Phase prediction, microstructure, and mechanical properties of spark plasma sintered Ni-Al-Ti-Mn-Co-Fe-Cr high entropy alloys

Emmanuel Olorundaisi; Bukola J Babalola; Moipone L Teffo; Ufoma S Anamu; Peter A Olubambi; Juwon Fayomi; Anthony O Ogunmefun

doi:10.1186/s11671-023-03889-3

Phase prediction, microstructure, and mechanical properties of spark plasma sintered Ni-Al-Ti-Mn-Co-Fe-Cr high entropy alloys

Discov Nano. 2023 Sep 19;18(1):117. doi: 10.1186/s11671-023-03889-3.

Authors

Emmanuel Olorundaisi¹, Bukola J Babalola², Moipone L Teffo³, Ufoma S Anamu², Peter A Olubambi², Juwon Fayomi⁴, Anthony O Ogunmefun²

Affiliations

¹ Centre for Nanoengineering and Advanced Materials, School of Mining, Metallurgy and Chemical Engineering, University of Johannesburg, Johannesburg, 2092, South Africa. olorundaisiemmanuel@gmail.com.
² Centre for Nanoengineering and Advanced Materials, School of Mining, Metallurgy and Chemical Engineering, University of Johannesburg, Johannesburg, 2092, South Africa.
³ Department of Chemical, Metallurgical and Materials Engineering, Institute for Nanoengineering Research, Tshwane University of Technology, Pretoria, South Africa.
⁴ Center for Additive Manufacturing, School of Engineering, RMIT University, Melbourne, 3000, Australia.

Abstract

The effect of mechanical alloying on the development of Ni-Al-Ti-Mn-Co-Fe-Cr high entropy alloys (HEAs) utilizing the spark plasma sintering (SPS) method is the main goal of this study. A bulk sample was fabricated using SPS after the alloys were mixed for 12 h. Thermodynamic simulation, X-ray diffraction, scanning electron microscopy, nanoindentation, and microhardness were used to investigate the microstructure and mechanical properties of the as-mixed powders. The master alloy was made of NiAl and was subsequently alloyed with Ti, Mn, Co, Fe, and Cr at different compositions to develop HEAs at a sintering temperature of 850 °C, a heating rate of 100 °C/min, a pressure of 50 MPa, and a dwelling time of 5 min. A uniform dispersion of the alloying material can be seen in the microstructure of the sintered HEAs with different weight elements. The grain size analysis shows that the Ni₂₅Al₂₅Ti₈Mn₈Co₁₅Fe₁₄Cr₅ alloy exhibited a refined structure with a grain size of 2.36 ± 0.27 µm compared to a coarser grain size of 8.26 ± 0.43 μm attained by the NiAl master alloy. Similarly, the HEAs with the highest alloying content had a greater microstrain value of 0.0449 ± 0.0036, whereas the unalloyed NiAl had 0.00187 ± 0.0005. Maximum microhardness of 139 ± 0.8 HV, nanohardness of 18.8 ± 0.36 GPa, elastic modulus of 207.5 ± 1.65 GPa, elastic recovery (W_e/W_t) of 0.556 ± 0.035, elastic strain to failure (H/E_r) of 0.09.06 ± 0.0027, yield pressure (H³/[Formula: see text]) of 0.154 ± 0.0055 GPa, and the least plasticity index (W_p/W_t) of 0.444 ± 0.039 were attained by Ni₂₅Al₂₅Ti₈Mn₈Co₁₅Fe₁₄Cr₅. A steady movement to the left may be seen in the load-displacement curve. Increased resistance to indentation by the developed HEAs was made possible by the increase in alloying metals, which ultimately led to higher nanohardness and elastic modulus.

Keywords: Crystal structure; High entropy alloy; Microstructure; Nanoindentation; Nickel aluminide; Phase formation.