چكيده به لاتين
Due to the growing world population of elderly people, it is imperative to use optimum materials and components in medical applications. Titanium and its alloys are one of the most widely used metals in biological applications. One of the weaknesses of these alloys is their low strength and mechanical properties compared to some other metals and superalloys. Implementation of severe plastic deformation methods can increase the strength and hardness of titanium and make it possible to use it in medical application such as dental implants. It should be noted that simply increasing the strength of a material is not sufficient for its use in biological applications, and other properties such as biocompatibility, surface condition and good corrosion resistance are among the very important properties to consider. Despite the favorable properties of pure titanium in medical applications, its strength is not desirable and should be improved by appropriate methods. In this study, a combination of two methods of severe plastic deformation was used to achieve this goal. In order to increase the strength of bulk material, pure titanium was first processed by equal channel angular method (ECAP), and then to improve the surface properties, surface attrition treatment (SMAT) was used. The 5 mm zirconia beads (free of any toxic substances) used as a shot-peening media. Micro-hardness and nanoindentation were used to investigate some of the mechanical properties. Surface properties were evaluated by measurement of surface roughness and wettability. The microstructure of the material was also examined by electron microscopy, SEM and EBSD. Cell differentiation was evaluated through alkaline phosphate assay and human osteosarcoma cell line was cultured on samples to study the biocompatibility. The results of these experiments showed that the combination of two severe plastic deformation methods, equal channel angular and surface mechanical attrition treatment leads to increased hardness up to 45%, enhanced surface properties as well as the improved biocompatibility. Application of ECAP resulted to structure refinement from the anneal condition with mean grain size of 25 µm to 740 nm in six passes sample. In addition, as a result of the SMAT process, a nanostructured layer is formed on the surface in which the average grain size drops to approximately 300 nm. Therefore, it seems that combination of these two methods is an acceptable procedure to optimize the performance of titanium in biological applications.
