Computational and Experimental Studies on Structural and Mechanical Properties of Ni-Al-Co-Cr-Cu-Mn-Ti High Entropy Alloys

Abstract

This study investigates the structural and mechanical properties of a promising Ni-Al-Cr-Cu-Mn-Ti high-entropy alloy (HEA) system, known for its potential to balance high strength and ductility, using an integrated computational and experimental approach. CALPHAD-based Thermo-Calc modeling was used to predict the phase formation and stability across equiatomic and non-equiatomic compositions. The alloys were synthesized via mechanical alloying and spark plasma sintering, with microstructural and mechanical characterization performed using XRD, SEM-EDS, and hardness testing. The results reveal a complex microstructure across all compositions, primarily comprising disordered-ordered solid solutions (BCC_B2 and FCC_L12) and intermetallic phases (Heusler_L21, Cr₃Mn₅, and Ni₃Ti_D024). Notably, the equiatomic composition (Alloy A) demonstrated the highest experimental hardness (789.8 HV), which was attributed to its dominant BCC_B2#2 phase, significantly exceeding its predicted value (204.7 HV). This notable discrepancy highlights the significant contribution of processing-induced microstructural features, such as nanoscale crystallite sizes (2.03-5.01 nm), which are not fully captured by the thermodynamic model, to the enhanced mechanical properties. A dual-phase structure balancing strength and ductility was observed, consistent with the valence electron concentration of 7.14, which promotes the coexistence of the FCC and BCC phases. The lightweight HEAs (density 6.78 g/cm3) demonstrate promising mechanical properties for aerospace, automotive, and energy applications. This study demonstrates that the synergy between computational modeling and experimental validation is crucial for designing and optimizing HEAs, revealing that processing-induced microstructural refinement significantly enhances properties beyond thermodynamic predictions, thereby enabling the rational design of alloys with tailored properties for demanding applications.