Designing new biocompatible glass-forming Ti75-xZr10NbxSi15 (x=0, 15) alloys: corrosion, passivity, and apatite formation

Glass-forming Ti-based alloys are considered as potential new materials for implant applications. Ti75Zr10Si15 and Ti60Zr10Nb15Si15 alloys (free of cytotoxic elements) can be produced as melt-spun ribbons with glassy matrix and embedded single -type nanocrystals. The corrosion and passivation behavior of these alloys in their homogenized melt-spun states have been investigated in Ringer solution at 37 degrees C in comparison to their cast multiphase crystalline counterparts and to cp-Ti and -type Ti-40Nb. All tested materials showed very low corrosion rates as expressed in corrosion current densities i(corr)<50 nA/cm(2). Electrochemical and surface analytical studies revealed a high stability of the new alloys passive states in a wide potential range. This corresponds to low passive current densities i(pass)=2 +/- 1 mu A/cm(2) based on the growth of oxide films with thickness d <10 nm. A homogeneous constituent distribution in the melt-spun alloys is beneficial for stable surface passivity. The addition of Nb does not only improve the glass-forming ability and the mechanical properties but also supports a high pitting resistance even at extreme anodic polarization up to 4V versus SCE were oxide thickness values of d approximate to 35 nm are reached. With regard to the corrosion properties, the Nb-containing nearly single-phase glassy alloy can compete with the -type Ti-40Nb alloy. SBF tests confirmed the ability for formation of hydroxyapatite on the melt-spun alloy surfaces. All these properties recommend the new glass-forming alloys for application as wear- and corrosion-resistant coating materials for implants. (c) 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 27-38, 2016.