Designing corrosion‐resistant HEAs using machine learning and fabricating corrosion‐resistant hea thin films through controlled coating conditions for biomedical applications.

High-entropy alloys (HEAs) have emerged as a promising class of biomaterials due to their unique microstructural stability, mechanical strength, and superior corrosion resistance. This thesis presents a comprehensive investigation into the development, characterization, and performance of novel HEAs for biomedical applications, with a specific focus on orthopedic implants. Four interconnected studies were conducted, each addressing critical aspects of alloy design, thin film deposition, and performance evaluation. In the first study, TiTaNbZrMo HEA thin films were sputtered on NiTi shape memory alloy substrates to mitigate nickel ion release—a factor that limits the clinical use of NiTi-based implants. The results demonstrated that deposition at low chamber pressure yielded dense, crack-free coatings with significantly enhanced corrosion resistance, bioactivity, and adhesion strength. The second study leveraged machine learning (ML) techniques to design novel HEA compositions by correlating compositional and electrochemical parameters with corrosion potential. Two predicted alloys, Ti34.8Ta17Nb21.4Zr14.2Mo12.6 (HEA1) and Ti35Ta23Nb20.8Zr14.2Mo7 (HEA2), were fabricated and experimentally validated, showing superior corrosion resistance compared to conventional alloys. In the third study, the microstructure, bioactivity, and corrosion behavior of the ML-designed alloys were comprehensively evaluated. Both alloys exhibited a refined microstructure with well-distributed constituent phases, improved passivation behavior and stable oxide film formation, confirming their potential for biomedical applications. The final study extended this evaluation by combining electrochemical and non-electrochemical methods to investigate the corrosion mechanisms of the two ML-designed alloys under simulated harsh environments, including corrosive water and salt-spray chamber tests. The results revealed that the alloys not only resisted localized corrosion but also maintained their stability in aggressive media, highlighting the role of corrosion-resistant elements (such as Ta, Nb, and Mo) in their composition. Collectively, these studies highlight the synergistic integration of thin film engineering and machine learning-driven alloy design in advancing next-generation biomedical HEAs. The findings provide a solid foundation for optimizing alloy compositions and deposition conditions, paving the way for durable, biocompatible, and corrosion-resistant implants.