Thermochemical Surface Treatment of Nitinol Alloys and the Functional Stability in Biological Environment

Nitinol alloys have been used in biomedical applications because of their superior properties like shape memory and superelasticity. One of the concerns in these alloys is corrosion and degradation of the alloys in human body environment. In this work, surface treatments were applied on medical grade Nitinol alloy and the superelasicity was monitored during two months soaking in Ringer's solution for commercial orthodontic arch wires. Cyclic potentiodynamic polarization results show that the combination of chemical etching and heat treatment in controlled atmosphere improve the corrosion and pitting resistance of the alloy. The superelastic test results indicated that the plateau stress levels of the alloy was changed during soaking in corrosive medium in as received alloy; while the surface treated sample demonstrated relatively constant values. It seems that depletion of the alloy's surface from Ni during chemical treatment and subsequent heat treatment result in a stable oxide formation on the surface of the alloy which protect the alloy inside the human body environment.

کلیدواژه ها:

Nitinol ، Superelasticity ، Surface modification ، Cyclic-polarization ، Ringer's solution ، آلیاژ نایتینول ، سوپرالاستیسیته ، عملیات سطحی ، پلاریزاسیون سیکلی ، محلول رینگر