In vitro corrosion behavior of Ti-O film deposited on fluoride-treated Mg–Zn–Y–Nd alloy

• Published in: Applied surface science Vol. 258; no. 8; pp. 3571 - 3577
• Main Authors: Hou, S.S., Zhang, R.R., Guan, S.K., Ren, C.X., Gao, J.H., Lu, Q.B., Cui, X.Z.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2012; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Corrosion resistance; Cross-disciplinary physics: materials science; rheology; Degradable stents; Exact sciences and technology; Fluoride layer; Mg–Zn–Y–Nd alloy; Physics; Ti-O film; Corrosion resistance; Fluoride layer; Degradable stents; Ti-O film; Mg–Zn–Y–Nd alloy; Corrosion; Mg-Zn-Y-Nd alloy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2011.11.116

► Mg alloy substrate under composite coating has an largely improved corrosion resistance, potential to meet the requirement of long-term mechanical of Mg alloy. ► Since substrate is well protected by composite coating, Ti-O film can keep the surface integrity, hence to function as a coating with good biocompatibility. ► Pitting corrosion was found on the composite coating, resulting in more milder and slower corrosion with time. This may be beneficial to stent degradation. In this paper, a new composite coating was fabricated on magnesium alloy by a two-step approach, to improve the corrosion resistance and biocompatibility of Mg–Zn–Y–Nd alloy. First, fluoride conversion layer was synthesized on magnesium alloy surface by immersion treatment in hydrofluoric acid and then, Ti-O film was deposited on the preceding fluoride layer by magnetron sputtering. FE-SEM images revealed a smooth and uniform surface consisting of aggregated nano-particles with average size of 100nm, and a total coating thickness of ∼1.5μm, including an outer Ti-O film of ∼250nm. The surface EDS and XRD data indicated that the composite coating was mainly composed of crystalline magnesium fluoride (MgF2), and non-crystalline Ti-O. Potentiodynamic polarization tests revealed that the composite coated sample have a corrosion potential (Ecorr) of −1.60V and a corrosion current density (Icorr) of 0.17μA/cm2, which improved by 100mV and reduced by two orders of magnitude, compared with the sample only coated by Ti-O. EIS results showed a polarization resistance of 3.98kΩcm2 for the Ti-O coated sample and 0.42kΩcm2 for the composite coated sample, giving an improvement of about 100 times. After 72h immersion in SBF, widespread damage and deep corrosion holes were observed on the Ti-O coated sample surface, while the integrity of composite coating remained well after 7d. In brief, the data suggested that single Ti-O film on degradable magnesium alloys was apt to become failure prematurely in corrosion environment. Ti-O film deposited on fluoride-treated magnesium alloys might potentially meet the requirements for future clinical magnesium alloy stent application.