Corrosion of Ti-based bulk metallic glasses for small diameter dental implants

[摘要] Ti-based bulk metallic glasses (BMGs) have been proposed to be an alternative to conventional Ti alloys to be used to manufacture small dental implants. For this application, it is important to determine whether they have suitable corrosion resistance. The corrosion behaviour of BMGs and the alloy, Ti6Al4V was tested in physiological saline (PS), with and without the addition of albumin and hydrogen peroxide. Albumin is the main protein in extracellular fluid, and peroxide (H2O2) is a transient biological species used here to simulate the presence of reactive oxygen species (ROS) that can be formed during infection or inflammation. Electrochemical tests on BMG_Sn2 showed that addition of albumin to PS suppresses the cathodic reaction and enhances the pitting resistance of BMG_Sn2, while H2O2 decreases the pitting resistance of BMG_Sn2. The addition of albumin to H2O2-containing PS suppresses both anodic and cathodic reactions. Most Ti-based BMGs contain a high content of Cu. However, Cu is potentially less biocompatible compared with other elements which can be used to enhance the glass forming potential. In this case, Ga was used to partly replace Cu, up to 10 at.%. Experiments were conducted to check that this partial substitution does not have a detrimental effect on corrosion resistance. It was found that substitution of 10 at.% Ga did not modify the corrosion resistance of Ti-based BMGs in 0.9 wt.% NaCl solution. It was also found that some degree of structural relaxation can slightly improve the corrosion resistance. Mechanically-assisted crevice corrosion (MACC) is a corrosion process associated with abrasive damage to test surfaces. The abrasion causes damage to the passive surface film, leading to a burst of metal dissolution from the bare metal surface. The metal ions hydrolyse and result in local acidity in the crevice. The acid environment delays the repassivation of Ti and can eventually cause severe corrosion. Such wear damage and local acidity have been found for cemented femoral stems and modular orthopaedic Ti implants. There is concern that MACC may also be a risk for dental implants, so it is important to be able to evaluate risk in quantitative way. A new device was developed that can retain the local acidity produced by MACC. A series of parallel tests on BMGs and Ti6Al4V using this device were conducted to compare their MACC resistance. The results have shown that Ti-based BMGs show better MACC resistance than Ti6Al4V evidenced by lower MACC currents, associated with milder local chemistry changes and less wear and corrosion products generated. It has also been shown that MACC gets increasingly worse for Ti6Al4V with time but this was not observed for BMGs in the current test period (16 ks). This can be explained by the fact that Ti-based BMGs possess greater wear resistance than Ti6Al4V, which means the passive film may be better preserved under the abrasive conditions.

[发布机构] University:University of Birmingham;Department:School of Metallurgy and Materials

[关键词] Q Science;Q Science (General)