Remarkable grain growth resistance of Zr doped nanocrystalline AlCoCrCuFeNi high entropy alloy

K Sikdar and A Mahata and C Chattopadhyay and D Roy and R Mitra, PHILOSOPHICAL MAGAZINE, 105, 1314-1336 (2025).

DOI: 10.1080/14786435.2025.2495815

The present work demonstrates the synthesis of 1 at. % Zr-doped nanocrystalline AlCoCrCuFeNi high entropy alloy (HEA) by mechanical alloying. It comprises FCC and BCC phases, where Cu and Cr constitute the host lattice. The microstructure and mechanical property stability of the newly developed alloy were examined by annealing it at temperatures up to 1173 K (similar to 0.75 Tm). X-ray diffraction analysis has revealed superior stability of the FCC phase with an enhancement in its volume fraction with rise in annealing temperature. Transmission electron microscopy has confirmed that an average grain size of 27 nm is retained after 1173 K exposure. Analysis of the growth kinetics suggests a higher activation energy barrier for the FCC phase, which is controlled by long-range diffusion. Besides, it has also indicated the presence of solute atoms in the grain boundary region. Based on the contribution of grain boundary solute atoms assessed using the surface segregation model, a thermodynamic grain size stability map has been constructed. The molecular dynamics (MD) simulation has revealed the segregation of Zr atoms at the grain boundary regions of the annealed HEA. Evaluation of the post-anneal microhardness has shown it to be higher for the Zr-doped HEA (8.67 +/- 0.5 GPa) by 30% compared to the base composition (6.65 +/- 0.6 GPa). Analysis using the modified Hall-Petch model for the annealed alloy shows that grain boundaries are the primary source of strengthening.

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