Investigating the microstructural and mechanical properties of nickel-aluminide based high entropy Alloys: a combined CALPHAD-Based modeling and nanoindentation study

This research explores the microstructural and mechanical properties of milled and sintered Ni-Al-Co-Cr-Cu-Mn-Ti high-entropy alloys (HEAs), employing a synergistic approach that integrates CALPHAD-based thermodynamic modeling with experimental nanoindentation techniques. The study meticulously investigated the behavior of HEAs subjected to mechanical alloying over varied durations (5, 10, and 15 h), followed by sintering under optimized conditions (900 °C, 100 °C/min heating rate, 50 MPa pressure, and 5 min holding time). Through Thermo-Calc predictions and subsequent validation via SEM-EDS and XRD analyses, a complex multiphase structure encompassing BCC_B2 solid solution, FCC_L21, and various intermetallic phases was revealed. Nanoindentation analysis used to characterize their mechanical properties at the nanoscale showed that the equiatomic alloy A, sintered at 900 °C for 15 min, exhibited the highest hardness (HIT = 14.9 GPa) and elastic modulus (EIT = 234.47 GPa), alongside the lowest indentation depth (923.431 ± 0.004 nm) at a 300 mN load, indicative of strong interatomic bonding and a uniform microstructure. In contrast, the non-equiatomic alloy C demonstrated the highest indentation depth (962.271 ± 0.005 nm) and a pop-in effect, suggesting the presence of localized defects or inhomogeneities potentially compromising its mechanical integrity. These findings underscore the critical role of compositional strategy and process optimization in tailoring the microstructural and mechanical properties of HEAs for advanced engineering applications, offering a methodical approach for the design and development of novel HEAs with enhanced performance characteristics.