Abstract
High-entropy alloys (HEAs) have emerged as promising materials for advanced engineering applications due to their unique combination of properties. This thesis investigates the design, synthesis, and characterization of novel nickel-aluminide based high entropy alloys (HEAs) within the Ni-Al-Co-Cr-Cu-Mn-Ti system. Utilizing a combined computational and experimental approach, the research explores both equiatomic and non-equiatomic compositions to develop advanced materials with enhanced structural and mechanical properties. The study employs CALPHAD-based Thermo-Calc software to predict phase formation and stability across various compositions and temperatures. These computational predictions are subsequently validated through experimental synthesis using a two-step process of mechanical alloying and spark plasma sintering. Comprehensive characterization is conducted using X-ray diffractometry (XRD), scanning electron microscopy (SEM), nanoindentation, and Vickers micro-hardness testing. Optimization of processing parameters was achieved using response surface methodology (RSM), with sintering temperature and milling time as key variables affecting relative density and microhardness. Key findings include the identification of complex microstructures comprising disordered-ordered solid solutions (primarily BCC_B2 and FCC_L12), spinodal decomposed variants (BCC_B2#2 and BCC_B2#3), and intermetallic phases (HEUSLER_L12, Cr3Mn5, and Ni3Ti_D024). The BCC_B2#2 phase is identified as a significant contributor to high hardness, with potential applications in high-temperature environments. This research contributes to the fundamental understanding of nickel-aluminide based HEAs and establishes clear correlations between alloy composition, processing parameters, microstructure, and resulting mechanical properties. The study demonstrates the efficacy of integrating computational modeling with experimental validation in HEA development. It provides insights into tailoring the balance between strength and ductility in these alloys, addressing the demand for lightweight, high-performance materials in aerospace, automotive, and energy sectors. The accuracy of CALPHAD-based predictions for complex multi-component systems is confirmed, enhancing confidence in computational alloy design approaches. This research contributes to the field by introducing a new HEA system, advancing understanding of phase formation in multi-component alloys, and establishing methodologies for efficient alloy design and optimization. The findings have significant implications for the development of advanced materials with tailored properties for specific applications.