Abstract
This research focuses on the development of Ni-Al-Ti-Mn-Co-Fe-Cr High Entropy Alloys (HEAs) using the spark plasma sintering (SPS) process. With the sole aim of improving its mechanical and microstructural properties for automobile applications. The research is an aggregate of three categories: thermodynamic simulation, optimization of sintering parameters, and characterization and evaluation of the microstructural and mechanical properties of NiAl-based high entropy alloys. The thermodynamic simulation was used to identify and quantify the phases' presence using Thermo-Calc® software version 2021b with the TCHEA5 HEAs database. From the simulation result, four phases were predominantly observed: BCC, FCC, SIGMA, and HEUSLER. The composition of the constituent element greatly influenced the amount of phases present. The developed HEAs meet the criteria for developing an HEAs in terms of the interacting parameters (Ω ≥ 1.1), atomic size (0 ≤ δ ≤ 6.5), enthalpy of mixing (-22 ≤ ΔHmix ≤ 7), and the entropy of mixing (11 ≤ ΔSmix ≤ 19.5). The simulation result set the pace for the experiment. The design of experiment (DOE) approach was adopted to reduce the number of experiments and eliminate trial by error. The user-defined design (UDD) under the response surface model (RSM) was used to predict the optimal sintering parameters, and an experiment was conducted to validate the result. The modeling output, however, indicated that full densification of 99% can be accomplished at a sintering temperature (ST) of 850 °C, a Pressure of 50 MPa, a Dwell Time of 5 Min, and an HR of 100 °C/min. The latter part of the research focuses on the characterization and evaluation of the microstructural and mechanical properties of the sintered HEAs. The uniform distribution of the alloying materials is visible in the microstructure of the sintered HEAs at different weight constituents. The Ni50Al50 exhibited a coarse-grained structure with the highest grain size of 8.26 μm, while the lowest grain size of 2.36 μm was observed for the Ni25Al25Ti8Mn8Co15Fe14Cr5 alloy. The Ni25Al25Ti8Mn8Co15Fe14Cr5 has the highest microhardness, nanohardness, and elastic modulus of 139.2±0.8 HV, 18.8±0.36 GPa, and 207.5±1.6 GPa respectively, while Ni50Al50 has the least values of 103.5±1.2 HV, 10.2±0.4 GPa, and 180±5 GPa, accordingly. The exceptional mechanical characteristics of Ni25Al25Ti8Mn8Co15Fe14Cr5 may be ascribed to its greater volume fraction of BCC (65.3 %) in comparison to the other produced HEAs.