Bioactive Ceramic Surface Modification of β-Type Ti-Nb-Ta-Zr System Alloy by Alkali Solution Treatment

Abstract

Biomedical -type titanium alloys have been developed or are under development all over the world. In particular, researchers in Japan have been developed Ti-29Nb-13Ta-4.6Zr alloy (TNTZ)--type titanium alloy-for biomedical applications. Bioactive ceramic surface modification is effective for further improvement in the biocompatibility of TNTZ. Calcium phosphate ceramics such as hydroxyapatite (Ca 10 (PO 4 ) 6 OH 2 ; HAP), -calcium pyrophosphate (-Ca 2 P 2 O 7 ; CPP), and -tricalcium phosphate (-Ca 3 (PO 4 ) 2 ; -TCP) exhibit bioactivity. In this study, the formability and morphology of HAP on the surface of TNTZ, covered with sodium titanate film by alkali solution treatment were investigated before and after immersion in a simulated body fluid (SBF).A reticulate structure with a considerable number of large cracks and mainly composed of sodium titanate and niobate films having a thickness of 400 nm to 800 nm is formed on the specimen surface of TNTZ after immersing in 3, 5, and 10 kmolÁm À3 NaOH solutions for 86.4 and 172.8 ks. As the concentration of the alkali solution and the immersion time are increased, the formability of HAP improves because of the presence of a large amount of oxygen and the sodium in sodium titanate and niobate film. HAP is completely formed on the entire specimen surface of TNTZ immersed in the SBF for 1209.6 ks after immersing in 5 and 10 kmolÁm À3 NaOH solutions for 172.8 ks. Alkali treatment at 333 K in 5 kmolÁm À3 NaOH solutions for 172.8 ks is proposed to be an excellent condition to rapidly form HAP and fully cover the specimen surface of TNTZ with it. The bonding strength between TNTZ (alkali treatment at 333 K in 5 kmolÁm À3 NaOH solutions for 172.8 ks) and HAP is around 2 MPa, which was half or less than half the value required for biomedical applications. The inclusion of a baking treatment after the alkali treatment in order to improve the bonding strength degraded the HAP formability. Furthermore, the formability decreases with an increase in the baking temperature.

Electrochemical properties, chemical composition and thickness of passive film formed on novel Ti–20Nb–10Zr–5Ta alloy

“…The Ti-29Nb-13Ta-4.6Zr alloy appears to be promising for orthopaedic applications due its to acceptable cytotoxicity and low Young's modulus of 60 GPa [2]. It was reported that the functionality of the latter alloy can be improved by bioactive ceramic surface modification using alkali treatment [6]. The mechanical properties of Ti alloys can be tailored by compositional variation, thermomechanical processing and microstructure control.…”

Effects of Alloying Elements on the HAp Formability on Ti Alloys after Alkali Treatment

“…However, the HAp formability of different types of Ti alloys with various kinds and amounts of alloying elements varies after alkali treatment. The HAp formability of TNTZ is lower than that of pure Ti, 13) for example. Therefore, to improve the HAp formability on the TNTZ surface, it is important to understand the relationship between alloying elements (Nb, Ta and Zr) and the HAp formability.…”

“…When sodium tantalate is in a crystalline phase on the surface, it barely releases the Na + ions, leading to the formation of only a small number of TaOH groups on the surface and low production of HAp from ionic activity in the SBF. However, the sodium tantalate layers should be in the amorphous state, 13) suggesting that the TixTa (x = 10, 20, 30, or 40 mass%) alloys should have good HAp formability. For pure Ta, the clear and sharp peaks of Na 5 TaO 5 in the TF-XRD profile (Fig.…”

Biologically and Mechanically Biocompatible Titanium Alloys

“…There is another report 34) that the formability of HAP is less in pure Nb (CP-Nb) than in pure Ta (CP-Ta) and pure Zr (CP-Zr) as summarized in Table 2. The formability of HAP is the lowest in CP-Nb.…”