Tantalum coating inhibits Ni-migration from titanium out-diffusion in NiTi shape memory biomedical alloy

K. McNamara, S. Beloshapkin, K. M. Hossain, M. S. Dhoubhadel, S. A.M. Tofail

Research output: Contribution to journalArticlepeer-review

Abstract

Despite the presence of over 56% Ni by weight, equiatomic NiTi is generally considered biocompatible as it naturally oxidises to form a surface oxide mainly composed of biocompatible oxides of titanium (TiOx). This layer is formed by an oxidation mechanism that promotes out-diffusion of Ti leaving a Ti-depleted, Ni rich subsurface. The long-term in vivo stability of the naturally grown TiOx layer has been a concern as Ni can leach out through this thin, defective layer. The leaching of nickel (Ni) is thus a continuing threat to the alloy's otherwise outstanding biocompatibility. We have found that a layer of reactively sputtered tantalum (Ta) oxide on the bulk NiTi restricts Ti-out-migration through a biocompatible Ti/Ta inter-diffusion layer that provides a larger barrier against Ni leaching. We have investigated this inter-diffusion as a function of sputtering process parameters and post processing treatments. Surface and interface analytical techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, cross sectional transmission electron microscopy and non-destructive ion beam analysis techniques such as Rutherford backscattering spectrometry and particle induced X-ray emission were used to evaluate the nature of this inter-diffusion layer which can improve long-term biocompatibility of NiTi.

Original languageEnglish
Article number147621
JournalApplied Surface Science
Volume535
DOIs
Publication statusPublished - 1 Jan 2021

Keywords

  • Biomedical alloy
  • Minimally invasive surgical devices
  • Ni-leaching
  • NiTi
  • RBS
  • Shape memory alloy
  • Tantalum oxide coating
  • Ti migration
  • XPS

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