Geleneksel ve yeni nesil biyomedikal alaşımlarda biyouyumluluk-mikroyapı-mekanik özellik ilişkisi

The aim of the work presented herein is to investigate the biocompatibility – mechanical property – microstructure relationship in conventional and potential biomedical alloys. For this purpose, well known and potential biomedical alloys were analyzed in terms of the aforementioned parameters by constructing a relationship between them, and the gained knowledge was also partially extended to structural materials. Initially, biocompatibility of NiTi shape memory alloys (SMAs) was investigated in relation to alloy geometry and body location dependency. In this analysis, it was observed that different alloy geometries yield different surface properties due to the particular processing route applied to obtain a certain geometry, which affects biocompatibility response of the alloy. Moreover, each geometry appeared to be safer for a different body location, showing that biocompatibility response of NiTi SMAs vary depending on alloy geometry, surface properties and body location. Next, biocompatibility of a NiTi SMAs used for a different application, NiTi orthodontic archwires was analyzed, with a focus on the evaluation of the biocompatibility testing method of NiTi orthodontic archwires, by comparing ex situ tested archwires with the ones retrieved from patients. The outcomes of this analysis evidence the importance of incorporation of actual loading conditions into ex situ experiments for a more realistic biocompatibility testing procedure. In order to incorporate actual mechanical conditions into the ex situ testing of NiTi orthodontic archwires, an archwire bound to brackets on a dental mold was also tested ex situ and compared to an ex situ tested undeformed wire. The results of this set of experiments indicated that actual loading conditions that orthodontic archwires are normally subjected to can be successfully simulated by providing wire-bracket contact in ex situ experiments and the wire-bracket contact sites constitute critical points for the nucleation of corrosion products due to the stress concentration and stress assisted corrosion created at these locations. As the biocompatibility analysis on NiTi SMAs demonstrated, surface properties, microstructure and mechanical loading conditions constitute important parameters for determining the biocompatibility response of metallic biomaterials. For further investigating the microstructure – mechanical property relationship and its correlation to biocompatibility, mechanical deformation response of a potential biomedical alloy, namely the NbZr alloy, was examined under impact loading for various microstructures, specifically for various degrees of anisotropy. This analysis demonstrated that impact response of metallic materials, which constitutes a critical type of mechanical loading condition for implants, strongly depend on microstructural properties. In order to further clarify the role of microstructure on the impact response of metallic materials, the impact behavior of a structural metallic material, namely a high-manganese austenitic steel was investigated. The reason for the preference of this type of alloy was its complex microstructure with intense slip-twin interactions. The outcomes of this investigation indicated that under impact loading, either slip or twin mechanism gets activated, unlike the slip-twin interactions that normally dominates deformation under conventional modes of loading. This behavior is attributed to the unusually high deformation rate of this type of loading and presented guidelines for the understanding of the role of each microstructural mechanism on the deformation response of metallic materials. Overall, the findings of the current thesis emphasize the importance of analyzing the biocompatibility-microstructure-mechanical property relationship for a successful assessment of biocompatibility of biomaterials. Moreover, the work presented herein clearly demonstrates that adopting the corresponding knowledge to the design procedure of new biomedical applications is of utmost importance for the safety of patients.