Atomic Layer Deposition of aTiO2 Layer on Nitinol and Its Corrosion Resistance in a Simulated Body Fluid

Abstract

Nitinol is a group of nearly equiatomic alloys composed of nickel and titanium, which was developed in the 1970s. Its properties, such as superelasticity and Shape Memory Effect, have enabled its use, especially for biomedical purposes. Due to the fact that Nitinol exhibits good corrosion resistance in a chloride environment, an unusual combination of strength and ductility, a high tendency for self-passivation, high fatigue strength, low Young’s modulus and excellent biocompatibility, its use is still increasing. In this research, Atomic Layer Deposition (ALD) experiments were performed on a continuous vertical cast (CVC) NiTi rod (made in-house) and on commercial Nitinol as the control material, which was already in the rolled state. The ALD deposition of the TiO2 layer was accomplished in a Beneq TFS 200 system at 250 °C. The pulsing times for TiCl4 and H2O were 250 ms and 180 ms, followed by appropriate purge cycles with nitrogen (3 s after the TiCl4 and 2 s after the H2O pulses). After 1100 repeated cycles of ALD depositing, the average thickness of the TiO2 layer for the CVC NiTi rod was 52.2 nm and for the commercial Nitinol, it was 51.7 nm, which was confirmed by X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscope (SEM) using Energy-dispersive X-ray (EDX) spectroscopy. The behaviour of the CVC NiTi and commercial Nitinol with and without the TiO2 layer was investigated in a simulated body fluid at body temperature (37 °C) to explain their corrosion resistance. Potentiodynamic polarisation measurements showed that the lowest corrosion current density (0.16 μA/cm2) and the wider passive region were achieved by the commercial NiTi with TiO2. Electrochemical Impedance Spectroscopy measurements revealed that the CVC NiTi rod and the commercial Nitinol have, for the first 48 h of immersion, only resistance through the oxide layer, as a consequence of the thin and compact layer. On the other hand, the TiO2/CVC NiTi rod and TiO2/commercial Nitinol had resistances through the oxide and porous layers the entire immersion time since the TiO2 layer was formatted on the surfaces.

Corrosion and passive film characteristics of 3D-printed NiTi shape memory alloys in artificial saliva

“…The peak value of the binding energy listed in Table 6 [43,44] is used for L-PBF NiTi component fitting. Figure 9 a 1 -c 1 shows the oxide composition of Ni 2p 3/2 in the inner and outer layers of the passive film.…”

A brief overview and application of Nickel-Titanium shape memory alloy in dentistry

“…The process of spontaneous formation of transition metal oxides is measured by the Gibbs free energy [32]. The more significant presence of Ti oxide on the surface of nickel-titanium alloys is explained by its formation requiring four times less energy than Ni oxide.…”

TiNi-Based Material with Shape-Memory Effect for Surgical Treatment of Diseases of Small Intestine in Newborn and Young Children

“…This is due to their unique functional properties, shape-memory effects and super elasticity, as well as a high level of biocompatibility [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. The latter is ensured by their corrosion resistivity and electrochemical passivity of the superficial oxide layer composed of TiO 2 [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Moreover, the physical–mechanical characteristics of such alloys are close to the characteristics of body tissues [ 24 , 25 , 26 , 27 ].…”