| Titanium and titanium alloys possess excellent mechanical properties, better biocompatibility and strong corrosion resistance, and have been used as biomaterials. But when they are used as dental prostheses, some limitations emerge. For instance, denture base and clasp made of pure titanium are prone to fracture and even deformation, because of their low strengths. In addition, the wear resistance of titanium denture also can't meet the requirement. They must be renewed regularly to avoid temporomandibular joint disordering. Ti-6A1-4V and Ti-6Al-7Nb alloy with higher strength contain the high cytotoxic elements such as Al and V. Therefore, new types of titanium alloys without toxic elements are being developed to overcome the drawbacks of pure titanium and Ti-6Al-4V/Ti-6Al-7Nb alloys. In the present study, the element In, which was commonly used in the dental precious metallic alloys, was firstly introduced into titanium, and Ti-1In, Ti-5In, Ti-10In and Ti-15In alloys were prepared. And then, Sn which is a phase stabilizer and Moβphase stabilizer were added (lat.%,3at.%, and 5at.%, respectively) into Ti-5In. The structure and properties of the Ti-In, Ti-In-Sn and Ti-In-Mo alloys were then studied, and the effect of the type and content of alloying elements on the properties was also investigated.The results showed that the element In tended to volatile during the arc melting process, resulting in the deviation of alloy composition from the nominal composition. EDS results indicated that the loss of In increased with increasing nominal In content. The three types of Ti-In alloys exhibited typical lamella and acicular microstructure, except Ti-5In-5Mo, which showed equiaxialβgrains in the matrix of acicular a phase. The strengthening effect of solute element in Ti-In and Ti-In-Sn increased the strength of the alloy, although decreased the elongation percentage of the alloy to some extent and exerted no obvious effect on bending modulus.βphase stabilizer Mo also strengthened the Ti-In-Mo alloys, and the addition of 1% and 3% Mo increased the strengths. However, addition of 5% Mo yielded a double yielding phenomenon and therefore resulted in lower strength. The elastic modulus of Ti-In-Mo alloys decreased with increasing Mo content.The results of wear resistance showed that the alloying elements played an important role in the friction and wear properties. First of all, the stable coefficient of friction decreased with the increase of strength. Furthermore, for the a phase stabilizing elements such as In and Sn, when the adding content was low (such as Ti-1In,Ti-5In,Ti-10In,Ti-5In-1Sn and Ti-5In-3Sn), their effect on the wear resistance was limited, i.e. the friction coefficient firstly exhibited a transient lower platform, and then went to transition stage and stable stage; when the adding content increased (such as Ti-15In and Ti-5In-5Sn), the lower platform in friction coefficient disappeared, and the characteristics of abrasive wear became significant as well as the increased wear rate. In contrast, addition of 1at.% Mo caused the disappearance of lower platform in friction coefficient curves. Analysis showed that the low platform of friction resulted from the antiwear mechanism of the oxide film on the surface. The results indicated that the worn of Ti-15In, Ti-5In-5Sn and Ti-5In-3Mo was attributed to abrasive wear, whereas the worn of other alloys was combined effect of adhesion wear and abrasive wear.The results of electrochemical corrosion investigation revealed that Ti-In based alloys possessed superior corrosion resistance in simulated saliva, comparable to that of pure titanium TA2, and their passive current density was around 10μA/cm2. In the presence of NaF, the corrosion resistance of Ti-In based alloys decreased significantly, and the passive current density increased one or two orders of magnitude due to the existence of F-, indicating increased corrosion rate. The corroded surface morphology suggested different corrosion mechanisms. In the presence of H2O2, Ti-In based alloys tended to be oxidized or corroded, resulting in the shortened growth time and increased thickness of the oxide layer. Thus, the open current potential increased. With the increasing concentration of H2O2, the roughness of the oxide layer increased, along with the change of the surface structure, as a result of which, Rp decreased first and then increased.The results of ion release tests indicated that the overall amount of released ions increased owing to the addition of alloying elements, which was mainly attributed to the release of titanium ions. The release rate of ions increased as the following order: TA2<Ti-5In<Ti-5In-5Sn<Ti-5In-5Mo. Surface investigation results demonstrated the TiO2 film main structure, along with In2O3, SnO2 and/or MoO3. This structure endowed Ti-In based alloys superior biocompatibility. The hemolysis rate of all of the tested alloys was lower than 1%, which was much smaller than 5% and wouldn't cause acute hemolysis. In addition, the cytotoxicity of Ti-In based alloys was below grade 1, according to relevant standards. |
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