Pitting Phenomena of Nanotube Formed Ti-Nb Alloy Surface

Titanium and Ti alloys have been used extensively as bone-implant materials due to their high strength-to-weight ratio, good biocompatibility and excellent corrosion resistance. Titanium, however, being relatively inert, cannot directly bond to bone, and osseointegration via the natural oxide is a long process.

Objective: There is an increased interest in reducing the time needed for ossointegration. For example, nanoporous Ca-P coating on implants have shown apposition of human bone growth within 2-3 weeks post-surgery. In this work, we have fabricated TiO₂ nanoporous surface using a simple anodization process with various applied voltage, and then the pitting behavior of TiO₂ nanoporous by the potentiostat method was investigated.

Methods: We chose Ti-20Nb and 40Nb binary alloy. It has excellent biocompatibility and be expected to act as a b-stabilizer. Small alloy buttons of 10mm in diameter were prepared by arc melting on a water sealed copper hearth under an argon gas atmosphere with a non-consumable tungsten electrode. All the following experiments were performed in phosphate/sodium fluoride electrolytes. For formation of nanotube, the different potentials(10 ~ 30V) were applied on the anodized surfaces in the these electrolyte. The pitting behaviors were investigated using potentiostat(EG&G Co, 2273. USA) in 0.9% NaCl solution at 36.5 ±1°C. Phase constitutions and microstructure of the samples were characterized by OM, SEM and XRD, respectively.

Results:The structure of alloy was changed from a-phase to b-phase with addition of Nb element. The crystalline structures of titanium oxide films were composed of a mixture of anatase and rutile, and surface morphology exhibited a porous cell structure. The nanorube diameter(70~120nm) increased linearly with anodizing potential from 10 up to 30V. The pitting potentials of nanotube formed Ti-20Nb and 40Nb showed 750mV amd 990mV, respectively.

Conclusions: Different tube diameters could be produced by controlling the applied potential.(Corresponding Author: hcchoe@chosun.ac.kr)