Nanomechanical evaluation of nickel–titanium surface properties after alkali and electrochemical treatments

Abstract

In this paper, the suitability of alkali treatment followed by heat treatment at 6008C, and spark oxidation for nickel-titanium, intended for medical applications such as pins, wires and clamps, was evaluated on the basis of nanomechanical and wear testing. In addition, the chemical composition and topography of the surface layer, wetting ability, corrosion resistance and influence of the heat treatment on structure of the alloy were also investigated. The results showed that the highest hardness was observed for alkali-treated samples, and this could be correlated with the structure of the sample that contained martensite and a higher phase transformation temperature. This treatment caused a very large increase of nickel in the top layer and decreased resistance in pitting corrosion. These results disqualified the treatment to be considered as useful for medical applications. On the other hand, the hardness of the oxidized samples was at the same level as that obtained for ground reference samples. Moreover, the oxide layer was enriched with phosphorus, and it was predominantly composed of TiO 2 and phosphorus oxides. This 3.1 mm thick layer had good adhesion to the substrate as indicated by scratch testing and wear resistant in nanowear testing. However, the oxidation did not significantly increase the corrosion resistance of the alloy compared with reference samples.

Evaluation of NaOH pre-treatment on the corrosion behavior and surface characteristics of hydroxyapatite coated NiTi alloy

“…Moreover, increasing the concentration of the NaOH solution intensified the Ni/Ti ratio in the treated samples. These findings are in agreement with Chrzanowski et al [22] reporting increased nickel content in the surface top layer with NaOH treatment which would pose the potential risk of decreasing the biocompatibility due to the heightened risk of Ni release.…”

“…NaOH treatment is a well-known method that has been applied to various substrate-coating couples. While there are numerous studies focusing on the positive effects of this treatment on the biocompatibility and the following deposition characteristics of the apatite layer [16][17][18][19][20], only a few discussed its disadvantages focusing on NiTi especially on Ni release after surface treatment using NaOH [21,22]. Hence, combining different strategies as NaOH pre-treatment and HA coating to improve the biocompatibility of NiTi samples needs further attention due to the inevitable risk of Ni release.…”

Biocompatible, Smooth, Plasma-Treated Nickel–Titanium Surface – An Adequate Platform for Cell Growth

“…3 However, to improve the biological performance of the alloy, which mostly relates to the suppression of the nickel release, many types of treatments have been investigated. 1 , 14 , 15 , 21 , 27 , 30 – 37 , 39 , 46 , 47 A few types of these treatments dominate the literature: electropolishing, thermal, anodic-oxidation, and coating formation using Chemical Vapour Deposition (CVD) or Physical Vapour Deposition (PVD) methods focused on DLC coating. The large benefits of electropolishing, should be viewed in the context of the high risk related to the volatile mixtures used (sulfuric acid + methanol) 48 and highly corrosive (i.e., HF) electrolytes; the use of such media is questionable when alternatives are available.…”

Nitinol Modified by In Situ Generated Diazonium Salts as Adhesion Promoters for Photopolymerized Pyrrole

“…Its biocompatibility results from the presence of a thin protective titanium dioxide surface layer that enhances the corrosion resistance and reduces the release of Ni 2+ ions,, which are cytotoxic and carcinogen ,,. A great deal of attention has been paid to the surface modification of NiTi in order to impart and/or improve surface properties such as biocompatibility,, bioactivity, and corrosion resistance ,,…”