechanical damage.

Main Results:

• NiTi SMAs exhibited approximately three times higher passivity current density compared to Ti6Al4V and austenitic stainless steels, indicating greater ion release.
• While NiTi showed good resistance to pitting in standard scans, its passive film demonstrated inferior durability and protective characteristics compared to Ti6Al4V after mechanical disruption.
• The passive film on NiTi was found to be comparable or inferior to that of austenitic stainless steels in terms of stability.

Conclusions:

• NiTi SMAs release more ions and possess a less robust passive film than Ti6Al4V in simulated body fluid.
• The findings suggest potential biocompatibility limitations for NiTi SMAs, particularly in applications requiring long-term stability and resistance to mechanical stress.
• Further research into surface modifications or alternative alloys may be necessary to enhance the corrosion resistance and biocompatibility of NiTi for medical implants.