| dc.description.abstract | Metallic materials are used for osteosynthesis, and outcomes are expected to be complete healing. The latter part generally becomes unachievable when human subjects need complicated surgery. This situation generally requires patient-specific treatment and often is not achieved as implants available in the market do not offer such treatment. Advancement in additive manufacturing paves the way for such treatment as it affords the fabrication of near-net shape parts. However, parts produced by additive manufacturing exhibit properties that differ from those prepared by conventional processing routes, especially for Ti alloys. These differences arise due to higher cooling rates and thermal gradients during additive manufacturing, which yield different microstructures and phases. The obtained microstructure possessed high mechanical strength but poor ductility and is one of the main obstacles for additive manufacturing processes in their acceptance as one of the processing routes in biomedical applications. In this thesis, a heat treatment schedule was devised to modify the microstructure, addressing the aforementioned concerns to enhance the performance of materials used as implants for orthopedic fixation. In addition, additive manufacturing of a next-generation β-Ti alloy was performed to understand the effect of processing parameters on the fabricated alloy performance. Fabricated alloys were studied for optimal processing parameters and dense sample coupons were further studied for structural, texture, mechanical, electrochemical, and biological characteristics.
In Chapter 1, a comprehensive literature review on the additive manufacturing of Ti-6Al-4V extra low interstitial (ELI) is presented, and the effect of post-processing, especially heat treatment, has been presented. In addition, challenges in the additive manufacturing of β-Ti alloy are also compiled along with the motivation for the present thesis. In Chapter 2, details of processing employed, and various characterization techniques commonly utilized are mentioned.
In Chapter 3, the effect of heat treatment on additively manufactured (AM) bone plates is discussed, which is compared with Ti-6Al-4V ELI bone plates of the same geometry manufactured conventionally. A comparison of all three conditions was made by structural, texture, mechanical, electrochemical, and biological characterization. It is observed that the biomechanical performance of heat-treated plates is comparable to that of plates manufactured using wrought Ti-6Al-4V ELI (WR). In Chapter 4, the effect of heat treatment (HT) is assessed to evaluate the anisotropic behavior of fracture toughness in mode I in all three conditions mentioned in Chapter 3. Improvement in fracture toughness is observed, and anisotropy was reduced in HT conditions. The improved fracture toughness is closer to the WR material. A mechanism has been proposed to understand the fracture toughness improvement post-heat treatment.
In Chapter 5, the effect of heat treatment on tribological and electrochemical performance is evaluated and compared to that of AM. The improvement in tribological performance is due to the microstructural modifications, which improved the surface chemistry to form a dense passive layer. A mechanism is proposed to understand the effect of microstructure on tribocorrosion response for the different testing conditions. In Chapter 6, patient-specific treatment of upper limbs in human subjects was performed by utilizing the heat-treated bone plates. X-ray CT scan data of patients were studied and analyzed for surgical planning to design patient-specific bone plates, which were later subjected to heat treatment. The outcomes of surgery were excellent, which were further clinically evaluated based on improved functional outcomes of the patient post-healing. In Chapter 7, directed energy deposition (DED) of Ti-35Nb-5Ta-7Zr alloy is performed to understand the feasibility of the process and obtain processing parameters to fabricate dense components. The detailed characterization suggested complete β phase stability in fabricated components, which resulted in low elastic modulus with strong <100> crystallographic texture and is expected to help in addressing the challenge of stress shielding.
In Chapter 8, the overall findings of the work in this thesis are summarized. The future scope based on the outcome of this work is also presented. | en_US |
